WorldWideScience

Sample records for area csi photocathodes

  1. Development of Large Area CsI Photocathodes for the ALICE/HMPID RICH Detector

    CERN Document Server

    Hoedlmoser, H; Schyns, E

    2005-01-01

    The work carried out within the framework of this PhD deals with the measurement of the photoelectric properties of large area thin film Cesium Iodide (CsI) photocathodes (PCs) which are to be used as a photon converter in a proximity focusing RICH detector for High Momentum Particle Identification (HMPID) in the ALICE experiment at the LHC. The objective was to commission a VUV-scanner setup for in-situ measurements of the photoelectric response of the CsI PCs immediately after the thin film coating process and the use of this system to investigate the properties of these photon detectors. Prior to this work and prior to the finalization of the ALICE/HMPID detector design, R&D work investigating the properties of CsI PCs had been performed at CERN and at other laboratories in order to determine possible substrates and optimized thin film coating procedures. These R&D studies were usually carried out with small samples on different substrates and with various procedures with sometimes ambiguous result...

  2. Sealed gaseous photomultiplier with CsI photocathode

    International Nuclear Information System (INIS)

    A sealed gaseous photomultiplier tube (PMT) with a CsI photocathode has been developed using a micropattern gas detector (MPGD) made of Pyrex glass. A microblasting technique (MB) was employed for the production of a new hole-type MPGD. We investigated gaseous PMTs with a semi-transparent CsI photocathode for two different gas mixtures of Ne(90%)+i-C4H10 (10%) and Ne (90%)+CF4 (10%) at a gas pressure of 700 torr. Gains of up to 105 were attained with the microblasted glass plate (MB-GP) for both neon gas mixtures. Quantum efficiencies of up to 0.5% were obtained for UV light at the wavelength of 170 nm. The results of the aging test and the characteristics in a high magnetic-field environment are described for the gaseous PMT filled with neon gas mixture.

  3. Temporal resolution limit estimation of x-ray streak cameras using a CsI photocathode

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiang; Gu, Li; Zong, Fangke; Zhang, Jingjin; Yang, Qinlao, E-mail: qlyang@szu.edu.cn [Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Institute of Optoelectronics, Shenzhen University, Shenzhen 518060 (China)

    2015-08-28

    A Monte Carlo model is developed and implemented to calculate the characteristics of x-ray induced secondary electron (SE) emission from a CsI photocathode used in an x-ray streak camera. Time distributions of emitted SEs are investigated with an incident x-ray energy range from 1 to 30 keV and a CsI thickness range from 100 to 1000 nm. Simulation results indicate that SE time distribution curves have little dependence on the incident x-ray energy and CsI thickness. The calculated time dispersion within the CsI photocathode is about 70 fs, which should be the temporal resolution limit of x-ray streak cameras that use CsI as the photocathode material.

  4. Gain of a gas photomultiplier with CsI photocathode

    International Nuclear Information System (INIS)

    A Gas PMT with the CsI photocathode was fabricated as a phototube of a glass vessel identical to a conventional vacuum PMT. A GEM and a Micromegas were installed in the phototube of the Gas PMT. The Gas PMT was operated with two different gas mixtures, Ar (90%) + CH4 (10%) and Ne (90%) + CF4 (10%), at the gas pressure of 1 atm. The gain of 105 was obtained for both the gas mixtures. It was found that the gain of the Gas PMT can be described using the Townsend ionization coefficient for the Micromegas. The imaging capability of the Ne gas mixture was checked by an optical imaging capillary (CP) gas detector, using X-ray beams. The image of an X-ray resolution chart indicates that the imaging resolution is determined by the diameter of the capillary, here 100 μm. The Ne gas mixture appropriate to the Gas PMT is well suited for a fine imaging detector

  5. Structural transformation of CsI thin film photocathodes under exposure to air and UV irradiation

    CERN Document Server

    Tremsin, A S; Siegmund, O H W

    2000-01-01

    Transmission electron microscopy has been employed to study the structure of polycrystalline CsI thin films and its transformation under exposure to humid air and UV irradiation. The catastrophic degradation of CsI thin film photocathode performance is shown to be associated with the film dissolving followed by its re-crystallization. This results in the formation of large lumps of CsI crystal on the substrate surface, so that the film becomes discontinuous and its performance as a photocathode is permanently degraded. No change in the surface morphology and the film crystalline structure was observed after the samples were UV irradiated.

  6. Heat enhancement of radiation resistivity of evaporated CsI, KI and KBr photocathodes

    CERN Document Server

    Tremsin, A S

    2000-01-01

    The photoemissive stability of as-deposited and heat-treated CsI, KI and KBr evaporated thin films under UV radiation is examined in this paper. After the deposition, some photocathodes were annealed for several hours at 90 deg. C in vacuum and their performance was then compared to the performance of non-heated samples. We observed that the post-evaporation thermal treatment not only increases the photoyield of CsI and KI photocathodes in the spectral range of 115-190 nm, but also reduces CsI, KI and KBr photocurrent degradation that occurs after UV irradiation. KBr evaporated layers appeared to be more radiation-resistant than CsI and KI layers. Post-deposition heat treatment did not result in any significant variation of KBr UV sensitivity.

  7. First results of the two-phase argon avalanche detector performance with CsI photocathode

    OpenAIRE

    Bondar, A.(Budker Institute of Nuclear Physics (SB RAS), Novosibirsk State University, Novosibirsk, Russia); Buzulutskov, A.; Grebenuk, A.; Pavlyuchenko, D.; Snopkov, R.; Tikhonov, Y.

    2007-01-01

    The performance of a two-phase Ar avalanche detector with CsI photocathode was studied, with regard to potential application in coherent neutrino-nucleus scattering and dark matter search experiments. The detector comprised a 1 cm thick liquid Ar layer and a triple-GEM multiplier operated in the saturated vapor above the liquid phase; the CsI photocathode was deposited on the first GEM. Successful detection of both primary scintillation and ionization signals, produced by beta-particles in li...

  8. Sealed GEM photomultiplier with a CsI photocathode: ion feedback and ageing

    International Nuclear Information System (INIS)

    We present the performance of a sealed gaseous photomultiplier consisting of a cascade of 3 or 4 Gas Electron Multiplier (GEM) elements coupled to a semitransparent CsI photocathode, in Ar/CH4 (95/5). A few-month stability study of the photocathode in a sealed mode is presented. Increasing the number of GEMs in cascade substantially reduces the ageing of the detector under strong irradiation. The ion feedback to the photocathode has probably a minor effect on the ageing rate

  9. Measurement of the quantum efficiency of CsI, amorphous silicon and organometallic reflective photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Malamud, G. (LPNHE, Ecole Polytechnique, IN2P3-CNRS, 91128 Palaiseau (France)); Mine, P. (LPNHE, Ecole Polytechnique, IN2P3-CNRS, 91128 Palaiseau (France)); Vartsky, D. (LPNHE, Ecole Polytechnique, IN2P3-CNRS, 91128 Palaiseau (France)); Equer, B. (PICM, Ecole Polytechnique, CNRS (UPR258), 91128 Palaiseau (France)); Besson, P. (CE Saclay, DAPNIA/SED, 91191 Gif-sur-Yvette Cedex (France)); Bourgeois, P. (CE Saclay, DAPNIA/SED, 91191 Gif-sur-Yvette Cedex (France)); Breskin, A. (LPNHE, Ecole Polytechnique, IN2P3-CNRS, 91128 Palaiseau (France)); Chechik, R. (The Weizmann Institute of Science, 76100 Rehovot (Israel))

    1994-09-01

    We performed a systematic investigation of the quantum efficiency of some solid reflective photocathodes in the spectral range 140-240 nm. The measurements were made without gaseous amplification in vacuum and in methane. No significant difference was found among CsI photocathodes prepared by vacuum deposition at different institutes, either from powders or from crystals of different origins, and measured either in vacuum or in methane. Amorphous silicon photocathodes were prepared by the plasma enhanced chemical vapor deposition technique. We present the results for several doping conditions of amorphous silicon and for p-n junctions. Some organometallic photocathodes, containing iron or other transition metals (cerium), were evaporated and measured. Among them decamethylferrocene exhibits the highest quantum efficiency in the range 190-240 nm. ((orig.))

  10. A fast position sensitive photodetector based on a CsI reflective photocathode

    International Nuclear Information System (INIS)

    A fast detector was built for UV photon detection that depends on a CsI sensitized pad cathode. The rapidity of the detector is compared with that of a more classical chamber filled with photosensitive gases such as TEA or TMAE. Estimates of the quantum yield of the photocathode at 160 and 200 nm are given. The performances obtained make it a good photodetector candidate to be operated at high luminosity accelerators. (author) 7 refs., 19 figs

  11. Quantum efficiency measurement system for large area CsI photodetectors

    CERN Document Server

    Cusanno, F; Colilli, S; Crateri, R; Fratoni, R; Frullani, S; Garibaldi, F; Giuliani, F; Gricia, M; Lucentini, M; Mostarda, A; Santavenere, F; Veneroni, P; Breuer, H; Iodice, M; Urciuoli, G M; De Cataldo, G; De Leo, R; Lagamba, L; Braem, André

    2003-01-01

    A proximity focusing freon/CsI RICH detector has been built for kaon physics at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab), Hall A. The Cherenkov photons are detected by a UV photosensitive CsI film which has been obtained by vacuum evaporation. A dedicated evaporation facility for large area photocathodes has been built for this task. A measuring system has been built to allow the evaluation of the absolute quantum efficiency (QE) just after the evaporation. The evaporation facility is described here, as well as the quantum efficiency measurement device. Results of the QE on-line measurements, for the first time on large area photocathodes, are reported.

  12. Photoelectron extraction efficiency from a CsI photocathode and THGEM operation in He−CF4 and He−CH4 mixtures

    International Nuclear Information System (INIS)

    This work presents the experimental measurements obtained for UV-induced photo-electron extraction efficiency from a CsI photocathode into He with CF4 and CH4 gas mixtures. A 1000Å CsI photocathode was deposited on a gold plated THGEM for photo-electron conversion. Charge-gain measurements were obtained with a Single-THGEM detector operating in these gas mixtures using a continuous UV lamp for the extraction of photo-electrons. Charge-gains in excess of 105 were obtained for gas mixtures containing percentages of quencher higher than 20% while photo-electron extraction efficiency achieved ∼ 50% for He/CF4 and ∼ 30% for He/CH4. Single photon electron measurements were also performed to assess the maximal gains reached in this regime. A discussion for future GPM cryogenic applications is presented

  13. CSI Index Of Customer's Satisfaction Applied In The Area Of Public Transport

    Science.gov (United States)

    Poliaková, Adela

    2015-06-01

    In Western countries, the new visions are applied in quality control for an integrated public transport system. Public transport puts the customer at the centre of our decision making in achieving customer satisfaction with provided service. Sustainable surveys are kept among customers. A lot of companies are collecting huge databases containing over 30,000 voices of customers, which demonstrates the current satisfaction levels across the public transport service. Customer satisfaction with a provided service is a difficult task. In this service, the quality criteria are not clearly defined, and it is therefore difficult to define customer satisfaction. The paper introduces a possibility of CSI index application in conditions of the Slovak Republic transport area.

  14. Evaluation of the amperex 56 TVP photomultiplier. [characteristics: photoelectron time spread, anode pulse amplitude and photocathode sensing area

    Science.gov (United States)

    Lo, C. C.; Leskovar, B.

    1976-01-01

    Characteristics were measured for the Amperex 56 TVP 42 mm-diameter photomultiplier. Some typical photomultiplier characteristics-such as gain, dark current, transit and rise times-are compared with data provided. Photomultiplier characteristics generally not available such as the single photoelectron time spread, the relative collection efficiency, the relative anode pulse amplitude as a function of the voltage between the photocathode and focusing electrode, and the position of the photocathode sensing area were measured and are discussed for two 56 TVP's. The single photoelectron time spread, the relative collection efficiency, and the transit time difference as a function of the voltage between photocathode and focusing electrode were also measured and are discussed, particularly with respect to the optimization of photomultiplier operating conditions for timing applications.

  15. Control Structures Interaction (CSI) Technology

    Science.gov (United States)

    Layman, W. E.

    1989-01-01

    Control Structures Interaction (CSI) technology for control of space structures is being developed cooperatively by JPL, LaRC and MSFC for NASA OAST/RM. The mid-'90s goal of JPL's CSI program is to demonstrate with analysis, ground and flight tests, the super quiet structures needed for large diffraction-limited instruments such as optical stellar interferometers and large advanced successors to the Hubble Space Telescope. Microprecision CSI technology is intended as a new "building block" for use by the designers of large optical systems. The thrust of the microprecision CSI technology effort is to achieve nanometer-levels of space structure stability/accuracy with designs which employ otherwise conventional spacecraft technologies. JPL design experiences have indicated the following CSI technology development areas are especially applicable to large optical system projects: (1) Active structural members; (2) Control/structures design methods; (3) Microdynamic effects characterization; and (4) Ground and flight test validation of CSI methods.

  16. Role of the substrate reflectance and surface-bulk treatments in CsI quantum efficiency

    CERN Document Server

    Singh, B K; Nitti, M A; Valentini, A

    2003-01-01

    We have experimentally investigated the following aspects related to the quantum efficiency of CsI photocathodes: the type of substrate, the film thickness and the effect of a 'bulk treatment' during the film growth. We discovered that, using a high reflectivity aluminium substrate, the photoemission of very thin CsI film is enhanced. Our study also revealed that photocathodes become less sensitive to moisture when a negative bias voltage is applied to the substrate during the film deposition process.

  17. Controls-Structures Interaction (CSI) technology program summary. Earth orbiting platforms program area of the space platforms technology program

    Science.gov (United States)

    Newsom, Jerry R.

    1991-01-01

    Control-Structures Interaction (CSI) technology embraces the understanding of the interaction between the spacecraft structure and the control system, and the creation and validation of concepts, techniques, and tools, for enabling the interdisciplinary design of an integrated structure and control system, rather than the integration of a structural design and a control system design. The goal of this program is to develop validated CSI technology for integrated design/analysis and qualification of large flexible space systems and precision space structures. A description of the CSI technology program is presented.

  18. Precision fabrication of large area silicon-based geometrically enhanced x-ray photocathodes using plasma etching

    Science.gov (United States)

    Opachich, Y. P.; Chen, N.; Bell, P. M.; Bradley, D. K.; Feng, J.; Gopal, A.; Hilsabeck, T. J.; Huffman, E.; Koch, J. A.; Landen, O. L.; MacPhee, A. G.; Nagel, S. R.; Udin, S.

    2015-08-01

    Geometrically enhanced photocathodes are currently being developed for use in applications that seek to improve detector efficiency in the visible to X-ray ranges. Various photocathode surface geometries are typically chosen based on the detector operational wavelength region, along with requirements such as spatial resolution, temporal resolution and dynamic range. Recently, a structure has been identified for possible use in the X-ray region. This anisotropic high aspect ratio structure has been produced in silicon using inductively coupled plasma (ICP) etching technology. The process is specifically developed with respect to the pattern density and geometry of the photocathode chip to achieve the desired sidewall profile angle. The tapered sidewall profile angle precision has been demonstrated to be within +/- 2.5° for a ~ 12° wall angle, with feature sizes that range between 4-9 μm in diameter and 10-25 μm depth. Here we discuss the device applications, design and present the method used to produce a set of geometrically enhanced high yield X-ray photocathodes in silicon.

  19. Masked Photocathode for Photoinjector

    Energy Technology Data Exchange (ETDEWEB)

    Qiang, Ji

    2010-01-21

    In this research note, we propose a scheme to insert a photocathode inside a photoinjector for generating high brightness electron beam. Instead of mounting the photocathode onto the electrode, a masked electrode with small hole is used to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material very simple by rotating the photocathode behind the mask into the hole. This will significantly increase the usage lifetime of a photocathode. Furthermore, this also helps reduce the dark current or secondary electron emission from the photocathode. The hole on the mask also provides a transverse cut-off to the Gaussian laser profile which can be beneficial from the beam dynamics point of view.

  20. Masked Photocathode for Photoinjector

    International Nuclear Information System (INIS)

    In this research note, we propose a scheme to insert a photocathode inside a photoinjector for generating high brightness electron beam. Instead of mounting the photocathode onto the electrode, a masked electrode with small hole is used to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material very simple by rotating the photocathode behind the mask into the hole. This will significantly increase the usage lifetime of a photocathode. Furthermore, this also helps reduce the dark current or secondary electron emission from the photocathode. The hole on the mask also provides a transverse cut-off to the Gaussian laser profile which can be beneficial from the beam dynamics point of view.

  1. Reflective UV photocathodes with gas-phase electron extraction: Solid, liquid, and absorbed thin films

    Energy Technology Data Exchange (ETDEWEB)

    Seguinot, J.; Ypsilantis, T. (College de France, 75 - Paris (France)); Charpak, G.; Giomataris, Y.; Tischhauser, J. (European Organization for Nuclear Research, Geneva (Switzerland)); Peskov, V. (World Lab., Geneva (Switzerland))

    1990-11-15

    The photoemission quantum efficiency of reflective photocathodes in methane gas has been investigated in the spectral range between 140 and 250 nm. The spectral response of solid metals and CsI, as well as of liquid and solid TMAE film, have been measured. The high quantum efficiency of CsI (35% at 170 nm) makes it attractive for BaF{sub 2} or xenon scintillation detection. A BaF{sub 2} crystal coupled to an ionization chamber with a reflective CsI photocathode has been successfully tested. Adsorbed TMAE films can significantly increase the quantum yields of metal and CsI (to 46% at 170 nm), making them suitable for fast RICH and other applications. (orig.).

  2. A Masked Photocathode in Photoinjector

    Energy Technology Data Exchange (ETDEWEB)

    Qiang, Ji

    2010-12-14

    In this paper, we propose a masked photocathode inside the photoinjector for generating high brightness election beam. Instead of mounting the photocathode onto an electrode, an electrode with small hole is used as a mask to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material easy by rotating the photocathode behind the electrode into the hole. Furthermore, this helps reduce the dark current or secondary electron emission from the photocathode material. The masked photocathode also provides transverse cut-off to a Gaussian laser beam that reduces electron beam emittance growth from nonlinear space-charge effects.

  3. Photoemission and optical constant measurements of Cesium Iodide thin film photocathode

    CERN Document Server

    Triloki,; Gupta, Nikita; Jammal, Nabeel F A; Singh, B K

    2014-01-01

    Performance of cesium iodide (CsI) as a reflective photocathode is presented. Absolute quantum efficiency (QE) measurement of 500 nm thick CsI film has been carried out in the wavelength range of 150 nm to 200 nm. Optical absorbance of 500 nm thick CsI film in the spectral range of 190 nm to 900 nm is analyzed and optical energy band gap is calculated using Tauc plot. To see the dispersive behavior of CsI film, refractive index has been determined by envelop plot of transmittance data, using Swanepoel method. Additional information on morphological and elemental composition results of CsI film, gained by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively are also reported in present work.

  4. Photocathode RF guns

    International Nuclear Information System (INIS)

    Free-electron oscillators and amplifiers require electron accelerators capable of delivering pulse trains of electron bunches of high charge density in a wiggler or undulator. A high electron density implies a high peak current (100 A to 2000 A) and a low transverse beam emittance ( 8 nC in picoseconds) with extremely small emittances (< 10 π x mm x mrad). Several approaches have been proposed to attain such performance. This article discusses the use of photocathodes in attaining the aforementioned performance requirements. Photocathodes have been used as electron sources in lasertrons and for the production of spin-polarized electrons. A photocathode is a light-activated electron source that gives unprecedented control over all aspects of the electron distribution: peak current, spatial profile, and temporal profile. This control is possible because the electron distribution is not determined by grids or a cathode, but rather by an incident laser pulse on the photocathode. 44 references, 21 figures

  5. Acicular photomultiplier photocathode structure

    Science.gov (United States)

    Craig, Richard A.; Bliss, Mary

    2003-09-30

    A method and apparatus for increasing the quantum efficiency of a photomultiplier tube by providing a photocathode with an increased surface-to-volume ratio. The photocathode includes a transparent substrate, upon one major side of which is formed one or more large aspect-ratio structures, such as needles, cones, fibers, prisms, or pyramids. The large aspect-ratio structures are at least partially composed of a photoelectron emitting material, i.e., a material that emits a photoelectron upon absorption of an optical photon. The large aspect-ratio structures may be substantially composed of the photoelectron emitting material (i.e., formed as such upon the surface of a relatively flat substrate) or be only partially composed of a photoelectron emitting material (i.e., the photoelectron emitting material is coated over large aspect-ratio structures formed from the substrate material itself.) The large aspect-ratio nature of the photocathode surface allows for an effective increase in the thickness of the photocathode relative the absorption of optical photons, thereby increasing the absorption rate of incident photons, without substantially increasing the effective thickness of the photocathode relative the escape incidence of the photoelectrons.

  6. Comparison of the photoemission behaviour between negative electron affinity GaAs and GaN photocathodes

    International Nuclear Information System (INIS)

    In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoemission behaviour, namely the activation process and quantum yield decay, between the two typical types of III—V compound photocathodes have been investigated using a multi-information measurement system. The activation experiment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs—O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes. (interdisciplinary physics and related areas of science and technology)

  7. DIAMOND AMPLIFIED PHOTOCATHODES.

    Energy Technology Data Exchange (ETDEWEB)

    SMEDLEY,J.; BEN-ZVI, I.; BOHON, J.; CHANG, X.; GROVER, R.; ISAKOVIC, A.; RAO, T.; WU, Q.

    2007-11-26

    High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.

  8. Dense-Pinch Photocathode

    Science.gov (United States)

    Asmus, John F.; Lovberg, Ralph H.

    1988-05-01

    A promising approach to the generation of low-emittance e-beams for particle beam and FEL application employs a photoelectron cathode. IF such an e-beam source is to be viable at high power, a high-performance hard-UV illuminator is needed. Toward this end, experiments have been performed by illuminating a metal photocathode with the VUV radiation from a laser-guided gas-embedded high-density high-Z pinch. Such a VUV source is interesting because the plasma is created at high density and is optically thick. Thus, it is both a stable and an efficient radiator. Coupled with a copper photocathode it has generated a-beam current densities up to 60 A/sq-cm. The test device has been modified to utilize a pinch formed from a liquid jet in vacuum, rather than the laser-guided discharge in high-pressure gas. This is more suitable for rep-rate operation as it dispenses with the VUV-absorbing interposed gas, the channel-forming laser, and gas transport at high average power. A decane-jet device has been tested at 10 Hz with a peak pulse VUV power of 100 MW.

  9. Photocathode aging in MCP PMT

    International Nuclear Information System (INIS)

    We study aging of alkali-antimonide photocathodes in the microchannel plate photomultiplier tubes (MCP PMT) manufactured in Novosibirsk by ''Ekran FEP'' company. Such PMTs are used in the particle identification systems of KEDR, SND and CMD-3 experiments carried out at e+e− colliders VEPP-4M and VEPP-2000 in the Budker Institute of Nuclear Physics. The quantum efficiency (QE) degradation of a PMT equipped with MCP Chevron has been measured at different photon counting rates from 4⋅107 to 6⋅1010 s−1cm−2. It is found that the QE decrease is proportional to the charge extracted from the MCP nearest to the photocathode rather than to the output charge. The comparison of different types of alkali-antimonide photocathodes has shown that the treatment of photocathode with vapors of cesium and antimony can dramatically reduce the photocathode aging rate. The photocathode lifetime of the best MCP PMT sample has been measured at the photon counting rate of 107 cm−2s−1 and the initial gain of 106. The peak quantum efficiency degraded by 20% after accumulation of 3.3 C/cm2 anode charge.

  10. Latest bialkali photocathode with ultra high sensitivity

    International Nuclear Information System (INIS)

    Among photosensitive devices in use today, the photomultiplier tube (PMT) is a versatile device providing extremely high sensitivity, exceptionally low noise and ultra-fast response. It can detect photons at ultra low light level such as single photon counting level. One of the most important characteristics of the PMT is the quantum efficiency (QE) of the photocathode. Among various kinds of photocathodes, a bialkali photocathode is commonly used for particle physics experiments since it has higher sensitivity and lower dark current than other photocathodes. QE of the conventional bialkali photocathode is 27%. Since 2007, we have made a significant improvement in the QE of the bialkali photocathode, achieving as high as 43% at peak wavelength by precise control of the photocathode activation process. This photocathode was named ultra bialkali (UBA) and was incorporated into PMTs successfully. Additionally, we have developed another new kind of bialkali photocathode for very low-temperature environments. At -175 oC, the new bialkali photocathode shows good cathode linearity up to 300 nA, and it has 28% QE and lower dark current than the UBA photocathode. A PMT with the new photocathode is expected to be an ideal detector for Dark Matter experiments or double-beta decay.

  11. Developments of a large area VUV sensitive gas PMT with GEM/μPIC

    International Nuclear Information System (INIS)

    A new large area UV photon detector with micro pattern gaseous detectors is developed and evaluated. A semitransparent CsI photocathode deposited on a MgF2 window was combined with 10cm x 10cm GEM and μPIC. Using Ar+C2H6 (10%) gas, we achieved the gas gain of more than 105 which is enough to detect single photoelectron. We, then, irradiated vacuum UV photons (VUV, around 172nm) from the newly developed LaF3(Nd) scintillator to the detector and the single photoelectrons were successfully detected. We also demonstrated the imaging capability of the detector with μPIC readout systems.

  12. CSI: Immigrant Children--Clues for Teacher Education

    Science.gov (United States)

    Larke, Patricia J.

    2012-01-01

    The metaphor of the popular television shows "CSI: New York," "CSI: Miami," and "CSI: Las Vegas" (CSI stands for "crime scene investigation") is applicable to investigating issues of immigrant children in teacher preparation programs (TPP). One of the fundamental principles of CSI is to solve the crime by critically examining clues as evidence…

  13. Polarization and charge limit studies of strained GaAs photocathodes

    International Nuclear Information System (INIS)

    This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of ∼ 2.5 A/cm2 at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don't have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes

  14. Development of large area hybrid photodiodes for the LHCb ring imaging Cherenkov detectors

    International Nuclear Information System (INIS)

    The authors report on the development of large area hybrid photo diodes (HPD) which are one of the proposed photodetectors for the RICH counters of the LHCb experiment. The HPD's consist of a cylindrical vacuum envelope of 127 mm diameter capped with a spherical vacuum envelope of 127 mm diameter capped with a spherical borosilicate UV-glass entrance window. Focusing electrodes demagnify the image on a silicon detector of 50 mm diameter comprising 2048 pads with a surface of 1 mm2 each. The analogue readout electronics is integrated in the vacuum tube. As an intermediate step a HPD with a UV sensitive CsI photocathode has been produced which allowed to verify the electron optics of the HPD. A large UHV evaporation plant for the production of HPD's with visible light transmissive bialkali photocathodes (K2CsSb) has been built and successfully operated. The evaporation process is optimized for maximum quantum efficiency and life time of the photocathodes. A cold Indium sealing technique developed for a minimum thermal load of the photocathode and the silicon sensor has proven to provide excellent vacuum tightness

  15. Development of large area hybrid photodiodes for the LHCb ring imaging Cherenkov detectors

    CERN Document Server

    Chesi, Enrico Guido; Go, A; Joram, C; Séguinot, Jacques; Ypsilantis, Thomas; Ypsilantis, Thomas

    1998-01-01

    98-037 We report on the development of large area hybrid photo diodes (HPD) which are one of the proposed photodetectors for the RICH counters of the LHCb experiment. The HPD's consist of a cylindrical vacuum envelope of 127 mm diameter capped with a spherical borosilicate UV-glass entrance window. Focusing electrodes demagnify the image on a silicon detector of 50~mm diameter comprising 2048 pads with a surface of 1~mm$^2$ each. The analogue readout electronics is integrated in the vacuum tube. As an intermediate step a HPD with a UV sensitive CsI photocathode has been produced which allowed to verify the electron optics of the HPD. A large UHV evaporation plant for the production of HPD's with visible light transmittive bialkali photocathodes (K$_2$CsSb) has been built and successfully operated. The evaporation process is optimized for maximum quantum efficiency and life time of the photocathodes. A cold Indium sealing technique developed for a minimum thermal load of the photocathode and the silicon sensor...

  16. Development of large area hybrid photodiodes for the LHCb ring imaging Cherenkov detectors

    CERN Document Server

    Braem, André; Dulinski, W; Filthaut, Frank; Go, A; Joram, C; Lion, G; Séguinot, Jacques; Weilhammer, Peter; Wicht, P; Ypsilantis, Thomas

    1999-01-01

    We report on the development of large area hybrid photodiodes (HPD) which are one of the proposed photodetectors for the RICH counters of the LHCb experiment. The HPD's consist of a cylindrical vacuum envelope of 127 mm diameter capped with a spherical borosilicate UV- glass entrance window. Focusing electrodes demagnify the image on a silicon detector of 50 mm diameter comprising 2048 pads with a surface of 1 mm/sup 2/ each. The analogue readout electronics is integrated in the vacuum tube. As an intermediate step a HPD with a UV sensitive CsI photocathode has been produced which allowed to verify the electron optics of the HPD. A large UHV evaporation plant for the production of HPD's with visible light transmissive bialkali photocathodes (K/sub 2/CsSb) has been built and successfully operated. The evaporation process is optimized for maximum quantum efficiency and life time of the photocathodes. A cold indium sealing technique developed for a minimum thermal load of the photocathode and the silicon sensor ...

  17. Saturated photodissociation of CsI

    International Nuclear Information System (INIS)

    Every CsI molecule in a small volume was photodissociated with a laser pulse; a second pulsed laser detected each Cs atom through resonance ionization spectroscopy. Besides proving one-molecule detection, cross sections for photodissociation of CsI were obtained as a function of wavelength. (Auth.)

  18. New Photocathode materials for electron-ion-colliders

    Energy Technology Data Exchange (ETDEWEB)

    Lukaszew, Rosa A. [College of William and Mary, Williamsburg, VA (United States)

    2015-02-25

    Our aim has been to explore new photocathode materials and schemes to develop strategies and technologies for next generation nuclear physics accelerator capabilities, particularly for Electron Ion Colliders (EIC). Thus, we investigated thin film deposition and ensuing properties for several adequate magnetic materials applicable to spin-polarized photocathodes. We also implemented a full experimental setup for light incidence at an acute angle onto the photocathode surface in order to excite surface Plasmon resonance hence increasing light absorption by a metallic surface. We successfully tested the setup with a thermionic cathode as well as Plasmonic silver-MgO samples and obtained very encouraging results. Our first results are very encouraging since the photocurrent measured on this preliminary plasmonic Ag-MgO sample under low power (~ 1mW) cw red light from a HeNe laser was 256 pA, thus two orders magnitude larger than that reported by others following also plasmonic approaches. We extended our studies to shorter wavelengths and we also started preliminary work on chemically ordered MnAl thin films –a component of the tertiary Ag-Mn-Al (silmanal) alloy in order to develop spin-polarized photocathodes capable of sustaining surface Plasmon resonance. It is worthwhile mentioning that a graduate student has been directly involved during this project ensuring the training of next generation of scientists in this area of research.

  19. Analyses of CsI aerosol deposition tests in WIND project with ART and VICTORIA codes

    International Nuclear Information System (INIS)

    Deposition behavior of cesium iodide (CsI) was analyzed with ART and VICTORIA-92 codes for a test of the aerosol re-vaporization test series performed in WIND project at JAERI. In the test analyzed, CsI aerosol was injected into piping of test section where metaboric acid (HBO2) was placed in advance on the floor area. It was confirmed in the present analysis that similar results on the CsI deposition were obtained between ART and VICTORIA when influences of chemical interactions were negligibly small. The analysis with VICTORIA agreed satisfactorily with the test results in analytical cases that cesium metaborate (CsBO2) was injected into the test section instead of CsI to simulate the pre-existence of HBO2 effect. (author)

  20. Quantum efficiency of cesium iodide photocathodes in the 120-220 nm spectral range traceable to a primary detector standard

    CERN Document Server

    Rabus, H; Richter, M; Ulm, G; Friese, J; Gernhäuser, R; Kastenmüller, A; Maier-Komor, P; Zeitelhack, K

    1999-01-01

    Differently prepared CsI samples have been investigated in the 120-220 nm spectral range for their quantum efficiency, spatial uniformity and the effect of radiation aging. The experiments were performed at the PTB radiometry laboratory at the Berlin synchrotron radiation facility BESSY. A calibrated GaAsP Schottky photodiode was used as transfer detector standard to establish traceability to the primary detector standard, because this type of photodiode - unlike silicon p-on-n photodiodes - proved to be of sufficiently stable response when exposed to vacuum ultraviolet radiation. The paper reviews the experimental procedures that were employed to characterize and calibrate the GaAsP photodiode and reports the results that were obtained on the investigated CsI photocathodes.

  1. Progress in the photocathode linac project

    International Nuclear Information System (INIS)

    The progress achieved so far in the Photocathode Linac Project have developed and tested linear accelerator structures at 2856 MHz, commissioned the klystron modulator and microwave systems, and developed the beamline, and are ready to commence acceleration experiments

  2. Final Report, Photocathodes for High Repetition Rate Light Sources

    Energy Technology Data Exchange (ETDEWEB)

    Ben-Zvi, Ilan [Stony Brook University

    2014-04-20

    This proposal brought together teams at Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL) and Stony Brook University (SBU) to study photocathodes for high repetition rate light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). The work done under this grant comprises a comprehensive program on critical aspects of the production of the electron beams needed for future user facilities. Our program pioneered in situ and in operando diagnostics for alkali antimonide growth. The focus is on development of photocathodes for high repetition rate Free Electron Lasers (FELs) and Energy Recovery Linacs (ERLs), including testing SRF photoguns, both normal-conducting and superconducting. Teams from BNL, LBNL and Stony Brook University (SBU) led this research, and coordinated their work over a range of topics. The work leveraged a robust infrastructure of existing facilities and the support was used for carrying out the research at these facilities. The program concentrated in three areas: a) Physics and chemistry of alkali-antimonide cathodes b) Development and testing of a diamond amplifier for photocathodes c) Tests of both cathodes in superconducting RF photoguns and copper RF photoguns

  3. PHOTOCATHODES FOR THE ENERGY RECOVERY LINACS

    International Nuclear Information System (INIS)

    This paper presents an overview of existing and emerging technologies on electron sources that can service various Energy Recovering Linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed

  4. Free-electron laser triggered photocathodes

    International Nuclear Information System (INIS)

    The possibility of using free-electron laser (FEL) triggered photocathodes to produce high-quality e-beams for self-amplified spontaneous emission or oscillator FEL devices is explored. The use of the same e-beam, driving the photocathode and the FEL, makes the system naturally free of any synchronization problem, arising when an external laser is used. Examples of the interplay between the generation of electron and optical bursts are also investigated

  5. Photocathodes for the energy recovery linacs

    International Nuclear Information System (INIS)

    This paper presents an overview of existing and emerging technologies on electron sources that can service various Energy Recovering Linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed

  6. Photocathodes for the energy recovery linacs

    International Nuclear Information System (INIS)

    This paper presents an overview of existing and emerging technologies on electron sources that can service various energy recovering linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed

  7. Photocathodes for the energy recovery linacs

    Science.gov (United States)

    Rao, T.; Burrill, A.; Chang, X. Y.; Smedley, J.; Nishitani, T.; Hernandez Garcia, C.; Poelker, M.; Seddon, E.; Hannon, F. E.; Sinclair, C. K.; Lewellen, J.; Feldman, D.

    2006-02-01

    This paper presents an overview of existing and emerging technologies on electron sources that can service various energy recovering linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed.

  8. Parallel-vector computation for CSI-design code

    Science.gov (United States)

    Nguyen, Duc T.

    1990-01-01

    Computational aspects of Control-Structure Interaction (CSI) DESIGN code is reviewed. Numerical intensive computation portions of CSI-DESIGN code were identified. Improvements in computational speed for the CSI-DESIGN code can be achieved by exploiting parallel and vector capabilities offered by modern computers, such as the Alliant, Convex, Cray-2, and Cray-YMP. Four options to generate the coefficient stiffness matrix and to solve the system of linear, simultaneous equations are currently available in the CSI-DESIGN code. A preprocessor to use RCM (Reverse Cuthill-Mackee) algorithm for bandwidth minimization was also developed for the CSI-DESIGN code. Preliminary results obtained by solving a small-scale, 97 node CSI finite element model (for eigensolution) have indicated that this new CSI-DESIGN code is 5 to 6 times faster (using 1 Alliant processor) than the old version of CSI-DESIGN code. This speed-up was achieved due to the RCM algorithm and the use of a new skyline solver. Efforts are underway to further improve the vector speed for CSI-DESIGN code, to evaluate its performance on a larger scale CSI model (such as phase zero CSI model) to make the code run efficiently on multiprocessor, parallel computer environment, and to make the code portable among different parallel computers available at NASA LaRC, such as Alliant, Convex, and Cray computers.

  9. Advanced photocathode simulation and theory

    Science.gov (United States)

    Jensen, K. L.; Feldman, D. W.; O'Shea, P. G.

    2003-07-01

    A low work function dispenser type photocathode that is self-annealing or repairing would have a substantial impact on Free Electron Lasers (FELs). On such a cathode, the emitting surface is constantly renewed by replenishment of low-work-function material. A photo-dispenser cathode should operate at a relatively low temperature compared to a conventional dispenser cathode and is anticipated to be robust and long-lived. Coatings cause a reduction in the transport barrier experienced by the electrons through a complex modification of the potential at the surface, e.g., a reduction in work function due to dipole effects. In this work, we describe our theoretical program to address such effects, as part of a program concurrent with experimental efforts to develop dispenser cathodes for use in high power RF photoinjectors. In particular, we discuss the development of a generalised Transmission Coefficient approach, its application to photoemission from metals, and progress towards developing a methodology for the determination of the general emission barrier profile.

  10. Advanced photocathode simulation and theory

    International Nuclear Information System (INIS)

    A low work function dispenser type photocathode that is self-annealing or repairing would have a substantial impact on Free Electron Lasers (FELs). On such a cathode, the emitting surface is constantly renewed by replenishment of low-work-function material. A photo-dispenser cathode should operate at a relatively low temperature compared to a conventional dispenser cathode and is anticipated to be robust and long-lived. Coatings cause a reduction in the transport barrier experienced by the electrons through a complex modification of the potential at the surface, e.g., a reduction in work function due to dipole effects. In this work, we describe our theoretical program to address such effects, as part of a program concurrent with experimental efforts to develop dispenser cathodes for use in high power RF photoinjectors. In particular, we discuss the development of a generalised Transmission Coefficient approach, its application to photoemission from metals, and progress towards developing a methodology for the determination of the general emission barrier profile

  11. Development of photocathodes for gas counters

    International Nuclear Information System (INIS)

    A lot of ways of physics needs the development of high sensibility imaging devices with large sensitive surface. The problems brought by the building of such devices may be solved by the use of gaz counters. But we must sensitize these counters to low energy photons (< 10 eV). We have particularly studied the response of solid state photocathodes working directly into the counter. We show first a method to increase the quantum efficiency of photocathodes. We experiment this method and take few conclusions. We also show a method to measure the photoelectric threshold of a metal under gas and we apply this method. Because of the limitations of our apparatus we have built a system which permit to manufacture and mesure photocathodes. This apparatus which have numerous possibilities and an automatic data taking system is described. We also describe results of its exploitation and the type of investigation that we are going to develop

  12. Photocathode device that replenishes photoemissive coating

    Energy Technology Data Exchange (ETDEWEB)

    Moody, Nathan A.; Lizon, David C.

    2016-06-14

    A photocathode device may replenish its photoemissive coating to replace coating material that desorbs/evaporates during photoemission. A linear actuator system may regulate the release of a replenishment material vapor, such as an alkali metal, from a chamber inside the photocathode device to a porous cathode substrate. The replenishment material deposits on the inner surface of a porous membrane and effuses through the membrane to the outer surface, where it replenishes the photoemissive coating. The rate of replenishment of the photoemissive coating may be adjusted using the linear actuator system to regulate performance of the photocathode device during photoemission. Alternatively, the linear actuator system may adjust a plasma discharge gap between a cartridge containing replenishment material and a metal grid. A potential is applied between the cartridge and the grid, resulting in ejection of metal ions from the cartridge that similarly replenish the photoemissive coating.

  13. Amorphous NEA Silicon Photocathodes - A Robust RF Gun Electron Source. Final Report

    International Nuclear Information System (INIS)

    Amorphous silicon (a-Si) has been shown to have great promise as a negative electron affinity visible wavelength photocathode suitable for radio frequency (RF) gun systems. The specific operating wavelength can be shifted by growing it as a germanium alloy (a-Si(1-x)Ge(x)) rather than as pure silicon. This class of photoemitters has been shown to possess a high degree of immunity to charged particle flux. Such particle flux can be a significant problem in the operation of other photocathodes in RF gun systems. Its emission characteristics in the form of current per unit area, or current density, and emission angle, or beam spread are well matched for use in RF guns. Photocathodes made of a-Si can be fabricated on a variety of substrates including those most commonly employed in RF gun systems. Such photocathodes can be made for operation in either transmission or reflection mode. By growing them utilizing radio frequency plasma enhanced chemical vapor deposition, the unit cost is quite low, the quality is high and it is straightforward to grow custom size substrates and full or limited regions to confine the electron emission to the desired area. Quality emitters have been fabricated on tantalum, molybdenum, tungsten, titanium, copper, stainless steel, float glass, borosilicate glass and gallium arsenide. In addition to performing well in dedicated test chambers, a-Si photocathodes have been shown to function well in self-contained vacuum tubes. In this employment, they are subjected to a strenuous environment. Successful operation in this configuration provides additional confidence in their application to high energy linac photoinjectors and potentially as part of reliable, low cost photocathode driven RF gun systems that could become ready replacements for the diode and triode guns used on medical accelerators. Their applications in stand-alone vacuum tubes is just beginning to be explored.

  14. Review of sustainability indices and indicators: Towards a new City Sustainability Index (CSI)

    International Nuclear Information System (INIS)

    The purpose of this paper is to discuss conceptual requirements for a City Sustainability Index (CSI) and to review existing major sustainability indices/indicators in terms of the requirements. The following indices are reviewed: Ecological Footprint (EF), Environmental Sustainability Index (ESI), Dashboard of Sustainability (DS), Welfare Index, Genuine Progress Indicator (GPI), Index of Sustainable Economic Welfare, City Development Index, emergy/exergy, Human Development Index (HDI), Environmental Vulnerability Index (EVI), Environmental Policy Index (EPI), Living Planet Index (LPI), Environmentally-adjusted Domestic Product (EDP), Genuine Saving (GS), and some applications of composite indices or/and multivariate indicators to local or regional context as case studies. The key conceptual requirements for an adequate CSI are: (i) to consider environmental, economic and social aspects (the triple bottom line of sustainability) from the viewpoint of strong sustainability; (ii) to capture external impacts (leakage effects) of city on other areas beyond the city boundaries particularly in terms of environmental aspects; (iii) to create indices/indicators originally for the purpose of assessing city sustainability; and (iv) to be able to assess world cities in both developed and developing countries using common axes of evaluation. Based on the review, we conclude that it is necessary to create a new CSI that enables us to assess and compare cities' sustainability performance in order to understand the global impact of cities on the environment and human life as compared with their economic contribution. In the future, the CSI will be able to provide local authorities with guidance toward sustainable paths. - Highlights: ► We derive the four key requirements for a new City Sustainability Index (CSI) system. ► First, the triple bottom line must be considered in terms of strong sustainability. ► Second, environmental leakage effects beyond city boundaries should

  15. Graphene shield enhanced photocathodes and methods for making the same

    Science.gov (United States)

    Moody, Nathan Andrew

    2014-09-02

    Disclosed are graphene shield enhanced photocathodes, such as high QE photocathodes. In certain embodiments, a monolayer graphene shield membrane ruggedizes a high quantum efficiency photoemission electron source by protecting a photosensitive film of the photocathode, extending operational lifetime and simplifying its integration in practical electron sources. In certain embodiments of the disclosed graphene shield enhanced photocathodes, the graphene serves as a transparent shield that does not inhibit photon or electron transmission but isolates the photosensitive film of the photocathode from reactive gas species, preventing contamination and yielding longer lifetime.

  16. On the theory of photocathode rf guns

    Institute of Scientific and Technical Information of China (English)

    GAO Jie

    2009-01-01

    In this paper we give a set of analytical formulae to describe the characteristics of photocathode rf guns at any rf frequencies, such as energy, energy spread, bunch length, out going current, and emittance etc.as functions of the laser injection phase, which are useful in the design and practical operation of rf guns.

  17. Wind Load Module For CSi ETABS

    OpenAIRE

    Holst, Eirik Aasved

    2015-01-01

    For korrekt dimensjonering av konstruksjoner er det viktig å medberegne miljøbelastninger, inkludert vindlaster. I Norge bestemmes vindlaster ved bruk av NS-EN 1991-1-4:2005+NA:2009. Regelverket er utformet for håndberegninger, og legger ikke til rette for bruk av datasystemer for effektiv lastberegning. Denne masteroppgaven går ut på å designe og implementere en utvidelse til analyse-programmet CSi ETABS. Utvidelsen må kunne etablere en objektmodell basert på geometrien til en 3D-modell. ...

  18. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Brendel' , V M; Bukin, V V; Garnov, Sergei V; Bagdasarov, V Kh; Denisov, N N; Garanin, Sergey G; Terekhin, V A; Trutnev, Yurii A

    2012-12-31

    A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation. (laser technologies)

  19. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

    Science.gov (United States)

    Brendel', V. M.; Bukin, V. V.; Garnov, Sergei V.; Bagdasarov, V. Kh; Denisov, N. N.; Garanin, Sergey G.; Terekhin, V. A.; Trutnev, Yurii A.

    2012-12-01

    A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation.

  20. Kelvin Probe Studies of Cesium Telluride Photocathode for AWA Photoinjector

    OpenAIRE

    Wisniewski, Eric; Velazquez, Daniel; Yusof, Zikri; Spentzouris, Linda; Terry, Jeff; Harkay, Katherine

    2012-01-01

    Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch (~50 nC) in a long bunch train. Here, we present a study of the work function of cesium telluride photocathode using the Kelvin Probe technique. The study incl...

  1. Imaging Hybrid Photon Detectors with a Reflective Photocathode

    CERN Document Server

    Ferenc, D

    2000-01-01

    Modern epitaxially grown photocathodes, like GaAsP, bring a very high inherent quantum efficiency, but are rather expensive due to the complicated manufacturing and mounting process. We argue that such photocathodes could be used in reflective mode, in order to avoid the risky and expensive removal of the epitaxial growth substrate. Besides that the quantum efficiency should increase considerably. In this paper we present results of the development of large imaging Hybrid Photon Detectors (HPDs), particularly designed for such reflective photocathodes.

  2. Nanostructured Silicon Photocathodes for Solar Water Splitting Patterned by the Self-Assembly of Lamellar Block Copolymers.

    Science.gov (United States)

    Shen, Lang; He, Chunlin; Qiu, Jing; Lee, Sung-Min; Kalita, Abinasha; Cronin, Stephen B; Stoykovich, Mark P; Yoon, Jongseung

    2015-12-01

    We studied a type of nanostructured silicon photocathode for solar water splitting, where one-dimensionally periodic lamellar nanopatterns derived from the self-assembly of symmetric poly(styrene-block-methyl methacrylate) block copolymers were incorporated on the surface of single-crystalline silicon in configurations with and without a buried metallurgical junction. The resulting nanostructured silicon photocathodes with the characteristic lamellar morphology provided suppressed front-surface reflection and increased surface area, which collectively contributed to the enhanced photocatalytic performance in the hydrogen evolution reaction. The augmented light absorption in the nanostructured silicon directly translated to the increase of the saturation current density, while the onset potential decreased with the etching depth because of the increased levels of surface recombination. The pp(+)-silicon photocathodes, compared to the n(+)pp(+)-silicon with a buried solid-state junction, exhibited a more pronounced shift of the current density-potential curves upon the introduction of the nanostructured surface owing to the corresponding increase in the liquid/silicon junction area. Systematic studies on the morphology, optical properties, and photoelectrochemical characteristics of nanostructured silicon photocathodes, in conjunction with optical modeling based on the finite-difference time-domain method, provide quantitative description and optimal design rules of lamellar-patterned silicon photocathodes for solar water splitting. PMID:26575400

  3. Upgrade of a Photocathode RF Gun at SPring-8

    CERN Document Server

    Taniuchi, Tsutomu; Dewa, Hideki; Hanaki, Hirofumi; Kobayashi, Toshiaki; Mizuno, Akihiko; Suzuki, Shinsuke; Tomizawa, Hiromitsu; Yanagida, Kenichi

    2004-01-01

    The test bench of a photocathode RF gun at SPring-8 has been upgraded. The radiation shielded area was expanded about 3 times larger and the maximum beam energy was increased from up to 30 MeV including a 3-m long accelerating tube. The clean room for the drive laser system was newly built and the performance and reliability of the laser was improved. After the construction of the shielded room and set up of the components, the RF conditioning of the waveguides, the gun cavity and the accelerating tube was successfully performed and the beam characteristics such as the emittance and bunch length were measured. In this presentation, further plans for the improvement of the beam quality will also be presented.

  4. First attempts to combine capillary tubes with photocathodes

    CERN Document Server

    Peskov, Vladimir; Sokolova, T; Radionov, I

    1999-01-01

    We describe our efforts to combine glass capillary plates, operating as a gas amplification structure at approx 1 atm, with photocathodes sensitive to visible light. Such capillary tubes are a by-product of the manufacture of Microchannel Plates and are commercially available. Preliminary tests indicate that gas gains >10 sup 3 could be achieved without photon feedback. With two capillary plates in tandem (double-step multiplication) overall gains up to 10 sup 5 were possible at counting rate <100 Hz/mm sup 2. This approach may open new possibilities for detection of visible photons by gaseous detectors. Potential advantages are: high gains, large sensitive area, high granularity, and insensitivity to magnetic fields.

  5. Status update on the photocathode RF LINAC project

    International Nuclear Information System (INIS)

    We present the progress achieved so far in the Photocathode Linac Project. We have developed and tested linear accelerator structures at 2856 MHz, designed and performed preliminary tests on the photocathode gun, commissioned the klystron modulator and microwave systems to extract 3.2 MW of pulsed power, developed the beam-line, and are ready to commence acceleration experiments. (author)

  6. Kelvin Probe Studies of Cesium Telluride Photocathode for AWA Photoinjector

    CERN Document Server

    Wisniewski, Eric; Yusof, Zikri; Spentzouris, Linda; Terry, Jeff; Harkay, Katherine

    2012-01-01

    Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch (~50 nC) in a long bunch train. Here, we present a study of the work function of cesium telluride photocathode using the Kelvin Probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the effect of UV exposure on the work function, and the evolution of the work function during and after photocathode rejuvenation via heating.

  7. MIMO channel capacity with full CSI at Low SNR

    KAUST Repository

    Tall, Abdoulaye

    2012-10-01

    In this paper, we characterize the ergodic capacity of Multiple Input Multiple Output (MIMO) Rayleigh fading channels with full channel state information (CSI) at both the transmitter (CSI-T) and the receiver (CSI-R) at asymptotically low signal-to-noise ratio (SNR). A simple analytical expression of the capacity is derived for any number of transmit and receive antennas. This characterization clearly shows the substantial gain in terms of capacity over the no CSI-T case and gives a good insight on the effect of the number of antennas used. In addition, an On-Off transmission scheme is proposed and is shown to be asymptotically capacity-achieving. © 2012 IEEE.

  8. Constructing n-ZnO@Au heterogeneous nanorod arrays on p-Si substrate as efficient photocathode for water splitting

    Science.gov (United States)

    Bao, Zhijia; Xu, Xiaoyong; Zhou, Gang; Hu, Jingguo

    2016-07-01

    Developing ingenious heterostructure photoelectrodes in photoelectrochemical (PEC) cells to both harvest more solar photons and steer desired charge separation flow is a prerequisite challenge for PEC water splitting. Herein a hierarchical p-Si/n-ZnO@Au heterostructure was constructed via large-area growth of one-dimensional (1D) ZnO nanorod arrays (NRAs) on p-Si substrate followed by decorating with Au nanoparticles (NPs), which exhibited remarkably improved photocathode activity for PEC water splitting relative to the bare Si and Si/ZnO NRAs photocathodes. In addition to structural superiorities of 1D NRAs, a series of dynamic contributions from complementary band-gap structure, p–n heterojunctions and Au plasmon towards photon harvesting and charge separation were demonstrated to ensure a well-steered collection of photoelectrons at the exposed ZnO nanorods and Au NPs, enabling substantially improved photocathode performance.

  9. Constructing n-ZnO@Au heterogeneous nanorod arrays on p-Si substrate as efficient photocathode for water splitting.

    Science.gov (United States)

    Bao, Zhijia; Xu, Xiaoyong; Zhou, Gang; Hu, Jingguo

    2016-07-29

    Developing ingenious heterostructure photoelectrodes in photoelectrochemical (PEC) cells to both harvest more solar photons and steer desired charge separation flow is a prerequisite challenge for PEC water splitting. Herein a hierarchical p-Si/n-ZnO@Au heterostructure was constructed via large-area growth of one-dimensional (1D) ZnO nanorod arrays (NRAs) on p-Si substrate followed by decorating with Au nanoparticles (NPs), which exhibited remarkably improved photocathode activity for PEC water splitting relative to the bare Si and Si/ZnO NRAs photocathodes. In addition to structural superiorities of 1D NRAs, a series of dynamic contributions from complementary band-gap structure, p-n heterojunctions and Au plasmon towards photon harvesting and charge separation were demonstrated to ensure a well-steered collection of photoelectrons at the exposed ZnO nanorods and Au NPs, enabling substantially improved photocathode performance. PMID:27306198

  10. In Situ Observation of Dark Current Emission in a High Gradient rf Photocathode Gun

    Science.gov (United States)

    Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.; Baryshev, Sergey V.; Chen, Huaibi; Conde, Manoel; Gai, Wei; Ha, Gwanghui; Jing, Chunguang; Wang, Faya; Wisniewski, Eric

    2016-08-01

    Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (˜100 μ m ) dark current imaging experiment has been performed in an L -band photocathode gun operating at ˜100 MV /m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. The postexaminations with scanning electron microscopy and white light interferometry reveal the origins of ˜75 % strong emission areas overlap with the spots where rf breakdown has occurred.

  11. Advances in DC photocathode electron guns

    International Nuclear Information System (INIS)

    At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides a source of polarized electrons for the main accelerator. The gun is required to produce high average current with long operational lifetimes and high system throughout. Recent work has shown that careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source operation. These conditions include vacuum and the related effect of ion back-bombardment, and precise control of all of the electrons emitted from the cathode. In this paper, the authors will review recent results and discuss implications for future photocathode guns

  12. Advances in DC photocathode electron guns

    International Nuclear Information System (INIS)

    At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides a source of polarized electrons for the main accelerator. The gun is required to produce high average current with long operational lifetimes and high system throughput. Recent work has shown that careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source operation. These conditions include vacuum and the related effect of ion backbombardment, and precise control of all of the electrons emitted from the cathode. In this paper, we will review recent results and discuss implications for future photocathode guns. copyright 1999 American Institute of Physics

  13. Advances in DC photocathode electron guns

    International Nuclear Information System (INIS)

    At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides a source of polarized electrons for the main accelerator. The gun is required to produce high average current with long operational lifetimes and high system throughput. Recent work has shown that careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source operation. These conditions include vacuum and the related effect of ion backbombardment, and precise control of all of the electrons emitted from the cathode. In this paper, we will review recent results and discuss implications for future photocathode guns

  14. Optimization of laser fired contact processes in c-Si solar cells

    Science.gov (United States)

    Sánchez-Aniorte, I.; Colina, M.; Perales, F.; Molpeceres, C.

    In this work, we study the optimization of aluminium laser-fired contacts (LFC) [1] in combination with c-Si passivated solar cell [2,3]. The samples consist in p-type Fz c-Si wafers with two different passivating configurations; both thermally-grown silicon oxide (SiO2) and plasma deposited silicon carbide (SiCx) were used as the passivating rear layer. Finally, a 2 μ m Aluminum layer was deposited at the front and rear surface. A nanosecond Nd:YAG laser operating at 532 nm was used to fire the aluminum locally through the thin passivating layer. Green lasers offer the possibility to obtain a selective removal of the passivating layer, since the underlying silicon results typically less affected than when using IR radiation. Morphological and electrical analysis permitted to identify the optimal laser parameters to achieve good ohmic contacts and to reduce the laser-damaged area.

  15. Magnetic field effects on the photocathode uniformity of Hamamatsu R7081 photomultiplier tubes

    International Nuclear Information System (INIS)

    We tested the effects of magnetic fields on a photomultiplier tube (PMT), namely, Hamamatsu R7081, with a large surface area photocathode. The output signals of the PMT were affected in such a way that the magnetic fields deflected photoelectrons to the first dynode. We measured the effects produced by the orientation of the PMT relative to the magnetic fields and the variations in the output signals with respect to the incident light positions in the magnetic fields.

  16. Clinical application of 1H-chemical-shift imaging (CSI) to brain diseases

    International Nuclear Information System (INIS)

    An H-1 chemical shift imaging (CSI) was developed as part of the clinical MRI system, by which magnetic resonance spectra (MRS) can be obtained from multiple small voxels and metabolite distribution in the brain can be visualized. The present study was to determine the feasibility and clinical potential of using an H-1 CSI. The device used was a Magnetom H 15 apparatus. The study population was comprised of 25 healthy subjects, 20 patients with brain tumor, 4 with ischemic disease, and 6 with miscellaneous degenerative disease. The H-1 CSI was obtained by the 3-dimensional Fourier transformation. After suppressing the lipid signal by the inversion-recovery method and the water signal by the chemical-shift selective pulse with a following dephasing gradient, 2-directional 16 x 16 phase encodings were applied to the 16 x 16∼18 x 18 cm field of view, in which a 8 x 8 x 2∼10 x 10 x 2 cm area was selected by the stimulated echo or spin-echo method. The metabolite mapping and its contour mapping were created by using the curve-fitted area, with interpolation to the 256 x 256 matrix. In the healthy group, high resolution spectra for N-acetyl aspartate (NAA), creatine, choline (Cho), and glutamine/glutamate were obtained from each voxel; and metabolite mapping and contour mapping also clearly showed metabolite distribution in the brain. In the group of brain tumor, an increased Cho and lactate and loss of NAA were observed, along with heterogeneity within the tumor and changes in the surrounding tissue; and there was a good correlation between lactate peak and tumor malignancy. The group of ischemic and degenerative disease had a decreased NAA and increased lactate on both spectra and metabolite mapping, depending on disease stage. These findings indicated that H-1 CSI is helpful for detecting spectra over the whole brain, as well as for determining metabolite distribution. (N.K.)

  17. Modern theory and applications of photocathodes

    International Nuclear Information System (INIS)

    Over the last thirty years, the Spicer Three-Step model has provided a very useful description of the process of photoemission for both fundamental and practical applications. By treating photoemission in terms of three successive steps-optical absorption, electron transport, and escape across the surface this theory allows photoemission to be related to parameters of the emitter, such as the optical absorption coefficient, electron scattering mechanisms, and the height of the potential barrier at the surface. Using simple equations and established parameters, the Three-Step model predicts the performance of cathodes and provides detailed understanding of the unexpected phenomena that appear when photocathodes are pushed into new practical domains. As an example, time responses are estimated for existing cathodes, and are found to cover a range of six orders of magnitude. Further, the time response is found to be directly related to the sensitivity (i.e., quantum efficiency) of the cathode. The quantum yield systematically decreases with the time response. Thus, metals are predicted to have the shortest time response (as little as 10-15 sec) and the smallest quantum efficiency (as little as 10-4 electrons per photon), whereas the negative affinity photocathodes have high yield (as high as 0.6 electrons per photon) but long response times (as long as 10-9 sec). Other applications of the Three-Step model are discussed

  18. Photo-cathode preparation system of the A0 photo-injector

    Energy Technology Data Exchange (ETDEWEB)

    Moyses Kuchnir et al.

    2002-08-23

    The A0 Photo-Injector is an electron accelerator located in the AZero high bay area of Fermilab. A pulsed laser system generates electron bunches by the photo-electric effect when hitting a photo-cathode in a 1.5-cell, 1.3 GHz RF gun. A 9-cell, 1.3 GHz superconducting resonant cavity then accelerates the electrons to 15 MeV. The 10 ps time resolved waveform of the laser pulses is transferred to the electron bunches. This report is focused on the first hardware component of this accelerator, the Photo-cathode Preparation System. The reason for its existence is in the nature of the photo-electric material film used: Cs{sub 2}Te (Cesium Telluride), a very reactive compound that once coated on the cathode requires that it be transported and used in ultra high vacuum (UHV), i.e. < 10{sup -9} Torr.

  19. Simulation study of the field emission and photoemission on metallic photocathodes. Emitted beam dynamics

    International Nuclear Information System (INIS)

    After a bibliographic research on field emission, photoemission and photo-field emission, the principle of the field equations (Poisson and Maxwell's) resolution by the finite element method is developed. The PRIAM program is shown to be efficient (adaptive mesh and refinement in the selected area). Several possibilities exist to reduce the effect of space charge such as the decrease of the laser pulse duration, the increase of the electric field and the application of a magnetic field. Calculations of the transverse emittance for a metallic plan photocathode have been made at different moments of the emission: transverse emittance is small at the beginning and at the end of the emission. It passes by a maximum which can be the origin of the electronic beam explosion for strong field. If a small emittance is wanted, one must illuminate the photocathode by a short pulsed laser

  20. Beam dynamics studies for photocathode RF gun

    International Nuclear Information System (INIS)

    Photocathode RF guns are very popular choice as injector for low emittance beams especially to light sources world wide. In demand for these gun is increasing steadily and efforts are on to make 2.6 cell RF Gun as SAMEER as proto type for future use at various laboratories. The base design of this 2.6 cell RF Gun is ready and fabrication is planned in near future. In this paper, we present beam dynamic study results of the gun and methodology to arrive at the operating point. Simulation results for Gaussian with nano-second pulse length will be discussed in detail and proposal for generation of few MeV beam will be presented. (author)

  1. Femtosecond electron microscopy using photocathode RF gun

    International Nuclear Information System (INIS)

    The revealing and understanding of ultrafast structural-change induced dynamics are essential not only in physics, chemistry and biology, but also are indispensable for the development of new materials, new devices and applications. Both new RF gun based ultrafast relativistic electron diffraction and microscopy (UED and UEM) have being developed in Osaka University to probe directly structural changes at the atomic scale with sub-100 fs temporal resolution in materials. The first prototype of relativistic-energy UEM using a femtosecond photocathode RF gun has been developed. Both ultrafast diffraction and image measurements have been succeeded using a femtosecond electron beam. In this paper, the development of the UEM prototype and the first experiments of relativistic-energy electron imaging will be reported. (author)

  2. Trojan horse underdense plasma photocathode acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Karger, Oliver [Hamburg Univ. (Germany). Inst. fuer Experimentalphysik; DESY, FLA Arbeitsbereich Beschleunigerphysik, Hamburg (Germany); Koenigstein, Thomas; Pretzler, Georg [Duesseldorf Univ. (Germany). Inst. fuer Laser- und Plasmaphysik; Rosenzweig, James B. [California Univ., Los Angeles, CA (United States). Dept. of Physics and Astronomy; Hidding, Bernhard [Hamburg Univ. (Germany). Inst. fuer Experimentalphysik; DESY, FLA Arbeitsbereich Beschleunigerphysik, Hamburg (Germany); California Univ., Los Angeles, CA (United States). Dept. of Physics and Astronomy

    2013-07-01

    Relativistic electron beams with small emittance and size are needed for advanced applications such as free electron lasers (FEL) and other coherent light sources in the X-ray regime. Present laser plasma acceleration schemes are hardly able to provide electron beams of sufficient quality on a stable level. The concept of underdense plasma photocathode acceleration uses a beam-driven plasma wave in a two component gas mixture consisting a low ionisation threshold medium (LIT) and a high ionisation threshold medium (HIT) and a low-energy laser pulse. Shapeable electron bunches with sub-fs-length and unprecedented normalized emittance down to 10{sup -9} m rad can be produced. Based on this method, laboratory-sized-experimental setups may enable performance much better than today's conventional coherent hard X-ray sources. The presentation discusses the basic concept, shows recent numero-analytical results and the R and D towards experimental realization.

  3. High energy photocathodes for laser fusion diagnostics

    International Nuclear Information System (INIS)

    Laser fusion experiments at the National Ignition Facility require time-resolved x-ray images of the ignition target self-emission. The photon energies are expected to be greater than 10 keV. Photoemission quantum yield measurement data and photoelectron energy spectrum data are presently unavailable in this photon energy range, but are essential in the design of x-ray imaging diagnostics. We developed an apparatus to measure the quantum efficiency of primary and secondary photoelectron emission and to estimate the energy spectrum of the secondary photoelectrons. The apparatus has been tested using photon energies less than 10 keV to allow comparisons with prior work. A method for preparing photocathodes with geometrically enhanced photoefficiency has been developed.

  4. Jefferson Lab IR demo FEL photocathode quantum efficiency scanner

    Science.gov (United States)

    Gubeli, J.; Evans, R.; Grippo, A.; Jordan, K.; Shinn, M.; Siggins, T.

    2001-12-01

    Jefferson Laboratory's Free Electron Laser (FEL) incorporates a cesiated gallium arsenide (GaAs) DC photocathode gun as its electron source. By using a set of scanning mirrors, the surface of the GaAs wafer is illuminated with a 543.5nm helium-neon laser. Measuring the current flow across the biased photocathode generates a quantum efficiency (QE) map of the 1-in. diameter wafer surface. The resulting QE map provides a very detailed picture of the efficiency of the wafer surface. By generating a QE map in a matter of minutes, the photocathode scanner has proven to be an exceptional tool in quickly determining sensitivity and availability of the photocathode for operation.

  5. Fabrication and Measurement of Low Work Function Cesiated Dispenser Photocathodes

    CERN Document Server

    Moody, Nathan A; Jensen, Kevin

    2005-01-01

    Photoinjector performance is a limiting factor in the continued development of high powered FELs and electron beam-based accelerators. Presently available photocathodes are plagued with limited efficiency and short lifetime in an RF-gun environment, due to contamination or evaporation of a photosensitive surface layer. An ideal photocathode should have high efficiency at long wavelengths, long lifetime in practical vacuum environments, and prompt emission. Cathodes with high efficiency typically have limited lifetime, and vice versa, and the needs of the photocathode are generally at odds with those of the drive laser. A potential solution is the low work function dispenser cathode, where lifetime issues are overcome by periodic in situ regeneration that restores the photosensitive surface layer, analogous to those used in the microwave power tube industry. This work reports on the fabrication techniques and performance of cesiated metal photocathodes and cesiated dispenser cathodes, with a focus on understan...

  6. Dye-sensitized nickel(II)oxide photocathodes for tandem solar cell applications

    International Nuclear Information System (INIS)

    To date, nickel(II) oxide (NiO) is one of the few p-type semiconductors that has successfully been used for the construction of dye-sensitized photocathodes as well as tandem dye-sensitized solar cells. In this study we present a novel fabrication method for the preparation of mesoporous NiO films based on preformed NiO nanopowders. Critical properties such as pore-size distribution, crystallinity, and internal surface area of the resulting NiO films were controlled through the sintering process and optimized for their application as dye-sensitized photocathodes, resulting in a significantly increased photovoltaic performance, compared to earlier studies. A series of different sensitizers and electrolytes was scrutinized for their application in dye-sensitized NiO photocathodes. Despite its limited absorption range the dye coumarin 343 clearly outperforms other sensitizers used in this study. Values for short-circuit current densities of 2.13 mA cm-2 and overall energy conversion efficiencies of 0.033% under simulated sunlight (AM1.5, 1000 W m-2) are the highest values reported in literature so far

  7. Improved light transitions from scintillators to new photocathode windows

    International Nuclear Information System (INIS)

    Replacement of a quartz photocathode window by an YAlO3 (YAP) window yielded improved light transitions from BGO crystals (1.78 times) and PbWO4 crystals (1.76 times) to the photocathode. This improvement is due to the higher refractive index of YAP (1.95), which matches much better the indices of BGO (2.14) and PbWO4 (2.18) than quartz (1.47). (author)

  8. Advanced 3D Photocathode Modeling and Simulations Final Report

    International Nuclear Information System (INIS)

    High brightness electron beams required by the proposed Next Linear Collider demand strong advances in photocathode electron gun performance. Significant improvement in the production of such beams with rf photocathode electron guns is hampered by the lack high-fidelity simulations. The critical missing piece in existing gun codes is a physics-based, detailed treatment of the very complex and highly nonlinear photoemission process

  9. High quantum efficiency S-20 photocathodes for photon counting applications

    CERN Document Server

    Orlov, Dmitry A; Pinto, Serge Duarte; Glazenborg, Rene; Kernen, Emilie

    2016-01-01

    Based on conventional S-20 processes, a new series of high quantum efficiency (QE) photocathodes has been developed that can be specifically tuned for use in the ultraviolet, blue or green regions of the spectrum. The QE values exceed 30% at maximum response, and the dark count rate is found to be as low as 30 Hz/cm2 at room temperature. This combination of properties along with a fast temporal response makes these photocathodes ideal for application in photon counting detectors.

  10. Kelvin probe studies of cesium telluride photocathode for AWA photoinjector

    International Nuclear Information System (INIS)

    Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch (≈50nC) in a long bunch train. Here, we present a study of the work function of cesium telluride photocathode using the Kelvin probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the effect of UV exposure on the work function, and the evolution of the work function during and after photocathode rejuvenation via heating. -- Highlights: ► The correlation between Quantum Efficiency (QE) and work function. ► How QE and work function evolve together. ► Rejuvenation of the photocathode via heating and the effect on work function. ► The effects on the work function due to exposure to UV light

  11. Kelvin probe studies of cesium telluride photocathode for AWA photoinjector

    Energy Technology Data Exchange (ETDEWEB)

    Wisniewski, Eric E., E-mail: ewisniew@anl.gov [High Energy Physics Division, Argonne National Laboratory, 9700 S. Cass, Lemont, IL 60439 (United States); Physics Department, Illinois Institute of Technology, 3300 South Federal Street, Chicago, IL 60616 (United States); Velazquez, Daniel [High Energy Physics Division, Argonne National Laboratory, 9700 S. Cass, Lemont, IL 60439 (United States); Physics Department, Illinois Institute of Technology, 3300 South Federal Street, Chicago, IL 60616 (United States); Yusof, Zikri, E-mail: zyusof@hawk.iit.edu [High Energy Physics Division, Argonne National Laboratory, 9700 S. Cass, Lemont, IL 60439 (United States); Physics Department, Illinois Institute of Technology, 3300 South Federal Street, Chicago, IL 60616 (United States); Spentzouris, Linda; Terry, Jeff [Physics Department, Illinois Institute of Technology, 3300 South Federal Street, Chicago, IL 60616 (United States); Sarkar, Tapash J. [Rice University, 6100 Main, Houston, TX 77005 (United States); Harkay, Katherine [Accelerator Science Division, Argonne National Laboratory, 9700 S. Cass, Lemont, IL 60439 (United States)

    2013-05-21

    Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch (≈50nC) in a long bunch train. Here, we present a study of the work function of cesium telluride photocathode using the Kelvin probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the effect of UV exposure on the work function, and the evolution of the work function during and after photocathode rejuvenation via heating. -- Highlights: ► The correlation between Quantum Efficiency (QE) and work function. ► How QE and work function evolve together. ► Rejuvenation of the photocathode via heating and the effect on work function. ► The effects on the work function due to exposure to UV light.

  12. R and D ERL: Photocathode Deposition and Transport System

    International Nuclear Information System (INIS)

    The purpose of the photocathode deposition and transport system is to (1) produce a robust, high yield multialkali photocathode and (2) have a method of transporting the multialkali photocathode for insertion into a super conducting RF electron gun. This process is only successful if a sufficient quantum efficiency lifetime of the cathode, which is inserted in the SRF electron gun, is maintained. One important element in producing a multialkali photocathode is the strict vacuum requirements of 10-11 torr to assure success in the production of longlived photocathodes that will not have their QE or lifetime depleted due to residual gas poisoning in a poor vacuum. A cutaway view of our third generation deposition system is shown in figure 1. There are certain design criteria and principles required. One must be able to install, remove, rejuvenate and replace a cathode without exposing the source or cathode to atmosphere. The system must allow one to deposit Cs, K, and Sb on a cathode tip surface at pressures in the 10-10 to 10-9 torr range. The cathode needs to be heated to as high as 850 C for cleaning and maintained at 130 C to 150 C during deposition. There should also be the capability for in-situ QE measurements. In addition the preparation of dispenser photocathodes must be accounted for, thus requiring an ion source for cathode cleaning. Finally the transport cart must be mobile and be able to negotiate the ERL facility labyrinth.

  13. Validation of the CSI Health Station 6K Blood Pressure Kiosk®

    OpenAIRE

    Buxton, Iain L. O.; Adams, John Q.; Gore, Mark; Sullivan, Charles R.

    2007-01-01

    Established in 1978, Computerized Screening Inc. (CSI) is the manufacturer of medical kiosks that combine non-invasive & invasive preventive health-screening technology and services in the U.S. The centerpiece of CSI’s health complement is the CSI Health Station, one-stop health information and screening using patented technology. The CSI Health Station (Model 6K) represents the corporation’s evolution from its self-administered automated blood pressure monitors (Model 3K). CSI Health Station...

  14. Large Photocathode Photodetectors Using Photon Amplification and Phase-Space Compression

    CERN Document Server

    Carrio, Alex; Greener, Kevin; McGuiness, Sean; Podrasky, Victor; Sullivan, John; Winn, David R; Bilki, Burak; Onel, Yasar

    2014-01-01

    We describe a simple technique to both amplify incident photons and compress their angular x area phase space. These Optical Compressor Amplifier Tubes (OCA Tube) use techniques analogous to image intensifiers, using vacuum photocathodes to detect photons as converted to photoelectrons, amplify the photons via photoelectron bombardment of fast scintillators, and compress the optical phase space onto optical fibers, so that small, high gain photodetectors, like miniature PMT or SiPM, can be used to detect photons from large areas, at comparatively low cost. The properties of and benefits of OCA tubes are described.

  15. Experimental demonstration of a classical approach for flexible space structure control: NASA CSI testbeds

    Science.gov (United States)

    Bond, Wie

    1991-01-01

    The results of active control experiments performed for the Mini-Mast truss structure are presented. The primary research objectives were: (1) to develop active structural control concepts and/or techniques; (2) to verify the concept of robust non-minimum-phase compensation for a certain class of non-colocated structural control problems through ground experiments; (3) to verify a 'dipole' concept for persistent disturbance rejection control of flexible structures; and (4) to identify CSI (Control Structure Interaction) issues and areas of emphasis for the next generation of large flexible spacecraft. The classical SISO (Single Input and Single Output) control design approach was employed.

  16. Equation of state and metallization of CsI

    International Nuclear Information System (INIS)

    Self-consistent, nonrelativistic augmented-plane-wave (APW) calculations for CsI were carried out to generate the band structure, the static-lattice equation of state (EOS), and the volume dependence of the electronic energy-band gap. The theoretical room-temperature isothermal compression curve agrees well with static and ultrasonic measurements at low pressure. Our calculations do not agree with two recent sets of diamond-anvil-cell measurements above 10 GPa. The calculated band gaps are too small at low pressure, but, at high pressure, are consistent with both the experimental results and the Herzfeld-model prediction. These results suggest that the insulator-to-metal transition occurs in the range 100 +- 10 GPa. A calculation of the shock compression curve of CsI shows that the thermally excited electrons cause a significant softening of the Hugoniot curve. The experimental zero-pressure band gaps of the isoelectronic compounds Xe, CsI, and BaTe are linearly correlated with ln(v/v/sub H/), where v/sub H/ is the specific volume of metallization predicted by the Herzfeld model. Based on this correlation, and on the similarity of the APW calculated EOS's of Xe and CsI, which agree closely with experimental compression measurements, we predict that BaTe will become metallic at approximately 30 GPa

  17. Fabrication and measurement of regenerable low work function dispenser photocathodes

    Science.gov (United States)

    Moody, Nathan A.

    Laser-switched photoemitters are a source of electrons for high current applications such as free electron lasers. Laser-modulated photoemission permits rapid switching of the electron beam, far surpassing what can be achieved using electric-field gated emission. Photoinjector systems consist of a drive laser producing short bunches of photons and an efficient photocathode, which converts photon bunches into electron beam pulses. Development of both technologies is required, but the scope of this project is restricted to improvement of the photocathode. Most high-efficiency photocathodes employ cesium-based surface coatings to reduce work function and enable efficient electron emission in the visible range. Lifetime is severely limited by the loss of this delicate coating, which degrades rapidly in practical vacuum environments. More robust photocathodes exist, but have much lower efficiency, and place unrealistic demands on drive laser power and stability. This research proposes a novel dispenser concept that dramatically extends the lifetime of high efficiency cesium-based cathodes by continuously or periodically restoring the cesium surface monolayer during an in situ rejuvenation process. Sintered tungsten provides an interface between a cesium reservoir and the photoemitting surface. During temperature-controlled rejuvenation, cesium diffuses through and across the sintered tungsten to create and sustain a low-work function photocathode. The prototype dispenser cathode was fabricated and tested for two modes of operation: continuous and periodic near-room temperature rejuvenation. The data are compared with a photoemission model of partially covered surfaces under design for integration with existing beam simulations. Overall performance suggests that this cesium-delivery mechanism can significantly enhance the efficiency and operational lifetime of a wide variety of present and future cesium-based photocathodes. Also reported are surface characterization, ion

  18. Proceedings of the workshop on photocathodes for polarized electron sources for accelerators

    International Nuclear Information System (INIS)

    Application of the GaAs polarized electron source to studies of surface magnetism; thermal stability of Cs on NES III-V-Photocathodes and its effect on quantum efficiency; AFEL accelerator; production and detection of SPIN polarized electrons; emittance measurements on a 100-keV beam from a GaAs photocathode electron gun; modern theory of photoemission and its applications to practical photocathodes; experimental studies of the charge limit phenomenon in GaAs photocathodes; new material for photoemission electron source; semiconductor alloy InGaAsP grown on GaAs substrate; NEA photocathode surface preparation; technology and physics; metalorganic chemical vapor deposition of GaAs-GaAsP spin-polarized photocathodes; development of photocathodes injectors for JLC-ATF; effect of radiation trapping on polarization of photoelectrons from semiconductors; and energy analysis of electrons emitted by a semiconductor photocathode

  19. Influence of varied doping structure on photoemissive property of photocathode

    Institute of Scientific and Technical Information of China (English)

    Niu Jun; Zhang Yi-Jun; Chang Ben-Kang; Xiong Ya-Juan

    2011-01-01

    The built-in electric fields within a varied doping GaAs photocathode may promote the transport of electrons from the bulk to the surface, thus the quantum efficiency of the cathode can be enhanced remarkably. But this enhancement,which might be due to the increase in either the number or the energy of electrons reaching the surface, is not clear at present. In this paper, the energy distributions of electrons in a varied doping photocathode and uniform doping photocathode before and after escaping from the cathode surface are analysed, and the number of electrons escaping from the surface in different cases is calculated for the two kinds of photocathodes. The results indicate that the varied doping structure can not only increase the number of electrons reaching the surface but also cause an offset of the electron energy distribution to high energy. That is the root reason for the enhancement of the quantum efficiency of a varied doping GaAs photocathode.

  20. Photocathode Optimization for a Dynamic Transmission Electron Microscope: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Ellis, P; Flom, Z; Heinselman, K; Nguyen, T; Tung, S; Haskell, R; Reed, B W; LaGrange, T

    2011-08-04

    The Dynamic Transmission Electron Microscope (DTEM) team at Harvey Mudd College has been sponsored by LLNL to design and build a test setup for optimizing the performance of the DTEM's electron source. Unlike a traditional TEM, the DTEM achieves much faster exposure times by using photoemission from a photocathode to produce electrons for imaging. The DTEM team's work is motivated by the need to improve the coherence and current density of the electron cloud produced by the electron gun in order to increase the image resolution and contrast achievable by DTEM. The photoemission test setup is nearly complete and the team will soon complete baseline tests of electron gun performance. The photoemission laser and high voltage power supply have been repaired; the optics path for relaying the laser to the photocathode has been finalized, assembled, and aligned; the internal setup of the vacuum chamber has been finalized and mostly implemented; and system control, synchronization, and data acquisition has been implemented in LabVIEW. Immediate future work includes determining a consistent alignment procedure to place the laser waist on the photocathode, and taking baseline performance measurements of the tantalum photocathode. Future research will examine the performance of the electron gun as a function of the photoemission laser profile, the photocathode material, and the geometry and voltages of the accelerating and focusing components in the electron gun. This report presents the team's progress and outlines the work that remains.

  1. Effect of plasmonic near field on the emittance of plasmon-enhanced photocathode

    CERN Document Server

    Jiang, Zeng-gong; Li, Xu-dong; Zhang, Meng; Gu, Duan

    2016-01-01

    The introduction of the surface plasmon polarizations makes the emittance of the photocathode complicated. In this paper, the emittance of plasmon-enhanced photocathode is analyzed. It is first demonstrated that the plasmonic near field can increase the emittance of the plasmon-enhanced photocathode. A simulation method has been used to estimate the emittance caused by plasmonic near field, and the suppression method also has been discussed, both of which are significant for the design of high performance plasmon-enhanced photocathode.

  2. The development of gaseous detectors with solid photocathodes for low temperature applications

    CERN Document Server

    Periale, L.; Iacobaeus, C.; Francke, T.; Lund-Jensen, B.; Pavlopoulos, N.; Picchi, P.; Pietropaolo, F.

    2004-01-01

    There are several applications and fundamental research areas which require the detection of VUV light at cryogenic temperatures. For these applications we have developed and successfully tested special designs of gaseous detectors with solid photocathodes able to operate at low temperatures: sealed gaseous detectors with MgF2 windows and windowless detectors. We have experimentally demonstrated, that both primary and secondary (due to the avalanche multiplication inside liquids) scintillation lights could be recorded by photosensitive gaseous detectors. The results of this work may allow one to significantly improve the operation of some noble liquid gas TPCs.

  3. Deflecting cavity for a temporal response measurement of a photocathode

    International Nuclear Information System (INIS)

    Technologies for the next generation light sources based on energy-recovery linac (ERL) are under development in our group. Photocathode related technology is a key technology for the ERL based light sources. Temporal shape control of the photocathode gun generated electron beam is indispensable to generate ultra-small emittance electron beam. A 1300 MHz deflecting cavity has been developed for a temporal shape measurement of an electron beam from a 250-kV DC photocathode electron gun. The cavity is a rectangle shaped TM120 mode with the unloaded quality factor Q0=17660. The deflecting angle is ±9.5 mrad for the electron bunch with ±50 ps with 134.7 W input RF power. (author)

  4. A study on robust NEA photocathode

    International Nuclear Information System (INIS)

    Electron source is one of the most important components in the advanced linac based application such as linear colliders, next generation light sources like Free Electron Laser (FEL) and Energy Recovery Linac (ERL). They require polarized and very low emittance electron beam as the electron source. In general, there are strong demands on the high performance cathode giving high polarization, high brightness (high current density and low emittance), and short pulse. NEA (Negative Electron Affinity)-GaAs photocathode is a unique technology which is capable for generating high polarized and extremely low emittance beam. Quantum efficiency of the cathode is high even in near IR region, so it is favor to generate a beam with the high current density from this point of view. These advantages are originated from the NEA surface where the vacuum state is lower than the bottom of the conduction band. On the other hand, the NEA surface is easily damaged, and the extractable current density is limited from this fact. To overcome this disadvantage, a robust NEA surface on GaAs cathode as a replacement of the current Cs-O NEA surface is studied. According to the hetero-junction hypothesis, Cs-Te thin film deposited on GaAs surface forms the NEA surface state. We performed the Cs-Te evaporation experiment on a clean GaAs and photo-electron emission was examined in a wide range of wavelength. We succeeded the activation of GaAs with the Cs-Te evaporation and found a high quantum efficiency up to 900 nm wavelength which strongly suggested a NEA surface formation. (author)

  5. CSI computer system/remote interface unit acceptance test results

    Science.gov (United States)

    Sparks, Dean W., Jr.

    1992-01-01

    The validation tests conducted on the Control/Structures Interaction (CSI) Computer System (CCS)/Remote Interface Unit (RIU) is discussed. The CCS/RIU consists of a commercially available, Langley Research Center (LaRC) programmed, space flight qualified computer and a flight data acquisition and filtering computer, developed at LaRC. The tests were performed in the Space Structures Research Laboratory (SSRL) and included open loop excitation, closed loop control, safing, RIU digital filtering, and RIU stand alone testing with the CSI Evolutionary Model (CEM) Phase-0 testbed. The test results indicated that the CCS/RIU system is comparable to ground based systems in performing real-time control-structure experiments.

  6. CSI Flight Computer System and experimental test results

    Science.gov (United States)

    Sparks, Dean W., Jr.; Peri, F., Jr.; Schuler, P.

    1993-01-01

    This paper describes the CSI Computer System (CCS) and the experimental tests performed to validate its functionality. This system is comprised of two major components: the space flight qualified Excitation and Damping Subsystem (EDS) which performs controls calculations; and the Remote Interface Unit (RIU) which is used for data acquisition, transmission, and filtering. The flight-like RIU is the interface between the EDS and the sensors and actuators positioned on the particular structure under control. The EDS and RIU communicate over the MIL-STD-1553B, a space flight qualified bus. To test the CCS under realistic conditions, it was connected to the Phase-0 CSI Evolutionary Model (CEM) at NASA Langley Research Center. The following schematic shows how the CCS is connected to the CEM. Various tests were performed which validated the ability of the system to perform control/structures experiments.

  7. Ablation of CsI by XUV Capillary Discharge Laser

    Science.gov (United States)

    Pira, Peter; Zelinger, Zdenek; Burian, Tomas; Vysin, Ludek; Wild, Jan; Juha, Libor; Lancok, Jan; Nevrly, Vaclav

    2015-09-01

    XUV capillary discharge laser (CDL) is suitable source for ablation of ionic crystals as material which is difficult to ablate by conventional laser. Single crystal of CsI was irradiated by 2.5 ns pulses of a 46.9 nm radiation at 2 Hz. The CDL beam was focused by Sc/Si multilayer spherical mirror. Attenuation length of CsI for this wavelength is 38 nm. Ablation rate was calculated after irradiation of 10, 20, 30, 50 and 100 pulses. Depth of the craters was measured by optical profiler (white light interferometry). Ablation threshold was determined from craters after irradiation with the changing fluence and compared with modeling by XUV-ABLATOR.

  8. Opportunistic Relaying without CSI: Optimizing Variable-Rate HARQ

    OpenAIRE

    Khosravirad, Saeed R.; Szczecinski, Leszek; Labeau, Fabrice

    2014-01-01

    We analyze the opportunistic relaying based on HARQ transmission over the block-fading channel with absence of channel state information (CSI) at the transmitter nodes. We assume that both the source and the relay are allowed to vary their transmission rate between the HARQ transmission rounds. We solve the problem of throughput maximization with respect to the transmission rates using double-recursive Dynamic Programming. Simplifications are also proposed to diminish the complexity of the op...

  9. Deposition of CsI aerosol in horizontal straight pipe under inert and superheated steam environment

    International Nuclear Information System (INIS)

    In a severe accident of an LWR, fission products (FPs) aerosol released from a reactor core region will be deposited on the inner surface of the reactor coolant piping. In such conditions, the piping might be subjected to a thermal load due to decay heat from the deposited FPs. It is very important to quantify the FP aerosol deposition on the piping surfaces. Therefore the FP aerosol behavior in piping is being investigated in the WIND (Wide Range Piping Integrity Demonstration) project at Japan Atomic Energy Research Institute. The objectives of present study are to characterize the aerosol deposition on piping surfaces under various thermal-hydraulic conditions and to obtain insights for the validation of analytical models. A chemical analysis of the deposited aerosol showed that no evidence was found for the decomposition of CsI under inert and superheated steam environments. The major deposition mechanisms are identified to be the condensation of CsI vapor and the thermophoretic aerosol transportation from the carrier gas to the colder piping surfaces. Thermo-fluiddynamic analyses of the carrier gas with WINDFLOW code implied that a precise prediction is required for the evaluation of the amount and the spatial distribution of the aerosol deposition. Remarkable aerosol deposition onto the floor area and enlargement of the deposited aerosol were observed in the test with a superheated steam environment. An additional test will be shortly performed in order to reconfirm the findings obtained under a superheated steam environment. (J.P.N.)

  10. Novel Control Strategy for VSI and CSI Active Filters and Comparing These Two Types of Filters

    Directory of Open Access Journals (Sweden)

    Gholam Reza Arab

    2014-10-01

    Full Text Available Recently to eliminate the harmonics and improve the power factor of the power networks, much attention has been attracted to active filters. The advantages of these filters are lower volume and their better compensating characteristics than the passive filters. In conventional sliding mode controllers, the source current waveform is fluctuated in near to zero values. In this paper, using a new sliding technique, lower Total Harmonic Distortion (THD in source current is obtained and the current waveform is improved. As well as, two novel control strategies for two types of active filters, VSI and CSI is proposed and then these two types of filters are compared to reduce THD value of source current.The proposed controlled strategies are simulated by MATLAB/Simulink. The Simulation results confirm that the proposed strategies reduce the THD of source current more than other strategies, and active filter based on CSI has a better performance than active filter based on VSI with a dead time area (for avoiding short circuit of the source in high powers.

  11. Spectral response calibration of Au and Csl transmission photocathodes of X-ray streak camera in a 60-5500 eV photon energy region%软X射线条纹相机透射式Au与CsI阴极谱响应灵敏度标定

    Institute of Scientific and Technical Information of China (English)

    曾鹏; 袁铮; 邓博; 袁永腾; 李志超; 刘慎业; 赵屹东; 洪才浩; 郑雷; 崔明启

    2012-01-01

    本文利用北京同步辐射光源(BSRF),提出了对条纹相机Au和Csl透射阴极谱响应灵敏度进行绝对标定的方案,给出了在60—5500 eV能区的绝对谱响应灵敏度,标定不确定度好于10%.同时,基于Henke等人的计算模型,给出了透射阴极的相对谱响应灵敏度,并且进行了CH支撑衬底X射线透过率的修正.结果表明标定值与理论值符合较好.%A method is described of measuring absolute spectral response for Au and CsI transmission photocathodes in soft X-ray streak camera,which is of great importance for the inertial confinement fusion(ICF) diagnostics.Transmission photocathode is conventionally employed as photo-to-electron conversion accessories.To derive quantity information of X-ray spectra,the absolute response of photocathode must be calibrated in a range of interest.Here Au and CsI transmission photocathodes with slits are calibrated respectively on Beijing Synchrotron Radiation Facility(BSRF),in a photon energy range of 60 eV—5500 eV.This method has an uncertainty less than 10%and good feasibility.Calibration results are in good agreement with the calculation results obtained from the Henke’s photon emission model,with CH substrate effect revised.

  12. SUPPRESSION OF AFTERPULSING IN PHOTOMULTIPLIERS BY GATING THE PHOTOCATHODE

    Science.gov (United States)

    A number of gating schemes to minimize the long-term afterpulse signal in photomultipliers have been evaluated. Blocking the excitation pulse by gating the photocathode was found to reduce the gate-on afterpulse background by a factor of 230 over that for nongated operation. Thi...

  13. Design and construction a full copper photocathode RF gun

    International Nuclear Information System (INIS)

    The design and construction of an all copper S-band one-and-half cell photocathode electron gun without a choke joint is described. The methods utilized to determine the field balance at the operational frequency without usage of the bead pulling perturbation measurement is given together wit the computational data

  14. Extreme Makeover CSI edition: identity crimes, plastic bodies and genre hybridity in popular television

    OpenAIRE

    Bull, Sofia

    2015-01-01

    This article examines discourses on identity and bodily plasticity in the forensic crime drama CSI: Crime Scene Investigation (2000–). It argues that CSI engages with the same cultural debates as makeover reality TV, but in ways that articulate a number of oppositional perspectives on self-transformation practices governed by the programme's investment in an essentialist and determinist understanding of genetics. The article traces CSI's reconfiguration of the motif of disguise and inverted u...

  15. Control-Structure-Interaction (CSI) technologies and trends to future NASA missions

    Science.gov (United States)

    1990-01-01

    Control-structure-interaction (CSI) issues which are relevant for future NASA missions are reviewed. This goal was achieved by: (1) reviewing large space structures (LSS) technologies to provide a background and survey of the current state of the art (SOA); (2) analytically studying a focus mission to identify opportunities where CSI technology may be applied to enhance or enable future NASA spacecraft; and (3) expanding a portion of the focus mission, the large antenna, to provide in-depth trade studies, scaling laws, and methodologies which may be applied to other NASA missions. Several sections are presented. Section 1 defines CSI issues and presents an overview of the relevant modeling and control issues for LLS. Section 2 presents the results of the three phases of the CSI study. Section 2.1 gives the results of a CSI study conducted with the Geostationary Platform (Geoplat) as the focus mission. Section 2.2 contains an overview of the CSI control design methodology available in the technical community. Included is a survey of the CSI ground-based experiments which were conducted to verify theoretical performance predictions. Section 2.3 presents and demonstrates a new CSI scaling law methodology for assessing potential CSI with large antenna systems.

  16. Diffusive transport of Na(I) and Cs(I) in compacted natural clay

    International Nuclear Information System (INIS)

    Diffusive transport of Cs(I) and Na(I) has been studied in compacted natural clay. The clay was sourced from the western part of India and has been characterized to have smectite as the main clay component. Diffusion of Na(I) in clay was found faster compared to that of Cs(I). The diffusion profile of Cs(I) was analyzed using thin film solution of Fick's second law of Diffusion. The apparent diffusion coefficient of Cs(I) was found 3.1 x 10-12 m2/sec. (author)

  17. The effect of surface cleaning on quantum efficiency in AlGaN photocathode

    International Nuclear Information System (INIS)

    Highlights: • In order to preparative the transmission-mode AlGaN photocathodes in the future, the photocathode has a thin emission layer, and the lattice mismatch at the back interface was eased by varying Al composition of AlGaN sub-layer. • The boiling KOH solution and the mixture of sulfuric acid and hydrogen peroxide can effectively remove the alumina and carbon from the AlGaN photocathode surface, respectively. • The quantum efficiency of the activated AlGaN photocathode has up to 35.1% and improved by 50% from that of cleaned by traditional cleaning technology. - Abstract: To improve the quantum efficiency of AlGaN photocathode, various surfaces cleaning techniques for the removal of alumina and carbon from AlGaN photocathode surface were investigated. The atomic compositions of AlGaN photocathode structure and surface were measured by the X-ray photoelectron spectroscopy and Ar+ ion sputtering. It is found that the boiling KOH solution and the mixture of sulfuric acid and hydrogen peroxide, coupled with the thermal cleaning at 850 °C can effectively remove the alumina and carbon from the AlGaN photocathode surface. The quantum efficiency of AlGaN photocathode is improved to 35.1% at 240 nm, an increase of 50% over the AlGaN photocathode chemically cleaned by only the mixed solution of sulfuric acid and hydrogen peroxide and thermally cleaned at 710 °C

  18. Femtosecond response time measurements of a Cs2Te photocathode

    CERN Document Server

    Aryshev, A; Honda, Y; Terunuma, N; Urakawa, J

    2015-01-01

    We present the response time measurements of a Cs2Te photocathode illuminated with two 100 fs duration, variable time separation laser pulses at 266 nm wavelength. The response time was confirmed in dispersive region downstream of a 12-cell standing wave S-band acceleration structure using a well-known RF zero-crossing technique. At the same time it was also measured by changing mechanical path-length difference between two micro-bunches. Both methods agree that Cs2Te photocathode time response is of the order of 250 fs and thereby it is possible to generate and control a THz sequence of relativistic electron bunches by a conventional S-band RF gun. This result further opens a possibility to construct wide-range tunable THz FEL.

  19. UV pulse shaping for the photocathode RF gun

    International Nuclear Information System (INIS)

    Recently, manipulation with the drive laser plays a significant role in high brightness electron beam production by the photocathode RF gun. The article takes efforts on the temporal shaping of the driving laser for the photocathode RF gun. Method based on pulse stacking by birefringent crystal of α-BBO serials was tried to directly shape ultraviolet laser pulse. Using four pieces of α-BBO crystals to separate an input UV pulse with appropriate duration into 16 sub-pulses can form a ps-spaced pulse train suitable for coherent THz production. The group delay dispersion induced by the crystals was also carefully considered. To avoid beam deterioration by long path propagation, imaging relay of the shaped pulse was applied.

  20. Pulse selection control for the IR FEL photocathode drive laser

    Energy Technology Data Exchange (ETDEWEB)

    Jordan, K.; Evans, R.; Garza, O. [and others

    1997-08-01

    The method for current control of a photocathode source is described. This system allows for full remote control of a photocathode drive laser for resulting electron beam currents ranging from less than one microamp to a full current ranging from less than one microamp to a full current of five milliamps. All current modes are obtained by gating the drive laser with a series of electro-optical cells. The system remotely generates this control signal by assuming a mode of operation with the following properties selectable: Current mode as continuous or gated, micropulse density, macropulse gate width from single shot to 1ms duration, macropulse synchronization to A/C line voltage (60 Hz) or an external trigger, 60 Hz phase and slewing through 60 Hz when applicable. All selections are derived from programmable logic devices operating from a master-oscillator resulting in a discrete, phase stable, pulse control for the drive laser.

  1. UV pulse shaping for the photocathode RF gun

    Energy Technology Data Exchange (ETDEWEB)

    Yan Lixin, E-mail: yanlx@mail.tsinghua.edu.cn [Accelerator Laboratory, Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Key Laboratory of Particle and Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084 (China); Key Laboratory of High Energy Radiation Imaging Fundamental Science for National Defense, Beijing 100084 (China); Du Qiang; Du Yingchao; Hua Jianfei; Huang Wenhui; Tang Chuanxiang [Accelerator Laboratory, Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Key Laboratory of Particle and Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084 (China); Key Laboratory of High Energy Radiation Imaging Fundamental Science for National Defense, Beijing 100084 (China)

    2011-05-01

    Recently, manipulation with the drive laser plays a significant role in high brightness electron beam production by the photocathode RF gun. The article takes efforts on the temporal shaping of the driving laser for the photocathode RF gun. Method based on pulse stacking by birefringent crystal of {alpha}-BBO serials was tried to directly shape ultraviolet laser pulse. Using four pieces of {alpha}-BBO crystals to separate an input UV pulse with appropriate duration into 16 sub-pulses can form a ps-spaced pulse train suitable for coherent THz production. The group delay dispersion induced by the crystals was also carefully considered. To avoid beam deterioration by long path propagation, imaging relay of the shaped pulse was applied.

  2. CSI flight experiment projects of the Naval Research Laboratory

    Science.gov (United States)

    Fisher, Shalom

    1993-02-01

    The Naval Research Laboratory (NRL) is involved in an active program of CSI flight experiments. The first CSI flight experiment of the Naval Research Laboratory, the Low Power Atmospheric Compensation Experiment (LACE) dynamics experiment, has successfully measured vibrations of an orbiting satellite with a ground-based laser radar. The observations, made on January 7, 8 and 10, 1991, represent the first ever measurements of this type. In the tests, a narrowband heterodyne CO2 laser radar, operating at a wavelength of 10.6 microns, detected vibration induced differential-Doppler signatures of the LACE satellite. Power spectral densities of forced oscillations and modal frequencies and damping rates of free-damped vibrations were obtained and compared with finite element structural models of the LACE system. Another manifested flight experiment is the Advanced Controls Technology Experiment (ACTEX) designed to demonstrate active and passive damping with piezo-electric (PZT) sensors and actuators. This experiment was developed under the management of the Air Force Phillips Laboratory with integration of the experiment at NRL. It is to ride as a secondary, or 'piggyback,' experiment on a future Navy satellite.

  3. Photocathode-Uniformity Tests of the Hamamatsu R5912 Photomultiplier Tubes Used in the Milagro Experiment

    CERN Document Server

    Vasileiou, V; Smith, A J

    2007-01-01

    The Milagro experiment observes the extensive air showers produced by very high energy gamma-rays impacting the Earth's atmosphere. Milagro uses 898 Hamamatsu R5912 Photomultiplier Tubes. To complete our Monte Carlo simulations, we tested the photocathode uniformity of our PMTs. The main finding was that the PMT gain and detection efficiency are a function of the distance from the center of the photocathode. Both quantities become considerably smaller as the illumination position nears the edge of the photocathode.

  4. Characterization of diamond film and bare metal photocathodes as a function of temperature and surface preparation

    International Nuclear Information System (INIS)

    High current photocathodes using bare metal and polycrystalline diamond films illuminated by ultraviolet lasers are being developed at Los Alamos for use in a new generation of linear induction accelerators. These photocathodes must be able to produce multiple 60 ns pulses separated by several to tens of nanoseconds. The vacuum environment in which the photocathodes must operate is 10-5 torr. (author). 9 figs., 10 refs

  5. Recent developments in high voltage photocathode DC gun for accelerator

    International Nuclear Information System (INIS)

    A photoinjector which can generate a high brightness, low emittance and short duration electron bunches is required for future light source accelerators and applications such as electron microscopes. A DC high voltage gun which has a semiconductor photocathode in a high DC electric field is one of the technology choices for the generation of high quality electron beam. Many techniques to the development of semiconductor based photoemission gun are introduced in briefly. (author)

  6. Brookhaven Accelerator Test Facility photocathode gun and transport beamline

    International Nuclear Information System (INIS)

    We present an analysis of the electron beam emitted from a laser driven photocathode injector (Gun, operating at 2856 MHZ), through a Transport beamline, to the LINAC entrance for the Brookhaven Accelerator Test Facility (ATF). The beam parameters including beam energy, and emittance are calculated. Some of our results, are tabulated and the phase plots of the beam parameters, from Cathode, through the Transport line elements, to the LINAC entrance, are shown

  7. Applications of Laser and Synchrotron Based ARPES to Photocathode Research

    Energy Technology Data Exchange (ETDEWEB)

    Rameau J.; Smedley J.; Muller, E.; Kidd, T.; Johnson, P.; Allen, P.; Carr, L.; Valla, T.

    2010-10-12

    Laser angle resolved photoelectron spectroscopy (ARPES) provides unique information about angle and energy distribution of photoelectrons. Laser ARPES gives unique insight into how NEA materials work. ARPES combined with some ancillary measurements gives a very complete picture of system electronic physics. For H:C[100] there is now a clear program for engineering as well as development analogous systems. ARPES well suited for identifying 'ideal' photocathodes with intrinsically low emittance and high QE.

  8. Status of the photocathode linac project at CAT

    International Nuclear Information System (INIS)

    We present the progress achieved so far in the Photocathode Linac Project. We have successfully developed, for the first time in CAT, the technology to build linear accelerator structures. We have also developed the klystron modulator and microwave systems, and are ready to commence acceleration experiments. An undulator has been built for a free-electron laser, which can generate intense tunable radiation using the electron beam (author)

  9. Thermal emittance measurements of a cesium potassium antimonide photocathode

    OpenAIRE

    Bazarov, Ivan; Cultrera, Luca; Bartnik, Adam; Dunham, Bruce; Karkare, Siddharth; Li, Yulin; Liu, Xianghong; Maxson, Jared; Roussel, William

    2011-01-01

    Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56+/-0.03 mm-mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.

  10. Thermal emittance measurements of a cesium potassium antimonide photocathode

    Science.gov (United States)

    Bazarov, Ivan; Cultrera, Luca; Bartnik, Adam; Dunham, Bruce; Karkare, Siddharth; Li, Yulin; Liu, Xianghong; Maxson, Jared; Roussel, William

    2011-05-01

    Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56±0.03 mm mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.

  11. Perception-Induced Effects of Corporate Social Irresponsibility (CSiR) for Stereotypical and Admired Firms.

    Science.gov (United States)

    Voliotis, Seraphim; Vlachos, Pavlos A; Epitropaki, Olga

    2016-01-01

    How do stakeholders react to Corporate Social Irresponsibility (CSiR)? What are the emotional mechanisms and behavioral outcomes following CSiR perception? The psychology of CSR literature has yet to address these important questions and has largely considered CSR and CSiR as the opposite poles of the same continuum. In contrast, we view CSR and CSiR as distinct constructs and theorize about the cognitive (perceptual), emotional, and behavioral effects of CSiR activity on observers (i.e., primary and secondary stakeholders) building on theories of intergroup perception. Specifically, building on the Stereotype Content Model (SCM; Fiske et al., 2002) and the BIAS map (i.e., Behaviors from Intergroup Affect and Stereotypes; Cuddy et al., 2007)-which extends the SCM by predicting behavioral responses-we make predictions on potential stakeholder reactions to CSiR focusing on two practice-relevant cases: (a) a typical for-profit firm that engages in a CSiR activity, (b) an atypical admired firm that engages in CSiR activity. PMID:27445931

  12. Perception-Induced Effects of Corporate Social Irresponsibility (CSiR) for Stereotypical and Admired Firms

    Science.gov (United States)

    Voliotis, Seraphim; Vlachos, Pavlos A.; Epitropaki, Olga

    2016-01-01

    How do stakeholders react to Corporate Social Irresponsibility (CSiR)? What are the emotional mechanisms and behavioral outcomes following CSiR perception? The psychology of CSR literature has yet to address these important questions and has largely considered CSR and CSiR as the opposite poles of the same continuum. In contrast, we view CSR and CSiR as distinct constructs and theorize about the cognitive (perceptual), emotional, and behavioral effects of CSiR activity on observers (i.e., primary and secondary stakeholders) building on theories of intergroup perception. Specifically, building on the Stereotype Content Model (SCM; Fiske et al., 2002) and the BIAS map (i.e., Behaviors from Intergroup Affect and Stereotypes; Cuddy et al., 2007)—which extends the SCM by predicting behavioral responses—we make predictions on potential stakeholder reactions to CSiR focusing on two practice-relevant cases: (a) a typical for-profit firm that engages in a CSiR activity, (b) an atypical admired firm that engages in CSiR activity. PMID:27445931

  13. The Communication Styles Inventory (CSI): a six-dimensional behavioral model of communication styles and its relation with personality

    NARCIS (Netherlands)

    R.E. de Vries; A. Bakker-Pieper; F.E. Konings; B. Schouten

    2013-01-01

    In this study, a six-dimensional model of communication styles is proposed and operationalized using the Communication Styles Inventory (CSI). The CSI distinguishes between six domain-level communicative behavior scales, Expressiveness, Preciseness, Verbal Aggressiveness, Questioningness, Emotionali

  14. Correlation of CsK2Sb photocathode lifetime with antimony thickness

    Energy Technology Data Exchange (ETDEWEB)

    Mamun, M. A. [Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia 23529, USA; The Applied Research Center, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA; Hernandez-Garcia, C. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA; Poelker, M. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA; Elmustafa, A. A. [Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia 23529, USA; The Applied Research Center, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA

    2015-06-01

    CsK2Sb photocathodes with quantum efficiency on the order of 10% at 532 nm, and lifetime greater than 90 days at low voltage, were successfully manufactured via co-deposition of alkali species emanating from an effusion source. Photocathodes were characterized as a function of antimony layer thickness and alkali consumption, inside a vacuum chamber that was initially baked, but frequently vented without re-baking. Photocathode lifetime measured at low voltage is correlated with the antimony layer thickness. Photocathodes manufactured with comparatively thick antimony layers exhibited the best lifetime. We speculate that the antimony layer serves as a reservoir, or sponge, for the alkali.

  15. Correlation of CsK{sub 2}Sb photocathode lifetime with antimony thickness

    Energy Technology Data Exchange (ETDEWEB)

    Mamun, M. A., E-mail: mmamu001@odu.edu; Elmustafa, A. A. [Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia 23529 (United States); The Applied Research Center, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Hernandez-Garcia, C.; Poelker, M. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)

    2015-06-01

    CsK{sub 2}Sb photocathodes with quantum efficiency on the order of 10% at 532 nm, and lifetime greater than 90 days at low voltage, were successfully manufactured via co-deposition of alkali species emanating from an effusion source. Photocathodes were characterized as a function of antimony layer thickness and alkali consumption, inside a vacuum chamber that was initially baked, but frequently vented without re-baking. Photocathode lifetime measured at low voltage is correlated with the antimony layer thickness. Photocathodes manufactured with comparatively thick antimony layers exhibited the best lifetime. We speculate that the antimony layer serves as a reservoir, or sponge, for the alkali.

  16. Correlation of CsK2Sb photocathode lifetime with antimony thickness

    Directory of Open Access Journals (Sweden)

    M. A. Mamun

    2015-06-01

    Full Text Available CsK2Sb photocathodes with quantum efficiency on the order of 10% at 532 nm, and lifetime greater than 90 days at low voltage, were successfully manufactured via co-deposition of alkali species emanating from an effusion source. Photocathodes were characterized as a function of antimony layer thickness and alkali consumption, inside a vacuum chamber that was initially baked, but frequently vented without re-baking. Photocathode lifetime measured at low voltage is correlated with the antimony layer thickness. Photocathodes manufactured with comparatively thick antimony layers exhibited the best lifetime. We speculate that the antimony layer serves as a reservoir, or sponge, for the alkali.

  17. Measurement of initial emittance of back illuminated transparent superconducting multi-alkali photocathode

    International Nuclear Information System (INIS)

    We have manufactured the back-illuminated superconducting photocathode for the FEL with high pulse repetition. The novelty of this photocathode is adopting the transparent superconducting thin film LiTi2O4 as a substrate. LTO reflects RF field because of a short penetration depth of superconductor and this feature protects optical components from RF damage. Using the photocathode, a high quality beam with a low energy spread and a low space spread is expected to be produced. This paper presents experimental results of the initial emittance of multi-alkali photocathode on SrTiO3 substrate. (author)

  18. Offshore wind farm with a series multiterminal CSI HVDC

    Energy Technology Data Exchange (ETDEWEB)

    Jovcic, Dragan [Department of Engineering, King' s College, University of Aberdeen, Aberdeen AB24 3UE (United Kingdom)

    2008-04-15

    This paper presents an integrated design of an offshore wind farm and an interconnection circuit based on a series multiterminal HVDC link with current source inverters (CSI). The transmission converters are used to achieve variable speed operation for a group of generators, and this enables use of very simple generators. The series converter connection eliminates offshore transformers. The paper discusses the control systems for both, generator side and grid side converters. A 200 MW wind farm is simulated on PSCAD/EMTDC platform and the responses confirm satisfactory operation for a range of wind speed changes. It is shown that each generator group can operate with a different and optimal frequency and that wind variations on individual units cannot jeopardize system stability. The main challenges for the proposed topology are system insulation and management of transmission line losses, and the paper studies some possible solutions. (author)

  19. Decoupled front/back dielectric textures for flat ultra-thin c-Si solar cells.

    Science.gov (United States)

    Isabella, Olindo; Vismara, Robin; Ingenito, Andrea; Rezaei, Nasim; Zeman, M

    2016-03-21

    The optical analysis of optically-textured and electrically-flat ultra-thin crystalline silicon (c-Si) slabs is presented. These slabs were endowed with decoupled front titanium-dioxide (TiO2) / back silicon-dioxide (SiO2) dielectric textures and were studied as function of two types of back reflectors: standard silver (Ag) and dielectric modulated distributed Bragg reflector (MDBR). The optical performance of such systems was compared to that of state-of-the-art flat c-Si slabs endowed with so-called front Mie resonators and to those of similar optical systems still endowed with the same back reflectors and decoupled front/back texturing but based on textured c-Si and dielectric coatings (front TiO2 and back SiO2). Our optimized front dielectric textured design on 2-µm thick flat c-Si slab with MDBR resulted in more photo-generated current density in c-Si with respect to the same optical system but featuring state-of-the-art Mie resonators ( + 6.4%), mainly due to an improved light in-coupling between 400 and 700 nm and light scattering between 700 and 1050 nm. On the other hand, the adoption of textured dielectric layers resulted in less photo-generated current density in c-Si up to -20.6% with respect to textured c-Si, depending on the type of back reflector taken into account. PMID:27136888

  20. The behavior of cesium iodide radioaerosols during CsI sublimation from metal surface

    International Nuclear Information System (INIS)

    One of the biologically most dangerous volatile fission products getting into the environment during hypothetical severe accidents at NPPs are CsI radioaerosols. This is the reason why great attention is now being devoted to a study of the behavior of CsI radioaerosols in the steam-gas phase. We studied the behavior of CsI aerosols using a setup made of a steam generator, a reaction chamber with a Pt heater, a condenser, bubblers with a Na2S2O3 solution, and a Petryanov filter. The method of radionuclide diagnostic was used for study of the CsI behavior during sublimation from the metal surface. The theoretical mass ratio between cesium and iodine in the CsI molecule is equal to 1.04. So, an upward deviation from this theoretical value will show an increase in the amount of cesium, and, respectively, a downward deviation will indicate an increase in the amount of iodine. Thus, change in the Cs/I ratio was a parameter with the help of which we considered estimating the extent of the oxidation hydrolysis of CsI aerosols. (orig.)

  1. Relay Precoder Optimization in MIMO-Relay Networks With Imperfect CSI

    KAUST Repository

    Ubaidulla, P.

    2011-11-01

    In this paper, we consider robust joint designs of relay precoder and destination receive filters in a nonregenerative multiple-input multiple-output (MIMO) relay network. The network consists of multiple source-destination node pairs assisted by a MIMO-relay node. The channel state information (CSI) available at the relay node is assumed to be imperfect. We consider robust designs for two models of CSI error. The first model is a stochastic error (SE) model, where the probability distribution of the CSI error is Gaussian. This model is applicable when the imperfect CSI is mainly due to errors in channel estimation. For this model, we propose robust minimum sum mean square error (SMSE), MSE-balancing, and relay transmit power minimizing precoder designs. The next model for the CSI error is a norm-bounded error (NBE) model, where the CSI error can be specified by an uncertainty set. This model is applicable when the CSI error is dominated by quantization errors. In this case, we adopt a worst-case design approach. For this model, we propose a robust precoder design that minimizes total relay transmit power under constraints on MSEs at the destination nodes. We show that the proposed robust design problems can be reformulated as convex optimization problems that can be solved efficiently using interior-point methods. We demonstrate the robust performance of the proposed design through simulations. © 2011 IEEE.

  2. A pulsed electron injector using a metal photocathode irradiated by an excimer laser

    International Nuclear Information System (INIS)

    The hot cathode of an electron gun is replaced by a metallic photocathode driven by an excimer laser. The current, current density, and emittance of the 500-kV electron beam produced by the photoelectron source are presented. In addition, the temperature of the photocathode is varied to study the possibility of a hybrid source

  3. Chlorination reaction kinetics of CsI under cladding hull waste treatment condition. A TGA study

    International Nuclear Information System (INIS)

    The reaction between cesium iodide (CsI) and chlorine gas was quantitatively investigated using a thermo- gravimetric analysis system. A comparison between calculated and experimental results on the chlorine molar flow rate revealed that the reaction lies within the gas phase diffusion limited region under the condition of this work. Using the experimental data, the second-order nucleation and growth model was identified as the best geometry function to describe the morphological changes of CsI during the chlorination reaction. Combining the gas phase diffusion equation and geometry function, a reaction rate equation was proposed for the reaction between CsI and Cl2. (author)

  4. Adsorption and revaporisation studies of thin iodine oxide and CsI aerosol deposits from containment surface materials in LWRs

    Energy Technology Data Exchange (ETDEWEB)

    Tietze, S.; Foreman, M.; Ekberg, C. [Chalmers Univ. of Technology, Goeteborg (Sweden); Kaerkelae, T.; Auvinen, A.; Tapper, U.; Jokiniemi, J. [VTT Technical Research Centre of Finland, Espoo (Finland)

    2013-07-15

    speciation of the particles. The formation of HIO{sub 3} was verified with Raman analysis regardless of the reaction temperature. Furthermore, elemental iodine was also observed in the measured Raman spectra. Probably, iodine oxide particles had reacted with air humidity forming iodic acid and elemental iodine. IOx and CsI particles that were deposited on various sample surfaces were synthesized at 120 deg. C. According to XPS analysis, it seemed that IOx particles were mainly in form of HIO{sub 3} on the metal and on the painted surfaces. The XPS spectrum of CsI was observed on all metal and painted samples on which CsI particles were deposited. However, the CsI particles seemed to have dissolved at least partially by air humidity. Iodine was observed at areas outside the caesium iodide deposits on metal and on painted surfaces. According to the XPS analyses, iodine was in oxidised form. The measurements indicated that iodine may have reacted with the oxidized metal surfaces to form metal iodates. Only trace amounts of oxidized iodine were detected on the painted surfaces. An interesting result in the XPS analysis was that a part of the acquired signal from CsI on the painted surfaces seemed to originate deeper from the structure of the paint when it was pre-treated either with heat or gamma irradiation. SEM analysis revealed that heat and gamma irradiation treatment increased the porosity of the paint. Therefore, dissolved CsI may have been transported into the matrix of the paint. Besides copper the studied metal surfaces underwent slow reactions with the iodine of the aerosol deposits which showed in the high revaporisation rates at room temperature and elevated temperatures. On the copper and paint samples it could be shown that these surfaces react more easily with the iodine from cesium iodide deposits. From the chemically converted metal iodides only copper iodide remained on the surfaces after exposure to hot humid air and as well after immersion in boiling water

  5. Adsorption and revaporisation studies of thin iodine oxide and CsI aerosol deposits from containment surface materials in LWRs

    International Nuclear Information System (INIS)

    the particles. The formation of HIO3 was verified with Raman analysis regardless of the reaction temperature. Furthermore, elemental iodine was also observed in the measured Raman spectra. Probably, iodine oxide particles had reacted with air humidity forming iodic acid and elemental iodine. IOx and CsI particles that were deposited on various sample surfaces were synthesized at 120 deg. C. According to XPS analysis, it seemed that IOx particles were mainly in form of HIO3 on the metal and on the painted surfaces. The XPS spectrum of CsI was observed on all metal and painted samples on which CsI particles were deposited. However, the CsI particles seemed to have dissolved at least partially by air humidity. Iodine was observed at areas outside the caesium iodide deposits on metal and on painted surfaces. According to the XPS analyses, iodine was in oxidised form. The measurements indicated that iodine may have reacted with the oxidized metal surfaces to form metal iodates. Only trace amounts of oxidized iodine were detected on the painted surfaces. An interesting result in the XPS analysis was that a part of the acquired signal from CsI on the painted surfaces seemed to originate deeper from the structure of the paint when it was pre-treated either with heat or gamma irradiation. SEM analysis revealed that heat and gamma irradiation treatment increased the porosity of the paint. Therefore, dissolved CsI may have been transported into the matrix of the paint. Besides copper the studied metal surfaces underwent slow reactions with the iodine of the aerosol deposits which showed in the high revaporisation rates at room temperature and elevated temperatures. On the copper and paint samples it could be shown that these surfaces react more easily with the iodine from cesium iodide deposits. From the chemically converted metal iodides only copper iodide remained on the surfaces after exposure to hot humid air and as well after immersion in boiling water. Both, non aged and

  6. Effects of atomic hydrogen and deuterium exposure on high polarization GaAs photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    M. Baylac; P. Adderley; J. Brittian; J. Clark; T. Day; J. Grames; J. Hansknecht; M. Poelker; M. Stutzman; A. T. Wu; A. S. Terekhov

    2005-12-01

    Strained-layer GaAs and strained-superlattice GaAs photocathodes are used at Jefferson Laboratory to create high average current beams of highly spin-polarized electrons. High electron yield, or quantum efficiency (QE), is obtained only when the photocathode surface is atomically clean. For years, exposure to atomic hydrogen or deuterium has been the photocathode cleaning technique employed at Jefferson Laboratory. This work demonstrates that atomic hydrogen cleaning is not necessary when precautions are taken to ensure that clean photocathode material from the vendor is not inadvertently dirtied while samples are prepared for installation inside photoemission guns. Moreover, this work demonstrates that QE and beam polarization can be significantly reduced when clean high-polarization photocathode material is exposed to atomic hydrogen from an rf dissociator-style atomic hydrogen source. Surface analysis provides some insight into the mechanisms that degrade QE and polarization due to atomic hydrogen cleaning.

  7. Characterization of x-ray photocathode in transmission mode for imaging application

    International Nuclear Information System (INIS)

    The performance of an Al x-ray transmission photocathode was experimentally characterized by measuring the total electron yield from backsurface photocathodes of varying thickness. It was demonstrated that the backsurface electron yield is proportional to the x-ray photocurrent transmitted through the photocathode for thicknesses thicker than the optimum thickness. The optimum photocathode thickness with the highest conversion efficiency was found to be approximately 70 nm at 2.963 keV. An escape depth of the secondary electrons was determined to be approximately 13 nm from the yield-versus-thickness data fitted with a semiempirical equation. Using this parameter, the dependence of the optimum photocathode thickness on the x-ray energy was calculated for the 30-10000 eV range. As one example of imaging applications, different photoemission images in the transmission and reflection modes are also presented.

  8. A mechanism of Cu work function reduction in CsBr/Cu photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Halliday, Matthew T.; Hess, Wayne P.; Shluger, AL

    2016-03-14

    Thin films of CsBr deposited on Cu(100) have been proposed as next-generation photocathode materials for applications in particle accelerators and free-electron lasers. However, the mechanisms underlying an improved photocathode performance remain poorly understood. We present density Functional Theory (DFT) calculations of the work function reduction following the application of CsBr thin film coatings to Cu photocathodes. The effects of structure and van der Waals forces are examined. Calculations suggest that CsBr films can reduce the work function by around 1.5 eV, which would explain the exponential increase in quantum efficiency (QE) of coated vs. uncoated photocathodes. A model explaining experimentally observed laser activation of photocathode is provided whereby the photo-induced creation of di-vacancies at the surface, and their subsequent diffusion throughout the lattice and segregation at the interface leads to a further increase in QE after a period of laser irradiation.

  9. Kelvin probe studies of cesium telluride photocathode for the AWA photoinjector

    Energy Technology Data Exchange (ETDEWEB)

    Velazquez, D.; Wisniewski, E. E.; Yusof, Z.; Harkay, K.; Spentzouris, L.; Terry, J. [Physics Department at Illinois Institute of Technology, Chicago, IL 60616 and High Energy Physics Division at Argonne National Laboratory, Lemont, IL 60439 (United States); High Energy Physics Division at Argonne National Laboratory, Lemont, IL 60439 (United States); Accelerator Science Division at Argonne National Laboratory, Lemont, IL 60439 (United States); Physics Department at Illinois Institute of Technology, Chicago, IL 60616 (United States)

    2012-12-21

    Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (> 1%), is robust in a photoinjector, and long lifetime. This photocathode is fabricated in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch ({approx}50 nC) in a long bunch train. We present some results from a study of the work function of cesium telluride photocathode using the Kelvin Probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the effect of UV light exposure on the work function, and the evolution of the work function during and after photocathode rejuvenation via heating.

  10. Pulse Selection Control for the IR FEL Photocathode Drive Laser

    Science.gov (United States)

    Jordan, K.; Evans, R.; Garza, O.; Hill, R.; Shinn, M.; Song, J.; Venhaus, D.

    1997-05-01

    The method for current control of the photocathode source is described. This device allows remote control of drive laser output pulses for resulting beam currents of less than 1 microamp to full current of 5 milliamps. The low current modes are accomplished by counting discrete micropulses and gating electro-optical cells. The higher current modes are done by varying both the photons per pulse and the frequency of the laser output pulses. Programmable Logic Devices (PLDs) provide the choice in micropulses per macropulse and the macropulse frequency. All macropulses are line locked to 60 Hz and have the ability to be slewed through a line cycle in discrete steps.

  11. A stabilised blue-violet LED for VPT photocathode evaluation

    CERN Document Server

    Hobson, Peter R

    2000-01-01

    A highly stable blue-violet light source ( peak wavelength 430 nm) based on the IPL 10630PAL self-monitoring LED is described. A thermoelectric cooler has been used to stabilise the 10630PAL device and the external LED current-control electronics to +- 0.1% K. The light intensity was measured to be stable to +- 0.03% for five hours, the repeatability was +- 0.1% The output spectrum of the LED is a good match to the scintillation emission of PbWO4, and this source will be used to evaluate the spatial and angular uniformity of VPT photocathodes for the endcap calorimeter.

  12. Ultra-low emittance X-band photocathode RF gun

    Institute of Scientific and Technical Information of China (English)

    TANG Chuan-Xiang; LIU Xiao-Han

    2009-01-01

    In this paper,we present the simulation results of a 1.6 cell X-band photocathode RF gun for ultra-low emittance electron beams.It will work at 9.3 GHz.The emittance,bunch length,electron energy and energy spread at the gun exit are optimized at bunch charge of 1pC using PARMELA.Electron bunches type coupler is adopted in this gun and an initial simulation by MAFIA is also given in this paper.

  13. Lasertron, a pulsed RF-source using laser triggered photocathode

    International Nuclear Information System (INIS)

    A new pulsed RF-source, 'Lasertron', are being developed as a possible RF-power source for future electron-positron linear colliders. In a series of systematic study, a prototype lasertron has been fabricated and tested. A peak power of 80 kW is attained at 2.856 GHz RF-frequency in 1-μs time duration. This paper describes the experimental results of the lasertron including the developments of the photocathode and the laser system. Test results are compared with the analysis of beam dynamics in the lasertron. (author)

  14. Nanosecond length electron pulses from a laser-excited photocathode

    International Nuclear Information System (INIS)

    A photocathode made from polycrystalline lanthanum hexaboride (LaB6) has produced nanosecond length electron pulses when excited by an excimer laser at 308nm. Peak currents in excess of 1A have been observed, with quantum yields of 4 x 10-5 being measured. A method for extracting the electrons from an emission-limited cathode, plasma extraction, has been demonstrated. This technique uses a low power continuous discharge to provide the electric field needed to extract the photoelectrons. This technique may be useful in producing high repetition rate short pulse ion sources. 10 refs., 4 figs

  15. Thermal emittance and response time of a cesium antimonide photocathode

    Science.gov (United States)

    Cultrera, Luca; Bazarov, Ivan; Bartnik, Adam; Dunham, Bruce; Karkare, Siddharth; Merluzzi, Richard; Nichols, Matthew

    2011-10-01

    Measurements of the intrinsic emittance and response time of a Cs3Sb photocathode are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. Photoemission response time is evaluated using a RF deflecting cavity synchronized to a picosecond laser pulse train. We find that Cs3Sb has both small mean transverse energy, 160 ± 10 meV at 532 nm laser wavelength, and a prompt response time (below the resolution of our measurement) making it a suitable material for high brightness electron photoinjectors.

  16. Uplink Contention-based CSI Feedback with Prioritized Layers for a Multi-Carrier System

    DEFF Research Database (Denmark)

    Kaneko, Megumi; Hayashi, Kazunori; Popovski, Petar;

    2012-01-01

    , several works have considered contention-based CSI feedback in the UL control channel. We propose such a feedback scheme for a generic MC system, based on the idea of variable collision protection, where the probability that a feedback information experiences a collision depends on its importance. By......Optimized resource allocation of the Downlink (DL) in wireless systems utilizing Multi-Carrier (MC) transmission requires Channel State Information (CSI) feedback for each user/subchannel to the Base Station (BS), consuming a high amount of Uplink (UL) radio resources. To alleviate this problem...... partitioning the CSI into orthogonal layers of priority, and allocating different numbers of feedback slots to each layer, this scheme ensures that the feedback success probability is higher for the CSI with better quality, which is more likely to be used by the scheduler. Furthermore, we present a theoretical...

  17. Enhanced quantum efficiency for CsI grown on a graphite-based substrate coating

    CERN Document Server

    Friese, J; Homolka, J; Kastenmüller, A; Maier-Komor, P; Peter, M; Zeitelhack, K; Kienle, P; Körner, H J

    1999-01-01

    Quantum efficiencies (QE) in the vacuum ultraviolet (VUV) wavelength region have been measured for solid CsI layers on various substrates. The CsI films were deposited applying electron beam evaporation. The QE measurements were performed utilizing synchrotron radiation as well as light from a deuterium lamp. A GaAsP diode with a sensitivity calibration traceable to a primary radiation standard was used for normalization. For CsI layers grown on resin-stabilized graphite films a significant enhancement of QE was observed. Substrates suitable for gas detector applications and aging properties were investigated. The procedures to prepare and reproduce high quantum efficient CsI layers are described.

  18. The Langley Research Center CSI phase-0 evolutionary model testbed-design and experimental results

    Science.gov (United States)

    Belvin, W. K.; Horta, Lucas G.; Elliott, K. B.

    1991-01-01

    A testbed for the development of Controls Structures Interaction (CSI) technology is described. The design philosophy, capabilities, and early experimental results are presented to introduce some of the ongoing CSI research at NASA-Langley. The testbed, referred to as the Phase 0 version of the CSI Evolutionary model (CEM), is the first stage of model complexity designed to show the benefits of CSI technology and to identify weaknesses in current capabilities. Early closed loop test results have shown non-model based controllers can provide an order of magnitude increase in damping in the first few flexible vibration modes. Model based controllers for higher performance will need to be robust to model uncertainty as verified by System ID tests. Data are presented that show finite element model predictions of frequency differ from those obtained from tests. Plans are also presented for evolution of the CEM to study integrated controller and structure design as well as multiple payload dynamics.

  19. A Stable, Non-Cesiated III-Nitride Photocathode for Ultraviolet Astronomy Application

    Science.gov (United States)

    Bell, Lloyd

    In this effort, we propose to develop a new type of cesium-free photocathode using III-nitride (III-N) materials (GaN, AlN, and their alloys) and to achieve highly efficient, solar blind, and stable UV response. Currently, detectors used in UV instruments utilize a photocathode to convert UV photons into electrons that are subsequently detected by microchannel plate or CCD. The performance of these detectors critically depends on the efficiency and stability of their photocathodes. In particular, photocathode instability is responsible for many of the fabrication difficulties commonly experienced with this class of detectors. In recent years, III-N (in particular GaN) photocathodes have been demonstrated with very high QE (>50%) in parts of UV spectral range. Moreover, due to the wide bandgaps of III-nitride materials, photocathode response can be tailored to be intrinsically solar-blind. However, these photocathodes still rely on cesiation for activation, necessitating all-vacuum fabrication and sealed-tube operation. The proposed photocathode structure will achieve activation through methods for band structure engineering such as delta-doping and polarization field engineering. Compared to the current state-of-the-art in flight-ready microchannel plate sealed tubes, photocathodes based on III-N materials will yield high QE and significantly enhance both fabrication yield and reliability, since they do not require cesium or other highly reactive materials for activation. This performance will enable a ~4 meter medium class UV spectroscopic and imaging mission that is of high scientific priority for NASA. This work will build on the success of our previous APRA-funded effort. In that work, we demonstrated III-nitride photocathode operation without the use of cesium and stable response with respect to time. These accomplishments represent major improvements to the state-of-the-art for photocathode technologies. In the proposed effort, we will implement III

  20. Magnetron Driven L Band RF Gun using a Photocathode Emitter

    Science.gov (United States)

    Evans, Kirk; Fisher, Amnon; Friedman, Moshe

    1996-11-01

    Magnetron Driven L Band RF Gun using a Photocathode Emitter A tunable 5 megawatt L-Band injection locked magnetron amplifier is used to drive a 1-1/2 cell RF cavity gun, to produce a 2.5 megavolt electron beam. A tunable RF source relaxes the precision of the cavity gun construction, and therefore simplifies the design and reduces the overall cost. The design of the L-Band ( 1.3 GHz) RF cavity linear accelerator is presented, along with Superfish, SOS computer simulations, and calculations of beam energy and temporal qualities. Measurements of a few robust photocathode materials as well as measurements of the beam qualities of the final accelerator are presented. Future work will utilize new semiconductor laser diodes that can be electrically driven in the gigahertz range. This makes possible an electron gun system which can run at the RF frequency used to accelerate the electron beam. Such a system produces a "lock to clock" and synchronized RF and electron beam source which can be run single shot or any rep rate up to the RF frequency.

  1. Law Company ERP Software Market Analysis of St. Petersburg and Stockholm - CASE: CSI Helsinki Oy

    OpenAIRE

    Miettinen, Marko; Hämäläinen, Mikko

    2010-01-01

    This study is a part of bachelor studies in Laurea University of Applied Sciences and was commissioned by the case company, CSI Helsinki. CSI Helsinki provides enterprise resource planning (ERP) and customer relationship management (CRM) solutions for the leading consulting businesses in Finland and focuses on leading law companies abroad. Since the first ERP systems were developed in the 1960s they have been used by companies to improve management of business functions and gain competiti...

  2. Controlling mRNA stability and translation with the CRISPR endoribonuclease Csy4.

    Science.gov (United States)

    Borchardt, Erin K; Vandoros, Leonidas A; Huang, Michael; Lackey, Patrick E; Marzluff, William F; Asokan, Aravind

    2015-11-01

    The bacterial CRISPR endoribonuclease Csy4 has recently been described as a potential RNA processing tool. Csy4 recognizes substrate RNA through a specific 28-nt hairpin sequence and cleaves at the 3' end of the stem. To further explore applicability in mammalian cells, we introduced this hairpin at various locations in mRNAs derived from reporter transgenes and systematically evaluated the effects of Csy4-mediated processing on transgene expression. Placing the hairpin in the 5' UTR or immediately after the start codon resulted in efficient degradation of target mRNA by Csy4 and knockdown of transgene expression by 20- to 40-fold. When the hairpin was incorporated in the 3' UTR prior to the poly(A) signal, the mRNA was cleaved, but only a modest decrease in transgene expression (∼2.5-fold) was observed. In the absence of a poly(A) tail, Csy4 rescued the target mRNA substrate from degradation, resulting in protein expression, which suggests that the cleaved mRNA was successfully translated. In contrast, neither catalytically inactive (H29A) nor binding-deficient (R115A/R119A) Csy4 mutants were able to exert any of the effects described above. Generation of a similar 3' end by RNase P-mediated cleavage was unable to rescue transgene expression independent of Csy4. These results support the idea that the selective generation of the Csy4/hairpin complex resulting from cleavage of target mRNA might serve as a functional poly(A)/poly(A) binding protein (PABP) surrogate, stabilizing the mRNA and supporting translation. Although the exact mechanism(s) remain to be determined, our studies expand the potential utility of CRISPR nucleases as tools for controlling mRNA stability and translation. PMID:26354771

  3. Visualization of a City Sustainability Index (CSI): Towards Transdisciplinary Approaches Involving Multiple Stakeholders

    OpenAIRE

    Koichiro Mori; Toyonobu Fujii; Tsuguta Yamashita; Yutaka Mimura; Yuta Uchiyama; Kengo Hayashi

    2015-01-01

    We have developed a visualized 3-D model of a City Sustainability Index (CSI) based on our original concept of city sustainability in which a sustainable city is defined as one that maximizes socio-economic benefits while meeting constraint conditions of the environment and socio-economic equity on a permanent basis. The CSI is based on constraint and maximization indicators. Constraint indicators assess whether a city meets the necessary minimum conditions for city sustainability. Maximizati...

  4. Uplink Contention-Based CSI Feedback with Prioritized Layers for a Multi-Carrier System

    OpenAIRE

    Kaneko, Megumi; Hayashi, Kazunori; Popovski, Petar; Yomo, Hiroyuki; Sakai, Hideaki

    2011-01-01

    Optimized resource allocation of the Downlink (DL) in wireless systems utilizing Multi-Carrier (MC) transmission requires Channel State Information (CSI) feedback for each user/subchannel to the Base Station (BS), consuming a high amount of Uplink (UL) radio resources. To alleviate this problem, several works have considered contention-based CSI feedback in the UL control channel. We propose such a feedback scheme for a generic MC system, based on the idea of variable collision protection, wh...

  5. Uplink Contention-based CSI Feedback with Prioritized Layers for a Multi-Carrier System

    OpenAIRE

    Kaneko, Megumi; Hayashi, Kazunori; Popovski, Petar; Yomo, Hiroyuki; Sakai, Hideaki

    2012-01-01

    Optimized resource allocation of the Downlink (DL) in wireless systems utilizing Multi-Carrier (MC) transmission requires Channel State Information (CSI) feedback for each user/subchannel to the Base Station (BS), consuming a high amount of Uplink (UL) radio resources. To alleviate this problem, several works have considered contention-based CSI feedback in the UL control channel. We propose such a feedback scheme for a generic MC system, based on the idea of variable collision protection, wh...

  6. csi2p modulates microtubule dynamics and organizes the bipolar spindle for chromosome segregation

    OpenAIRE

    Costa, Judite; Fu, Chuanhai; Khare, V. Mohini; Tran, Phong T.

    2014-01-01

    Proper chromosome segregation is of paramount importance for proper genetic inheritance. Defects in chromosome segregation can lead to aneuploidy, which is a hallmark of cancer cells. Eukaryotic chromosome segregation is accomplished by the bipolar spindle. Additional mechanisms, such as the spindle assembly checkpoint and centromere positioning, further help to ensure complete segregation fidelity. Here we present the fission yeast csi2 +. csi2p localizes to the spindle poles, where it regul...

  7. Environmental Disclosure of Electric Power Companies Listed in the Corporate Sustainability Index (CSI)

    OpenAIRE

    Clésia Ana Gubiani; Vanderlei dos Santos; Ilse Maria Beuren

    2012-01-01

    The study aimed to verify the level of disclosure of environmental information in the administration reports of the energy companies listed in the Corporate Sustainability Index (CSI). A descriptive and quantitative research was done, using the content analysis technique on the administration reports from 2006 to 2008. The sample consisted of 11 electric power companies listed in the CSI. For quantitative analysis of the disclosure index, the data collection instrument was based on the study ...

  8. Cognitive radio based on Cooperative spectrum sharing with imperfect CSI

    Directory of Open Access Journals (Sweden)

    P. Radha1 , K. Sudha

    2013-05-01

    Full Text Available Cognitive radio is an emerging technology that aims for efficient spectrum usage. Cognitive radios have been proposed as a solution to the spectrum underutilization problem and have been proven to increase spectrum efficiency . However, in this we are analyzing the performance of the cognitive radio based on cooperative spectrum sharing. Here we propose a twophase spectrum sharing protocol which supports relaying functionality, it take the advantage of situation when primary system is fails to achieve its target rate due to weak channel situations the secondary system allocates some of its transmitters for helping the primary system to achieve its target rate by acting as decode –and-forward relay .As a reward the secondary system gains spectrum access by using remaining transmitters to transmit its own signal. Analytic and simulation results confirm the efficiency of the proposed spectrum sharing protocol. We show that the both primary and secondary are able to achieve better outage performance with increasing the secondary transmitters. And also it is shown that primary user’s interference probability is always equal to 0.75 when CSI of interference links is imperfect.

  9. Energy-Efficient Relaying over Multiple Slots with Causal CSI

    CERN Document Server

    Ho, Chin Keong; Sun, Sumei

    2012-01-01

    In many communication scenarios, such as in cellular systems, the energy cost is substantial and should be conserved, yet there is a growing need to support many real-time applications that require timely data delivery. To model such a scenario, in this paper we consider the problem of minimizing the expected sum energy of delivering a message of a given size from a source to a destination subject to a deadline constraint. A relay is present and can assist after it has decoded the message. Causal channel state information (CSI), in the form of present and past SNRs of all links, is available for determining the optimal power allocation for the source and relay. We obtain the optimal power allocation policy by dynamic programming and explore its structure. We also obtain conditions for which the minimum expected sum energy is bounded given a general channel distribution. In particular, we show that for Rayleigh and Rician fading channels, relaying is necessary for the minimum expected sum energy to be bounded....

  10. Observation of Significant Quantum Efficiency Enhancement from a Polarized Photocathode with Distributed Bragg Reflector

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Shukui [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Poelker, Matthew [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Stutzman, Marcy L. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Chen, Yiqiao [SVT Associates, Inc., Eden Prairie, MN (United States); Moy, Aaron [SVT Associates, Inc., Eden Prairie, MN (United States)

    2015-09-01

    Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we present recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator.

  11. Radiation hardness test of un-doped CsI crystals and Silicon Photomultipliers for the Mu2e calorimeter

    CERN Document Server

    Baccaro, Stefania; Cordelli, Marco; Diociaiuti, Eleonora; Donghia, Raffaella; Giovannella, Simona; Loreti, Stefano; Miscetti, Stefano; Pillon, Mario; Sarra, Ivano

    2016-01-01

    The Mu2e calorimeter is composed by 1400 un-doped CsI crystals coupled to large area UV extended Silicon Photomultipliers arranged in two annular disks. This calorimeter has to provide precise information on energy, timing and position. It should also be fast enough to handle the high rate background and it must operate and survive in a high radiation environment. Simulation studies estimated that, in the hottest regions, each crystal will absorb a dose of 300 Gy and will be exposed to a neutron fluency of 6 x 10^{11} n/cm^2 in 3 years of running. Test of un-doped CsI crystals irradiated up to 900 Gy and to a neutron fluency up to 9 x 10^{11} n/cm^2 have been performed at CALLIOPE and FNG ENEA facilities in Italy. We present our study on the variation of light yield (LY) and longitudinal response uniformity (LRU) of these crystals after irradiation. The ionization dose does not modify LRU while a 20% reduction in LY is observed at 900 Gy. Similarly, the neutron flux causes an acceptable LY deterioration (<...

  12. Photocathode-Uniformity Tests of the Hamamatsu R5912 Photomultiplier Tubes Used in the Milagro Experiment

    Science.gov (United States)

    Vasileiou, V.; Ellsworth, R. W.; Smith, A.

    The Milagro experiment observes the extensive air showers produced by very high energy gamma-rays impacting the Earth’s atmosphere. Milagro uses 898 Hamamatsu R5912 Photomultiplier Tubes. To complete our Monte Carlo simulations, we tested the photocathode uniformity of our PMTs. The main finding was that the PMT gain and detection efficiency are a function of the distance from the center of the photocathode. Both quantities become considerably smaller as the illumination position nears the edge of the photocathode. Inclusion of the measured quantities in our MC simulations greatly increased the agreement between the simulations and the experiment.

  13. Performance of the 8-in. R5912 photomultiplier tube with super bialkali photocathode

    Science.gov (United States)

    Wang, W.; Qian, S.; Xia, J.; Ning, Z.; Cheng, Y.; Qi, M.; Heng, Y.; Wang, Z.; Li, X.; Liu, S.; Lei, X.

    2015-08-01

    An enhanced R5912 family photomultiplier (8-inch.) model with super bialkali photocathode was developed by Hamamatsu. The spectral responses of the standard and enhanced photocathode were compared and a relative increase of 39% at 400 nm was found for the enhanced one. Additional measurements on the relative detection efficiency at a gain of 1E7 showed a consistent improvement of the quantum efficiency. Good uniformity was observed on the super bialkali photocathode. Additional tests proved that both the charge resolution and time properties were not affected by the new cathode technology. Dark count rate and dark current values were found larger in the super bialkali model compared to the standard one.

  14. A new-type photocathode for polarized electron source with distributed bragg reflector

    International Nuclear Information System (INIS)

    In order to increase the quantum efficiency of the strained GaAs photocathode for the highly polarized electron source, we designed a new type photocathode with a distributed Bragg reflector(DBR). A Fabry-Perot cavity is formed by the DBR and the GaAs surface. The large enhancement of quantum efficiency was observed at the laser wavelength which satisfied the condition for the resonant absorption of incident laser light. From this experiment, it becomes promising to make the photocathode which has the quantum efficiency more than ∼1% together with the electron spin polarization higher than 80%. (author)

  15. Development of NEA-GaAs photocathode gun used for JAERI-FEL

    International Nuclear Information System (INIS)

    The photocathode DC-gun with high average current, low beam emittance and long operational lifetime is considered to be indispensable for ERL-FEL and X-FEL. We have started the developmental program of a electron gun with the NEA-GaAs photocathode for the first time in JAERI. In order to overcome an NEA lifetime problem, the JAERI electron gun system consists of an extreme high vacuum gun chamber and MBE apparatus, an electron source consists of a NEA-diamond film as enhancement electron current device and a superlattice photocathode. (author)

  16. First Eigenmode Transmission by High Efficient CSI Estimation for Multiuser Massive MIMO Using Millimeter Wave Bands.

    Science.gov (United States)

    Maruta, Kazuki; Iwakuni, Tatsuhiko; Ohta, Atsushi; Arai, Takuto; Shirato, Yushi; Kurosaki, Satoshi; Iizuka, Masataka

    2016-01-01

    Drastic improvements in transmission rate and system capacity are required towards 5th generation mobile communications (5G). One promising approach, utilizing the millimeter wave band for its rich spectrum resources, suffers area coverage shortfalls due to its large propagation loss. Fortunately, massive multiple-input multiple-output (MIMO) can offset this shortfall as well as offer high order spatial multiplexing gain. Multiuser MIMO is also effective in further enhancing system capacity by multiplexing spatially de-correlated users. However, the transmission performance of multiuser MIMO is strongly degraded by channel time variation, which causes inter-user interference since null steering must be performed at the transmitter. This paper first addresses the effectiveness of multiuser massive MIMO transmission that exploits the first eigenmode for each user. In Line-of-Sight (LoS) dominant channel environments, the first eigenmode is chiefly formed by the LoS component, which is highly correlated with user movement. Therefore, the first eigenmode provided by a large antenna array can improve the robustness against the channel time variation. In addition, we propose a simplified beamforming scheme based on high efficient channel state information (CSI) estimation that extracts the LoS component. We also show that this approximate beamforming can achieve throughput performance comparable to that of the rigorous first eigenmode transmission. Our proposed multiuser massive MIMO scheme can open the door for practical millimeter wave communication with enhanced system capacity. PMID:27399715

  17. Measurement of photocathode spectral response at cryogenic temperature

    Science.gov (United States)

    Menegolli, A.; Prata, M.; Prata, M. C.; Raselli, G. L.; Vignoli, C.

    2007-03-01

    Noble-gas liquids, such as xenon and argon, have been recently proposed as light scintillators in some experiments dedicated to neutrino physics and dark matter research. These experiments need the use of photomultiplier tubes directly immersed in the liquid phase and operating at cryogenic temperatures. We carried out an investigation about the spectral response and its variation from room to cryogenic temperature for two different kind of cryogenic photocathodes manufactured by Electron Tubes Ltd. and Hamamatsu Photonics K.K. Measurements were carried out by means of a xenon continuous lamp and a UV-VIS monocromator which allows the analysis from 300 to 700 nm with 5 nm resolution. Cryogenic tests were made at the liquid nitrogen temperature (77 K).

  18. An alkali dispenser photocathode (Al-Li)-Ag-O-Li

    International Nuclear Information System (INIS)

    We propose a new Li-actived metallic photocathode that could be used in high-current photo-injectors for linear accelerators. An Ag thin film is evaporated in UHV on the surface of a piece of (Al-Li) alloy. After treating at 380 deg C Li diffuses through Ag and decreases the surface work function to 2.7 eV. The emission yields Qe, in electrons per incident photon, are higher than those measured with (Al-Li) alone. Oxidation of the surface allows one to increase again Qe which reaches Qe∼1.7x10-3 for photon energies of 3.5 and 4.6 eV respectively (energies corresponding to photons delivered by a frequency triples -or quadruples- YAG laser)

  19. Design and construction of the photocathode electron gun cavity

    International Nuclear Information System (INIS)

    A 1300-MHz, two-cell rf accelerator cavity has been constructed for the high-brightness photocathode electron source program. Each cell has an rf drive. Cell 1 has a replacement photocathode plug on the back wall and has a shape designed for linear radial fields. Cell two has a more standard high-shunt-impedance shape. SUPERFISH values for shunt impedances are, respectively, 29.5 and 45.8 MΩ/m. Peak surface field maximums are 58.9 and 32.1 MV/m for an electron acceleration of 0.9 and 1.0 MeV. Drive coupling is matched for 55 and 86% beam loading at 1-A average current. The system has vacuum pumping ports, into both cells and is baked at 300 degree C. Typical operating pressures are in the low 10-10-torr range. Cell frequencies are fine tuned by a combination of operating temperature and cell nose pulling. Cell-to-cell coupling was intended to be low (K = 0.0002); however, because of the high Qs (13,300 and 20,000), substantial coupling effects are seen. Cutting the vacuum-port slots shifted the frequencies by 1.5 MHz and gave an apparent 10% increase in the cavity Qs. Construction of the cavity required a series of four brazes with several annealing cycles. All joints are flat, and the sequence is such that each joint is brazed horizontally; as a result, all joints were successfully brazed on the first attempt. The latest experiment measurements are given in another paper at this conference. 2 refs., 3 figs

  20. Ultrafast laser pulse heating of metallic photocathodes and its contribution to intrinsic emittance

    CERN Document Server

    Maxson, J; Cultrera, L; Karkare, S; Padmore, H

    2016-01-01

    The heating of the electronic distribution of a copper photocathode is calculated under the two-temperature model for ultrafast laser illumination with fluences typical for use in RF photoinjectors. Using the finite temperature-extended relations for the photocathode intrinsic emittance and quantum efficiency, the time-dependent emittance growth due to this laser heating is calculated. This laser heating is seen to limit the intrinsic emittance achievable for photoinjectors using short laser pulses and low quantum efficiency metal photocathodes. A pump-probe photocathode experiment in a standard 1.6 cell S-band gun is proposed, in which simulations show the time dependent thermal emittance modulation from the laser heating can persist for meters downstream and, in principle, be measured using a slice emittance diagnostic.

  1. Towards a Robust, Efficient Dispenser Photocathode: the Effect of Recesiation on Quantum Efficiency

    International Nuclear Information System (INIS)

    Future electron accelerators and Free Electron Lasers (FELs) require high brightness electron sources; photocathodes for such devices are challenged to maintain long life and high electron emission efficiency (high quantum efficiency, or QE). The UMD dispenser photocathode design addresses this tradeoff of robustness and QE. In such a dispenser, a cesium-based surface layer is deposited on a porous substrate. The surface layer can be replenished from a subsurface cesium reservoir under gentle heating, allowing cesium to diffuse controllably to the surface and providing demonstrably more robust photocathodes. In support of the premise that recesiation is able to restore contaminated photocathodes, we here report controlled contamination of cesium-based surface layers with subsequent recesiation and the resulting effect on QE. Contaminant gases investigated include examples known from the vacuum environment of typical electron guns.

  2. Measurement of Low Workfunction Cesiated Metals for Use in Dispenser Photocathodes

    CERN Document Server

    Moody, N A; O'Shea, P G

    2005-01-01

    Photoinjector performance is a limiting factor in the continued development of high powered FELs. Presently available photocathodes have limited efficiency and short lifetime in an RF-gun environment, due to contamination or evaporation of a photosensitive surface layer. An ideal photocathode should have high efficiency at visible wavelengths, long lifetime in practical vacuum environments, and prompt emission. High efficiency cathodes typically have limited lifetime, and the needs of the photocathode are generally at odds with those of the drive laser. A potential solution is the low work function dispenser cathode, where short lifetimes are overcome by periodic in situ regeneration that restores the photosensitive surface layer, analogous to methods used in the power tube industry. This work reports on the fabrication techniques and performance of cesiated metal photocathodes and cesiated dispenser cathodes, with a focus on understanding and improving quantum efficiency and lifetime, analyzing issues of emi...

  3. High-Efficiency GaN-Based UV Imaging Photocathodes for Application in Harsh Environments Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This proposal is directed toward the development of innovative high-efficiency UV photocathodes based on the wide bandgap III-nitride semiconductors for reliable...

  4. Downramp-assisted underdense photocathode electron bunch generation in plasma wakefield accelerators

    OpenAIRE

    Knetsch, Alexander; Karger, Oliver; Wittig, Georg; Groth, Henning; Xi, Yunfeng; Deng, Aihua; Rosenzweig, James Benjamin; Bruhwiler, David Leslie; Smith, Johnathan; Jaroszynski, Dino Anthony; Sheng, Zheng-Ming; Manahan, Grace Gloria; Xia, Guoxing; Jamison, Steven; Hidding, Bernhard

    2014-01-01

    It is shown that the requirements for high quality electron bunch generation and trapping from an underdense photocathode in plasma wakefield accelerators can be substantially relaxed through localizing it on a plasma density downramp. This depresses the phase velocity of the accelerating electric field until the generated electrons are in phase, allowing for trapping in shallow trapping potentials. As a consequence the underdense photocathode technique is applicable by a much larger number o...

  5. Downramp-assisted underdense photocathode electron bunch generation in plasma wakefield accelerators

    CERN Document Server

    Knetsch, Alexander; Wittig, Georg; Groth, Henning; Xi, Yunfeng; Deng, Aihua; Rosenzweig, James Benjamin; Bruhwiler, David Leslie; Smith, Johnathan; Jaroszynski, Dino Anthony; Sheng, Zheng-Ming; Manahan, Grace Gloria; Xia, Guoxing; Jamison, Steven; Hidding, Bernhard

    2014-01-01

    It is shown that the requirements for high quality electron bunch generation and trapping from an underdense photocathode in plasma wakefield accelerators can be substantially relaxed through localizing it on a plasma density downramp. This depresses the phase velocity of the accelerating electric field until the generated electrons are in phase, allowing for trapping in shallow trapping potentials. As a consequence the underdense photocathode technique is applicable by a much larger number of accelerator facilities. Furthermore, dark current generation is effectively suppressed.

  6. Design, Fabrication and Testing of Two Different Laboratory Prototypes of CSI-based Induction Heating Units

    Science.gov (United States)

    Roy, M.; Sengupta, M.

    2012-09-01

    Induction heating is a non-contact heating process which became popular due to its energy efficiency. Current source inverter (CSI) based induction heating units are commonly used in the industry. Most of these CSIs are thyristor based, since thyristors of higher ratings are easily available. These being load commutated apparatus a start-up circuit is needed to initiate commutation. In this paper the design and fabrication of two laboratory prototypes have been presented. The first one, a SCR-based CSI fed controlled induction heating unit (IHU), has been tested with two different types of start-up procedures. Thereafter the fabrication and performance of another IGBT-based CSI is compared with the thyristor-based CSI for a 2 kW, 10 kHz application. These two types of CSIs are fully fabricated in laboratory along with the IHU. Performance analysis and simulation of two different CSIs has been done by using SequelGUI2. The triggering pulses for the inverter devices (for both CSI devices as well as auxilliary thyristor of start-up circuit) have been generated and closed-loop control has been done in FPGA platform built around an Altera make cyclone EPIC12Q240C processor which can be programmed using Quartus II software. Close agreement between simulated and experimental results highlight the accuracy of the experimental work.

  7. Development of new photocathode materials and its quantum efficiency improvement for high brightness electron gun

    International Nuclear Information System (INIS)

    New photocathode material is being developed for high charge electron guns. We succeeded in developing an iridium cerium (Ir5Ce) photocathode and Cu:C12A7 electride photocathode. The iridium cerium photocathode has a reasonably high QE (∼9.1×10-4 (a)213nm at room temperature) and long lifetime (> LaB6). Furthermore, the QE of Ir5Ce photocathode was increased to a maximum value of 2.70×10-3 by heating at 1006°C. These great advantages of Ir5Ce photocathode led to generate the electron beams with a maximum charge of 4.4 nC/bunch using a new-type RF gun at a test bench of KEK electron linac. Cu:C12A7 is originally an electrical insulator. Cu:C12A7, however exhibits an excellent electrical conductivity and low work function (≈2.5 eV) after a reduction process at 1100°C for 48 hours using a titanium powder. Finally, we found that Cu:C12A7 electride has a QE of 8.72×10-4 (a)213nm at 600°C. (author)

  8. Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

    OpenAIRE

    M. Ruiz-Osés; Schubert, S.; Attenkofer, K.; Ben-Zvi, I.; Liang, X; Muller, E; Padmore, H; Rao, T.; T. Vecchione; Wong, J; Xie, J.; Smedley, J.

    2014-01-01

    Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K2CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolv...

  9. Study of radiation hardness of pure CsI crystals for Belle-II calorimeter

    Science.gov (United States)

    Boyarintsev, A.; Boyarintseva, Y.; Gektin, A.; Shiran, N.; Shlyakhturov, V.; Taranyuk, V.; Timoshenko, N.; Bobrov, A.; Garmash, A.; Golkovski, M.; Kuzmin, A.; Matvienko, D.; Savrovski, P.; Shebalin, V.; Shwartz, B.; Vinokurova, A.; Vorobyev, V.; Zhilich, V.; Krumshtein, Z. V.; Nozdrin, A. A.; Olshevsky, A. G.

    2016-03-01

    A study of the radiation hardness of pure CsI crystals 30 cm long was performed with a uniformly absorbed dose of up to 14.3 krad. This study was initiated by the proposed upgrade of the end cap calorimeter of the Belle-II detector, using pure CsI crystals. A set of 14 crystals of truncated pyramid shape used in this study was produced at the Institute for Scintillation Materials NAS from 14 different ingots grown with variations of the growing technology. Interrelationship of crystal scintillation characteristics, radiation hardness and the growing technology was observed.

  10. Neutron beam test of CsI crystal for dark matter search

    OpenAIRE

    Park, H.; Choi, D H; Hahn, I. S.; Hwang, M. J.; Kang, W. G.; Kim, H. J.; Kim, J. H.; Kim, S.C.; Kim, S K; Kim, T. Y.; Kim, Y.D.(Center for Underground Physics, Institute for Basic Science (IBS), Daejon, 305-811, Korea); Kwon, Y. J.; Lee, H. S.; Lee, J. H.; Lee, M. H.

    2002-01-01

    We have studied the response of Tl-doped and Na-doped CsI crystals to nuclear recoils and $\\gamma$'s below 10 keV. The response of CsI crystals to nuclear recoil was studied with mono-energetic neutrons produced by the $^3$H(p,n)$^3$He reaction. This was compared to the response to Compton electrons scattered by 662 keV $\\gamma$-ray. Pulse shape discrimination between the response to these $\\gamma$'s and nuclear recoils was studied, and quality factors were estimated. The quenching factors fo...

  11. Aspergillus oryzae type III polyketide synthase CsyA is involved in the biosynthesis of 3,5-dihydroxybenzoic acid.

    Science.gov (United States)

    Seshime, Yasuyo; Juvvadi, Praveen Rao; Kitamoto, Katsuhiko; Ebizuka, Yutaka; Nonaka, Takamasa; Fujii, Isao

    2010-08-15

    As a novel superfamily of type III polyketide synthases in microbes, four genes csyA, csyB, csyC, and csyD, were found in the genome of Aspergillus oryzae, an industrially important filamentous fungus. In order to analyze their functions, we carried out the overexpression of csyA under the control of alpha-amylase promoter in A. oryzae and identified 3,5-dihydroxybenzoic acid (DHBA) as the major product. Feeding experiments using (13)C-labeled acetates confirmed that the acetate labeling pattern of DHBA coincided with that of orcinol derived from orsellinic acid, a polyketide formed by the condensation and cyclization of four acetate units. Further oxidation of methyl group of orcinol by the host fungus could lead to the production of DHBA. Comparative molecular modeling of CsyA with the crystal structure of Neurospora crassa 2'-oxoalkylresorcylic acid synthase indicated that CsyA cavity size can only accept short-chain acyl starter and tetraketide formation. Thus, CsyA is considered to be a tetraketide alkyl-resorcinol/resorcylic acid synthase. PMID:20630753

  12. Comparative research on the transmission-mode GaAs photocathodes of exponential-doping structures

    International Nuclear Information System (INIS)

    Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have been proven to have a higher quantum efficiency than uniform doping structures. On the basis of our early research on the surface photovoltage of GaAs photocathodes, and comparative research before and after activation of reflection-mode GaAs photocathodes, we further the comparative research on transmission-mode GaAs photocathodes. An exponential doping structure is the typical varied doping structure that can form a uniform electric field in the active layer. By solving the one-dimensional diffusion equation for no equilibrium minority carriers of transmission-mode GaAs photocathodes of the exponential doping structure, we can obtain the equations for the surface photovoltage (SPV) curve before activation and the spectral response curve (SRC) after activation. Through experiments and fitting calculations for the designed material, the body-material parameters can be well fitted by the SPV before activation, and proven by the fitting calculation for SRC after activation. Through the comparative research before and after activation, the average surface escape probability (SEP) can also be well fitted. This comparative research method can measure the body parameters and the value of SEP for the transmission-mode GaAs photocathode more exactly than the early method, which only measures the body parameters by SRC after activation. It can also help us to deeply study and exactly measure the parameters of the varied doping structures for transmission-mode GaAs photocathodes, and optimize the Cs-O activation technique in the future. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  13. Comparative research on the transmission-mode GaAs photocathodes of exponential-doping structures

    Science.gov (United States)

    Chen, Liang; Qian, Yun-Sheng; Zhang, Yi-Jun; Chang, Ben-Kang

    2012-03-01

    Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have been proven to have a higher quantum efficiency than uniform doping structures. On the basis of our early research on the surface photovoltage of GaAs photocathodes, and comparative research before and after activation of reflection-mode GaAs photocathodes, we further the comparative research on transmission-mode GaAs photocathodes. An exponential doping structure is the typical varied doping structure that can form a uniform electric field in the active layer. By solving the one-dimensional diffusion equation for no equilibrium minority carriers of transmission-mode GaAs photocathodes of the exponential doping structure, we can obtain the equations for the surface photovoltage (SPV) curve before activation and the spectral response curve (SRC) after activation. Through experiments and fitting calculations for the designed material, the body-material parameters can be well fitted by the SPV before activation, and proven by the fitting calculation for SRC after activation. Through the comparative research before and after activation, the average surface escape probability (SEP) can also be well fitted. This comparative research method can measure the body parameters and the value of SEP for the transmission-mode GaAs photocathode more exactly than the early method, which only measures the body parameters by SRC after activation. It can also help us to deeply study and exactly measure the parameters of the varied doping structures for transmission-mode GaAs photocathodes, and optimize the Cs-O activation technique in the future.

  14. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Energy Technology Data Exchange (ETDEWEB)

    Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  15. Non-conventional photocathodes based on Cu thin films deposited on Y substrate by sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Perrone, A. [Department of Mathematics and Physics “E. De Giorgi”, University of Salento, 73100 Lecce (Italy); National Institute of Nuclear Physics and University of Salento, 73100 Lecce (Italy); D’Elia, M. [Department of Mathematics and Physics “E. De Giorgi”, University of Salento, 73100 Lecce (Italy); Gontad, F., E-mail: francisco.gontad@le.infn.it [Department of Mathematics and Physics “E. De Giorgi”, University of Salento, 73100 Lecce (Italy); National Institute of Nuclear Physics and University of Salento, 73100 Lecce (Italy); Di Giulio, M.; Maruccio, G. [Department of Mathematics and Physics “E. De Giorgi”, University of Salento, 73100 Lecce (Italy); Cola, A. [National Council Research, Institute for Microelectronics and Microsystems, 73100 Lecce (Italy); Stankova, N.E. [Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia (Bulgaria); Kovacheva, D.G. [Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Broitman, E. [Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden)

    2014-07-01

    Copper (Cu) thin films were deposited on yttrium (Y) substrate by sputtering. During the deposition, a small central area of the Y substrate was shielded to avoid the film deposition and was successively used to study its photoemissive properties. This configuration has two advantages: the cathode presents (i) the quantum efficiency and the work function of Y and (ii) high electrical compatibility when inserted into the conventional radio-frequency gun built with Cu bulk. The photocathode was investigated by scanning electron microscopy to determine surface morphology. X-ray diffraction and atomic force microscopy studies were performed to compare the structure and surface properties of the deposited film. The measured electrical resistivity value of the Cu film was similar to that of high purity Cu bulk. Film to substrate adhesion was also evaluated using the Daimler–Benz Rockwell-C adhesion test method. Finally, the photoelectron performance in terms of quantum efficiency was obtained in a high vacuum photodiode cell before and after laser cleaning procedures. A comparison with the results obtained with a twin sample prepared by pulsed laser deposition is presented and discussed.

  16. Beyond injection: Trojan horse underdense photocathode plasma wakefield acceleration

    International Nuclear Information System (INIS)

    An overview on the underlying principles of the hybrid plasma wakefield acceleration scheme dubbed 'Trojan Horse' acceleration is given. The concept is based on laser-controlled release of electrons directly into a particle-beam-driven plasma blowout, paving the way for controlled, shapeable electron bunches with ultralow emittance and ultrahigh brightness. Combining the virtues of a low-ionization-threshold underdense photocathode with the GV/m-scale electric fields of a practically dephasing-free beam-driven plasma blowout, this constitutes a 4th generation electron acceleration scheme. It is applicable as a beam brightness transformer for electron bunches from LWFA and PWFA systems alike. At FACET, the proof-of-concept experiment 'E-210: Trojan Horse Plasma Wakefield Acceleration' has recently been approved and is in preparation. At the same time, various LWFA facilities are currently considered to host experiments aiming at stabilizing and boosting the electron bunch output quality via a trojan horse afterburner stage. Since normalized emittance and brightness can be improved by many orders of magnitude, the scheme is an ideal candidate for light sources such as free-electron-lasers and those based on Thomson scattering and betatron radiation alike.

  17. Synchronizaiton Between Laser and Electron Beam at Photocathode RF Gun

    CERN Document Server

    Sakumi, Akira; Fukasawa, Atsushi; Kumagai, Noritaka; Muroya, Yusa; Tomizawa, Hiromitsu; Ueda, T; Uesaka, Mitsuru; Urakawa, Junji; Yoshii, K

    2005-01-01

    The chemical reactions of hot, room temperature and critical water in a time-range of picosecond and sub-picosecond have been carried out by the 18 MeV S-band linac and a Mg photocathode RF gun with the irradiation of third harmonic Ti: Sapphire laser, at Nuclear Engineering Research Laboratory (NERL), the University of Tokyo. Although this short bunch and 100 fs laser light are enough to perform the experiment of radiation chemistry in the time-range of sub-picosecond, the total time-resolution become worse by the instability of synchronization between laser and radio frequency of linac. We found that the fluctuation of room temperature causes the instability, particularly the cycle of turning on/off of the air-conditioner. It is shown that 0.3 °C (peak-to-peak) fluctuation of the laser-room temperature have approximately corresponded to the instability of 6 ps. We are trying to decrease the fluctuation of the room temperature, together with the local temperature stability of the Ti: Sapphire crysta...

  18. Superlattice Photocathodes for Accelerator-Based Polarized Electron Source Applications

    International Nuclear Information System (INIS)

    A major improvement in the performance of the SLC was achieved with the introduction of thin strained-layer semiconductor crystals. After some optimization, polarizations of 75-85% became standard with lifetimes that were equal to or better than that of thick unstrained crystals. Other accelerators of polarized electrons, generally operating with a much higher duty factor, have now successfully utilized similar photocathodes. For future colliders, the principal remaining problem is the limit on the total charge that can be extracted in a time scale of 10 to 100 ns. In addition, higher polarization is critical for exploring new physics, especially supersymmetry. However, it appears that strained-layer crystals have reached the limit of their optimization. Today strained superlattice crystals are the most promising candidates for better performance. The individual layers of the superlattice can be designed to be below the critical thickness for strain relaxation, thus in principle improving the polarization. Thin layers also promote high electron conduction to the surface. In addition the potential barriers at the surface for both emission of conduction-band electrons to vacuum and for tunneling of valence-band holes to the surface can be significantly less than for single strained-layer crystals, thus enhancing both the yield at any intensity and also decreasing the limitations on the total charge. The inviting properties of the recently developed AlInGaAs/GaAs strained superlattice with minimal barriers in the conduction band are discussed in detail

  19. Characteristics of test cavity for cryogenic photocathode RF-gun

    International Nuclear Information System (INIS)

    The cryogenic C-band photocathode RF-gun operating at 20 K is under development at LEBRA in Nihon University. The RF-gun is of the BNL-type 2.6-cell pillbox cavity with the resonant frequency of 5712 MHz. The 6N8 high purity OFC copper (corresponding to RRR-3000) is used as the cavity material. From the theoretical evaluation of the anomalous skin effect, the quality factor Q of the cavity at the operating temperature of 20K has been expected to be approximately 60000. Considering a low cooling capacity of the cryogenic system, initial operation of the RF gun is assumed at a duty factor of 0.01%. The cavity basic design and the beam bunching simulation were carried out using Poisson Superfish and General Particle Tracer (GPT). Machining and diffusion bonding of the cavity was carried out in KEK. The Q0 value of the π-mode resonance at the room temperature (23.5°C) deduced from the Smith chart was approximately 11440 after diffusion bonding. (author)

  20. Designs for waveguide and structured photocathodes with high quantum efficiency

    International Nuclear Information System (INIS)

    Conventional S20 multialkali photocathodes have a wide wavelength coverage from 850 nm, but their high transparency and the surface work function result in low quantum efficiencies at longer wavelengths. Theoretical modelling of the photon and excited electron interactions that define the cathode performance provides a realistic prediction of the measured response. The theory emphasizes that the basic light absorption is strongly sensitive to the cathode thickness, wavelength, polarization and incident angle. Parameters can be selected which predict that even at long wavelengths (e.g. 900 nm), absorption may be increased from ∼1% to ∼100%. Cathode topographies can be designed to exploit these responses and offer increased absorption at the longer wavelengths. Alternative designs, which include waveguiding of light within the cathode window, or in structured surfaces, can similarly lead to almost total absorption of the incident light by increasing the number of interactions. These concepts of optimal incidence and waveguiding have been both theoretically modelled and demonstrated in newly fabricated cathode designs. The methods have variously reached quantum efficiencies in excess of 50% at wavelengths in the range from 200 to > 750 nm under different operational conditions. The improvement factors relative to normal incidence on planar cathodes increase for longer wavelengths, and examples of 20-50 times by ∼900 nm were noted. Whilst the absolute S20 efficiency values at long wavelengths are still small, the improvements offer a usable sensitivity even beyond 1 μm, as demonstrated by spectroscopy data up to at least 1140 nm

  1. Beyond injection: Trojan horse underdense photocathode plasma wakefield acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Hidding, B.; Rosenzweig, J. B.; Xi, Y.; O' Shea, B.; Andonian, G.; Schiller, D.; Barber, S.; Williams, O.; Pretzler, G.; Koenigstein, T.; Kleeschulte, F.; Hogan, M. J.; Litos, M.; Corde, S.; White, W. W.; Muggli, P.; Bruhwiler, D. L.; Lotov, K. [Institut fuer Laser- und Plasmaphysik, Heinrich-Heine-Universitaet Duesseldorf 40225 Duesseldorf (Germany) and Particle Beam Physics Laboratory, Department for Physics and Astronomy, UCLA (United States); Particle Beam Physics Laboratory, Department for Physics and Astronomy, UCLA (United States); Institut fuer Laser- und Plasmaphysik, Heinrich-Heine-Universitaet Duesseldorf 40225 Duesseldorf (Germany); Stanford Linear Accelerator Center (United States); Max-Planck-Institut fuer Physik, Muenchen (Germany); Tech-X Corporation, Boulder, Colorado (United States) and 1348 Redwood Ave., Boulder, Colorado 80304 (United States); Budker Institute of Nuclear Physics SB RAS, 630090, Novosibirsk (Russian Federation) and Novosibirsk State University, 630090, Novosibirsk (Russian Federation)

    2012-12-21

    An overview on the underlying principles of the hybrid plasma wakefield acceleration scheme dubbed 'Trojan Horse' acceleration is given. The concept is based on laser-controlled release of electrons directly into a particle-beam-driven plasma blowout, paving the way for controlled, shapeable electron bunches with ultralow emittance and ultrahigh brightness. Combining the virtues of a low-ionization-threshold underdense photocathode with the GV/m-scale electric fields of a practically dephasing-free beam-driven plasma blowout, this constitutes a 4th generation electron acceleration scheme. It is applicable as a beam brightness transformer for electron bunches from LWFA and PWFA systems alike. At FACET, the proof-of-concept experiment 'E-210: Trojan Horse Plasma Wakefield Acceleration' has recently been approved and is in preparation. At the same time, various LWFA facilities are currently considered to host experiments aiming at stabilizing and boosting the electron bunch output quality via a trojan horse afterburner stage. Since normalized emittance and brightness can be improved by many orders of magnitude, the scheme is an ideal candidate for light sources such as free-electron-lasers and those based on Thomson scattering and betatron radiation alike.

  2. Study of silicon tip photocathodes in DC and RF photo-injectors; Etude de photocathodes a pointe de silicium dans des canons continus et hyperfrequence

    Energy Technology Data Exchange (ETDEWEB)

    Jaber, Zakaria [Lab. de Physique Corpusculaire, Clermont-Ferrand-2 Univ., 63 - Aubiere (France)

    1999-02-02

    Nowadays the electron beams with a high intensity are particularly interesting in research and the applied physics. Producing such beams for which high intensity and low emittance are synonyms with efficiency, means developing new high luminosity electron sources, i.e. the photocathodes. This thesis, essentially experimental, is oriented in this way. After an introduction of Clermont-Ferrand and the LAL of Orsay experimental apparatus where the experiments took place, the chapter one presents the field emission and the photo-field emission. Then, we prove that the quantum efficiency of the photocathodes with silicon tips is higher for wavelengths near 800 nm. This fact is essential because it allows the use of lasers in the fundamental wavelength - Titan-Saphir for instance. In the chapter 2, we remind how the silicon tips are realized and how to improve surface conditions. Procedures and the surface analysis with the SEM and XPS are described. With a Nd-Yag laser, pumped with laser diode setting up with the participation of IRCOM Opticians of Limoges, the photocathode supplied 1 Ampere per pulse at a quantum efficiency of 0.25%. The description of this experiment and the results are the object of the chapter 3. The space charge outside the photocathode space prevents the electrons to go through. The Child-Langmuir formula limits the current with the DC gun at about 30 Ampere. To improve this result we have to use a photo-injector. In chapter 4 we prove that the silicon tip photocathode are compatible with RF gun requirements by PRIAM modeling and low level measure in a cold model of CANDELA RF gun. Technical department of CERN helped us to prepare this very sensitive experiment. (author)

  3. In-situ multi-information measurement system for preparing gallium nitride photocathode

    International Nuclear Information System (INIS)

    We introduce the first domestic in-situ multi-information measurement system for a gallium nitride (GaN) photocathode. This system can successfully fulfill heat cleaning and activation for GaN in an ultrahigh vacuum environment and produce a GaN photocathode with a negative electron affinity (NEA) status. Information including the heat cleaning temperature, vacuum degree, photocurrent, electric current of cesium source, oxygen source, and the most important information about the spectral response, or equivalently, the quantum efficiency (QE) can be obtained during preparation. The preparation of a GaN photocathode with this system indicates that the optimal heating temperature in a vacuum is about 700 °C. We also develop a method of quickly evaluating the atomically clean surface with the vacuum degree versus wavelength curve to prevent possible secondary contamination when the atomic level cleaning surface is tested with X-ray photoelectron spectroscopy. The photocurrent shows a quick enhancement when the current ratio between the cesium source and oxygen source is 1.025. The spectral response of the GaN photocathode is flat in a wavelength range from 240 nm to 365 nm, and an abrupt decline is observed at 365 nm, which demonstrates that with the in-situ multi-information measurement system the NEA GaN photocathode can be successfully prepared. (rapid communication)

  4. Design of quantum efficiency measurement system for variable doping GaAs photocathode

    Science.gov (United States)

    Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

    2008-03-01

    To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

  5. Robust Beamforming for Security in MIMO Wiretap Channels With Imperfect CSI

    Science.gov (United States)

    Mukherjee, Amitav; Swindlehurst, A. Lee

    2011-01-01

    In this paper, we investigate methods for reducing the likelihood that a message transmitted between two multiantenna nodes is intercepted by an undetected eavesdropper. In particular, we focus on the judicious transmission of artificial interference to mask the desired signal at the time it is broadcast. Unlike previous work that assumes some prior knowledge of the eavesdropper's channel and focuses on maximizing secrecy capacity, we consider the case where no information regarding the eavesdropper is available, and we use signal-to-interference-plus-noise-ratio (SINR) as our performance metric. Specifically, we focus on the problem of maximizing the amount of power available to broadcast a jamming signal intended to hide the desired signal from a potential eavesdropper, while maintaining a prespecified SINR at the desired receiver. The jamming signal is designed to be orthogonal to the information signal when it reaches the desired receiver, assuming both the receiver and the eavesdropper employ optimal beamformers and possess exact channel state information (CSI). In practice, the assumption of perfect CSI at the transmitter is often difficult to justify. Therefore, we also study the resulting performance degradation due to the presence of imperfect CSI, and we present robust beamforming schemes that recover a large fraction of the performance in the perfect CSI case. Numerical simulations verify our analytical performance predictions, and illustrate the benefit of the robust beamforming schemes.

  6. Distributed cognitive two-way relay beamformer designs under perfect and imperfect CSI

    KAUST Repository

    Pandarakkottilil, Ubaidulla

    2011-09-01

    In this paper, we present distributed two-way relay beamformer designs for a cognitive radio network (CRN) in which a pair of cognitive (or secondary) transceiver nodes communicate with each other assisted by a set of cognitive two-way relay nodes. The secondary nodes share the spectrum with a licensed primary user (PU) node, and each node is assumed to be equipped with a single transmit/receive antenna. The interference to the PU resulting from the transmission from the cognitive nodes is kept below a specified limit. First, we consider relay beamformer designs assuming the availability of perfect channel state information (CSI). For this case, a mean-square error (MSE)-constrained beamformer that minimizes the total relay transmit power, and an MSE-balancing beamformer with a constraint on the total relay transmit power are proposed. Next, we consider relay beamformer designs assuming that the available CSI is imperfect. For this case too, we consider the same problems as those in the case of perfect CSI, and propose beamformer designs that are robust to the errors in the CSI. We show that the proposed designs can be reformulated as convex optimization problems that can be solved efficiently. Through numerical simulations, we illustrate the performance of the proposed designs. © 2011 IEEE.

  7. Pressure dependence of structural phase transition and superconducting transition in CsI

    CERN Document Server

    Nirmala-Louis, C

    2003-01-01

    The self-consistent band structure calculation for CsI performed both in CsCl and HCP structures using the TB-LMTO method is reported. The equilibrium lattice constant, bulk modulus and the phase-transition pressure at which the compound undergoes structural phase transition from CsCl to HCP are predicted from the total-energy calculations. The band structure, density of states (DOS), electronic charge distributions, metallization and superconducting transition temperature (T sub c) of CsI are obtained as a function of pressure for both the CsCl and HCP structures. It is found that the charge transfer from s and p states to d state causes metallization and superconductivity in CsI. The highest T sub c estimated is 2.11 K and the corresponding pressure is 1.8 Mbar. This value is in agreement with the recent experimental observation. The experimental trend - ''metallization and superconductivity is rather insensitive to the crystal structure of CsI'' - is also confirmed in our work. (Abstract Copyright [2003], ...

  8. CSI Web Adventures: A Forensics Virtual Apprenticeship for Teaching Science and Inspiring STEM Careers

    Science.gov (United States)

    Miller, Leslie; Chang, Ching-I; Hoyt, Daniel

    2010-01-01

    CSI: The Experience, a traveling museum exhibit and a companion web adventure, was created through a grant from the National Science Foundation as a potential model for informal learning. The website was designed to enrich and complement the exhibit by modeling the forensic process. Substantive science, real-world lab techniques, and higher-level…

  9. Optimizing the CsI thickness for chest dual-shot dual-energy detectors

    Science.gov (United States)

    Kim, Dong Woon; Kim, Junwoo; Youn, Hanbean; Jeon, Hosang; Kim, Ho Kyung

    2016-03-01

    Dual-energy imaging method has been introduced to improve conspicuity of abnormalities in radiographs. The method typically uses the fast kilovoltage-switching approach, which acquires low and high-energy projections in successive x-ray exposures with the same detector. However, it is typically known that there exists an optimal detector thickness regarding specific imaging tasks or energies used. In this study, the dual-energy detectability has been theoretically addressed for various combinations of detector thicknesses for low and high-energy spectra using the cascaded-systems analysis. Cesium iodide (CsI) is accounted for the x-ray converter in the hypothetical detector. The simple prewhitening model shows that a larger CsI thickness (250 mg cm-2 for example) would be preferred to the the typical CsI thickness of 200 mg cm-2 for better detectability. On the other hand, the typical CsI thickness is acceptable for the prewhitening model considering human-eye filter. The theoretical strategy performed in this study will be useful for a better design of detectors for dual-energy imaging.

  10. Exploring K-3 Teachers' Implementation of Comprehension Strategy Instruction (CSI) Using Expectancy-Value Theory

    Science.gov (United States)

    Foley, Laura S.

    2011-01-01

    This research investigated factors that influence the implementation levels of evidence-based comprehension strategy instruction (CSI) among K-3 teachers. An explanatory design was chosen to gather and probe the data. Quantitative data were gathered via a mailed survey distributed through a representative sample of the 40 school districts (through…

  11. Achievable Rates of Cognitive Radio Networks Using Multi-Layer Coding with Limited CSI

    KAUST Repository

    Sboui, Lokman

    2016-03-01

    In a Cognitive Radio (CR) framework, the channel state information (CSI) feedback to the secondary transmitter (SU Tx) can be limited or unavailable. Thus, the statistical model is adopted in order to determine the system performance using the outage concept. In this paper, we adopt a new approach using multi-layer-coding (MLC) strategy, i.e., broadcast approach, to enhance spectrum sharing over fading channels. First, we consider a scenario where the secondary transmitter has no CSI of both the link between SU Tx and the primary receiver (cross-link) and its own link. We show that using MLC improves the cognitive rate compared to the rate provided by a singlelayer- coding (SLC). In addition, we observe numerically that 2-Layer coding achieves most of the gain for Rayleigh fading. Second, we analyze a scenario where SU Tx is provided by partial CSI about its link through quantized CSI. We compute its achievable rate adopting the MLC and highlight the improvement over SLC. Finally, we study the case in which the cross-link is perfect, i.e., a cooperative primary user setting, and compare the performance with the previous cases. We present asymptotic analysis at high power regime and show that the cooperation enhances considerably the cognitive rate at high values of the secondary power budget.

  12. Selective adsorption and radiochemical separation of Cs(I) using zinc ferrocyanide resin

    International Nuclear Information System (INIS)

    Zinc ferrocyanide resin has been used for the rapid and selective adsorption of Cs(I) and its separation from other elements. The effects of various parameters, such as time of equilibration, pH, resin concentration and interfering anions and cations have been evaluated. (author). 4 refs., 1 tab

  13. High quality single shot ultrafast MeV electron diffraction from a photocathode radio-frequency gun

    International Nuclear Information System (INIS)

    A compact ultrafast electron diffractometer, consisting of an s-band 1.6 cell photocathode radio-frequency gun, a multi-function changeable sample chamber, and a sensitive relativistic electron detector, was built at Shanghai Jiao Tong University. High-quality single-shot transmission electron diffraction patterns have been recorded by scattering 2.5 MeV electrons off single crystalline gold and polycrystalline aluminum samples. The high quality diffraction pattern indicates an excellent spatial resolution, with the ratio of the diffraction ring radius over the ring rms width beyond 10. The electron pulse width is estimated to be about 300 fs. The high temporal and spatial resolution may open new opportunities in various areas of sciences

  14. QE and Suns-Voc study on the epitaxial CSiTF solar cells

    Institute of Scientific and Technical Information of China (English)

    AI Bin; SHEN Hui; BAN Qun; LIANG Zongcun; CHEN Rulong; SHI Zhengrong; LIAO Xianbo

    2005-01-01

    In order to clarify the major factors having confined the efficiencies of as-prepared crystalline silicon thin film (CSiTF) solar cells on the SSP (silicon sheets from powder) ribbons, QE (quantum efficiency) and Suns-Voc study were performed on the epitaxial CSiTF solar cells fabricated on the SSP ribbons, the SSP ribbons after surface being zone melting recrystallized (ZMR) and single crystalline silicon (sc-Si) substrates.The results show that the epi-layers deposited on the SSP ribbons have rough surfaces,which not only increases the diffusion reflectance on the surfaces but also makes the anti-reflection coatings become structure-loosened, both of which would deteriorate the light trapping effect; in addition, the epi-layers deposited on the SSP ribbons possess poor crystallographic quality, so the heavy grain boundary (GB) recombination limits the diffusion length of the minority carriers in the epi-layers, which makes the as-prepared CSiTF solar cells suffer the worse spectra response at long-wavelength range. Nearly all the dark characteristic parameters of the CSiTF solar cells are far away from the ideal values. The performances of the CSiTF solar cells are especially affected by too high I02 (the dark saturation current of space charge region) values and too low Rsh (parallel resistance) values. The higher I02 values are mainly caused by the heavy GB recombination resulting from the poor crystallographic qualities of the silicon active layers in the space charge regions, while the lower Rsh values are attributed to the electrical leakage at the un-passivated PN junction or solar cell edges after the solar cells are cut by the laser scriber.

  15. Characterizing and Optimizing Photocathode Laser Distributions for Ultra-low Emittance Electron Beam Operations

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, F. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Bohler, D. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Ding, Y. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Gilevich, S. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Huang, Z. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Loos, H. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Ratner, D. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Vetter, S. [SLAC National Accelerator Lab., Menlo Park, CA (United States)

    2015-12-07

    Photocathode RF gun has been widely used for generation of high-brightness electron beams for many different applications. We found that the drive laser distributions in such RF guns play important roles in minimizing the electron beam emittance. Characterizing the laser distributions with measurable parameters and optimizing beam emittance versus the laser distribution parameters in both spatial and temporal directions are highly desired for high-brightness electron beam operation. In this paper, we report systematic measurements and simulations of emittance dependence on the measurable parameters represented for spatial and temporal laser distributions at the photocathode RF gun systems of Linac Coherent Light Source. The tolerable parameter ranges for photocathode drive laser distributions in both directions are presented for ultra-low emittance beam operations.

  16. First operation of cesium telluride photocathodes in the TTF injector RF gun

    CERN Document Server

    Sertore, D; Flöttmann, K; Stephan, F; Zapfe, K; Michelato, P

    2000-01-01

    During the run 1998/1999 a new injector based on a laser-driven RF gun was brought in operation at the TESLA Test Facility (TTF) linac at DESY, in order to produce the beam structure and quality required either by TeV collider and SASE FEL experiments. High quantum efficiency cesium telluride photocathodes, prepared at Milano and transferred to DESY, have been successfully operated in the RF gun. A bunch charge of 50 nC, only limited by space charge effects, was achieved. The photocathodes have shown an operative lifetime of several months. A new cathode surface finishing has showed a promising decrease of the photocathode dark current. Measurements of dark current, quantum efficiency and lifetime are reported.

  17. Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes

    Science.gov (United States)

    Zhang, Xuemei; Wu, Xu; Centeno, Anthony; Ryan, Mary P.; Alford, Neil M.; Riley, D. Jason; Xie, Fang

    2016-03-01

    Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap.

  18. Impact evaluation of ion back-bombardment of NEA-GaAs photocathode

    International Nuclear Information System (INIS)

    We study GaAs photocathode with NEA (Negative Electron Affinity) surface as electron source of accelerator. Advantage of NEA GaAs photocathode is generating ultra-low emittance and polarized electron beam with circularly polarized laser. However, the cathode is so sensitive and quantum efficiency degradation limits the operational lifetime. Among several processes, Ion Back-bombardment (IBB) is the most serious phenomenon to limit the lifetime. In IBB, ions generated by ionization of residual gas molecule with electron beam collide to cathode and degrade NEA surface. We improve photocathode test bench in Hiroshima University to prevent vacuum pressure evolution during the experiment and control ion orbits to switch the IBB effect. In this study, we simulate ion orbits and evaluate distribution of ion collision on cathode to switch the IBB in on cathode. With this modification, IBB effect on the cathode lifetime will be evaluated more quantitatively. (author)

  19. Effect of Sb thickness on the performance of bialkali-antimonide photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Mamun, Md Abdullah A., E-mail: mmamu001@odu.edu; Elmustafa, Abdelmageed A. [Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia 23529 and The Applied Research Center, Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Hernandez-Garcia, Carlos; Mammei, Russell; Poelker, Matthew [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)

    2016-03-15

    The alkali species Cs and K were codeposited using an effusion source, onto relatively thick layers of Sb (50 nm to ∼7 μm) grown on GaAs and Ta substrates inside a vacuum chamber that was baked and not-vented, and also baked and vented with clean dry nitrogen but not rebaked. The characteristics of the Sb films, including sticking probability, surface roughness, grain size, and crystal properties were very different for these conditions, yet comparable values of photocathode yield [or quantum efficiency (QE)] at 284 V were obtained following codeposition of the alkali materials. Photocathodes manufactured with comparatively thick Sb layers exhibited the highest QE and the best 1/e lifetime. The authors speculate that the alkali codeposition enabled optimized stoichiometry for photocathodes manufactured using thick Sb layers, which could serve as a reservoir for the alkali materials.

  20. Photoelectrochemical water splitting: silicon photocathodes for hydrogen evolution

    Science.gov (United States)

    Warren, Emily L.; Boettcher, Shannon W.; McKone, James R.; Lewis, Nathan S.

    2010-08-01

    The development of low cost, scalable, renewable energy technologies is one of today's most pressing scientific challenges. We report on progress towards the development of a photoelectrochemical water-splitting system that will use sunlight and water as the inputs to produce renewable hydrogen with oxygen as a by-product. This system is based on the design principle of incorporating two separate, photosensitive inorganic semiconductor/liquid junctions to collectively generate the 1.7-1.9 V at open circuit needed to support both the oxidation of H2O (or OH-) and the reduction of H+ (or H2O). Si microwire arrays are a promising photocathode material because the high aspect-ratio electrode architecture allows for the use of low cost, earth-abundant materials without sacrificing energy-conversion efficiency, due to the orthogonalization of light absorption and charge-carrier collection. Additionally, the high surfacearea design of the rod-based semiconductor array inherently lowers the flux of charge carriers over the rod array surface relative to the projected geometric surface of the photoelectrode, thus lowering the photocurrent density at the solid/liquid junction and thereby relaxing the demands on the activity (and cost) of any electrocatalysts. Arrays of Si microwires grown using the Vapor Liquid Solid (VLS) mechanism have been shown to have desirable electronic light absorption properties. We have demonstrated that these arrays can be coated with earth-abundant metallic catalysts and used for photoelectrochemical production of hydrogen. This development is a step towards the demonstration of a complete artificial photosynthetic system, composed of only inexpensive, earth-abundant materials, that is simultaneously efficient, durable, and scalable.

  1. Electronic structure and optical properties of CsI, CsI(Ag), and CsI(Tl)

    Science.gov (United States)

    Zhang, Zheng; Zhao, Qiang; Li, Yang; Ouyang, Xiao-Ping

    2016-05-01

    The band structure, electronic density of states and optical properties of CsI and of CsI doped with silver or thallium are studied by using a first-principles calculation based on density functional theory (DFT). The exchange and the correlation potentials among the electrons are described by using the generalized gradient approximation (GGA). The results of our study show that the electronic structure changes somewhat when CsI is doped with silver or thallium. The band gaps of CsI(Ag) and CsI(Tl) are smaller than that of CsI, and the width of the conduction band of CsI is increased when CsI is doped with thallium or silver. Two peaks located in the conduction band of CsI(Ag) and CsI(Tl) are observed from their electronic densities of states. The absorption coefficients of CsI, CsI(Ag), and CsI(Tl) are zero when their photon energies are below 3.5 eV, 1.5 eV, and 3.1 eV, respectively. The results show that doping can improve the detection performance of CsI scintillators. Our study can explain why doping can improve the detection performance from a theoretical point of view. The results of our research provide both theoretical support for the luminescent mechanisms at play in scintillator materials when they are exposed to radiation and a reference for CsI doping from the point of view of the electronic structure.

  2. Equivalent Method of Solving Quantum Efficiency of Reflection-Mode Exponential Doping GaAs Photocathode

    Institute of Scientific and Technical Information of China (English)

    NIU Jun; YANG Zhi; CHANG Ben-Kang

    2009-01-01

    The mathematical expression of the electron diffusion and drift length LDE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reflection-mode uniform doping cathode, substituting L_(DE) for L_D, the equivalent quantum efficiency equation of the reflection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in fine.The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode.

  3. An in-situ photocathode loading system for the SLC Polarized Electron Gun

    International Nuclear Information System (INIS)

    An ultra-high vacuum loadlock system capable of operating at high voltage has been added to the SLC Polarized Electron Gun. The unit incorporates facilities for heat cleaning, activating and measuring the quantum efficiency of photocathodes. A tray of up to four photocathodes can be exchanged without bringing the activation unit or gun up to atmosphere. Low voltage quantum efficiencies of 20% have been obtained for bulk GaAs at 633 nm and 6% for a 0.3 micron GaAs layer at 755 nm. Results for other cathodes as well as operational characteristics are discussed

  4. CdTeO3 Deposited Mesoporous NiO Photocathode for a Solar Cell

    OpenAIRE

    Chuan Zhao; Xiaoping Zou; Sheng He

    2014-01-01

    Semiconductor sensitized NiO photocathodes have been fabricated by successive ionic layer adsorption and reaction (SILAR) method depositing CdTeO3 quantum dots onto mesoscopic NiO films. A solar cell using CdTeO3 deposited NiO mesoporous photocathode has been fabricated. It yields a photovoltage of 103.7 mV and a short-circuit current density of 0.364 mA/cm2. The incident photon to current conversion efficiency (IPCE) value is found to be 12% for the newly designed NiO/CdTeO3 solar cell. It s...

  5. Development of modulated electron beam for intensity modulated radiation therapy (IMRT) on a photocathode electron gun

    International Nuclear Information System (INIS)

    Radiation therapy of cancer is developing to un-uniform irradiation, for concentrating dose to a cancer tumor and reducing dose to normal tissue. As a step toward the Intensity modulated radiation therapy, we examined dynamic optical modulation of electron beam produced by a photocathode electron gun. Images on photo-masks were transferred onto a photocathode by relay imaging. Electron beam could be controlled by a remote mirror. Modulated electron beam maintained its shape on acceleration, had a fine spatial resolution, and could be moved dynamically by optical methods. As a second step, optical modulation of electron beam and dynamic control succeeded by a digital micro mirror device (DMD). (author)

  6. Design of a high duty cycle, asymmetric emittance RF photocathode injector for linear collider applications

    International Nuclear Information System (INIS)

    One of the attractive features of the superconducting approach to linear collider design is that the transverse emittances demanded are much larger than in normal conducting schemes. For TESLA design parameters, the damping rings appear to be relatively large and expensive, and it is therefore of some interest to look into alternative sources. For electrons, a promising source candidate is an rf photocathode. In this paper, the authors present conceptual design work towards development of an asymmetric emittance rf photocathode source which can operate at the TESLA repetition rates and duty cycle, and is capable of emitting beams with the required emittances and charge per pulse

  7. Measurement of temporal response of transmission-type spin-polarized photocathodes

    International Nuclear Information System (INIS)

    Spin polarized electron beam is essential for the high energy particle physics experiment 'International Linear Collider'. In Nagoya University, transmission-type spin-polarized photocathodes, in which the laser light is injected from the back side of the photocathode have been developed. In the development of the electron source, the quantum efficiency of 0.5% and the polarization of ∼90% were achieved. However, the response time of the transmission-type electron source is not evaluated. We are planning to measure the response time by using a RF deflecting cavity. In this paper, the details of the measurement system are reported. (author)

  8. Design and beam dynamics simulations of an S-band photocathode rf gun

    Science.gov (United States)

    Kumar, Arvind; Pant, K. K.; Krishnagopal, S.

    2002-10-01

    We are building an S-band photocathode rf gun as an injector to a 30MeV electron linac for FEL applications. Here we discuss details of design simulations performed using superfish and gdfidl and compare with results of cold tests performed on prototype cells of the photocathode rf gun. We also discuss beam dynamics simulations performed using parmela and report results from simulations to achieve a normalized transverse rms emittance of about 1π mm mrad for a 10ps pulse with 1nC charge in the presence of a solenoid magnetic field used for emittance compensation.

  9. Compact narrow-band THz radiation source based on photocathode rf gun

    International Nuclear Information System (INIS)

    Narrow-band THz coherent Cherenkov radiation can be driven by a subpicosecond electron bunch traveling along the axis of a hollow cylindrical dielectric-lined waveguide. We present a scheme of compact THz radiation source based on the photocathode rf gun. On the basis of our analytic result, the subpicosecond electron bunch with high charge (800 pC) can be generated directly in the photocathode rf gun. According to the analytical and simulated results, a narrow emission spectrum peaked at 0.24 THz with 2 megawatt (MW) peak power is expected to gain in the proposed scheme (the length of the facility is about 1.2 m). (authors)

  10. X-ray Photoemission Spectroscopy Studies of Cesium Antimonide Photocathodes for Photoinjector Applications

    Science.gov (United States)

    Martini, Irene; Chevallay, Eric; Fedosseev, Valentin; Hessler, Christoph; Neupert, Holger; Nistor, Valentin; Taborelli, Mauro

    Within the CLIC (Compact Linear Collider) project, feasibility studies of a photoinjector option for the drive beam as an alternative to its baseline design using a thermionic electron gun (Geschonke et al. [1]) are on-going. This R&D program covers both the laser and the photocathode side. Cesium antimonide cathodes were produced at CERN by co-deposition onto copper substrates and characterized by photoemission and by XPS (X-ray Photoemission Spectroscopy) analysis. A systematic study on newly produced and used photocathodes was conducted in order to correlate the surface composition to the photoemissive properties.

  11. Characterization of quantum efficiency and robustness of cesium-based photocathodes

    Science.gov (United States)

    Montgomery, Eric J.

    High quantum efficiency, robust photocathodes produce picosecond-pulsed, high-current electron beams for photoinjection applications like free electron lasers. In photoinjectors, a pulsed drive laser incident on the photocathode causes photoemission of short, dense bunches of electrons, which are then accelerated into a relativistic, high quality beam. Future free electron lasers demand reliable photocathodes with long-lived quantum efficiency at suitable drive laser wavelengths to maintain high current density. But faced with contamination, heating, and ion back-bombardment, the highest efficiency photocathodes find their delicate cesium-based coatings inexorably lost. In answer, the work herein presents careful, focused studies on cesium-based photocathodes, particularly motivated by the cesium dispenser photocathode. This is a novel device comprised of an efficiently photoemissive, cesium-based coating deposited onto a porous sintered tungsten substrate, beneath which is a reservoir of elemental cesium. Under controlled heating cesium diffuses from the reservoir through the porous substrate and across the surface to replace cesium lost to harsh conditions---recently shown to significantly extend the lifetime of cesium-coated metal cathodes. This work first reports experiments on coated metals to validate and refine an advanced theory of photoemission already finding application in beam simulation codes. Second, it describes a new theory of photoemission from much higher quantum efficiency cesium-based semiconductors and verifies its predictions with independent experiment. Third, it investigates causes of cesium loss from both coated metal and semiconductor photocathodes and reports remarkable rejuvenation of full quantum efficiency for contaminated cesium-coated surfaces, affirming the dispenser prescription of cesium resupply. And fourth, it details continued advances in cesium dispenser design with much-improved operating characteristics: lower temperature

  12. Thermal Emittance Measurement of the Cs2Te Photocathode in FZD Superconducting RF

    CERN Document Server

    Xiang, R; Michel, P; Murcek, P; Teichert, J

    2010-01-01

    The thermal emittance of the photocathode is an interesting physical property for the photoinjector, because it decides the minimum emittance the photoinjector can finally achieve. In this paper we will report the latest results of the thermal emittance of the Cs2Te photocathode in FZD Superconducting RF gun. The measurement is performed with solenoid scan method with very low bunch charge and relative large laser spot on cathode, in order to reduce the space charge effect as much as possible, and meanwhile to eliminate the wake fields and the effect from beam halos.

  13. Perovskite BiFeO3 thin film photocathode performance with visible light activity

    Science.gov (United States)

    Yilmaz, P.; Yeo, D.; Chang, H.; Loh, L.; Dunn, S.

    2016-08-01

    Perovskite materials are now an important class of materials in the application areas of photovoltaics and photocatalysis. Inorganic perovskites such as BiFeO3 (BFO) are promising photocatalyst materials with visible light activity and inherent stability. Here we report the large area sol-gel synthesis of BFO films for solar stimulated water photo oxidation. By modifying the sol-gel synthesis process we have produced a perovskite material that has p-type behaviour and a flat band potential of ∼1.15 V (versus NHE). The photocathode produces a density of ‑0.004 mA cm‑2 at 0 V versus NHE under AM1.5 G illumination. We further show that 0.6 μmol h‑1 of O2 was produced at an external bias of ‑0.5 V versus Ag/AgCl. The addition of a non-percolating conducting network of Ag increases the photocurrent to ‑0.07 mA cm‑2 at 0 V versus NHE (at 2% Ag loading) with an increase to 2.7 μmol h‑1 for O2 production. We attribute the enhancement in photoelectrochemical performance to increased light absorption due light scattering by the incorporated Ag particles, improved charge transfer kinetics at the Ag/BFO interface and reduced over potential losses. We support these claims by an observed shift in flat band and onset potentials after Ag modification through UV–vis spectroscopy, Mott–Schottky plots and j–v curve analysis.

  14. Perovskite BiFeO3 thin film photocathode performance with visible light activity.

    Science.gov (United States)

    Yilmaz, P; Yeo, D; Chang, H; Loh, L; Dunn, S

    2016-08-26

    Perovskite materials are now an important class of materials in the application areas of photovoltaics and photocatalysis. Inorganic perovskites such as BiFeO3 (BFO) are promising photocatalyst materials with visible light activity and inherent stability. Here we report the large area sol-gel synthesis of BFO films for solar stimulated water photo oxidation. By modifying the sol-gel synthesis process we have produced a perovskite material that has p-type behaviour and a flat band potential of ∼1.15 V (versus NHE). The photocathode produces a density of -0.004 mA cm(-2) at 0 V versus NHE under AM1.5 G illumination. We further show that 0.6 μmol h(-1) of O2 was produced at an external bias of -0.5 V versus Ag/AgCl. The addition of a non-percolating conducting network of Ag increases the photocurrent to -0.07 mA cm(-2) at 0 V versus NHE (at 2% Ag loading) with an increase to 2.7 μmol h(-1) for O2 production. We attribute the enhancement in photoelectrochemical performance to increased light absorption due light scattering by the incorporated Ag particles, improved charge transfer kinetics at the Ag/BFO interface and reduced over potential losses. We support these claims by an observed shift in flat band and onset potentials after Ag modification through UV-vis spectroscopy, Mott-Schottky plots and j-v curve analysis. PMID:27420393

  15. Light yield of an undoped CsI crystal coupled directly to a photomultiplier tube at 77 Kelvin

    OpenAIRE

    Liu, Jing; Yamashita, Masaki; Soma, Arun Kumar

    2016-01-01

    A light yield of 20.4 $\\pm$ 0.8 photoelectrons/keV was achieved with an undoped CsI crystal coupled directly to a photomultiplier tube at 77 Kelvin. This is by far the largest yield in the world achieved with CsI crystals. An energy threshold that is several times lower than the current dark matter experiments utilizing CsI(Tl) crystals may be achievable using this technique. Together with novel CsI crystal purification methods, the technique may be used to improve the sensitivities of dark m...

  16. A surfeit of science: The "CSI effect" and the media appropriation of the public understanding of science.

    Science.gov (United States)

    Cole, Simon A

    2015-02-01

    Over the past decade, popular media has promulgated claims that the television program CSI and its spinoffs and imitators have had a pernicious effect on the public understanding of forensic science, the so-called "CSI effect." This paper analyzes those media claims by documenting the ways in which the media claims that CSI "distorts" an imagined "reality." It shows that the media appropriated the analytic stance usually adopted by science advocates, portraying the CSI effect as a social problem in science communication. This appropriation was idiosyncratic in that it posited, as a social problem, a "surfeit" of knowledge and positive imagery about science, rather than the more familiar "deficits." In addition, the media simultaneously appropriated both "traditional" and "critical" PUS discourses. Despite this apparent contradiction, the paper concludes that, in both discourses, the media and its expert informants insist upon their hegemony over "the public" to articulate the "reality" of forensic science. PMID:23825289

  17. Uptake behaviour of Cs(I) from aqueous solutions by hydrous ferric oxide and hydrous tungsten oxide: a radiotracer study

    International Nuclear Information System (INIS)

    The objective of the present study was to investigate the applicability of hydrous ferric oxide (HFO) and hydrous tungsten oxide (HTO) for the treatment of aqueous solutions containing Cs(I) at micro/tracers concentrations utilizing a radiotracer technique

  18. Light yield of an undoped CsI crystal coupled directly to a photomultiplier tube at 77 Kelvin

    CERN Document Server

    Liu, Jing; Soma, Arun Kumar

    2016-01-01

    A light yield of 20.4 $\\pm$ 0.8 photoelectrons/keV was achieved with an undoped CsI crystal coupled directly to a photomultiplier tube at 77 Kelvin. This is by far the largest yield in the world achieved with CsI crystals. An energy threshold that is several times lower than the current dark matter experiments utilizing CsI(Tl) crystals may be achievable using this technique. Together with novel CsI crystal purification methods, the technique may be used to improve the sensitivities of dark matter and coherent elastic neutrino-nucleus scattering experiments. Also measured were the scintillation light decay constants of the undoped CsI crystal at both room temperature and 77 Kelvin. The results are consistent with those in the literature.

  19. CsI calorimeter development for a high-precision, general-purpose detector for a Tau-Charm Factory

    International Nuclear Information System (INIS)

    Design, fabrication techniques, and preliminary tests for a CsI calorimeter for the Tau-Charm Factory (TCF) proposed for construction in Spain are presented. Selected CsI calorimeter studies undertaken by the US Tau-Charm Collaboration, including simulations of machine-induced detector backgrounds in the CsI calorimeter, radiation change characterization of CsI(Tl) and CsI(Na) crystals from five manufacturers, crystal segmentation and photodiode/wavelength shifter readout schemes, and development of mechanical support structure, are reviewed. A test of a prototype CsI calorimeter conducted in the TRIUMF in M11 (120--400 MeV) and M13 (30--120 MeV) beamlines is discussed

  20. CsI as Multifunctional Redox Mediator for Enhanced Li-Air Batteries.

    Science.gov (United States)

    Lee, Chan Kyu; Park, Yong Joon

    2016-04-01

    We introduce CsI as a multifunctional redox mediator to enhance the performance of Li-air batteries. CsI dissolved in the electrolyte is ionized into Cs(+) and I(-), which perform their roles in the Li anode and air electrode, respectively. The I(-) ions in the electrolyte facilitate the dissolution of Li2O2 in the air electrode as a redox mediator, which reduces the overpotential of the cell. The low overpotential also leads to the suppression of parasitic reactions occurring in the high-voltage range, such as the decomposition of the electrolyte and the reaction between Li2O2 and carbon. At the same time, the Cs(+) ions act as an electrostatic shield at the sharp points of the Li anode, hindering the growth of Li dendrite. The combined effects of reduced parasitic reactions and hindered Li-dendrite growth successfully improve the cyclic performance of Li-air cells. PMID:26999060

  1. Modified Grid-Connected CSI for Hybrid PV/Wind Power Generation System

    Directory of Open Access Journals (Sweden)

    D. Amorndechaphon

    2012-01-01

    Full Text Available The principle of a power conditioning unit for hybrid PV/wind power generation system is proposed. The proposed power conditioner is based on the current source inverter (CSI topology. All energy sources are connected in parallel with a DC-bus through the modified wave-shaping circuits. To achieve the unity power factor at the utility grid, the DC-link current can be controlled via the wave-shaping circuits with the sinusoidal PWM scheme. In this work, the carrier-based PWM scheme is also proposed to minimize the utility current THD. The power rating of the proposed system can be increased by connecting more PV/wind modules through their wave-shaping circuits in parallel with the other modules. The details of the operating principles, the system configurations, and the design considerations are described. The effectiveness of the proposed CSI is demonstrated by simulation results.

  2. Outage Performance of Decode-and-Forward in Two-Way Relaying with Outdated CSI

    KAUST Repository

    Hyadi, Amal

    2015-01-07

    In this paper, we analyze the outage behavior of decode-and-forward relaying in the context of selective two-way cooperative systems. First, a new relay selection metric is proposed to take into consideration both transmission rates and instantaneous link conditions between cooperating nodes. Afterwards, the outage probability of the proposed system is derived for Nakagami-m fading channels in the case when perfect channel state information is available and then extended to the more realistic scenario where the available channel state information (CSI) is outdated due to fast fading. New expressions for the outage probability are obtained, and the impact of imperfect CSI on the performance is evaluated. Illustrative numerical results, Monte Carlo simulations, and comparisons with similar approaches are presented to assess the accuracy of our analytical derivations and confirm the performance gain of the proposed scheme.

  3. Charge Lifetime Study of K2CsSb Photocathode Inside a JLAB DC High Voltage Gun

    International Nuclear Information System (INIS)

    Two photocathodes are frequently considered for generating high average current electron beams and/or beams with high brightness for current and future accelerator applications: GaAs:Cs and K2CsSb. Each photocathode has advantages and disadvantages, and need to demonstrate performance at 'production' accelerator facilities. To this end a K2CsSb photocathode was manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure ∼ 5 x 10-11 Torr. This photocathode was installed inside a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at 440 or 532 nm, to generate beams up to 20 mA. Photocathode charge lifetime measurements indicate that under some conditions this cathode has exceptionally high charge lifetime, without measurable QE decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. These studies also suggest a complex QE decay mechanism likely related to chemistry and localized heating via the laser beam.

  4. Novel Cathode and Photocathode Materials for Dye-Sensitized Solar Cells

    Czech Academy of Sciences Publication Activity Database

    Kavan, Ladislav; Vlčková Živcová, Zuzana; Krýsová, Hana; Cígler, Petr; Liska, P.; Zakeeruddin, S. M.; Grätzel, M.

    Taipei: International Society of Electrochemistry , 2015. 826. [Annual Meeting of the International Society of Electrochemistry . Green Electrochemistry for Tomorrow´s Society /66./. 04.10.2015-09.10.2015, Taipei] R&D Projects: GA ČR GA13-07724S Institutional support: RVO:61388955 Keywords : dye-sensitized solar cells * photocathodes * electrochemistry Subject RIV: CG - Electrochemistry

  5. Characterisation of Pb thin films prepared by the nanosecond pulsed laser deposition technique for photocathode application

    International Nuclear Information System (INIS)

    Pb thin films were prepared by the nanosecond pulsed laser deposition technique on Si (100) and polycrystalline Nb substrates for photocathode application. As the photoemission performances of a cathode are strongly affected by its surface characteristics, the Pb films were grown at different substrate temperatures with the aim of modifying the morphology and structure of thin films. An evident morphological modification in the deposited films with the formation of spherical grains at higher temperatures has been observed. X-ray diffraction measurements showed that a preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C while the Pb (200) plane became strongly pronounced with the increase in the substrate temperature. Finally, a Pb thin film deposited on Nb substrate at 30 °C and tested as the photocathode showed interesting results for the application of such a device in superconducting radio frequency guns. - Highlights: • Pb thin films obtained by the nanosecond pulsed laser deposition technique at different substrate temperature. • The substrate temperature modifies the morphology and structure of Pb films. • Pb thin film was deposited at room temperature for photocathode application. • The Pb thin film photocathode was tested and the quantum efficiency of the device improved after laser cleaning treatment of the film surface

  6. Engineering MoSx/Ti/InP Hybrid Photocathode for Improved Solar Hydrogen Production

    Science.gov (United States)

    Li, Qiang; Zheng, Maojun; Zhong, Miao; Ma, Liguo; Wang, Faze; Ma, Li; Shen, Wenzhong

    2016-01-01

    Due to its direct band gap of ~1.35 eV, appropriate energy band-edge positions, and low surface-recombination velocity, p-type InP has attracted considerable attention as a promising photocathode material for solar hydrogen generation. However, challenges remain with p-type InP for achieving high and stable photoelectrochemical (PEC) performances. Here, we demonstrate that surface modifications of InP photocathodes with Ti thin layers and amorphous MoSx nanoparticles can remarkably improve their PEC performances. A high photocurrent density with an improved PEC onset potential is obtained. Electrochemical impedance analyses reveal that the largely improved PEC performance of MoSx/Ti/InP is attributed to the reduced charge-transfer resistance and the increased band bending at the MoSx/Ti/InP/electrolyte interface. In addition, the MoSx/Ti/InP photocathodes function stably for PEC water reduction under continuous light illumination over 2 h. Our study demonstrates an effective approach to develop high-PEC-performance InP photocathodes towards stable solar hydrogen production. PMID:27431993

  7. Silicon decorated with amorphous cobalt molybdenum sulfide catalyst as an efficient photocathode for solar hydrogen generation.

    Science.gov (United States)

    Chen, Yang; Tran, Phong D; Boix, Pablo; Ren, Yi; Chiam, Sing Yang; Li, Zhen; Fu, Kunwu; Wong, Lydia H; Barber, James

    2015-04-28

    The construction of viable photoelectrochemical (PEC) devices for solar-driven water splitting can be achieved by first identifying an efficient independent photoanode for water oxidation and a photocathode for hydrogen generation. These two photoelectrodes then must be assembled with a proton exchange membrane within a complete coupled system. Here we report the preparation of a Si/a-CoMoSx hybrid photocathode which shows impressive performance (onset potential of 0.25 V vs RHE and photocurrent jsc of 17.5 mA cm(-2) at 0 V vs RHE) in pH 4.25 phosphate solution and under simulated AM 1.5 solar illumination. This performance is among the best reported for Si photocathodes decorated with noble-metal-free catalysts. The electrode preparation is scalable because it relies on a photoassisted electrodeposition process employing an available p-type Si electrode and [Co(MoS4)2](2-) precursor. Investigation of the mechanism of the Si/a-CoMoSx electrode revealed that under conditions of H2 photogeneration this bimetallic sulfide catalyst is highly efficient in extracting electrons from illuminated Si and subsequently in reducing protons into H2. The Si/a-CoMoSx photocathode is functional over a wide range of pH values, thus making it a promising candidate for the construction of a complete solar-driven water splitting PEC device. PMID:25801437

  8. Research and development of high-temperature operating photocathode electron source for high brightness electron gun

    International Nuclear Information System (INIS)

    We have been developing a novel photocathode RF gun system with an advanced RF cavity structure and a new photocathode material for the SuperKEKB electron linac. This injector is required to obtain a low emittance and high charge electron beams in order to achieve the highest luminosity in the world. The required beam parameters are 5 nC and 20 mm·mrad from the RF gun. Moreover, 10 nC electron beams for positron production will be also generated by the same RF gun. In order to obtain extremely high charge electron beams, Yb-based laser system is being upgraded for higher power and a high temperature photocathode system for a quantum efficiency (QE) enhancement will be introduced to the new RF gun system. This paper reports on the research and development of the system of high temperature photocathode for QE enhancement to be able to generate high charge electron beams (∼10 nC) at the RF gun in SuperKEKB electron linac. (author)

  9. ACCORDI, JOINT-VENTURE E INVESTIMENTI DIRETTI DELL’INDUSTRIA ITALIANA NELLA CSI: UN’ANALISI QUALITATIVA

    OpenAIRE

    Giampaolo Vitali; Chiara Monti

    1996-01-01

    Le joint venture italiane nella Csi rappresentano un utile strumento di internazionalizzazione dell'impresa, tanto dal punto di vista della diversificazione dei mercati di sbocco, quanto da quello della delocalizzazione di attività produttive in paesi a basso costo del lavoro. Il censimento delle operazioni aventi finalità produttive condotte dalle imprese italiane nella Csi e attive al 1995 consente di approfondire tali aspetti. In particolare, la ricerca evidenzia i caratteri distintivi dei...

  10. Der Cerebral State Index (CSI) als Indikator der Narkosetiefe - Detektion von Wachheit

    OpenAIRE

    Kiel, Tobias

    2010-01-01

    Ziel der klinischen Studie war die Validierung des EEG-basierten CSI. Die Fähigkeit, Wachheit von Bewusstlosigkeit zu unterscheiden sowie das Verhalten bei zu-/abnehmender Anästhetikakonzentration wurden untersucht. Elektive Patienten erhielten Anästhetika gemäß klinischem Standard. Während der Ein-/Ausleitung der Narkose wurden Patienten zum Händedruck aufgefordert. Die ausbleibende/zurückkehrende Reaktion wurde als Bewusstseinsverlust/Bewusstseinswiederkehr definiert. Die Vorhersagewahrsche...

  11. Linear Precoding for the MIMO Multiple Access Channel with Finite Alphabet Inputs and Statistical CSI

    OpenAIRE

    Wu, Yongpeng; Wen, Chao-Kai; Xiao, Chengshan; Gao, Xiqi; Schober, Robert

    2014-01-01

    In this paper, we investigate the design of linear precoders for the multiple-input multiple-output (MIMO) multiple access channel (MAC). We assume that statistical channel state information (CSI) is available at the transmitters and consider the problem under the practical finite alphabet input assumption. First, we derive an asymptotic (in the large system limit) expression for the weighted sum rate (WSR) of the MIMO MAC with finite alphabet inputs and Weichselberger's MIMO channel model. S...

  12. A Post-genomic Forensic Crime Drama : CSI: Crime Scene Investigation as Cultural Forum on Science

    OpenAIRE

    Bull, Sofia

    2012-01-01

    This thesis examines how the first 10 seasons of CSI: Crime Scene Investigation (CBS, 2000–) engage with discourses on science. Investigating CSI’s representation of scientific practices and knowledge, it explicitly attempts to look beyond the generic assumption that forensic crime dramas simply ‘celebrate’ science. The material is analysed at three different levels, studying CSI’s wider cultural discursive context, genre linkages, and audio-visual form. In order to fully account for the seri...

  13. Conceptualising corporate social responsibility (CSR) and corporate social investment (CSI): the South African context

    OpenAIRE

    Robert E. Hinson; Tidings P. Ndhlovu

    2011-01-01

    Purpose – With globalisation pressures and increasing burdens on governments to provide comprehensive social services, there is now a need to better understand how firms play their part in sharing these burdens. Views vary from those who believe that CSR and CSI are distractions from profit maximisation to those who argue that participation in such activities contributes to positive social transformation and also benefits participating firms themselves. This paper seeks to conceptualise these...

  14. Robust Group Sparse Beamforming for Multicast Green Cloud-RAN with Imperfect CSI

    OpenAIRE

    Shi, Yuanming; Zhang, Jun; Letaief, Khaled B.

    2015-01-01

    In this paper, we investigate the network power minimization problem for the multicast cloud radio access network (Cloud-RAN) with imperfect channel state information (CSI). The key observation is that network power minimization can be achieved by adaptively selecting active remote radio heads (RRHs) via controlling the group-sparsity structure of the beamforming vector. However, this yields a non-convex combinatorial optimization problem, for which we propose a three-stage robust group spars...

  15. Optimal Stochastic Coordinated Beamforming for Wireless Cooperative Networks with CSI Uncertainty

    OpenAIRE

    Shi, Yuanming; Zhang, Jun; Letaief, Khaled B.

    2013-01-01

    Transmit optimization and resource allocation for wireless cooperative networks with channel state information (CSI) uncertainty are important but challenging problems in terms of both the uncertainty modeling and performance op- timization. In this paper, we establish a generic stochastic coordinated beamforming (SCB) framework that provides flex- ibility in the channel uncertainty modeling, while guaranteeing optimality in the transmission strategies. We adopt a general stochastic model for...

  16. Exploring K-3 Teachers' Implementation of Comprehension Strategy Instruction (CSI) Using Expectancy-Value Theory

    OpenAIRE

    Foley, Laura Slack

    2011-01-01

    This research investigated factors that influence the implementation levels of evidence-based comprehension strategy instruction (CSI) among K–3 teachers. An explanatory design was chosen to gather and probe the data. Quantitative data were gathered via a mailed survey distributed through a representative sample of the 40 school districts (through a stratified-random selection of teachers) in a state in the Rocky Mountain West. Expectancy-value theory was applied as it affects self-rep...

  17. 49th Annual Convention of the Computer Society of India CSI

    CERN Document Server

    Govardhan, A; Raju, K; Mandal, J

    2015-01-01

    Volume 1 contains 73 papers presented at CSI 2014: Emerging ICT for Bridging the Future: Proceedings of the 49th Annual Convention of Computer Society of India. The convention was held during 12-14, December, 2014 at Hyderabad, Telangana, India. This volume contains papers mainly focused on Fuzzy Systems, Image Processing, Software Engineering, Cyber Security and Digital Forensic, E-Commerce, Big Data, Cloud Computing and ICT applications.

  18. Mathematical Modeling and Analysis of Different Vector Controlled CSI Fed 3-Phase Induction Motor Drive

    OpenAIRE

    Mark, Arul Prasanna; Vairamani, Rajasekaran; Irudayaraj, Gerald Christopher Raj

    2014-01-01

    The main objective of this paper is to build a simple mathematical competent model that describes the circuits and interconnections of a 3-phase squirrel cage induction motor used for industrial applications. This paper presents the detailed analysis of theoretical concepts used in mathematical modeling, simulation’ and hardware implementation. The objective of this work is to compare the dynamic performances of the vector control methods for CSI fed IM drives. Based on the results, dynamic p...

  19. CSI Index Of Customer’s Satisfaction Applied In The Area Of Public Transport

    OpenAIRE

    Poliaková Adela

    2015-01-01

    In Western countries, the new visions are applied in quality control for an integrated public transport system. Public transport puts the customer at the centre of our decision making in achieving customer satisfaction with provided service. Sustainable surveys are kept among customers. A lot of companies are collecting huge databases containing over 30,000 voices of customers, which demonstrates the current satisfaction levels across the public transport service. Customer satisfaction with a...

  20. Minimax robust power split in AF relays based on uncertain long-term CSI

    KAUST Repository

    Nisar, Muhammad Danish

    2011-09-01

    An optimal power control among source and relay nodes in presence of channel state information (CSI) is vital for an efficient amplify and forward (AF) based cooperative communication system. In this work, we study the optimal power split (power control) between the source and relay node in presence of an uncertainty in the CSI. The prime contribution is to solve the problem based on an uncertain long-term knowledge of both the first and second hop CSI (requiring less frequent updates), and under an aggregate network-level power constraint. We employ the minimax optimization methodology to arrive at the minimax robust optimal power split, that offers the best possible guarantee on the end-to-end signal to noise ratio (SNR). The derived closed form analytical expressions admit simple intuitive interpretations and are easy to implement in real-world AF relaying systems. Numerical results confirm the advantages of incorporating the presence of uncertainty into the optimization problem, and demonstrate the usefulness of the proposed minimax robust optimal power split. © 2011 IEEE.

  1. Yield, variance and spatial distribution of electron-hole pairs in CsI

    Energy Technology Data Exchange (ETDEWEB)

    Gao, F., E-mail: fei.gao@pnl.gov [Pacific Northwest National Laboratory, Richland, WA 99352 (United States); Xie, Y.; Kerisit, S.; Campbell, L.W. [Pacific Northwest National Laboratory, Richland, WA 99352 (United States); Weber, W.J. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)

    2011-10-01

    A Monte Carlo (MC) method previously developed has been applied to simulate the interaction of photons, with energies ranging from 50 eV to {approx}1 MeV, with CsI and the subsequent electron cascades. The MC model has been employed to compute nano-scale spatial distributions of electron-hole pairs and important intrinsic properties, including W, the mean energy per electron-hole pair, and the Fano factor, F. W exhibits discontinuities at the shell edges that follow the photoionization cross-sections and decreases with increase in photon energy (from {approx}19 to 15 eV), with an asymptotic value of 15.2 eV at high energy. This decrease may contribute to the initial rise in relative light yield with incident energy observed experimentally for CsI, thus suggesting that nonlinearity may be associated with intrinsic properties of the material at low energies. F is calculated to increase with increase in energy and has an asymptotic value of 0.28. A significant number of electron-hole pairs is produced through the different ionization channels of core shells and the corresponding relaxation processes, which may explain why F is larger for CsI than for Si or Ge. Finally, the calculated spatial distributions show that the electron-hole pairs are primarily distributed along fast electron tracks. These spatial distributions constitute important input for large-scale simulations of electron-hole pair transport.

  2. Yield, variance and spatial distribution of electron–hole pairs in CsI

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Fei; Xie, YuLong; Kerisit, Sebastien N.; Campbell, Luke W.; Weber, William J.

    2011-10-01

    A Monte Carlo (MC) method previously developed has been applied to simulate the interaction of photons, with energies ranging from 50 eV to ~ 1 MeV, with CsI and the subsequent electron cascades. The MC model has been employed to compute nano-scale spatial distributions of electron-hole pairs and important intrinsic properties, including W, the mean energy per electron-hole pair, and the Fano factor, F. W exhibits discontinuities at the shell edges that follow the photoionization cross sections and decreases with increasing photon energy (from ~19 to 15 eV), with an asymptotic value of 15.2 eV at high energy. This decrease may contribute the initial rise in relative light yield with incident energy observed experimentally for CsI, thus suggesting that nonlinearity may be associated with intrinsic properties of the material at low energies. F is calculated to increase with increasing energy and has an asymptotic value of 0.28. A significant number of electron-hole pairs are produced through the different ionization channels of core shells and corresponding relaxation processes, which may explain why F is larger for CsI than for Si or Ge. Finally, the calculated spatial distributions show that the electron-hole pairs are primarily distributed along fast electron tracks. These spatial distributions constitute important input for large-scale simulations of electron-hole pair transport.

  3. Yield, variance and spatial distribution of electron-hole pairs in CsI

    International Nuclear Information System (INIS)

    A Monte Carlo (MC) method previously developed has been applied to simulate the interaction of photons, with energies ranging from 50 eV to ∼1 MeV, with CsI and the subsequent electron cascades. The MC model has been employed to compute nano-scale spatial distributions of electron-hole pairs and important intrinsic properties, including W, the mean energy per electron-hole pair, and the Fano factor, F. W exhibits discontinuities at the shell edges that follow the photoionization cross-sections and decreases with increase in photon energy (from ∼19 to 15 eV), with an asymptotic value of 15.2 eV at high energy. This decrease may contribute to the initial rise in relative light yield with incident energy observed experimentally for CsI, thus suggesting that nonlinearity may be associated with intrinsic properties of the material at low energies. F is calculated to increase with increase in energy and has an asymptotic value of 0.28. A significant number of electron-hole pairs is produced through the different ionization channels of core shells and the corresponding relaxation processes, which may explain why F is larger for CsI than for Si or Ge. Finally, the calculated spatial distributions show that the electron-hole pairs are primarily distributed along fast electron tracks. These spatial distributions constitute important input for large-scale simulations of electron-hole pair transport.

  4. Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

    Science.gov (United States)

    Wan, Yimao; Yan, Di; Bullock, James; Zhang, Xinyu; Cuevas, Andres

    2015-12-01

    A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiNx) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiNx stack, recombination current density J0 values of 9, 11, 47, and 87 fA/cm2 are obtained on 10 Ω.cm n-type, 0.8 Ω.cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J0 on n-type 10 Ω.cm wafers is further reduced to 2.5 ± 0.5 fA/cm2 when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiNx stack is thermally stable at 400 °C in N2 for 60 min on all four c-Si surfaces. Capacitance-voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiNx stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.

  5. Effects of Ni+ and Ar+ ions implantation on magnetic properties of C/Si thin film

    International Nuclear Information System (INIS)

    The study of Ni+ and Ar+ ions effects on the magnetic properties of C/Si thin film was carried out. The Ni+ and Ar+ ions were implanted on C/Si thin up to the doses of 5 x 1016 ion/cm2 Identification by XRD indicates Ni+ and Ar+ ion intensity of diffraction peaks for C (002) and Ni (010). The ion implantation could cause the decline in the peak intensity of C (002). The peak intensity of C (002) decreases with the increasing of dose, whereas, the peak intensity of Ni (010) increases with increasing of ion dose. These results indicate the occurrence of distribution of Ni atoms on the surface of C/Si thin film. Measurement of magnetic properties by VSM (Vibrating Sample Magnetometer) indicates a change in magnetic properties of carbon nano structures on a thin film with addition of implantation dose. These magnetic properties increase with the addition of Ni+ ion dose, as indicated by the increase in the values of Ms (saturated magnetization), Mr (remanent magnetization) and Hc (coercive field), i.e 28%, 21% and 42% respectively. Measurement of GMR with Four Point Probe also shows an increase in the value of MR of about 26% at 7.5 kOe magnetic field with increasing ion dose. (author)

  6. Study of silicon tip photocathodes in DC and RF photo-injectors

    International Nuclear Information System (INIS)

    Nowadays the electron beams with a high intensity are particularly interesting in research and the applied physics. Producing such beams for which high intensity and low emittance are synonyms with efficiency, means developing new high luminosity electron sources, i.e. the photocathodes. This thesis, essentially experimental, is oriented in this way. After an introduction of Clermont-Ferrand and the LAL of Orsay experimental apparatus where the experiments took place, the chapter one presents the field emission and the photo-field emission. Then, we prove that the quantum efficiency of the photocathodes with silicon tips is higher for wavelengths near 800 nm. This fact is essential because it allows the use of lasers in the fundamental wavelength - Titan-Saphir for instance. In the chapter 2, we remind how the silicon tips are realized and how to improve surface conditions. Procedures and the surface analysis with the SEM and XPS are described. With a Nd-Yag laser, pumped with laser diode setting up with the participation of IRCOM Opticians of Limoges, the photocathode supplied 1 Ampere per pulse at a quantum efficiency of 0.25%. The description of this experiment and the results are the object of the chapter 3. The space charge outside the photocathode space prevents the electrons to go through. The Child-Langmuir formula limits the current with the DC gun at about 30 Ampere. To improve this result we have to use a photo-injector. In chapter 4 we prove that the silicon tip photocathode are compatible with RF gun requirements by PRIAM modeling and low level measure in a cold model of CANDELA RF gun. Technical department of CERN helped us to prepare this very sensitive experiment. (author)

  7. Comparison of CsBr and KBr coated Cu photocathodes. Effects of laser irradiation and work function changes

    Energy Technology Data Exchange (ETDEWEB)

    He, Weidong [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); VilayurGanapathy, Subramanian [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Joly, Alan G. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Droubay, Timothy C. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Chambers, Scott A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Maldonado, Juan R. [Stanford Univ., CA (United States); Hess, Wayne P. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2013-02-20

    Thin films (7 nm layers) of CsBr and KBr were deposited on Cu(100) to investigate photoemission properties of these potential photocathode materials. After thin film deposition and prolonged laser ultraviolet (UV) irradiation (266 nm picosecond laser) photoemission quantum efficiency increases by factors of 26 and 77 for KBr/Cu(100) and CsBr/Cu(100) photocathodes, respectively. Immediately following thin film deposition, a decrease in work function is observed, compared to bare Cu, in both cases. Quantum efficiency enhancements are attributed to the decrease in photocathode work function, due to the deposition of alkali halide thin films, and photo-induced processes, that introduce defect states into the alkali halide bandgap, induced by UV laser irradiation. It is possible that alkali metal formation occurs during UV irradiation and that this further contributes to photoemission enhancement. Our results suggest that KBr, a relatively stable alkali-halide, has potential for photocathode applications.

  8. Study of bi-alkali photocathode growth on glass by X-ray techniques for fast timing response photomultipliers

    Science.gov (United States)

    Xie, Junqi; Demarteau, Marcel; Wagner, Robert; Ruiz-Oses, Miguel; Liang, Xue; Ben-Zvi, Ilan; Attenkofer, Klaus; Schubert, Susanne; Smedley, John; Wong, Jared; Padmore, Howard; Woll, Arthur

    2014-03-01

    Bi-alkali antimonide photocathode is an essential component in fast timing response photomultipliers. Real-time in-situ grazing incidence x-ray diffraction and post-growth x-ray reflectivity measurement were performed to study the photocathode deposition process on glass substrate. Grazing incidence x-ray diffraction patterns show the formation of Sb crystalline, dissolution of crystalline phase Sb by the application of K vapor and reformation of refined crystal textures. XRR result exhibits that the film thickness increases ~ 4.5 times after K diffusion and almost have no change after Cs diffusion. Further investigation is expected to understand the photocathode growth process and provide guidelines for photocathode development.

  9. Design and fabrication of prototype 6×6 cm2 microchannel plate photodetector with bialkali photocathode for fast timing applications

    International Nuclear Information System (INIS)

    Planar microchannel plate-based photodetectors with a bialkali photocathode are able to achieve photon detection with very good time and position resolution. A 6×6 cm2 photodetector production facility was designed and built at Argonne National Laboratory. Small form-factor MCP-based photodetectors completely constructed out of glass were designed and prototypes were successfully fabricated. Knudsen effusion cells were incorporated in the photocathode growth chamber to achieve uniform and high quantum efficiency photocathodes. The thin film uniformity was simulated and measured for an antimony film deposition, showing uniformity of better than 10%. Several prototype devices with bialkali photocathodes have been fabricated with the described system and their characteristics were evaluated in the large signal (multi-PE) limit. A typical prototype device exhibits time-of-flight resolution of ~27 psec and differential time resolution of ~9 psec, corresponding to spatial resolution of ~0.65 mm

  10. Nanomechanical and electrical properties of Nb thin films deposited on Pb substrates by pulsed laser deposition as a new concept photocathode for superconductor cavities

    Science.gov (United States)

    Gontad, F.; Lorusso, A.; Panareo, M.; Monteduro, A. G.; Maruccio, G.; Broitman, E.; Perrone, A.

    2015-12-01

    We report a design of photocathode, which combines the good photoemissive properties of lead (Pb) and the advantages of superconducting performance of niobium (Nb) when installed into a superconducting radio-frequency gun. The new configuration is obtained by a coating of Nb thin film grown on a disk of Pb via pulsed laser deposition. The central emitting area of Pb is masked by a shield to avoid the Nb deposition. The nanomechanical properties of the Nb film, obtained through nanoindentation measurements, reveal a hardness of 2.8±0.3 GPa, while the study of the electrical resistivity of the film shows the appearance of the superconducting transitions at 9.3 K and 7.3 K for Nb and Pb, respectively, very close to the bulk material values. Additionally, morphological, structural and contamination studies of Nb thin film expose a very low droplet density on the substrate surface, a small polycrystalline orientation of the films and a low contamination level. These results, together with the acceptable Pb quantum efficiency of 2×10-5 found at 266 nm, demonstrate the potentiality of the new concept photocathode.

  11. Dynamic optical modulation of an electron beam on a photocathode RF gun: Toward intensity-modulated radiation therapy (IMRT)

    International Nuclear Information System (INIS)

    In intensity-modulated radiation therapy (IMRT), the aim is to deliver reduced doses of radiation to normal tissue. As a step toward IMRT, we examined dynamic optical modulation of an electron beam produced by a photocathode RF gun. Images on photomasks were transferred onto a photocathode by relay imaging. The resulting beam was controlled by a remote mirror. The modulated electron beam maintained its shape on acceleration, had a fine spatial resolution, and could be moved dynamically by optical methods

  12. Dynamic optical modulation of an electron beam on a photocathode RF gun: Toward intensity-modulated radiation therapy (IMRT)

    Science.gov (United States)

    Kondoh, Takafumi; Kashima, Hiroaki; Yang, Jinfeng; Yoshida, Yoichi; Tagawa, Seiichi

    2008-10-01

    In intensity-modulated radiation therapy (IMRT), the aim is to deliver reduced doses of radiation to normal tissue. As a step toward IMRT, we examined dynamic optical modulation of an electron beam produced by a photocathode RF gun. Images on photomasks were transferred onto a photocathode by relay imaging. The resulting beam was controlled by a remote mirror. The modulated electron beam maintained its shape on acceleration, had a fine spatial resolution, and could be moved dynamically by optical methods.

  13. Photocathodes based on semiconductor superlattices for streak tubes for IR region of 0.9-1.0 um

    Science.gov (United States)

    Nolle, Eduard L.

    1995-05-01

    A possibility of temporal analysis of picosecond light pulses in the IR region with the help of photocathodes based on semiconductor superlattices (SL) of type I (InP/InGaAs) with Schottky barrier is discussed. A new principle of avalanche photoelectron emission from such an SL at interband absorption of light is suggested. The principle is based on the electrons free length path increasing in a SL with narrow quantum wells under high electric field applied to the SL. The idea makes it possible to develop a new device - avalanche photocathode with internal amplification for the IR region of 0.9-2 micrometers and temporal resolution better than 30 ps. It is proposed to use doped as well as undoped SL as basis for photocathodes sensitive to the IR radiation in the range of up to 10 micrometers . The photoemission from such structures is caused by the intersubband absorption of light in quantum wells. The use of undoped SL greatly reduced the thermoemission current of the photocathode but requires additional excitation of the SL by light pulses with energy approximately corresponding to the band gap of the narrow band gap material of the SL. The temporal resolution of such photocathodes is supposed to be less than 30 ps. The conditions for the avalanche photoelectron emission obtaining are determined, and the SL parameters which meet the requirement of maximum quantum efficiency of the photocathode are calculated.

  14. Molecular cloning and characterization of Siamese crocodile (Crocodylus siamensis) copper, zinc superoxide dismutase (CSI-Cu,Zn-SOD) gene.

    Science.gov (United States)

    Sujiwattanarat, Penporn; Pongsanarakul, Parinya; Temsiripong, Yosapong; Temsiripong, Theeranan; Thawornkuno, Charin; Uno, Yoshinobu; Unajak, Sasimanas; Matsuda, Yoichi; Choowongkomon, Kiattawee; Srikulnath, Kornsorn

    2016-01-01

    Superoxide dismutase (SOD, EC 1.15.1.1) is an antioxidant enzyme found in all living cells. It regulates oxidative stress by breaking down superoxide radicals to oxygen and hydrogen peroxide. A gene coding for Cu,Zn-SOD was cloned and characterized from Siamese crocodile (Crocodylus siamensis; CSI). The full-length expressed sequence tag (EST) of this Cu,Zn-SOD gene (designated as CSI-Cu,Zn-SOD) contained 462bp encoding a protein of 154 amino acids without signal peptides, indicated as intracellular CSI-Cu,Zn-SOD. This agreed with the results from the phylogenetic tree, which indicated that CSI-Cu,Zn-SOD belonged to the intracellular Cu,Zn-SOD. Chromosomal location determined that the CSI-Cu,Zn-SOD was localized to the proximal region of the Siamese crocodile chromosome 1p. Several highly conserved motifs, two conserved signature sequences (GFHVHEFGDNT and GNAGGRLACGVI), and conserved amino acid residues for binding copper and zinc (His(47), His(49), His(64), His(72), His(81), Asp(84), and His(120)) were also identified in CSI-Cu,Zn-SOD. Real-time PCR analysis showed that CSI-Cu,Zn-SOD mRNA was expressed in all the tissues examined (liver, pancreas, lung, kidney, heart, and whole blood), which suggests a constitutively expressed gene in these tissues. Expression of the gene in Escherichia coli cells followed by purification yielded a recombinant CSI-Cu,Zn-SOD, with Km and Vmax values of 6.075mM xanthine and 1.4×10(-3)mmolmin(-1)mg(-1), respectively. This Vmax value was 40 times lower than native Cu,Zn-SOD (56×10(-3)mmolmin(-1)mg(-1)), extracted from crocodile erythrocytes. This suggests that cofactors, protein folding properties, or post-translational modifications were lost during the protein purification process, leading to a reduction in the rate of enzyme activity in bacterial expression of CSI-Cu,Zn-SOD. PMID:26523498

  15. Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Yimao, E-mail: yimao.wan@anu.edu.au; Yan, Di; Bullock, James; Zhang, Xinyu; Cuevas, Andres [Research School of Engineering, The Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

    2015-12-07

    A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiN{sub x}) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiN{sub x} stack, recombination current density J{sub 0} values of 9, 11, 47, and 87 fA/cm{sup 2} are obtained on 10 Ω·cm n-type, 0.8 Ω·cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J{sub 0} on n-type 10 Ω·cm wafers is further reduced to 2.5 ± 0.5 fA/cm{sup 2} when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiN{sub x} stack is thermally stable at 400 °C in N{sub 2} for 60 min on all four c-Si surfaces. Capacitance–voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiN{sub x} stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.

  16. A High-Gradient CW R Photo-Cathode Electron Gun for High Current Injectors

    Energy Technology Data Exchange (ETDEWEB)

    Robert Rimmer

    2005-05-01

    The paper describes the analysis and preliminary design of a high-gradient photo-cathode RF gun optimized for high current CW operation. The gun cell shape is optimized to provide maximum acceleration for the newly emitted beam while minimizing wall losses in the structure. The design is intended for use in future high-current high-power CW FELs but the shape optimization for low wall losses may be advantageous for other applications such as XFELs or Linear Colliders using high peak power low duty factor guns where pulse heating is a limitation. The concept allows for DC bias on the photocathode in order to repel ions and improve cathode lifetime.

  17. Effect of humid air exposure on photoemissive and structural properties of KBr thin film photocathode

    CERN Document Server

    Rai, R; Ghosh, N; Singh, B K

    2014-01-01

    We have investigated the influence of water molecule absorption on photoemissive and structural properties of potassium bromide (KBr) thin film photocathode under humid air exposure at relative humidity (RH) 65%. It is evident from photoemission measurement that the photoelectron yield of KBr photocathode is degraded exponentially with humid air exposed time. Structural studies of the "as-deposited" and "humid air aged" films reveal that there is no effect of RH on film's crystalline face centered cubic (fcc) structure. However, the average crystallite size of "humid air exposed film" KBr film has been increased as compared to "as-deposited". In addition, topographical properties of KBr film are also examined by means of scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) and it is observed that granular characteristic of film has been altered, even for short exposure to humid air.

  18. Electric field effects on the quantum efficiency of Cesium-iodide photocathodes in gas media

    International Nuclear Information System (INIS)

    We have measured the quantum efficiency (QE) of Cesium iodide photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH4, C2H6 AND i-C4H10 both in charge collection and multiplication modes. It was found that in the collection mode the QE value in gases is lower compared to that of vacuum and is independent on the field; in gas media the QE starts to increase at the transition between collection and multiplication modes and reaches the vacuum value at high gas gain. We explain this effect by a decrease of the electron-molecule elastic backscattering while entering the multiplication mode. We conclude that the electric field effects observed here, would also apply for other photocathodes and gas mixtures. An enhancement of the QE after micro discharges was observed and is discussed in detail. (authors) 30 refs, 10 figs

  19. In situ Observation of Dark Current Emission in a High Gradient RF Photocathode Gun

    CERN Document Server

    Shao, Jiahang; Baryshev, Sergey V; Chen, Huaibi; Conde, Manoel; Gai, Wei; Ha, Gwanghui; Jing, Chunguang; Shi, Jiaru; Wang, Faya; Wisniewski, Eric

    2016-01-01

    Undesirable electron field emission (a.k.a. dark current) in high gradient RF photocathode guns deteriorates the quality of photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 um) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Dark current from the cathode has been observed to be dominated by several separated strong emitters. The field enhancement factor, beta, of selected regions on the cathode has been measured. The post scanning electron microscopy (SEM) and white light interferometer (WLI) surface examinations reveal the origins of ~75% strong emitters overlap with the spots where rf breakdown have occurred.

  20. Study on Quantum Efficiency Stability of Reflection-Mode GaN Negative Electronic Affinity Photocathode

    Directory of Open Access Journals (Sweden)

    Wei Liu

    2014-02-01

    Full Text Available The aim of this study is to analyze the decaying and recovering mechanism of the quantum efficiency for reflection-mode GaN NEA photocathode. One kind of reflection-mode GaN NEA photocathode is designed and grown in the laboratory. The quantum efficiency curves are obtained immediately and six hours later after the sample is fully activated, the quantum efficiency data at different wavelengths are acquired according to the two different quantum efficiency curves, Through the analysis of experiment result, the inner factors resulting in quantum efficiency decaying are discussed. Taking the factors into consideration, the method of supplementing Cs is applied in recovering the quantum efficiency, the quantum efficiency can be partly recovered. The reason that the quantum efficiency can not be completely recorvered is also anylized.

  1. Planar field emitters and high efficiency photocathodes based on ultrananocrystalline diamond

    Energy Technology Data Exchange (ETDEWEB)

    Sumant, Anirudha V.; Baryshev, Sergey V.; Antipov, Sergey P.

    2016-08-16

    A method of forming a field emitter comprises disposing a first layer on a substrate. The first layer is seeded with nanodiamond particles. The substrate with the first layer disposed thereon is maintained at a first temperature and a first pressure in a mixture of gases which includes nitrogen. The first layer is exposed to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, which has a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %. The field emitter has about 10.sup.12 to about 10.sup.14 emitting sites per cm.sup.2. A photocathode can also be formed similarly by forming a nitrogen doped ultrananocrystalline diamond film on a substrate similar to the field emitter, and then hydrogen terminating the film. The photocathode is responsive to near ultraviolet light as well as to visible light.

  2. Modified Grid-Connected CSI for Hybrid PV/Wind Power Generation System

    OpenAIRE

    Amorndechaphon, D.; S. Premrudeepreechacharn; Higuchi, K.; X. Roboam

    2012-01-01

    The principle of a power conditioning unit for hybrid PV/wind power generation system is proposed. The proposed power conditioner is based on the current source inverter (CSI) topology. All energy sources are connected in parallel with a DC-bus through the modified wave-shaping circuits. To achieve the unity power factor at the utility grid, the DC-link current can be controlled via the wave-shaping circuits with the sinusoidal PWM scheme. In this work, the carrier-based PWM scheme is also pr...

  3. Longitudinal uniformity, time performance and irradiation test of pure CsI crystals

    OpenAIRE

    Angelucci, M.; Atanova, O.; Baccaro, S; Cemmi, A.; Cordelli, M.; Donghia, R.; S. Giovannella; Happacher, F.; Miscetti, S.; I. Sarra; Soleti, S. R.

    2016-01-01

    To study an alternative to BaF2, as the crystal choice for the Mu2e calorimeter, thirteen pure CsI crystals from Opto Materials and ISMA producers have been characterized by determining their light yield (LY) and longitudinal response uniformity (LRU), when read with a UV extended PMT. The crystals show a LY of ~ 100 p.e./MeV (~ 150 p.e./MeV) when wrapped with Tyvek and coupled to the PMT without (with) optical grease. The LRU is well represented by a linear slope that is on average around -0...

  4. Performance study of single undoped CsI crystals for the Mu2e experiment

    OpenAIRE

    Donghia, Raffaella

    2016-01-01

    The Mu2e experiment at Fermilab aims to measure the charged lepton flavor violating neutrinoless muon to electron conversion. The goal of the experiment is to reach a single event sensitivity of 2.5 x 10^{-17}, to set an upper limit on the muon conversion rate at 6.7 x 10^{-17} in a three years run. For this purpose, the Mu2e detector is designed to identify electrons from muon conversion and reduce the background to a negligible level. It consists of a low mass straw tracker and a pure CsI c...

  5. CSI-aided MAC with Multiuser Diversity for Cognitive Radio Networks

    CERN Document Server

    Lu, Yuan

    2011-01-01

    Cognitive Radio (CR) aims to increase the spectrum utilization by allowing secondary users (SU) to access unused licensed spectrum bands. To maximize the throughput given limited sensing capability, SUs need to strike a balance between sensing the channels that are not heavily used by primary users (PU) and avoiding collisions with other SUs. To randomize sensing decisions without resorting to multiuser sensing policies, it is proposed to exploit the spatially-variant fading channel conditions on different links by adapting the reward to the channel state information (CSI). Moreover, the proposed channel-adaptive policy favors links with high achievable transmission rate and thus further improves the network throughput.

  6. A columnar cesium iodide (CsI) drift plane layer for gas avalanche microdetectors

    International Nuclear Information System (INIS)

    A new method is proposed to improve the spatial and time resolutions, and the detection efficiency with respect to the angle of the incident particles, for gas avalanche micro detectors. The new technique uses a thin (∼200 microm) columnar CsI layer at the drift plane that acts as an efficient source of electrons produced by secondary emission due to the incident particles, and as an electron multiplier. In this paper, the authors present the measurements of the electron multiplication factor and detection efficiency of this layer, using a 90Sr β-source

  7. On the low SNR capacity of log-normal turbulence channels with full CSI

    KAUST Repository

    Benkhelifa, Fatma

    2014-09-01

    In this paper, we characterize the low signal-To-noise ratio (SNR) capacity of wireless links undergoing the log-normal turbulence when the channel state information (CSI) is perfectly known at both the transmitter and the receiver. We derive a closed form asymptotic expression of the capacity and we show that it scales essentially as λ SNR where λ is the water-filling level satisfying the power constraint. An asymptotically closed-form expression of λ is also provided. Using this framework, we also propose an on-off power control scheme which is capacity-achieving in the low SNR regime.

  8. Remote Manipulator System (RMS)-based Controls-Structures Interaction (CSI) flight experiment feasibility study

    Science.gov (United States)

    Demeo, Martha E.

    1990-01-01

    The feasibility of an experiment which will provide an on-orbit validation of Controls-Structures Interaction (CSI) technology, was investigated. The experiment will demonstrate the on-orbit characterization and flexible-body control of large flexible structure dynamics using the shuttle Remote Manipulator System (RMS) with an attached payload as a test article. By utilizing existing hardware as well as establishing integration, operation and safety algorithms, techniques and procedures, the experiment will minimize the costs and risks of implementing a flight experiment. The experiment will also offer spin-off enhancement to both the Shuttle RMS (SRMS) and the Space Station RMS (SSRMS).

  9. Laser-fired contact optimization in c-Si solar cells

    OpenAIRE

    P. Ortega; Orpella, A.; Martin, I.; Lopez, G.; Voz, C.; Sanchez Aniorte, Maria Isabel; Molpeceres Alvarez, Carlos Luis; Alcubilla, R.

    2011-01-01

    In this work we study the optimization of laser-fired contact (LFC) processing parameters, namely laser power and number of pulses, based on the electrical resistance measurement of an aluminum single LFC point. LFC process has been made through four passivation layers that are typically used in c-Si and mc-Si solar cell fabrication: thermally grown silicon oxide (SiO2), deposited phosphorus-doped amorphous silicon carbide (a-SiCx/H(n)), aluminum oxide (Al2O3) and silicon nitride (SiNx/H) fil...

  10. Characterization and development of photocathodes using laser induced time-of-flight spectroscopy

    Science.gov (United States)

    Ramirez-Homs, E.; Velazquez, D.; Spentzouris, L.; Terry, J.

    2011-10-01

    The emittance of a beam generated for use in particle accelerators is a critical performance parameter. In order to achieve peak performance, intrinsic transverse emittance on the order of 0.1mm-mrad is required. This initial emittance is about an order of magnitude lower than provided by today's sources. Several important efforts are being made to reach this lower emittance with cathode design modifications. A photocathode design study and implementation of experimental techniques for the characterization is proposed and discussed.

  11. Porous copper zinc tin sulfide thin film as photocathode for double junction photoelectrochemical solar cells.

    Science.gov (United States)

    Dai, Pengcheng; Zhang, Guan; Chen, Yuncheng; Jiang, Hechun; Feng, Zhenyu; Lin, Zhaojun; Zhan, Jinhua

    2012-03-21

    Porous copper zinc tin sulfide (CZTS) thin film was prepared via a solvothermal approach. Compared with conventional dye-sensitized solar cells (DSSCs), double junction photoelectrochemical cells using dye-sensitized n-type TiO(2) (DS-TiO(2)) as the photoanode and porous p-type CZTS film as the photocathode shows an increased short circuit current, external quantum efficiency and power conversion efficiency. PMID:22322239

  12. Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes

    OpenAIRE

    Xuemei Zhang; Xu Wu; Anthony Centeno; Ryan, Mary P.; Alford, Neil M.; D. Jason Riley; Fang Xie

    2016-01-01

    Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that u...

  13. Intense Electron Beams from GaAs Photocathodes as a Tool for Molecular and Atomic Physics

    OpenAIRE

    Krantz, C.

    2009-01-01

    We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at stable cathode lifetimes of 24 h or more. ...

  14. Intense electron beams from GaAs photocathodes as a tool for molecular and atomic physics

    Energy Technology Data Exchange (ETDEWEB)

    Krantz, Claude

    2009-10-28

    We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at usable cathode lifetimes of 24 h or more. The benefits of the cold electron beam with respect to its application to electron cooling and electron-ion recombination experiments are discussed. Benchmark experiments demonstrate the superior cooling force and energy resolution of the photoelectron beam compared to its thermionic counterparts. The long period of operation allowed to study the long-time behaviour of the GaAs samples during multiple usage cycles at the Electron Target and repeated in-vacuum surface cleaning by atomic hydrogen exposure. An electron emission spectroscopy setup has been implemented at the photocathode preparation chamber of the Electron Target. Among others, this new facility opened the way to a novel application of GaAs (Cs) photocathodes as robust, ultraviolet-driven electron emitters. Based on this principle, a prototype of an electron gun, designed for implementation at the HITRAP setup at GSI, has been built and taken into operation successfully. (orig.)

  15. State-of-the-art Pb photocathodes deposited by pulsed laser deposition

    International Nuclear Information System (INIS)

    In this article we present and discuss the current status of thin film Pb photocathodes deposited by pulsed laser deposition (PLD) with different laser parameters, such as laser fluence, wavelength or pulse duration. The PLD technique appears very efficient for the fabrication of pure Pb photocathodes, providing good adherence and respectable quantum efficiency. The films deposited on the picosecond and subpicosecond regimes are practically free of big droplets and fragments, whereas in the nanosecond regime their presence cannot be neglected. All the films present a granular structure and polycrystalline character with preferential orientation along the (111) crystalline planes, irrespective of the laser pulse duration or wavelength. The main results obtained from the photoemission performance of Pb thin films deposited by PLD demonstrate their chemical stability under vacuum conditions and respectable quantum efficiency with a maximum of 7.3×10−5 for films deposited on the subpicosecond regime. The photoemission properties confirm that Pb thin films deposited by PLD are a notable alternative for the fabrication of photocathodes for superconductive radio-frequency electron guns. - Highlights: • Lead samples were grown by Pulsed Laser Deposition at different laser parameters • All films present a granular morphology • Lead films grow preferentially along the 111 crystalline planes of the cubic net • A maximum quantum efficiency of 7.3 × 10-5 has been found

  16. Polarization Possibilities of Small Spin-Orbit Interaction in Strained-Superlattice Photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    2010-08-25

    Strained-superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important. The strained-superlattice structure based on GaAsP/GaAs, with a maximum polarization as high as 90% and more than 1% quantum efficiency, is presently the prime candidate for the ILC polarized electron photocathodes. A recent systematic study shows, however, that the peak polarization seems saturated even though the heavy-hole (HH) and light-hole (LH) band splitting is increased significantly, indicating that there is a material specific spin relaxation mechanism. It is widely accepted that the D'yakonov-Perel mechanism is the dominant spin relaxation mechanism in the III-V compound superlattice structures with a low p-doping ({le} 10{sup 17} cm{sup -3}), and that the spin relaxation may be reduced by choosing a material with a smaller spin-orbit interaction. As the spin-orbit interaction in phosphides is much smaller than in arsenides, strained-superlattice structure based on InGaP/GaAs were investigated. The computer code SPECCODE developed by Subashiev and Gerchikov has been used for calculating the band structures in superlattice.

  17. Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes.

    Science.gov (United States)

    Zhang, Xuemei; Wu, Xu; Centeno, Anthony; Ryan, Mary P; Alford, Neil M; Riley, D Jason; Xie, Fang

    2016-01-01

    Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap. PMID:26997140

  18. Silver Iodide-Chitosan Nanotag Induced Biocatalytic Precipitation for Self-Enhanced Ultrasensitive Photocathodic Immunosensor.

    Science.gov (United States)

    Gong, Lingshan; Dai, Hong; Zhang, Shupei; Lin, Yanyu

    2016-06-01

    In this work, we first exposed that the application of p-type semiconductor, silver iodide-chitosan nanoparticle (SICNP), acted as peroxidase mimetic to catalyze the bioprecipitation reaction for signal-amplification photocathodic immunosensing of human interleukin-6 (IL-6). After immobilization of captured antibody onto a polyethylenimine-functionalized carbon nitride (CN) matrix, SICNPs as photoactive tags and peroxidase mimetics were labeled on secondary antibodies, which were subsequently introduced onto the sensing interface to construct sandwich immunoassay platform through antigen-antibody specific recognition. Due to the matched energy levels between CN and AgI, the photocurrent intensity and photostability of SICNP were dramatically improved with rapid separation and transportation of photogenerated carriers. Moreover, the insoluble product in effective biocatalytic precipitation reaction served as electron acceptor to scavenge the photoexcited electron, leading to great amplification of the photocurrent signal of SICNP again. With the help of multiamplification processes, this photocathodic immunosensor presented a turn-on photoelectrochemical performance for IL-6, which showed wide linear dynamic range from 10(-6) to 10 pg/mL with the ultralow detection limit of 0.737 ag/mL. This work also performed the promising application of SICNP in developing an ultrasensitive, cost-effective, and enzyme-free photocathodic immunosensor for biomarkers. PMID:27180822

  19. Heat load of a GaAs photocathode in an SRF electron gun

    Institute of Scientific and Technical Information of China (English)

    WANG Er-Dong; ZHAO Kui; J(o)rg Kewisch; Ilan Ben-Zvi; Andrew Burrill; Trivini Rao; WU Qiong; Animesh Jain; Ramesh Gupta; Doug Holmes

    2011-01-01

    A great deal of effort has been made over the last decades to develop a better polarized electron source for high energy physics. Several laboratories operate DC guns with a gallium arsenide photocathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved by using a superconducting radio frequency (SRF) electron gun, which delivers beams of a higher brightness than that from DC guns because the field gradient at the cathode is higher. SRF guns with metal and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since a bulk gallium arsenide (GaAs) photocathode is normal conducting, a problem arises from the heat load stemming from the cathode. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and verification by measuring the quality factor of the gun with and without the cathode at 2 K. We simulate heat generation and flow from the GaAs cathode using the ANSYS program. By following the findings with the heat load model, we designed and fabricated a new cathode holder (plug) to decrease the heat load from GaAs.

  20. Intense electron beams from GaAs photocathodes as a tool for molecular and atomic physics

    International Nuclear Information System (INIS)

    We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at usable cathode lifetimes of 24 h or more. The benefits of the cold electron beam with respect to its application to electron cooling and electron-ion recombination experiments are discussed. Benchmark experiments demonstrate the superior cooling force and energy resolution of the photoelectron beam compared to its thermionic counterparts. The long period of operation allowed to study the long-time behaviour of the GaAs samples during multiple usage cycles at the Electron Target and repeated in-vacuum surface cleaning by atomic hydrogen exposure. An electron emission spectroscopy setup has been implemented at the photocathode preparation chamber of the Electron Target. Among others, this new facility opened the way to a novel application of GaAs (Cs) photocathodes as robust, ultraviolet-driven electron emitters. Based on this principle, a prototype of an electron gun, designed for implementation at the HITRAP setup at GSI, has been built and taken into operation successfully. (orig.)

  1. Development of a photo-cathode rf electron gun for ultra-short bunch generation

    International Nuclear Information System (INIS)

    The photocathode rf electron gun is a high brightness electron source because the initial electron bunch shape can be controlled by the cathode illuminating laser pulse and then the bunch is rapidly accelerated by the high gradient electric field in the rf gun cavity. The rf guns are widely used not only as a injector for large facility but also application researches. At Waseda University, I and collaborators have been developing an rf electron gun since 1999. We performed optimization of cavity structure, improvement of rf tuner and development of photocathode material, then we succeeded in operating 3.6 cell rf gun. In these backgrounds, I conceived a new type rf gun cavity structure for ultra-short electron bunch generation, named Energy-Chirping-Cell attached rf gun (ECC rf gun). Less than 100 fs (rms) bunch can be produced with 100 pC charge by this ECC rf gun in the simulation. Such a high peak current bunch has a possibility to apply for the coherent THz radiation source and single shot electron diffraction microscope. Encouraged by this successful simulation results, we manufactured an ECC rf gun and measured the bunch length at Waseda University. The experimental results showed a good agreement with simulation and we found that the bunch length from ECC rf gun was less than 500 fs (rms). In this paper, the introduction of the photocathode rf gun, principle and experimental results of ECC rf gun, and future prospective will be described. (author)

  2. Detection of soft X-rays with NEA III-V photocathodes. [Negative Electron Affinity X-ray detector for astronomy

    Science.gov (United States)

    Bardas, D.; Kellogg, E.; Murray, S.; Enck, R., Jr.

    1978-01-01

    A description is presented of the results of tests on an X-ray photomultiplier containing a negative electron affinity (NEA) photocathode. This device makes it possible to investigate the response of the NEA photocathode to X-rays of various energies. The obtained data provide a basis for the determination of the photoelectron yield and energy resolution of the considered photocathode as a function of energy in the range from 0.8 to 3 keV. The investigation demonstrates the feasibility of using an NEA III-V photocathode for the detection of soft X-rays.

  3. Environmental Disclosure of Electric Power Companies Listed in the Corporate Sustainability Index (CSI

    Directory of Open Access Journals (Sweden)

    Clésia Ana Gubiani

    2012-12-01

    Full Text Available The study aimed to verify the level of disclosure of environmental information in the administration reports of the energy companies listed in the Corporate Sustainability Index (CSI. A descriptive and quantitative research was done, using the content analysis technique on the administration reports from 2006 to 2008. The sample consisted of 11 electric power companies listed in the CSI. For quantitative analysis of the disclosure index, the data collection instrument was based on the study of Rover, Murcia and Borba (2008, which proposes eight environmental categories and 36 subcategories. For the whole analysis of the data were elaborated networks of the items disclosed in each company, using the software UNICET ®. The survey results showed that there is satisfactory disclosure in the categories of environmental policies and education, training and research environment. However, it was found that there is need for greater disclosure of categories of products impacts and processes in the environment, power polices and financial environmental information. It was concluded that the information disclosed in the administration reports of the companies surveyed about the environmental information do not respect the principle of full disclosure.

  4. MIMO Precoding in Underlay Cognitive Radio Systems with Completely Unknown Primary CSI

    CERN Document Server

    Mukherjee, Amitav; Swindlehurst, A Lee

    2012-01-01

    This paper studies a novel underlay MIMO cognitive radio (CR) system, where the instantaneous or statistical channel state information (CSI) of the interfering channels to the primary receivers (PRs) is completely unknown to the CR. For the single underlay receiver scenario, we assume a minimum information rate must be guaranteed on the CR main channel whose CSI is known at the CR transmitter. We first show that low-rank CR interference is preferable for improving the throughput of the PRs compared with spreading less power over more transmit dimensions. Based on this observation, we then propose a rank minimization CR transmission strategy assuming a minimum information rate must be guaranteed on the CR main channel. We propose a simple solution referred to as frugal waterfilling (FWF) that uses the least amount of power required to achieve the rate constraint with a minimum-rank transmit covariance matrix. We also present two heuristic approaches that have been used in prior work to transform rank minimizat...

  5. Performance study of single undoped CsI crystals for the Mu2e experiment

    CERN Document Server

    Donghia, Raffaella

    2016-01-01

    The Mu2e experiment at Fermilab aims to measure the charged lepton flavor violating neutrinoless muon to electron conversion. The goal of the experiment is to reach a single event sensitivity of 2.5 x 10^{-17}, to set an upper limit on the muon conversion rate at 6.7 x 10^{-17} in a three years run. For this purpose, the Mu2e detector is designed to identify electrons from muon conversion and reduce the background to a negligible level. It consists of a low mass straw tracker and a pure CsI crystal calorimeter. In this paper, the performance of undoped CsI single crystal is reported. Crystals from many vendors have been characterized by determining their Light Yield (LY) and Longitudinal Response Uniformity (LRU), when read with a UV extended PMT, and their time resolution when coupled to a Silicon Photomultiplier. The crystals show a LY of ~ 100 photoelectrons per MeV when wrapped with Tyvek and coupled to the PMT without optical grease. The LRU is well represented by a linear slope that is on average 0.6%/c...

  6. CSI Feedback-based CS for Underwater Acoustic Adaptive Modulation OFDM System with Channel Prediction

    Institute of Scientific and Technical Information of China (English)

    蒯小燕; 孙海信; 齐洁; 程恩; 许小卡; 郭瑜辉; 陈友淦

    2014-01-01

    In this paper, we investigate the performance of adaptive modulation (AM) orthogonal frequency division multiplexing (OFDM) system in underwater acoustic (UWA) communications. The aim is to solve the problem of large feedback overhead for channel state information (CSI) in every subcarrier. A novel CSI feedback scheme is proposed based on the theory of compressed sensing (CS). We propose a feedback from the receiver that only feedback the sparse channel parameters. Additionally, prediction of the channel state is proposed every several symbols to realize the AM in practice. We describe a linear channel prediction algorithm which is used in adaptive transmission. This system has been tested in the real underwater acoustic channel. The linear channel prediction makes the AM transmission techniques more feasible for acoustic channel communications. The simulation and experiment show that significant improvements can be obtained both in bit error rate (BER) and throughput in the AM scheme compared with the fixed Quadrature Phase Shift Keying (QPSK) modulation scheme. Moreover, the performance with standard CS outperforms the Discrete Cosine Transform (DCT) method.

  7. Nanoscale triboactivity of functionalized c-Si surfaces by Fe+ ion implantation

    Science.gov (United States)

    Nunes, B.; Alves, E.; Colaço, R.

    2016-04-01

    In the present work, we present a study of the effect of Fe+ ion implantation on the tribological response at nanoscale contact lengths of crystalline silicon (c-Si) surfaces. (1 0 0) silicon wafers were implanted with Fe+ at a fluence of 2  ×  1017 cm-2, followed by annealing treatments at temperatures of 800 °C and 1000 °C. After microstructural characterization, nanoabrasive wear tests were performed with an atomic force microscope (AFM) using an AFM diamond tip with a stiff steel cantilever that enables the application of loads between 1 μN and 8 μN. After the nanowear tests, the same AFM was used to visualize and measure the worn craters. It was observed that the as-implanted samples present the poorest nanowear response, i.e. the highest wear rate, even higher than that of the unimplanted Si wafers used as a reference. Nevertheless, annealing treatments result in a measurable increase in the nanowear resistance. In this way we show that Fe+ ion implantation of c-Si, followed by the proper post-heat treatment, results in the formation of FeSi2 nanoprecipitates finely dispersed in a recrystallized matrix. This can be a valuable way of optimizing the nanotribological behavior of silicon.

  8. Longitudinal uniformity, time performance and irradiation test of pure CsI crystals

    CERN Document Server

    Angelucci, M; Baccaro, S; Cemmi, A; Cordelli, M; Donghia, R; Giovannella, S; Happacher, F; Miscetti, S; Sarra, I; Soleti, S R

    2016-01-01

    To study an alternative to BaF2, as the crystal choice for the Mu2e calorimeter, thirteen pure CsI crystals from Opto Materials and ISMA producers have been characterized by determining their light yield (LY) and longitudinal response uniformity (LRU), when read with a UV extended PMT. The crystals show a LY of ~ 100 p.e./MeV (~ 150 p.e./MeV) when wrapped with Tyvek and coupled to the PMT without (with) optical grease. The LRU is well represented by a linear slope that is on average around -0.6 %/cm. The timing performances of the Opto Materials crystal, read with a UV extended MPPC, have been evaluated with minimum ionizing particles. A timing resolution of ~ 330 ps (~ 440 ps) is achieved when connecting the photosensor to the MPPC with (without) optical grease. The crystal radiation hardness to a ionization dose has also been studied for one pure CsI crystal from SICCAS. After exposing it to a dose of 900 Gy, a decrease of 33% in the LY is observed while the LRU remains unchanged.

  9. Opportunistic Energy-Aware Amplify-and-Forward Cooperative Systems with Imperfect CSI

    KAUST Repository

    Amin, Osama

    2015-07-29

    Recently, much attention has been paid to the green design of wireless communication systems using energy efficiency (EE) metrics that should capture all energy consumption sources to deliver the required data. In this paper, we design an energyefficient relay assisted communication system based on estimated channel state information (CSI). It employs amplify-andforward relaying and switches between different communication schemes, which are known as direct-transmission, two-hop and cooperative-transmission schemes, using the estimated CSI in order to maximize the EE. Two estimation strategies are assumed, namely disintegrated channel estimation and cascaded channel estimation. To formulate an accurate EE metric for the proposed opportunistic amplify-and-forward system, the channel estimation cost is reflected on the EE metric by including its impact in the signal-to-noise ratio term and in the energy consumption during the channels estimation phase. Based on the formulated EE metric, we propose an adaptive power allocation algorithm to maximize the EE of the proposed opportunistic amplify-andforward system with channel estimation. Furthermore, we study the impact of the estimation parameters on the proposed system via simulation examples.

  10. Variation of carrier concentration and interface trap density in 8MeV electron irradiated c-Si solar cells

    International Nuclear Information System (INIS)

    The capacitance and conductance measurements were carried out for c-Si solar cells, irradiated with 8 MeV electrons with doses ranging from 5kGy – 100kGy in order to investigate the anomalous degradation of the cells in the radiation harsh environments. Capacitance – Voltage measurements indicate that there is a slight reduction in the carrier concentration upon electron irradiation due to the creation of radiation induced defects. The conductance measurement results reveal that the interface state densities and the trap time constant increases with electron dose due to displacement damages in c-Si solar cells

  11. Effect of underlying silicon layer on microstructure and photoluminescence of rapid-thermal-annealed carbon and C/Si nanofilms

    International Nuclear Information System (INIS)

    Highlights: •Photoluminescence (PL) of carbon films originated from recombination of confined electron–hole pairs. •Broad PL was an interesting topic using varied methods for Si and C reaction. •Asymmetrical broad PL of two-layer Si/C and three-layer Si/C/Si was demonstrated previously. •Here, another C/Si (underlying Si layer) films have further investigated for enhancement of symmetry-like PL. •The effect and mechanism of underlying Si layer thickness on microstructure and PL evolution of two-layer C/Si was studied. -- Abstract: A composite material for broad photoluminescence (PL) from asymmetry to more symmetry-like was proposed by the formation of Si nanocrystals (nc-Si), SiC nanoparticles (np-SiC) and sp2 carbon cluster which were made from the two-layer C/Si on Si(1 0 0) using rapid-thermal-annealing at 750 °C for 1 min. The effect of underlying Si layer thickness on the microstructure and broad PL of the annealed carbon and two-layer C/Si films has been investigated. Fourier-transform-infrared-absorption spectra indicated that very weak Si–C bonding peak was observed for the annealed single-C film and the enhanced intensity occurred at two-layer C/Si films with underlying thickness of 10–25 nm. Compared to the single-C film, the two-layer C/Si film was beneficial for formation of SiC which increased with Si thickness. A more symmetry-like broad PL band around 400–700 nm was observed at the annealed C/Si films with higher Si thickness of 25 nm while the annealed C film has weak and narrow band. Also, the enhanced symmetry-like PL band was attributed to more amount of np-SiC formation at the bottom of C/Si film together with reduced C thickness which can be potentially applied into white light emission material. The detailed mechanism of broad PL was proposed in terms of microstructure evolution

  12. Nitride Conversion: A Novel Approach to c-Si Solar Cell Metallization

    Science.gov (United States)

    Hook, David Henry

    Metallization of commercial-grade c-Si solar cells is currently accomplished by screen-printing fine lines of a Ag/PbO-glass paste amalgam (Ag-frit) onto the insulating SiNx antireflective coating (ARC) that lies atop the shallow n-type emitter layer of the cell. Upon annealing, the glass etches SiNx and permits the crystallization of Ag near the electrically-active emitter interface, thus contacting the cell. While entirely functional, the contact interface produced by Ag-frit metallization is non-ideal, and Ag metal itself is expensive; its use adds to overall solar cell costs. The following work explores the use of Ti-containing alloys as metallization media for c-Si solar cells. There is a -176 kJ [mol N]--1 free energy change associated with the conversion of Si3N4 to TiN. By combining Ti with a low-melting point metal, this reaction can take place at temperatures as low as 750°C in the bulk. Combinations of Ti with Cu, Sn, Ag, and Pb ternary and binary systems are investigated. On unmetallized, c-Si textured solar cells it is shown that 900 nm of stoichiometric Ti6Sn 5 is capable of converting the SiNx ARC to TiN and Ti5Si3, both of which are conducting materials with electrically low-barriers to contact with n-type Si. Alongside electron microscopy, specific contact resistivity (rho c) measurements are used to determine the interfacial quality of TiN/Ti5Si3 contacts to n-Si. Circular transmission line model (CTLM) measurements are utilized for the characterization of reacted Ag0.05Cu0.69Ti0.26, Sn0.35 Ag0.27Ti0.38, and Ti6Sn5 contacts. rhoc values as low as 26 muOcm 2 are measured for reacted Ti6Sn5-SiN x on conventional c-Si solar cells. This value is approximately 2-3 orders of magnitude lower than rhoc of contacts produced by traditional Ag-frit metallization. Viable 1x1 cm, Ti6Sn5-metallized solar cells on 5x5 cm substrates were fabricated through a collaboration with the Georgia Institute of Technology (GA Tech). Front-side metallization was performed

  13. Performance of a multi-anode photomultiplier employing an ultra bi-alkali photo-cathode and rugged dynodes

    Science.gov (United States)

    Toizumi, T.; Inagawa, S.; Nakamori, T.; Kataoka, J.; Tsubuku, Y.; Yatsu, Y.; Shimokawabe, T.; Kawai, N.; Okada, T.; Ohtsu, I.

    2009-06-01

    We report on the performance testing of a multi-anode photomultiplier (MAPMT), the R8900-200-M16MOD-UBA, newly developed by Hamamatsu Photonics K.K. Although the R8900 series offers the great advantage of a highly sensitive surface ( ⩾80% of physical area), the quantum efficiency (Q.E.) was relatively low (at up to 20%). This paper describes two substantial changes we have made to the R8900-200-M16MOD-UBA: (1) improving the Q.E. to the 40% level by employing an ultra bi-alkali (UBA) photo-cathode and (2) constructing a rugged dynode that can withstand vibration for future use in space. We measured each pixel signal at the single photoelectron level and the signals of scintillation photons by using a 16-pixel plastic scintillator array. Thanks to high Q.E., good energy resolution of 29.9% (FWHM) was obtained for 59.5 keV γ-rays. We also demonstrated tolerance to vibration up to 17 Grms in possible launching vehicles.

  14. Cooled Transmission-Mode NEA-Photocathode with a Band-Graded Active Layer for High Brightness Electron Source

    Science.gov (United States)

    Jones, L. B.; Rozhkov, S. A.; Bakin, V. V.; Kosolobov, S. N.; Militsyn, B. L.; Scheibler, H. E.; Smith, S. L.; Terekhov, A. S.

    2009-08-01

    A Free-Electron Laser (FEL) places many exacting demands on a Negative Electron Affinity (NEA) photocathode, such as the need for an ultra-fast response time, low energy spread for emitted electrons, high quantum efficiency (Q.E.) and a high average photocurrent. However, these key requirements are conflicting, and cannot be fulfilled by conventional photocathode design. For example, to achieve ˜10 ps response time, the photocathode active layer should be thinned to ˜100-150 nm, but this thickness is insufficient to provide near-complete absorption of light with hv≈ɛg so high Q.E. cannot be achieved. Complete optical absorption and high Q.E. can be obtained using a thin active layer at higher photon energies, but this generates photoelectrons with excess kinetic energy within the semiconductor. These photoelectrons do not thermalise in a thin active layer, so yield a broad energy distribution in the emitted electrons. Moreover, cooling of the conventional semiconductor photocathode structure is ineffective due to its fragility, so it cannot be pressed firmly to a heat sink to attain good thermal contact. Consequently, the maximum CW photocurrent is limited to a few miiliamps. The goal of our work is to develop a new design of NEA-photocathode which is optimised for FEL applications.

  15. Development of High Quantum Efficiency UV/Blue Photocathode Epitaxial Semiconductor Heterostructures for Scintillation and Cherenkov Radiation Detection

    Science.gov (United States)

    Leopold, Daniel J.

    2002-01-01

    The primary goal of this research project was to further extend the use of advanced heteroepitaxial-semiconductor crystal growth techniques such as molecular beam epitaxy (MBE) and to demonstrate significant gains in UV/blue photonic detection by designing and fabricating atomically-tailored heteroepitaxial GaAlN/GaInN photocathode device structures. This NASA Explorer technology research program has focused on the development of photocathodes for Cherenkov and scintillation radiation detection. Support from the program allowed us to enhance our MBE system to include a nitrogen plasma source and a magnetic bearing turbomolecular pump for delivery and removal of high purity atomic nitrogen during GaAlN/GaInN film growth. Under this program we have also designed, built and incorporated a cesium activation stage. In addition, a connected UHV chamber with photocathode transfer/positioner components as well as a hybrid phototube stage was designed and built to make in-situ quantum efficiency measurements without ever having to remove the photocathodes from UHV conditions. Thus we have constructed a system with the capability to couple atomically-tailored MBE-grown photocathode heterostructures with real high gain readout devices for single photon detection evaluation.

  16. Development of a low-cost-high-sensitivity Compton camera using CsI (Tl) scintillators (γI)

    Science.gov (United States)

    Kagaya, M.; Katagiri, H.; Enomoto, R.; Hanafusa, R.; Hosokawa, M.; Itoh, Y.; Muraishi, H.; Nakayama, K.; Satoh, K.; Takeda, T.; Tanaka, M. M.; Uchida, T.; Watanabe, T.; Yanagita, S.; Yoshida, T.; Umehara, K.

    2015-12-01

    We have developed a novel low-cost gamma-ray imaging Compton camera γI that has a high detection efficiency. Our motivation for the development of this detector was to measure the arrival directions of gamma rays produced by radioactive nuclides that were released by the Fukushima Daiichi nuclear power plant accident in 2011. The detector comprises two arrays of inorganic scintillation detectors, which act as a scatterer and an absorber. Each array has eight scintillation detectors, each comprising a large CsI (Tl) scintillator cube of side 3.5 cm, which is inexpensive and has a good energy resolution. Energies deposited by the Compton scattered electrons and subsequent photoelectric absorption, measured by each scintillation counter, are used for image reconstruction. The angular resolution was found to be 3.5° after using an image-sharpening technique. With this angular resolution, we can resolve a 1 m2 radiation hot spot that is located at a distance of 10 m from the detector with a wide field of view of 1 sr. Moreover, the detection efficiency 0.68 cps/MBq at 1 m for 662 keV (7.6 cps/μSv/h) is sufficient for measuring low-level contamination (i.e., less than 1 μSv/h) corresponding to typical values in large areas of eastern Japan. In addition to the laboratory tests, the imaging capability of our detector was verified in various regions with dose rates less than 1 μSv/h (e.g., Fukushima city).

  17. Psychometric Evaluation of a Coping Strategies Inventory Short-Form (CSI-SF in the Jackson Heart Study Cohort

    Directory of Open Access Journals (Sweden)

    Herman Taylor

    2007-12-01

    Full Text Available This study sought to establish the psychometric properties of a Coping Strategies Inventory Short Form (CSISF by examining coping skills in the Jackson Heart Study cohort. We used exploratory and confirmatory factor analysis, Pearson’s correlation, and Cronbach Alpha to examine reliability and validity in the CSI-SF that solicited responses from 5302 African American men and women between the ages of 35 and 84. One item was dropped from the 16-item CSI-SF, making it a 15-item survey. No significant effects were found for age and gender, strengthening the generalizability of the CSI-SF. The internal consistency reliability analysis revealed reliability between alpha = 0.58-0.72 for all of the scales, and all of the fit indices used to examine the CSI-SF provided support for its use as an adequate measure of coping. This study provides empirical support for utilizing this instrument in future efforts to understand the role of coping in moderating health outcomes.

  18. Growth and scintillation properties of pure CsI crystals grown by micro-pulling-down method

    Czech Academy of Sciences Publication Activity Database

    Totsuka, D.; Yanagida, T.; Fujimoto, Y.; Pejchal, Jan; Yokota, Y.; Yoshikawa, A.

    2012-01-01

    Roč. 34, č. 7 (2012), s. 1087-1091. ISSN 0925-3467 Institutional research plan: CEZ:AV0Z10100521 Keywords : growth from melt, * micro-pulling-down * pure CsI * scintillator Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.918, year: 2012

  19. Application of columnar cesium iodide (CsI) as a secondary-electron emission source to gas avalanche detectors

    International Nuclear Information System (INIS)

    A columnar cesium iodide (CsI) layer as a secondary-electron emission (SEE) source was applied to conventional gas avalanche detectors to improve their operating characteristics. The concentration of the primary electrons to a small interaction region allows gas avalanche detectors to have better spatial and timing resolutions. In this study, the signal enhancement and timing resolution of a microstrip gas chamber (MSGC) coupled with the columnar CsI layer were investigated. A large amount of electron amplification occurred within the columnar CsI layer when it was activated, greatly enhancing the signal pulse amplitude over that coming from the ionization in the gas drift region alone. The measured timing resolution of the MSGC detector having an anode width of 5 μm, a cathode width of 95 μm, and a pitch of 200 μm was about 5.5 ns rms at a reduced gas pressure to 30 torr. The SEE efficiency of the columnar CsI layer was also investigated and estimated with about 6%. (author)

  20. Effective Passivation of C-Si by Intrinsic A-Si:h Layer for hit Solar Cells

    Directory of Open Access Journals (Sweden)

    Shahaji More

    2011-01-01

    Full Text Available The influence of HF solution etching on surface roughness of c-Si wafer was investigated using AFM. Ultra thin(2-3 nm intrinsic a-Si:H is necessary to achieve high VOC and Fill factor, as it effectively passivates the defects on the surface of c-Si and increase tunneling probability of minority charge carriers. However, to achieve control over ultra-thin intrinsic a-Si:H layer thickness and passivation properties, the films were deposited by Hot-wire CVD. We used tantalum filament and silane (SiH4 as a precursor gas, where as the deposition parameter such as filament temperature temperature was varied. The deposition rate, Dark and Photoconductivity were measured for all the films. The optimized intrinsic a-Si:H layer was inserted between p typed doped layers and n type c-Si wafers to fabricate HIT solar cells. The Current-Voltage characteristics were studied to understand the passivation effect of intrinsic layer on c-Si surface. The high saturation current density (Jsat > 10–7 A/cm2 and Ideality factor (n > 2 were observed. We achieved the efficiency of 3.28 % with the optimized intrinsic and doped a-Si:H layers using HWCVD technique.

  1. Novel Robust Optimization and Power Allocation of Time Reversal-MIMO-UWB Systems in an Imperfect CSI

    Directory of Open Access Journals (Sweden)

    Sajjad Alizadeh

    2013-03-01

    Full Text Available Time Reversal (TR technique is an attractive solution for a scenario where the transmission system employs low complexity receivers with multiple antennas at both transmitter and receiver sides. The TR technique can be combined with a high data rate MIMO-UWB system as TR-MIMO-UWB system. In spite of TR's good performance in MIMO-UWB systems, it suffers from performance degradation in an imperfect Channel State Information (CSI case. In this paper, at first a robust TR pre-filter is designed together with a MMSE equalizer in TR-MIMO-UWB system where is robust against channel imperfection conditions. We show that the robust pre-filter optimization technique, considerably improves the BER performance of TR-MIMO-UWB system in imperfect CSI, where temporal focusing of the TR technique is kept, especially for high SNR values. Then, in order to improve the system performance more than ever, a power loading scheme is developed by minimizing the average symbol error rate in an imperfect CSI. Numerical and simulation results are presented to confirm the performance advantage attained by the proposed robust optimization and power loading in an imperfect CSI scenario.

  2. A CsI low temperature detector for dark matter search

    CERN Document Server

    Angloher, G; Gektin, A; Gironi, L; Gotti, C; Gütlein, A; Hauff, D; Maino, M; Nagorny, S S; Nisi, S; Pagnanini, L; Pattavina, L; Pessina, G; Petricca, F; Pirro, S; Pröbst, F; Reindl, F; Schäffner, K; Schieck, J; Seidel, W; Vasyukov, S

    2016-01-01

    Cryogenic detectors have a long history of success in the field of rare event searches. In particular scintillating calorimeters are very suitable detectors for this task since they provide particle discrimination: the simultaneous detection of the thermal and the light signal produced by a particle interaction in scintillating crystals allows to identify the nature of particle, as the light yield depends thereon. We investigate the performance of two large CsI (undoped) crystals ($\\sim$122 g each) operated as scintillating calorimeters at milli-Kelvin temperatures in terms of calorimetric properties and background rejection capabilities. Furthermore, we discuss the feasibility of this detection approach towards a background-free future dark matter experiment based on alkali halides crystals, with active particle discrimination via the two-channel detection.

  3. CSI: Dognapping workshop : an outreach experiment designed to produce students that are hooked on science.

    Energy Technology Data Exchange (ETDEWEB)

    Boyle, Timothy J.; Gorman, Anna K.; Pratt, Harry D., III; Hernandez-Sanchez, Bernadette A.; Lambert, Timothy N.; Ottley, Leigh Anna M.; Baros, Christina Marie

    2008-04-01

    The CSI: Dognapping Workshop is a culmination of the more than 65 Sandian staff and intern volunteers dedication to exciting and encouraging the next generation of scientific leaders. This 2 hour workshop used a 'theatrical play' and 'hands on' activities that was fun, exciting and challenging for 3rd-5th graders while meeting science curriculum standards. In addition, new pedagogical methods were developed in order to introduce nanotechnology to the public. Survey analysis indicated that the workshop had an overall improvement and positive impact on helping the students to understand concepts from materials science and chemistry as well as increased our interaction with the K-5 community. Anecdotal analyses showed that this simple exercise will have far reaching impact with the results necessary to maintain the United States as the scientific leader in the world. This experience led to the initiation of over 100 Official Junior Scientists.

  4. A high speed digitizing photomultiplier tube base for the KTeV CsI calorimeter

    International Nuclear Information System (INIS)

    A circuit has been designed to digitize PMT signals over an 18-bit dynamic range with 8-bits of resolution. The crucial element of the circuit is the custom charge integrating and encoding (QIE) ASIC. This chip is designed to operate at rates up to 53 MHz, and, in conjunction with an 8-bit FADC, generates 12-bit floating point output. Bench tests of a 17-bit version of the digital base demonstrated excellent noise performance, linearity and pedestal and gain stability. Twenty-five channels of digitizing PMT bases have been built and used for readout of a CsI array in a test beam at CERN. Performance of these devices in a beam environment is discussed

  5. 3D Imaging of Dielectric Objects Buried under a Rough Surface by Using CSI

    Directory of Open Access Journals (Sweden)

    Evrim Tetik

    2015-01-01

    Full Text Available A 3D scalar electromagnetic imaging of dielectric objects buried under a rough surface is presented. The problem has been treated as a 3D scalar problem for computational simplicity as a first step to the 3D vector problem. The complexity of the background in which the object is buried is simplified by obtaining Green’s function of its background, which consists of two homogeneous half-spaces, and a rough interface between them, by using Buried Object Approach (BOA. Green’s function of the two-part space with planar interface is obtained to be used in the process. Reconstruction of the location, shape, and constitutive parameters of the objects is achieved by Contrast Source Inversion (CSI method with conjugate gradient. The scattered field data that is used in the inverse problem is obtained via both Method of Moments (MoM and Comsol Multiphysics pressure acoustics model.

  6. Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

    International Nuclear Information System (INIS)

    Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K2CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K2CsSb upon cesium deposition, is correlated with changes in the quantum efficiency

  7. Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

    Science.gov (United States)

    Ruiz-Osés, M.; Schubert, S.; Attenkofer, K.; Ben-Zvi, I.; Liang, X.; Muller, E.; Padmore, H.; Rao, T.; Vecchione, T.; Wong, J.; Xie, J.; Smedley, J.

    2014-12-01

    Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K2CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K2CsSb upon cesium deposition, is correlated with changes in the quantum efficiency.

  8. Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

    Energy Technology Data Exchange (ETDEWEB)

    Ruiz-Osés, M.; Ben-Zvi, I.; Liang, X.; Muller, E. [Stony Brook University, Stony Brook, New York 11794 (United States); Schubert, S. [Helmholtz-Zentrum Berlin, Albert-Einstein Str. 15, 12489 Berlin (Germany); Brookhaven National Laboratory, Upton, New York 11973 (United States); Attenkofer, K.; Rao, T.; Smedley, J., E-mail: smedley@bnl.gov [Brookhaven National Laboratory, Upton, New York 11973 (United States); Padmore, H.; Vecchione, T.; Wong, J. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Xie, J. [Argonne National Laboratory, Lemont, Illinois 60439 (United States)

    2014-12-01

    Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K{sub 2}CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K{sub 2}CsSb upon cesium deposition, is correlated with changes in the quantum efficiency.

  9. Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

    Directory of Open Access Journals (Sweden)

    M. Ruiz-Osés

    2014-12-01

    Full Text Available Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K2CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100 substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K2CsSb upon cesium deposition, is correlated with changes in the quantum efficiency.

  10. An Experimental Study of the Quantum Efficiency and Topology of Copper Photocathode Due to Plasma Cleaning and Etching

    CERN Document Server

    Palmer, Denni T; Kirby, Robert

    2005-01-01

    We have developed an experimental research program to the study of the photoemission properties of copper photocathodes as a function of various plasma cleaning/etching parameters. The quantum efficiency, QE, and topology, Ra and Rpp, of Copper Photocathodes, , will be monitored while undergoing plasma cleaning/etching process. We will monitor the QE as a function of time for the various test coupons while we optimize the various plasma processing parameters. In addition, surface topology, will be studied to determine the suitability of the cleaning/etching process to produce an acceptable photoemitter. We propose to use two metrics in the evaluation of the plasma cleaning process as an acceptable cleaning method for metallic photocathodes, Quantum Efficiency versus Wavelength and Surface roughness: Ra and Rpp represent the Average Roughness and Peak to Peak Roughness parameters, respectively.

  11. A study of the oxidation hydrolysis of CsI radioaerosols in a steam-air medium using filtering units

    International Nuclear Information System (INIS)

    A study of the oxidation hydrolysis of radioaerosols is an issue of acute importance from both scientific and practical points of view. This can be explained by the facts that there is currently virtually no experimental data on this process and that the problem of the localization of CsI radioaerosols during accidents at nuclear power enterprises still remains unsolved. We carried out a study of the oxidation hydrolysis of 137CS131I radioaerosols in a steam-vapor medium during their localization on a column with filtering units, specifically: (1) 'Bekipor WB12' metal fiber (Cr-Ni-Mo alloy, fiber thickness ∼12 μm, density ∼0.05 g/cm3, specific surface area ∼450 cm2/g; (2) spiral filtering unit made of a wire measuring 8.0 m in length and 0.6 mm in diameter (working area parameters: length ∼115 mm, diameter ∼14 mm, and specific surface area ∼0.01 cm2/g; (3) 'TRUMEM stainless steel membrane filter (diameter ∼20 mm, thickness 0.2 mm, specific surface area ∼5000 cm2/g, pore size ∼2 μm; (4) three-layer de-ashed paper filter known as 'white band' (pore diameter 3.5 μm and specific surface ∼8000 cm2/g). The results of the study allowed us to suggest that the sublimation of 137CS131I from a platinum heater under specific conditions can lead to the formation of the following compounds 137CsOH, 137CS131I - 137CsOH, 137CS131I3, and 131I2. The oxidation hydrolysis of 13lCS131I radioaerosols and the interaction of hydrolysis products with the surfaces of the metal and paper filtering units took place under the following conditions: air-flow temperature 403-423 Κ, steam content in the air flow about 3-4 to 90 vol.%, and the linear velocity of the flow in the sorption column from 6 to 24 cm/s. The filtering units managed to localize from ∼5 to ∼98 % of the initial amount of 137CS131I (0:17-70 mg) supplied to the filtering system, which depended on the filtering material, the size of its inner surface, and the conditions of the experiment.

  12. A polarized photoluminescence study of strained layer GaAs photocathodes

    International Nuclear Information System (INIS)

    Photoluminescence measurements have been made on a set of epitaxially grown strained GaAs photocathode structures. The photocathodes are designed to exhibit a strain-induced enhancement of the electron spin polarization obtainable by optical pumping with circularly polarized radiation of near band gap energy. For the case of non-strained GaAs, the degree of spin polarization is limited to 50% by crystal symmetry. Under an appropriate uniaxial compression or tension, however, the valence band structure near the gap minimum is modified such that a spin polarization of 100% is theoretically possible. A total of nine samples with biaxial compressive strains ranging from zero to ∼0.8% are studied. X-ray diffraction analysis, utilizing Bragg reflections, is used to determine the crystal lattice structure of the samples. Luminescence spectra and luminescence circular polarization data are obtained at room temperature, ∼78 K and ∼12 K. The degree of luminescence circular polarization is used as a relative measure of the photo-excited electron spin polarization. The room temperature luminescence circular polarization data is compared with the measured electron spin polarization when the samples are used as electron photo-emitters with a negative electron affinity surface preparation. The luminescence data is also analyzed in conjunction with the crystal structure data with the goal of understanding the strain dependent valence band structure, optical pumping characteristics and spin depolarization mechanisms of the photocathode structures. A simple model is used to describe the luminescence data, obtained for the set of samples. Within the assumptions of the model, the deformation potentials a, b and d for GaAs are determined. The measured values are a = -10.16±.21 eV, b = -2.00±.05 eV and d = -4.87±.29 eV. Good agreement with published values of the deformation potentials provides support for the model used to describe the data

  13. A polarized photoluminescence study of strained layer GaAs photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Mair, R.A.

    1996-07-01

    Photoluminescence measurements have been made on a set of epitaxially grown strained GaAs photocathode structures. The photocathodes are designed to exhibit a strain-induced enhancement of the electron spin polarization obtainable by optical pumping with circularly polarized radiation of near band gap energy. For the case of non-strained GaAs, the degree of spin polarization is limited to 50% by crystal symmetry. Under an appropriate uniaxial compression or tension, however, the valence band structure near the gap minimum is modified such that a spin polarization of 100% is theoretically possible. A total of nine samples with biaxial compressive strains ranging from zero to {approximately}0.8% are studied. X-ray diffraction analysis, utilizing Bragg reflections, is used to determine the crystal lattice structure of the samples. Luminescence spectra and luminescence circular polarization data are obtained at room temperature, {approx}78 K and {approx}12 K. The degree of luminescence circular polarization is used as a relative measure of the photo-excited electron spin polarization. The room temperature luminescence circular polarization data is compared with the measured electron spin polarization when the samples are used as electron photo-emitters with a negative electron affinity surface preparation. The luminescence data is also analyzed in conjunction with the crystal structure data with the goal of understanding the strain dependent valence band structure, optical pumping characteristics and spin depolarization mechanisms of the photocathode structures. A simple model is used to describe the luminescence data, obtained for the set of samples. Within the assumptions of the model, the deformation potentials a, b and d for GaAs are determined. The measured values are a = -10.16{+-}.21 eV, b = -2.00{+-}.05 eV and d = -4.87{+-}.29 eV. Good agreement with published values of the deformation potentials provides support for the model used to describe the data.

  14. Initial simulation studies of electron bunch from RF photocathode gun of DLS project

    International Nuclear Information System (INIS)

    A Free Electron Laser based compact light source, named as Delhi Light Source (DLS), is under construction at IUAC. The facility aims to produce THz and Infrared radiation by injecting high quality electron beam into an undulator magnet. In addition, intense X-rays can be obtained by bombarding the electron beam with a laser beam by the method of Inverse Compton scattering. The complete project is divided in to three phases. The first phase of the project aims at generating pre-bunched electron beam from a 2.6 cell room temperature RF photocathode gun operating at 2.86 GHz. The bunch train with a repetition rate of 10 Hz, will consist of 2, 4, 8 or 16 micro-bunches . By varying the separation between the microbunches, the tuning of the THz radiation produced from the undulator magnet can be performed. Metal photocathode will be used initially to generate the electron micro-bunches to keep the temporal spread small. This paper describes the simulation studies using ASTRA code for optimization of various parameters from RF photocathode gun upto the undulator entrance. The multiple parameters are optimized one at a time, for a single electron bunch, ensuring the desired output parameter is contained within tolerable limits. Beam optics simulation with multi electron bunches are also studied with variable number of 2, 4 and 8 micro-bunches with different micro-bunch spacing. In the simulation studies, attention is paid to optimize the fundamental beam parameters like the transverse emittance, energy spread, transverse/longitudinal beam size etc. The paper describes the simulation results with single and multi-electron bunches. (author)

  15. Measurements of the radiolytic oxidation of aqueous CsI using a sparging apparatus

    International Nuclear Information System (INIS)

    Radiolytic oxidation is considered to be the main mechanism for the formation of I2 from aqueous CsI in containment of a water cooled reactor after a LOCA. Despite the amount of study over the last 60 years on the radiation chemistry of iodine there has been no consistent set of experiments spanning a wide enough range of conditions to verify models with confidence. This paper describes results from a set of experiments carried out in order to remedy this deficiency. In this work the rate of evolution of I2 from sparged irradiated CsI solution labeled with 131I was measured on-line over a range of conditions. This work involved the measurement of the effects of pH, temperature, O2 concentration, I- concentration, phosphate concentration, dose-rate and impurities on the rate of evolution of I2. The range of conditions was chosen in order to span as closely as possible conditions expected in a LOCA but also to help to elucidate some of the mechanisms especially at high pH. pH was found to be a very important factor influencing iodine volatility, over the temperature range studied the extent of oxidation reduced with temperature but this was compensated for by the decrease in partition coefficient. Oxygen concentration was more important in solutions not containing phosphate. The fractional oxidation was not particularly dependent on iodide concentration but GI2 was very dependent on [I-]. There was no effect of added impurities, Fe, Mn, Mo or organics although in separate work silver was found to have a very important effect. During attempts to interpret the data it was found that it was necessary to include the iodine atom as a volatile species with a partition coefficient of 1.9 taken from thermodynamic data. The modelling work is described in a separate paper. (author) 15 figs., 1 tab., 19 refs

  16. Inorganic scintillators of Li+ doped CsI for neutron detection

    International Nuclear Information System (INIS)

    The scintillation method is still one of the main methods used for the detection of ionizing radiations. The universality of this method is considered to be its major advantage. It may be used for registration of almost all types of radiation in a wide range of energy (1 eV - 10 GeV). In recent years has been an increasing demand for new types of neutron detectors to be used in applications such as spectrometers, photodetectors, materials characterization, and so on. For these applications, inorganic scintillators play an important role in the detection and spectroscopy of neutrons. Scintillation crystals based on cesium iodide (CsI) have relatively low hygroscope, easy handling and low cost, features that favor their use as radiation detectors. In this work, lithium doped CsI crystals were grown using the vertical Bridgman technique. In this technique, the charge is maintained at high temperature for 10 h for the material melting and complete reaction. The temperature gradient 21 deg C/cm and 1 mm/h descending velocity are chosen as technique parameters. The concentration of the lithium doping element (Li) studied was 10-3 M. The optical transmittance measurements were made in the CsI:Li crystal at room temperature, using a spectrophotometer with a wavelength in the range 200 nm to 900 nm. Analyses were carried out to evaluate the scintillators developed, concerning neutron radiation from AmBe source, with the energy range of 1 MeV to 12 MeV. In this paper was investigated, the feasibility of the CsI:Li crystal as a neutron detector to be used for monitoring, due to the fact that in our work environment there are two nuclear research reactors and calibration systems. (author)

  17. Immobilized nickel hexacyanoferrate on activated carbons for efficient attenuation of radio toxic Cs(I) from aqueous solutions

    International Nuclear Information System (INIS)

    Highlights: • Rice hulls and areca nut wastes are utilized to obtain activated carbons. • Nickel hexacyanoferrate is immobilized on activated carbon samples. • Materials are characterized by SEM–EDX and XRD data. • Materials are employed in attenuation of Cs(I) under batch and column studies. • Possible mechanism is deduced at solid/solution interface. - Abstract: The aim of this study is to immobilize nickel hexacyanoferrate onto the large surface of activated carbons (ACs) precursor to rice hulls and areca nut waste materials. These nickel hexacyanoferrate immobilized materials are then assessed in the effective attenuation of radio logically important cesium ions from aqueous solutions. The solid samples are characterized by the XRD analytical method and surface morphology is obtained from the SEM images. The batch reactor experiments show that an increase in sorptive pH (2.0–10.0) apparently not affecting the high percent uptake of Cs(I). Equilibrium modeling studies suggest that the data are reasonably and relatively fitted well to the Langmuir adsorption isotherm. Kinetic studies show that sorption process is fairly rapid and the kinetic data are fitted well to the pseudo-second order rate model. Increasing the background electrolyte concentration from 0.001 to 0.1 mol/L NaCl causes insignificant decrease in Cs(I) removal which infers the higher selectivity of these materials for Cs(I) from aqueous solutions. Further, the column reactor operations enable to obtain the breakthrough data which are then fitted to the Thomas non-linear equation as to obtain the loading capacity of column for Cs(I). The results show that the modified materials show potential applicability in the attenuation of radio toxic cesium from aqueous solution

  18. Modular magnet power supplies for CUTE-FEL beamline and photocathode gun based linac

    International Nuclear Information System (INIS)

    DC current-controlled power supplies are developed for application in CUTE-FEL beamline at BP and FEL Lab, RRCAT and photocathode gun based linac being set up at Radiation and Photochemistry Division, Bhabha Atomic Research Centre. In all, 29 power supplies for various magnets are developed. Power supply design is standardized for output ratings up to 20 A and 325 W on a standard 6U card with full-function feedback control and local-remote operation interface electronics on the same card. Individual power supply cards can be configured for series-parallel operation to increase output power rating. (author)

  19. Research of photo-cathode RF gun and superconducting accelerator experiment

    International Nuclear Information System (INIS)

    Photo-cathode superconducting accelerator experiment system includes Nd: YAG mode-locked laser, Cs2Te cathode, 2 + 1/2 RF gun, L band 3.5 MW microwave source, 1.3 GHz superconducting cavity, 500 W continuous microwave source, coaxial input coupler, 4.2 K cryostat, helium liquefied system, control system, beam diagnosis system, and vacuum system. In June 2001, the experiment of this system was carried out in CAEP. The electron beam energy gained in the superconducting cavity is 0.58 MeV, and the micro-pulse current is 0.1A

  20. Study of multi-alkali photocathode to realize high quantum efficiency and high endurance

    International Nuclear Information System (INIS)

    CsK2Sb multi-alkali photocathode is considered to be one of the best candidate of the high brightness electron source of the advanced electron accelerator such as Energy Recovery Linac (ERL) and Free Electron Laser (FEL) because of the excellent features: high quantum efficiency, long lifetime, and driven by green laser. We developed an evaporation system to study the cathode performances, such as quantum efficiency (QE) and the cathode lifetime. CsK2Sb thin film cathode was successfully made in this chamber. The cathode lifetime was measured and the result suggests that the cathode has an extremely long lifetime regarding to the extracted charge density. (author)

  1. Photoemission and optical constant measurements of a Cesium Iodide thin film photocathode

    International Nuclear Information System (INIS)

    The performance of cesium iodide as a reflective photocathode is presented. The absolute quantum efficiency of a 500 nm thick film of cesium iodide has been measured in the wavelength range 150 nm–200 nm. The optical absorbance has been analyzed in the wavelength range 190 nm–900 nm and the optical band gap energy has been calculated. The dispersion properties were determined from the refractive index using an envelope plot of the transmittance data. The morphological and elemental film composition have been investigated by atomic force microscopy and X-ray photo-electron spectroscopy techniques

  2. Quantum yield measurements of photocathodes illuminated by pulsed ultraviolet laser radiation

    International Nuclear Information System (INIS)

    The electron quantum yields from polycrystalline lanthanum hexaboride and barium irradiated by near ultraviolet laser excitation have been determined. These measurements show that the quantum yields from these materials are dependent on the processing and previous history of the photocathode material. For lanthanum hexaboride, a yield of 7 x 10-6 with 337 nm irradiation has been achieved. For barium, a yield of 1 x 10-6 has been measured with excitation at 308 nm. These results are discussed and future plans are outlined. 4 refs., 4 figs

  3. Software Tools for the Analysis of the Photocathode Response of Photomultiplier Vacuum Tubes

    OpenAIRE

    Fabbri, R.

    2013-01-01

    The central institute of electronics (ZEA-2) in the Forschungszentrum Juelich (FZJ) has developed a system to scan the response of the photocathode of photomultiplier tubes (PMT). The PMT sits tight on a supporting structure, while a blue light emitting diode is moved along its surface by two stepper motors, spanning both the x and y coordinates. All the system is located in a light-tight box made by wood. A graphical software was developed in-situ to perform the scan operations under differe...

  4. Generation of femtosecond electron bunches using a laser photocathode RF gun linac

    International Nuclear Information System (INIS)

    Electron beams with pulse durations of picoseconds and femtoseconds have been applied to the accelerator physics application such as free electron lasers and laser-Comptom x-rays. The ultrashort electron bunches are also key element in time-resolved measurements including pulse radiolysis to improve the time resolution of the measurements. In this study, femtosecond electron bunches were generated using a laser photocathode RF gun linac and a magnetic bunch compressor at ISIR, Osaka University. The bunch lengths were evaluated by detecting coherent transition radiation (CTR) emitted from the electron bunches using a Michelson interferometer. (author)

  5. Generation and measurement of sub-picosecond electron bunch in photocathode rf gun

    International Nuclear Information System (INIS)

    We consider a scheme to generate a sub-picosecond electron bunch in the photocathode rf gun by improving the acceleration gradient in the gun, suitably tuning the bunch charge, the laser spot size and the acceleration phase, and reducing the growth of transverse emittance by laser shaping. A nondestructive technique is also reported to measure the electron bunch length, by measuring the high-frequency spectrum of wakefield radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric. (authors)

  6. Analysis of emittance compensation and simulation results to photo-cathode RF gun

    CERN Document Server

    LiuShengGuang

    2002-01-01

    The emittance compensation technology will be used on the photo-cathode RF gun for Shanghai SDUV-FEL. The space charge force and its effect on electron beam transverse emittance in RF gun is studied, the principle of emittance compensation in phase-space is discussed. The authors have designed a compensation solenoid and calculated its magnetic field distribution. Its performance has been studied by the code PARMELA. A simulation result indicates that the normalized transverse RMS emittance for electron beam of 1.5 nC is 1.612 pi mm centre dot mrad, electron energy E = 5.71 MeV

  7. Slice emittance measurement for photocathode RF gun with solenoid scanning and RF deflecting cavity

    Science.gov (United States)

    Li, Chen; Huang, WenHui; Du, YingChao; Yan, LiXin; Tang, ChuanXiang

    2011-12-01

    The radiation of high-gain short-wavelength free-electron laser depends on the slice transverse emittance of the electron bunch. This essay introduces the method of slice emittance measurement, and shows the brief setup of this experiment using the solenoid scanning and RF deflecting cavity at Tsinghua University. The preliminary experimental results show that the slice rms emittance of the electron bunch generated by photocathode RF gun has considerable variations along the bunch and is typically less than 0.55 mm mrad for the laser rms radius of 0.4 mm.

  8. A Monolithically Integrated Gallium Nitride Nanowire/Silicon Solar Cell Photocathode for Selective Carbon Dioxide Reduction to Methane.

    Science.gov (United States)

    Wang, Yichen; Fan, Shizhao; AlOtaibi, Bandar; Wang, Yongjie; Li, Lu; Mi, Zetian

    2016-06-20

    A gallium nitride nanowire/silicon solar cell photocathode for the photoreduction of carbon dioxide (CO2 ) is demonstrated. Such a monolithically integrated nanowire/solar cell photocathode offers several unique advantages, including the absorption of a large part of the solar spectrum and highly efficient carrier extraction. With the incorporation of copper as the co-catalyst, the devices exhibit a Faradaic efficiency of about 19 % for the 8e(-) photoreduction to CH4 at -1.4 V vs Ag/AgCl, a value that is more than thirty times higher than that for the 2e(-) reduced CO (ca. 0.6 %). PMID:27128407

  9. Improved Electron Yield and Spin-Polarization from III-V Photocathodes via Bias Enhanced Carrier Drift: Final Report

    International Nuclear Information System (INIS)

    In this DOE STTR program, Saxet Surface Science, with the Stanford Linear Accelerator Center as partner, designed, built and tested photocathode structures such that optimal drift-enhanced spin-polarization from GaAs based photoemitters was achieved with minimal bias supply requirements. The forward bias surface grid composition was optimized for maximum polarization and yield, together with other construction parameters including doping profile. This program has culminated in a cathode bias structure affording increased electron spin polarization when applied to III-V based photocathodes. The optimized bias structure has been incorporated into a cathode mounting and biasing design for use in a polarized electron gun.

  10. Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst.

    Science.gov (United States)

    Morales-Guio, Carlos G; Tilley, S David; Vrubel, Heron; Grätzel, Michael; Hu, Xile

    2014-01-01

    Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7 mA cm(-2) at 0 V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production. PMID:24402352

  11. Covalent Immobilization of a Molecular Catalyst on Cu2O Photocathodes for CO2 Reduction.

    Science.gov (United States)

    Schreier, Marcel; Luo, Jingshan; Gao, Peng; Moehl, Thomas; Mayer, Matthew T; Grätzel, Michael

    2016-02-17

    Sunlight-driven CO2 reduction is a promising way to close the anthropogenic carbon cycle. Integrating light harvester and electrocatalyst functions into a single photoelectrode, which converts solar energy and CO2 directly into reduced carbon species, is under extensive investigation. The immobilization of rhenium-containing CO2 reduction catalysts on the surface of a protected Cu2O-based photocathode allows for the design of a photofunctional unit combining the advantages of molecular catalysts with inorganic photoabsorbers. To achieve large current densities, a nanostructured TiO2 scaffold, processed at low temperature, was deposited on the surface of protected Cu2O photocathodes. This led to a 40-fold enhancement of the catalytic photocurrent as compared to planar devices, resulting in the sunlight-driven evolution of CO at large current densities and with high selectivity. Potentiodynamic and spectroelectrochemical measurements point toward a similar mechanism for the catalyst in the bound and unbound form, whereas no significant production of CO was observed from the scaffold in the absence of a molecular catalyst. PMID:26804626

  12. Performance of a DC GaAs photocathode gun for the Jefferson lab FEL

    International Nuclear Information System (INIS)

    The performance of the 320 kV DC photocathode gun has met the design specifications for the 1 kW IR Demo FEL at Jefferson Lab. This gun has shown the ability to deliver high average current beam with outstanding lifetimes. The GaAs photocathode has delivered 135 pC per bunch, at a bunch repetition rate of 37.425 MHz, corresponding to 5 mA average CW current. In a recent cathode lifetime measurement, 20 h of CW beam was delivered with an average current of 3.1 mA and 211 C of total charge from a 0.283 cm2 illuminated spot. The cathode showed a 1/e lifetime of 58 h and a 1/e extracted charge lifetime of 618 C. We have achieved quantum efficiencies of 5% from a GaAs wafer that has been in service for 13 months delivering in excess 2400 C with only three activation cycles

  13. Improved Ion Resistance for III-V Photocathodes in High Current Guns

    Energy Technology Data Exchange (ETDEWEB)

    Mulhollan, Gregory, A.

    2012-11-16

    The two photocathode test systems were modified, baked and recommissioned. The first system was dedicated to ion studies and the second to electron stimulated recovery (ESR) work. The demonstration system for the electron beam rejuvenation was set up, tested and demonstrated to one of the SSRL team (Dr. Kirby) during a site visit. The requisite subsystems were transferred to SSRL, installed and photoemission studies conducted on activated surfaces following electron beam exposure. Little surface chemistry change was detected in the photoemission spectra following the ESR process. The yield mapping system for the ion (and later, the electron beam rejuvenation) studies was implemented and use made routine. Ion species and flux measurements were performed for H, He, Ne, Ar, Kr and Xe ions at energies of 0.5, 1.0 and 2.0 kV. Gas induced photoyield measurements followed each ion exposure measurement. These data permit the extraction of photoyield induced change per ion (by species) at the measured energies. Electron beam induced rejuvenation was first demonstrated in the second chamber with primary electron beam energy and dependency investigations following. A Hiden quadrupole mass spectrometer for the electron stimulated desorption (ESD) measurements was procured. The UHV test systems needed for subsequent measurements were configured, baked, commissioned and utilized for their intended purposes. Measurements characterizing the desorption products from the ESD process and secondary electron (SE) yield at the surfaces of negative electron affinity GaAs photocathodes have been performed. One US Utility Patent was granted covering the ESR process.

  14. Compact vacuum tubes with GaAs(Cs,O) photocathodes for studying spin-dependent phenomena

    Science.gov (United States)

    Alperovich, V. L.; Orlov, D. A.; Grishaev, V. G.; Kosolobov, S. N.; Jaroshevich, A. S.; Scheibler, H. E.; Terekhov, A. S.

    2009-08-01

    Compact proximity focused vacuum tubes with GaAs(Cs,O) photocathodes are used for experimental studying spindependent phenomena. Firstly, spin-dependent emission of optically oriented electrons from p-GaAs(Cs,O) into vacuum in a magnetic field normal to the surface was observed in a nonmagnetic vacuum diode. This phenomenon is explained by the jump in the electron g-factor at the semiconductor-vacuum interface. Due to this jump, the effective electron affinity on the semiconductor surface depends on the mutual direction of optically oriented electron spins and the magnetic field, resulting in the spin-dependent photoemission. It is demonstrated that the observed effect can be used for the determination of spin diffusion length in semiconductors. Secondly, we developed a prototype of a new spin filter, which consists of a vacuum tube with GaAs(Cs,O) photocathode and a nickel-covered venetian blind dynode. Preliminary results on spin-dependent reflection of electrons from the oxidized polycrystal nickel layer are presented.

  15. Heat load of a P-doped GaAs photocathode in SRF electron gun

    Energy Technology Data Exchange (ETDEWEB)

    Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Jain, A.; Gupta, R.; Holmes, D.

    2010-05-23

    Many efforts were made over the last decades to develop a better polarized electron source for the high energy physics. Several laboratories operate DC guns with the Gallium-Arsenide photo-cathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved using a Superconducting RF electron gun, which delivers beams of higher brightness than DC guns does, because the field gradient at the cathode is higher. SRF guns with metal cathodes and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since the cathode will be normal conducting, the problem about the heat load stemming from the cathode arises. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and the verification by measuring the quality factor of the gun with and without cathode.

  16. Solar Hydrogen Production from Zinc Telluride Photocathode Modified with Carbon and Molybdenum Sulfide.

    Science.gov (United States)

    Jang, Youn Jeong; Lee, Jaehyuk; Lee, Jinwoo; Lee, Jae Sung

    2016-03-30

    A zinc telluride (ZnTe) film modified with MoS2 and carbon has been studied as a new photocathode for solar hydrogen production from photoelectrochemical (PEC) water splitting. The modification enhances PEC activity and stability of the photocathode. Thus, the MoS2/C/ZnTe/ZnO electrode exhibits highly improved activity of -1.48 mA cm(-2) at 0 VRHE with a positively shifted onset potential up to 0.3 VRHE relative to bare ZnO/ZnTe electrode (-0.19 mA cm(-2), 0.18 VRHE) under the simulated 1 sun illumination. This represents the highest value ever reported for ZnTe-based electrodes in PEC water splitting. The carbon densely covers the surface of ZnTe to protect it against photocorrosion in aqueous electrolyte and improves charge separation. In addition, MoS2 further enhances the PEC performance as a hydrogen evolution co-catalyst. PMID:26909873

  17. Nanostructured Ternary FeCrAl Oxide Photocathodes for Water Photoelectrolysis.

    Science.gov (United States)

    Kondofersky, Ilina; Müller, Alexander; Dunn, Halina K; Ivanova, Alesja; Štefanić, Goran; Ehrensperger, Martin; Scheu, Christina; Parkinson, Bruce A; Fattakhova-Rohlfing, Dina; Bein, Thomas

    2016-02-17

    A sol-gel method for the synthesis of semiconducting FeCrAl oxide photocathodes for solar-driven hydrogen production was developed and applied for the production of meso- and macroporous layers with the overall stoichiometry Fe0.84Cr1.0Al0.16O3. Using transmission electron microscopy and energy-dispersive X-ray spectroscopy, phase separation into Fe- and Cr-rich phases was observed for both morphologies. Compared to prior work and to the mesoporous layer, the macroporous FeCrAl oxide photocathode had a significantly enhanced photoelectrolysis performance, even at a very early onset potential of 1.1 V vs RHE. By optimizing the macroporous electrodes, the device reached current densities of up to 0.68 mA cm(-2) at 0.5 V vs RHE under AM 1.5 with an incident photon-to-current efficiency (IPCE) of 28% at 400 nm without the use of catalysts. Based on transient measurements, this performance increase could be attributed to an improved collection efficiency. At a potential of 0.75 V vs RHE, an electron transfer efficiency of 48.5% was determined. PMID:26743183

  18. Silicon/Carbon Nanotube Photocathode for Splitting Water

    Science.gov (United States)

    Amashukeli, Xenia; Manohara, Harish; Greer, Harold F.; Hall, Lee J.; Gray, Harry B.; Subbert, Bryan

    2013-01-01

    A proof-of-concept device is being developed for hydrogen gas production based on water-splitting redox reactions facilitated by cobalt tetra-aryl porphyrins (Co[TArP]) catalysts stacked on carbon nanotubes (CNTs) that are grown on n-doped silicon substrates. The operational principle of the proposed device is based on conversion of photoelectron energy from sunlight into chemical energy, which at a later point, can be turned into electrical and mechanical power. The proposed device will consist of a degenerately n-doped silicon substrate with Si posts covering the surface of a 4-in. (approximately equal to 10cm) wafer. The substrate will absorb radiation, and electrons will move radially out of Si to CNT. Si posts are designed such that the diameters are small enough to allow considerable numbers of electrons to transport across to the CNT layer. CNTs will be grown on top of Si using conformal catalyst (Fe/Ni) deposition over a thin alumina barrier layer. Both metallic and semiconducting CNT will be used in this investigation, thus allowing for additional charge generation from CNT in the IR region. Si post top surfaces will be masked from catalyst deposition so as to prevent CNT growth on the top surface. A typical unit cell will then consist of a Si post covered with CNT, providing enhanced surface area for the catalyst. The device will then be dipped into a solution of Co[TArP] to enable coating of CNT with Co(P). The Si/CNT/Co [TArP] assembly then will provide electrons for water splitting and hydrogen gas production. A potential of 1.23 V is needed to split water, and near ideal band gap is approximately 1.4 eV. The combination of doped Si/CNT/Co [TArP] will enable this redox reaction to be more efficient.

  19. Silicon nanowire arrays coupled with cobalt phosphide spheres as low-cost photocathodes for efficient solar hydrogen evolution.

    Science.gov (United States)

    Bao, Xiao-Qing; Fatima Cerqueira, M; Alpuim, Pedro; Liu, Lifeng

    2015-07-01

    We demonstrate the first example of silicon nanowire array photocathodes coupled with hollow spheres of the emerging earth-abundant cobalt phosphide catalysts. Compared to bare silicon nanowire arrays, the hybrid electrodes exhibit significantly improved photoelectrochemical performance toward the solar-driven H2 evolution reaction. PMID:26050844

  20. Silicon nanowire arrays coupled with cobalt phosphide spheres as low-cost photocathodes for efficient solar hydrogen evolution

    OpenAIRE

    Bao, Xiao-Qing; Cerqueira, M. F.; Alpuim, P.; Liu, Lifeng

    2015-01-01

    We demonstrate the first example of silicon nanowire array photocathodes coupled with hollow spheres of the emerging earth-abundant cobalt phosphide catalysts. Compared to bare silicon nanowire arrays, the hybrid electrodes exhibit significantly improved photoelectrochemical performance toward the solar-driven H2 evolution reaction.

  1. Gated photocathode design for the P510 electron tube used in the National Ignition Facility (NIF) optical streak cameras

    Science.gov (United States)

    Datte, P.; James, G.; Celliers, P.; Kalantar, D.; Vergel de Dios, G.

    2015-08-01

    The optical streak cameras currently used at the National Ignition Facility (NIF) implement the P510 electron tube from Photonis1. The existing high voltage electronics provide DC bias voltages to the cathode, slot, and focusing electrodes. The sweep deflection plates are driven by a ramp voltage. This configuration has been very successful for the majority of measurements required at NIF. New experiments require that the photocathode be gated or blanked to reduce the effects of undesirable scattered light competing with low light level experimental data. The required ~2500V gate voltage is applied between the photocathode and the slot electrode in response to an external trigger to allow the electrons to flow. Otherwise the slot electrode is held approximately 100 Volts more negative than the potential of the photocathode, preventing electron flow. This article reviews the implementation and performance of the gating circuit that applies an electronic gate to the photocathode with a nominal 50ns rise and fall time, and a pulse width between 50ns and 2000ns.

  2. Hydrogen Production Using a Molybdenum Sulfide Catalyst on a Titanium-Protected n+p-Silicon Photocathode

    DEFF Research Database (Denmark)

    Seger, Brian; Laursen, Anders Bo; Vesborg, Peter Christian Kjærgaard; Pedersen, Thomas; Hansen, Ole; Dahl, Søren; Chorkendorff, Ib

    2012-01-01

    A low-cost substitute: A titanium protection layer on silicon made it possible to use silicon under highly oxidizing conditions without oxidation of the silicon. Molybdenum sulfide was electrodeposited on the Ti-protected n+p-silicon electrode. This electrode was applied as a photocathode for wat...

  3. Modulation transfer function characteristic of uniform-doping transmission-mode GaAs/GaAlAs photocathode

    Institute of Scientific and Technical Information of China (English)

    Ren Ling; Chang Ben-Kang

    2011-01-01

    The resolution characteristic can be obtained by the modulation transfer function(MTF)of a GaAs/GaAlAs photocathode.After establishing the theoretical model of GaAs(100)-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers,this paper calculates the trajectories of photoelectrons in a photocathode.Thus the distribution of photoelectron spots on the emit-face is obtained,which is namely the point spread function.The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function.The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length,and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration.Furthermore,the resolution is enhanced considerably by increasing the active-layer thickness,especially at high spatial frequencies.The best spatial resolution is 860 lp/mm,for the GaAs photocathode of doping concentration 1×1019cm-3,electron diffusion length 3.6 μm and the active-layer thickness 2 μm,under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode's resolution for preparing a high performance GaAs photocathode,and improve the resolution of a low light level image intensifier.

  4. Use of a photomultiplier with a single-crystal and polycrystal GaAs photocathode for polarimetric astronomical observations

    Science.gov (United States)

    Bergner, Iu. K.; Iudin, R. V.; Miroshnichenko, A. S.; Iutanov, N. Iu.

    Laboratory investigations of photomultipliers with a single-crystal and polycrystal GaAs photocathode are reported. Data processing formulas for polarimetric and photometric observations which take the detector's proper polarization into account are given. It is shown that the photomultiplier FEU-138 meets the requirements for precision photometric and polarimetric astronomical research.

  5. Development of Thin Film Amorphous Silicon Tandem Junction Based Photocathodes Providing High Open-Circuit Voltages for Hydrogen Production

    Directory of Open Access Journals (Sweden)

    F. Urbain

    2014-01-01

    Full Text Available Hydrogenated amorphous silicon thin film tandem solar cells (a-Si:H/a-Si:H have been developed with focus on high open-circuit voltages for the direct application as photocathodes in photoelectrochemical water splitting devices. By temperature variation during deposition of the intrinsic a-Si:H absorber layers the band gap energy of a-Si:H absorber layers, correlating with the hydrogen content of the material, can be adjusted and combined in a way that a-Si:H/a-Si:H tandem solar cells provide open-circuit voltages up to 1.87 V. The applicability of the tandem solar cells as photocathodes was investigated in a photoelectrochemical cell (PEC measurement set-up. With platinum as a catalyst, the a-Si:H/a-Si:H based photocathodes exhibit a high photocurrent onset potential of 1.76 V versus the reversible hydrogen electrode (RHE and a photocurrent of 5.3 mA/cm2 at 0 V versus RHE (under halogen lamp illumination. Our results provide evidence that a direct application of thin film silicon based photocathodes fulfills the main thermodynamic requirements to generate hydrogen. Furthermore, the presented approach may provide an efficient and low-cost route to solar hydrogen production.

  6. Measurements of the radiolytic oxidation of aqueous CsI using a sparging apparatus

    Energy Technology Data Exchange (ETDEWEB)

    Ashmore, C.B.; Brown, D.; Sims, H.E. [AEA Technology, Harwell (United Kingdom); Gwyther, J.R. [NE plc Berkeley Technology Centre, Berkeley (United Kingdom)

    1996-12-01

    Radiolytic oxidation is considered to be the main mechanism for the formation of I{sub 2} from aqueous CsI in containment of a water cooled reactor after a LOCA. Despite the amount of study over the last 60 years on the radiation chemistry of iodine there has been no consistent set of experiments spanning a wide enough range of conditions to verify models with confidence. This paper describes results from a set of experiments carried out in order to remedy this deficiency. In this work the rate of evolution of I{sub 2} from sparged irradiated CsI solution labeled with {sup 131}I was measured on-line over a range of conditions. This work involved the measurement of the effects of pH, temperature, O{sub 2} concentration, I{sup -} concentration, phosphate concentration, dose-rate and impurities on the rate of evolution of I{sub 2}. The range of conditions was chosen in order to span as closely as possible conditions expected in a LOCA but also to help to elucidate some of the mechanisms especially at high pH. pH was found to be a very important factor influencing iodine volatility, over the temperature range studied the extent of oxidation reduced with temperature but this was compensated for by the decrease in partition coefficient. Oxygen concentration was more important in solutions not containing phosphate. The fractional oxidation was not particularly dependent on iodide concentration but G{sub I2} was very dependent on [I{sup -}]. There was no effect of added impurities, Fe, Mn, Mo or organics although in separate work silver was found to have a very important effect. During attempts to interpret the data it was found that it was necessary to include the iodine atom as a volatile species with a partition coefficient of 1.9 taken from thermodynamic data. The modelling work is described in a separate paper. (author) 15 figs., 1 tab., 19 refs.

  7. Impact of I/Q imbalance on the performance of two-way CSI-assisted AF relaying

    KAUST Repository

    Qi, Jian

    2013-04-01

    In this paper, we investigate half-duplex two-way dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) relaying in the presence of in-phase and quadrature-phase (I/Q) imbalance. A compensation approach for the I/Q imbalance is proposed, which employs the received signals together with their conjugations to detect the desired signal. We also derive the average symbol error probability of the considered half-duplex two-way dual-hop CSI-assisted AF relaying networks with and without compensation for I/Q imbalance in Rayleigh fading channels. Numerical results are provided and show that the proposed compensation method mitigates the impact of I/Q imbalance to a certain extent. © 2013 IEEE.

  8. Ultraviolet luminescence of CsI and CsCl excited by soft x-ray laser

    Energy Technology Data Exchange (ETDEWEB)

    Jaegle, P.; Sebban, S.; Carillon, A.; Jamelot, G.; Klisnick, A.; Zeitoun, P.; Rus, B.; Nantel, M.; Albert, F.; Ros, D. [Laboratoire de Spectroscopie Atomique et Ionique, Universite Paris-Sud, 91405, Orsay (France)

    1997-03-01

    We present the observation of solid material luminescence excited by soft x-ray laser. The 21.2 nm photons of the soft x-ray laser of the Laboratoire d`Utilisation des Lasers Intenses (Palaiseau, France) have been used to induce ultraviolet luminescence in CsCl and CsI. The laser supplied up to 6{times}10{sup 12} photons in 80 ps. A single laser shot was sufficient to obtain luminescence spectra with very good resolution. In the case of CsI, the use of two illumination conditions, differing by a factor 150 in intensity, showed the collapse of luminescence efficiency for very strong illumination. The quenching effect is discussed in terms of the large increase of crystal excitation mean density, altering the usual process of luminescence centers production. {copyright} {ital 1997 American Institute of Physics.}

  9. Ab-initio calculation study on the formation mechanism of boron-oxygen complexes in c-Si

    International Nuclear Information System (INIS)

    Boron-oxygen (B-O) complex in crystalline silicon (c-Si) solar cells is responsible for the light-induced efficiency degradation of solar cell. However, the formation mechanism of B-O complex is not clear yet. By Ab-initio calculation, it is found that the stagger-type oxygen dimer (O2ist) should be the component of B-O complex, whose movement occurs through its structure reconfiguration at low temperature, instead of its long-distance diffusion. The O2ist can form two stable “latent centers” with the Bs, which are recombination-inactive. The latent centers can be evolved into the metastable recombination centers via their structure transformation in the presence of excess carriers. These results can well explain the formation behaviors of B-O complexes in c-Si

  10. Adaptación del Inventario de Estrategias de Afrontamiento (CSI a la población penitenciaria de Mexico

    Directory of Open Access Journals (Sweden)

    Francisco Javier Rodríguez-Díaz

    2014-01-01

    Full Text Available El objetivo del estudio es adaptar el CSI - Inventario de Estrategias de Afrontamiento - al contexto penitenciario. La muestra - 261 penados, 97% varones (n=253 - del Sistema Postpenitenciario y Atención a Liberados (DSPAL del Estado Jalisco, México. Los instrumentos utilizados: Ficha Penitenciaria de Historia de Vida y el Inventario CSI. Los resultados refieren una estructura de primer orden casi idéntica a la obtenida para la población general, con niveles de consistencia interna satisfactorios, al mismo tiempo que la interpretación de segundo orden no confirma la estructura de segundo y tercer orden. Se discuten las implicaciones de los resultados para intervención penitenciaria.

  11. n-type emitter surface passivation in c-Si solar cells by means of antireflective amorphous silicon carbide layers

    OpenAIRE

    Ferré Tomas, Rafel; Martín García, Isidro; Ortega Villasclaras, Pablo Rafael; Vetter, Michael; Torres, I.; Alcubilla González, Ramón

    2006-01-01

    Emitter saturation current densities (JOe) of phosphorus-diffused planar c-Si solar cell emitters passivated by silicon carbide (SiCx) layers have been determined in a wide sheet resistance range (20-500 Ω/sp). Phosphorus diffusions were performed using solid planar diffusion sources without employing any drive-in step. Stacks of two SiCx layers were deposited by plasma enhanced chemical vapor deposition: first a thin silicon rich layer with excellent passivating properties and th...

  12. Microstructure and Thermal Properties of the GeS2-In2S3-CsI Glasses

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The homogeneous G eS2-In2 S3-Csl glassy samples were prepared by conventional melt-quenching method.When the molar ratio of In2 S3 to CsI remains 1, the non-crystalline region can extend to the composition 0.4 GeS2 - 0.3 In2 S3 - 0.3 CsI.And with the addition of CsI, the glass-forming ability of this serial glass reaches its maximum at the composition 0.8 GeS2 - 0.1 In2 S3 - 0.1 CsI.According to the Raman spectra, the microstructure of these glasses is mainly constituted by [ GeS4 ] and [ InS4-xIx]tetrahedra, which are interconnected by the bridging sulfur atoms; meanwhile, the ethane- liked structural units [ S3 Ge- GeS3 ] can be formed because of the lacking of sulfur; Cs+ ion, which is ndded from CsI, exists as the nearest neighbor of I-ion in the glassy network.

  13. Influence of boron vapor on transport behavior of deposited CsI during heating test simulating a BWR severe accident condition

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Isamu, E-mail: sato.isamu@jaea.go.jp; Onishi, Takashi; Tanaka, Kosuke; Iwasaki, Maho; Koyama, Shin-ichi

    2015-06-15

    In order to evaluate influence of B on the release and transport of Cs and I during severe accidents, basic experiments have been performed on the interaction between deposited Cs/I compounds and vapor/aerosol B compounds. CsI and B{sub 2}O{sub 3} were utilized as a Cs/I compound and a B compound, respectively. Deposited CsI on the thermal gradient tube (TGT) at temperatures ranging from 423 K to 1023 K was reacted with vapor/aerosol B{sub 2}O{sub 3}, and then observed how it changed Cs/I deposition profiles. As a result, vapor/aerosol B{sub 2}O{sub 3} stripped a portion of deposited CsI within a temperature range from 830 K to 920 K to make gaseous CsBO{sub 2} and I{sub 2}. In addition, gaseous I{sub 2} was re-deposited at a temperature range from 530 K to 740 K, while CsBO{sub 2} travelled through the sampling tubes and filters without deposition. It is evident that B enables Cs compounds such as CsBO{sub 2} to transport Cs to the colder regions.

  14. Delay analysis of a point-to-multipoint spectrum sharing network with CSI based power allocation

    KAUST Repository

    Khan, Fahd Ahmed

    2012-10-01

    In this paper, we analyse the delay performance of a point-to-multipoint cognitive radio network which is sharing the spectrum with a point-to-multipoint primary network. The channel is assumed to be independent but not identically distributed and has Nakagami-m fading. A constraint on the peak transmit power of the secondary user transmitter (SU-Tx) is also considered in addition to the peak interference power constraint. Based on the constraints, a power allocation scheme which requires knowledge of the instantaneous channel state information (CSI) of the interference links is derived. The SU-Tx is assumed to be equipped with a buffer and is modelled using the M/G/1 queueing model. Closed form expressions for the probability distribution function (PDF) and cumulative distribution function (CDF) of the packet transmission time is derived. Using the PDF, the expressions for the moments of transmission time are obtained. In addition, using the moments, the expressions for the performance measures such as the total average waiting time of packets and the average number of packets waiting in the buffer of the SU-Tx are also obtained. Numerical simulations corroborate the theoretical results. © 2012 IEEE.

  15. Improved radiation resistant properties of electron irradiated c-Si solar cells

    Science.gov (United States)

    Ali, Khuram; Khan, Sohail A.; MatJafri, M. Z.

    2016-08-01

    This work investigates the radiation tolerance of c-Si solar cells under electron energy of 9 MeV with fluence of 5.09×1016 cm-2. The solar cells were fabricated and characterized before and after electron irradiation through current-voltage (I-V), capacitance-voltage (C-V), and frequency dependent conductance (Gp) measurements. The results revealed that all the output parameters such as short circuit current (Isc), open circuit voltage (Voc), series resistance (Rs), and efficiency (η) were degraded after electron irradiation. Capacitance-Voltage measurements show that there is a slight decrease in the base carrier concentration (ND), while a small increase in depletion layer width (WD) was due to an increase in the base carrier concentration. Enhancements in the density of interface states (Nss), and trap time constant (τ) have been observed after electron irradiation. The results has revealed that back surface field (BSF) solar cell with front surface passivation (FSP) presented lowest efficiency degradation ratio of 11.3% as compared to 15.3% of the solar cell without FSP. The subsequent annealing of irradiated Si solar cell devices revealed that the Si solar cell with FSP demonstrated high efficiency recovery ratio of 94% as compared to non-FSP solar cell.

  16. Minimax robust relay selection based on uncertain long-term CSI

    KAUST Repository

    Nisar, Muhammad Danish

    2014-02-01

    Cooperative communications via multiple relay nodes is known to provide the benefits of increase diversity and coverage. Simultaneous transmission via multiple relays, however, requires strong coordination between nodes either in terms of slot-based transmission or distributed space-time (ST) code implementation. Dynamically selecting a single best relay out of multiple relays and then using it alone for cooperative transmission alleviates the need for this strong coordination while still reaping the benefits of increased diversity and coverage. In this paper, we consider the design of relay selection (RS) under an imperfect knowledge of long-term channel state information (CSI) at the relay nodes, and we pursue minimax optimization to arrive at a robust RS approach that promises the best guarantee on the worst-case end-to-end signal-to-noise ratio (SNR). We provide some intuitive examples and extensive simulation results, not only in terms of worst-case SNR performance but also in terms of average bit-error-rate (BER) performance, to demonstrate the benefits of the proposed minimax robust RS scheme. © 2013 IEEE.

  17. Law and Justice on TV. The Wire vs. CSI and Ally McBeal

    Directory of Open Access Journals (Sweden)

    Gianluigi Rossini

    2012-04-01

    Full Text Available The aim of this paper is to analyse the ways in which law is represented in the celebrated TV series The Wire, broadcasted in United States between 2002 and 2008. The analysis focuses particularly on the thematization of the relationship between the concept of law and that of justice, that is between 'positive law' and 'natural law'. This theme is pursued in the context of American television series of great success such as CSI: Crime Scene Investigation (CBS, 2000- and Ally McBeal (Fox, 1997-2002 . The comparison highlights the way in which in The Wire the terms of the problem are completely eroded through the representation of a sort of 'disappearance of justice'. In this series the natural law becomes insignificant both because it is no more the point of reference of the actions activated by the institutions, and because an informed, in-depth and not prejudicial gaze on the social reality of the contemporary metropolis brings into question the very idea of a justice absolute and distanced from the contingent circumstances.

  18. Molybdenum Disulfide as a Protection Layer and Catalyst for Gallium Indium Phosphide Solar Water Splitting Photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Britto, Reuben J.; Benck, Jesse D.; Young, James L.; Hahn, Christopher; Deutsch, Todd G.; Jaramillo, Thomas F.

    2016-06-02

    Gallium indium phosphide (GaInP2) is a semiconductor with promising optical and electronic properties for solar water splitting, but its surface stability is problematic as it undergoes significant chemical and electrochemical corrosion in aqueous electrolytes. Molybdenum disulfide (MoS2) nanomaterials are promising to both protect GaInP2 and to improve catalysis since MoS2 is resistant to corrosion and also possesses high activity for the hydrogen evolution reaction (HER). In this work, we demonstrate that GaInP2 photocathodes coated with thin MoS2 surface protecting layers exhibit excellent activity and stability for solar hydrogen production, with no loss in performance (photocurrent onset potential, fill factor, and light limited current density) after 60 hours of operation. This represents a five-hundred fold increase in stability compared to bare p-GaInP2 samples tested in identical conditions.

  19. Emittance Studies of the BNL/SLAC/UCLA 1.6 Cell Photocathode RF Gun

    Energy Technology Data Exchange (ETDEWEB)

    Palmer, D.T.; /SLAC; Wang, X.J.; /Brookhaven; Miller, R.H.; /SLAC; Babzien, M.; Ben-Zvi, I.; /Brookhaven; Pellegrini, C.; /UCLA; Sheehan, J.; Skaritka, J.; /Brookhaven; Winick, H.; /SLAC; Woodle, M.; Yakimenko, V.; /Brookhaven

    2011-09-09

    The symmetrized 1.6 cell S-band photocathode gun developed by the BNL/SLAC/UCLA collaboration is in operation at the Brookhaven Accelerator Test Facility (ATF). A novel emittance compensation solenoid magnet has also been designed, built and is in operation at the ATF. These two subsystems form an emittance compensated photoinjector used for beam dynamics, advanced acceleration and free electron laser experiments at the ATF. The highest acceleration field achieved on the copper cathode is 150 MV/m, and the guns normal operating field is 130 MV/m. The maximum rf pulse length is 3 {mu}s. The transverse emittance of the photoelectron beam were measured for various injection parameters. The 1 nC emittance results are presented along with electron bunch length measurements that indicated that at above the 400 pC, space charge bunch lengthening is occurring. The thermal emittance, {epsilon}{sub o}, of the copper cathode has been measured.

  20. Enhanced Photocatalytic Hydrogen Production By Surface Modification of p-Gap Photocathodes

    DEFF Research Database (Denmark)

    Malizia, Mauro; Seger, Brian; Chorkendorff, Ib;

    2014-01-01

    Photocatalytic water splitting is considered one of the most promising approaches for reducing both the reliance on fossil fuels and the emission of greenhouse gases such CO2 in the atmosphere. A working photocatalytic water splitting device must provide the voltage required for splitting water......-circuit voltage consists of forming a p-n heterojunction on GaP. We deposit different n-type metal oxides (TiO2, Nb2O5, ...) thus forming an heterojunction which significantly enhances charge separation upon light irradiation by forming a built-in potential at the junction interface. This built-in potential...... effectively drives electrons towards the surface of the photoelectrode with the hydrogen evolution reaction occurring at more positive potential compared to the bare p-GaP under the same operating conditions. The observed open-circuit voltage for the modified photocathodes is +0.70 V RHE, representing an...

  1. Generation of quasiequally spaced ultrashort microbunches in a photocathode rf gun

    International Nuclear Information System (INIS)

    A photocathode rf gun can generate trains of THz subpicosecond electron bunches by illuminating the cathode with trains of laser pulses, but it suffers from the increasing charge in the beam. The THz structure blurs and tends to disappear when the longitudinal space charge forces begin to play a significant role in the beam evolution. In this paper, we propose a scheme to restrain the space charge forces by expanding the transverse size of the laser pulses to reduce the charge density and adopting a multicell gun to increase the beam energy. Thus, quasiequally spaced ultrashort microbunches with relatively high charges can be generated according to our studies. Postacceleration can be used to freeze the longitudinal phase space dynamics. The proposed scheme is in principle able to generate intense multi-color narrow-band THz radiation and offers a promising way towards the tunable intense narrow-band THz sources

  2. Influence of wet chemical cleaning on quantum efficiency of GaN photocathode

    Institute of Scientific and Technical Information of China (English)

    Wang Xiao-Hui; Gao Pin; Wang Hong-Gang; Li Biao; Chang Ben-Kang

    2013-01-01

    GaN samples 1-3 are cleaned by a 2:2:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%) to de-ionized water; hydrochloric acid (37%); or a 4:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%).The samples are activated by Cs/O after the same annealing process.X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows:sample 1 has the largest proportion of Ga,N,and O among the three samples,while its C content is the lowest.After activation the quantum efficiency curves show sample 1 has the best photocathode performance.We think the wet chemical cleaning method is a process which will mainly remove C contamination.

  3. A high-charge and short-pulse RF photocathode gun for wake-field acceleration

    Science.gov (United States)

    Gai, W.; Li, X.; Conde, M.; Power, J.; Schoessow, P.

    1998-02-01

    In this paper we present a design report on 1-1/2 cell, L-Band RF photocathode gun which is capable of generating and accelerating electron beams with peak currents >10 kA. We address several critical issues of high-current RF photoinjectors such as longitudinal space charge effect, and transverse emittance growth. Unlike conventional short electron pulse generation, this design does not require magnetic pulse compression. Based on numerical simulations using SUPERFISH and PARMELA, this design will produce 100 nC beam at 18 MeV with r.m.s. bunch length 1.25 mm and normalized transverse emittance 108 mm mrad. Applications of this source beam for wake-field acceleration are also discussed.

  4. Development of a 3.5 cell S-band photocathode RF electron gun

    International Nuclear Information System (INIS)

    We have been developing a photocathode rf electron gun. Last year, we succeeded in operating a new design 1.6 cell rf gun cavity with large mode separation of 8.6 MHz. Encouraging by this success, we designed a 3.5 cell rf gun cavity and start manufacturing. It will produce a high quality electron beam with energy of more than 10 MeV. In order to optimize the operating conditions, we performed beam tracing simulation studies using SUPERFISH and PARMELA. The design of 3.5 cell rf gun cavity, results of simulation studies and current status of 3.5 cell cavity manufacturing will be presented at the conference. (author)

  5. Development of photocathode rf electron gun for ultra-short bunch generation

    International Nuclear Information System (INIS)

    We have been developing an S-band photocathode rf electron gun at Waseda University. Our rf-gun cavity was firstly designed by BNL and then, modified by our group. In this paper, we will introduce a newly designed rf-gun cavity with energy chirping cell (ECC). To generate an energy chirped electron bunch, we attached extra-cell for 1.6cell rf-gun cavity. Cavity design was done by Superfish and particle tracing by GPT/PARMELA. By optimizing the chirping cell, we observed linear chirped electron bunch and it can be compressed by the velocity bunching through the 2.3m drift space down to 100fsec. This cavity was already manufactured on the collaboration with KEK. In this conference, the design of ECC-RF-Gun, the results of low level test and plan of beam test will be presented. (author)

  6. A comprehensive comparison of dye-sensitized NiO photocathodes for solar energy conversion.

    Science.gov (United States)

    Wood, Christopher J; Summers, Gareth H; Clark, Charlotte A; Kaeffer, Nicolas; Braeutigam, Maximilian; Carbone, Lea Roberta; D'Amario, Luca; Fan, Ke; Farré, Yoann; Narbey, Stéphanie; Oswald, Frédéric; Stevens, Lee A; Parmenter, Christopher D J; Fay, Michael W; La Torre, Alessandro; Snape, Colin E; Dietzek, Benjamin; Dini, Danilo; Hammarström, Leif; Pellegrin, Yann; Odobel, Fabrice; Sun, Licheng; Artero, Vincent; Gibson, Elizabeth A

    2016-04-20

    We investigated a range of different mesoporous NiO electrodes prepared by different research groups and private firms in Europe to determine the parameters which influence good quality photoelectrochemical devices. This benchmarking study aims to solve some of the discrepancies in the literature regarding the performance of p-DSCs due to differences in the quality of the device fabrication. The information obtained will lay the foundation for future photocatalytic systems based on sensitized NiO so that new dyes and catalysts can be tested with a standardized material. The textural and electrochemical properties of the semiconducting material are key to the performance of photocathodes. We found that both commercial and non-commercial NiO gave promising solar cell and water-splitting devices. The NiO samples which had the two highest solar cell efficiency (0.145% and 0.089%) also gave the best overall theoretical H2 conversion. PMID:26734947

  7. A new two-step tuning procedure for a photocathode gun

    International Nuclear Information System (INIS)

    An important aspect of the development of multi-cell RF accelerating structures is tuning the resonant frequency f of the operating mode, field balance eb, and waveguide to cavity coupling coefficient β to the desired values. Earlier theoretical analyses have not been able to predict all three parameters simultaneously for a coupled-cavity system. We have developed a generalized circuit analysis to predict f, eb, and β of a coupled structure, based on the RF properties of the individual, uncoupled, cells. This has been used to develop a simplified two-step tuning procedure to tune a BNL/SLAC/UCLA type 1.6 cell S-band photocathode gun by varying RF properties of individual half and full cells, which are easily measurable. This procedure has been validated by tuning two true-to-scale prototypes made of aluminum and ETP copper to the desired values of the RF parameters

  8. The quantum efficiency of dispenser photocathodes: Comparison of theory to experiment

    Science.gov (United States)

    Jensen, Kevin L.; Feldman, Donald W.; O'Shea, Patrick G.

    2004-11-01

    The quantum efficiency (QE) characteristics of commercially available dispenser cathodes were measured, giving QEs of (for Scandate) 6.5×10-5, 2.0×10-4, and 8.0×10-4, and (for M-type) 3.0×10-4, 1.4×10-3, and 2.6×10-3, for wavelengths of 532, 355, and 266nm, respectively, corresponding to harmonics of an Nd:YAG laser. A time-dependent photoemission model was developed to analyze the data, as well as dispenser and metal photocathode data in the literature, and quantitatively good agreement is found, demonstrating the utility of the code as a predictive estimator of performance.

  9. Highly polarized and high quantum efficiency electron source using transmission-type photocathode

    International Nuclear Information System (INIS)

    Recently, we developed transmission-type spin polarized photocathodes (PCs). In the development, a commercially available GaP wafer with high Zn doping of 1.4 x 1017 cm-3 was employed instead of a GaAs substrate because that is transparent for 780-nm excitation laser light. In the early phase of the development, both of the electron spin polarization and quantum efficiency were relatively lower than conventional reflection-type PCs. Nowadays, the electron spin polarization of ∼90% and quantum efficiency of 0.4% was already achieved simultaneously using the transmission PC with GaAs-GaAsP strained superlattice layers. We are making further R and D to improve it's quantum efficiency and further experiments such as generation of short pulse beam are scheduled. (author)

  10. Simulation study on ultrashort pulse electron generation in laser photocathode RF gun linac

    International Nuclear Information System (INIS)

    A new S-band femtosecond electron linear accelerator, which was constructed with a laser driven photocathode RF gun, a linear accelerator (linac) and a magnetic pulse compressor, was developed in Osaka University for the study of radiation-induced ultrafast physical and chemical reactions in femtosecond time regions. In order to generate the ultrashort pulse electrons, we simulated the electron generation in the RF gun with a picosecond Nd: YLF laser light by PARMELA code with space-charge effects. The energy modulation of the electron pulse in the linac was also calculated with the optimum of the RF phase. The pulse compression in the magnetic pulse compressor was simulated by Trace-3D code. A few tens femtosecond electron pulse was obtained by optimizing the magnetic fields in the magnetic pulse compressor. (author)

  11. A new design of large area MCP-PMT for the next generation neutrino experiment

    International Nuclear Information System (INIS)

    This manuscript discusses a new design of large area MCP-PMT for the next generation neutrino experiments. The main motivation of the design is to improve the quantum efficiency (photo detection efficiency) of the PMT. Two sets of small MCP units, the transmission photocathode coated on the front hemisphere and the reflection photocathode coated on the rear hemisphere are assembled in the same glass envelope to form nearly 4π viewing angle to enhance the efficiency of the photoelectron detection. The photoelectrons from the 4π photocathode are collected and amplified by two sets of MCP units. Our goal is eventually to produce 20 in. diameter PMT following such an approach. We will report preliminary results of our ptoelectronic simulation and the results of a 5 in. diameter prototype PMT. Future plans and prospects are discussed at the end.

  12. Y thin films by ultrashort pulsed laser deposition for photocathode application

    Energy Technology Data Exchange (ETDEWEB)

    Lorusso, A., E-mail: antonella.lorusso@le.infn.it [Mathematic and Physics Department, University of Salento, Via Arnesano, 73100 Lecce (Italy); National Institute of Nuclear Physics, Via Arnesano, 73100 Lecce (Italy); De Giorgi, M.L. [Mathematic and Physics Department, University of Salento, Via Arnesano, 73100 Lecce (Italy); National Institute of Nuclear Physics, Via Arnesano, 73100 Lecce (Italy); Fotakis, C. [Institute of Electronic Structure and Laser (IELS), Foundation of Research and Technology-Hellas (FORTH) P.O. Box 1385, Vassilika Vouton, GR-711 10 Heraklion (Greece); Maiolo, B.; Miglietta, P. [Mathematic and Physics Department, University of Salento, Via Arnesano, 73100 Lecce (Italy); Papadopoulou, E.L. [Institute of Electronic Structure and Laser (IELS), Foundation of Research and Technology-Hellas (FORTH) P.O. Box 1385, Vassilika Vouton, GR-711 10 Heraklion (Greece); Perrone, A. [Mathematic and Physics Department, University of Salento, Via Arnesano, 73100 Lecce (Italy); National Institute of Nuclear Physics, Via Arnesano, 73100 Lecce (Italy)

    2012-09-01

    Highlights: Black-Right-Pointing-Pointer We deposit Y thin films by pulsed laser ablation with 0.5 and 5 ps pulse durations. Black-Right-Pointing-Pointer Y thin films deposition is interesting for photocathode application. Black-Right-Pointing-Pointer Y thin films are well adherent to the substrate with a high abundance of nano-particles on the film surface. Black-Right-Pointing-Pointer Nano-particles abundance decreases as a function of the laser fluence. - Abstract: In this work, the deposition of Y thin films by laser beams with 0.5 ps and 5 ps pulse durations at different laser fluences (1.2-6.4 J/cm{sup 2}) is reported. The morphology of the deposited films and of the ablated target surface is investigated by scanning electron microscopy analyses. The present results show that the films, well adherent to the substrates, are characterized by a high abundance of sub-micrometric particulates with average size less than 0.3 {mu}m, whose density decreases with increasing laser fluence. The formation of columnar structures observed on the target surface seems to be responsible of the poor film homogeneity. Acceptable deposition rate in the range of 0.08-0.16 Angstrom-Sign /pulse with 5 ps pulse duration is found; on the contrary with 0.5 ps pulse duration, it is not possible to get information on deposition rate as a function of the laser fluence due to the high non-uniformity of the films. A comparison with the results previously obtained in ns regime is presented and discussed. The achievements of our investigation will be useful to optimize the synthesis of photocathodes based on Y films for the production of bright electron beams in radio-frequency photoinjectors.

  13. Interrelationship between long-wave current sensitivity and thermionic current of Ag-O-Cs photocathode and problems of its tolerable physical model

    Science.gov (United States)

    Rabinovich, A. I.; Pakhomov, M. T.

    1993-01-01

    Interrelation between current sensitivity at (lambda) >= 1.06 micrometers and thermoemission current (calculate data and their correlation with experimental results) is used as an indicator of choice between the donor and acceptor models of Ag-O-Cs-photocathode.

  14. Quantum efficiency of transmission-mode AlxGa1-xAs/GaAs photocathodes with graded-composition and exponential-doping structure

    Science.gov (United States)

    Feng, Cheng; Zhang, Yijun; Qian, Yunsheng; Xu, Yuan; Liu, Xinxin; Jiao, Gangcheng

    2016-06-01

    A transmission-mode AlxGa1-xAs/GaAs photocathode with the combination of composition-graded AlxGa1-xAs window layer and exponential-doping GaAs emission layer is developed to maximize the cathode performance. The theoretical quantum efficiency model with this complex structure containing twofold built-in electric fields is deduced by solving the one dimensional continuity equations combined with the three-step model. By comparison of spectral characteristics of photocathodes with different composition and doping structures, and through analysis of cathode structure parameters, it is found that the twofold built-in electric fields can effectively improve photoemission performance of AlxGa1-xAs/GaAs photocathode, which is related to Al proportion variation range and thicknesses of window layer and emission layer. The quantum efficiency model would provide theoretical guidance for better design of transmission-mode graded bandgap photocathodes.

  15. Low temperature characteristic of ITO/SiO x /c-Si heterojunction solar cell

    Science.gov (United States)

    Du, H. W.; Yang, J.; Li, Y.; Gao, M.; Chen, S. M.; Yu, Z. S.; Xu, F.; Ma, Z. Q.

    2015-09-01

    Based on the temperature-dependent measurements and the numerical calculation, the temperature response of the photovoltaic parameters for a ITO/SiO x /c-Si heterojunction solar cell have been investigated in the ascending sorting of 10-300 K. Under unique energy concentrated photon irradiation with the wavelength of 405 nm and power density of 667 mW cm-2, it was found that the short-circuit current (I SC) was nonlinearly increased and the open-circuit voltage (V OC) decreased with temperature. The good passivation of the ITO/c-Si interface by a concomitant SiO x buffer layer leads to the rare recombination of carriers in the intermediate region. The inversion layer model indicated that the band gap of c-silicon was narrowed and the Fermi level of n-type silicon (E\\text{F}n ) tended to that of the intrinsic Fermi level (E\\text{F}i ) (in the middle of band gap) with the increase of the temperature, which lessened the built-in voltage (V D) and thus the V OC. However, the reduction by 90% of V OC is attributed to the shift of E\\text{F}n in c-silicon rather than the energy band narrowing. Through the analysis of the current-voltage relationship and the data fitting, we infer that the series resistance (R s) is not responsible for the increase of I SC, but the absorption coefficient and the depletion-width of c-silicon are the causes of the enhancing I SC. Mostly, the interaction of the photon-generated excess ‘cold hole’ and the acoustic phonon in n-Si would influence the variation of I ph or I SC with temperature.

  16. Emitter formation using laser doping technique on n- and p-type c-Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    López, G., E-mail: gema.lopez@upc.edu; Ortega, P.; Colina, M.; Voz, C.; Martín, I.; Morales-Vilches, A.; Orpella, A.; Alcubilla, R.

    2015-05-01

    Highlights: • We use laser doping technique to create highly-doped regions. • Dielectric layers are used as both passivating layer and dopant source. • The high quality of the junctions makes laser doping technique using dielectric layers as dopant source suitable for solar cells applications. - Abstract: In this work laser doping technique is used to create highly-doped regions defined in a point-like structure to form n+/p and p+/n junctions applying a pulsed Nd-YAG 1064 nm laser in the nanosecond regime. In particular, phosphorous-doped silicon carbide stacks (a-SiC{sub x}/a-Si:H (n-type)) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and aluminum oxide (Al{sub 2}O{sub 3}) layers deposited by atomic layer deposition (ALD) on 2 ± 0.5 Ω cm p- and n-type FZ c-Si substrates respectively are used as dopant sources. Laser power and number of pulses per spot are explored to obtain the optimal electrical behavior of the formed junctions. To assess the quality of the p+ and n+ regions, the junctions are electrically contacted and characterized by means of dark J–V measurements. Additionally, a diluted HF treatment previous to front metallization has been explored in order to know its impact on the junction quality. The results show that fine tuning of the energy pulse is critical while the number of pulses has minor effect. In general the different HF treatments have no impact in the diode electrical behavior except for an increase of the leakage current in n+/p junctions. The high electrical quality of the junctions makes laser doping, using dielectric layers as dopant source, suitable for solar cell applications. Particularly, a potential open circuit voltage of 0.64 V (1 sun) is expected for a finished solar cell.

  17. Measurement of the tradeoff between intrinsic emittance and quantum efficiency from a NaKSb photocathode near threshold

    International Nuclear Information System (INIS)

    We measure the tradeoff between the quantum efficiency and intrinsic emittance from a NaKSb photocathode at three increasing wavelengths (635, 650, and 690 nm) at or below the energy of the bandgap plus the electron affinity, hν≤Eg+Ea. These measurements were performed using a high voltage dc gun for varied photocathode surface fields of 1.4−4.4 MV/m. Measurements of intrinsic emittance are performed using two different methods and were found to agree. At the longest wavelength available, 690 nm, the intrinsic emittance was 0.26 μm/mm-rms with a quantum efficiency of ∼10−4. The suitability of NaKSb emitting at threshold for various low emittance applications is discussed

  18. Measurement of the tradeoff between intrinsic emittance and quantum efficiency from a NaKSb photocathode near threshold

    Energy Technology Data Exchange (ETDEWEB)

    Maxson, Jared, E-mail: jmm586@cornell.edu; Cultrera, Luca; Gulliford, Colwyn; Bazarov, Ivan [Cornell Laboratory for Accelerator-Based Sciences and Education, Cornell University, Ithaca, New York 14853 (United States)

    2015-06-08

    We measure the tradeoff between the quantum efficiency and intrinsic emittance from a NaKSb photocathode at three increasing wavelengths (635, 650, and 690 nm) at or below the energy of the bandgap plus the electron affinity, hν≤E{sub g}+E{sub a}. These measurements were performed using a high voltage dc gun for varied photocathode surface fields of 1.4−4.4 MV/m. Measurements of intrinsic emittance are performed using two different methods and were found to agree. At the longest wavelength available, 690 nm, the intrinsic emittance was 0.26 μm/mm-rms with a quantum efficiency of ∼10{sup −4}. The suitability of NaKSb emitting at threshold for various low emittance applications is discussed.

  19. Observation of relaxation time of surface charge limit for InGaN photocathodes with negative electron affinity

    Science.gov (United States)

    Sato, Daiki; Nishitani, Tomohiro; Honda, Yoshio; Amano, Hiroshi

    2016-05-01

    A thin p-type InGaN with a negative electron affinity (NEA) surface was used to measure the relaxation time of a surface charge limit (SCL) by irradiating rectangular laser beam pulses at changing time interval. The p-type InGaN film was grown by metal organic vapor phase epitaxy and the NEA activation was performed after the sample was heat cleaned. 13 nC per pulse with 10 ms width was obtained from the InGaN photocathode. The current decreased exponentially from the beginning of the pulse. The initial current value after the laser irradiation decreased with the time interval. As a result, the SCL relaxation time was estimated through the InGaN photocathode measurements at 100 ms.

  20. SU-E-I-11: Cascaded Linear System Model for Columnar CsI Flat Panel Imagers with Depth Dependent Gain and Blur

    Energy Technology Data Exchange (ETDEWEB)

    Peng, B; Lubinsky, A; Zheng, H; Zhao, W [Stony Brook University, Stony Brook, NY (United States); Teymurazyan, A [Lakehead University, Thunder Bay, Ontario (Canada)

    2014-06-01

    Purpose: To implement a depth dependent gain and blur cascaded linear system model (CLSM) for optimizing columnar structured CsI indirect conversion flat panel imager (FPI) for advanced imaging applications. Methods: For experimental validation, depth dependent escape efficiency, e(z), was extracted from PHS measurement of different CsI scintillators (thickness, substrate and light output). The inherent MTF and DQE of CsI was measured using high resolution CMOS sensor. For CLSM, e(z) and the depth dependent MTF(f,z), were estimated using Monte Carlo simulation (Geant4) of optical photon transport through columnar CsI. Previous work showed that Monte Carlo simulation for CsI was hindered by the non-ideality of its columnar structure. In the present work we allowed variation in columnar width with depth, and assumed diffusive reflective backing and columns. Monte Carlo simulation was performed using an optical point source placed at different depth of the CsI layer, from which MTF(z,f) and e(z) were computed. The resulting e(z) with excellent matching with experimental measurements were then applied to the CLSM, Monte Carlo simulation was repeated until the modeled MTF, DQE(f) also match experimental measurement. Results: For a 150 micron FOS HL type CsI, e(z) varies between 0.56 to 0.45, and the MTF at 14 cycles/mm varies between 62.1% to 3.9%, from the front to the back of the scintillator. The overall MTF and DQE(f) at all frequencies are in excellent agreement with experimental measurements at all frequencies. Conclusion: We have developed a CLSM for columnar CsI scintillators with depth dependent gain and MTF, which were estimated from Monte Carlo simulation with novel optical simulation settings. Preliminary results showed excellent agreement between simulation results and experimental measurements. Future work is aimed at extending this approach to optimize CsI screen optic design and sensor structure for achieving higher DQE(f) in cone-beam CT, which uses

  1. Study of pure and Pb{sup 2+} ions doped CsI crystals under alpha particles excitations

    Energy Technology Data Exchange (ETDEWEB)

    Pereira, Maria da Conceicao Costa; Madi Filho, Tufic; Hamada, Margarida Mizue, E-mail: macoper@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2011-07-01

    Scintillation crystals have been used in various fields, such as high energy physics, nuclear instrumentation, radiation measurements, medical imaging, nuclear tomography, astrophysics and other fields of science and engineering. For these applications, the development of good performance scintillation crystals is required. Scintillation crystals based on cesium iodide (CsI) matrix are matters with relatively low hygroscope, easy handling and low cost, characteristics that favor their use as radiation detectors. In this work, pure CsI crystal and lead doped CsI crystals were grown using the Bridgman vertical technique. The concentration of the lead doping element (Pb) was studied in the range of 10{sup -2} M to 5x10{sup -4} M. The distribution of the doping element in the crystalline volume was determined by flame atomic absorption. The CsI:Pb crystal with nominal concentration of 10{sup -3} M was cut into 14 slices of 6 mm. The results show a higher concentration at the top of the crystal with a decrease in the initial phase of growth. The dopant concentration of Pb showed good uniformity from the slice 2 to the slice 12: the region is, therefore, suitable for use as radiation detector. The luminescence emission of these crystals were measured. A predominant luminescence band near 450 nm and a single broad band around 320 nm were found with the addition of the Pb{sup 2+} ions. Analyses were carried out to evaluate the developed scintillators, concerning alpha particles. The resolution of 5.6% was obtained for the CsI:Pb 5x10{sup -4} M crystal, when excited with alpha particles from a {sup 241}Am source, with energy of 5.54 MeV. (author)

  2. Review and present status of preparation of thin layer lead photocathodes for e- injectors of superconducting RF linacs

    Science.gov (United States)

    Lorkiewicz, Jerzy; Nietubyc, Robert; Sekutowicz, Jacek; Barlak, Marek; Kostin, Denis; Kosinska, Anna; Barday, Roman; Xiang, Rong; Mirowski, Robert; Grabowski, Wojciech; Witkowski, Jan

    2015-09-01

    Results are reported on using evaporation and UHV arc lead deposition to create thin-layer superconducting Pb photocathodes on niobium wall of electron gun. Evaporated photocathodes were prepared and tested for the first time in 2014. A complete XFEL-type photo-injector with an evaporated photocathode underwent successful quality check at DESY - an acceptable working point was reached. On the other hand poor adhesion to niobium proved to be the most serious shortcoming of the evaporated Pb layers. UHV arc deposition seems to be much more promising in this context as it allows energetic coating. Filtered arc coating lead to creation of uniform, 2 μm thick lead layers with casual spherical extrusions which enhance locally electric field and leads to high dark current. Conditioning in electric field is needed to reduce the field emission effects from these layers to acceptably low value. Using non-filtered UHV lead deposition enabled fast coating up to a thickness above 10 μm. Pb films obtained in this way require further post-processing in pulsed plasma ion beams in a rod plasma injector. In order to reach a sufficiently planar film surface the pulsed heat flow through a lead layer on niobium was modeled and computed.

  3. Cs(I) transport studies employing Calix-crown-6 ligands dissolved in phenyl trifluoro methyl sulphone

    International Nuclear Information System (INIS)

    Cs(I) transport was investigated from acidic feeds employing flat sheet supported liquid membranes containing several calix-crown-6 ligands, viz., with calix(4)arene-bis-18-crown-6 (CC), calix(4)arene-bis-1,2-benzo-crown-6 (CBC), calix(4)arene-bis-2,3-naphtho-crown-6 (CNC), (bis-octyloxy)calix(4)arene-mono-crown-6 (CMC) dissolved in Phenyl Trifluoro Methyl Sulphone (PTMS). The transport of the metal ion followed the trend: CBC ∼ CC > CNC > CMC. Co-transport of nitric acid was found to affect the metal ion transport rates at higher feed acidities. (author)

  4. 如何看"CSI"诠释"顾客满意度指数"的几个概念

    Institute of Scientific and Technical Information of China (English)

    良言

    2002-01-01

    @@ 顾客满意度指数的产生 "顾客满意度指数"(Customer Satisfaction Index,简称CSI),是市场经济发展的产物.在市场经济条件下,产品和服务质量是由顾客来评价的,就是由"顾客对其要求已被满足的程度的感受"即"顾客满意"与否决定的.

  5. Measurement of the quenching and channeling effects in a CsI crystal used for a WIMP search

    CERN Document Server

    Lee, J H; Seong, I S; Kim, B H; Kim, J H; Li, J; Park, J W; Lee, J K; Kim, K W; Bhang, H; Kim, S C; Choi, Seonho; Choi, J H; Joo, H W; Lee, S J; Olsen, S L; Myung, S S; Kim, S K; Kim, Y D; Kang, W G; So, J H; Kim, H J; Lee, H S; Hahn, I S; Leonard, D S; Li, Y J; Yue, Q; Li, X R

    2015-01-01

    We have studied channeling effects in a Cesium Iodide (CsI) crystal that is similar in composition to the ones being used in a search for Weakly Interacting Massive Particles (WIMPs) dark matter candidates, and measured its energy-dependent quenching factor, the relative scintillation yield for electron and nuclear recoils. The experimental results are reproduced with a GEANT4 simulation that includes a model of the scintillation efficiency as a function of electronic stopping power. We present the measured and simulated quenching factors and the estimated effects of channeling.

  6. Measurement of the quenching and channeling effects in a CsI crystal used for a WIMP search

    International Nuclear Information System (INIS)

    We have studied channeling effects in a cesium iodide (CsI) crystal that is similar in composition to the ones being used in a search for Weakly Interacting Massive Particles (WIMPs) dark matter candidates, and measured its energy-dependent quenching factor, the relative scintillation yield for electron and nuclear recoils. The experimental results are reproduced with a GEANT4 simulation that includes a model of the scintillation efficiency as a function of electronic stopping power. We present the measured and simulated quenching factors and the estimated effects of channeling

  7. Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions

    OpenAIRE

    Chih-Hsien Cheng; An-Jye Tzou; Jung-Hung Chang; Yu-Chieh Chi; Yung-Hsiang Lin; Min-Hsiung Shih; Chao-Kuei Lee; Chih-I Wu; Hao-Chung Kuo; Chun-Yen Chang; Gong-Ru Lin

    2016-01-01

    The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1−x) buffer is demonstrated. The a-SixC1−x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1−x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when...

  8. Scintillation light simulation in big-sized BaF$_{2}$ and pure CsI crystals

    CERN Document Server

    Usubov, Zafar

    2016-01-01

    We have investigated scintillation light distribution in BaF$_{2}$ and pure CsI crystals with dimensions 3x3x20 cm$^{3}$ using the Geant4 toolkit. The diffuse wrapping material is selected as coating for the crystals. The simulated cosmic muons and 105 MeV electrons are used as beam particles. The optical attenuation along the crystals is explored with the simulation data. We have demonstrated the impact of the crystal surface finish on the light distribution at the crystal end, optical photon arrival time, incidence angle distributions, and optical attenuation for the studied crystals.

  9. Detection efficiency study of CdWO4, CsI (Tl) and PbWO4 for 9 MeV industrial CT

    International Nuclear Information System (INIS)

    To find out the more applicable scintillation crystal for 9 MeV accelerator industrial CT system, experiments were carried out with such scintillators as CdWO4, CsI (Tl), PbWO4. The detection system was set up with CCD camera, collimator and scintillator. Detection counts of 25 mm to 45 mm CsI (Tl), CdWO4 and PbWO4 were taken under the same experiment conditions. After repetitious measurement, the diagram of detection efficiency to scintillator length was done. The result turns out that detection efficiency varies with different scintillation crystals. When upwrapped in reflector film, 35 mm length CsI (Tl) gets the best detection accounts; While wrapped in reflector film, 45 mm CdWO4 gets the best. (authors)

  10. Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of SiC bonds

    CERN Document Server

    Cernicharo, J; Gottlieb, C A; Agundez, M; Prieto, L Velilla; Baraban, J H; Changala, P B; Guelin, M; Kahane, C; Martin-Drumel, M A; Patel, N A; Reilly, N J; Stanton, J F; Quintana-Lacaci, G; Thorwirth, S; Young, K H

    2015-01-01

    We report the discovery in space of a disilicon species, SiCSi, from observations between 80 and 350 GHz with the IRAM 30m radio telescope. Owing to the close coordination between laboratory experiments and astrophysics, 112 lines have now been detected in the carbon-rich star CWLeo. The derived frequencies yield improved rotational and centrifugal distortion constants up to sixth order. From the line profiles and interferometric maps with the Submillimeter Array, the bulk of the SiCSi emis- sion arises from a region of 6 arcseconds in radius. The derived abundance is comparable to that of SiC2. As expected from chemical equilibrium calculations, SiCSi and SiC2 are the most abundant species harboring a SiC bond in the dust formation zone and certainly both play a key role in the formation of SiC dust grains.

  11. Status of SPring-8 Photocathode Rf Gun for Future Light Sources

    CERN Document Server

    Tomizawa, H; Dewa, H; Hanaki, H; Kobayashi, T; Mizuno, A; Suzuki, S; Taniuchi, T; Yanagida, K

    2005-01-01

    We have been studying photocathode single-cell pillbox rf gun for future light sources since 1996. We achieved a rmaximum field gradient of 187 MV/m with chemical-etching processed cavity. We have been developed stable and highly qualified UV-laser source for the rf gun intensively last 3 years. The UV-laser pulse (10 Hz) energy is up to 850 uJ/pulse. The energy stability (rms) of laser has been improved down to 0.2~0.3 % at the fundamental and 0.7~1.3% at the third harmonic generation. This stability is held for two months continuously. In this improvement, we just passively stabilized the system in a humidity-controlled clean room. On the other hand, the ideal spatial and temporal profiles of a shot-by-shot single laser pulse are essential to suppress the emittance growth of the electron beam from the rf gun. We prepared a deformable mirror for spatial shaping, and a spatial light modulator based on fused-silica plates for temporal shaping. With a deformable mirror, we obtained an emittance of1.6

  12. A cesium bromide photocathode excited by 405 nm radiation

    Energy Technology Data Exchange (ETDEWEB)

    Maldonado, J. R.; Cheng, Y. T.; Pease, Fabian W.; Hesselink, L. [Electrical Engineering Department, Stanford University, Stanford, California 94305 (United States); Pianetta, P. [SLAC National Accelerator Center, Menlo Park, CA 94025 (United States)

    2014-07-14

    In several applications, such as electron beam lithography and X-ray differential phase contrast imaging, there is a need for a free electron source with a current density at least 10 A/cm{sup 2} yet can be shaped with a resolution down to 20 nm and pulsed. Additional requirements are that the source must operate in a practical demountable vacuum (>1e-9 Torr) and be reasonably compact. In prior work, a photocathode comprising a film of CsBr on metal film on a sapphire substrate met the requirements except it was bulky because it required a beam (>10 W/cm{sup 2}) of 257 nm radiation. Here, we describe an approach using a 405 nm laser which is far less bulky. The 405 nm laser, however, is not energetic enough to create color centers in CsBr films. The key to our approach is to bombard the CsBr film with a flood beam of about 1 keV electrons prior to operation. Photoelectron efficiencies in the range of 100–1000 nA/mW were demonstrated with lifetimes exceeding 50 h between electron bombardments. We suspect that the electron bombardment creates intraband color centers whence electrons can be excited by the 405 nm photons into the conduction band and thence into the vacuum.

  13. Tailoring the emissive properties of photocathodes through materials engineering: Ultra-thin multilayers

    Science.gov (United States)

    Velázquez, Daniel; Seibert, Rachel; Ganegoda, Hasitha; Olive, Daniel; Rice, Amy; Logan, Kevin; Yusof, Zikri; Spentzouris, Linda; Terry, Jeff

    2016-01-01

    We report on an experimental verification that emission properties of photocathodes can be manipulated through the engineering of the surface electronic structure. Ultrathin multilayered MgO/Ag(0 0 1)/MgO films were grown by pulsed laser deposition, tuning the thickness n of the flanking MgO layers to 0, 2, 3, and 4 monolayers. We observed an increase in quantum efficiency and simultaneous decrease in work function with layer thickness. The scale and trend direction of measurements are in good but not excellent agreement with theory. Angle resolved photoemission data for the multilayered sample n = 3 showed that the emission profile has a metallic-like momentum dispersion. Deviations from theoretical predictions [K. Németh et al., PRL 104, 046801 (2010)] are attributed to imperfections of real surfaces in contrast with the ideal surfaces of the calculation. Photoemissive properties of cathodes are critical for electron beam applications such as photoinjectors for Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). An ideal photoemitter has a high quantum efficiency, low work function, low intrinsic emittance and long lifetime. It has been demonstrated here that emission properties may be systematically tailored by control of layer thickness in ultrathin multilayered structures. The reproducibility of the emission parameters under specific growth conditions is excellent, even though the interfaces themselves have varying degrees of roughness.

  14. Cathodic electrodeposition of p-CuSCN nanorod and its dye-sensitized photocathodic property

    Science.gov (United States)

    Sun, Lina; Ichinose, Keigo; Sekiya, Tomohiro; Sugiura, Takashi; Yoshida, Tsukasa

    Mechanism of cathodic electrodeposition of CuSCN from ethanolic solutions containing Cu2+ and SCN- was studied in detail. Job's plot for the absorption spectra of mixed solution in various Cu2+: SCN- ratios have revealed the presence of [Cu(SCN)2]0 as a soluble species responsible to the electrode process in SCN- rich solutions. From Levich analysis of diffusion limited current employing a rotating disc electrode (RDE), diffusion coefficients of 5.2 × 10-6 cm2 s-1 and 3.0 × 10-6 cm2 s-1 in ethanol at 298 K were determined for [Cu(SCN)2]0 and [Cu(SCN)]+, respectively. Morphology as well as crystallographic orientation of the product films significantly changed by the composition of the electrolytic baths. When the bath contains excess of Cu2+ and mixed solvent up to 50% ethanol content to water was used, strong anisotropic crystal growth along the c-axis was observed. When electrolysis was carried out under stationary conditions, the nanorod structures in high aspect ratios could be obtained, due to the limited transport of the active species to the tip of the rods. When rhodamine B was adsorbed onto such CuSCN as a sensitizer, dye-sensitized photocathodic current was observed with an incident photon to current conversion efficiency (IPCE) of 4.4% at the absorption maximum, suggesting its usefulness as the hole conducting electrode in construction of nanostructured solar cells.

  15. Using TiO2 as a Conductive Protective Layer for Photocathodic H2 Evolution

    DEFF Research Database (Denmark)

    Seger, Brian; Pedersen, Thomas; Laursen, Anders Bo;

    2013-01-01

    allows it to conduct electrons from the Si while simultaneously protecting the Si from surface passivation. By using a Pt catalyst the electrode achieves an H2 evolution onset of 520 mV vs NHE and a Tafel slope of 30 mV when illuminated by the red part (λ > 635 nm) of the AM 1.5 spectrum. The saturation...... photocurrent (H2 evolution) was also significantly enhanced by the antireflective properties of the TiO2 layer. It was shown that with proper annealing conditions these electrodes could run 72 h without significant degradation. An Fe2+/Fe3+ redox couple was used to help elucidate details of the band diagram....... during photocatalytic H2 evolution. Although TiO2 is a semiconductor, we show that it behaves like a metallic conductor would under photocathodic H2 evolution conditions. This behavior is due to the fortunate alignment of the TiO2 conduction band with respect to the hydrogen evolution potential, which...

  16. Revealing the Semiconductor-Catalyst Interface in Buried Platinum Black Silicon Photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Aguiar, Jeffery A.; Anderson, Nicholas C.; Neale, Nathan R.

    2016-06-07

    Nanoporous 'black' silicon semiconductors interfaced with buried platinum nanoparticle catalysts have exhibited stable activity for photoelectrochemical hydrogen evolution even after months of exposure to ambient conditions. The mechanism behind this stability has not been explained in detail, but is thought to involve a Pt/Si interface free from SiOx layer that would adversely affect interfacial charge transfer kinetics. In this paper, we resolve the chemical composition and structure of buried Pt/Si interfaces in black silicon photocathodes from a micron to sub-nanometer level using aberration corrected analytical scanning transmission electron microscopy. Through a controlled electrodeposition of copper on samples aged for one month in ambient conditions, we demonstrate that the main active catalytic sites are the buried Pt nanoparticles located below the 400-800 nm thick nanoporous SiOx layer. Though hydrogen production performance degrades over 100 h under photoelectrochemical operating conditions, this burying strategy preserves an atomically clean catalyst/Si interface free of oxide or other phases under air exposure and provides an example of a potential method for stabilizing silicon photoelectrodes from oxidative degradation in photoelectrochemical applications.

  17. Next Generation High Brightness Electron Beams From Ultra-High Field Cryogenic Radiofrequency Photocathode Sources

    CERN Document Server

    Rosenzweig, J B; Dolgashev, V; Emma, C; Fukusawa, A; Li, R; Limborg, C; Maxson, J; Musumeci, P; Nause, A; Pakter, R; Pompili, R; Roussel, R; Spataro, B; Tantawi, S

    2016-01-01

    Recent studies of the performance of radio-frequency (RF) copper structures operated at cryogenic temperatures have shown a dramatic increase in the maximum surface electric field that may be reached. We propose to utilize this development to enable a new generation of photoinjectors operated at cryogenic temperatures that may attain, through enhancement of the launch field at the photocathode by a factor of four, well over an order of magnitude increase in peak electron beam brightness. We present detailed studies of the beam dynamics associated with such a system, concentrating on an emittance-compensated S-band photoinjector that may directly substitute that of the LCLS X-ray free-electron laser. We show in this case that the increase in brightness leads directly to a factor of two reduction in gain length, with attendant increase in X-ray radiative efficiency. Extreme low emittance scenarios obtained at low operating charge, appropriate for dramatically pushing performance limits of ultrafast electron dif...

  18. Cu2O Nanowire Photocathodes for Efficient and Durable Solar Water Splitting.

    Science.gov (United States)

    Luo, Jingshan; Steier, Ludmilla; Son, Min-Kyu; Schreier, Marcel; Mayer, Matthew T; Grätzel, Michael

    2016-03-01

    Due to its abundance, scalability, and nontoxicity, Cu2O has attracted extensive attention toward solar energy conversion, and it is the best performing metal oxide material. Until now, the high efficiency devices are all planar in structure, and their photocurrent densities still fall well below the theoretical value of 14.5 mA cm(-2) due to the incompatible light absorption and charge carrier diffusion lengths. Nanowire structures have been considered as a rational and promising approach to solve this issue, but due to various challenges, performance improvements through the use of nanowires have rarely been achieved. In this work, we develop a new synthetic method to grow Cu2O nanowire arrays on conductive fluorine-doped tin oxide substrates with well-controlled phase and excellent electronic and photonic properties. Also, we introduce an innovative blocking layer strategy to enable high performance. Further, through material engineering by combining a conformal nanoscale p-n junction, durable protective overlayer, and uniform catalyst decoration, we have successfully fabricated Cu2O nanowire array photocathodes for hydrogen generation from solar water splitting delivering unprecedentedly high photocurrent densities of 10 mA cm(-2) and stable operation beyond 50 h, establishing a new benchmark for metal oxide based photoelectrodes. PMID:26866762

  19. Software Tools for the Analysis of the Photocathode Response of Photomultiplier Vacuum Tubes

    CERN Document Server

    Fabbri, R

    2013-01-01

    The central institute of electronics (ZEA-2) in the Forschungszentrum Juelich (FZJ) has developed a system to scan the response of the photocathode of photomultiplier tubes (PMT). The PMT sits tight on a supporting structure, while a blue light emitting diode is moved along its surface by two stepper motors, spanning both the x and y coordinates. All the system is located in a light-tight box made by wood. A graphical software was developed in-situ to perform the scan operations under different configurations (e.g., the step size of the scan and the number of measurements per point). During each point measurement the current output generated in the vacuum photomultiplier is processed in sequence by a pre-amplifier (mainly to convert the current signal into a voltage signal), an amplifier, and by an ADC module (typically a CAEN N957). The information of the measurement is saved in files at the end of the scan. Recently, software based on the CERN ROOT and on the Qt libraries was developed to help the user anal...

  20. Generation of femtosecond electron single pulse using laser photocathode RF gun

    International Nuclear Information System (INIS)

    A new laser photocathode RF electron gun was installed in the second linac of the S-band twin linac system of Nuclear Engineering Research Laboratory(NERL) of University of Tokyo in August in 1997. Since then, the behavior of the new gun has been tested and the characteristic parameters have been evaluated. At the exit of the gun, the energy is 4.7 MeV, the charge per bunch 1 nC, the pulse width is 10 ps(FWHM), respectively, for 6 MW RF power supply from a klystron. The electron bunch is accelerated up to 17 MeV. The horizontal normalized emittance is 1 π mm.mrad. Then, the bunch is compressed to be 440 fs(FWHM) with 0.35 nC by the chicane-type magnetic pulse compressor. The gun is planned to be used for femtosecond X-ray generation via the head-on Thomson scattering and laser wakefield acceleration in 1998. (author)

  1. Femtosecond electron beam generation by S-band laser photocathode RF gun and linac

    International Nuclear Information System (INIS)

    A laser photocathode RF electron gun was installed in the second linac of the S-hand twin linac system of Nuclear Engineering Research Laboratory (NERL) of University of Tokyo in August in 1997. Since then, the behavior of the new gun has been tested and the characteristic parameters have been evaluated. At the exit of the gun, the energy is 3.5 MeV, the charge per bunch 1∼2 nC, the pulse width is 10 ps(FWHM), respectively, for 6 MW RF power supply from a klystron. The electron bunch is accelerated up to 17 MeV and horizontal and vertical normalized emittances of 3 π mm.mrad are achieved. Then, the bunch is compressed to be 440 fs(FWHM) with 0.35 nC by the chicane-type magnetic pulse compressor. The linac with the gun and a new femto- and picosecond laser system is planned to be installed for femtosecond pulseradiolysis for radiation chemistry in 1999

  2. On-line measurement system of GaAs photocathodes and its applications

    Science.gov (United States)

    Zou, Jijun; Feng, Lin; Lin, Gangyong; Rao, Yuntao; Yang, Zhi; Qian, Yunsheng; Chang, Benkang

    2007-11-01

    The preparation process of GaAs photocathodes is very complicated, in order to prepare the high performance cathodes, it is crucial to obtain information enough to evaluate the preparation process in real time. Based on a particular transfer light setup and a flexible communication network, we develop an on-line measurement system for GaAs cathode preparation, which is used to measure the pressure of activation chamber, sample temperature, photocurrent, spectral response curves, and currents heating Cs and oxygen dispensers during the heat-cleaning or activation processes of cathodes. According to these signals, we present some simple and real-time evaluation techniques for cathode preparation. Several peaks of pressure are observed in the pressure variations measured during heat cleaning. These peaks corresponding to the desorption of AsO, As IIO 3, Ga IIO and Ga IIO 3 from the sample surface at different temperatures, respectively, are used to evaluate the effect of heat cleaning very well, while the signals measured during activation can be used to analyze and optimize the activation technique. Based on a revised quantum efficiency equation, many performance parameters of cathodes are obtained from the fitting of spectral response curves. According to these parameters, the performance of cathode material and the effect of activation can be evaluated.

  3. Emittance measurement and optimization for the photocathode RF gun with laser profile shaping

    International Nuclear Information System (INIS)

    The Laser Undulator Compact X-ray source (LUCX) is a test bench for a compact high brightness X-ray generator, based on inverse Compton Scattering at KEK, which requires high intensity multi-bunch trains with low transverse emittance. A photocathode RF gun with emittance compensation solenoid is used as an electron source. Much endeavor has been made to increase the beam intensity in the multi-bunch trains. The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects, so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough. A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform. In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance. With the uniform driving laser and the unbalanced RF gun, the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm.mrad to 3.66 πmm·mrad. (authors)

  4. Design of a high repetition rate S-band photocathode gun

    Science.gov (United States)

    Han, Jang-Hui; Cox, Matthew; Huang, Houcheng; Pande, Shivaji

    2011-08-01

    Photocathode RF guns have been developed in many laboratories for generating high quality electron beams for free-electron lasers based on linear accelerators. Such guns can generate electron beams with an exceptionally high peak current as well as a small transverse emittance. Their applications have been recently expanded for ultrafast electron diffraction, coherent terahertz radiation, and X-ray or γ-ray radiation by Compton scattering. In this paper, we design an S-band normal-conducting gun with capabilities of high quality beam generation and high repetition rate operation. The RF design and thermal analysis of the gun cavity and coupler are introduced. Optimal position of the gun focusing solenoid for low emittance beam generation is found by performing particle tracking simulations. Then, the gun system is designed to be able to afford the optimal solenoid position. The cooling-water channel surrounding the gun cavity and coupler is designed and analyzed numerically. The pressure in the gun is simulated with a vacuum model containing the detailed inner structure of the gun. An injector for a free-electron laser application is designed by using this gun and the beam dynamics simulation is shown. A cold test with a prototype gun for confirmation of the RF design is reported.

  5. Experimental studies of emittance growth and energy spread in a photocathode RF gun

    CERN Document Server

    Yang, J; Okada, Y; Yorozu, M; Yanagida, T; Endo, A

    2002-01-01

    In this paper we report on a low emittance electron source, based on a photocathode RF gun, a solenoid magnet and a subsequent linac. The dependencies of the beam transverse emittance and relative energy spread with respect to the laser injection phase of the radio-frequency (RF) gun, the RF phase of the linac and the bunch charge were investigated experimentally. It was found that a lower beam emittance is observed when the laser injection phase in the RF gun is low. The emittance increases almost linearly with the bunch charge under a constant solenoid magnetic field. The corrected relative energy spread of the beam is not strongly dependent on the bunch charge. Finally, an optimal normalized rms transverse emittance of 1.91+-0.28 pi mm mrad at a bunch charge of 0.6 nC was obtained when the RF gun was driven by a picosecond Nd:YAG laser. A corrected relative rms energy spread of 0.2-0.25% at a bunch charge of 0.3-2 nC was obtained after the beam was accelerated to 14 MeV by the subsequent linac.

  6. Experimental studies of emittance growth and energy spread in a photocathode RF gun

    International Nuclear Information System (INIS)

    In this paper we report on a low emittance electron source, based on a photocathode RF gun, a solenoid magnet and a subsequent linac. The dependencies of the beam transverse emittance and relative energy spread with respect to the laser injection phase of the radio-frequency (RF) gun, the RF phase of the linac and the bunch charge were investigated experimentally. It was found that a lower beam emittance is observed when the laser injection phase in the RF gun is low. The emittance increases almost linearly with the bunch charge under a constant solenoid magnetic field. The corrected relative energy spread of the beam is not strongly dependent on the bunch charge. Finally, an optimal normalized rms transverse emittance of 1.91±0.28 πmm mrad at a bunch charge of 0.6 nC was obtained when the RF gun was driven by a picosecond Nd:YAG laser. A corrected relative rms energy spread of 0.2-0.25% at a bunch charge of 0.3-2 nC was obtained after the beam was accelerated to 14 MeV by the subsequent linac

  7. A Comparative Study of Z-Source Inverter Fed Three-Phase IM Drive with CSI and VSI fed IM

    Directory of Open Access Journals (Sweden)

    Deepak Kumar

    2013-07-01

    Full Text Available This paper cite comparative performance characteristics of Z-Source inverter fed IM drives with mostly used VSI & CSI fed IM drives. ZSI has both voltages buck and boost capabilities as they allow inverters to be operated in the shoot through state. It employs an exclusive Z-Source network (LC component to dc-link the main inverter circuit to the power source (rectifier. By controlling the shoot-through duty cycle, the inverter system using IGBTS reduces the line harmonics, improves power factor, increases reliability and extends output voltage range. It has reduced harmonics, low switching stress power and low common mode noise as compared to VSI. Simulation results are given to compare the behavior of conventional and proposed topology and also demonstrate the new features of the improved topology i.e ZSI fed IM. Simulation results of  ZSI fed IM gives different performance characteristics as compared to VSI & CSI fed IM drives such as its stator & rotor current characteristics, speed characteristics , torque characteristics which put a gloss on the VSI fed IM performance

  8. Experimental measurement of a high resolution CMOS detector coupled to CsI scintillators under X-ray radiation

    International Nuclear Information System (INIS)

    The purpose of the present study was to assess the information content of structured CsI:Tl scintillating screens, specially treated to be compatible to a CMOS digital imaging optical sensor, in terms of the information capacity (IC), based on Shannon's mathematical communication theory. IC was assessed after the experimental determination of the Modulation Transfer Function (MTF) and the Normalized Noise Power Spectrum (NNPS) in the mammography and general radiography energy range. The CMOS sensor was coupled to three columnar CsI:Tl scintillator screens obtained from the same manufacturer with thicknesses of 130, 140 and 170 μm respectively, which were placed in direct contact with the optical sensor. The MTF was measured using the slanted-edge method while NNPS was determined by 2D Fourier transforming of uniformly exposed images. Both parameters were assessed by irradiation under the mammographic W/Rh (130, 140 and 170 μm CsI screens) and the RQA-5 (140 and 170 μm CsI screens) (IEC 62220-1) beam qualities. The detector response function was linear for the exposure range under investigation. At 70 kVp, under the RQA-5 conditions IC values were found to range between 2229 and 2340 bits/mm2. At 28 kVp the corresponding IC values were found to range between 2262 and 2968 bits/mm2. The information content of CsI:Tl scintillating screens in combination to the high resolution CMOS sensor, investigated in the present study, where found optimized for use in digital mammography imaging systems. - Highlights: • Three structured CsI:Tl screens (130,140 & 170 um) were coupled to a CMOS sensor. • MTF of the CsI/CMOS was higher than GOS:Tb and CsI based digital imaging systems. • IC of CsI:Tl/CMOS was found optimized for use in digital mammography systems

  9. Investigating Water Splitting with CaFe2O4 Photocathodes by Electrochemical Impedance Spectroscopy.

    Science.gov (United States)

    Díez-García, María Isabel; Gómez, Roberto

    2016-08-24

    Artificial photosynthesis constitutes one of the most promising alternatives for harvesting solar energy in the form of fuels, such as hydrogen. Among the different devices that could be developed to achieve efficient water photosplitting, tandem photoelectrochemical cells show more flexibility and offer high theoretical conversion efficiency. The development of these cells depends on finding efficient and stable photoanodes and, particularly, photocathodes, which requires having reliable information on the mechanism of charge transfer at the semiconductor/solution interface. In this context, this work deals with the preparation of thin film calcium ferrite electrodes and their photoelectrochemical characterization for hydrogen generation by means of electrochemical impedance spectroscopy (EIS). A fully theoretical model that includes elementary steps for electron transfer to the electrolyte and surface recombination with photogenerated holes is presented. The model also takes into account the complexity of the semiconductor/solution interface by including the capacitances of the space charge region, the surface states and the Helmholtz layer (as a constant phase element). After illustrating the predicted Nyquist plots in a general manner, the experimental results for calcium ferrite electrodes at different applied potentials and under different illumination intensities are fitted to the model. The excellent agreement between the model and the experimental results is illustrated by the simultaneous fit of both Nyquist and Bode plots. The concordance between both theory and experiments allows us to conclude that a direct transfer of electrons from the conduction band to water prevails for hydrogen photogeneration on calcium ferrite electrodes and that most of the carrier recombination occurs in the material bulk. In more general vein, this study illustrates how the use of EIS may provide important clues about the behavior of photoelectrodes and the main strategies

  10. Design of the fundamental power coupler and photocathode inserts for the 112MHz superconducting electron gun

    Energy Technology Data Exchange (ETDEWEB)

    Xin, T.; Ben-Zvi, I.; Belomestnykh, S.; Chang, X.; Rao, T.; Skaritka, J.; Wu, Q.; Wang, E.; Liang, X.

    2011-07-25

    A 112 MHz superconducting quarter-wave resonator electron gun will be used as the injector of the Coherent Electron Cooling (CEC) proof-of-principle experiment at BNL. Furthermore, this electron gun can be the testing cavity for various photocathodes. In this paper, we present the design of the cathode stalks and a Fundamental Power Coupler (FPC) designated to the future experiments. Two types of cathode stalks are discussed. Special shape of the stalk is applied in order to minimize the RF power loss. The location of cathode plane is also optimized to enable the extraction of low emittance beam. The coaxial waveguide structure FPC has the properties of tunable coupling factor and small interference to the electron beam output. The optimization of the coupling factor and the location of the FPC are discussed in detail. Based on the transmission line theory, we designed a half wavelength cathode stalk which significantly brings down the voltage drop between the cavity and the stalk from more than 5.6 kV to 0.1 kV. The transverse field distribution on cathode has been optimized by carefully choosing the position of cathode stalk inside the cavity. Moreover, in order to decrease the RF power loss, a variable diameter design of cathode stalk has been applied. Compared to the uniform shape of stalk, this design gives us much smaller power losses in important locations. Besides that, we also proposed a fundamental power coupler based on the designed beam parameters for the future proof-of-principle CEC experiment. This FPC should give a strong enough coupling which has the Q external range from 1.5e7 to 2.6e8.

  11. The Chemistry Scoring Index (CSI: A Hazard-Based Scoring and Ranking Tool for Chemicals and Products Used in the Oil and Gas Industry

    Directory of Open Access Journals (Sweden)

    Tim Verslycke

    2014-06-01

    Full Text Available A large portfolio of chemicals and products is needed to meet the wide range of performance requirements of the oil and gas industry. The oil and gas industry is under increased scrutiny from regulators, environmental groups, the public, and other stakeholders for use of their chemicals. In response, industry is increasingly incorporating “greener” products and practices but is struggling to define and quantify what exactly constitutes “green” in the absence of a universally accepted definition. We recently developed the Chemistry Scoring Index (CSI which is ultimately intended to be a globally implementable tool that comprehensively scores and ranks hazards to human health, safety, and the environment for products used in oil and gas operations. CSI scores are assigned to products designed for the same use (e.g., surfactants, catalysts on the basis of product composition as well as intrinsic hazard properties and data availability for each product component. As such, products with a lower CSI score within a product use group are considered to have a lower intrinsic hazard compared to other products within the same use group. The CSI provides a powerful tool to evaluate relative product hazards; to review and assess product portfolios; and to aid in the formulation of products.

  12. The approximation of energetic dependences of mass attenuation coefficients of γ-radiation for CsI and Zn Se scintillators

    International Nuclear Information System (INIS)

    The formulae for energetic dependences of the mass attenuation coefficients of γ-radiation of CsI and Zn Se scintillators in the range of energies of 0.01-100 MeV are found. The difference of approximative dependences from the source data is less than 3%

  13. Optical modulation of electron beam using the opto-semiconductor device on the photocathode RF gun for the radiation therapy

    International Nuclear Information System (INIS)

    The radiation therapy of cancer is developing to un-uniform irradiation, for concentrating dose to a tumor and reducing dose to normal tissue. For the un-uniform irradiation, optical modulation of electron beam using the Digital Micro Mirror Device was studied on a photocathode RF gun. The optical modulation of electron beam and dynamic control succeeded by a digital micro mirror device. Fundamental data such as the spatial resolution and the contrast of the optical modulated electron beam was measured. It will be reported that the relations between the intensity distribution and the emittance. (author)

  14. Highly stable copper oxide composite as an effective photocathode for water splitting via a facile electrochemical synthesis strategy

    KAUST Repository

    Zhang, Zhonghai

    2012-01-01

    Hydrogen generation through photoelectrochemical (PEC) water splitting using solar light as an energy resource is believed to be a clean and efficient way to overcome the global energy and environmental problems. Extensive research effort has been focused on n-type metal oxide semiconductors as photoanodes, whereas studies of p-type metal oxide semiconductors as photocathodes where hydrogen is generated are scarce. In this paper, highly efficient and stable copper oxide composite photocathode materials were successfully fabricated by a facile two-step electrochemical strategy, which consists of electrodeposition of a Cu film on an ITO glass substrate followed by anodization of the Cu film under a suitable current density and then calcination to form a Cu 2O/CuO composite. The synthesized Cu 2O/CuO composite was composed of a thin layer of Cu 2O with a thin film of CuO on its top as a protecting coating. The rational control of chemical composition and crystalline orientation of the composite materials was easily achieved by varying the electrochemical parameters, including electrodeposition potential and anodization current density, to achieve an enhanced PEC performance. The best photocathode material among all materials prepared was the Cu 2O/CuO composite with Cu 2O in (220) orientation, which showed a highly stable photocurrent of -1.54 mA cm -2 at a potential of 0 V vs reversible hydrogen electrode at a mild pH under illumination of AM 1.5G. This photocurrent density was more than 2 times that generated by the bare Cu 2O electrode (-0.65 mAcm -2) and the stability was considerably enhanced to 74.4% from 30.1% on the bare Cu 2O electrode. The results of this study showed that the top layer of CuO in the Cu 2O/CuO composite not only minimized the Cu 2O photocorrosion but also served as a recombination inhibitor for the photogenerated electrons and holes from Cu 2O, which collectively explained much enhanced stability and PEC activity of the Cu 2O/CuO composite

  15. A Si Photocathode Protected and Activated with a Catalytic Ti and Ni Composite Film for Solar Hydrogen Production in Water

    OpenAIRE

    Lai, Yi-Hsuan; Park, Hyun S.; Zhang, Jenny Z; Peter D. Matthews; Wright, Dominic S.; Reisner, Erwin

    2015-01-01

    An efficient, stable and scalable hybrid photoelectrode for visible-light-driven H2 generation in an aqueous pH 9.2 electrolyte solution is reported. The photocathode consists of a p-type Si substrate layered with a Ti and Ni-containing composite film, which acts as both a protection and electrocatalyst layer on the Si substrate. The film is prepared by the simple drop casting of the molecular single-source precursor, [{Ti2(OEt)9(NiCl)}2] (TiNipre), onto the p-Si surface at room temperature, ...

  16. Collision induced dissociation of CsI and Cs2I2 to ion pairs by Kr, Xe, and SF6

    Science.gov (United States)

    Parks, E. K.; Inoue, M.; Wexler, S.

    1982-02-01

    Absolute cross sections as functions of collision energy have been determined for collision induced dissociation of cesium iodide monomer and dimer to ion pairs. In these studies a beam of accelerated Xe, Kr, or SF6 projectiles was crossed with a thermal beam of cesium iodide. The partial cross sections for each product-ion channel were determined by time-of-flight mass spectrometry. For the rare gas-monomer collisions, the dependence of each partial cross section on the internal temperature of the CsI was also obtained. Collisions of Xe with CsI produced three-body dissociation as well as the formation of the molecular ions CsXe+ and IXe-. The formation of both the positive and negative molecular ions is primarily a reflection of the similar masses of Cs+ and I-, and was not observed in previously studied systems. For the same reason, Cs2I+ and CsI-2 resulting from collisions of Xe with Cs2I2 were formed with comparable intensities. At energies well above threshold, the total dissociation cross section for the rare gases colliding with CsI or Cs2I2 is large (≳10 Å2). Those for SF6 are approximately a factor of 5 smaller for the monomer, but only slightly smaller for the dimer. No ions containing SF6 were observed. The cross sections for three-body dissociation as well as molecular ion formation are relatively small in the region of the thermodynamic threshold (decreasing in the series Xe, Kr, and Ar). Analysis of the experimental results indicates that dissociation in this region only occurs for CsI molecules having considerable internal excitation, an effect related almost entirely to the projectile-target relative masses. A model which takes into account the coupling of internal motion with relative translational motion is shown to give an excellent description of the dissociation in the threshold region. Collinear trajectory calculations of the rare gases colliding with CsI were also performed in order to determine the threshold for dissociation as a

  17. Impact of carrier recombination on fill factor for large area heterojunction crystalline silicon solar cell with 25.1% efficiency

    Science.gov (United States)

    Adachi, Daisuke; Hernández, José Luis; Yamamoto, Kenji

    2015-12-01

    We have achieved a certified 25.1% conversion efficiency in a large area (151.9 cm2) heterojunction (HJ) crystalline Si (c-Si) solar cell with amorphous Si (a-Si) passivation layer. This efficiency is a world record in a both-side-contacted c-Si solar cell. Our high efficiency HJ c-Si solar cells are investigated from the standpoint of the effective minority carrier lifetime (τe), and the impact of τe on fill factor (FF) is discussed. The τe measurements of our high efficiency HJ c-Si solar cells reveal that τe at an injection level corresponding to an operation point of maximum power is dominated by the carrier recombination at the a-Si/c-Si interface. By optimization of the process conditions, the carrier recombination at the a-Si/c-Si interface is reduced, which leads to an improvement of the FF by an absolute value of 2.7%, and a conversion efficiency of 25.1% has been achieved. These results indicate that the reduction of carrier recombination centers at the a-Si/c-Si interface should be one of the most crucial issues for further improvement of FF even in the HJ c-Si solar cells with efficiency over 25%.

  18. Energetic resolution study on pure and CsBr doped CsI under gamma excitations and alpha particles

    International Nuclear Information System (INIS)

    Pure and doped CsI crystals were grown using the Bridgman technique. Bromine was the doping element which was studied in the range of 1.5x10-1 M to 10-2 M. The distribution of the doping element at crystalline volume was determined by neutron activation. Concerning gamma radiation response it was carried out measurements to evaluate the developed scintillators in the energy range of 350 keV to 1330 keV. For alpha particles measurements an 241Am source was used with 5.54 MeV energy. The resolution of 3.7% was obtained for the CsI:Br 10-2 M crystal, when excited with alpha particles from an 241Am source. For CsI:Br 10-1 M crystal 9.1% resolution was obtained when excited with gamma radiation from 22Na source, with 1275 keV energy. (author)

  19. Exact Outage Probability of Dual-Hop CSI-Assisted AF Relaying Over Nakagami-m Fading Channels

    KAUST Repository

    Xia, Minghua

    2012-10-01

    In this correspondence, considering dual-hop channel state information (CSI)-assisted amplify-and-forward (AF) relaying over Nakagami- m fading channels, the cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) is derived. In particular, when the fading shape factors m1 and m2 at consecutive hops take non-integer values, the bivariate H-function and G -function are exploited to obtain an exact analytical expression for the CDF. The obtained CDF is then applied to evaluate the outage performance of the system under study. The analytical results of outage probability coincide exactly with Monte-Carlo simulation results and outperform the previously reported upper bounds in the low and medium SNR regions.

  20. Reality and fiction in US TV series: Lost, CSI and The West Wing. Narrative strategies and verosimilitude

    Directory of Open Access Journals (Sweden)

    Anna Tous Rovirosa

    2010-12-01

    Full Text Available The purpose of this paper is to present a methodology of analysis of TV series, taking into account the use of reality and fiction in the narrative construction of these series, as well as the use of verosimilitude in „real-world‟ series. With the methodology chosen, the purpose is to distinguish between the usage of reality and fiction, on one hand, and the usage of thematic recurrence, myth and metaTV references, on the other. The methodology consists of the edition of televisual text. For, inasmuch as we consider that drama series are a text, they can be edited. The empirical analysis deals with three US TV series: Lost, ABC: 2004-, CSI: Crime Scene Investigation, CBS: 2000- and The West Wing, NBC: 1999-2006. They all belong to the drama‟s era, but each of them represents a specific subgenre: adventures and science-fiction, crime and forensic, and workplace and politics.

  1. Development Status and Performance Comparisons of Environmental Barrier Coating Systems for SiCSiC Ceramic Matrix Composites

    Science.gov (United States)

    Zhu, Dongming; Harder, Bryan

    2016-01-01

    Environmental barrier coatings (EBC) and SiCSiC ceramic matrix composites (CMCs) will play a crucial role in future aircraft turbine engine systems, because of their ability to significantly increase engine operating temperatures, reduce engine weight and cooling requirements. This paper presents current NASA EBC-CMC development emphases including: the coating composition and processing improvements, laser high heat flux-thermal gradient thermo-mechanical fatigue - environmental testing methodology development, and property evaluations for next generation EBC-CMC systems. EBCs processed with various deposition techniques including Plasma Spray, Electron Beam - Physical Vapor Deposition, and Plasma Spray Physical Vapor Deposition (PS-PVD) will be particularly discussed. The testing results and demonstrations of advanced EBCs-CMCs in complex simulated engine thermal gradient cyclic fatigue, oxidizing-steam and CMAS environments will help provide insights into the coating development strategies to meet long-term engine component durability goals.

  2. High Power Beam Test and Measurement of Emittance Evolution of a 1.6-Cell Photocathode RF Gun at Pohang Accelerator Laboratory

    Science.gov (United States)

    Park, Jang-Ho; Park, Sung-Ju; Kim, Changbum; Parc, Yong-Woon; Hong, Ju-Ho; Huang, Jung-Yun; Xiang, Dao; Wang, Xijie; Ko, In Soo

    2007-04-01

    A Brookhaven National Laboratory (BNL) GUN-IV type photocathode rf gun has been fabricated to use in femtosecond electron diffraction (FED), femtosecond far infrared radiation (fs-FIR) facility, and X-ray free electron laser (XFEL) facilities at the Pohang Accelerator Laboratory (PAL). The gun consists of a 1.6-cell cavity with a copper cathode, a solenoid magnet, beam diagnostic components and auxiliary systems. We report here the measurement of the basic beam parameters which confirm a successful fabrication of the photocathode RF gun system. The emittance evolution is measured by an emittance meter and compared with the PARMELA simulation, which shows a good agreement.

  3. The possibly important role played by Ga2O3 during the activation of GaN photocathode

    International Nuclear Information System (INIS)

    Three different chemical solutions are used to remove the possible contamination on GaN surface, while Ga2O3 is still found at the surface. After thermal annealing at 710 °C in the ultrahigh vacuum (UHV) chamber and activated with Cs/O, all the GaN samples are successfully activated to the effective negative electron affinity (NEA) photocathodes. Among all samples, the GaN sample with the highest content of Ga2O3 after chemical cleaning obtains the highest quantum efficiency. By analyzing the property of Ga2O3, the surface processing results, and electron affinity variations during Cs and Cs/O2 deposition on GaN of other groups, it is suggested that before the adsorption of Cs, Ga2O3 is not completely removed from GaN surface in our samples, which will combine with Cs and lead to a large decrease in electron affinity. Furthermore, the effective NEA is formed for GaN photocathode, along with the surface downward band bending. Based on this assumption, a new dipole model Ga2O3-Cs is suggested, and the experimental effects are explained and discussed

  4. Synthesis of Ultra-Thin Single Crystal MgO/Ag/MgO Multilayer for Controlled Photocathode Emissive Properties

    Science.gov (United States)

    Velazquez, Daniel; Seibert, Rachel; Yusof, Zikri; Terry, Jeff; Spentzouris, Linda

    2015-03-01

    Developments of new accelerator technologies such as free-electron lasers and high-energy accelerators, among others, continuously set requirements for particle sources to produce higher beam flux. The emissive properties of these photocathodes directly influence the accelerator beam flux and thus the performance of the accelerator as a whole. The objective of this project is to test the possibility of engineering the photoemissive properties of materials for potential use as photocathodes. For this purpose we use a Density Functional Theory calculations by collaborator Karoly Nemeth et al. [Phys. Rev. Lett. 104, 046801, 2010], which predict a thickness dependent change in the band structure that results in a change in the work function and dispersion of occupied states at the Fermi level. Multilayered MgO/Ag/MgO in the crystallographic orientations (001) and (111) were grown on Ag/MgO(001) and Ag/Si(111), respectively using pulsed laser deposition (PLD). A series of surface probing techniques were used to characterize physical, chemical and photoemissive properties of the films.

  5. p-Type dye-sensitized solar cell based on nickel oxide photocathode with or without Li doping

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hui-Tzu; Mishra, D.K. [Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan (China); Chen, Peter [Department of Photonics, National Cheng Kung University, Tainan, Taiwan (China); Ting, Jyh-Ming, E-mail: jting@mail.ncku.edu.tw [Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan (China)

    2014-01-25

    Highlights: • Microwave-assisted hydrothermal synthesis of NiO nanostructures with Li-doping at low temperature. • p-Type dye-sensitized solar cell based on NiO photocathode. • Study on the effect of Li doping concentration on the cell performance. -- Abstract: Nickel oxide (NiO) nanostructures are synthesized using a microwave-assisted hydrothermal method. The hydrothermal bath has a solution of nickel salt mixed with precipitating agent. During the synthesis the microwave temperature, the concentration of nickel salt and precipitating agent along with the pH of the reaction solutions are changed and different morphologies of nickel oxide are obtained. The resulting nickel oxide nanostructures are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller method and X-ray photoelectron spectroscopy. Thus formed NiO has been used as a photocathode in dye-sensitized solar cell. Lithium doped NiO showed better IPCE as well as solar to electrical conversion efficiency than the undoped NiO.

  6. Photocathodes inside superconducting cavities. Studies on the feasibility of a superconducting photoelectron source of high brightness. External report

    International Nuclear Information System (INIS)

    We have done studies and experiments to explore the feasibility of a photoemission RF gun with a superconducting accelerator cavity. This concept promises to provide an electron beam of high brightness in continuous operation. It is thus of strong interest for a free-electron-laser or a linear collider based on a superconducting accelerator. In a first step we studied possible technical solutions for its components, especially the material of the photocathode and the geometrical shape of the cavity. Based on these considerations, we developed the complete design for a prototype electron source. The cathode material was chosen to be alkali antimonide. In spite of its sensitivity, it seems to be the best choice for a gun with high average current due to its high quantum efficiency. The cavity shape was at first a reentrant-type single cell of 500 MHz. It is now replaced by a more regular two-and-half cell shape, an independent half cell added for emittance correction. Its beam dynamics properties are investigated by numerical simulations; we estimated a beam brightness of about 5x1011 A/(m.rad)2. But the mutual interactions between alkali antimonide photocathode and superconducting cavity must be investigated experimentally, because they are completely unkown. (orig.)

  7. Development of brazing technique for a 1.6 cell BNL/SLAC/UCLA type photocathode guns by hydrogen brazing

    International Nuclear Information System (INIS)

    Two prototypes of a 1.6 cell BNL/SLAC/UCLA type RF photocathode gun, a precision machined RF structure capable of supporting gradients in excess of 80 MV/m, have been successfully brazed and leak rates of 10-10 mbar l/s have been achieved. Brazing, is carried out in two steps in a hydrogen furnace, it involves joining of two RF cavities, 6 cylindrical ports, one rectangular waveguide and one seal plate. The cavities and waveguide are made of copper and the ports and seal plate are of stainless steel. Fixtures were designed and fabricated indigenously to maintain the required assembly tolerances during brazing. This was important for brazing of ports, two of which are brazed to one cavity at an angle of 22.50 at diametrically opposite locations, and the remaining four are brazed to the other cavity in mutually perpendicular orientations. All joints were brazed using copper-silver eutectic (72-28) alloy in foil and wire forms. This paper discusses the brazing requirement, design of fixtures, and the procedure adopted for brazing of the photocathode gun. The paper also discusses results of the tests carried out to qualify the brazed joints. (author)

  8. Engineering of Sub-Nanometer SiOx Thickness in Si Photocathodes for Optimized Open Circuit Potential.

    Science.gov (United States)

    Das, Chittaranjan; Kot, Malgorzata; Henkel, Karsten; Schmeisser, Dieter

    2016-09-01

    Silicon is one of the most promising materials to be used for tandem-cell water-splitting devices. However, the electrochemical instability of bare Si makes it difficult to be used for stable devices. Besides that, the photovoltage loss in Si, caused by several factors (e.g., metal oxide protection layer and/or SiO2 /Si or catalyst/Si interface), limits its use in these devices. In this work, we present that an optimized open circuit potential (OCP) of Si can be obtained by controlling the SiOx thickness in sub-nanometer range. It can be done by means of a simple and cost-effective way using the combination of a wet chemical etching and the low temperature atomic layer deposition (ALD) of TiO2 . We have found that a certain thickness of the native SiOx is necessary to prevent further oxidation of the Si photocathode during the ALD growth of TiO2 . Moreover, covering the Si photocathode with an ALD TiO2 layer enhances its stability. PMID:27510311

  9. Activation Layer Stabilization of High Polarization Photocathodes in Sub-Optimal RF Gun Environments

    Energy Technology Data Exchange (ETDEWEB)

    Gregory A. Mulhollan

    2010-11-16

    Specific activation recipes for bulk, 100 nm thick MBE grown and high polarization III-V photocathode material have been developed which mitigate the effects of exposure to background gasses. Lifetime data using four representative gasses were acquired for bulk GaAs, 100 nm unstrained GaAs and strained superlattice GaAs/GaAsP, all activated both with Cs and then Cs and Li (bi-alkali). Each photoemitter showed marked resilience improvement when activated using the bi-alkali recipe compared to the standard single alkali recipe. A dual alkali activation system at SLAC was constructed, baked and commissioned with the purpose of performing spin-polarization measurements on electrons emitted from the bi-alkali activated surfaces. An end station at SSRL was configured with the required sources for energy resolved photoemission measurements on the bi-alkali activated and CO2 dosed surfaces. The bi-alkali recipes were successfully implemented at SLAC/SSRL. Measurements at SLAC of the photoelectron spin-polarization from the modified activation surface showed no sign of a change in value compared to the standard activated material, i.e., no ill effects. Analysis of photoemission data indicates that the addition of Li to the activation layer results in a multi-layer structure. The presence of Li in the activation layer also acts as an inhibitor to CO2 absorption, hence better lifetimes in worse vacuum were achieved. The bi-alkali activation has been tested on O2 activated GaAs for comparison with NF3 activated surfaces. Comparable resilience to CO2 exposure was achieved for the O2 activated surface. An RF PECVD amorphous silicon growth system was modified to allow high temperature heat cleaning of GaAs substrates prior to film deposition. Growth versus thickness data were collected. Very thin amorphous silicon germanium layers were optimized to exhibit good behavior as an electron emitter. Growth of the amorphous silicon germanium films on the above substrates was fine tuned

  10. Comparison of blue–green response between transmission-mode GaAsP- and GaAs-based photocathodes grown by molecular beam epitaxy

    Science.gov (United States)

    Gang-Cheng, Jiao; Zheng-Tang, Liu; Hui, Guo; Yi-Jun, Zhang

    2016-04-01

    In order to develop the photodetector for effective blue–green response, the 18-mm-diameter vacuum image tube combined with the transmission-mode Al0.7Ga0.3As0.9 P 0.1/GaAs0.9 P 0.1 photocathode grown by molecular beam epitaxy is tentatively fabricated. A comparison of photoelectric property, spectral characteristic and performance parameter between the transmission-mode GaAsP-based and blue-extended GaAs-based photocathodes shows that the GaAsP-based photocathode possesses better absorption and higher quantum efficiency in the blue–green waveband, combined with a larger surface electron escape probability. Especially, the quantum efficiency at 532 nm for the GaAsP-based photocathode achieves as high as 59%, nearly twice that for the blue-extended GaAs-based one, which would be more conducive to the underwater range-gated imaging based on laser illumination. Moreover, the simulation results show that the favorable blue–green response can be achieved by optimizing the emission-layer thickness in a range of 0.4 μm–0.6 μm. Project supported by the National Natural Science Foundation of China (Grant No. 61301023) and the Science and Technology on Low-Light-Level Night Vision Laboratory Foundation, China (Grant No. BJ2014001).

  11. Formation of a p-n heterojunction on GaP photocathodes for H-2 production providing an open-circuit voltage of 710 mV

    DEFF Research Database (Denmark)

    Malizia, Mauro; Seger, Brian; Chorkendorff, Ib;

    2014-01-01

    unprecedented for a p-GaP-based HER photocathode operating in an acidic electrolyte under simulated 1 Sun illumination. An additional, but highly significant benefit of a TiO2 layer is that it provides a remarkable operational stability of more than 24 h under constant operation. It was found that TiO2 and Nb2O...

  12. Asymmetric effect of market liquidity demand shocks on price shocks: Empirical studies based on the CSI 300 Index and the Futures

    OpenAIRE

    Xinzhe Xu; Chaojun Yang; Daolun Chen; Gongmeng Chen

    2013-01-01

    Purpose – With the launch of CSI 300 Index Futures trading on April 16, 2010, China's stock market presents a more diversified trend, such as arbitrage, trends strategy entering the market rapidly. Therefore, the liquidity demand also presents a higher frequency, and the change is more complex than the original situation. In recent years, many literatures are engaged in high-frequency trading (HFT) related research, and an important concern is the impact of HFT on market volatility and liquid...

  13. Measurements and Studies of Secondary Electron Emission of Diamond Amplified Photocathode

    Energy Technology Data Exchange (ETDEWEB)

    Wu,Q.

    2008-10-01

    The Diamond Amplified Photocathode (DAP) is a novel approach to generating electrons. By following the primary electron beam, which is generated by traditional electron sources, with an amplifier, the electron beam available to the eventual application is increased by 1 to 2 orders of magnitude in current. Diamond has a very wide band gap of 5.47eV which allows for a good negative electron affinity with simple hydrogenation, diamond can hold more than 2000MV/m field before breakdown. Diamond also provides the best rigidity among all materials. These two characters offer the capability of applying high voltage across very thin diamond film to achieve high SEY and desired emission phase. The diamond amplifier also is capable of handling a large heat load by conduction and sub-nanosecond pulse input. The preparation of the diamond amplifier includes thinning and polishing, cleaning with acid etching, metallization, and hydrogenation. The best mechanical polishing available can provide high purity single crystal diamond films with no less than 100 {micro}m thickness and <15 nm Ra surface roughness. The ideal thickness for 700MHz beam is {approx}30 {micro}m, which requires further thinning with RIE or laser ablation. RIE can achieve atomic layer removal precision and roughness eventually, but the time consumption for this procedure is very significant. Laser ablation proved that with <266nm ps laser beam, the ablation process on the diamond can easily achieve removing a few microns per hour from the surface and <100nm roughness. For amplifier application, laser ablation is an adequate and efficient process to make ultra thin diamond wafers following mechanical polishing. Hydrogenation will terminate the diamond surface with monolayer of hydrogen, and form NEA so that secondary electrons in the conduction band can escape into the vacuum. The method is using hydrogen cracker to strike hydrogen atoms onto the bare diamond surface to form H-C bonds. Two independent

  14. The formation of the positive, fixed charge at c-Si(111)/a-Si$_3$N$_{3.5}$:H interfaces

    CERN Document Server

    Hintzsche, L E; Marsman, M; Lamers, M W P E; Weeber, A W; Kresse, G

    2015-01-01

    Modern electronic devices are unthinkable without the well-controlled formation of interfaces at heterostructures. These often involve at least one amorphous material. Modeling such interfaces poses a significant challenge, since a meaningful result can only be expected by using huge models or by drawing from many statistically independent samples. Here we report on the results of high throughput calculations for interfaces between crystalline silicon (c-Si) and amorphous silicon nitride (a-Si$_3$N$_{3.5}$:H), which are omnipresent in commercially available solar cells. The findings reconcile only partly understood key features. At the interface, threefold coordinated Si atoms are present. These are caused by the structural mismatch between the amorphous and crystalline part. The local Fermi level of undoped c-Si lies well below that of a-SiN:H. To align the Fermi levels in the device, charge is transferred from the a-SiN:H part to the c-Si part resulting in an abundance of positively charged, threefold coord...

  15. Photocarrier radiometry for predicting the degradation of electrical parameters of monocrystalline silicon (c-Si) solar cell irradiated by 100 KeV proton beams

    Science.gov (United States)

    Song, P.; Liu, J. Y.; Yuan, H. M.; Oliullah, Md.; Wang, F.; Wang, Y.

    2016-09-01

    In this study, the monocrystalline silicon (c-Si) solar cell irradiated by 100 KeV proton beams at various fluences is investigated. A one-dimensional two-layer carrier density wave model has been developed to estimate the minority carrier lifetime of n-region and p-region of the non-irradiated c-Si solar cell by best fitting with the experimental photocarrier radiometry (PCR) signal (the amplitude and the phase). Furthermore, the lifetime is used to determine the initial defect density of the quasi-neutral region (QNR) of the solar cell to predict its I-V characteristics. The theoretically predicted short-circuit current density (Jsc), and open-circuit voltage (Voc) of the non-irradiated samples are in good agreement with experiment. Then a three-region defect distribution model for the c-Si solar cell irradiated by proton beams is carried out to describe the defect density distribution according to Monte Carlo simulation results and the initial defect density of the non-irradiated sample. Finally, we find that the electrical measurements of Jsc and Voc of the solar cells irradiated at different fluences using 100 KeV proton beams are consistent with the PCR predicting results.

  16. Chitin-Prussian blue sponges for Cs(I) recovery: From synthesis to application in the treatment of accidental dumping of metal-bearing solutions

    Energy Technology Data Exchange (ETDEWEB)

    Vincent, C. [Ecole des mines d' Alès, Centre des Matériaux des Mines d' Alès, C2MA/MPA/BCI, 6 avenue de Clavières, F-30319 Alès Cedex (France); Commissariat à l' Energie Atomique, CEA Marcoule, DEN/DTCD/SPDE/LPSD,BP 17171, F-30207 Bagnols sur Cèze (France); Barré, Y. [Commissariat à l' Energie Atomique, CEA Marcoule, DEN/DTCD/SPDE/LPSD,BP 17171, F-30207 Bagnols sur Cèze (France); Vincent, T. [Ecole des mines d' Alès, Centre des Matériaux des Mines d' Alès, C2MA/MPA/BCI, 6 avenue de Clavières, F-30319 Alès Cedex (France); Taulemesse, J.-M. [Ecole des mines d' Alès, Center des Matériaux des Mines d' Alès, 6 avenue de Clavières, F-30319 Alès Cedex (France); Robitzer, M. [Institut Charles Gerhardt – UMR5253, CNRS-UM2-ENSCM-UM1, ICGM-MACS-R2M2, 8 rue de l' Ecole Normale, F-34296 Montpellier Cedex 05 (France); Guibal, E., E-mail: Eric.Guibal@mines-ales.fr [Ecole des mines d' Alès, Centre des Matériaux des Mines d' Alès, C2MA/MPA/BCI, 6 avenue de Clavières, F-30319 Alès Cedex (France)

    2015-04-28

    Highlights: • Prussian blue microparticles incorporated in chitin sponges. • Efficient Cs(I) sorption after water absorption by dry hybrid sponge. • Water draining after sorption for metal confinement and water decontamination. • High decontamination factors and distribution coefficients for Cs(I) and {sup 137}Cs(I). • Effect of freezing conditions on porous structure and textural characterization. - Abstract: Prussian blue (i.e., iron[III] hexacyanoferrate[II], PB) has been synthesized by reaction of iron(III) chloride with potassium hexacyanoferrate and further immobilized in chitosan sponge (cellulose fibers were added in some samples to evaluate their impact on mechanical resistance). The composite was finally re-acetylated to produce a chitin-PB sponge. Experimental conditions such as the freezing temperature, the content of PB, the concentration of the biopolymer and the presence of cellulose fibers have been varied in order to evaluate their effect on the porous structure of the sponge, its water absorption properties and finally its use for cesium(I) recovery. The concept developed with this system consists in the absorption of contaminated water by the composite sponge, the in situ binding of target metal on Prussian blue load and the centrifugation of the material to remove treated water from soaked sponge. This material is supposed to be useful for the fast treatment of accidental dumping of Cs-contaminated water.

  17. Band Structure Parameters and Fermi Resonances of Exciton-Polaritons in CsI and CsBr under Hydrostatic Pressure

    Energy Technology Data Exchange (ETDEWEB)

    Lipp, M J; Yoo, C H; Strachan, D; Daniels, W B

    2005-11-29

    Most alkali halides crystallize in the fcc sodium chloride structure. In contrast, with the exception of CsF, the Cs-halides form the simple cubic cesium chloride (CsCl) structure at ambient conditions and they have a substantially different electronic structure than other alkali halides; in particular, they have several nearly degenerate electronic levels near the Brillouin zone center. Highly resolved Three-Photon Spectroscopy (TPS) measurements allow direct observation of the near band edge structure and, in the case of CsI, probe more states than one-photon techniques. A number of interesting phenomena, among them level repulsion (Fermi resonance), occur as these levels are tuned through one another by application of hydrostatic pressure. To the best of our knowledge, this has been observed for CsBr for the first time. Doubling the photon energy range compared to a previous publication [see Yoo et al. PRL 84, 3875 (2000)] allows direct observation of the n=1, 2 and 3 exciton-polariton members of the {Lambda}{sub 8}{sup -}-{Lambda}{sub 6}{sup +} transition in CsI and lets us establish unambiguous values for the bandgap (6.139 eV), binding energy (0.265 eV) and their pressure dependence up to 7 kbar. Similarly to CsI, the CsBr linewidth of the lowest {Lambda}{sub 4}{sup -} polariton (A) decreases upon compression.

  18. Chitin-Prussian blue sponges for Cs(I) recovery: From synthesis to application in the treatment of accidental dumping of metal-bearing solutions

    International Nuclear Information System (INIS)

    Highlights: • Prussian blue microparticles incorporated in chitin sponges. • Efficient Cs(I) sorption after water absorption by dry hybrid sponge. • Water draining after sorption for metal confinement and water decontamination. • High decontamination factors and distribution coefficients for Cs(I) and 137Cs(I). • Effect of freezing conditions on porous structure and textural characterization. - Abstract: Prussian blue (i.e., iron[III] hexacyanoferrate[II], PB) has been synthesized by reaction of iron(III) chloride with potassium hexacyanoferrate and further immobilized in chitosan sponge (cellulose fibers were added in some samples to evaluate their impact on mechanical resistance). The composite was finally re-acetylated to produce a chitin-PB sponge. Experimental conditions such as the freezing temperature, the content of PB, the concentration of the biopolymer and the presence of cellulose fibers have been varied in order to evaluate their effect on the porous structure of the sponge, its water absorption properties and finally its use for cesium(I) recovery. The concept developed with this system consists in the absorption of contaminated water by the composite sponge, the in situ binding of target metal on Prussian blue load and the centrifugation of the material to remove treated water from soaked sponge. This material is supposed to be useful for the fast treatment of accidental dumping of Cs-contaminated water

  19. High-gradient High-charge CW Superconducting RF gun with CsK2Sb photocathode

    CERN Document Server

    Pinayev, Igor; Tuozzolo, Joseph; Brutus, Jean Clifford; Belomestnykh, Sergey; Boulware, Chase; Folz, Charles; Gassner, David; Grimm, Terry; Hao, Yue; Jamilkowski, James; Jing, Yichao; Kayran, Dmitry; Mahler, George; Mapes, Michael; Miller, Toby; Narayan, Geetha; Sheehy, Brian; Rao, Triveni; Skaritka, John; Smith, Kevin; Snydstrup, Louis; Than, Yatming; Wang, Erdong; Wang, Gang; Xiao, Binping; Xin, Tianmu; Zaltsman, Alexander; Altinbas, Z; Ben-Zvi, Ilan; Curcio, Anthony; Di Lieto, Anthony; Meng, Wuzheng; Minty, Michiko; Orfin, Paul; Reich, Jonathan; Roser, Thomas; Smart, Loralie A; Soria, Victor; Theisen, Charles; Xu, Wencan; Wu, Yuan H; Zhao, Zhi

    2015-01-01

    High-gradient CW photo-injectors operating at high accelerating gradients promise to revolutionize many sciences and applications. They can establish the basis for super-bright monochromatic X-ray free-electron lasers, super-bright hadron beams, nuclear- waste transmutation or a new generation of microchip production. In this letter we report on our operation of a superconducting RF electron gun with a record-high accelerating gradient at the CsK2Sb photocathode (i.e. ~ 20 MV/m) generating a record-high bunch charge (i.e., 3 nC). We briefly describe the system and then detail our experimental results. This achievement opens new era in generating high-power electron beams with a very high brightness.

  20. Femtosecond timing-jitter between photo-cathode laser and ultra-short electron bunches by means of hybrid compression

    Science.gov (United States)

    Pompili, R.; Anania, M. P.; Bellaveglia, M.; Biagioni, A.; Castorina, G.; Chiadroni, E.; Cianchi, A.; Croia, M.; Di Giovenale, D.; Ferrario, M.; Filippi, F.; Gallo, A.; Gatti, G.; Giorgianni, F.; Giribono, A.; Li, W.; Lupi, S.; Mostacci, A.; Petrarca, M.; Piersanti, L.; Di Pirro, G.; Romeo, S.; Scifo, J.; Shpakov, V.; Vaccarezza, C.; Villa, F.

    2016-08-01

    The generation of ultra-short electron bunches with ultra-low timing-jitter relative to the photo-cathode (PC) laser has been experimentally proved for the first time at the SPARC_LAB test-facility (INFN-LNF, Frascati) exploiting a two-stage hybrid compression scheme. The first stage employs RF-based compression (velocity-bunching), which shortens the bunch and imprints an energy chirp on it. The second stage is performed in a non-isochronous dogleg line, where the compression is completed resulting in a final bunch duration below 90 fs (rms). At the same time, the beam arrival timing-jitter with respect to the PC laser has been measured to be lower than 20 fs (rms). The reported results have been validated with numerical simulations.

  1. A binary Al/Li alloy as a new material for the realization of high-intensity pulsed photocathodes

    Science.gov (United States)

    Septier, A.; Sabary, F.; Dudek, J. C.; Bergeret, H.; Leblond, B.

    1991-07-01

    We propose a new material for the fabrication of high-current photocathodes: a binary Al/Li alloy acting as a lithium dispenser cathode. This material would have the great advantage to allow regeneration of the Li layer after poisoning or air exposure, by a simple heating process. In a first experiment, we have measured the photoemission energy threshold, WΦ, of a piece of Al/Li alloy and the quantum yield, Y, as a function of the photon energy. After a heating process (340°C for 12 h) we obtained WΦ = 2 eV and Y = 6 × 10 -4 for 4.6 eV photon energy. In a second experiment another sample was illuminated with a 40 ps frequency-tripled YAG laser. After two heating processes, we obtained electron bunches containing 1 nC with an incident laser energy of 100 μJ per pulse.

  2. Recent Progress at SLAC Extracting High Charge from Highly-Polarized Photocathodes for Future-Collider Applications

    CERN Document Server

    Clendenin, J E; Garwin, E L; Harvey, S; Jiang, J; Kirby, R E; Luh, D A; Maruyama, T; Prepost, R; Prescott, C Y; Turner, J L

    2004-01-01

    Future colliders such as NLC and JLC will require a highly-polarized macropulse with charge that is more than an order of magnitude beyond that which could be produced for the SLC. The maximum charge from the SLC uniformly-doped GaAs photocathode was limited by the surface charge limit (SCL). The SCL effect can be overcome by using an extremely high (>1019 cm-3) surface dopant concentration. When combined with a medium dopant concentration in the majority of the active layer (to avoid depolarization), the surface concentration has been found to degrade during normal heat cleaning (1 hour at 600 C). The Be dopant as typically used in an MBE-grown superlattice cathode is especially susceptible to this effect compared to Zn or C dopant. Some relief can be found by lowering the cleaning temperature, but the long-term general solution appears to be atomic hydrogen cleaning.

  3. Development of ultra-violet femtosecond pulse radiolysis system based on a photocathode rf electron-gun linac

    International Nuclear Information System (INIS)

    Two important radical species of alkyl radical (R·) and hydroxyl radicals (OH·) in nuclear fuel reprocessing or radiation cancer therapy have absorption bands around the 250 nm in Ultra-violet region. Despite the OH· and R· are important active species in the radiation chemistry, since those absorption coefficients are small and lack of time resolution of pulse radiolysis, a direct study of the reaction dynamics has been difficult until now. In order to elucidate the formation and reaction with solutes, measurable wavelength was extended to ultraviolet of the femtosecond pulse radiolysis system using a photocathode RF gun accelerator. Problems of ultraviolet femtosecond pulse radiolysis measurement, the time dependent behaviors of R· and OH· are reported. (author)

  4. Experimental Observation of a 100-Femtosecond Single Electron Bunch in Photocathode Linac with Longitudinal Emittance Compensation Technique

    CERN Document Server

    Yang Jin Feng; Kondoh, Takafumi; Kozawa, Takahiro; Tagawa, Seiichi; Yoshida, Yoichi

    2005-01-01

    The realization of a 100fs electron pulse is important for the studies of ultrafast physical/chemical phenoena with a pump-probe method. We have developed a photocathode linear accelerator (linac) to generate such electron pulse with a magnetic pulse compressor. The nonlinear effect of the magnetic fields in the pulse compression was compensated carefully by optimizing the magnetic fields and the booster linac RF phase. A 105fs(rms) electron bunch with electron charge of 0.1nC was observed experimentally by using a femtosecond streak camera. The beam energy was 35MeV, and the normalized teraservers emittance was lower than 3mm-mrad. The dependences of the pulse length and the emittance on the electron charge were also measured and compared with the theoretical calculations.

  5. Some peculiarities of deformation at shock loading of CsI crystals and dynamics of individual dislocations

    International Nuclear Information System (INIS)

    Peculiarities of crystal deformation at shock (impact) loading are studied. The character of variation of the pulse value and shape along the sample is investigated. Dynamic braking of edge dislocations in CsI crystals with different concentration of anion impurities and thallium impurity is investigated on the basis of the new method of experimental data processing which does not use the model assumptions of the shape and duration of the pulse of tension. It is shown that in the 77-293 K temperature range the coefficient of viscous braking grows linearly with temperature. The anion impurities and thallium impurity at the concentrations used do not affect within the limits of the experimental error on the absolute value and temperature run of the viscous braking coefficient. The indication of transformation to the viscous regime of dislocation motion is yield to linearity of the dislocation path dependence on the distance to the free face plane. The dislocation braking coefficient is directly determined according to the dependence slope. Besides, in the process of measurements it should be taken into account the possibility of continuation of clastic vibrations in the sample after its resilience, as it occurred in some realizations of our experiments, and also residual sample deformation

  6. Recombination and thin film properties of silicon nitride and amorphous silicon passivated c-Si following ammonia plasma exposure

    International Nuclear Information System (INIS)

    Recombination at silicon nitride (SiNx) and amorphous silicon (a-Si) passivated crystalline silicon (c-Si) surfaces is shown to increase significantly following an ammonia (NH3) plasma exposure at room temperature. The effect of plasma exposure on chemical structure, refractive index, permittivity, and electronic properties of the thin films is also investigated. It is found that the NH3 plasma exposure causes (i) an increase in the density of Si≡N3 groups in both SiNx and a-Si films, (ii) a reduction in refractive index and permittivity, (iii) an increase in the density of defects at the SiNx/c-Si interface, and (iv) a reduction in the density of positive charge in SiNx. The changes in recombination and thin film properties are likely due to an insertion of N–H radicals into the bulk of SiNx or a-Si. It is therefore important for device performance to minimize NH3 plasma exposure of SiNx or a-Si passivating films during subsequent fabrication steps

  7. Surface passivation and optical characterization of Al2O3/a-SiCx stacks on c-Si substrates.

    Science.gov (United States)

    López, Gema; Ortega, Pablo R; Voz, Cristóbal; Martín, Isidro; Colina, Mónica; Morales, Anna B; Orpella, Albert; Alcubilla, Ramón

    2013-01-01

    The aim of this work is to study the surface passivation of aluminum oxide/amorphous silicon carbide (Al2O3/a-SiCx) stacks on both p-type and n-type crystalline silicon (c-Si) substrates as well as the optical characterization of these stacks. Al2O3 films of different thicknesses were deposited by thermal atomic layer deposition (ALD) at 200 °C and were complemented with a layer of a-SiCx deposited by plasma-enhanced chemical vapor deposition (PECVD) to form anti-reflection coating (ARC) stacks with a total thickness of 75 nm. A comparative study has been carried out on polished and randomly textured wafers. We have experimentally determined the optimum thickness of the stack for photovoltaic applications by minimizing the reflection losses over a wide wavelength range (300-1200 nm) without compromising the outstanding passivation properties of the Al2O3 films. The upper limit of the surface recombination velocity (S eff,max) was evaluated at a carrier injection level corresponding to 1-sun illumination, which led to values below 10 cm/s. Reflectance values below 2% were measured on textured samples over the wavelength range of 450-1000 nm. PMID:24367740

  8. Surface passivation and optical characterization of Al2O3/a-SiCx stacks on c-Si substrates

    Directory of Open Access Journals (Sweden)

    Gema López

    2013-11-01

    Full Text Available The aim of this work is to study the surface passivation of aluminum oxide/amorphous silicon carbide (Al2O3/a-SiCx stacks on both p-type and n-type crystalline silicon (c-Si substrates as well as the optical characterization of these stacks. Al2O3 films of different thicknesses were deposited by thermal atomic layer deposition (ALD at 200 °C and were complemented with a layer of a-SiCx deposited by plasma-enhanced chemical vapor deposition (PECVD to form anti-reflection coating (ARC stacks with a total thickness of 75 nm. A comparative study has been carried out on polished and randomly textured wafers. We have experimentally determined the optimum thickness of the stack for photovoltaic applications by minimizing the reflection losses over a wide wavelength range (300–1200 nm without compromising the outstanding passivation properties of the Al2O3 films. The upper limit of the surface recombination velocity (Seff,max was evaluated at a carrier injection level corresponding to 1-sun illumination, which led to values below 10 cm/s. Reflectance values below 2% were measured on textured samples over the wavelength range of 450–1000 nm.

  9. CSI Alberta : isotope analysis helps unlock the origin of water at oilsands projects

    Energy Technology Data Exchange (ETDEWEB)

    Ross, E.

    2009-10-15

    This article reported on a technology that uses carbon, nitrogen or oxygen isotope fingerprinting on water samples from oilsands operations to determine the origin of the water sample. The technique can identify if the water is snow melt or rainwater or groundwater. The technology is valuable in remote areas or areas where there is no long-term monitoring data such as in western and northern Canada. The purpose of the isotope program at the Alberta Research Council (ARC) is to gain as much baseline information on the water cycles and chemical cycles in an area before it is developed. The information can be used to potentially restore an oilsand site to its original state at some point in the future. Isotope technology could also support site restoration by comparing reclaimed sites to the baseline. Isotope technology converts water samples into various gases such as carbon dioxide and hydrogen and fires them through an electromagnet. The heavier molecules bend less as they fly through the flight tube. The number of molecules in each pathway are then counted to determine a ratio of those isotopes. ARC is also working with steam-assisted gravity drainage and oilsands mining companies on water isotope testing to determine the acid sensitivity of lakes. 1 fig.

  10. A gas scintillation counter with imaging optics and large area UV-detector

    CERN Document Server

    Nickles, J; Bräuning-Demian, A; Breskin, Amos; Chechik, R; Dangendorf, V; Rauschnabel, K; Schmidt-Böcking, H

    2002-01-01

    We report on the improvements in the position sensitive readout of a xenon-filled gas scintillation proportional counter. Using an imaging optic for UV-light in the region of 170 nm, the position resolution could be improved by more than 30%. In addition, we have obtained first encouraging results for the use of the recently developed gas electron multiplier together with a CsI-photocathode as a large area UV-detector system.

  11. A gas scintillation counter with imaging optics and large area UV-detector

    Energy Technology Data Exchange (ETDEWEB)

    Nickles, J. E-mail: nickles@hsb.uni-frankfurt.de; Braeuning, H.; Braeuning-Demian, A.; Dangendorf, V.; Breskin, A.; Chechik, R.; Rauschnabel, K.; Schmidt-Boecking, H

    2002-01-21

    We report on the improvements in the position sensitive readout of a xenon-filled gas scintillation proportional counter. Using an imaging optic for UV-light in the region of 170 nm, the position resolution could be improved by more than 30%. In addition, we have obtained first encouraging results for the use of the recently developed gas electron multiplier together with a CsI-photocathode as a large area UV-detector system.

  12. Novel assembly of an MoS2 electrocatalyst onto a silicon nanowire array electrode to construct a photocathode composed of elements abundant on the earth for hydrogen generation.

    Science.gov (United States)

    Tran, Phong D; Pramana, Stevin S; Kale, Vinayak S; Nguyen, Mai; Chiam, Sing Yang; Batabyal, Sudip K; Wong, Lydia H; Barber, James; Loo, Joachim

    2012-10-29

    Mild-mannered catalyst: a novel procedure to load a MoS(2) co-catalyst onto the surface of silicon under mild-conditions (room temperature, atmospheric pressure, aqueous solution) by a photo-assisted electrodeposition process employing commercially available precursors is reported. The obtained Si-NW@MoS(2) photocathode showed similar catalytic activity for light-driven H(2) generation compared with a Si-NW@Pt photocathode. PMID:23008230

  13. Analyses of CsI aerosol deposition in aerosol behavior tests in WIND project

    International Nuclear Information System (INIS)

    The aerosol deposition tests have been performed in WIND project at JAERI to characterize the aerosol behavior. The aerosol deposition tests named WAV1-D and WAV2-D were analyzed by aerosol behavior analysis codes, JAERI's ART and SNL's VICTORIA. The comparison calculation was performed for the confirmation of the analytical capabilities of the both codes and improvement of the models in ART. The deposition mass calculated by ART was larger than that by VICTORIA. This discrepancy is caused by differences in model for FP vapor condensation onto the wall surface. In the WAV2-D test, in which boric acid was placed on the floor area of the test section prior to the deposition phase to simulate the PWR primary coolant, there was a discrepancy in deposition mass between analytical results in both codes and experimental results. The discrepancy may be caused by existence of boric acid which is not considered in the codes. (author)

  14. Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions

    Science.gov (United States)

    Cheng, Chih-Hsien; Tzou, An-Jye; Chang, Jung-Hung; Chi, Yu-Chieh; Lin, Yung-Hsiang; Shih, Min-Hsiung; Lee, Chao-Kuei; Wu, Chih-I.; Kuo, Hao-Chung; Chang, Chun-Yen; Lin, Gong-Ru

    2016-01-01

    The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1-x) buffer is demonstrated. The a-SixC1-x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1-x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC1-x buffer. The C-rich SixC1-x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC1-x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Si-rich SixC1-x buffer, the device deposited on C-rich SixC1-x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively.

  15. Moments Based Framework for Performance Analysis of One-Way/Two-Way CSI-Assisted AF Relaying

    KAUST Repository

    Xia, Minghua

    2012-09-01

    When analyzing system performance of conventional one-way relaying or advanced two-way relaying, these two techniques are always dealt with separately and, thus, their performance cannot be compared efficiently. Moreover, for ease of mathematical tractability, channels considered in such studies are generally assumed to be subject to Rayleigh fading or to be Nakagami-$m$ channels with integer fading parameters, which is impractical in typical urban environments. In this paper, we propose a unified moments-based framework for general performance analysis of channel-state-information (CSI) assisted amplify-and-forward (AF) relaying systems. The framework is applicable to both one-way and two-way relaying over arbitrary Nakagami-$m$ fading channels, and it includes previously reported results as special cases. Specifically, the mathematical framework is firstly developed under the umbrella of the weighted harmonic mean of two Gamma-distributed variables in conjunction with the theory of Pad\\\\\\'e approximants. Then, general expressions for the received signal-to-noise ratios of the users in one-way/two-way relaying systems and the corresponding moments, moment generation function, and cumulative density function are established. Subsequently, the mathematical framework is applied to analyze, compare, and gain insights into system performance of one-way and two-way relaying techniques, in terms of outage probability, average symbol error probability, and achievable data rate. All analytical results are corroborated by simulation results as well as previously reported results whenever available, and they are shown to be efficient tools to evaluate and compare system performance of one-way and two-way relaying.

  16. Mo3S4 Clusters as an Effective H2 Evolution Catalyst on Protected Si Photocathodes

    DEFF Research Database (Denmark)

    Seger, Brian; Herbst, Konrad; Pedersen, Thomas;

    2014-01-01

    This work shows how a molecular Mo3S4 cluster bonded to a photoelectrode surface via a phosphonate ligand can be a highly effective co-catalyst in photocathodic hydrogen evolution systems. Using a TiO2 protected n+p Si photocathode, H2 evolution occurs with an onset of +0.33 V vs. RHE in an acid...... solution with this precious metal-free system. Using just the red part of the AM1.5 solar spectrum (λ > 635 nm), a saturation current of 20 mA/cm2 is achieved from an electrode containing Mo3S4 dropcasted onto a 100 nm TiO2/7 nm Ti/n+p Si electrode....

  17. Design of a high charge (10-100 nC) and short pulse (2-5 ps) RF photocathode gun for wakefield acceleration

    Science.gov (United States)

    Gai, W.; Li, X.; Conde, M.; Power, J.; Schoessow, P.

    1999-07-01

    In this paper we present a design report on a 1-1/2 cell, L Band RF photocathode gun that is capable of generating and accelerating electron beams with peak currents >10 kA. We have performed simulation for bunch intensities in the range of 10-100 nC with peak axial electrical field at the photocathode of 30-100 MV/m. Unlike conventional short electron pulse generation, this design does not require magnetic pulse compression. Based on numerical simulations using SUPERFISH and PARMELA, this design will produce 20-100 nC beam at 18 MeV with rms bunch length 0.6-1.25 mm and normalized transverse emittance 30-108 mm mrad. Applications of this beam for wakefield acceleration is also discussed.

  18. Scintillation response of CsI: Tl crystal under neutron, gamma, alpha particles and beta excitations

    International Nuclear Information System (INIS)

    Among the converters of X and gamma radiation in light photons, known as scintillators, the one which is the most efficient emits photons with a wavelength near 400 nm. Particularly, among them, the cesium iodine doped with thallium (CsI:Tl) crystal is that which matches better between the light emission spectrum (peak at 540 nm) and the quantum sensitivity curve of the photodiodes and CCD (Charge Coupled Device). This explains the renewed interest in using this crystal as scintillator. Although the CsI:Tl crystal is commercially available, its local development would give the possibility to obtain it in different geometric configurations and coupling. Moreover, there is a special interest in studying new conditions that will alter the properties of this crystal in order to achieve a optimal level of its functional characteristics. Having an efficient national scintillator with low cost is a strategic opportunity to study the response of a detector applied to different types of radiation. The crystal of cesium iodide activated with thallium (CsI:Tl) has a high gamma detection efficiency per unit volume. In this paper, the CsI:Tl crystal, grown by the vertical Bridgman technique in evacuated silica ampoules and with the purpose of use as radiation detectors, is described. To evaluate the scintillator, measures of the thallium distribution in the crystal volume were taken, with overall efficiency score. The scintillator response was studied through gamma radiation from sources of 137Cs, 60Co, 22Na, 54Mn, 131I and 99mTc; the beta radiation from source of 90Sr/90Y, alpha particles from 241Am source and the scintillator response to neutrons from Am/Be source. The energetic resolution for 137Cs gamma rays (662 keV) was 10%. The results showed the validity of using the CsI:Tl crystal developed in our laboratory, in many applications in the area of radiation detectors. (author)

  19. Characterization and performance of a high-power all-solid-state drive laser for application in high-current photo-cathode injectors

    International Nuclear Information System (INIS)

    This paper describes the characterization and performance of a diode-pumped, high-power, picosecond laser system designed for high-current photo-cathode accelerator injectors at repetition rates of both 74.85 MHz and 748.5 MHz. A comprehensive set of measurements and analyses are presented for the amplifier gain, thermally induced beam size variation, pulse width, harmonic conversion efficiency, beam quality, power stability, beam pointing stability, and timing jitter. This laser demonstrates excellent overall system performance.

  20. A Measurement Method of Time Jitter of a Laser Pulse with Respect to the Radio-Frequency Wave Phase in a Photocathode Radio-Frequency Gun

    Institute of Scientific and Technical Information of China (English)

    刘圣广; 李永贵; 王鸣凯

    2002-01-01

    In a photo-cathode radio-frequency (rf) gun, the micro-bunched charge output from the gun is dependent linearly on the laser injection phase, due to the Scottay effect in the process of photoemission and the procedure of the electron longitudinal acceleration. Based on this principle, a new method is proposed, which should be utilized to measure the time jitter between the driving laser pulse and the rf phase with a very high resolution of a few tens of femtoseconds.

  1. Unbiased Sunlight-Driven Artificial Photosynthesis of Carbon Monoxide from CO2 Using a ZnTe-Based Photocathode and a Perovskite Solar Cell in Tandem.

    Science.gov (United States)

    Jang, Youn Jeong; Jeong, Inyoung; Lee, Jaehyuk; Lee, Jinwoo; Ko, Min Jae; Lee, Jae Sung

    2016-07-26

    Solar fuel production, mimicking natural photosynthesis of converting CO2 into useful fuels and storing solar energy as chemical energy, has received great attention in recent years. Practical large-scale fuel production needs a unique device capable of CO2 reduction using only solar energy and water as an electron source. Here we report such a system composed of a gold-decorated triple-layered ZnO@ZnTe@CdTe core-shell nanorod array photocathode and a CH3NH3PbI3 perovskite solar cell in tandem. The assembly allows effective light harvesting of higher energy photons (>2.14 eV) from the front-side photocathode and lower energy photons (>1.5 eV) from the back-side-positioned perovskite solar cell in a single-photon excitation. This system represents an example of a photocathode-photovoltaic tandem device operating under sunlight without external bias for selective CO2 conversion. It exhibited a steady solar-to-CO conversion efficiency over 0.35% and a solar-to-fuel conversion efficiency exceeding 0.43% including H2 as a minor product. PMID:27359299

  2. Transmission photocathodes based on stainless steel mesh and quartz glass coated with N-doped DLC thin films prepared by reactive magnetron sputtering

    Science.gov (United States)

    Balalykin, N. I.; Huran, J.; Nozdrin, M. A.; Feshchenko, A. A.; Kobzev, A. P.; Arbet, J.

    2016-03-01

    The influence was investigated of N-doped diamond-like carbon (DLC) films properties on the quantum efficiency of a prepared transmission photocathode. N-doped DLC thin films were deposited on a silicon substrate, a stainless steel mesh and quartz glass (coated with 5 nm thick Cr adhesion film) by reactive magnetron sputtering using a carbon target and gas mixture Ar, 90%N2+10%H2. The elements' concentration in the films was determined by RBS and ERD. The quantum efficiency was calculated from the measured laser energy and the measured cathode charge. For the study of the vectorial photoelectric effect, the quartz type photocathode was irradiated by intensive laser pulses to form pin-holes in the DLC film. The quantum efficiency (QE), calculated at a laser energy of 0.4 mJ, rose as the nitrogen concentration in the DLC films was increased and rose dramatically after the micron-size perforation in the quartz type photocathodes.

  3. Optical telescopes for COMPASS RICH1 up-grade

    CERN Document Server

    Sulc, M; Alekseev, M; Angerer, H; Appolonio, M; Birsa, R; Bordalo, P; Bradamante, F; Bressan, A; Busso, L; Chiosso, V M; Ciliberti, P; Colantoni, M L; Costa, S; Dibiase, N; Dafni, T; Dalla Torre, S; Diaz, V; Duic, V; Delagnes, E; Deschamps, H; Eyrich, W; Faso, D; Ferrero, A; Finger, M; Finger, M Jr; Fischer, H; Gerassimov, S; Giorgi, M; Gobbo, B; Hagemann, R; von Harrach, D; Heinsius, F H; Joosten, R; Ketzer, B; Königsmann, K; Kolosov, V N; Konorov, I; Kramer, D; Kunne, F; Levorato, S; Maggiora, A; Magnon, A; Mann, A; Martin, A; Menon, G; Mutter, A; Nähle, O; Neyret, D; Nerling, F; Pagano, P; Paul, S; Panebianco, S; Panzieri, D; Pesaro, G; Pizzolotto, C; Polak, J; Rebourgeard, P; Rocco, E; Robinet, F; Schiavon, P; Schill, C; Schoenmeier, P; Silva, L; Slunecka, M; Steiger, L; Sozzi, F; Svec, M; Tessarotto, F; Teufel, A; Wollny, H

    2006-01-01

    The central photon detection area of the Ring Imaging Cherenkov detector at COMPASS, a particle physics experiment at CERN SPS dedicated to hadron physics, has been upgraded from the previous system formed by wire chambers with CsI layers to a very fast UV extended multi anode photo multiplier tube array (MAPMT), including 576 tubes. The active area covered by the MAPMTs is 7.3 times smaller than the one previously equipped with CsI photocathodes, so 576 optical concentrators transforming the image from the old system focal plane to the new photocathode plane were needed. The telescope system formed by two fused silica lenses was designed, produced and assembled. The first prismatic plano-convex field lens is placed in the focal plane of the RICH mirrors. The second condenser lens is off centered and tilted and has one aspherical surface. All lenses have antireflection coating.

  4. The PSIodine Code: A computer program to model experimental data on iodine and other species in irradiated CsI solutions sparged with argon, air, or nitrous oxide

    International Nuclear Information System (INIS)

    Highlights: → The PSIodine code predicts iodine radiolysis in CsI solutions and I2 mass transfer. → Code supports experimental data over a range of CsI concentrations and pH. → A model successfully predicts I2 reduction by nitrate radiolysis products. → Modelled I2 releases support radiolytic oxidation of AgI particle surfaces. - Abstract: Experimental study programmes were carried out at Paul Scherrer Institute (PSI), Switzerland on iodine behaviour under conditions relevant to postulated severe-accidents in NPP containments. To interpret the results obtained from bench-scale, gas-sparged and irradiated iodide solutions, a mechanistic computer code (PSIodine) was developed using the FACSIMILE Software to provide data for comparison. The code models reactions for the iodine oxidation states -1 to +5 in solution under strong (N2O-saturated) and weak oxidising (argon- and air-saturated) conditions. An empirical model was developed to transport I2 and other species from solution to the gas space by gas bubbles (sparging). By using measured I2 mass transfer rates for specific reaction vessels, the need to apply assumptions, e.g., uniform and estimated bubble sizes and concentration, diffusion coefficients, was circumvented. By using the same I2 transfer rate for irradiation of CsI solutions with and without additional ions, data for % I2 yields for initial chemical conditions can be compared. Reaction rate changes due to solution evaporation are also modelled. The predicted and experimental data (I2 fractional releases, pH changes and H2O2 formation) correlate well for initial CsI concentrations from 4.0 x 10-5 to 1.0 x 10-3 mol dm-3 and for pH 4.6-7.1 in weak oxidising systems (argon- and air-sparged solutions). Data correlations for strong oxidising conditions (N2O-saturated CsI solutions) are also satisfactory. Irradiated containment atmospheres can generate oxides of nitrogen, which form nitrate and nitrite ions in the sump. Nitrate concentrations up to 5

  5. CSI, de la série au jeu : « a more immersive experience »

    OpenAIRE

    Monnet-Cantagrel, Hélène

    2016-01-01

    CSI est une franchise de séries policières construites autour d’un même principe narratif de résolution des enquêtes par les techniques scientifiques d’investigation. D’objectif ouvertement commercial, de l’ordre du marketing, et répétitives, les franchises de médias n’ont pas toujours bonne presse, accusées de consacrer la transformation des biens culturels en produits industriels. Les franchises sont pourtant une pratique de plus en plus fréquente à la télévision - américaine - qui, depuis ...

  6. Coherence of a spin-polarized electron beam emitted from a semiconductor photocathode in a transmission electron microscope

    International Nuclear Information System (INIS)

    The brightness and interference fringes of a spin-polarized electron beam extracted from a semiconductor photocathode excited by laser irradiation are directly measured via its use in a transmission electron microscope. The brightness was 3.8 × 107 A cm−2 sr−1 for a 30-keV beam energy with the polarization of 82%, which corresponds to 3.1 × 108 A cm−2 sr−1 for a 200-keV beam energy. The resulting electron beam exhibited a long coherence length at the specimen position due to the high parallelism of (1.7 ± 0.3) × 10−5 rad, which generated interference fringes representative of a first-order correlation using an electron biprism. The beam also had a high degeneracy of electron wavepacket of 4 × 10−6. Due to the high polarization, the high degeneracy and the long coherence length, the spin-polarized electron beam can enhance the antibunching effect

  7. Growth of poly-crystalline Cu films on Y substrates by picosecond pulsed laser deposition for photocathode applications

    International Nuclear Information System (INIS)

    In this work, the deposition of Cu thin films on Y substrates for photocathode applications by pulsed laser deposition employing picosecond laser pulses is reported and compared with the use of nanosecond pulses. The influence of power density (6–50 GW/cm2) on the ablation of the target material, as well as on the properties of the resulting film, is discussed. The material transfer from the target to the substrate surface was found to be rather efficient, in comparison to nanosecond ablation, leading to the growth of films with high thickness. Scanning electron microscope analysis indicated a quasi-continuous film morphology, at low power density values, becoming granular with increasing power density. The structural investigation, through X-ray diffraction, revealed the poly-crystalline nature of the films, with a preferential growth along the (111) crystallographic orientation of Cu cubic network. Finally, energy-dispersive X-ray spectroscopy showed a low contamination level of the grown films, demonstrating the potential of a PLD technique for the fabrication of Cu/Y patterned structures, with applications in radiofrequency electron gun technology. - Highlights: • Cu thin films were successfully deposited on Y substrates through ultrafast PLD. • The film presents a quasi-continuous morphology. • The use of picosecond pulses increases the film thickness. • The Cu thin films are very adherent to the Y substrate

  8. Brazing of photocathode RF gun structures in Hydrogen atmosphere: Process qualification, effect of brazing on RF properties and vacuum compatibility

    International Nuclear Information System (INIS)

    In this paper, we report on the development of a brazing process for an ultra-high vacuum (UHV) compatible photocathode RF gun structure developed at our Centre. The choice of brazing alloy and its form, brazing clearance between parts to be joined and the brazing cycle adopted have been qualified through metallographic examination of identical joints on an OFE copper prototype that was cut open after brazing. The quality of brazed joint not only affects the UHV compatibility of the gun, but also influences the RF parameters finally achieved. A 2-D electromagnetic code, SUPERFISH, was used to predict the variation in RF parameters before and after brazing considering actual brazing clearances provided between the parts to be joined. Results obtained from low power RF measurements on the brazed gun structure confirm the integrity of the brazed joints and show good agreement with those predicted by electromagnetic simulations. The brazed gun structure has been leak-tested and pumped down to a vacuum level limited by the vacuum compatibility of the flange-fittings employed in the setup.

  9. Ultra-fast pulse radiolysis system combined with a laser photocathode RF gun and a femtosecond laser

    CERN Document Server

    Muroya, Y; Watanabe, T; Wu, G; Kobayashi, T; Yoshii, K; Ueda, T; Uesaka, M; Katsumura, Y

    2002-01-01

    In order to study the early events in radiation physics and chemistry, two kinds of new pulse radiolysis systems with higher time resolution based on pump-and-probe method have been developed at the Nuclear Engineering Research Laboratory, the University of Tokyo. The first one, a few picosecond (2 ps at FWHM) electron beam (pump) from an 18 MeV S-band Linac using a laser photocathode RF gun (BNL/KEK/SHI type: GUN IV) was operated with a femtosecond laser pulse (100 fs at FWHM), which also acted as the analyzing light (probe). The synchronization precision between the pump and the probe was 1.7 ps (rms). In a 1.0 cm sample cell, a time resolution of 12 ps was achieved. The second one, a picosecond (4 ps at FWHM) electron pulse from a 35 MeV S-band Linac employing a conventional thermionic gun with a sub-harmonic buncher, was synchronized with the femtosecond laser pulse, with a synchronization jitter of 2.8 ps (rms). A time resolution of 22 ps was obtained with 2 cm cell. This makes it possible to do the puls...

  10. Brazing of photocathode RF gun structures in Hydrogen atmosphere: Process qualification, effect of brazing on RF properties and vacuum compatibility

    Science.gov (United States)

    Kak, Ajay; Kulshreshtha, P.; Lal, Shankar; Kaul, Rakesh; Ganesh, P.; Pant, K. K.; Abhinandan, Lala

    2012-11-01

    In this paper, we report on the development of a brazing process for an ultra-high vacuum (UHV) compatible photocathode RF gun structure developed at our Centre. The choice of brazing alloy and its form, brazing clearance between parts to be joined and the brazing cycle adopted have been qualified through metallographic examination of identical joints on an OFE copper prototype that was cut open after brazing. The quality of brazed joint not only affects the UHV compatibility of the gun, but also influences the RF parameters finally achieved. A 2-D electromagnetic code, SUPERFISH, was used to predict the variation in RF parameters before and after brazing considering actual brazing clearances provided between the parts to be joined. Results obtained from low power RF measurements on the brazed gun structure confirm the integrity of the brazed joints and show good agreement with those predicted by electromagnetic simulations. The brazed gun structure has been leak-tested and pumped down to a vacuum level limited by the vacuum compatibility of the flange-fittings employed in the setup.

  11. Design simulations for a small emittance 2.7-cell photo-cathode rf-gun in jector

    Science.gov (United States)

    Yongzhang, Huang

    1997-05-01

    In order to produce the electron bunch with small emittance which is the key issue in the so-called SASE studies, the design studies on a two-and-half cell photocathode rf-gun has been conducted. The rf gun injector is optimized by using the code of Par mela. As a main result, the optimum is found to be a 2.7-cell cavity. The geometry and the coupling scheme of the requested cavity is studied in more detail with the codes of Mafia and Superfish. The beam iris of each cells is enlarged in order to wide n the mode separations. For the purpose of cancelling the influence of the coupling iris upon the field symmetry, the so-called symmetrical double-side input coupler is studied. The coupler will be assembled to the second cell and the critical matchin g has been achieved in the Mafia-T3 simulation. With this cavity, the final normalized rms emittance reaches the value of 0.81πmm-mrad at a charge of 1nC in the Parmela simulation.

  12. Design simulations for a small emittance 2.7-cell photo-cathode rf-gun injector

    International Nuclear Information System (INIS)

    In order to produce the electron bunch with small emittance which is the key issue in the so-called SASE studies, the design studies on a two-and-half cell photo-cathode rf-gun has been conducted. First of all, the main parameters of the rf-gun injector, for example, the cell lengths, the solenoidal strength and the accelerating gradient, were optimized by using the code of Parmela. As a main result, the optimum was found to be a 2.7-cell cavity. The geometry and the coupling scheme of the requested cavity was studied in some detail with the codes, Mafia and Superfish. The beam iris of each cells was enlarged in order to widen the mode separations. For the purpose of cancelling the influence of the coupling iris upon the field symmetry, the so-called symmetrical double-side input coupler was studied. The coupler will be assembled to the second cell and the critical matching has been achieved in the Mafia-T3 simulation. With this cavity, the final normalized rms emittance achieved the value of 0.81 πmm-mrad at a charge of 1nC in the Parmela simulation. (author)

  13. Solar Hydrogen Production Using Molecular Catalysts Immobilized on Gallium Phosphide (111)A and (111)B Polymer-Modified Photocathodes.

    Science.gov (United States)

    Beiler, Anna M; Khusnutdinova, Diana; Jacob, Samuel I; Moore, Gary F

    2016-04-20

    We report the immobilization of hydrogen-producing cobaloxime catalysts onto p-type gallium phosphide (111)A and (111)B substrates via coordination to a surface-grafted polyvinylimidazole brush. Successful grafting of the polymeric interface and subsequent assembly of cobalt-containing catalysts are confirmed using grazing angle attenuated total reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Photoelectrochemical testing in aqueous conditions at neutral pH shows that cobaloxime modification of either crystal face yields a similar enhancement of photoperformance, achieving a greater than 4-fold increase in current density and associated rates of hydrogen production as compared to results obtained using unfunctionalized electrodes tested under otherwise identical conditions. Under simulated solar illumination (100 mW cm(-2)), the catalyst-modified photocathodes achieve a current density ≈ 1 mA cm(-2) when polarized at 0 V vs the reversible hydrogen electrode reference and show near-unity Faradaic efficiency for hydrogen production as determined by gas chromatography analysis of the headspace. This work illustrates the modularity and versatility of the catalyst-polymer-semiconductor approach for directly coupling light harvesting to fuel production and the ability to export this chemistry across distinct crystal face orientations. PMID:26998554

  14. Study on energy difference compensation for high intense multi-bunch electron beam generated by a photocathode RF-gun

    International Nuclear Information System (INIS)

    At Waseda University, we have been studying a high quality electron beam generation and its application experiments with a Cs-Te photocathode RF-Gun. To generate more intense and stable electron beam, we have been developing the cathode irradiating UV laser which consists of optical fiber amplifier and LD pumped amplifier. As the result, more than 100 multi-bunch electron beam with 1nC each bunch charge was obtained. However, it has to be considered that the accelerating voltage will decrease because of the beam loading effect. So we have studied the RF amplitude modulation technique to compensate the bunch by bunch energy difference. The energy difference will caused by transient accelerating voltage in RF-Gun cavity and beam loading effect. As the result of this compensation method, the energy difference has been compensated to 1% p-p, while 5% p-p without compensation. In this conference, we will report our multi-bunch electron beam linac system, the details of energy compensation method using the RF amplitude modulation and the results of beam experiment. (author)

  15. Growth of poly-crystalline Cu films on Y substrates by picosecond pulsed laser deposition for photocathode applications

    Energy Technology Data Exchange (ETDEWEB)

    Gontad, F. [Università del Salento, Dipartimento di Matematica e Fisica “E. De Giorgi” and Istituto Nazionale di Fisica Nucleare, 73100 Lecce (Italy); Lorusso, A., E-mail: antonella.lorusso@le.infn.it [Università del Salento, Dipartimento di Matematica e Fisica “E. De Giorgi” and Istituto Nazionale di Fisica Nucleare, 73100 Lecce (Italy); Klini, A.; Manousaki, A. [Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FORTH), 100 N. Plastira St., GR 70013 Heraklion, Crete (Greece); Perrone, A. [Università del Salento, Dipartimento di Matematica e Fisica “E. De Giorgi” and Istituto Nazionale di Fisica Nucleare, 73100 Lecce (Italy); Fotakis, C. [Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FORTH), 100 N. Plastira St., GR 70013 Heraklion, Crete (Greece)

    2015-11-01

    In this work, the deposition of Cu thin films on Y substrates for photocathode applications by pulsed laser deposition employing picosecond laser pulses is reported and compared with the use of nanosecond pulses. The influence of power density (6–50 GW/cm{sup 2}) on the ablation of the target material, as well as on the properties of the resulting film, is discussed. The material transfer from the target to the substrate surface was found to be rather efficient, in comparison to nanosecond ablation, leading to the growth of films with high thickness. Scanning electron microscope analysis indicated a quasi-continuous film morphology, at low power density values, becoming granular with increasing power density. The structural investigation, through X-ray diffraction, revealed the poly-crystalline nature of the films, with a preferential growth along the (111) crystallographic orientation of Cu cubic network. Finally, energy-dispersive X-ray spectroscopy showed a low contamination level of the grown films, demonstrating the potential of a PLD technique for the fabrication of Cu/Y patterned structures, with applications in radiofrequency electron gun technology. - Highlights: • Cu thin films were successfully deposited on Y substrates through ultrafast PLD. • The film presents a quasi-continuous morphology. • The use of picosecond pulses increases the film thickness. • The Cu thin films are very adherent to the Y substrate.

  16. The influence of zero-mode on beam properties at 1.6 cell photocathode RF gun

    International Nuclear Information System (INIS)

    Recently, due to multi-bunch laser injection, it is worried that 0 mode, which is not considerable with single-bunch injection, could be excited by beam loading and would degrade the beam properties. Then, we evaluated the influence in a BNL/SLAC/UCLA 1.6 cell photocathode RF gun, which is made use of widely, by using particle tracking simulations. We assumed the charge in a bunch was 1 nC, and the frequency of the laser injection was the same as that of RF electric field (2856 MHz). As a result, the electric field of the 0 mode became larger and its phase changed by nearly 180deg compared with the case without beam loading. Hence, the influence of the 0 mode on the beam properties, i.e. energy spread, transverse emittance, and bunch length, showed the opposite behavior to the single-bunch injection scheme. The change in energy spread by 0 mode at 10deg laser injection phase was about -20% without beam loading and +40% with beam loading. (author)

  17. A method to give chemically stabilities of photoelectrodes for water splitting: Compositing of a highly crystalized TiO2 layer on a chemically unstable Cu2O photocathode using laser-induced crystallization process

    Science.gov (United States)

    Nishikawa, Masami; Fukuda, Masayuki; Nakabayashi, Yukihiro; Saito, Nobuo; Ogawa, Nobuhiro; Nakajima, Tomohiko; Shinoda, Kentaro; Tsuchiya, Tetsuo; Nosaka, Yoshio

    2016-02-01

    To prevent the self-reduction of the Cu2O photocathode for solar hydrogen production, we developed a compositing process of a highly crystalized TiO2 layer on the Cu2O photocathode using an excimer-laser-assisted metal-organic deposition (ELAMOD) process. The TiO2 layer was successfully crystalized without oxidation of Cu2O to CuO mainly owing to a photothermal effect with nanosecond duration time induced by laser absorption of the TiO2 precursor while the crystallization of the TiO2 layer by usual furnace heating process was accompanied by oxidation of Cu2O which degrade the water reduction ability. On the TiO2/Cu2O photocathode prepared by ELAMOD process, the self-reduction of Cu2O did not occur and then photocurrent due to water reduction was constant with reaction time while on the bare Cu2O photocathode, the photocurrent decreased owing to the occurrence of the self-reduction. This indicated that reaction stability of the photocathode was largely enhanced after compositing of the crystallineTiO2 layer. This ELAMOD process would be applicable for any kinds of chemically unstable photoelectrodes containing non-oxides such as sulfides and phosphides, and therefore any kinds of photoelectrodes would have potentials toward a practical use by improving their chemical stabilities.

  18. Photocarrier Radiometry for Noncontact Evaluation of Monocrystalline Silicon (c-Si) Solar Cell Irradiated by 1 MeV Electron Beams

    Science.gov (United States)

    Song, P.; Liu, J. Y.; Yuan, H. M.; Wang, F.; Wang, Y.

    2016-08-01

    In this paper, the monocrystalline silicon (c-Si) solar cell irradiated by 1 MeV electron beams was investigated using noncontact photocarrier radiometry (PCR). A theoretical 1D two-layer PCR model including the impedance effect of the p-n junction was used to characterize the transport properties (carrier lifetime, diffusion coefficient, and surface recombination velocities) of c-Si solar cells irradiated by 1 MeV electron beams with different fluences. The carrier transport parameters were derived by the best fit through PCR measurements. Furthermore, an Ev+0.56 eV trap was introduced into the band gap based on the minority carrier lifetime reduction. An I-V characteristic was obtained by both AFORS-HET simulation and experimental study, and the simulation results shows in good agreement with the experimental results. Moreover, the simulation and experiment results also indicate that the increase of fluences of electron beams results in the reduction of short-circuit current and open-circuit voltage.

  19. To Think and Watch the Evil: The Turn of the Screw as Cultural Reference in Television from Dark Shadows to C.S.I.

    Directory of Open Access Journals (Sweden)

    Anna Viola Sborgi

    2012-07-01

    Full Text Available Since its first publication, Henry James’s The Turn of the Screw (1898 has always haunted the imagination of artists (Benjamin Britten, Jack Clayton, Amenábar and has been widely used as a source for television narratives (Dan Curtis, US TV version starring Colin Firth, Tim Fywell. In serial productions, James’s story has been the object of extensive quotation and allusion, from the 1960 gothic soap opera Dark Shadows to the C.S.I. episode Turn of the Screw (Season 4, Episode 21. A milestone in literary history, the story now embodies a set of cultural references conveying different, complex meanings, which can only be disclosed in the light of contemporary forms of representing reality. The novella appeals to two apparently opposite tendencies in contemporary television: the morbid display of the real (C.S.I. and the quest for the supernatural (Buffy The Vampire Slayer, among others. A line can be traced from Dark Shadows, the show that pioneered the genre, to contemporary horror soaps about vampires and supernatural phenomena. This paper shows the ways in which James’ sophisticated novella makes its way through popular culture, and how its constant ambiguous, dilemmatic interplay between reality and imagination can be related to the double-sided drive of the contemporary public towards hyper-reality and the supernatural.

  20. In Situ PL and SPV Monitored Charge Carrier Injection During Metal Assisted Etching of Intrinsic a-Si Layers on c-Si.

    Science.gov (United States)

    Greil, Stefanie M; Rappich, Jörg; Korte, Lars; Bastide, Stéphane

    2015-06-01

    Although hydrogenated amorphous silicon is already widely examined regarding its structural and electronic properties, the chemical etching behavior of this material is only roughly understood. We present a detailed study of the etching properties of intrinsic hydrogenated amorphous silicon, (i)a-Si:H, layers on crystalline silicon, c-Si, within the framework of metal assisted chemical etching (MACE) using silver nanoparticles (Ag NPs). The etching processes are examined by in situ photoluminescence (PL) and in situ surface photovoltage (SPV) measurements, as these techniques allow a monitoring of the hole injection that takes place during MACE. By in situ PL measurements and SEM images, we could interpret the different stages of the MACE process of (i)a-Si:H layers and determine etch rates of (i)a-Si:H, that are found to be influenced by the size of the Ag NPs. In situ PL and in situ SPV measurements both enable researchers to determine when the Ag NPs reach the (i)a-Si:H/c-Si interface. Furthermore, a preferential MACE of (i)a-Si:H versus c-Si is revealed for the first time. This effect could be explained by an interplay of the different thermodynamic and structural properties of the two materials as well as by hole injection during MACE resulting in a field effect passivation. The presented results allow an application of the examined MACE processes for Si nanostructuring applications. PMID:25965159