Electron cloud in the CERN accelerators (PS, SPS, LHC)

International Nuclear Information System (INIS)

Iadarola, G; Rumolo, G

2013-01-01

Several indicators have pointed to the presence of an Electron Cloud (EC) in some of the CERN accelerators, when operating with closely spaced bunched beams. In particular, spurious signals on the pick ups used for beam detection, pressure rise and beam instabilities were observed at the Proton Synchrotron (PS) during the last stage of preparation of the beams for the Large Hadron Collider (LHC), as well as at the Super Proton Synchrotron (SPS). Since the LHC has started operation in 2009, typical electron cloud phenomena have appeared also in this machine, when running with trains of closely packed bunches (i.e. with spacings below 150ns). Beside the above mentioned indicators, other typical signatures were seen in this machine (due to its operation mode and/or more refined detection possibilities), like heat load in the cold dipoles, bunch dependent emittance growth and degraded lifetime in store and bunch-by-bunch stable phase shift to compensate for the energy loss due to the electron cloud. An overview of the electron cloud status in the different CERN machines (PS, SPS, LHC) will be presented in this paper, with a special emphasis on the dangers for future operation with more intense beams and the necessary countermeasures to mitigate or suppress the effect. (author)

Performance of Carbon Coatings for Mitigation of Electron Cloud in the SPS

CERN Document Server

Yin Vallgren, C; Costa Pinto, P; Neupert, H; Rumolo, G; Shaposhnikova, E; Taborelli, M; Kato, S

2011-01-01

Amorphous carbon (a-C) coatings have been tested in electron cloud monitors (ECM) in the Super Proton Synchrotron (SPS) and have shown for LHC type beams a reduction of the electron cloud current by a factor 104 compared to stainless steel (StSt). This performance has been maintained for more than 3 years under SPS operation conditions. Secondary electron yield (SEY) laboratory data confirm that after more than 1 year of SPS operation, the coating maintains a SEY below 1.0. The compatibility of coexisting StSt and a-C surfaces has been studied in an ECM having coated and uncoated areas. The results show no degradation of the properties of the a-C areas. The performance of diamond like carbon (DLC) coating has also been studied. DLC shows a less effective reduction of the EC current than a-C, but conditioning is faster than for StSt. Three a-C coated dipoles were inserted in the SPS. However, even with no EC detected, the dynamic pressure rise is similar to the one observed in the StSt reference dipoles. Measu...

Simulations of the Electron Cloud Build Up and Instabilities for Various ILC Damping Ring Configurations

International Nuclear Information System (INIS)

Pivi, Mauro; Raubenheimer, Tor O.; Wang, Lanfa; Ohmi, Kazuhito; Wanzenberg, Rainer; Wolski, Andrzej

2007-01-01

In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an electron cloud may be first produced by photoelectrons and ionization of residual gases and then increased by the secondary emission process. This paper reports the assessment of electron cloud effects in a number of configuration options for the ILC baseline configuration. Careful estimates were made of the secondary electron yield (sometimes in the literature also referred as secondary emission yield SEY or (delta), with a peak value (delta) max ) threshold for electron cloud build-up, and the related single- and coupled-bunch instabilities, as a function of beam current and surface properties for a variety of optics designs. When the configuration for the ILC damping rings was chosen at the end of 2005, the results from these studies were important considerations. On the basis of the joint theoretical and experimental work, the baseline configuration currently specifies a pair of 6 km damping rings for the positron beam, to mitigate the effects of the electron cloud that could present difficulties in a single 6 km ring. However, since mitigation techniques are now estimated to be sufficiently mature, a reduced single 6-km circumference is presently under consideration so as to reduce costs

Electron Cloud Observations during LHC Operation with 25 ns Beams

CERN Document Server

Li, Kevin; Iadarola, Giovanni; Mether, Lotta; Romano, Annalisa; Rumolo, Giovanni; Schenk, Michael

2016-01-01

While during the Run 1 (2010-2012) of the Large Hadron Collider (LHC) most of the integrated luminosity was produced with 50 ns bunch spacing, for the Run 2 start-up (2015) it was decided to move to the nominal bunch spacing of 25 ns. As expected, with this beam configuration strong electron cloud effects were observed in the machine, which had to be mitigated with dedicated 'scrubbing' periods at injection energy. This enabled to start the operation with 25 ns beams at 6.5 TeV, but e-cloud effects continued to pose challenges while gradually increasing the number of circulating bunch trains. This contribution will review the encountered limitations and the mitigation measures that where put in place and will discuss possible strategies for further performance gain.

Proceedings of Joint INFN-CERN-EuCARD-AccNet Workshop on Electron-Cloud Effects

International Nuclear Information System (INIS)

Cimino, R; Rumolo, Giovanni; Zimmermann, Frank

2013-01-01

This report contains the Proceedings of the Joint INFN-Frascati, INFN-Pisa, CERN-LER and EuCARD-AccNet Mini-Workshop on Electron-Cloud Effects, “ECLOUD12”, held at La Biodola, Isola d’Elba, from 5 to 9 June 2012. The ECLOUD12 workshop reviewed many recent electron-cloud (EC) observations at existing storage rings, EC predictions for future accelerators, electron-cloud studies at DAFNE, EC mitigation by clearing electrodes and graphite/carbon coatings, modeling of incoherent EC effects, self-consistent simulations, synergies with other communities like the Valencia Space Consortium and the European Space Agency. ECLOUD12 discussed new EC observations at existing machines including LHC, CesrTA, PETRA-3, J-PARC, and FNAL MI; latest experimental efforts to characterize the EC – including EC diagnostics, experimental techniques, mitigation techniques such as coating and conditioning, advanced chemical and physical analyses of various vacuum-chamber surfaces, beam instabilities and emittance growth –; the status of EC physics models and (new, more versatile and additional) simulation codes and their comparison with recently acquired experimental data; and the mitigation requirements and potential performance limitations imposed by the EC on upgraded and future machines, including HL-LHC, FAIR, ILC, Project-X, SuperB and SuperKEKB. A dedicated session addressed problems related to RF breakdown and multipacting for space applications. A number of open questions and future R&D needs were identified

Electron Cloud Buildup Characterization Using Shielded Pickup Measurements and Custom Modeling Code at CESRTA

CERN Document Server

Crittenden, James A

2013-01-01

The Cornell Electron Storage Ring Test Accelerator experimental program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1-m-long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. They detect cloud electrons migrating through an 18-mm-diameter pattern of small holes in the top of the chamber. A digitizing oscilloscope is used to record the signals, providing time-resolved information on cloud development. Carbon-coated, TiN-coated and uncoated aluminum chambers have been tested. Electron and positron beams of 2.1, 4.0 and 5.3 GeV with a variety of bunch populations and spacings in steps of 4 and 14 ns have been used. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to the physical phenomena determining cloud buildup such as the photoelectron produ...

Electron cloud effects in hadron beams

Energy Technology Data Exchange (ETDEWEB)

Petrov, Fedor; Boine-Frankenheim, Oliver; Weiland, Thomas [TU-Darmstadt, Institut fuer Theorie Elektromagnetischer Felder,Schlossgartenstr. 8 64289 Darmstadt (Germany)

2013-07-01

Accelerators operating with intense positively charged beams can suffer from the electron cloud phenomenon. For example, it is the intensity limiting factor in CERN LHC and SPS. In past decades a lot of progress in understanding the electron cloud effects was made worldwide. Methods to suppress or weaken the electron cloud phenomenon were proposed. Theories governing the bunch stability in presence of the electron cloud were developed. Recently the theory was introduced to describe the bunch energy loss due to the electron cloud. However, most of the publications concern the single bunch electron cloud effects. In reality bunches are packed into trains. A disturbance of the cloud caused by the bunch in the beginning of the train affects the subsequent bunches. We present a further investigation of single-bunch electron cloud effects and planned activities to study the phenomenon in case of multiple bunches.

Status of experimental studies of electron cloud effects at the Los Alamos proton storage ring

International Nuclear Information System (INIS)

Macek, R.J.; Browman, A.A.; Borden, M.J.; Fitzgerald, D.H.; McCrady, R.C.; Spickermann, T.J.; Zaugg, T.J.

2004-01-01

Various electron cloud effects (ECE) including the two-stream (e-p) instability at the Los Alamos Proton Storage Ring (PSR) have been studied extensively for the past five years with the goal of understanding the phenomena, mitigating the instability and ultimately increasing beam intensity. The specialized diagnostics used in the studies are two types of electron detectors, the retarding field analyzer and the electron sweepmg detector - which have been employed to measure characteristics of the electron cloud as functions of time, location in the ring and various influential beam parameters - plus a short stripline beam position monitor used to measure high frequency motion of the beam centroid. Highlights of this research program are summarized along with more detail on recent results obtained since the ECLOUD'02 workshop. Recent work mcludes a number of parametric studies of the various factors that affect the electron cloud signals, studies of the sources of initial or 'seed' electrons, additional observations of electron cloud dissipation after the beam pulse is extracted, studies of the 'first pulse instability' issue, more data on electron suppression as a cure for the instability, and observations of the effect of a one-turn weak kick on intense beams in the presence of a significant electron cloud.

Method of approximating the effects of blast mitigation materials on particulate-containing clouds formed by explosions

International Nuclear Information System (INIS)

Dyckes, G.W.

1983-09-01

A numerical model was developed for predicting the effect of blast mitigation materials on the rise and entrainment rate of explosively driven buoyant clouds containing radiotoxic particles. Model predictions for clouds from unmitigated explosions agree with published observations. More experimental data are needed to assess the validity of predictions for clouds from mitigated explosions

Modeling microwave/electron-cloud interaction

International Nuclear Information System (INIS)

Mattes, M; Sorolla, E; Zimmermann, F

2013-01-01

Starting from the separate codes BI-RME and ECLOUD or PyECLOUD, we are developing a novel joint simulation tool, which models the combined effect of a charged particle beam and of microwaves on an electron cloud. Possible applications include the degradation of microwave transmission in telecommunication satellites by electron clouds; the microwave-transmission techniques being used in particle accelerators for the purpose of electroncloud diagnostics; the microwave emission by the electron cloud itself in the presence of a magnetic field; and the possible suppression of electron-cloud formation in an accelerator by injecting microwaves of suitable amplitude and frequency. A few early simulation results are presented. (author)

CESR Conversion Damping Ring Studies of Electron Cloud Instabilities (CESR-TA)

International Nuclear Information System (INIS)

Rubin, David L.; Palmer, Mark A.

2011-01-01

In the International Linear Collider, two linear accelerators will accelerate bunches of positrons and electrons to over a hundred billion electron volts and collide them in a central detector. In order to obtain useful collision rates, the bunches, each containing twenty billion particles, must be compressed to a cross section of a few nanometers by a few hundred nanometers. In order to prepare these ultra high density bunches, damping rings (DRs) are employed before the linear accelerators. The DRs take the high emittance bunches that are provided by the electron and positron sources and, through the process of radiation damping, squeeze them into ultra low emittance beams that are ready for the main linear accelerators. In the damping rings, a number of effects can prevent the successful preparation of the beams. In the electron ring, an effect known as the fast ion instability can lead to beam growth and, in the positron ring, the build-up of an electron cloud (EC), which interacts with the circulating bunches, can produce the same effect. EC build-up and the subsequent interaction of the cloud with the positron beam in the DR have been identified as major risks for the successful construction of a linear collider. The CESRTA research program at the Cornell Electron Storage Ring (CESR) was developed in order to study the build-up of the EC, the details of its impact on ultra low emittance beams, as well as methods to mitigate the impact of the cloud. In the DR, the EC forms when synchrotron photons radiated from the circulating beam strike the walls of the vacuum chamber, resulting in the emission of photoelectrons. These low energy electrons can be accelerated across the vacuum chamber by the electric field of the beam, and strike the walls, causing the emission of secondary electrons. The secondary electrons are subsequently accelerated into the walls yet again via the same mechanism. The result is that the EC can rapidly begin to fill the vacuum chamber. In

CESR Conversion Damping Ring Studies of Electron Cloud Instabilities (CESR-TA)

Energy Technology Data Exchange (ETDEWEB)

Rubin, David L.; Palmer, Mark A.

2011-08-02

In the International Linear Collider, two linear accelerators will accelerate bunches of positrons and electrons to over a hundred billion electron volts and collide them in a central detector. In order to obtain useful collision rates, the bunches, each containing twenty billion particles, must be compressed to a cross section of a few nanometers by a few hundred nanometers. In order to prepare these ultra high density bunches, damping rings (DRs) are employed before the linear accelerators. The DRs take the high emittance bunches that are provided by the electron and positron sources and, through the process of radiation damping, squeeze them into ultra low emittance beams that are ready for the main linear accelerators. In the damping rings, a number of effects can prevent the successful preparation of the beams. In the electron ring, an effect known as the fast ion instability can lead to beam growth and, in the positron ring, the build-up of an electron cloud (EC), which interacts with the circulating bunches, can produce the same effect. EC build-up and the subsequent interaction of the cloud with the positron beam in the DR have been identified as major risks for the successful construction of a linear collider. The CESRTA research program at the Cornell Electron Storage Ring (CESR) was developed in order to study the build-up of the EC, the details of its impact on ultra low emittance beams, as well as methods to mitigate the impact of the cloud. In the DR, the EC forms when synchrotron photons radiated from the circulating beam strike the walls of the vacuum chamber, resulting in the emission of photoelectrons. These low energy electrons can be accelerated across the vacuum chamber by the electric field of the beam, and strike the walls, causing the emission of secondary electrons. The secondary electrons are subsequently accelerated into the walls yet again via the same mechanism. The result is that the EC can rapidly begin to fill the vacuum chamber. In

Coherent Radiation of Electron Cloud

International Nuclear Information System (INIS)

Heifets, S.

2004-01-01

The electron cloud in positron storage rings is pinched when a bunch passes by. For short bunches, the radiation due to acceleration of electrons of the cloud is coherent. Detection of such radiation can be used to measure the density of the cloud. The estimate of the power and the time structure of the radiated signal is given in this paper

Recent Experimental Results on Amorphous Carbon Coatings for Electron Cloud Mitigation

CERN Document Server

Yin Vallgren, C; Chiggiato, P; Costa Pinto, P; Neupert, H; Taborelli, M; Rumolo, G; Shaposhnikova, E; Vollenberg, W

2011-01-01

Amorphous carbon (a-C) thin films, produced in different coating configurations by using DC magnetron sputtering, have been investigated in laboratory for low secondary electron yield (SEY) applications. After the coatings had shown a reliable low initial SEY, the a-C thin films have been applied in the CERN Super Proton Synchrotron (SPS) and tested with Large Hadron Collider (LHC) type beams.Currently, we have used a-C thin film coated in so-called liner configuration for the electron cloud monitors. In addition the vacuum chambers of three dipole magnets have been coated and inserted into the machine. After describing the different configurations used for the coatings, results of the tests in the machine and a summary of the analyses after extraction will be presented. Based on comparison between different coating configurations, a new series of coatings has been applied on three further dipole magnet vacuum chambers. They have been installed and will be tested in coming machine development runs.

Low Secondary Electron Yield Carbon Coatings for Electron-cloud Mitigation in Modern Particle Accelerators

CERN Document Server

Yin Vallgren, Christina; Calatroni, Sergio; Chiggiato, Paolo; Costa Pinto, Pedro; Marques, Hugo; Neupert, Holger; Taborelli, Mauro; Vollenberg, Wilhelmus; Wevers, Ivo; Yaqub, Kashif

2010-01-01

Electron-cloud is one of the main limitations for particle accelerators with positively charged beams of high intensity and short bunch spacing, as the SPS at CERN. The Secondary Electron Yield (SEY) of the inner surface of the vacuum chamber is the main parameter governing the phenomenon. The effect could be eliminated by coating the vacuum chambers with a material of low SEY, which does not require bake-out and is robust against air exposure. For such a purpose amorphous carbon (a-C) coatings were produced by magnetron sputtering of graphite targets. They exhibit maximum SEY between 0.95 and 1.05 after air transfer to the measuring instrument. After 1 month of air exposure the SEY rises by 10 - 20 % of the initial values. Storage in desiccator or by packaging in Al foil makes this increase negligible. The coatings have a similar X-ray photoelectron spectroscopy (XPS) C1s spectrum for a large set of deposition parameters and exhibit an enlarged linewidth compared to HOPG graphite. The static outgassing witho...

Investigation into electron cloud effects in the International Linear Collider positron damping ring

Energy Technology Data Exchange (ETDEWEB)

Crittenden, J. A.; Conway, J.; Dugan, G. F.; Palmer, M. A.; Rubin, D. L.; Shanks, J.; Sonnad, K. G.; Boon, L.; Harkay, K.; Ishibashi, T.; Furman, M. A.; Guiducci, S.; Pivi, M. T. F.; Wang, L.

2014-03-01

We report modeling results for electron cloud buildup and instability in the International Linear Collider positron damping ring. Updated optics, wiggler magnets, and vacuum chamber designs have recently been developed for the 5 GeV, 3.2-km racetrack layout. An analysis of the synchrotron radiation profile around the ring has been performed, including the effects of diffuse and specular photon scattering on the interior surfaces of the vacuum chamber. The results provide input to the cloud buildup simulations for the various magnetic field regions of the ring. The modeled cloud densities thus obtained are used in the instability threshold calculations. We conclude that the mitigation techniques employed in this model will suffice to allow operation of the damping ring at the design operational specifications

Mitigation of the electron-cloud effect in the PSR and SNS protonstorage rings by tailoring the bunch profile

CERN Document Server

Pivi, M T

2003-01-01

For the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and for the Proton Storage Ring (PSR) at Los Alamos, both with intense and very long bunches, the electron cloud develops primarily by the mechanism of trailing-edge multipacting. We show, by means of simulations for the PSR, how the resonant nature of this mechanism may be effectively broken by tailoring the longitudinal bunch profile at fixed bunch charge, resulting in a significant decrease in the electron-cloud effect. We briefly discuss the experimental difficulties expected in the implementation of this cure.

MITIGATION OF THE ELECTRON-CLOUD EFFECT IN THE PSR AND SNS PROTONSTORAGE RINGS BY TAILORING THE BUNCH PROFILE

International Nuclear Information System (INIS)

Pivi, Mauro T F

2003-01-01

For the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and for the Proton Storage Ring (PSR) at Los Alamos, both with intense and very long bunches, the electron cloud develops primarily by the mechanism of trailing-edge multipacting. We show, by means of simulations for the PSR, how the resonant nature of this mechanism may be effectively broken by tailoring the longitudinal bunch profile at fixed bunch charge, resulting in a significant decrease in the electron-cloud effect. We briefly discuss the experimental difficulties expected in the implementation of this cure

Electron clouds in high energy hadron accelerators

Energy Technology Data Exchange (ETDEWEB)

Petrov, Fedor

2013-08-29

The formation of electron clouds in accelerators operating with positrons and positively charge ions is a well-known problem. Depending on the parameters of the beam the electron cloud manifests itself differently. In this thesis the electron cloud phenomenon is studied for the CERN Super Proton Synchrotron (SPS) and Large Hadron Collider (LHC) conditions, and for the heavy-ion synchrotron SIS-100 as a part of the FAIR complex in Darmstadt, Germany. Under the FAIR conditions the extensive use of slow extraction will be made. After the acceleration the beam will be debunched and continuously extracted to the experimental area. During this process, residual gas electrons can accumulate in the electric field of the beam. If this accumulation is not prevented, then at some point the beam can become unstable. Under the SPS and LHC conditions the beam is always bunched. The accumulation of electron cloud happens due to secondary electron emission. At the time when this thesis was being written the electron cloud was known to limit the maximum intensity of the two machines. During the operation with 25 ns bunch spacing, the electron cloud was causing significant beam quality deterioration. At moderate intensities below the instability threshold the electron cloud was responsible for the bunch energy loss. In the framework of this thesis it was found that the instability thresholds of the coasting beams with similar space charge tune shifts, emittances and energies are identical. First of their kind simulations of the effect of Coulomb collisions on electron cloud density in coasting beams were performed. It was found that for any hadron coasting beam one can choose vacuum conditions that will limit the accumulation of the electron cloud below the instability threshold. We call such conditions the ''good'' vacuum regime. In application to SIS-100 the design pressure 10{sup -12} mbar corresponds to the good vacuum regime. The transition to the bad vacuum

Electron cloud and ion effects

CERN Document Server

Arduini, Gianluigi

2002-01-01

The significant progress in the understanding and control of machine impedances has allowed obtaining beams with increasing brilliance. Dense positively charged beams generate electron clouds via gas ionization, photoemission and multipacting. The electron cloud in turn interacts with the beam and the surrounding environment originating fast coupled and single bunch instabilities, emittance blow-up, additional loads to vacuum and cryogenic systems, perturbation to beam diagnostics and feedbacks and it constitutes a serious limitation to machine performance. In a similar way high brilliance electron beams are mainly affected by positively charged ions produced by residual gas ionization. Recent observations of electron cloud build-up and its effects in present accelerators are reviewed and compared with theory and with the results of state-of-the-art computer simulations. Two-stream instabilities induced by the interaction between electron beams and ions are discussed. The implications for future accelerators ...

Electron cloud observations: a retrospective

International Nuclear Information System (INIS)

Harkay, K.

2004-01-01

A growing number of observations of electron cloud effects (ECEs) have been reported in positron and proton rings. Low-energy, background electrons ubiquitous in high-intensity particle accelerators. Amplification of electron cloud (EC) can occur under certain operating conditions, potentially giving rise to numerous effects that can seriously degrade accelerator performance. EC observations and diagnostics have contributed to a better understanding of ECEs, in particular, details of beam-induced multipacting and cloud saturation effects. Such experimental results can be used to provide realistic limits on key input parameters for modeling efforts and analytical calculations to improve prediction capability. Electron cloud effects are increasingly important phenomena in high luminosity, high brightness, or high intensity machines - Colliders, Storage rings, Damping rings, Heavy ion beams. EC generation and instability modeling increasingly complex and benchmarked against in situ data: (delta), (delta) 0 , photon reflectivity, and SE energy distributions important. Surface conditioning and use of solenoidal windings in field-free regions are successful cures: will they be enough? What are new observations and how do they contribute to body of work and understanding physics of EC?

Electron Cloud Effect in the Linear Colliders

International Nuclear Information System (INIS)

Pivi, M

2004-01-01

Beam induced multipacting, driven by the electric field of successive positively charged bunches, may arise from a resonant motion of electrons, generated by secondary emission, bouncing back and forth between opposite walls of the vacuum chamber. The electron-cloud effect (ECE) has been observed or is expected at many storage rings [1]. In the beam pipe of the Damping Ring (DR) of a linear collider, an electron cloud is produced initially by ionization of the residual gas and photoelectrons from the synchrotron radiation. The cloud is then sustained by secondary electron emission. This electron cloud can reach equilibrium after the passage of only a few bunches. The electron-cloud effect may be responsible for collective effects as fast coupled-bunch and single-bunch instability, emittance blow-up or incoherent tune shift when the bunch current exceeds a certain threshold, accompanied by a large number of electrons in the vacuum chamber. The ECE was identified as one of the most important R and D topics in the International Linear Collider Report [2]. Systematic studies on the possible electron-cloud effect have been initiated at SLAC for the GLC/NLC and TESLA linear colliders, with particular attention to the effect in the positron main damping ring (MDR) and the positron Low Emittance Transport which includes the bunch compressor system (BCS), the main linac, and the beam delivery system (BDS). We present recent computer simulation results for the main features of the electron cloud generation in both machine designs. Thus, single and coupled-bunch instability thresholds are estimated for the GLC/NLC design

Electron cloud dynamics in the Cornell Electron Storage Ring Test Accelerator wiggler

Directory of Open Access Journals (Sweden)

C. M. Celata

2011-04-01

Full Text Available The interference of stray electrons (also called “electron clouds” with accelerator beams is important in modern intense-beam accelerators, especially those with beams of positive charge. In magnetic wigglers, used, for instance, for transverse emittance damping, the intense synchrotron radiation produced by the beam can generate an electron cloud of relatively high density. In this paper the complicated dynamics of electron clouds in wigglers is examined using the example of a wiggler in the Cornell Electron Storage Ring Test Accelerator experiment at the Cornell Electron Storage Ring. Three-dimensional particle-in-cell simulations with the WARP-POSINST computer code show different density and dynamics for the electron cloud at locations near the maxima of the vertical wiggler field when compared to locations near the minima. Dynamics in these regions, the electron cloud distribution vs longitudinal position, and the beam coherent tune shift caused by the wiggler electron cloud will be discussed.

Properties of the electron cloud in a high-energy positron and electron storage ring

International Nuclear Information System (INIS)

Harkay, K.C.; Rosenberg, R.A.

2003-01-01

Low-energy, background electrons are ubiquitous in high-energy particle accelerators. Under certain conditions, interactions between this electron cloud and the high-energy beam can give rise to numerous effects that can seriously degrade the accelerator performance. These effects range from vacuum degradation to collective beam instabilities and emittance blowup. Although electron-cloud effects were first observed two decades ago in a few proton storage rings, they have in recent years been widely observed and intensely studied in positron and proton rings. Electron-cloud diagnostics developed at the Advanced Photon Source enabled for the first time detailed, direct characterization of the electron-cloud properties in a positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron-cloud production mechanisms and details of the beam-cloud interaction can be inferred. A significant longitudinal variation of the electron cloud is also observed, due primarily to geometrical details of the vacuum chamber. Such experimental data can be used to provide realistic limits on key input parameters in modeling efforts, leading ultimately to greater confidence in predicting electron-cloud effects in future accelerators.

Experimental Electron Cloud Studies in the CERN Proton Synchrotron

CERN Document Server

Mahner, E; Caspers, Friedhelm

2008-01-01

Indications for a beam-induced electron cloud build-up are observed since 2000 for the nominal LHC beam in the PS to SPS transfer line and during the last turns before ejection from the PS. A new electron cloud setup was designed, built, and installed in the PS. It contains shielded button-type pickups, a dipole magnet, a vacuum gauge, and a dedicated stripline electrode to experimentally verify the beneficial effect of electron cloud clearing electrodes. During the 2007 run, the electron cloud effect was also clearly observed in the PS and efficient electron cloud suppression has been obtained for negative and positive bias voltages on the clearing electrode. Here, we present electron cloud measurements with different filling patterns and bunch spacings in the PS.

The Case Of The Elusive Electron Cloud

CERN Multimedia

2001-01-01

Fig. 1 Electron cloud following a controlled beam bump. 'Elementary my dear Watson, you see this footprint proves it was the butler in the foyer with the butcher's knife.' Sir Arthur Conan Doyle's Sherlock Holmes may at first appear a long way from particle physics, but first appearances are often deceiving... The mysteries behind the 'Electron Cloud Effect', a dangerous electron multiplication phenomenon which could possibly limit the LHC's performance, have recently been under a detective level investigation that is yielding data that would make even the valiant Holmes balk. The electron cloud, a group of free floating electrons in the collider, is caused by electron multiplication on the vacuum chamber wall and was first observed in 1976. The cloud that develops is a serious problem because it can lead to beam growth, increased gas release from the collider surface, and a supplementary heat load to the LHC cryogenic system. The phenomenon has been observed since 1999 in the SPS where unexpected pressure...

Electron cloud effects: codes and simulations at KEK

International Nuclear Information System (INIS)

Ohmi, K

2013-01-01

Electron cloud effects had been studied at KEK-Photon Factory since 1995. e-p instability had been studied in proton rings since 1965 in BINP, ISR and PSR. Study of electron cloud effects with the present style, which was based on numerical simulations, started at 1995 in positron storage rings. The instability observed in KEKPF gave a strong impact to B factories, KEKB and PEPII, which were final stage of their design in those days. History of cure for electron cloud instability overlapped the progress of luminosity performance in KEKB. The studies on electron cloud codes and simulations in KEK are presented. (author)

Recent electron-cloud simulation results for the main damping rings of the NLC and TESLA linear colliders

International Nuclear Information System (INIS)

Pivi, M.; Raubenheimer, T.O.; Furman, M.A.

2003-01-01

In the beam pipe of the Main Damping Ring (MDR) of the Next Linear Collider (NLC), ionization of residual gases and secondary emission give rise to an electron-cloud which stabilizes to equilibrium after few bunch trains. In this paper, we present recent computer simulation results for the main features of the electron cloud at the NLC and preliminary simulation results for the TESLA main damping rings, obtained with the code POSINST that has been developed at LBNL, and lately in collaboration with SLAC, over the past 7 years. Possible remedies to mitigate the effect are also discussed. We have recently included the possibility to simulate different magnetic field configurations in our code including solenoid, quadrupole, sextupole and wiggler

Electron-Cloud Build-Up: Summary

International Nuclear Information System (INIS)

Furman, M.A.

2007-01-01

I present a summary of topics relevant to the electron-cloud build-up and dissipation that were presented at the International Workshop on Electron-Cloud Effects 'ECLOUD 07' (Daegu, S. Korea, April 9-12, 2007). This summary is not meant to be a comprehensive review of the talks. Rather, I focus on those developments that I found, in my personal opinion, especially interesting. The contributions, all excellent, are posted in http://chep.knu.ac.kr/ecloud07/

Electron Cyclotron Resonances in Electron Cloud Dynamics

International Nuclear Information System (INIS)

Celata, Christine; Celata, C.M.; Furman, Miguel A.; Vay, J.-L.; Yu, Jennifer W.

2008-01-01

We report a previously unknown resonance for electron cloud dynamics. The 2D simulation code 'POSINST' was used to study the electron cloud buildup at different z positions in the International Linear Collider positron damping ring wiggler. An electron equilibrium density enhancement of up to a factor of 3 was found at magnetic field values for which the bunch frequency is an integral multiple of the electron cyclotron frequency. At low magnetic fields the effects of the resonance are prominent, but when B exceeds ∼(2 pi mec/(elb)), with lb = bunch length, effects of the resonance disappear. Thus short bunches and low B fields are required for observing the effect. The reason for the B field dependence, an explanation of the dynamics, and the results of the 2D simulations and of a single-particle tracking code used to elucidate details of the dynamics are discussed

Simulating electron clouds in heavy-ion accelerators

International Nuclear Information System (INIS)

Cohen, R.H.; Friedman, A.; Covo, M. Kireeff; Lund, S.M.; Molvik, A.W.; Bieniosek, F.M.; Seidl, P.A.; Vay, J.-L.; Stoltz, P.; Veitzer, S.

2005-01-01

Contaminating clouds of electrons are a concern for most accelerators of positively charged particles, but there are some unique aspects of heavy-ion accelerators for fusion and high-energy density physics which make modeling such clouds especially challenging. In particular, self-consistent electron and ion simulation is required, including a particle advance scheme which can follow electrons in regions where electrons are strongly magnetized, weakly magnetized, and unmagnetized. The approach to such self-consistency is described, and in particular a scheme for interpolating between full-orbit (Boris) and drift-kinetic particle pushes that enables electron time steps long compared to the typical gyroperiod in the magnets. Tests and applications are presented: simulation of electron clouds produced by three different kinds of sources indicates the sensitivity of the cloud shape to the nature of the source; first-of-a-kind self-consistent simulation of electron-cloud experiments on the high-current experiment [L. R. Prost, P. A. Seidl, F. M. Bieniosek, C. M. Celata, A. Faltens, D. Baca, E. Henestroza, J. W. Kwan, M. Leitner, W. L. Waldron, R. Cohen, A. Friedman, D. Grote, S. M. Lund, A. W. Molvik, and E. Morse, 'High current transport experiment for heavy ion inertial fusion', Physical Review Special Topics, Accelerators and Beams 8, 020101 (2005)], at Lawrence Berkeley National Laboratory, in which the machine can be flooded with electrons released by impact of the ion beam on an end plate, demonstrate the ability to reproduce key features of the ion-beam phase space; and simulation of a two-stream instability of thin beams in a magnetic field demonstrates the ability of the large-time-step mover to accurately calculate the instability

Electron cloud observations at the ISIS Proton Synchrotron

CERN Document Server

Pertica, A.

2013-04-22

The build up of electron clouds inside a particle accelerator vacuum chamber can produce strong transverse and longitudinal beam instabilities which in turn can lead to high levels of beam loss often requiring the accelerator to be run below its design specification. To study the behaviour of electron clouds at the ISIS Proton Synchrotron, a Micro-Channel Plate (MCP) based electron cloud detector has been developed. The detector is based on the Retarding Field Analyser (RFA) design and consists of a retarding grid, which allows energy analysis of the electron signal, and a MCP assembly placed in front of the collector plate. The MCP assembly provides a current gain over the range 300 to 25K, thereby increasing the signal to noise ratio and dynamic range of the measurements. This paper presents the first electron cloud observations at the ISIS Proton Synchrotron. These results are compared against signals from a beam position monitor and a fast beam loss monitor installed at the same location.

Theory and measurement of the electron cloud effect

CERN Document Server

Harkay, K C

1999-01-01

Photoelectrons produced through the interaction of synchrotron radiation and the vacuum chamber walls can be accelerated by a charged particle beam, acquiring sufficient energy to produce secondary electrons (SEs) in collisions with the walls. If the secondary-electron yield (SEY) coefficient of the wall material is greater than one, a runaway condition can develop. In addition to the SEY, the degree of amplification depends on the beam intensity and temporal distribution. As the electron cloud builds up along a train of stored bunches, a transverse perturbation of the head bunch can be communicated to trailing bunches in a wakefield-like interaction with the cloud. The electron cloud effect is especially of concern for the high-intensity PEP-II (SLAC) and KEK B-factories and at the Large Hadron Collider (LHC) at CERN. An initiative was undertaken at the Advanced Photon Source (APS) storage ring to characterize the electron cloud in order to provide realistic limits on critical input parameters in the models ...

Cyclotron Resonances in Electron Cloud Dynamics

International Nuclear Information System (INIS)

Celata, C.M.; Furman, M.A.; Vay, J.L.; Grote, D.P.; Ng, J.T.; Pivi, M.F.; Wang, L.F.

2009-01-01

A new set of resonances for electron cloud dynamics in the presence of a magnetic field has been found. For short beam bunch lengths and low magnetic fields where l b c , (l b = bunch duration, ω c = non-relativistic cyclotron frequency) resonances between the bunch frequency and harmonics of the cyclotron frequency cause an increase in the electron cloud density in narrow ranges of magnetic field near the resonances. For ILC parameters the increase in the density is up to a factor ∼ 3, and the spatial distribution of the electrons is broader near resonances, lacking the well-defined density 'stripes' of multipactoring found for non-resonant cases. Simulations with the 2D computer code POSINST, as well as a single-particle tracking code, were used to elucidate the physics of the dynamics. The resonances are expected to affect the electron cloud dynamics in the fringe fields of conventional lattice magnets and in wigglers, where the magnetic fields are low. Results of the simulations, the reason for the bunch-length dependence, and details of the dynamics will be discussed

Electron Cloud Parameterization Studies in the LHC

CERN Document Server

Dominguez, O; Baglin, V; Bregliozzi, G; Jimenez, J M; Metral, E; Rumolo, G; Schulte, D; Zimmermann, F

2011-01-01

During LHC beam commissioning with 150, 75 and 50-ns bunch spacing, important electron-cloud effects, like pressure rise, cryogenic heat load, beam instabilities or emittance growth, were observed. The main strategy to combat the LHC electron cloud, defined about ten years ago, relies on the surface conditioning arising from the chamber-surface bombardment with cloud electrons. In a standard model, the conditioning state of the beam-pipe surface is characterized by three parameters: 1. most importantly, the secondary emission yield δmax; 2. the incident electron energy at which the yield is maximum, ε_max; and 3. the probability of elastic reflection of low-energy primary electrons hitting the chamber wall, R. Since at the LHC no in-situ secondary-yield measurements are available, we compare the relative local pressure-rise measurements taken for different beam configurations against simulations in which surface parameters are scanned. This benchmarking of measurements and simulations is used to infer the s...

Electron cloud buildup studies for the LHC

CERN Document Server

AUTHOR|(CDS)2160803; Boine-Frankenheim, Oliver

Electron clouds can develop in accelerators operating with positively charged particles. The con- sequences of e-cloud related effects are very important for the operation of the Large Hadron Collider (LHC) at CERN, and for the design of future accelerators including the LHC luminosity upgrade (HL-LHC). High electron densities are generated by an interaction between the beam and the confining chamber. Primary electrons, that can be generated through various mecha- nisms, are accelerated by the beam and impinge on the chamber walls, thereby extracting more electrons from the material. Furthermore they also deposit their kinetic energy in the process, which has to be compensated by the cooling system. Especially in cryogenic environments, as it is the case for a large part of the LHC, high heat loads can pose a serious problem. In order to improve the understanding of the electron cloud, simulation studies are performed with the code PyECLOUD, developed at CERN. The work of the first half of the project is desc...

Electron cloud effects in SIS-18 and SIS-100

Energy Technology Data Exchange (ETDEWEB)

Petrov, Fedor; Boine-Frankenheim, Oliver [Technische Universitaet Darmstadt, Institut fuer Theorie Elektromagnetischer Felder (TEMF) (Germany); Gesellschaft fuer Schwerionenforschung (GSI) GmbH, Darmstadt (Germany); Weiland, Thomas [Technische Universitaet Darmstadt, Institut fuer Theorie Elektromagnetischer Felder (TEMF) (Germany)

2011-07-01

Electron cloud build-up and associated instabilities are studied in simulations under conditions relevant to SIS-18 and to the projected SIS-100 heavy ion synchrotrons. In both rings coasting beams are foreseen during slow extraction of the beam. Trapped electrons could lead to a reduction of the extraction efficiency. We present the results of electron cloud studies for bunched and for coasting beams. In these two regimes the main production mechanisms are significantly different. For coasting beams the most important mechanism is residual gas ionization, for bunched beam the main source of electrons is secondary emission. In the case of coasting beams electrons are generated in the vicinity of the beam center and a two-stream instability may occur for the projected intensities.Electron clouds due to bunched beams are of concern in SIS-100 because no special coating of the stainless steel beam pipe is presently foreseen. Finally we also discuss experimental studies of electron cloud generation in SIS-18.

A New Electronic Commerce Architecture in the Cloud

OpenAIRE

Guigang Zhang; Chao Li; Sixin Xue; Yuenan Liu; Yong Zhang; Chunxiao Xing

2012-01-01

In this paper, the authors propose a new electronic commerce architecture in the cloud that satisfies the requirements of the cloud. This architecture includes five technologies, which are the massive EC data storage technology in the cloud, the massive EC data processing technology in the cloud, the EC security management technology in the cloud, OLAP technology for EC in the cloud, and active EC technology in the cloud. Finally, a detailed discussion of future trends for EC in the cloud env...

Electron-cloud measurements and simulations for the APS

International Nuclear Information System (INIS)

Furman, M.A.; Pivi, M.; Harkay, K.C.; Rosenberg, R.A.

2001-01-01

We compare experimental results with simulations of the electron cloud effect induced by a positron beam at the APS synchrotron light source at ANL, where the electron cloud effect has been observed and measured with dedicated probes. We find good agreement between simulations and measurements for reasonable values of certain secondary electron yield (SEY) parameters, most of which were extracted from recent bench measurements at SLAC

Measurement of Electron Cloud Effects in SPS

CERN Document Server

Jiménez, J M

2004-01-01

The electron cloud is not a new phenomenon, indeed, it was observed already in other machines like the proton storage rings in BINP Novosibirsk or in the Intersecting Storage Ring (ISR) at CERN. Inside an accelerator beam pipe, the electrons can collectively and coherently interact with the beam potential and degrade the performance of the accelerators operating with intense positively charged bunched beams. In the LHC, electron multipacting is expected to take place in the cold and warm beam pipe due to the presence of the high intensities bunched beams, creating an electron cloud. The additional heat load induced by the electron cloud onto the LHC beam screens of the cold magnets of the LHC bending sections (the arcs represent ~21 km in length) was, and is still, considered as one of the main possible limitation of LHC performances. Since 1997 and in parallel with the SPS studies with LHC-type beams, measurements in other machines or in the laboratory have been made to provide the input parameters required ...

National electronic medical records integration on cloud computing system.

Science.gov (United States)

Mirza, Hebah; El-Masri, Samir

2013-01-01

Few Healthcare providers have an advanced level of Electronic Medical Record (EMR) adoption. Others have a low level and most have no EMR at all. Cloud computing technology is a new emerging technology that has been used in other industry and showed a great success. Despite the great features of Cloud computing, they haven't been utilized fairly yet in healthcare industry. This study presents an innovative Healthcare Cloud Computing system for Integrating Electronic Health Record (EHR). The proposed Cloud system applies the Cloud Computing technology on EHR system, to present a comprehensive EHR integrated environment.

Simulation of wake potentials induced by relativistic proton bunches in electron clouds

Energy Technology Data Exchange (ETDEWEB)

Petrov, Fedor; Boine-Frankenheim, Oliver; Weiland, Thomas [Technische Universitaet Darmstadt (Germany). Institut fuer Theorie Elektromagnetischer Felder (TEMF)

2012-07-01

Electron clouds limit the intensity of modern high intensity hadron accelerators. Presently electron clouds are the main limiting factor for the LHC operation with 25 ns bunch trains. The bunches passing through an electron cloud induce a wake field. When the electron cloud density exceeds a certain threshold beam instabilities occur. The presence of electron clouds results in a shift of the synchronous phase, which increases if the bunch spacing is reduced. For LHC and SPS conditions we compare the longitudinal electron cloud wake potentials and stopping powers obtained using a simplified 2D electrostatic Particle-in-Cell code with fully electromagnetic simulations using VORPAL. In addition we analyze the wake fields induced by displaced or tilted bunches.

Electron-cloud effects in high-luminosity colliders

Energy Technology Data Exchange (ETDEWEB)

Zimmermann, F.

1998-01-01

Electron-cloud instabilities are expected to be important in most high-luminosity double-ring colliders. In this report, the author describes a few parameter regimes and some critical parameter dependences of this type of instability, and illustrate these with simulation results for the PEP-II and KEK B factories, the LHC, the VLHC, and DAPHNE. In addition, the author studies the possibility and the potential impact of an electron cloud in the interaction region.

Studies of dynamics of electron clouds in STAR silicon drift detectors

CERN Document Server

Bellwied, R; Brandon, N; Caines, H; Chen, W; Dimassimo, D; Dyke, H; Hall, J R; Hardtke, D; Hoffmann, G W; Humanic, T J; Kotova, A I; Kotov, I V; Kraner, H W; Li, Z; Lynn, D; Middelkamp, P; Ott, G; Pandey, S U; Pruneau, C A; Rykov, V L; Schambach, J; Sedlmeir, J; Sugarbaker, E R; Takahashi, J; Wilson, W K

2000-01-01

The dynamics of electrons generated in silicon drift detectors was studied using an IR LED. Electrons were generated at different drift distances. In this way, the evolution of the cloud as a function of drift time was measured. Two methods were used to measure the cloud size. The method of cumulative functions was used to extract the electron cloud profiles. Another method obtains the cloud width from measurements of the charge collected on a single anode as a function of coordinate of the light spot. The evolution of the electron cloud width with drift time is compared with theoretical calculations. Experimental results agreed with theoretical expectations.

Emittance growth induced by electron cloud in proton storage rings

CERN Document Server

Benedetto, Elena; Coppa, G

2006-01-01

In proton and positron storage rings with many closely spaced bunches, a large number of electrons can accumulate in the beam pipe due to various mechanisms (photoemission, residual gas ionization, beam-induced multipacting). The so-formed electron cloud interacts with the positively charged bunches, giving rise to instabilities, emittance growth and losses. This phenomenon has been observed in several existing machines such as the CERN Super Proton Synchrotron (SPS), whose operation has been constrained by the electron-cloud problem, and it is a concern for the Large Hadron Collider (LHC), under construction at CERN. The interaction between the beam and the electron cloud has features which cannot be fully taken into account by the conventional and known theories from accelerators and plasma physics. Computer simulations are indispensable for a proper prediction and understanding of the instability dynamics. The main feature which renders the beam-cloud interactions so peculiar is that the the electron cloud...

Electron-Cloud Wake Fields

CERN Document Server

Rumolo, Giovanni

2002-01-01

The electron cloud gives rise to coherent and incoherent single-bunch wake fields, both in the longitudinal and in the transverse direction, and to coherent coupled-bunch wakes. These wake fields can be computed using the simulation programs ECLOUD and HEADTAIL developed at CERN. We present the wake fields simulated for the LHC beam in the CERN SPS and at injection into the LHC in different magnetic field configurations (field-free region, dipole, and solenoid), where the magnetic field affects both the elec-tron motion during a bunch passage and the overall electron distribution in the beam pipe.

Theory and measurement of the electron cloud effect

International Nuclear Information System (INIS)

Harkey, K. C.

1999-01-01

Photoelectrons produced through the interaction of synchrotrons radiation and the vacuum chamber walls can be accelerated by a charged particle beam, acquiring sufficient energy to produce secondary electrons (SES) in collisions with the walls. If the secondary-electron yield (SEY) coefficient of the wall material is greater than one, a run-away condition can develop. In addition to the SEY, the degree of amplification depends on the beam intensity and temporal distribution. As the electron cloud builds up along a train of stored bunches, a transverse perturbation of the head bunch can be communicated to trailing bunches in a wakefield-like interaction with the cloud. The electron cloud effect is especially of concern for the high-intensity PEP-II (SLAC) and KEK B-factories and at the Large Hadron Collider (LHC) at CERN. An initiative was undertaken at the Advanced Photon Source (APS) storage ring to characterize the electron cloud in order to provide realistic limits on critical input parameters in the models and improve their predictive capabilities. An intensive research program was undertaken at CERN to address key issues relating to the LHC. After giving an overview, the recent theoretical and experimental results from the APS and the other laboratories will be discussed

Impact of Microwaves on the Electron Cloud and Incoherent Effects

CERN Document Server

Decker, Franz Josef; Zimmermann, Frank

2002-01-01

We consider the use of microwaves for manipulating the electron cloud, describing an exploratory experiment at PEP-II as well as computer simulations of the electron cloud build-up in the presence of a microwave for an LHC dipole. We then show that the incoherent effects of the electron cloud - energy loss and transverse emittance growth due to scattering of the electrons - are negligible. This suggests that the disturbance of the coherent motion may be another possible application of microwaves, which could prevent beam emittance growth and beam loss.

Electron Cloud Build Up and Instability in the CLIC Damping Rings

CERN Document Server

Rumolo, G; Papaphilippou, Y

2008-01-01

Electron cloud can be formed in the CLIC positron damping ring and cause intolerable tune shift and beam instability. Build up simulations with the Faktor2 code, developed at CERN, have been done to predict the cloud formation in the arcs and wigglers of the damping rings. HEADTAIL simulations have been used to study the effect of this electron cloud on the beam and assess the thresholds above which the electron cloud instability would set in.

Electron cloud sizes in gas-filled detectors

International Nuclear Information System (INIS)

Boggende, A.J.F. den; Schrijver, C.J.

1984-01-01

Electron cloud sizes have been calculated for gas mixtures containing Ar, Xe, CO 2 , CH 4 , and N 2 for drifts through a constant electric field. The transport coefficients w and D/μ are in good agreement with experimental data of various sources for pure gases. Results of measurements, also performed in this work, for Ar+CO 2 , Ar+CH 4 , and Ar+Xe+CO 2 mixtures are in fair agreement with the calculated cloud sizes. For a large number of useful gas mixtures calculated electron cloud sizes are presented and discussed, most of which are given for the first time. A suggestion is made for an optimal gas mixture for an X-ray position sensitive proportional counter for medium and low energies. (orig.)

Improvement in the cloud mask for Terra MODIS mitigated by electronic crosstalk correction in the 6.7 μm and 8.5 μm channels

Science.gov (United States)

Sun, Junqiang; Madhavan, S.; Wang, M.

2016-09-01

MODerate resolution Imaging Spectroradiometer (MODIS), a remarkable heritage sensor in the fleet of Earth Observing System for the National Aeronautics and Space Administration (NASA) is in space orbit on two spacecrafts. They are the Terra (T) and Aqua (A) platforms which tracks the Earth in the morning and afternoon orbits. T-MODIS has continued to operate over 15 years easily surpassing the 6 year design life time on orbit. Of the several science products derived from MODIS, one of the primary derivatives is the MODIS Cloud Mask (MOD035). The cloud mask algorithm incorporates several of the MODIS channels in both reflective and thermal infrared wavelengths to identify cloud pixels from clear sky. Two of the thermal infrared channels used in detecting clouds are the 6.7 μm and 8.5 μm. Based on a difference threshold with the 11 μm channel, the 6.7 μm channel helps in identifying thick high clouds while the 8.5 μm channel being useful for identifying thin clouds. Starting 2010, it had been observed in the cloud mask products that several pixels have been misclassified due to the change in the thermal band radiometry. The long-term radiometric changes in these thermal channels have been attributed to the electronic crosstalk contamination. In this paper, the improvement in cloud detection using the 6.7 μm and 8.5 μm channels are demonstrated using the electronic crosstalk correction. The electronic crosstalk phenomena analysis and characterization were developed using the regular moon observation of MODIS and reported in several works. The results presented in this paper should significantly help in improving the MOD035 product, maintaining the long term dataset from T-MODIS which is important for global change monitoring.

Relation between parameters of self-sustaining magnetically confined electron cloud and external conditions

International Nuclear Information System (INIS)

Yu Qingchang

1991-01-01

On the basis of the fluid theory of the axisymmetrical self-sustaining magnetically confined electron clouds an approximate analytical method is developed. By means of this method the relations between the parameters of this type of electron cloud and external conditions are studied. The parameters include electron density, electron temperature, drift angular frequency of electrons, radius of the electron cloud and electric potential at the centre of the electron cloud. They depend on the voltage, magnetic induction, pressure, electromagnetic field distribution in the confinement device and parameters of electron-atom collisions

Dynamic electronic institutions in agent oriented cloud robotic systems.

Science.gov (United States)

Nagrath, Vineet; Morel, Olivier; Malik, Aamir; Saad, Naufal; Meriaudeau, Fabrice

2015-01-01

The dot-com bubble bursted in the year 2000 followed by a swift movement towards resource virtualization and cloud computing business model. Cloud computing emerged not as new form of computing or network technology but a mere remoulding of existing technologies to suit a new business model. Cloud robotics is understood as adaptation of cloud computing ideas for robotic applications. Current efforts in cloud robotics stress upon developing robots that utilize computing and service infrastructure of the cloud, without debating on the underlying business model. HTM5 is an OMG's MDA based Meta-model for agent oriented development of cloud robotic systems. The trade-view of HTM5 promotes peer-to-peer trade amongst software agents. HTM5 agents represent various cloud entities and implement their business logic on cloud interactions. Trade in a peer-to-peer cloud robotic system is based on relationships and contracts amongst several agent subsets. Electronic Institutions are associations of heterogeneous intelligent agents which interact with each other following predefined norms. In Dynamic Electronic Institutions, the process of formation, reformation and dissolution of institutions is automated leading to run time adaptations in groups of agents. DEIs in agent oriented cloud robotic ecosystems bring order and group intellect. This article presents DEI implementations through HTM5 methodology.

Observation of Electron Cloud Instabilities and Emittance Dilution at the Cornell Electron-Positron Storage Ring Test Accelerator

International Nuclear Information System (INIS)

Holtzapple, R.L.; Campbell, R.C.; McArdle, K.E.; Miller, M.I.; Totten, M.M.; Tucker, S.L.; Billing, M.G.; Dugan, G.F.; Ramirez, G.A.; Sonnad, K.G.; Williams, H.A.; Flanagan, J.; Palmer, M.A.

2016-01-01

Electron cloud related emittance dilution and instabilities of bunch trains limit the performance of high intensity circular colliders. One of the key goals of the Cornell electron-positron storage ring Test Accelerator (CesrTA) research program is to improve our understanding of how the electron cloud alters the dynamics of bunches within the train. Single bunch beam diagnotics have been developed to measure the beam spectra, vertical beam size, two important dynamical effects of beams interacting with the electron cloud, for bunch trains on a turn-by-turn basis. Experiments have been performed at CesrTA to probe the interaction of the electron cloud with stored positron bunch trains. The purpose of these experiments was to characterize the dependence of beam-electron cloud interactions on the machine parameters such as bunch spacing, vertical chromaticity, and bunch current. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains; 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the observations from these experiments and analyze the effects of the electron cloud on the stability of bunches in a train under many different operational conditions

Trapping of Electron Cloud LLC/Cesrta Quadrupole and Sextupole Magnets

International Nuclear Information System (INIS)

Wang, L.

2011-01-01

The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R and D (1). One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in CESRTA and ILC quadrupole and sextupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with a long lifetime in a quadrupole and sextupole magnet due to the mirror field trapping mechanism. We study the effects of magnet strength, bunch current, ante-chamber effect, bunch spacing effect and secondary emission yield (SEY) in great detail. The development of an electron cloud in magnets is the main concern where a weak solenoid field is not effective. Quadrupole and sextupole magnets have mirror field configurations which may trap electrons by the mirror field trapping mechanism (2). Fig.1 shows the orbit of a trapped electron in a quadrupole magnet. The electron makes gyration motion (called transverse motion) and also moves along the field line (called longitudinal motion). At the mirror point (middle of the field line), there is a maximum longitudinal energy and minimum transverse energy. When the electron moves away from the mirror point, its longitudinal energy reduces and the transverse energy increases as the magnetic field increases. If the magnetic field is strong enough, the longitudinal energy becomes zero at one point and then the electron is turned back by the strong field. Note that the electrons are trapped in the region near the middle of the field lines. Although all quadrupole and sextupole magnets can trap electrons in principle, the

Measurement of Electron Clouds in Large Accelerators by Microwave Dispersion

Energy Technology Data Exchange (ETDEWEB)

De Santis, S.; Byrd, J.M.; /LBL, Berkeley; Caspers, F.; /CERN; Krasnykh, A.; /SLAC; Kroyer, T.; /CERN; Pivi, M.T.F.; /SLAC; Sonnad, K.G.; /LBL, Berkeley

2008-03-19

Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation at high currents. Furthermore, it is difficult to probe their density over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave transmitted over a section of the accelerator and used it to measure the average electron cloud density over a 50 m section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center.

Electron temperatures within magnetic clouds between 2 and 4 AU: Voyager 2 observations

Science.gov (United States)

Sittler, E. C.; Burlaga, L. F.

1998-08-01

We have performed an analysis of Voyager 2 plasma electron observations within magnetic clouds between 2 and 4 AU identified by Burlaga and Behannon [1982]. The analysis has been confined to three of the magnetic clouds identified by Burlaga and Behannon that had high-quality data. The general properties of the plasma electrons within a magnetic cloud are that (1) the moment electron temperature anticorrelates with the electron density within the cloud, (2) the ratio Te/Tp tends to be >1, and (3) on average, Te/Tp~7.0. All three results are consistent with previous electron observations within magnetic clouds. Detailed analyses of the core and halo populations within the magnetic clouds show no evidence of either an anticorrelation between the core temperature TC and the electron density Ne or an anticorrelation between the halo temperature TH and the electron density. Within the magnetic clouds the halo component can contribute more than 50% of the electron pressure. The anticorrelation of Te relative to Ne can be traced to the density of the halo component relative to the density of the core component. The core electrons dominate the electron density. When the density goes up, the halo electrons contribute less to the electron pressure, so we get a lower Te. When the electron density goes down, the halo electrons contribute more to the electron pressure, and Te goes up. We find a relation between the electron pressure and density of the form Pe=αNeγ with γ~0.5.

Electron-cloud build-up in hadron machines

International Nuclear Information System (INIS)

Furman, M.A.

2004-01-01

The first observations of electron-proton coupling effect for coasting beams and for long-bunch beams were made at the earliest proton storage rings at the Budker Institute of Nuclear Physics (BINP) in the mid-60's [1]. The effect was mainly a form of the two-stream instability. This phenomenon reappeared at the CERN ISR in the early 70's, where it was accompanied by an intense vacuum pressure rise. When the ISR was operated in bunched-beam mode while testing aluminum vacuum chambers, a resonant effect was observed in which the electron traversal time across the chamber was comparable to the bunch spacing [2]. This effect (''beam-induced multipacting''), being resonant in nature, is a dramatic manifestation of an electron cloud sharing the vacuum chamber with a positively-charged beam. An electron-cloud-induced instability has been observed since the mid-80's at the PSR (LANL) [3]; in this case, there is a strong transverse instability accompanied by fast beam losses when the beam current exceeds a certain threshold. The effect was observed for the first time for a positron beam in the early 90's at the Photon Factory (PF) at KEK, where the most prominent manifestation was a coupled-bunch instability that was absent when the machine was operated with an electron beam under otherwise identical conditions [4]. Since then, with the advent of ever more intense positron and hadron beams, and the development and deployment of specialized electron detectors [5-9], the effect has been observed directly or indirectly, and sometimes studied systematically, at most lepton and hadron machines when operated with sufficiently intense beams. The effect is expected in various forms and to various degrees in accelerators under design or construction. The electron-cloud effect (ECE) has been the subject of various meetings [10-15]. Two excellent reviews, covering the phenomenology, measurements, simulations and historical development, have been recently given by Frank Zimmermann [16

Shielded button electrodes for time-resolved measurements of electron cloud buildup

International Nuclear Information System (INIS)

Crittenden, J.A.; Billing, M.G.; Li, Y.; Palmer, M.A.; Sikora, J.P.

2014-01-01

We report on the design, deployment and signal analysis for shielded button electrodes sensitive to electron cloud buildup at the Cornell Electron Storage Ring. These simple detectors, derived from a beam-position monitor electrode design, have provided detailed information on the physical processes underlying the local production and the lifetime of electron densities in the storage ring. Digitizing oscilloscopes are used to record electron fluxes incident on the vacuum chamber wall in 1024 time steps of 100 ps or more. The fine time steps provide a detailed characterization of the cloud, allowing the independent estimation of processes contributing on differing time scales and providing sensitivity to the characteristic kinetic energies of the electrons making up the cloud. By varying the spacing and population of electron and positron beam bunches, we map the time development of the various cloud production and re-absorption processes. The excellent reproducibility of the measurements also permits the measurement of long-term conditioning of vacuum chamber surfaces

Simulation of the electron cloud density in BEPC II

International Nuclear Information System (INIS)

Liu Yudong; Guo Zhiyuan; Wang Jiuqing

2004-01-01

Electron Cloud Instability (ECI) may take place in positron storage ring when the machine is operated with multi-bunch positron beam. According to the actual shape of the vacuum chamber in the BEPC II, a program has been developed. With the code, authors can calculate the electron density in the chamber with different length of antechamber and the different secondary electron yield respectively. By the simulation, the possibility to put clearing electrodes in the chamber to reduce the electron density in the central region of the chamber is investigated. The simulation provides meaningful and important results for the BEPC II project and electron cloud instability research

Experimental studies of stable confined electron clouds using Gabor lenses

CERN Document Server

Meusel, O.; Glaeser, B.; Schulte, K.

2013-04-22

Based on the idea of D. Gabor [1] space charge lenses are under investigation to be a powerful focussing device for intense ion beams. A stable confined electron column is used to provide strong radially symmetric electrostatic focussing, e.g. for positively charged ion beams. The advantages of Gabor lenses are a mass independent focussing strength, space charge compensation of the ion beam and reduced magnetic or electric fields compared to conventional focussing devices. Collective phenomena of the electron cloud result in aberrations and emittance growth of the ion beam. The knowledge of the behaviour of the electron cloud prevents a decrease of the beam brilliance. Numerical models developed to describe the electron confinement and dynamics within a Gabor lens help to understand the interaction of the ion beam with the electron column and show the causes of non-neutral plasma instabilities. The diagnosis of the electron cloud properties helps to evaluate the numerical models and to investigate the influen...

Electron-Cloud Simulation and Theory for High-Current Heavy-Ion Beams

International Nuclear Information System (INIS)

Cohen, R; Friedman, A; Lund, S; Molvik, A; Lee, E; Azevedo, T; Vay, J; Stoltz, P; Veitzer, S

2004-01-01

Stray electrons can arise in positive-ion accelerators for heavy ion fusion or other applications as a result of ionization of ambient gas or gas released from walls due to halo-ion impact, or as a result of secondary- electron emission. We summarize the distinguishing features of electron cloud issues in heavy-ion-fusion accelerators and a plan for developing a self-consistent simulation capability for heavy-ion beams and electron clouds. We also present results from several ingredients in this capability: (1) We calculate the electron cloud produced by electron desorption from computed beam-ion loss, which illustrates the importance of retaining ion reflection at the walls. (2) We simulate of the effect of specified electron cloud distributions on ion beam dynamics. We consider here electron distributions with axially varying density, centroid location, or radial shape, and examine both random and sinusoidally varying perturbations. We find that amplitude variations are most effective in spoiling ion beam quality, though for sinusoidal variations which match the natural ion beam centroid oscillation or breathing mode frequencies, the centroid and shape perturbations can also have significant impact. We identify an instability associated with a resonance between the beam-envelope ''breathing'' mode and the electron perturbation. We estimate its growth rate, which is moderate (compared to the reciprocal of a typical pulse duration). One conclusion from this study is that heavy-ion beams are surprisingly robust to electron clouds, compared to a priori expectations. (3) We report first results from a long-timestep algorithm for electron dynamics, which holds promise for efficient simultaneous solution of electron and ion dynamics

Electron-cloud simulation and theory for high-current heavy-ion beams

Directory of Open Access Journals (Sweden)

R. H. Cohen

2004-12-01

Full Text Available Stray electrons can arise in positive-ion accelerators for heavy-ion fusion or other applications as a result of ionization of ambient gas or gas released from walls due to halo-ion impact, or as a result of secondary-electron emission. We summarize the distinguishing features of electron-cloud issues in heavy-ion-fusion accelerators and a plan for developing a self-consistent simulation capability for heavy-ion beams and electron clouds (also applicable to other accelerators. We also present results from several ingredients in this capability. (1 We calculate the electron cloud produced by electron desorption from computed beam-ion loss, which illustrates the importance of retaining ion reflection at the walls. (2 We simulate the effect of specified electron-cloud distributions on ion beam dynamics. We consider here electron distributions with axially varying density, centroid location, or radial shape, and examine both random and sinusoidally varying perturbations. We find that amplitude variations are most effective in spoiling ion beam quality, though for sinusoidal variations which match the natural ion beam centroid oscillation or breathing-mode frequencies, the centroid and shape perturbations can also have significant impact. We identify an instability associated with a resonance between the beam-envelope “breathing” mode and the electron perturbation. We estimate its growth rate, which is moderate (compared to the reciprocal of a typical pulse duration. One conclusion from this study is that heavy-ion beams are surprisingly robust to electron clouds, compared to a priori expectations. (3 We report first results from a long-time-step algorithm for electron dynamics, which holds promise for efficient simultaneous solution of electron and ion dynamics.

Simulations of the electron cloud buildup and its influence on the microwave transmission measurement

Energy Technology Data Exchange (ETDEWEB)

Haas, Oliver Sebastian, E-mail: o.haas@gsi.de [GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64291 Darmstadt (Germany); Boine-Frankenheim, Oliver [GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64291 Darmstadt (Germany); Technische Universität Darmstadt, Institut für Theorie Elektromagnetischer Felder, Schlossgartenstraße 8, 64289 Darmstadt (Germany); Petrov, Fedor [Technische Universität Darmstadt, Institut für Theorie Elektromagnetischer Felder, Schlossgartenstraße 8, 64289 Darmstadt (Germany)

2013-11-21

An electron cloud density in an accelerator can be measured using the Microwave Transmission (MWT) method. The aim of our study is to evaluate the influence of a realistic, nonuniform electron cloud on the MWT. We conduct electron cloud buildup simulations for beam pipe geometries and bunch parameters resembling roughly the conditions in the CERN SPS. For different microwave waveguide modes the phase shift induced by a known electron cloud density is obtained from three different approaches: 3D Particle-In-Cell (PIC) simulation of the electron response, a 2D eigenvalue solver for waveguide modes assuming a dielectric response function for cold electrons, a perturbative method assuming a sufficiently smooth density profile. While several electron cloud parameters, such as temperature, result in minor errors in the determined density, the transversely inhomogeneous density can introduce a large error in the measured electron density. We show that the perturbative approach is sufficient to describe the phase shift under realistic electron cloud conditions. Depending on the geometry of the beam pipe, the external magnetic field configuration and the used waveguide mode, the electron cloud density can be concentrated at the beam pipe or near the beam pipe center, leading to a severe over- or underestimation of the electron density. -- Author-Highlights: •Electron cloud distributions are very inhomogeneous, especially in dipoles. •These inhomogeneities affect the microwave transmission measurement results. •Electron density might be over- or underestimated, depending on setup. •This can be quantified with several models, e.g. a perturbative approach.

Model of the electron acceleration in the clouds of radio galaxies

International Nuclear Information System (INIS)

Fedorenko, V.N.

1980-01-01

The mechanism of electron turbulent acceleration in the clouds of radio galaxies is studied. It is suggested that clouds of radio galaxies are continuously filled by relativistic matter. A self-consistent turbulent acceleration regime in the clouds of radio galaxies is shown to be realized. The synchrotron energetic losses of the ultra-relativistic electrons are compensated by the turbulent acceleration due to Langmuir and Alfven waves. The source of Langmuir waves turbulence is the relativistic matter emanating from the galaxy nuclei and relaxating within the ''hot spots'' of the clouds

Electron cloud diagnostics in use at the Los Alamos PSR

International Nuclear Information System (INIS)

Macek, R. J.; Browman, A.; Borden, M.; Fitzgerald, D.; Wang, T. S.; Zaugg, T.; Harkay, K.; Rosenberg, R.

2003-01-01

A variety of electron cloud diagnostics have been deployed at the Los Alamos Proton Storage Ring (PSR) to detect, measure, and characterize the electron cloud generated in this high intensity, long bunch accumulator ring. These include a version of the ANL-developed retarding field analyzers (RFA) augmented with LANL-developed electronics, a variant of the RFA denoted as the electron sweeping diagnostic (ESD), biased collection plates, and gas pulse measuring devices. The designs and experience with the performance and applicability to PSR are discussed

Electron-Cloud Build-up in the FNAL Main Injector

International Nuclear Information System (INIS)

Furman, M.A.

2007-01-01

We present a summary on ongoing simulation results for the electron-cloud buildup in the context of the proposed FNAL Main Injector (MI) intensity upgrade [1] in a fieldfree region at the location of the RFA electron detector [2]. By combining our simulated results for the electron flux at the vacuum chamber wall with the corresponding measurements obtained with the RFA we infer that the peak secondary electron yield (SEY) (delta) max is ∼> 1.4, and the average electron density is n e ∼> 10 10 m -3 at transition energy for the specific fill pattern and beam intensities defined below. The sensitivity of our results to several variables remains to be explored in order to reach more definitive results. Effects from the electron cloud on the beam are being investigated separately [3

Simulation of a Feedback System for the Attenuation of e-Cloud Driven Instability

International Nuclear Information System (INIS)

Vay, J.-L.; Furman, M.A.; Fox, J.; Rivetta, C.; de Maria, R.; Rumolo, G.

2009-01-01

Electron clouds impose limitations on current accelerators that may be more severe for future machines, unless adequate measures of mitigation are taken. Recently, it has been proposed to use feedback systems operating at high frequency (in the GHz range) to damp single-bunch transverse coherent oscillations that may otherwise be amplified during the interaction of the beam with ambient electron clouds. We have used the simulation package WARP-POSINST and the code Headtail to study the growth rate and frequency patterns in space-time of the electron cloud driven beam breakup instability in the CERN SPS accelerator with, or without, an idealized feedback model for damping the instability.

Measurements of the electron cloud in the APS storage ring

International Nuclear Information System (INIS)

Harkey, K. C.

1999-01-01

Synchrotron radiation interacting with the vacuum chamber walls in a storage ring produce photoelectrons that can be accelerated by the beam, acquiring sufficient energy to produce secondary electrons in collisions with the walls. If the secondary-electron yield (SEY) coefficient of the wall material is greater than one, as is the case with the aluminum chambers in the Advanced Photon Source (APS) storage ring, a runaway condition can develop. As the electron cloud builds up along a train of stored positron or electron bunches, the possibility exists that a transverse perturbation of the head bunch will be communicated to trailing bunches due to interaction with the cloud. In order to characterize the electron cloud, a special vacuum chamber was built and inserted into the ring. The chamber contains 10 rudimentary electron-energy analyzers, as well as three targets coated with different materials. Measurements show that the intensity and electron energy distribution are highly dependent on the temporal spacing between adjacent bunches and the amount of current contained in each bunch. Furthermore, measurements using the different targets are consistent with what would be expected based on the SEY of the coatings. Data for both positron and electron beams are presented

Fast Transverse Beam Instability Caused by Electron Cloud Trapped in Combined Function Magnets

Energy Technology Data Exchange (ETDEWEB)

Antipov, Sergey [Univ. of Chicago, IL (United States)

2017-03-01

Electron cloud instabilities affect the performance of many circular high-intensity particle accelerators. They usually have a fast growth rate and might lead to an increase of the transverse emittance and beam loss. A peculiar example of such an instability is observed in the Fermilab Recycler proton storage ring. Although this instability might pose a challenge for future intensity upgrades, its nature had not been completely understood. The phenomena has been studied experimentally by comparing the dynamics of stable and unstable beam, numerically by simulating the build-up of the electron cloud and its interaction with the beam, and analytically by constructing a model of an electron cloud driven instability with the electrons trapped in combined function dipoles. Stabilization of the beam by a clearing bunch reveals that the instability is caused by the electron cloud, trapped in beam optics magnets. Measurements of microwave propagation confirm the presence of the cloud in the combined function dipoles. Numerical simulations show that up to 10$^{-2}$ of the particles can be trapped by their magnetic field. Since the process of electron cloud build-up is exponential, once trapped this amount of electrons significantly increases the density of the cloud on the next revolution. In a combined function dipole this multi-turn accumulation allows the electron cloud reaching final intensities orders of magnitude greater than in a pure dipole. The estimated fast instability growth rate of about 30 revolutions and low mode frequency of 0.4 MHz are consistent with experimental observations and agree with the simulations. The created instability model allows investigating the beam stability for the future intensity upgrades.

New Electron Cloud Detectors for the PS Main Magnets

CERN Document Server

Yin Vallgren, Ch; Gilardoni, S; Taborelli, M; Neupert, H; Ferreira Somoza, J

2014-01-01

Electron cloud (EC) has already been observed during normal operation of the PS, therefore it is necessary to study its in fluence on any beam instability for the future LHC Injector Upgrade (LIU). Two new electron cloud detectors have been discussed, developed and installed during the Long Shutdown (LS1) in one of the PS main magnets. The first measurement method is based on current measurement by using a shielded button-type pick-up. Due to the geometry and space limitation in the PS magnet, the button-type pick-up made of a 96%Al2O3 block coated with a thin layer of solvent-based Ag painting, placed 30 degrees to the bottom part of the vacuum chamber was installed in the horizontal direction where the only opening of the magnet coil is. The other newly developed measurement method is based on detection of photons emitted by the electrons from the electron cloud impinging on the vacuum chamber walls. The emitted photons are reected to a quartz window. A MCP-PMT (Micro-Channel Plate Photomultiplier Tube) wit...

Observation of magnetic resonances in electron clouds in a positron storage ring

International Nuclear Information System (INIS)

Pivi, M.T.F.; Ng, J.S.T.; Cooper, F.; Kharakh, D.; King, F.; Kirby, R.E.; Kuekan, B.; Spencer, C.M.; Raubenheimer, T.O.; Wang, L.F.

2010-01-01

The first experimental observation of magnetic resonances in electron clouds is reported. The resonance was observed as a modulation in cloud intensity for uncoated as well as TiN-coated aluminum surfaces in the positron storage ring of the PEP-II collider at SLAC. Electron clouds frequently arise in accelerators of positively charged particles, and severely impact the machines' performance. The TiN coating was found to be an effective remedy, reducing the cloud intensity by three orders of magnitude.

Electron cloud density measurements in accelerator beam-pipe using resonant microwave excitation

Energy Technology Data Exchange (ETDEWEB)

Sikora, John P., E-mail: jps13@cornell.edu [CLASSE, Cornell University, Ithaca, NY 14853 (United States); Carlson, Benjamin T. [Carnegie Mellon University, Pittsburgh, PA 15213 (United States); Duggins, Danielle O. [Gordon College, Wenham, MA 01984 (United States); Hammond, Kenneth C. [Columbia University, New York, NY 10027 (United States); De Santis, Stefano [LBNL, Berkeley, CA 94720 (United States); Tencate, Alister J. [Idaho State University, Pocatello, ID 83209 (United States)

2014-08-01

An accelerator beam can generate low energy electrons in the beam-pipe, generally called electron cloud, that can produce instabilities in a positively charged beam. One method of measuring the electron cloud density is by coupling microwaves into and out of the beam-pipe and observing the response of the microwaves to the presence of the electron cloud. In the original technique, microwaves are transmitted through a section of beam-pipe and a change in EC density produces a change in the phase of the transmitted signal. This paper describes a variation on this technique in which the beam-pipe is resonantly excited with microwaves and the electron cloud density calculated from the change that it produces in the resonant frequency of the beam-pipe. The resonant technique has the advantage that measurements can be localized to sections of beam-pipe that are a meter or less in length with a greatly improved signal to noise ratio.

Electron-Cloud Build-Up: Theory and Data

International Nuclear Information System (INIS)

Furman, M.A.

2010-01-01

We present a broad-brush survey of the phenomenology, history and importance of the electron-cloud effect (ECE). We briefly discuss the simulation techniques used to quantify the electron-cloud (EC) dynamics. Finally, we present in more detail an effective theory to describe the EC density build-up in terms of a few effective parameters. For further details, the reader is encouraged to refer to the proceedings of many prior workshops, either dedicated to EC or with significant EC contents, including the entire 'ECLOUD' series. In addition, the proceedings of the various flavors of Particle Accelerator Conferences contain a large number of EC-related publications. The ICFA Beam Dynamics Newsletter series contains one dedicated issue, and several occasional articles, on EC. An extensive reference database is the LHC website on EC.

Electron cloud studies for SIS-18 and for the FAIR synchrotrons

Energy Technology Data Exchange (ETDEWEB)

Petrov, Fedor; Weiland, Thomas [Technische Universitaet Darmstadt, Institut fuer Theorie Elektromagnetischer Felder (TEMF), Darmstadt (Germany); Boine-Frankenheim, Oliver [Gesellschaft fuer Schwerionenforschung (GSI) GmbH, Darmstadt (Germany)

2010-07-01

Electron clouds generated by residual gas ionization pose a potential threat to the stability of the circulating heavy ion beams in the existing SIS-18 synchrotron and in the projected SIS-100. The electrons can potentially accumulate in the space charge potential of the long bunches. As an extreme case we study the accumulation of electrons in a coasting beam under conditions relevant in the SIS-18. Previous studies of electron clouds in coasting beams used particle-in-cell (PIC) codes to describe the generation of the cloud and the interaction with the ion beam. PIC beams exhibit much larger fluctuation amplitudes than real beams. The fluctuations heat the electrons. Therefore the obtained neutralization degree is strongly reduced, relative to a real beam. In our simulation model we add a Langevin term to the electron equation of motion in order to account for the heating process. The effect of natural beam fluctuations on the neutralization degree is studied. The modification of the beam response function as well as the stability limits in the presence of the electrons is discussed.

Transverse blowup along bunch train caused by electron cloud in BEPC

International Nuclear Information System (INIS)

Liu Yudong; Guo Zhiyuan; Qin Qing; Wang Jiuqing; Zhao Zheng

2006-01-01

Electron cloud instability (ECI) may take place in a storage ring when the machine is operated with a multi-bunch positively charged beam. Transverse blowup due to electron cloud has been observed in some machines and is considered to be a major limit factor in the development of high current and high luminosity electron positron colliders. With a streak camera, the transverse blowup along the bunch train was first observed in an experiment at the Beijing Electron-Positron Collider (BEPC) and the simulation results were used to compared with the observation. (authors)

Electron Cloud Simulations of a Proton Storage Ring Using Cold Proton Bunches

International Nuclear Information System (INIS)

Sato, Y.; Holmes, Jeffrey A.; Lee, S.Y.; Macek, R.

2008-01-01

Using the ORBIT code we study the sensitivity of electron cloud properties with respect to different proton beam profiles, the secondary electron yield (SEY) parameter, and the proton loss rate. Our model uses a cold proton bunch to generate primary electrons and electromagnetic field for electron cloud dynamics. We study the dependence of the prompt and swept electron signals vs the bunch charge and the recovery of electron clouds after sweeping on the beam loss rate and the SEY. The simulation results are compared with the experimental data measured at the proton storage ring at the Los Alamos National Laboratory. Our simulations indicate that the fractional proton loss rate in the field-free straight section may be an exponential function of proton beam charge and may also be lower than the averaged fractional proton loss rate over the whole ring.

Progress in studies of Electron-Cloud-Induced Optics Distortions at CESRTA

International Nuclear Information System (INIS)

Crittenden, J.A.; Calvey, J.R.; Dugan, G.F.; Kreinick, D.L.; Leong, Z.; Livezey, J.A.; Palmer, M.A.; Rubin, D.L.; Sagan, D.C.; Holtzapple, R.L.; Furman, M.A.; Penn, G.; Venturini, M.; Pivi, M.; Wang, L.; Harkay, K.

2010-01-01

The Cornell Electron Storage Ring Test Accelerator (CesrTA) program has included extensive measurements of coherent betatron tune shifts for a variety of electron and positron beam energies, bunch population levels, and bunch train configurations. The tune shifts have been shown to result primarily from the interaction of the beam with the space-charge field of the beam-induced low energy electron cloud in the vacuum chamber. Comparison to several advanced electron cloud simulation program packages has allowed determination of the sensitivity of these measurements to physical parameters characterizing the synchrotron radiation flux, the production of photoelectrons on the vacuum chamberwall, the beam emittance, lattice optics, and the secondary-electron yield model. We report on progress in understanding the cloud buildup and decay mechanisms in magnetic fields and in field-free regions, addressing quantitatively the precise determination of the physical parameters of the modeling. Validation of these models will serve as essential input in the design of damping rings for future high-energy linear colliders.

Mitigation of the electron-cloud effect in the PSR and SNS proton storage rings by tailoring the bunch profile

International Nuclear Information System (INIS)

Pivi, M.; Furman, M.A.

2003-01-01

For the storage ring of the Spallation Neutron Source(SNS) at Oak Ridge, and for the Proton Storage Ring (PSR) at Los Alamos, both with intense and very long bunches, the electroncloud develops primarily by the mechanism of trailing-edge multipacting. We show, by means of simulations for the PSR, how the resonant nature of this mechanism may be effectively broken by tailoring the longitudinal bunch profile at fixed bunch charge, resulting in a significant decrease in the electron-cloud effect. We briefly discuss the experimental difficulties expected in the implementation of this cure

Experiments on the injection, confinement, and ejection of electron clouds in a magnetic mirror

International Nuclear Information System (INIS)

Eckhouse, S.; Fisher, A.; Rostoker, N.

1978-01-01

A cloud of (5 to 10 keV) electrons is injected into a magnetic mirror field. The magnetic field rises in 40--120 μsec to a maximum of 10 kG. Two methods of injection were tried: In the first, the injector is located at the mirror midplane and electrons are injected perpendicular to the magnetic field lines. In the second scheme, the injector is located near the mirror maximum. Up to about 10 11 electrons were trapped in both schemes with a mean kinetic energy of 0.3 MeV. Measured confinement time is limited only by the magnetic field decay time. The compressed electron cloud executes electrostatic oscillations. The frequency of the oscillation is proportional to the number of electrons trapped, and it is independent of the value of the magnetic field and the initial electron energy. The electron cloud was ejected along the mirror axis and properties of the ejected electron cloud were measured by x-ray pulses from bremstrahlung of electrons on the vacuum system wall and by collecting electrons on a Faraday cup

CLEARING OF ELECTRON CLOUD IN SNS

International Nuclear Information System (INIS)

WANG, L.; LEE, Y.Y.; RAPRIA, D.

2004-01-01

In this paper we describe a mechanism using the clearing electrodes to remove the electron cloud in the Spallation Neutron Source (SNS) accumulator ring, where strong multipacting could happen at median clearing fields. A similar phenomenon was reported in an experimental study at Los Alamos laboratory's Proton Synchrotron Ring (PSR). We also investigated the effectiveness of the solenoid's clearing mechanism in the SNS, which differs from the short bunch case, such as in B-factories. The titanium nitride (TiN) coating of the chamber walls was applied to reduce the secondary electron yield (SEY)

Progress in Studies of Electron-Cloud-Induced Optics Distortions at CesrTA

International Nuclear Information System (INIS)

Crittenden, James; Penn, Gregory; Venturini, Marco; Harkay, Katherine; Holtzapple, Robert; Pivi, Mauro; Wang, Lanfa

2012-01-01

The Cornell Electron Storage Ring Test Accelerator (CesrTA) program has included extensive measurements of coherent betatron tune shifts for a variety of electron and positron beam energies, bunch population levels, and bunch train configurations. The tune shifts have been shown to result primarily from the interaction of the beam with the space-charge field of the beam-induced low-energy electron cloud in the vacuum chamber. Comparison to several advanced electron cloud simulation codes has allowed determination of the sensitivity of these measurements to physical parameters characterizing the synchrotron radiation flux, the production of photo-electrons on the vacuum chamber wall, the beam emittance, lattice optics, and the secondary-electron yield model. We report on progress in understanding the cloud buildup and decay mechanisms in magnetic fields and in field-free regions, addressing quantitatively the precise determination of the physical parameters of the modeling. Validation of these models will serve as essential input in the design of damping rings for future high-energy linear colliders.

Measurements of the Electron Cloud Density in the PEP-II Low Energy Ring

Energy Technology Data Exchange (ETDEWEB)

Byrd, John; De Santis, Stefano; Sonnad, Kiran; Caspers, Fritz; Kroyer, Tom; Krasnykh, Anatoly; Pivi, Mauro

2008-06-01

Clouds of low energy electronsin the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energyelectron clouds over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave that is independently excited and transmitted over a section of the accelerator. We infer the absolute phase shift with relatively high accuracy from the phase modulation of the transmission due to the modulation of the electron cloud density from a gap in the positively charged beam. We have used this technique for the first time to measure the average electron cloud density over a 50 m straight section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center. We have also measured the variation of the density by using low field solenoid magnets to control the electrons.

Modeling Incoherent Electron Cloud Effects

International Nuclear Information System (INIS)

Vay, Jean-Luc; Benedetto, E.; Fischer, W.; Franchetti, G.; Ohmi, K.; Schulte, D.; Sonnad, K.; Tomas, R.; Vay, J.-L.; Zimmermann, F.; Rumolo, G.; Pivi, M.; Raubenheimer, T.

2007-01-01

Incoherent electron effects could seriously limit the beam lifetime in proton or ion storage rings, such as LHC, SPS, or RHIC, or blow up the vertical emittance of positron beams, e.g., at the B factories or in linear-collider damping rings. Different approaches to modeling these effects each have their own merits and drawbacks. We describe several simulation codes which simplify the descriptions of the beam-electron interaction and of the accelerator structure in various different ways, and present results for a toy model of the SPS. In addition, we present evidence that for positron beams the interplay of incoherent electron-cloud effects and synchrotron radiation can lead to a significant increase in vertical equilibrium emittance. The magnitude of a few incoherent e+e- scattering processes is also estimated. Options for future code development are reviewed

Experimental Investigation of Electron Cloud Containment in a Nonuniform Magnetic Field

Science.gov (United States)

Eninger, J. E.

1974-01-01

Dense clouds of electrons were generated and studied in an axisymmetric, nonuniform magnetic field created by a short solenoid. The operation of the experiment was similar to that of a low-pressure (approximately 0.000001 Torr) magnetron discharge. Discharge current characteristics are presented as a function of pressure, magnetic field strength, voltage, and cathode end-plate location. The rotation of the electron cloud is determined from the frequency of diocotron waves. In the space charge saturated regime of operation, the cloud is found to rotate as a solid body with frequency close to V sub a/phi sub a where V sub a is the anode voltage and phi suba is the total magnetic flux. This result indicates that, in regions where electrons are present, the magnetic field lines are electrostatic equipotentials (E bar, B bar = 0). Equilibrium electron density distributions suggested by this conditions are integrated with respect to total ionizing power and are found consistent with measured discharge currents.

Experimental investigation of electron cloud containment in a nonuniform magnetic field

International Nuclear Information System (INIS)

Eninger, J.E.

1974-05-01

Dense clouds of electrons were generated and studied in an axisymmetric, nonuniform magnetic field created by a short solenoid. The operation of the experiment was similar to that of a low-pressure (approximately 0.000001 torr) magnetron discharge. Discharge current characteristics are presented as a function of pressure, magnetic field strength, voltage, and cathode end-plate location. The rotation of the electron cloud is determined from the frequency of diocotron waves. In the space charge saturated regime of operation, the cloud is found to rotate as a solid body with frequency close to V/sub a/phi/sub a/ where V/sub a/ is the anode voltage and phi/sub a/ is the total magnetic flux. This result indicates that, in regions where electrons are present, the magnetic field lines are electrostatic equipotentials (E bar, B bar = 0). Equilibrium electron density distributions suggested by this condition are integrated with respect to total ionizing power and are found consistent with measured discharge currents. (U.S.)

A simulation study of electron-cloud instability and beam-induced multipacting in the LHC

International Nuclear Information System (INIS)

Zimmermann, F.

1997-02-01

In the LHC beam pipe, photoemission and secondary emission give rise to a quasi-stationary electron cloud, which is established after a few bunch passages. The response of this electron cloud to a transversely displaced bunch resembles a short-range wakefield and can cause a fast instability. In addition, beam-induced multipacting of the electrons may lead to an enhanced gas desorption and an associated pressure increase. In this paper the authors report preliminary simulation results of the electron-cloud build-up both in a dipole magnet and in a straight section of the LHC at top energy. The effective wakefield created by the electron cloud translates into an instability rise time of about 25 ms horizontally and 130 ms vertically. This rise time is not much larger than that of the resistive-wall instability at injection energy

Electron cloud development in the Proton Storage Ring and in the Spallation Neutron Source

International Nuclear Information System (INIS)

Pivi, M.T.F.; Furman, M.A.

2002-01-01

We have applied our simulation code ''POSINST'' to evaluate the contribution to the growth rate of the electron-cloud instability in proton storage rings. Recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source(SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos are presented in this paper. A key ingredient in our model is a detailed description of the secondary emitted-electron energy spectrum. A refined model for the secondary emission process including the so-called true secondary, rediffused and backscattered electrons has recently been included in the electron-cloud code

Considerations for Cloud Security Operations

OpenAIRE

Cusick, James

2016-01-01

Information Security in Cloud Computing environments is explored. Cloud Computing is presented, security needs are discussed, and mitigation approaches are listed. Topics covered include Information Security, Cloud Computing, Private Cloud, Public Cloud, SaaS, PaaS, IaaS, ISO 27001, OWASP, Secure SDLC.

HINS R and D Collaboration on Electron Cloud Effects: Midyear Report

International Nuclear Information System (INIS)

Furman, M.A.; Sonnad, K.; Vay, J.-L.

2006-01-01

We present a report on ongoing activities on electron-cloud R and D for the MI upgrade. These results update and extend those presented in Refs. 1, 2. In this report we have significantly expanded the parameter range explored in bunch intensity Nb, RMS bunch length σ z and peak secondary emission yield (SEY) (delta) max , but we have constrained our simulations to a field-free region. We describe the threshold behaviors in all of the above three parameters. For (delta) max (ge) 1.5 we find that, even for N b = 1 x 10 11 , the electron cloud density, when averaged over the entire chamber, exceeds the beam neutralization level, but remains significantly below the local neutralization level (ie., when the electron density is computed in the neighborhood of the beam). This 'excess' of electrons is accounted for by narrow regions of high concentration of electrons very close to the chamber surface, especially at the top and bottom of the chamber, akin to virtual cathodes. These virtual cathodes are kept in equilibrium, on average, by a competition between space-charge forces (including their images) and secondary emission, a mechanism that shares some features with the space-charge saturation of the current in a diode at high fields. For N b = 3 x 10 11 the electron cloud build-up growth rate and saturation density have a strong dependence on σ z as σ z decreases below ∼ 0.4 m, when the average electron-wall impact energy roughly reaches the energy E max where (delta) peaks. We also present improved results on emittance growth simulations of the beam obtained with the code WARP/POSINST in quasi-static mode, in which the beam-(electron cloud) interaction is lumped into N s 'stations' around the ring, where N s = 1, 2,..., 9. The emittance shows a rapid growth of ∼ 20% during the first ∼ 100 turns, followed by a much slower growth rate of ∼ 0.03%/turn. Concerning the electron cloud detection technique using microwave transmission, we present an improved

Electron cloud studies for the LHC and future proton colliders

CERN Document Server

Domínguez Sánchez de la Blanca, César Octavio; Zimmermann, Frank

2014-01-01

The Large Hadron Collider (LHC) is the world’s largest and most powerful particle collider. Its main objectives are to explore the validity of the standard model of particle physics and to look for new physics beyond it, at unprecedented collision energies and rates. A good luminosity performance is imperative to attain these goals. In the last stage of the LHC commissioning (2011-2012), the limiting factor to achieving the design bunch spacing of 25 ns has been the electron cloud effects. The electron cloud is also expected to be the most important luminosity limitation after the first Long Shut-Down of the LHC (LS1), when the machine should be operated at higher energy and with 25-ns spacing, as well as for the planned luminosity upgrade (HL-LHC) and future high energy proton colliders (HE-LHC and VHE-LHC). This thesis contributes to the understanding of the electron cloud observations during the first run of the LHC (2010-2012), presents the first beam dynamics analysis for the next generation of high en...

Experimental Observations of In-Situ Secondary Electron Yield Reduction in the PEP-II Particle Accelerator Beam Line

International Nuclear Information System (INIS)

Pivi, Mauro

2010-01-01

Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders (LC) such as ILC and CLIC. To test a series of promising possible electron cloud mitigation techniques as surface coatings and grooves, in the Positron Low Energy Ring (LER) of the PEP-II accelerator, we have installed several test vacuum chambers including (i) a special chamber to monitor the variation of the secondary electron yield of technical surface materials and coatings under the effect of ion, electron and photon conditioning in situ in the beam line; (ii) chambers with grooves in a straight magnetic-free section; and (iii) coated chambers in a dedicated newly installed 4-magnet chicane to study mitigations in a magnetic field region. In this paper, we describe the ongoing R and D effort to mitigate the electron cloud effect for the LC damping ring, focusing on the first experimental area and on results of the reduction of the secondary electron yield due to in situ conditioning.

Combined phenomena of beam-beam and beam-electron cloud interactionsin circular e^{+}e^{-} colliders

Directory of Open Access Journals (Sweden)

Kazuhito Ohmi

2002-10-01

Full Text Available An electron cloud causes various effects in high intensity positron storage rings. The positron beam and the electron cloud can be considered a typical two-stream system with a certain plasma frequency. Beam-beam interaction is another important effect for high luminosity circular colliders. Colliding two beams can be considered as a two-stream system with another plasma frequency. We study the combined phenomena of the beam-electron cloud and beam-beam interactions from a viewpoint of two complex two-stream effects with two plasma frequencies.

Secondary Electron Yield Measurements and Groove Chambers Tests in the PEP-II Beam Line Straights Sections

International Nuclear Information System (INIS)

Pivi, M

2008-01-01

Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders such as ILC and CLIC [1, 2]. In the Positron Low Energy Ring (LER) of the PEP-II accelerator, we have installed vacuum chambers with rectangular grooves in a straight magnetic-free section to test this promising possible electron cloud mitigation technique. We have also installed a special chamber to monitor the secondary electron yield of TiN and TiZrV (NEG) coating, Copper, Stainless Steel and Aluminum under the effect of electron and photon conditioning in situ in the beam line. In this paper, we describe the ongoing R and D effort to mitigate the electron cloud effect for the ILC damping ring, the latest results on in situ secondary electron yield conditioning and recent update on the groove tests in PEP-II

Simulation and Analysis of Microwave Transmission through an Electron Cloud, a Comparison of Results

International Nuclear Information System (INIS)

Sonnad, Kiran; Sonnad, Kiran; Furman, Miguel; Veitzer, Seth; Stoltz, Peter; Cary, John

2007-01-01

Simulation studies for transmission of microwaves through electron clouds show good agreement with analytic results. The electron cloud produces a shift in phase of the microwave. Experimental observation of this phenomena would lead to a useful diagnostic tool for accessing the local density of electron clouds in an accelerator. These experiments are being carried out at the CERN SPS and the PEP-II LER at SLAC and is proposed to be done at the Fermilab main injector. In this study, a brief analysis of the phase shift is provided and the results are compared with that obtained from simulations

Electron Cloud Effects in Accelerators

International Nuclear Information System (INIS)

Furman, M A

2013-01-01

We present a brief summary of various aspects of the electron-cloud effect (ECE) in accelerators. For further details, the reader is encouraged to refer to the proceedings of many prior workshops, either dedicated to EC or with significant EC contents, including the entire 'ECLOUD' series. In addition, the proceedings of the various flavors of Particle Accelerator Conferences contain a large number of EC-related publications. The ICFA Beam Dynamics Newsletter series contains one dedicated issue, and several occasional articles, on EC. An extensive reference database is the LHC website on EC. (author)

Application of Coherent Tune Shift Measurements to the Characterization of Electron Cloud Growth

International Nuclear Information System (INIS)

Kreinick, D.L.; Crittenden, J.A.; Dugan, G.; Holtzapple, R.L.; Randazzo, M.; Furman, M.A.; Venturini, M.; Palmer, M.A.; Ramirez, G.

2011-01-01

Measurements of coherent tune shifts at the Cornell Electron Storage Ring Test Accelerator (CesrTA) have been made for electron and positron beams under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of several electron cloud simulation programs allows the evaluation of important parameters in these models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders. We outline recent improvements to the analysis techniques that should improve the fidelity of the modeling.

Simulation of the interaction of positively charged beams and electron clouds

International Nuclear Information System (INIS)

Markovik, Aleksandar

2013-01-01

The incoherent (head-tail) effect on the bunch due to the interaction with electron clouds (e-clouds) leads to a blow up of the transverse beam size in storage rings operating with positively charged beams. Even more the e-cloud effects are considered to be the main limiting factor for high current, high-brightness or high-luminosity operation of future machines. Therefore the simulation of e-cloud phenomena is a highly active field of research. The main focus in this work was set to a development of a tool for simulation of the interaction of relativistic bunches with non-relativistic parasitic charged particles. The result is the Particle-In-Cell Program MOEVE PIC Tracking which can track a 3D bunch under the influence of its own and external electromagnetic fields but first and foremost it simulates the interaction of relativistic positively charged bunches and initially static electrons. In MOEVE PIC Tracking the conducting beam pipe can be modeled with an arbitrary elliptical cross-section to achieve more accurate space charge field computations for both the bunch and the e-cloud. The simulation of the interaction between positron bunches and electron clouds in this work gave a detailed insight of the behavior of both particle species during and after the interaction. Further and ultimate goal of this work was a fast estimation of the beam stability under the influence of e-clouds in the storage ring. The standard approach to simulate the stability of a single bunch is to track the bunch particles through the linear optics of the machine by multiplying the 6D vector of each particle with the transformation matrices describing the lattice. Thereby the action of the e-cloud on the bunch is approximated by a pre-computed wake kick which is applied on one or more points in the lattice. Following the idea of K.Ohmi the wake kick was pre-computed as a two variable function of the bunch part exiting the e-cloud and the subsequent parts of a bunch which receive a

Benchmarking headtail with electron cloud instabilities observed in the LHC

CERN Document Server

Bartosik, H.; Iadarola, G.; Papaphilippou, Y.; Rumolo, G.

2013-01-01

After a successful scrubbing run in the beginning of 2011, the LHC can be presently operated with high intensity proton beams with 50 ns bunch spacing. However, strong electron cloud effects were observed during machine studies with the nominal beam with 25 ns bunch spacing. In particular, fast transverse instabilities were observed when attempting to inject trains of 48 bunches into the LHC for the first time. An analysis of the turn-by-turn bunch-bybunch data from the transverse damper pick-ups during these injection studies is presented, showing a clear signature of the electron cloud effect. These experimental observations are reproduced using numerical simulations: the electron distribution before each bunch passage is generated with PyECLOUD and used as input for a set of HEADTAIL simulations. This paper describes the simulation method as well as the sensitivity of the results to the initial conditions for the electron build-up. The potential of this type of simulations and their clear limitations on th...

Joint CARE-ELAN, CARE-HHH-APD, and EUROTEV-WP3 Workshop on Electron Cloud Clearing

CERN Document Server

Scandale, Walter; Schulte, D; Zimmermann, F; Electron Cloud Effects and Technological Consequences; ECL2

2007-01-01

This report contains the Proceedings of the joint CARE-HHH-APD, CARE-ELAN, and EUROTEV-WP3 Mini-Workshop on 'Electron Cloud Clearing - Electron Cloud and Technical Consequences', "ECL2", held at CERN in Geneva, Switzerland, 1-2 March 2007). The ECL2 workshop explored novel technological remedies against electron-cloud formation in an accelerator beam pipe. A primary motivation for the workshop was the expected harmful electron-cloud effects in the upgraded LHC injectors and in future linear colliders, as well as recent beam observations in operating facilities like ANKA, CESR, KEKB, RHIC, and SPS. The solutions discussed at ECL2 included enamel-based clearing electrodes, slotted vacuum chambers, NEG coating, and grooves. Several of the proposed cures were assessed in terms of their clearing efficiency and the associated beam impedance. The workshop also reviewed new simulation tools like the 3D electron-ion build-up 'Faktor', modeling assumptions, analytical calculations, beam experiments, and laboratory meas...

Summary: Electron-cloud effects and fast-ion instability

International Nuclear Information System (INIS)

Furman, Miguel A.

2000-01-01

This is my summary of the talks on the electron-cloud effect and the fast-ion instability that were presented at the 8th ICFA Beam Dynamics Mini-Work shop on Two-Stream Instabilities in Particle Accelerators and Storage Rings,Santa Fe, NM, February 16--18, 2000

Electron-cloud updated simulation results for the PSR, and recent results for the SNS

International Nuclear Information System (INIS)

Pivi, M.; Furman, M.A.

2002-01-01

Recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos are presented in this paper. A refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has recently been included in the electron-cloud code

Electron-cloud instabilities and beam-induced multipacting in the LHC and in the VLHC

International Nuclear Information System (INIS)

Zimmermann, F.

1997-10-01

In the beam pipe of the Large Hadron Collider (LHC), photoemission and secondary emission give rise to a quasi-stationary electron cloud, which is established after a few buncn passages. The response of this electron cloud to a transversely displaced bunch resembles a short-range wakefield and can cause a fast instability. In additoin, beam-induced multipacting of the electrons may lead to an enhanced gas desorption and an associated pressure increase. In this paper the authors report preliminary simulation results of the electron-cloud build-up both in a dipole magnet and in a straight section of the LHC at top energy. The effective wakefield created by the electron cloud translates into an instability rise time of about 40 ms horizontally and 500 ms vertically. This rise time is not much larger than that of the resistive-wall instability at injection energy. Similar simulation studies show that the instability rise time for the proposed Very Large Hadron Collider (VLHC) is about 3--4 s in both trasnverse planes. The smaller growth rate in the VLHC, as compared with the LHC, is primarily due to the much lower bunch population

Characterization of electron clouds in the Cornell Electron Storage Ring Test Accelerator using TE-wave transmission

International Nuclear Information System (INIS)

De Santis, S.; Byrd, J.M.; Billing, M.; Palmer, M.; Sikora, J.; Carlson, B.

2010-01-01

A relatively new technique for measuring the electron cloud density in storage rings has been developed and successfully demonstrated (S. De Santis, J.M. Byrd, F. Caspers, A. Krasnykh, T. Kroyer, M.T.F. Pivi, and K.G. Sonnad, Phys. Rev. Lett. 100, 094801 (2008).). We present the experimental results of a systematic application of this technique at the Cornell Electron Storage Ring Test Accelerator. The technique is based on the phase modulation of the TE mode transmitted in a synchrotron beam pipe caused by the periodic variation of the density of electron plasma. Because of the relatively simple hardware requirements, this method has become increasingly popular and has been since successfully implemented in several machines. While the principles of this technique are straightforward, quantitative derivation of the electron cloud density from the measurement requires consideration of several effects, which we address in detail.

Progress on electron cloud effects calculations for the FNAL main injector

International Nuclear Information System (INIS)

Furman, Miguel A; Sonnad, Kiran G.; Furman, Miguel A.; Vay, Jean-Luc

2008-01-01

We have studied the response of the beam to an electron cloud for the Fermilab Main Injector using the Quasistatic Model [1] implemented into the particle-in-cell code Warp [2]. Specifically, we have addressed the effects due to varying the beam intensity, electron cloud density and chromaticity. In addition, we have estimated the contribution to emittance evolution due to beam space-charge effects. We have carried out a comparison between how the beam responds at injection energy and at top energy. We also present some results on the validation of the computational model, and report on progress towards improving the computational model

Electron-cloud simulation results for the PSR and SNS

International Nuclear Information System (INIS)

Pivi, M.; Furman, M.A.

2002-01-01

We present recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos. In particular, a complete refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has been included in the simulation code

Preliminary Analysis and Simulation Results of Microwave Transmission Through an Electron Cloud

International Nuclear Information System (INIS)

Sonnad, Kiran; Sonnad, Kiran; Furman, Miguel; Veitzer, Seth; Stoltz, Peter; Cary, John

2007-01-01

The electromagnetic particle-in-cell (PIC) code VORPAL is being used to simulate the interaction of microwave radiation through an electron cloud. The results so far show good agreement with theory for simple cases. The study has been motivated by previous experimental work on this problem at the CERN SPS [1], experiments at the PEP-II Low Energy Ring (LER) at SLAC [4], and proposed experiments at the Fermilab Main Injector (MI). With experimental observation of quantities such as amplitude, phase and spectrum of the output microwave radiation and with support from simulations for different cloud densities and applied magnetic fields, this technique can prove to be a useful probe for assessing the presence as well as the density of electron clouds

Simulations of Electron Cloud Effects on the Beam Dynamics for the FNAL Main Injector Upgrade

International Nuclear Information System (INIS)

Sonnad Kiran G.; Furman, Miguel; Vay, Jean-Luc; Venturini, Marco; Celata, Christine M.; Grote, David

2006-01-01

The Fermilab main injector (MI) is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort. This upgrade will involve a significant increasing of the bunch intensity relative to its present value. Such an increase will place the MI in a regime in which electron-cloud effects are expected to become important. We have used the electrostatic particle-in-cell code WARP, recently augmented with new modeling capabilities and simulation techniques, to study the dynamics of beam-electron cloud interaction. This work in progress involves a systematic assessment of beam instabilities due to the presence of electron clouds

The size and spatial distribution of microchannel plate output electron clouds

International Nuclear Information System (INIS)

Lapington, J.S.; Edgar, M.L.

1989-01-01

An experimental technique for measuring the spatial distribution of the output charge cloud from a microchannel plate (MCP), using a planar, charge-division-type anode is discussed. The anode simultaneously measures, for each charge cloud, both the position of the charge centroid and the fractional charge falling to one side of the split in the pattern. The measurements from several thousand events have been combined to calculate the average spatial distribution of the electron cloud and the dominant factors influencing the charge cloud distribution have been found to be the MCP gain and the MCP-anode accelerating field and geometry. Experimental research on the two dominant factors with respect to ranges of distribution is presented. 10 refs

Characterization of electron clouds in the Cornell Electron Storage Ring Test Accelerator using TE-wave transmission

Directory of Open Access Journals (Sweden)

S. De Santis

2010-07-01

Full Text Available A relatively new technique for measuring the electron cloud density in storage rings has been developed and successfully demonstrated [S. De Santis, J. M. Byrd, F. Caspers, A. Krasnykh, T. Kroyer, M. T. F. Pivi, and K. G. Sonnad, Phys. Rev. Lett. 100, 094801 (2008.PRLTAO0031-900710.1103/PhysRevLett.100.094801]. We present the experimental results of a systematic application of this technique at the Cornell Electron Storage Ring Test Accelerator. The technique is based on the phase modulation of the TE mode transmitted in a synchrotron beam pipe caused by the periodic variation of the density of electron plasma. Because of the relatively simple hardware requirements, this method has become increasingly popular and has been since successfully implemented in several machines. While the principles of this technique are straightforward, quantitative derivation of the electron cloud density from the measurement requires consideration of several effects, which we address in detail.

RFID-based Electronic Identity Security Cloud Platform in Cyberspace

OpenAIRE

Bing Chen; Chengxiang Tan; Bo Jin; Xiang Zou; Yuebo Dai

2012-01-01

With the moving development of networks, especially Internet of Things, electronic identity administration in cyberspace is becoming more and more important. And personal identity management in cyberspace associated with individuals in reality has been one significant and urgent task for the further development of information construction in China. So this paper presents a RFID-based electronic identity security cloud platform in cyberspace to implement an efficient security management of cyb...

Electron-microscope study of cloud and fog nuclei

Energy Technology Data Exchange (ETDEWEB)

Ogiwara, S; Okita, T

1952-01-01

Droplets of clouds on a mountain and of fog in an urban area were captured and the form, nature and size of their nuclei were studied by means of an electron-microscope and by a chamber of constant humidity. These nuclei have similar form and nature to the hygroscopic particles in haze and to the artificially produced combustion particles. No sea-salt nuclei were found in our observations, therefore, sea-spray appears to be an insignificant source of condensation nuclei. It was found that both the cloud and the fog nuclei originated in combustion products which were the mixture of hygroscopic and non-hygroscopic substances, and that the greater part of the nuclei did not contain pure sulfuric acid.

New simulation capabilities of electron clouds in ion beams with large tune depression

International Nuclear Information System (INIS)

Vay, J.L.; Furman, M.A.; Seidl, P.A.; Cohen, R.H.; Friedman, A.; Grote, D.P.; Kireeff-Covo, M.; Molvik, A.W.; Stoltz, P.H.; Veitzer, S.; Verboncoeur, J.P.

2006-01-01

The authors have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and electron clouds (e-clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D ''slice'' e-cloud code POSINST, as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new ''drift-Lorentz'' particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with electron clouds in the High-Current Experiment (HCX). They describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-clouds in the Large Hadron Collider (LHC)

Single-Bunch Instability Driven by the Electron Cloud Effect in the Positron Damping Ring of the International Linear Collider

International Nuclear Information System (INIS)

Pivi, Mauro; Raubenheimer, Tor O.; Ghalam, Ali; Harkay, Katherine; Ohmi, Kazuhito; Wanzenberg, Rainer; Wolski, Andrzej; Zimmermann, Frank

2005-01-01

Collective instabilities caused by the formation of an electron cloud (EC) are a potential limitation to the performances of the damping rings for a future linear collider. In this paper, we present recent simulation results for the electron cloud build-up in damping rings of different circumferences and discuss the single-bunch instabilities driven by the electron cloud

First electron-cloud studies at the Large Hadron Collider

CERN Document Server

Dominguez, O; Arduini, G; Metral, E; Rumolo, G; Zimmermann, F; Maury Cuna, H

2013-01-01

During the beam commissioning of the Large Hadron Collider (LHC) with 150, 75, 50, and 25-ns bunch spacing, important electron-cloud effects, like pressure rise, cryogenic heat load, beam instabilities, or emittance growth, were observed. Methods have been developed to infer different key beam-pipe surface parameters by benchmarking simulations and pressure rise as well as heat-load observations. These methods allow us to monitor the scrubbing process, i.e., the reduction of the secondary emission yield as a function of time, in order to decide on the most appropriate strategies for machine operation. To better understand the influence of electron clouds on the beam dynamics, simulations have been carried out to examine both the coherent and the incoherent effects on the beam. In this paper we present the methodology and first results for the scrubbing monitoring process at the LHC. We also review simulated instability thresholds and tune footprints for beams of different emittance, interacting with an electr...

New simulation capabilities of electron clouds in ion beams with large tune depression

International Nuclear Information System (INIS)

Vay, J.-L.; Furman, M.A.; Seidl, P.A.

2007-01-01

We have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and electron clouds (e-clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D 'slice' e-cloud code POSINST [M. Furman, this workshop, paper TUAX05], as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new 'drift-Lorentz' particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with electron clouds in the High-Current Experiment (HCX) [experimental results discussed by A. Molvik, this workshop, paper THAW02]. We describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-clouds in the Large Hadron Collider (LHC). (author)

New simulation capabilities of electron clouds in ion beams with large tune depression

International Nuclear Information System (INIS)

Lawrence Livermore National Laboratory

2006-01-01

We have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and electron clouds (e-clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D ''slice'' e-cloud code POSINST [M. Furman, this workshop, paper TUAX05], as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new ''drift-Lorentz'' particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with electron clouds in the High-Current Experiment (HCX) [experimental results discussed by A. Molvik, this workshop, paper THAW02]. We describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-clouds in the Large Hadron Collider (LHC)

Demonstration of electron clearing effect by means of a clearing electrode in high-intensity positron ring

International Nuclear Information System (INIS)

Suetsugu, Y.; Fukuma, H.; Wang, L.; Pivi, M.; Morishige, A.; Suzuki, Y.; Tsukamoto, M.; Tsuchiya, M.

2009-01-01

In the beam pipe of high-intensity positron/proton storage rings, undesired electron clouds may be first produced by photoelectrons and the ionization of residual gases; then the clouds increase by the secondary electron emission. In this study, a strip-line clearing electrode has been developed to mitigate the electron-cloud effect in high-intensity positron/proton storage rings. The electrode is composed of a thin tungsten layer with a thickness of 0.1 mm formed on a thin alumina ceramic layer with a thickness of 0.2 mm. The narrow alumina gap between the electrode and the beam pipe decreases the beam impedance and also enhances the heat transfer from the electrode to the beam pipe. A test model has been installed in the KEK B-factory (KEKB) positron ring, along with an electron monitor with a retarding grid. The electron density in a field free region decreased by one order of magnitude was observed on the application of ±500 V to the electrode at a beam current of 1.6 A with 1585 bunches. The reduction in the electron density was more drastic in a vertical magnetic field of 0.77 T, that is, the electron density decreased by several orders by applying +500 V to the electrode at the same beam current. This experiment is the first experiment demonstrating the principle of the clearing electrode that is used to mitigate the electron-cloud effect in a positron ring.

Accurate simulation of the electron cloud in the Fermilab Main Injector with VORPAL

Energy Technology Data Exchange (ETDEWEB)

Lebrun, Paul L.G.; Spentzouris, Panagiotis; /Fermilab; Cary, John R.; Stoltz, Peter; Veitzer, Seth A.; /Tech-X, Boulder

2010-05-01

Precision simulations of the electron cloud at the Fermilab Main Injector have been studied using the plasma simulation code VORPAL. Fully 3D and self consistent solutions that includes E.M. field maps generated by the cloud and the proton bunches have been obtained, as well detailed distributions of the electron's 6D phase space. We plan to include such maps in the ongoing simulation of the space charge effects in the Main Injector. Simulations of the response of beam position monitors, retarding field analyzers and microwave transmission experiments are ongoing.

Capabilities and Advantages of Cloud Computing in the Implementation of Electronic Health Record.

Science.gov (United States)

Ahmadi, Maryam; Aslani, Nasim

2018-01-01

With regard to the high cost of the Electronic Health Record (EHR), in recent years the use of new technologies, in particular cloud computing, has increased. The purpose of this study was to review systematically the studies conducted in the field of cloud computing. The present study was a systematic review conducted in 2017. Search was performed in the Scopus, Web of Sciences, IEEE, Pub Med and Google Scholar databases by combination keywords. From the 431 article that selected at the first, after applying the inclusion and exclusion criteria, 27 articles were selected for surveyed. Data gathering was done by a self-made check list and was analyzed by content analysis method. The finding of this study showed that cloud computing is a very widespread technology. It includes domains such as cost, security and privacy, scalability, mutual performance and interoperability, implementation platform and independence of Cloud Computing, ability to search and exploration, reducing errors and improving the quality, structure, flexibility and sharing ability. It will be effective for electronic health record. According to the findings of the present study, higher capabilities of cloud computing are useful in implementing EHR in a variety of contexts. It also provides wide opportunities for managers, analysts and providers of health information systems. Considering the advantages and domains of cloud computing in the establishment of HER, it is recommended to use this technology.

Concerning the maximum energy of ions accelerated at the front of a relativistic electron cloud expanding into vacuum

International Nuclear Information System (INIS)

Bulanov, S.V.; Esirkepov, T.Zh.; Koga, J.; Tajima, T.; Farina, D.

2004-01-01

Results of particle-in-cell simulations are presented that demonstrate characteristic interaction regimes of high-power laser radiation with plasma. It is shown that the maximum energy of fast ions can substantially exceed the electron energy. A theoretical model is proposed of ion acceleration at the front of a relativistic electron cloud expanding into vacuum in the regime of strong charge separation. The model describes the electric field structure and the dynamics of fast ions inside the electron cloud. The maximum energy the ions can gain at the front of the expanding electron cloud is found

Observation of transverse and longitudinal modes in non-neutral electron clouds confined in a magnetic mirror

International Nuclear Information System (INIS)

Eckhouse, S.; Fisher, A.; Rostoker, N.

1979-01-01

Electrostatic modes on non-neutral electron clouds confined in a magnetic mirror field have been investigated. The cloud contains 2 x 10 11 electrons at an average kinetic energy of 0.3 MeV for a magnetic field with a peak intensity of 9 kG at the midplane. It was found that the cloud is moving azimuthally as well as longitudinally. The azimuthal motion has an m=1 spatial nature. The longitudinal modes have a more complicated nature, but their frequency equals that of the azimuthal mode

Simulation of electron cloud effects to heavy ion beams

Energy Technology Data Exchange (ETDEWEB)

Yaman, Fatih; Gjonaj, Erion; Weiland, Thomas [Technische Universitaet Darmstadt (Germany). Institut fuer Theorie Elektromagnetischer Felder

2011-07-01

Electron cloud (EC) driven instability can cause beam loss, emittance growth, trajectory change and wake fields. Mentioned crucial effects of EC motivated researchers to understand the EC build up mechanism and the effects of EC to the beam. This motivation also induced the progress of developing new simulation codes. EC simulations can roughly be divided into two classes such as, softwares whose goals are to simulate the build up of the EC during the passage of a bunch train and the codes which model the interaction of a bunch with an EC. The aim of this study is to simulate the effects of electron cloud (EC) on the dynamics of heavy ion beams which are used in heavy ion synchrotron (SIS-18) at GSI. To do this, a 3-D and self-consistent simulation program based on particle in cell (PIC) method is used. In the PIC cycle, accurate solution of the Maxwell equations is obtained by employing discontinuous Galerkin finite element method. As a model, we assumed a perfectly conducting beam pipe which was uniformly (or randomly) loaded with the electrons. Then as parallel with the realistic cases in SIS-18, a single bunch consisting of U{sup +73} ions was extracted which could propagate in this pipe. Due to EC-ion bunch interaction, electrons gained energy and their displacements were observed. Electric and magnetic field components and EC charge density were calculated, numerically.

Elves and associated electron density changes due to cloud-to-ground and in-cloud lightning discharges

Science.gov (United States)

Marshall, R. A.; Inan, U. S.; Glukhov, V. S.

2010-04-01

A 3-D finite difference time domain model is used to simulate the lightning electromagnetic pulse (EMP) and its interaction with the lower ionosphere. Results agree with the frequently observed, doughnut-shaped optical signature of elves but show that the structure exhibits asymmetry due to the presence of Earth's ambient magnetic field. Furthermore, in-cloud (horizontal) lightning channels produce observable optical emissions without the doughnut shape and, in fact, produce a much stronger optical output for the same channel current. Electron density perturbations associated with elves are also calculated, with contributions from attachment and ionization. Results presented as a function of parameters such as magnetic field direction, dipole current orientation, altitude and amplitude, and ambient ionospheric density profile demonstrate the highly nonlinear nature of the EMP-ionosphere interaction. Ionospheric effects of a sequence of in-cloud discharges are calculated, simulating a burst of in-cloud lightning activity and resulting in large density changes in the overlying ionosphere.

An analytic model for the electrostatic contribution of the electron cloud to the vertical tune-shift

International Nuclear Information System (INIS)

Schaechter, Levi

2008-01-01

An analytic quasi-static model is developed for the analysis of the tune-shift associated with the presence of an electron cloud in a damping ring. The essential assumption is that in its direction of motion, a bunch experiences a uniform cloud density but the latter varies from one bunch to another. A second important component of the model is the life-time since it controls the build-up, the equilibrium as well as the decay of the cloud. It is demonstrated analytically that in case of a train of positron bunches, electrons may be trapped in the vertical direction for the entire train duration. Assuming that the ring is dominated by vertical magnetic fields due to either bends or wigglers, we found excellent agreement between the theoretical predictions and the experimental results reported at Cornell Electron/Positron Storage Ring. The ratio between the vertical and horizontal tune-shifts is shown to be indicative of the distribution of the cloud in the beam-chamber

Physical Mechanism, Spectral Detection, and Potential Mitigation of 3D Cloud Effects on OCO-2 Radiances and Retrievals

Science.gov (United States)

Cochrane, S.; Schmidt, S.; Massie, S. T.; Iwabuchi, H.; Chen, H.

2017-12-01

Analysis of multiple partially cloudy scenes as observed by OCO-2 in nadir and target mode (published previously and reviewed here) revealed that XCO2 retrievals are systematically biased in presence of scattered clouds. The bias can only partially be removed by applying more stringent filtering, and it depends on the degree of scene inhomogeneity as quantified with collocated MODIS/Aqua imagery. The physical reason behind this effect was so far not well understood because in contrast to cloud-mediated biases in imagery-derived aerosol retrievals, passive gas absorption spectroscopy products do not depend on the absolute radiance level and should therefore be less sensitive to 3D cloud effects and surface albedo variability. However, preliminary evidence from 3D radiative transfer calculations suggested that clouds in the vicinity of an OCO-2 footprint not only offset the reflected radiance spectrum, but introduce a spectrally dependent perturbation that affects absorbing channels disproportionately, and therefore bias the spectroscopy products. To understand the nature of this effect for a variety of scenes, we developed the OCO-2 radiance simulator, which uses the available information on a scene (e.g., MODIS-derived surface albedo, cloud distribution, and other parameters) as the basis for 3D radiative transfer calculations that can predict the radiances observed by OCO-2. We present this new tool and show examples of its utility for a few specific scenes. More importantly, we draw conclusions about the physical mechanism behind this 3D cloud effect on radiances and ultimately OCO-2 retrievals, which involves not only the clouds themselves but also the surface. Harnessed with this understanding, we can now detect cloud vicinity effects in the OCO-2 spectra directly, without actually running the 3D radiance simulator. Potentially, it is even possible to mitigate these effects and thus increase data harvest in regions with ubiquitous cloud cover such as the Amazon

Enhanced quasi-static particle-in-cell simulation of electron cloud instabilities in circular accelerators

Science.gov (United States)

Feng, Bing

Electron cloud instabilities have been observed in many circular accelerators around the world and raised concerns of future accelerators and possible upgrades. In this thesis, the electron cloud instabilities are studied with the quasi-static particle-in-cell (PIC) code QuickPIC. Modeling in three-dimensions the long timescale propagation of beam in electron clouds in circular accelerators requires faster and more efficient simulation codes. Thousands of processors are easily available for parallel computations. However, it is not straightforward to increase the effective speed of the simulation by running the same problem size on an increasingly number of processors because there is a limit to domain size in the decomposition of the two-dimensional part of the code. A pipelining algorithm applied on the fully parallelized particle-in-cell code QuickPIC is implemented to overcome this limit. The pipelining algorithm uses multiple groups of processors and optimizes the job allocation on the processors in parallel computing. With this novel algorithm, it is possible to use on the order of 102 processors, and to expand the scale and the speed of the simulation with QuickPIC by a similar factor. In addition to the efficiency improvement with the pipelining algorithm, the fidelity of QuickPIC is enhanced by adding two physics models, the beam space charge effect and the dispersion effect. Simulation of two specific circular machines is performed with the enhanced QuickPIC. First, the proposed upgrade to the Fermilab Main Injector is studied with an eye upon guiding the design of the upgrade and code validation. Moderate emittance growth is observed for the upgrade of increasing the bunch population by 5 times. But the simulation also shows that increasing the beam energy from 8GeV to 20GeV or above can effectively limit the emittance growth. Then the enhanced QuickPIC is used to simulate the electron cloud effect on electron beam in the Cornell Energy Recovery Linac

Study of Electron Cloud E ects in the DAFNE PHI-Factory for the KLOE-2 Run

CERN Document Server

Demma, T

2011-01-01

A strong horizontal instability has been observed in the the DAFNE positron ring since 2003. Experimental observations suggest an electron cloud induced coupled bunbh instability as a possible explanation. Here is reported a simulation study of the electron cloud effects in the positron ring of the DAFNE PHI factory with particular reference to the machine configuration designed for the KLOE-2 experiment.

Electron cloud instabilities in the Proton Storage Ring and Spallation Neutron Source

Directory of Open Access Journals (Sweden)

M. Blaskiewicz

2003-01-01

Full Text Available Electron cloud instabilities in the Los Alamos Proton Storage Ring and those foreseen for the Oak Ridge Spallation Neutron Source are examined theoretically, numerically, and experimentally.

Particle-in-Cell Calculations of the Electron Cloud in the ILC Positron Damping Ring Wigglers

International Nuclear Information System (INIS)

Celata, C.M.; Furman, M.A.; Vay, J.-L.; Grote, D.P.

2007-01-01

The self-consistent code suite WARP-POSINST is being used to study electron cloud effects in the ILC positron damping ring wiggler. WARP is a parallelized, 3D particle-in-cell code which is fully self-consistent for all species. The POSINST models for the production of photoelectrons and secondary electrons are used to calculate electron creation. Mesh refinement and a moving reference frame for the calculation will be used to reduce the computer time needed by several orders of magnitude. We present preliminary results for cloud buildup showing 3D electron effects at the nulls of the vertical wiggler field. First results from a benchmark of WARP-POSINST vs. POSINST are also discussed

Initial Self-Consistent 3D Electron-Cloud Simulations of the LHC Beam with the Code WARP+POSINST

International Nuclear Information System (INIS)

Vay, J; Furman, M A; Cohen, R H; Friedman, A; Grote, D P

2005-01-01

We present initial results for the self-consistent beam-cloud dynamics simulations for a sample LHC beam, using a newly developed set of modeling capability based on a merge [1] of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP [2] and the electron-cloud code POSINST [3]. Although the storage ring model we use as a test bed to contain the beam is much simpler and shorter than the LHC, its lattice elements are realistically modeled, as is the beam and the electron cloud dynamics. The simulated mechanisms for generation and absorption of the electrons at the walls are based on previously validated models available in POSINST [3, 4

Risk mitigation strategy for the ITER electron cyclotron upper port launcher

International Nuclear Information System (INIS)

Goede, A.P.H.; Bongers, W.A.; Elzendoorn, B.S.Q.; Graswinckel, M.F.; Baar, M.R. de

2010-01-01

A basic requirement for ITER equipment to meet is a high level of reliability, because ITER operation time is precious and radioactive operation leaves limited scope for repair. In order to reduce the risk of failure during ITER operation an effective risk mitigation strategy is necessary. This paper presents such strategy for the ITER electron cyclotron upper port launcher (ECUPL). A preliminary ECUPL risk analysis identifies possible failure modes. A probabilistic risk assessment quantifies the risk of failure using a 4 x 4 impact-likelihood matrix. Impact is quantified through technical, cost and schedule elements. Likelihood depends on the risk mitigation strategy adopted. A cost benefit analysis determines the most cost effective risk mitigation strategy. An essential element in risk mitigation is the testing of equipment prior to installation on the ITER machine. This paper argues the need for low- and highpower millimetre wave tests carried out on the fully assembled ECUPL. It presents a conceptual design for a dedicated on-site test bed that can handle 2 of 8 microwave beams at 2 MW long pulse operation.

Simulation of e-cloud driven instability and its attenuation using a simulated feedback system in the CERN SPS

International Nuclear Information System (INIS)

Vay, J.-L.; Furman, M.A.

2010-01-01

Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS, and a feedback system to control the single-bunch instabilities is under active development. We present the latest improvements to the WARP-POSINST simulation framework and feedback model, and its application to the self-consistent simulations of two consecutive bunches interacting with an electron cloud in the SPS. Simulations using an idealized feedback system exhibit adequate mitigation of the instability providing that the cutoff of the feedback bandwidth is at or above 450 MHz. Artifacts from numerical noise of the injected distribution of electrons in the modeling of portions of bunch trains are discussed, and benchmarking of WARP against POSINST and HEADTAIL are presented.

Numerical Simulations for the Beam-Induced Electron Cloud in the LHC Beam Screen

CERN Document Server

Brüning, Oliver Sim

1998-01-01

The following work summarises simulation results obtained at CERN for the beam-induced electron cloud and looks at possible cures for the heat load in the LHC beam screen. The synchrotron radiation in the LHC creates a continuous flow of photoelectrons. These electrons are accelerated by the electric field of the bunch and hit the vacuum chamber on the opposite side of the beam pipe where they crea te secondary electrons which are again accelerated by the next bunch. For a large secondary emission yield the above mechanism leads to an exponential growth of the electron cloud which is limited by space charge forces. The simulations use a two-dimensional mesh for the space charge calculations and include the effect of image charges on the vacuum chamber wall. Depending on the quantum yield for the production of photoelectrons, the secondary emission yield and the reflectivity, the heat load can vary from 0.1 W/m to more than 15 W/m.

Reconciliation of the cloud computing model with US federal electronic health record regulations.

Science.gov (United States)

Schweitzer, Eugene J

2012-01-01

Cloud computing refers to subscription-based, fee-for-service utilization of computer hardware and software over the Internet. The model is gaining acceptance for business information technology (IT) applications because it allows capacity and functionality to increase on the fly without major investment in infrastructure, personnel or licensing fees. Large IT investments can be converted to a series of smaller operating expenses. Cloud architectures could potentially be superior to traditional electronic health record (EHR) designs in terms of economy, efficiency and utility. A central issue for EHR developers in the US is that these systems are constrained by federal regulatory legislation and oversight. These laws focus on security and privacy, which are well-recognized challenges for cloud computing systems in general. EHRs built with the cloud computing model can achieve acceptable privacy and security through business associate contracts with cloud providers that specify compliance requirements, performance metrics and liability sharing.

Electron-Cloud Pinch Dynamics in Presence of Lattice Magnet Fields

CERN Document Server

Franchetti, G

2011-01-01

The pinch of the electron cloud due to a passing proton bunch was extensively studied in a field free region and in a dipolar magnetic field. For the latter study, a strong field approximation helped to formulate the equations of motion and to understand the complex electron pinch dynamics, which exhibited some similarities with the field-free situation. Here we extend the analysis to the case of electron pinch in quadrupoles and in sextupoles. We discuss the limits of validity for the strong field approximation and we evaluate the relative magnitude of the peak tune shift along the bunch expected for the different fields.

Reconciliation of the cloud computing model with US federal electronic health record regulations

Science.gov (United States)

2011-01-01

Cloud computing refers to subscription-based, fee-for-service utilization of computer hardware and software over the Internet. The model is gaining acceptance for business information technology (IT) applications because it allows capacity and functionality to increase on the fly without major investment in infrastructure, personnel or licensing fees. Large IT investments can be converted to a series of smaller operating expenses. Cloud architectures could potentially be superior to traditional electronic health record (EHR) designs in terms of economy, efficiency and utility. A central issue for EHR developers in the US is that these systems are constrained by federal regulatory legislation and oversight. These laws focus on security and privacy, which are well-recognized challenges for cloud computing systems in general. EHRs built with the cloud computing model can achieve acceptable privacy and security through business associate contracts with cloud providers that specify compliance requirements, performance metrics and liability sharing. PMID:21727204

High-accuracy diagnostic tool for electron cloud observation in the LHC based on synchronous phase measurements

CERN Document Server

Esteban Müller, J F; Shaposhnikova, E; Valuch, D; Mastoridis, T

2014-01-01

Electron cloud effects such as heat load in the cryogenic system, pressure rise and beam instabilities are among the main limitations for the LHC operation with 25 ns spaced bunches. A new observation tool was developed to monitor the e-cloud activity and has been successfully used in the LHC during Run 1 (2010-2012). The power loss of each bunch due to the e-cloud can be estimated using very precise bunch-by-bunch measurement of the synchronous phase shift. In order to achieve the required accuracy, corrections for reflection in the cables and some systematic errors need to be applied followed by a post-processing of the measurements. Results clearly show the e-cloud build-up along the bunch trains and its evolution during each LHC fill as well as from fill to fill. Measurements during the 2012 LHC scrubbing run reveal a progressive reduction in the e-cloud activity and therefore a decrease in the secondary electron yield (SEY). The total beam power loss can be computed as a sum of the contributions from all...

Service quality of cloud-based applications

CERN Document Server

Bauer, Eric

2014-01-01

This book explains why applications running on cloud might not deliver the same service reliability, availability, latency and overall quality to end users as they do when the applications are running on traditional (non-virtualized, non-cloud) configurations, and explains what can be done to mitigate that risk.

Electron-cloud simulation results for the SPS and recent results for the LHC

International Nuclear Information System (INIS)

Furman, M.A.; Pivi, M.T.F.

2002-01-01

We present an update of computer simulation results for some features of the electron cloud at the Large Hadron Collider (LHC) and recent simulation results for the Super Proton Synchrotron (SPS). We focus on the sensitivity of the power deposition on the LHC beam screen to the emitted electron spectrum, which we study by means of a refined secondary electron (SE) emission model recently included in our simulation code

Runaway electron beam generation and mitigation during disruptions at JET-ILW

Czech Academy of Sciences Publication Activity Database

Reux, C.; Plyusnin, V.; Alper, B.; Alves, D.; Bazylev, B.; Belonohy, E.; Boboc, A.; Brezinsek, S.; Coffey, I.; Decker, J.; Drewelow, P.; Devaux, S.; de Vries, P.C.; Fil, A.; Gerasimov, S.; Giacomelli, L.; Jachmich, S.; Khilkevitch, E.M.; Kiptily, V.; Koslowski, R.; Kruezi, U.; Lehnen, M.; Lupelli, I.; Lomas, P. J.; Manzanares, A.; Martin De Aguilera, A.; Matthews, G.F.; Mlynář, Jan; Nardon, E.; Nilsson, E.; Perez von Thun, C.; Riccardo, V.; Saint-Laurent, F.; Shevelev, A.E.; Sips, G.; Sozzi, C.

2015-01-01

Roč. 55, č. 9 (2015), 093013-093013 ISSN 0029-5515 Institutional support: RVO:61389021 Keywords : runaway electrons * disruptions * tokamak * JET * massive gas injection * disruption mitigation * runaway background plasma Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 4.040, year: 2015 http://iopscience.iop.org/article/10.1088/0029-5515/55/9/093013

Time-resolved Shielded-Pickup Measurements and Modeling of Beam Conditioning Effects on Electron Cloud Buildup at CesrTA

CERN Document Server

Crittenden, J A; Liu, X; Palmer, M A; Santos, S; Sikora, J P; Kato, S; Calatroni, S; Rumolo, G

2012-01-01

The Cornell Electron Storage Ring Test Accelerator program includes investigations into electron cloud buildup in vacuum chambers with various coatings. Two 1.1-mlong sections located symmetrically in the east and west arc regions are equipped with BPM-like pickup detectors shielded against the direct beam-induced signal. They detect cloud electrons migrating through an 18-mm-diameter pattern of 0.76 mm-diameter holes in the top of the chamber. A digitizing oscilloscope is used to record the signals, providing time-resolved information on cloud development. We present new measurements of the effect of beam conditioning on a newly-installed amorphous carbon coated chamber, as well as on an extensively conditioned chamber with a diamond-like carbon coating. The ECLOUD modeling code is used to quantify the sensitivity of these measurements to model parameters, differentiating between photoelectron and secondary-electron production processes.

Molecular clouds near supernova remnants

International Nuclear Information System (INIS)

Wootten, H.A.

1978-01-01

The physical properties of molecular clouds near supernova remnants were investigated. Various properties of the structure and kinematics of these clouds are used to establish their physical association with well-known remmnants. An infrared survey of the most massive clouds revealed embedded objects, probably stars whose formation was induced by the supernova blast wave. In order to understand the relationship between these and other molecular clouds, a control group of clouds was also observed. Excitation models for dense regions of all the clouds are constructed to evaluate molecular abundances in these regions. Those clouds that have embedded stars have lower molecular abundances than the clouds that do not. A cloud near the W28 supernova remnant also has low abundances. Molecular abundances are used to measure an important parameter, the electron density, which is not directly observable. In some clouds extensive deuterium fractionation is observed which confirms electron density measurements in those clouds. Where large deuterium fractionation is observed, the ionization rate in the cloud interior can also be measured. The electron density and ionization rate in the cloud near W28 are higher than in most clouds. The molecular abundances and electron densities are functions of the chemical and dynamical state of evolution of the cloud. Those clouds with lowest abundances are probably the youngest clouds. As low-abundance clouds, some clouds near supernova remnants may have been recently swept from the local interstellar material. Supernova remnants provide sites for star formation in ambient clouds by compressing them, and they sweep new clouds from more diffuse local matter

Simulation study of electron cloud induced instabilities and emittance growth for the CERN Large Hadron Collider proton beam

CERN Document Server

Benedetto, Elena; Schulte, Daniel; Rumolo, Giovanni

2005-01-01

The electron cloud may cause transverse single-bunch instabilities of proton beams such as those in the Large Hadron Collider (LHC) and the CERN Super Proton Synchrotron (SPS). We simulate these instabilities and the consequent emittance growth with the code HEADTAIL, which models the turn-by-turn interaction between the cloud and the beam. Recently some new features were added to the code, in particular, electric conducting boundary conditions at the chamber wall, transverse feedback, and variable beta functions. The sensitivity to several numerical parameters has been studied by varying the number of interaction points between the bunch and the cloud, the phase advance between them, and the number of macroparticles used to represent the protons and the electrons. We present simulation results for both LHC at injection and SPS with LHC-type beam, for different electron-cloud density levels, chromaticities, and bunch intensities. Two regimes with qualitatively different emittance growth are observed: above th...

Simulation and analysis of TE wave propagation for measurement of electron cloud densities in particle accelerators

Energy Technology Data Exchange (ETDEWEB)

Sonnad, Kiran G., E-mail: kgs52@cornell.edu [CLASSE, Cornell University, Ithaca, NY (United States); Hammond, Kenneth C. [Department of Physics, Harvard University, Cambridge, MA (United States); Schwartz, Robert M. [CLASSE, Cornell University, Ithaca, NY (United States); Veitzer, Seth A. [Tech-X Corporation, Boulder, CO (United States)

2014-08-01

The use of transverse electric (TE) waves has proved to be a powerful, noninvasive method for estimating the densities of electron clouds formed in particle accelerators. Results from the plasma simulation program VSim have served as a useful guide for experimental studies related to this method, which have been performed at various accelerator facilities. This paper provides results of the simulation and modeling work done in conjunction with experimental efforts carried out at the Cornell electron storage ring “Test Accelerator” (CESRTA). This paper begins with a discussion of the phase shift induced by electron clouds in the transmission of RF waves, followed by the effect of reflections along the beam pipe, simulation of the resonant standing wave frequency shifts and finally the effects of external magnetic fields, namely dipoles and wigglers. A derivation of the dispersion relationship of wave propagation for arbitrary geometries in field free regions with a cold, uniform cloud density is also provided.

Simulation study of electron cloud build up in the SPS MKD kickers

CERN Document Server

Rumolo, G

2009-01-01

During the 2008 run, an unusual behavior characterizing pressure and temperature increase in some of the dump kickers of the SPS was noticed. In particular, it was observed that 1) the MKDV2 kicker would exhibit maximum heating with 75 ns spaced LHC beams and 2) the pressure rise was specially critical in MKDV1 in presence of 50 ns spaced LHC beams [1]. While the anomalous heating of MKDV2 with 75 ns beams could be tentatively explained by the denser beam current spectrum that would more likely hit one of the kicker impedance peaks, the fast pressure rise in MKDV1 with 50 ns spaced beams was ascribed to a surface effect, namely beam induced multipacting leading to electron cloud formation. This report summarizes a simulation study that was done in order to check whether the electron cloud behavior in the dump kickers could explain the experimental observations.

Electron cloud in various kinds of magnetic field of BEPCII

International Nuclear Information System (INIS)

Liu Yudong; Guo Zhiyuan; Qin Qing; Wang Jiuqing

2006-01-01

Electron cloud instability (ECI) may take place in a positron storage ring when the machine is operated with a multi-bunch positron beam. According to the actual shape of the vacuum chamber in the BEPCII, a programme which is different from the other simulation codes has been developed. Because of the distance between dipole magnet and sextupole, the quadrupole magnet of BEPCII is very short, much of the photoelectrons can be produced and can move in magnetic fields. The motion of electrons in various kinds of magnetic fields is studied in detail, especially for the solenoid field which will be wound in the vacuum pipe of BEPCII. Simulation shows that the solenoid field is very effective to confine the electrons to the vicinity of the vacuum chamber wall and to make an electron free region at the vacuum pipe centre. (authors)

Analysis on Cloud Computing Database in Cloud Environment – Concept and Adoption Paradigm

Directory of Open Access Journals (Sweden)

Elena-Geanina ULARU

2012-08-01

Full Text Available With the development of the Internet’s new technical functionalities, new concepts have started to take shape. These concepts have an important role especially in the development of corporate IT. Such a concept is „the Cloud”. Various marketing campaigns have started to focus on the Cloud and began to promote it in different but confusing ways. This campaigns do little, to explain what cloud computing is and why it is becoming increasingly necessary. The lack of understanding in this new technology generates a lack of knowledge in business cloud adoption regarding database and also application. Only by focusing on the business processes and objectives an enterprise can achieve the full benefits of the cloud and mitigate the potential risks. In this article we create our own complete definition of the cloud and we analyze the essential aspects of cloud adoption for a banking financial reporting application.

On a possibility of creation of positive space charge cloud in a system with magnetic insulation of electrons

International Nuclear Information System (INIS)

Goncharov, A.A.; Dobrovol'skii, A.M.; Dunets, S.P.; Evsyukov, A.N.; Protsenko, I.M.

2009-01-01

We describe a new approach for creation an effective, low-cost, low-maintenance axially symmetric plasma optical tools for focusing and manipulating high-current beams of negatively charged particles, electrons and negative ions. This approach is based on fundamental plasma optical concept of magnetic insulation of electrons and non-magnetized positive ions providing creation of controlled uncompensated cloud of the space charge. The axially symmetric electrostatic plasma optical lens is well-known and well developed tool where this concept is used successfully. This provides control and focusing high-current positive ion beams in wide range of parameters. Here for the first time we present optimistic experimental results describing the application of an idea of magnetic insulation of electrons for generation of the stable cloud of positive space charge by focusing onto axis the converging stream of heavy ions produced by circular accelerator with closed electron drift. The estimations of a maximal concentration of uncompensated cloud of positive ions are also made

Security of Data Stored in the Cloud

OpenAIRE

Vrhovec, Andraž

2016-01-01

The goal of this diploma thesis is to give an overview of data security in cloud systems. The first part covers basics of cloud and security. Additionally it identifies some risks arising from the use of cloud computing. The second part focuses on cryptography, especially on ciphers, as a tool for mitigation of those risks. We try to convey some recent ideas (especially those interesting in the context of cloud computing) from the cryptographic world to the reader in an easy manner. We conclu...

Multipactor for e-cloud diagnostics

CERN Document Server

Costa Pinto, P; Edwards, P; Holz, M; Taborelli, M

2012-01-01

Electron cloud in particle accelerators can be mitigated by coating the vacuum beam pipe with thin films of low secondary electron yield (SEY). SEY of small samples can be measured in the laboratory. Verifying the performance of long pipes is more complex, since it requires their insertion in the accelerator and the subsequent measurement of the beam induced pressure rise. RF induced multipacting in a coaxial waveguide configuration is proposed as a test before insertion in the machine. The technique is applied to two main bending dipoles of the SPS, where the RF power is fed through a tungsten wire stretched along the vacuum chamber (6.4 m). A dipole with a bare stainless steel chamber shows a clear power threshold initiating an abrupt rise in reflected power and pressure. The effect is enhanced at RF frequencies corresponding to cyclotron resonances for given magnetic fields. Preliminary results show that the dipole with a carbon coated vacuum chamber does not exhibit any pressure rise or reflected RF power...

Qualitative analysis of the e-cloud formation

International Nuclear Information System (INIS)

Heifets, Samuel A

2002-01-01

The qualitative analysis of the electron cloud formation is presented. Two mechanisms of the cloud formation, generation of jets of primary photo-electrons and thermalization of electrons in the electron cloud, are analyzed and compared with simulations for the NLC damping ring [1

Developing and evaluating a cloud service relationship theory

CERN Document Server

Huntgeburth, Jan

2014-01-01

This book develops, evaluates and refines a cloud service relationship theory that explains how cloud users' uncertainties arise in these relationships and how they can be mitigated. To that end, the book employs principal-agent theory and the concepts of bounded rationality and social embeddedness. Beyond advancing IS research, the findings presented can greatly benefit governments, IT departments and IT providers, helping them to better understand cloud service relationships and to adjust their cloud service strategies accordingly.

Wake Field of the e-Cloud

International Nuclear Information System (INIS)

Heifets, Samuel A

2001-01-01

The wake field of the cloud is derived analytically taking into account the finite size of the cloud and nonlinearity of the electron motion. The analytic expression for the effective transverse wake field caused by the electron cloud in a positron storage ring is derived. The derivation includes the frequency spread in the cloud, which is the main effect of the nonlinearity of electron motion in the cloud. This approach allows calculation of the Q-factor and study the tune spread in a bunch

Practical Approaches to Mitigation of Specimen Charging in High-Resolution Transmission Electron Microscopy

Directory of Open Access Journals (Sweden)

Young-Min Kim

2010-09-01

Full Text Available Specimen charging that is associated with the electron bombardment on the sample is a practical hindrance to high-resolution transmission electron microscopy (HRTEM analysis because it causes a severe loss of resolution in either diffraction or image data. Conductive thin film deposition on an insulating specimen has been proposed as an effective approach to the mitigation of the specimen charging; however, this method is generally not useful in HRTEM imaging of materials because the deposited film induces another artifact in the HRTEM image contrast. In this study, we propose practical methods to mitigate the specimen charging that takes place during the HRTEM of materials. For bulk-type specimens prepared by either an ion-thinning or focused-ion beam (FIB process, a plasma cleaning treatment is significantly effective in eliminating the charging phenomenon. In the case of low-dimensional nanomaterials such as nanowires and nanoparticles, the plasma cleaning is not feasible; however, the charging effect can be effectively eliminated by adjusting the electron illumination condition. The proposed methods facilitate a decrease in the buildup of specimen charging, thereby enhancing the quality of high-resolution images significantly.

Simulation of Electron-Cloud Build-Up for the Cold Arcs of the LHC and Comparison with Measured Data

CERN Document Server

Maury Cuna, H; Rumolo, G; Tavian, L; Zimmermann, F

2011-01-01

The electron cloud generated by synchrotron radiation or residual gas ionization is a concern for LHC operation and performance. We report the results of simulations studies which examine the electron cloud build-up, at injection energy, 3.5 TeV for various operation parameters. In particular, we determine the value of the secondary emission yield corresponding to the multipacting threshold, and investigate the electron density, and heat as a function of bunch intensity for dipoles and field-free regions. We also include a comparison between simulations results and measured heat-load data from the LHC scrubbing runs in 2011.

Analysis of the security and privacy requirements of cloud-based electronic health records systems.

Science.gov (United States)

Rodrigues, Joel J P C; de la Torre, Isabel; Fernández, Gonzalo; López-Coronado, Miguel

2013-08-21

The Cloud Computing paradigm offers eHealth systems the opportunity to enhance the features and functionality that they offer. However, moving patients' medical information to the Cloud implies several risks in terms of the security and privacy of sensitive health records. In this paper, the risks of hosting Electronic Health Records (EHRs) on the servers of third-party Cloud service providers are reviewed. To protect the confidentiality of patient information and facilitate the process, some suggestions for health care providers are made. Moreover, security issues that Cloud service providers should address in their platforms are considered. To show that, before moving patient health records to the Cloud, security and privacy concerns must be considered by both health care providers and Cloud service providers. Security requirements of a generic Cloud service provider are analyzed. To study the latest in Cloud-based computing solutions, bibliographic material was obtained mainly from Medline sources. Furthermore, direct contact was made with several Cloud service providers. Some of the security issues that should be considered by both Cloud service providers and their health care customers are role-based access, network security mechanisms, data encryption, digital signatures, and access monitoring. Furthermore, to guarantee the safety of the information and comply with privacy policies, the Cloud service provider must be compliant with various certifications and third-party requirements, such as SAS70 Type II, PCI DSS Level 1, ISO 27001, and the US Federal Information Security Management Act (FISMA). Storing sensitive information such as EHRs in the Cloud means that precautions must be taken to ensure the safety and confidentiality of the data. A relationship built on trust with the Cloud service provider is essential to ensure a transparent process. Cloud service providers must make certain that all security mechanisms are in place to avoid unauthorized access

A preliminary comparative study of the electron-cloud effect for the PSR, ISIS, and the ESS

International Nuclear Information System (INIS)

Furman, M.A.; Pivi, M.T.F.

2003-01-01

We present preliminary electron-cloud simulation results for the Proton Storage Ring (PSR) at LANL, ISIS at RAL, and the European Spallation Source (ESS). For each storage ring, we simulate the build-up and dissipation of the electron cloud (EC) in a representative field-free section of the vacuum chamber. For all three cases, we choose the same residual gas temperature, secondary emission yield (SEY), and secondary emission spectrum. Other variables such as proton loss rate, bunch profile, intensity and energy, residual gas pressure and chamber geometry, are set at the corresponding values for each machine. Under these assumptions, we conclude that, of the three machines, the PSR is the most severely affected by the electron cloud effect (ECE), followed by the ESS, with ISIS a distant third. We illustrate a strong sensitivity of the ECE to the longitudinal bunch profile by choosing two different shapes for the case of the PSR, and a weak sensitivity to residual gas pressure. This preliminary study does not address the ECE in other regions of the machine, nor the beam instability that might arise from the EC

NAFFS: network attached flash file system for cloud storage on portable consumer electronics

Science.gov (United States)

Han, Lin; Huang, Hao; Xie, Changsheng

Cloud storage technology has become a research hotspot in recent years, while the existing cloud storage services are mainly designed for data storage needs with stable high speed Internet connection. Mobile Internet connections are often unstable and the speed is relatively low. These native features of mobile Internet limit the use of cloud storage in portable consumer electronics. The Network Attached Flash File System (NAFFS) presented the idea of taking the portable device built-in NAND flash memory as the front-end cache of virtualized cloud storage device. Modern portable devices with Internet connection have built-in more than 1GB NAND Flash, which is quite enough for daily data storage. The data transfer rate of NAND flash device is much higher than mobile Internet connections[1], and its non-volatile feature makes it very suitable as the cache device of Internet cloud storage on portable device, which often have unstable power supply and intermittent Internet connection. In the present work, NAFFS is evaluated with several benchmarks, and its performance is compared with traditional network attached file systems, such as NFS. Our evaluation results indicate that the NAFFS achieves an average accessing speed of 3.38MB/s, which is about 3 times faster than directly accessing cloud storage by mobile Internet connection， and offers a more stable interface than that of directly using cloud storage API. Unstable Internet connection and sudden power off condition are tolerable, and no data in cache will be lost in such situation.

Negative chlorine ion chemistry in the upper stratosphere and its application to an artificially created dense electron cloud

Directory of Open Access Journals (Sweden)

S. S. Prasad

1995-03-01

Full Text Available This paper discusses new potential reactions of chlorine-bearing anions (negative ions in the upper stratosphere. These reactions are then applied to the negative-ion chemistry following the injection of an electron cloud of very high density, of the order of 106-107 e- cm-3, in the 40-45-km region. The idea is to evaluate the recently proposed scheme to mitigate ozone depletion by converting the reactive chlorine atoms at these altitudes into Cl- ions which are unreactive towards ozone, i.e., electron scavenging of Cl. We find that the previously neglected photodetachment from Cl- is fast. For an overhead sun, this process may have a rate coefficient of 0.08 s-1 when multiple scattering is included. The rate could be even higher, depending on the ground albedo. Switching reaction between Cl-·H2O and HCl might lead to the formation of Cl-·HCl anion. Possible reactions of Cl-·H2O and Cl-·HCl with O atoms could produce ClO- and Cl-2. The production of ClO- in this manner is significant because Cl- having a high photodetachment rate constant would be regenerated in the very likely reactions of ClO- with O. When these possibilities are considered, then it is found that the chlorine anions may not be the major ions inside the electron cloud due to the rapid photodetachment from Cl-. Furthermore, in such a cloud, there may be the hazard that the Cl--Cl-·H2O-ClO--Cl- cycle amounts to catalytic destruction of two O atoms. Thus, the scheme could be risky if practised in the altitude region where atomic oxygen is an important constituent. Similar conclusions apply even if the ClO- species forms ClO-3 by three-body association with O2, instead of reacting with O. It must be emphasized that the present study is speculative at this time, because none of the relevant reactions have been investigated in the laboratory as yet. Nevertheless, it is very safe to say that the scheme of ozone preservation by electron scavenging of the upper stratospheric Cl is

Electronic Health Records in the Cloud: Improving Primary Health Care Delivery in South Africa.

Science.gov (United States)

Cilliers, Liezel; Wright, Graham

2017-01-01

In South Africa, the recording of health data is done manually in a paper-based file, while attempts to digitize healthcare records have had limited success. In many countries, Electronic Health Records (EHRs) has developed in silos, with little or no integration between different operational systems. Literature has provided evidence that the cloud can be used to 'leapfrog' some of these implementation issues, but the adoption of this technology in the public health care sector has been very limited. This paper aims to identify the major reasons why the cloud has not been used to implement EHRs for the South African public health care system, and to provide recommendations of how to overcome these challenges. From the literature, it is clear that there are technology, environmental and organisational challenges affecting the implementation of EHRs in the cloud. Four recommendations are provided that can be used by the National Department of Health to implement EHRs making use of the cloud.

Electron Cloud induced instabilities in the Fermilab Main Injector(MI) for the High Intensity Neutrino Source (HINS) project

International Nuclear Information System (INIS)

Sonnad, Kiran G.; Furman, Miguel A.; Vay, Jean-Luc; Venturini, Marco; Celata, Christine; Grote, David

2006-01-01

The electrostatic particle-in-cell codeWARP is currently being expanded in order to study electron cloud effects on the dynamics of the beam in storage rings. Results for the Fermilab main injector (MI) show the existence of a threshold in the electron density beyond which there is rapid emittance growth. The Fermilab MI is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort, which will result in a significant increasing of the bunch intensity relative to its present value, placing it in a regime where electron-cloud effects are expected to become important. Various results from the simulations using WARP are discussed here

Electron Cloud Generation and Trapping in a Quadrupole Magnet at the Los Alamos Proton Storage Ring

International Nuclear Information System (INIS)

Macek, Robert J.; Browman, Andrew A.; Ledford, John E.; TechSource, Santa Fe; Los Alamos; Borden, Michael J.; O'Hara, James F.; McCrady, Rodney C.; Rybarcyk, Lawrence J.; Spickermann, Thomas; Zaugg, Thomas J.; Pivi, Mauro T.F.

2008-01-01

Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR) have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the 'prompt' electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the 'swept' electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100 (micro)s. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the quadrupole

Electron cloud generation and trapping in a quadrupole magnet at the Los Alamos proton storage ring

Directory of Open Access Journals (Sweden)

Robert J. Macek

2008-01-01

Full Text Available Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the “prompt” electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the “swept” electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100  μs. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the quadrupole.

ELECTRON CLOUD AT COLLIMATOR AND INJECTION REGION OF THE SPALLATION NEUTRON SOURCE ACCUMULATOR RING

International Nuclear Information System (INIS)

WANG, L.; HSEUH, H.-C.; LEE, Y.Y.; RAPARIA, D.; WEI, J.; COUSINEAU, S.

2005-01-01

The beam loss along the Spallation Neutron Source's accumulator ring is mainly located at the collimator region and injection region. This paper studied the electron cloud build-up at these two regions with the three-dimension program CLOUDLAND

Beam-Beam Interaction, Electron Cloud and Intrabeam Scattering for Proton Super-bunches

CERN Document Server

Ruggiero, F; Rumolo, Giovanni; Papaphilippou, Y

2003-01-01

Super-bunches are long bunches with a flat longitudinal profile, which could potentially increase the LHC luminosity in a future upgrade. We present example parameters and discuss a variety of issues related to such superbunches, including beam-beam tune shift, tune footprints, crossing schemes, luminosity, intrabeam scattering, and electron cloud. We highlight the benefits, disadvantages and open questions.

A Risk Management Approach for a Sustainable Cloud Migration

Directory of Open Access Journals (Sweden)

Alifah Aida Lope Abdul Rahman

2017-11-01

Full Text Available Cloud computing is not just about resource sharing, cost savings and optimisation of business performance; it also involves fundamental concerns on how businesses need to respond on the risks and challenges upon migration. Managing risks is critical for a sustainable cloud adoption. It includes several dimensions such as cost, practising the concept of green IT, data quality, continuity of services to users and clients, guarantee tangible benefits. This paper presents a risk management approach for a sustainable cloud migration. We consider four dimensions of sustainability, i.e., economic, environmental, social and technology to determine the viability of cloud for the business context. The risks are systematically identified and analysed based on the existing in house controls and the cloud service provider offerings. We use Dempster Shafer (D-S theory to measure the adequacy of controls and apply semi-quantitative approach to perform risk analysis based on the theory of belief. The risk exposure for each sustainability dimension allows us to determine the viability of cloud migration. A practical migration use case is considered to determine the applicability of our work. The results identify the risk exposure and recommended control for the risk mitigation. We conclude that risks depend on specific migration case and both Cloud Service Provider (CSP and users are responsible for the risk mitigation. Inherent risks can evolve due to the cloud migration.

Longitudinal and transverse dynamics of ions from residual gas in an electron accelerator

Science.gov (United States)

Gamelin, A.; Bruni, C.; Radevych, D.

2018-05-01

The ion cloud produced from residual gas in an electron accelerator can degrade machine performances and produce instabilities. The ion dynamics in an accelerator is governed by the beam-ion interaction, magnetic fields and eventual mitigation strategies. Due to the fact that the beam has a nonuniform transverse size along its orbit, the ions move longitudinally and accumulate naturally at some points in the accelerator. In order to design effective mitigation strategies it is necessary to understand the ion dynamics not only in the transverse plane but also in the longitudinal direction. After introducing the physics behind the beam-ion interaction, we show how to get accumulation points for a realistic electron storage ring lattice. Simulations of the ion cloud dynamics, including the effect of magnetic fields on the ions, clearing electrodes and clearing gaps are shown. Longitudinal ion trapping due to the magnetic mirror effect in the dipole fringe fields is also detailed. Finally, the effectiveness of clearing electrode using longitudinal clearing fields is discussed and compared to clearing electrodes producing transverse field only.

A spherical electron cloud hopping model for studying product branching ratios of dissociative recombination.

Science.gov (United States)

Yu, Hua-Gen

2008-05-21

A spherical electron cloud hopping (SECH) model is proposed to study the product branching ratios of dissociative recombination (DR) of polyatomic systems. In this model, the fast electron-captured process is treated as an instantaneous hopping of a cloud of uniform spherical fractional point charges onto a target M+q ion (or molecule). The sum of point charges (-1) simulates the incident electron. The sphere radius is determined by a critical distance (Rc eM) between the incoming electron (e-) and the target, at which the potential energy of the e(-)-M+q system is equal to that of the electron-captured molecule M+q(-1) in a symmetry-allowed electronic state with the same structure as M(+q). During the hopping procedure, the excess energies of electron association reaction are dispersed in the kinetic energies of M+q(-1) atoms to conserve total energy. The kinetic energies are adjusted by linearly adding atomic momenta in the direction of driving forces induced by the scattering electron. The nuclear dynamics of the resultant M+q(-1) molecule are studied by using a direct ab initio dynamics method on the adiabatic potential energy surface of M+q(-1), or together with extra adiabatic surface(s) of M+q(-1). For the latter case, the "fewest switches" surface hopping algorithm of Tully was adapted to deal with the nonadiabaticity in trajectory propagations. The SECH model has been applied to study the DR of both CH+ and H3O+(H2O)2. The theoretical results are consistent with the experiment. It was found that water molecules play an important role in determining the product branching ratios of the molecular cluster ion.

LHC Report: Out of the clouds

CERN Multimedia

Giovanni Rumolo, Giovanni Iadarola and Hannes Bartosik for the LHC team

2015-01-01

In order for the LHC to deliver intense proton beams to the experiments, operators have to perform “scrubbing” of the beam pipes. This operation is necessary to reduce the formation of electron clouds, which would generate instabilities in the colliding beams.   Electron clouds are generated in accelerators running with positively charged particles when electrons - produced by the ionisation of residual molecules in the vacuum or by the photoelectric effect from synchrotron radiation - are accelerated by the beam field and hit the surface of the vacuum chamber producing other electrons. This avalanche-like process can result in the formation of clouds of electrons. Electron clouds are detrimental to the beam for a few reasons. First, the electrons impacting the walls desorb molecules and degrade the ultra-high vacuum in the beam chamber. Furthermore, they interact electromagnetically with the beam, leading to the oscillation and expansion of the particle bunches. This increases...

Self-Consistent 3D Modeling of Electron Cloud Dynamics and Beam Response

International Nuclear Information System (INIS)

Furman, Miguel; Furman, M.A.; Celata, C.M.; Kireeff-Covo, M.; Sonnad, K.G.; Vay, J.-L.; Venturini, M.; Cohen, R.; Friedman, A.; Grote, D.; Molvik, A.; Stoltz, P.

2007-01-01

We present recent advances in the modeling of beam electron-cloud dynamics, including surface effects such as secondary electron emission, gas desorption, etc, and volumetric effects such as ionization of residual gas and charge-exchange reactions. Simulations for the HCX facility with the code WARP/POSINST will be described and their validity demonstrated by benchmarks against measurements. The code models a wide range of physical processes and uses a number of novel techniques, including a large-timestep electron mover that smoothly interpolates between direct orbit calculation and guiding-center drift equations, and a new computational technique, based on a Lorentz transformation to a moving frame, that allows the cost of a fully 3D simulation to be reduced to that of a quasi-static approximation

Survey on Security Issues in Cloud Computing and Associated Mitigation Techniques

Science.gov (United States)

Bhadauria, Rohit; Sanyal, Sugata

2012-06-01

Cloud Computing holds the potential to eliminate the requirements for setting up of high-cost computing infrastructure for IT-based solutions and services that the industry uses. It promises to provide a flexible IT architecture, accessible through internet for lightweight portable devices. This would allow multi-fold increase in the capacity or capabilities of the existing and new software. In a cloud computing environment, the entire data reside over a set of networked resources, enabling the data to be accessed through virtual machines. Since these data-centers may lie in any corner of the world beyond the reach and control of users, there are multifarious security and privacy challenges that need to be understood and taken care of. Also, one can never deny the possibility of a server breakdown that has been witnessed, rather quite often in the recent times. There are various issues that need to be dealt with respect to security and privacy in a cloud computing scenario. This extensive survey paper aims to elaborate and analyze the numerous unresolved issues threatening the cloud computing adoption and diffusion affecting the various stake-holders linked to it.

Negative chlorine ion chemistry in the upper stratosphere and its application to an artificially created dense electron cloud

Directory of Open Access Journals (Sweden)

S. S. Prasad

Full Text Available This paper discusses new potential reactions of chlorine-bearing anions (negative ions in the upper stratosphere. These reactions are then applied to the negative-ion chemistry following the injection of an electron cloud of very high density, of the order of 10^6-10⁷ e^- cm^-3, in the 40-45-km region. The idea is to evaluate the recently proposed scheme to mitigate ozone depletion by converting the reactive chlorine atoms at these altitudes into Cl^- ions which are unreactive towards ozone, i.e., electron scavenging of Cl. We find that the previously neglected photodetachment from Cl^- is fast. For an overhead sun, this process may have a rate coefficient of 0.08 s^-1 when multiple scattering is included. The rate could be even higher, depending on the ground albedo. Switching reaction between Cl^-·H₂O and HCl might lead to the formation of Cl^-·HCl anion. Possible reactions of Cl^-·H₂O and Cl^-·HCl with O atoms could produce ClO^- and Cl^-₂. The production of ClO^- in this manner is significant because Cl^- having a high photodetachment rate constant would be regenerated in the very likely reactions of ClO^- with O. When these possibilities are considered, then it is found that the chlorine anions may not be the major ions inside the electron cloud due to the rapid photodetachment from Cl^-. Furthermore, in such a cloud, there may be the hazard that the Cl^--Cl^-·H₂O-ClO^--Cl^- cycle amounts to catalytic destruction of two O atoms. Thus, the scheme could be risky if practised in the altitude region where atomic oxygen is an important constituent. Similar conclusions apply even if the ClO^- species forms ClO^-₃ by three-body association with O₂

Mitigation of current quench by runaway electrons in LHCD discharges in the HT-7 tokamak

International Nuclear Information System (INIS)

Lu, H.W.; Hu, L.Q.; Lin, S.Y.; Zhong, G.Q.

2009-01-01

Production of runaway electrons during a major disruption has been observed in HT-7 Tokamak. The runaway current plateaus, which can carry part of the pre-disruptive current, are observed in lower-hybrid current drive (LHCD) limiter discharges. It is found that the runaway current can mitigate the disruptions effectively. Detailed observations are presented on the runaway electrons generated following disruptions in the HT-7 tokamak with carbon limited discharges. The results indicate that the magnetic oscillations play an important role in the activity of runaway electrons in disruption. (author)

Gas Condensates onto a LHC Type Cryogenic Vacuum System Subjected to Electron Cloud

CERN Multimedia

Baglin, V

2004-01-01

In the Large Hadron Collider (LHC), the gas desorbed via photon stimulated molecular desorption or electron stimulated molecular desorption will be physisorbed onto the beam screen held between 5 and 20 K. Studies of the effects of the electron cloud onto a LHC type cryogenic vacuum chamber have been done with the cold bore experiment (COLDEX) installed in the CERN Super Proton Synchrotron (SPS). Experiments performed with gas condensates such as H2, H2O, CO and CO2 are described. Implications for the LHC design and operation are discussed.

DDoS Attacks in Cloud Computing: Issues, Taxonomy, and Future Directions

OpenAIRE

Somani, Gaurav; Gaur, Manoj Singh; Sanghi, Dheeraj; Conti, Mauro; Buyya, Rajkumar

2015-01-01

Security issues related to the cloud computing are relevant to various stakeholders for an informed cloud adoption decision. Apart from data breaches, the cyber security research community is revisiting the attack space for cloud-specific solutions as these issues affect budget, resource management, and service quality. Distributed Denial of Service (DDoS) attack is one such serious attack in the cloud space. In this paper, we present developments related to DDoS attack mitigation solutions i...

Study of the transport parameters of cloud lightning plasmas

International Nuclear Information System (INIS)

Chang, Z. S.; Yuan, P.; Zhao, N.

2010-01-01

Three spectra of cloud lightning have been acquired in Tibet (China) using a slitless grating spectrograph. The electrical conductivity, the electron thermal conductivity, and the electron thermal diffusivity of the cloud lightning, for the first time, are calculated by applying the transport theory of air plasma. In addition, we investigate the change behaviors of parameters (the temperature, the electron density, the electrical conductivity, the electron thermal conductivity, and the electron thermal diffusivity) in one of the cloud lightning channels. The result shows that these parameters decrease slightly along developing direction of the cloud lightning channel. Moreover, they represent similar sudden change behavior in tortuous positions and the branch of the cloud lightning channel.

Experimental project - Cloud chamber

International Nuclear Information System (INIS)

Nour, Elena; Quinchard, Gregory; Soudon, Paul

2015-01-01

This document reports an academic experimental project dealing with the general concepts of radioactivity and their application to the cloud room experiment. The author first recalls the history of the design and development of a cloud room, and some definitions and characteristics of cosmic radiation, and proposes a description of the principle and physics of a cloud room. The second part is a theoretical one, and addresses the involved particles, the origins of electrons, and issues related to the transfer of energy (Bremsstrahlung effect, Bragg peak). The third part reports the experimental work with the assessment of a cloud droplet radius, the identification of a trace for each particle (alphas and electrons), and the study of the magnetic field deviation

Protection of electronic health records (EHRs) in cloud.

Science.gov (United States)

Alabdulatif, Abdulatif; Khalil, Ibrahim; Mai, Vu

2013-01-01

EHR technology has come into widespread use and has attracted attention in healthcare institutions as well as in research. Cloud services are used to build efficient EHR systems and obtain the greatest benefits of EHR implementation. Many issues relating to building an ideal EHR system in the cloud, especially the tradeoff between flexibility and security, have recently surfaced. The privacy of patient records in cloud platforms is still a point of contention. In this research, we are going to improve the management of access control by restricting participants' access through the use of distinct encrypted parameters for each participant in the cloud-based database. Also, we implement and improve an existing secure index search algorithm to enhance the efficiency of information control and flow through a cloud-based EHR system. At the final stage, we contribute to the design of reliable, flexible and secure access control, enabling quick access to EHR information.

The electron-cloud instability in PEP-II: An update

International Nuclear Information System (INIS)

Furman, M.A.; Lambertson, G.R.

1997-05-01

The authors present an update on the estimate of the growth time of the multi-bunch transverse instability in the PEP-II collider arising from the interaction of the positron beam with the accumulated electron cloud. They estimate the contributions to the growth rate arising from the dipole magnets and from the pumping straight sections. They emphasize those quantities upon which the instability is most sensitive. The simulation includes measured data on the secondary emission yield for TiN-coated samples of the actual vacuum chamber. Although the analysis is still in progress, they conclude that the instability risetime is of order 1 ms, which is well within the range controllable by the feedback system

Contributions to the Characterization and Mitigation of Rotorcraft Brownout

Science.gov (United States)

Tritschler, John Kirwin

Rotorcraft brownout, the condition in which the flow field of a rotorcraft mobilizes sediment from the ground to generate a cloud that obscures the pilot's field of view, continues to be a significant hazard to civil and military rotorcraft operations. This dissertation presents methodologies for: (i) the systematic mitigation of rotorcraft brownout through operational and design strategies and (ii) the quantitative characterization of the visual degradation caused by a brownout cloud. In Part I of the dissertation, brownout mitigation strategies are developed through simulation-based brownout studies that are mathematically formulated within a numerical optimization framework. Two optimization studies are presented. The first study involves the determination of approach-to-landing maneuvers that result in reduced brownout severity. The second study presents a potential methodology for the design of helicopter rotors with improved brownout characteristics. The results of both studies indicate that the fundamental mechanisms underlying brownout mitigation are aerodynamic in nature, and the evolution of a ground vortex ahead of the rotor disk is seen to be a key element in the development of a brownout cloud. In Part II of the dissertation, brownout cloud characterizations are based upon the Modulation Transfer Function (MTF), a metric commonly used in the optics community for the characterization of imaging systems. The use of the MTF in experimentation is examined first, and the application of MTF calculation and interpretation methods to actual flight test data is described. The potential for predicting the MTF from numerical simulations is examined second, and an initial methodology is presented for the prediction of the MTF of a brownout cloud. Results from the experimental and analytical studies rigorously quantify the intuitively-known facts that the visual degradation caused by brownout is a space and time-dependent phenomenon, and that high spatial frequency

In-situ measurements of the secondary electron yield in an accelerator environment: Instrumentation and methods

International Nuclear Information System (INIS)

Hartung, W.H.; Asner, D.M.; Conway, J.V.; Dennett, C.A.; Greenwald, S.; Kim, J.-S.; Li, Y.; Moore, T.P.; Omanovic, V.; Palmer, M.A.; Strohman, C.R.

2015-01-01

The performance of a particle accelerator can be limited by the build-up of an electron cloud (EC) in the vacuum chamber. Secondary electron emission from the chamber walls can contribute to EC growth. An apparatus for in-situ measurements of the secondary electron yield (SEY) in the Cornell Electron Storage Ring (CESR) was developed in connection with EC studies for the CESR Test Accelerator program. The CESR in-situ system, in operation since 2010, allows for SEY measurements as a function of incident electron energy and angle on samples that are exposed to the accelerator environment, typically 5.3 GeV counter-rotating beams of electrons and positrons. The system was designed for periodic measurements to observe beam conditioning of the SEY with discrimination between exposure to direct photons from synchrotron radiation versus scattered photons and cloud electrons. The samples can be exchanged without venting the CESR vacuum chamber. Measurements have been done on metal surfaces and EC-mitigation coatings. The in-situ SEY apparatus and improvements to the measurement tools and techniques are described

In-situ measurements of the secondary electron yield in an accelerator environment: Instrumentation and methods

Energy Technology Data Exchange (ETDEWEB)

Hartung, W.H., E-mail: wh29@cornell.edu; Asner, D.M.; Conway, J.V.; Dennett, C.A.; Greenwald, S.; Kim, J.-S.; Li, Y.; Moore, T.P.; Omanovic, V.; Palmer, M.A.; Strohman, C.R.

2015-05-21

The performance of a particle accelerator can be limited by the build-up of an electron cloud (EC) in the vacuum chamber. Secondary electron emission from the chamber walls can contribute to EC growth. An apparatus for in-situ measurements of the secondary electron yield (SEY) in the Cornell Electron Storage Ring (CESR) was developed in connection with EC studies for the CESR Test Accelerator program. The CESR in-situ system, in operation since 2010, allows for SEY measurements as a function of incident electron energy and angle on samples that are exposed to the accelerator environment, typically 5.3 GeV counter-rotating beams of electrons and positrons. The system was designed for periodic measurements to observe beam conditioning of the SEY with discrimination between exposure to direct photons from synchrotron radiation versus scattered photons and cloud electrons. The samples can be exchanged without venting the CESR vacuum chamber. Measurements have been done on metal surfaces and EC-mitigation coatings. The in-situ SEY apparatus and improvements to the measurement tools and techniques are described.

Effect of the Electron Cloud and CSR on the Upgrade of the PEP-II

International Nuclear Information System (INIS)

Heifets, Samuel A

2001-01-01

Effects of the electron cloud and of the coherent synchrotron radiation (CSR) on the possible upgrade of the PEP-II B-factory are studied. PEP-II B factory operates with parameters shown in Table 1 and already exceeds the design luminosity. Nevertheless, a possibility of upgrading the machine to even higher luminosities is under consideration [1]. Several scenarios are summarized in Table 2. This paper describes effects of the electron cloud and of the coherent synchrotron radiation (CSR) on the proposed upgrades of the PEP-II B-factory. The first effect was observed [3] and caused [4] the degradation of the emittance at KEK B-factory. The analytic expression for the e-wake [2] is used in calculations of the head-tail instability. Other obvious effects of higher beam currents such as additional heat load are not considered. The short wave length CSR has been recently observed at Brookhaven [6]. Consideration of the effect of such CSR on the beam dynamics is based on our previous paper [7

Data intensive ATLAS workflows in the Cloud

CERN Document Server

Rzehorz, Gerhard Ferdinand; The ATLAS collaboration

2018-01-01

From 2025 onwards, the ATLAS collaboration at the Large Hadron Collider (LHC) at CERN will experience a massive increase in data quantity as well as complexity. Including mitigating factors, the prevalent computing power by that time will only fulfil one tenth of the requirement. This contribution will focus on Cloud computing as an approach to help overcome this challenge by providing flexible hardware that can be configured to the specific needs of a workflow. Experience with Cloud computing exists, but there is a large uncertainty if and to which degree it can be able to reduce the burden by 2025. In order to understand and quantify the benefits of Cloud computing, the "Workflow and Infrastructure Model" was created. It estimates the viability of Cloud computing by combining different inputs from the workflow side with infrastructure specifications. The model delivers metrics that enable the comparison of different Cloud configurations as well as different Cloud offerings with each other. A wide range of r...

Electron cloud density analysis using microwave cavity resonance

International Nuclear Information System (INIS)

Shin, Y-M; Thangaraj, J C; Tan, C-Y; Zwaska, R

2013-01-01

We report on a method to detect an electron cloud in proton accelerators through the measurement of the phase shift of microwaves undergoing controlled reflections with an accelerator vacuum vessel. Previous phase shift measurement suffered from interference signals due to uncontrolled reflections from beamline components, leading to an unlocalized region of measurement and indeterminate normalization. The method in this paper introduces controlled reflectors about the area of interest to localize the measurement and allow normalization. This paper describes analyses of the method via theoretical calculations, electromagnetic modeling, and experimental measurements with a bench-top prototype. Dielectric thickness, location and spatial profile were varied and the effect on phase shift is described. The effect of end cap aperture length on phase shift measurement is also reported. A factor of ten enhancement in phase shift is observed at certain frequencies.

Automatic atlas based electron density and structure contouring for MRI-based prostate radiation therapy on the cloud

International Nuclear Information System (INIS)

Dowling, J A; Burdett, N; Chandra, S; Rivest-Hénault, D; Ghose, S; Salvado, O; Fripp, J; Greer, P B; Sun, J; Parker, J; Pichler, P; Stanwell, P

2014-01-01

Our group have been developing methods for MRI-alone prostate cancer radiation therapy treatment planning. To assist with clinical validation of the workflow we are investigating a cloud platform solution for research purposes. Benefits of cloud computing can include increased scalability, performance and extensibility while reducing total cost of ownership. In this paper we demonstrate the generation of DICOM-RT directories containing an automatic average atlas based electron density image and fast pelvic organ contouring from whole pelvis MR scans.

Automatic Atlas Based Electron Density and Structure Contouring for MRI-based Prostate Radiation Therapy on the Cloud

Science.gov (United States)

Dowling, J. A.; Burdett, N.; Greer, P. B.; Sun, J.; Parker, J.; Pichler, P.; Stanwell, P.; Chandra, S.; Rivest-Hénault, D.; Ghose, S.; Salvado, O.; Fripp, J.

2014-03-01

Our group have been developing methods for MRI-alone prostate cancer radiation therapy treatment planning. To assist with clinical validation of the workflow we are investigating a cloud platform solution for research purposes. Benefits of cloud computing can include increased scalability, performance and extensibility while reducing total cost of ownership. In this paper we demonstrate the generation of DICOM-RT directories containing an automatic average atlas based electron density image and fast pelvic organ contouring from whole pelvis MR scans.

Theoretical Studies of TE-Wave Propagation as a Diagnostic for Electron Cloud

International Nuclear Information System (INIS)

Penn, Gregory E.; Vay, Jean-Luc

2010-01-01

The propagation of TE waves is sensitive to the presence of an electron cloud primarily through phase shifts generated by the altered dielectric function, but can also lead to polarization changes and other effects, especially in the presence of magnetic fields. These effects are studied theoretically and also through simulations using WARP. Examples are shown related to CesrTA parameters, and used to observe different regimes of operation as well as to validate estimates of the phase shift.

Identify and rank key factors influencing the adoption of cloud computing for a healthy Electronics

Directory of Open Access Journals (Sweden)

Javad Shukuhy

2015-02-01

Full Text Available Cloud computing as a new technology with Internet infrastructure and new approaches can be significant benefits in providing medical services electronically. Aplying this technology in E-Health requires consideration of various factors. The main objective of this study is to identify and rank the factors influencing the adoption of e-health cloud. Based on the Technology-Organization-Environment (TOE framework and Human-Organization-Technology fit (HOT-fit model, 16 sub-factors were identified in four major factors. With survey of 60 experts, academics and experts in health information technology and with the help of fuzzy analytic hierarchy process had ranked these sub-factors and factors. In the literature, considering newness this study, no internal or external study, have not alluded these number of criteria. The results show that when deciding to adopt cloud computing in E-Health, respectively, must be considered technological, human, organizational and environmental factors.

Comparison of electron cloud simulation and experiments in the high-current experiment

International Nuclear Information System (INIS)

Cohen, R.H.; Friedman, A.; Covo, M. Kireeff; Lund, S.M.; Molvik, A.W.; Bieniosek, F.M.; Seidl, P.A.; Vay, J.-L.; Verboncoeur, J.; Stoltz, P.; Veitzer, S.

2004-01-01

A set of experiments has been performed on the High-Current Experiment (HCX) facility at LBNL, in which the ion beam is allowed to collide with an end plate and thereby induce a copious supply of desorbed electrons. Through the use of combinations of biased and grounded electrodes positioned in between and downstream of the quadrupole magnets, the flow of electrons upstream into the magnets can be turned on or off. Properties of the resultant ion beam are measured under each condition. The experiment is modeled via a full three-dimensional, two species (electron and ion) particle simulation, as well as via reduced simulations (ions with appropriately chosen model electron cloud distributions, and a high-resolution simulation of the region adjacent to the end plate). The three-dimensional simulations are the first of their kind and the first to make use of a timestep-acceleration scheme that allows the electrons to be advanced with a timestep that is not small compared to the highest electron cyclotron period. The simulations reproduce qualitative aspects of the experiments, illustrate some unanticipated physical effects, and serve as an important demonstration of a developing simulation capability

The Use of OMPS Near Real Time Products in Volcanic Cloud Risk Mitigation and Smoke/Dust Air Quality Assessments

Science.gov (United States)

Seftor, C. J.; Krotkov, N. A.; McPeters, R. D.; Li, J. Y.; Durbin, P. B.

2015-12-01

Near real time (NRT) SO2 and aerosol index (AI) imagery from Aura's Ozone Monitoring Instrument (OMI) has proven invaluable in mitigating the risk posed to air traffic by SO2 and ash clouds from volcanic eruptions. The OMI products, generated as part of NASA's Land, Atmosphere Near real-time Capability for EOS (LANCE) NRT system and available through LANCE and both NOAA's NESDIS and ESA's Support to Aviation Control Service (SACS) portals, are used to monitor the current location of volcanic clouds and to provide input into Volcanic Ash (VA) advisory forecasts. NRT products have recently been developed using data from the Ozone Mapping and Profiler Suite onboard the Suomi NPP platform; they are currently being made available through the SACS portal and will shortly be incorporated into the LANCE NRT system. We will show examples of the use of OMPS NRT SO2 and AI imagery to monitor recent volcanic eruption events. We will also demonstrate the usefulness of OMPS AI imagery to detect and track dust storms and smoke from fires, and how this information can be used to forecast their impact on air quality in areas far removed from their source. Finally, we will show SO2 and AI imagery generated from our OMPS Direct Broadcast data to highlight the capability of our real time system.

A cloud-based production system for information and service integration: an internet of things case study on waste electronics

Science.gov (United States)

Wang, Xi Vincent; Wang, Lihui

2017-08-01

Cloud computing is the new enabling technology that offers centralised computing, flexible data storage and scalable services. In the manufacturing context, it is possible to utilise the Cloud technology to integrate and provide industrial resources and capabilities in terms of Cloud services. In this paper, a function block-based integration mechanism is developed to connect various types of production resources. A Cloud-based architecture is also deployed to offer a service pool which maintains these resources as production services. The proposed system provides a flexible and integrated information environment for the Cloud-based production system. As a specific type of manufacturing, Waste Electrical and Electronic Equipment (WEEE) remanufacturing experiences difficulties in system integration, information exchange and resource management. In this research, WEEE is selected as the example of Internet of Things to demonstrate how the obstacles and bottlenecks are overcome with the help of Cloud-based informatics approach. In the case studies, the WEEE recycle/recovery capabilities are also integrated and deployed as flexible Cloud services. Supporting mechanisms and technologies are presented and evaluated towards the end of the paper.

Cloud services in organization

OpenAIRE

FUXA, Jan

2013-01-01

The work deals with the definition of the word cloud computing, cloud computing models, types, advantages, disadvantages, and comparing SaaS solutions such as: Google Apps and Office 365 in the area of electronic communications. The work deals with the use of cloud computing in the corporate practice, both good and bad practice. The following section describes the methodology for choosing the appropriate cloud service organization. Another part deals with analyzing the possibilities of SaaS i...

The Electron-Cloud Effect in the Arcs of the LHC

CERN Document Server

Furman, M A

1998-01-01

We present an update of our estimates for the power deposition arising from the electron-cloud effect in the dipole bending magnets in the arcs of the LHC. In addition, we present the estimate of the power deposition in the field-free regions in the arcs. We hold the number of particles per bunch and the bunch spacing fixed at their nominal values, and we assume throughout a high photon reflectivi ty. We explore the dependence of the power deposition on the photoelectric efficiency and on secondary emission yield parameters. We find a marked sensitivity to parameters that characterize secondary emission on the scale of 5 - 10 eV.

Comparison of Enamel and Stainless Steel Electron Cloud Clearing Electrodes Tested in the CERN Proton Synchrotron

CERN Document Server

Caspers, Friedhelm; Mahner, C; Wendel, JC

2010-01-01

During the 2007 run with the nominal LHC proton beam, electron cloud has been clearly identified and characterized in the PS using a dedicated setup with shielded button-type pickups. Efficient electron cloud suppression could be achieved with a stainless steel stripline-type electrode biased to negative and positive voltages up to ± 1 kV. For the 2008 run, a second setup was installed in straight section 84 of the PS where the stainless steel was replaced by a stripline composed of an enamel insulator with a resistive coating. In contrast to ordinary stripline electrodes this setup presents a very low beam coupling impedance and could thus be envisaged for long sections of high-intensity machines. Here, we present first comparative measurements with this new type of enamel clearing electrode using the nominal LHC beam with 72 bunches and 25 ns bunch spacing.

Electron cloud measurements in heavy-ion driver for HEDP and inertial fusion energy

International Nuclear Information System (INIS)

Kireeff Covo, Michel; Molvik, Arthur W.; Friedman, Alex; Cohen, Ronald; Vay, Jean-Luc; Bieniosek, Frank; Baca, David; Seidl, Peter A.; Logan, Grant; Vujic, Jasmina L.

2007-01-01

The high-current experiment (HCX) at LBNL is a driver scale single beam injector that provides a 1 MeV K + ion beam current of 0.18 A for 5 μs. It transports high-current beams with large fill factor (ratio of the maximum beam envelope radius to the beam pipe radius) and low emittance growth that are required to keep the cost of the power plant competitive and to satisfy the target requirements of focusing ion beams to high-power density. Beam interaction with the background gas and walls desorbs electrons that can multiply and accumulate, creating an electron cloud. This ubiquitous effect grows at higher fill factors and degrades the quality of the beam. We review simulations and diagnostics tools used to measure electron production, accumulation and its properties

Study of glow discharge positive column with cloud of disperse particles

International Nuclear Information System (INIS)

Polyakov, D.N.; Shumova, V.V.; Vasilyak, L.M.; Fortov, V.E.

2011-01-01

The study aims to describe plasma parameters changes induced by clouds of disperse micron size particles. Dust clouds were formed in the positive column of glow discharge in air at pressure 0.1-0.6 torr and current 0.1-3 mA. The simultaneous registration of discharge voltage and dust cloud parameters was carried out. Experimental results were simulated using diffusion model. The dust cloud is shown to smooth the radial electron concentration profile, increase electric field strength and electron temperature and stabilize the discharge. The cloud is demonstrated to be a trap for positive ions without increase of discharge current. -- Highlights: → 25% increase of longitudinal electric field strength in discharge with dust cloud. → The smoothing effect of dust cloud on radial electron and ion concentration profiles. → Dust cloud as a trap for positive ions without increase of discharge current. → Increase of electron temperature in discharge with dust cloud. → Increase of discharge stability in presence of dust cloud.

Application of new simulation algorithms for modeling rf diagnostics of electron clouds

International Nuclear Information System (INIS)

Veitzer, Seth A.; Smithe, David N.; Stoltz, Peter H.

2012-01-01

Traveling wave rf diagnostics of electron cloud build-up show promise as a non-destructive technique for measuring plasma density and the efficacy of mitigation techniques. However, it is very difficult to derive an absolute measure of plasma density from experimental measurements for a variety of technical reasons. Detailed numerical simulations are vital in order to understand experimental data, and have successfully modeled build-up. Such simulations are limited in their ability to reproduce experimental data due to the large separation of scales inherent to the problem. Namely, one must resolve both rf frequencies in the GHz range, as well as the plasma modulation frequency of tens of MHz, while running for very long simulations times, on the order of microseconds. The application of new numerical simulation techniques allow us to bridge the simulation scales in this problem and produce spectra that can be directly compared to experiments. The first method is to use a plasma dielectric model to measure plasma-induced phase shifts in the rf wave. The dielectric is modulated at a low frequency, simulating the effects of multiple bunch crossings. This allows simulations to be performed without kinetic particles representing the plasma, which both speeds up the simulations as well as reduces numerical noise from interpolation of particle charge and currents onto the computational grid. Secondly we utilize a port boundary condition model to simultaneously absorb rf at the simulation boundaries, and to launch the rf into the simulation. This method improves the accuracy of simulations by restricting rf frequencies better than adding an external (finite) current source to drive rf, and absorbing layers at the boundaries. We also explore the effects of non-uniform plasma densities on the simulated spectra.

Electron cloud in the CERN accelerator complex

CERN Document Server

AUTHOR|(CDS)2069325; Bartosik, Hannes; Belli, Eleonora; Iadarola, Giovanni; Li, Kevin Shing Bruce; Mether, Lotta Maria; Romano, Annalisa; Schenk, Michael

2016-01-01

Operation with closely spaced bunched beams causes the build-up of an Electron Cloud (EC) in both the LHC and the two last synchrotrons of its injector chain (PS and SPS). Pressure rise and beam instabilities are observed at the PS during the last stage of preparation of the LHC beams. The SPS was affected by coherent and incoherent emittance growth along the LHC bunch train over many years, before scrubbing has finally suppressed the EC in a large fraction of the machine. When the LHC started regular operation with 50 ns beams in 2011, EC phenomena appeared in the arcs during the early phases, and in the interaction regions with two beams all along the run. Operation with 25 ns beams (late 2012 and 2015), which is nominal for LHC, has been hampered by EC induced high heat load in the cold arcs, bunch dependent emittance growth and degraded beam lifetime. Dedicated and parasitic machine scrubbing is presently the weapon used at the LHC to combat EC in this mode of operation. This talk summarises the EC experi...

Electron cloud simulation of the ECR plasma

International Nuclear Information System (INIS)

Racz, R.; Biri, S.; Palinkas, J.

2011-01-01

Complete text of publication follows. The plasma of the Electron Cyclotron Resonance Ion Source (ECRIS) of ATOMKI is being continuously investigated by different diagnostic methods: using small-sized probes or taking X-ray and visible light photographs. In 2011 three articles were published by our team in a special edition of the IEEE Transactions on Plasma Science (Special Issue on Images in Plasma Science) describing our X-ray and visible light measurements and plasma modeling and simulating studies. Simulation is in many cases the base for the analysis of the photographs. The outcomes of the X-ray and visible light experiments were presented already in earlier issues of the Atomki Annual Report, therefore in this year we concentrate on the results of the simulating studies. The spatial distribution of the three main electron components (cold, warm and hot electron clouds) of the ECR plasmas was simulated by TrapCAD code. TrapCAD is a 'limited' plasma simulation code. The spatial and energy evolution of a large number of electrons can be realistically followed; however, these particles are independent, and no particle interactions are included. In ECRISs, the magnetic trap confines the electrons which keep together the ion component by their space charge. The electrons gain high energies while the ions remain very cold throughout the whole process. Thus, the spatial and energy simulation of the electron component gives much important and numerical information even for the ions. The electron components of ECRISs can artificially be grouped into three populations: cold, warm, and hot electrons. Cold electrons (1-200 eV) have not been heated by the microwave; they are mainly responsible for the visible light emission of the plasma. The energized warm electrons (several kiloelectronvolts) are able to ionize atoms and ions and they are mainly responsible for the characteristic Xray photons emitted by the plasma. Electrons having much higher energy than necessary for

MD421: Electron cloud studies on 25 ns beam variants (BCMS, 8b+4e)

CERN Document Server

Iadarola, Giovanni; Belli, Eleonora; Carver, Lee Robert; Dijkstal, Philipp; Li, Kevin Shing Bruce; Mether, Lotta; Romano, Annalisa; Rumolo, Giovanni; CERN. Geneva. ATS Department

2017-01-01

This note describes a Machine Development session performed with the main goal of studying the e-cloud mitigation that can be obtained by injecting mixed trains of 8b+4e beam type and trains having the standard 25 ns structure. Additionally, in the course of the MD, the pure 8b+4e beam was also checked to be stable when injected with low chromaticity and octupole current settings. Subsequently, the operational BCMS 25 ns beam was also injected with the 8b+4e settings and found to be unstable. The operational settings for injection were re-found by gradually increasing the chromaticity and octupole knobs until all the bunches of the injected beam could remain stable after injection.

Disruption mitigation studies in DIII-D

International Nuclear Information System (INIS)

Taylor, P.L.; Kellman, A.G.; Evans, T.E.

1999-01-01

Data on the discharge behavior, thermal loads, halo currents, and runaway electrons have been obtained in disruptions on the DIII-D tokamak. These experiments have also evaluated techniques to mitigate the disruptions while minimizing runaway electron production. Experiments injecting cryogenic impurity killer pellets of neon and argon and massive amounts of helium gas have successfully reduced these disruption effects. The halo current generation, scaling, and mitigation are understood and are in good agreement with predictions of a semianalytic model. Results from killer pellet injection have been used to benchmark theoretical models of the pellet ablation and energy loss. Runaway electrons are often generated by the pellets and new runaway generation mechanisms, modifications of the standard Dreicer process, have been found to explain the runaways. Experiments with the massive helium gas puff have also effectively mitigated disruptions without the formation of runaway electrons that can occur with killer pellets

A Generic Software Development Process Refined from Best Practices for Cloud Computing

OpenAIRE

Soojin Park; Mansoo Hwang; Sangeun Lee; Young B. Park

2015-01-01

Cloud computing has emerged as more than just a piece of technology, it is rather a new IT paradigm. The philosophy behind cloud computing shares its view with green computing where computing environments and resources are not as subjects to own but as subjects of sustained use. However, converting currently used IT services to Software as a Service (SaaS) cloud computing environments introduces several new risks. To mitigate such risks, existing software development processes must undergo si...

LHC Report: out of the clouds (part II)

CERN Multimedia

Giovanni Rumolo for the LHC team

2015-01-01

A large fraction of the LHC beam-time over the last two weeks has been devoted to the second phase of the scrubbing of the vacuum chambers. This was aimed at reducing the formation of electron clouds in the beam pipes, this time performed with 25-nanosecond spaced bunches. This operation is designed to prepare the machine for a smooth intensity ramp-up for physics with this type of beam.   The scrubbing of the accelerator beam pipes is done by running the machine under an intense electron cloud regime while respecting beam stability constraints. When electron cloud production becomes sufficiently intense, the probability of creating secondary electrons at the chamber walls decreases and this inhibits the whole process. In this way, the scrubbing operation eventually reduces the formation of electron clouds, which would otherwise generate instabilities in the colliding beams. The second phase of LHC scrubbing started on Saturday, 25 July, when 25 ns beams were circulated again in the LHC...

TU-F-CAMPUS-T-05: A Cloud-Based Monte Carlo Dose Calculation for Electron Cutout Factors

Energy Technology Data Exchange (ETDEWEB)

Mitchell, T; Bush, K [Stanford School of Medicine, Stanford, CA (United States)

2015-06-15

Purpose: For electron cutouts of smaller sizes, it is necessary to verify electron cutout factors due to perturbations in electron scattering. Often, this requires a physical measurement using a small ion chamber, diode, or film. The purpose of this study is to develop a fast Monte Carlo based dose calculation framework that requires only a smart phone photograph of the cutout and specification of the SSD and energy to determine the electron cutout factor, with the ultimate goal of making this cloud-based calculation widely available to the medical physics community. Methods: The algorithm uses a pattern recognition technique to identify the corners of the cutout in the photograph as shown in Figure 1. It then corrects for variations in perspective, scaling, and translation of the photograph introduced by the user’s positioning of the camera. Blob detection is used to identify the portions of the cutout which comprise the aperture and the portions which are cutout material. This information is then used define physical densities of the voxels used in the Monte Carlo dose calculation algorithm as shown in Figure 2, and select a particle source from a pre-computed library of phase-spaces scored above the cutout. The electron cutout factor is obtained by taking a ratio of the maximum dose delivered with the cutout in place to the dose delivered under calibration/reference conditions. Results: The algorithm has been shown to successfully identify all necessary features of the electron cutout to perform the calculation. Subsequent testing will be performed to compare the Monte Carlo results with a physical measurement. Conclusion: A simple, cloud-based method of calculating electron cutout factors could eliminate the need for physical measurements and substantially reduce the time required to properly assure accurate dose delivery.

Electron-cloud simulation studies for the CERN-PS in the framework of the LHC Injectors Upgrade project

CERN Document Server

Rioja Fuentelsaz, Sergio

The present study aims to provide a consistent picture of the electron cloud effect in the CERN Proton Synchrotron (PS) and to investigate possible future limitations due to the requirements foreseen by the LHC Injectors Upgrade (LIU) project. It consists of a complete simulation survey of the electron cloud build-up in the different beam pipe sections of the ring depending on several controllable beam parameters and vacuum chamber surface properties, covering present and future operation parameters. As the combined function magnets of the accelerator constitute almost the $80\\%$ in length of the ring, the implementation of a new feature for the simulation of any external magnetic field on the PyECLOUD code, made it possible to perform this study. All the results of the simulations are given as a function of the vacuum chamber surface properties in order to deduce them, both locally and globally, when compared with experimental data. In a first step, we characterize locally the maximum possible number of ...

Cloud chamber photographs of the cosmic radiation

CERN Document Server

Rochester, George Dixon

1952-01-01

Cloud Chamber Photographs of the Cosmic Radiation focuses on cloud chamber and photographic emulsion wherein the tracks of individual subatomic particles of high energy are studied. The publication first offers information on the technical features of operation and electrons and cascade showers. Discussions focus on the relationship in time and space of counter-controlled tracks; techniques of internal control of the cloud chamber; cascade processes with artificially-produced electrons and photons; and nuclear interaction associated with an extensive shower. The manuscript then elaborates on

A stability analysis of electron-positron pair equilibria of a two-temperature plasma cloud

Energy Technology Data Exchange (ETDEWEB)

Sikora, M [Colorado Univ., Boulder, CO (USA); Zbyszewska, M [Polska Akademia Nauk, Warsaw (Poland). Centrum Astronomiczne

1986-01-01

The stability of a two-temperature homogeneous static plasma cloud against pair density perturbations is examined. We assumed that the electrons and positrons, cooled via radiation process, are reheated via Coulomb interactions with much hotter protons. Pair equilibrium plasma states are shown to be unstable if deltan{sub e}/deltan{sub p}<0 and deltan{sub e}/deltaT{sub p}<0 on the equilibrium surface n{sub e}{sup eq}(n{sub p},T{sub p}), where n{sub e}=n{sub +}+n{sub -}, n{sub p} and T{sub p} denote electron plus positron density, proton density and proton temperature, respectively. The minimum proton temperature and maximum proton density for which unstable states can appear are: (kT{sub p}){sub min} approx few x m{sub e}c{sup 2} and (n{sub p}){sub max} approx few/Rsigma{sub T}, where R is the plasma cloud radius. We discuss our results in the context of an accreting black hole model assuming that the proton temperature is close to its virial value, kT{sub p}{sup vir} approx GMm{sub p}/R and that subsonic accretion flow is realized at R < tens Schwarzschild radii. The unstable states then correspond to the luminosity range 0.01 L{sub Edd}electron temperature range 2 x 10{sup 9}K

Electron Cloud Cyclotron Resonances in the Presence of a Short-bunch-length Relativistic Beam

International Nuclear Information System (INIS)

Celata, Christine; Celata, C.M.; Furman, Miguel A.; Vay, J.-L.; Wu, Jennifer W.

2008-01-01

Computer simulations using the 2D code 'POSINST' were used to study the formation of the electron cloud in the wiggler section of the positron damping ring of the International Linear Collider. In order to simulate an x-y slice of the wiggler (i.e., a slice perpendicular to the beam velocity), each simulation assumed a constant vertical magnetic field. At values of the magnetic field where the cyclotron frequency was an integral multiple of the bunch frequency, and where the field strength was less than approximately 0.6 T, equilibrium average electron densities were up to three times the density found at other neighboring field values. Effects of this resonance between the bunch and cyclotron frequency are expected to be non-negligible when the beam bunch length is much less than the product of the electron cyclotron period and the beam

BUSINESS MODELLING AND DATABASE DESIGN IN CLOUD COMPUTING

Directory of Open Access Journals (Sweden)

Mihai-Constantin AVORNICULUI

2015-04-01

Full Text Available Electronic commerce is growing constantly from one year to another in the last decade, few are the areas that also register such a growth. It covers the exchanges of computerized data, but also electronic messaging, linear data banks and electronic transfer payment. Cloud computing, a relatively new concept and term, is a model of access services via the internet to distributed systems of configurable calculus resources at request which can be made available quickly with minimum management effort and intervention from the client and the provider. Behind an electronic commerce system in cloud there is a data base which contains the necessary information for the transactions in the system. Using business modelling, we get many benefits, which makes the design of the database used by electronic commerce systems in cloud considerably easier.

Single event and TREE latchup mitigation for a star tracker sensor: An innovative approach to system level latchup mitigation

International Nuclear Information System (INIS)

Kimbrough, J.R.; Colella, N.J.; Davis, R.W.; Bruener, D.B.; Coakley, P.G.; Lutjens, S.W.; Mallon, C.E.

1994-08-01

Electronic packages designed for spacecraft should be fault-tolerant and operate without ground control intervention through extremes in the space radiation environment. If designed for military use, the electronics must survive and function in a nuclear radiation environment. This paper presents an innovative ''blink'' approach rather than the typical ''operate through'' approach to achieve system level latchup mitigation on a prototype star tracker camera. Included are circuit designs, flash x-ray test data, and heavy ion data demonstrating latchup mitigation protecting micro-electronics from current latchup and burnout due to Single Event Latchup (SEL) and Transient Radiation Effects on Electronics (TREE)

Carbon pellet cloud striations

International Nuclear Information System (INIS)

Parks, P.B.

1989-01-01

Fine scale striations, with alternating rows of bright and dark zones, have been observed in the ablation clouds of carbon pellets injected into the TEXT tokamak. The striations extend along the magnetic field for about 1 cm with quite regular cross-field variations characterized by a wavelength of a few mm. Their potential as a diagnostic tool for measuring q-profiles in tokamaks provides motivation for investigating the origin of the striations. The authors propose that the striations are not due to a sequence of high and low ablation rates because of the finite thermal magnetic islands localized at rational surfaces, q = m/n, would be responsible for reducing the electron flux to the pellet region; the length of the closed field line which forms the local magnetic axis of the island is too long to prevent a depletion of plasma electrons in a flux tube intercepting the pellet for the duration 2 rp / vp . Instead, they propose that striations are the manifestation of the saturated state of growing fluctuations inside the cloud. The instability is generated by E x B rotation of the ablation cloud. The outward centrifugal force points down the ablation density gradient inducing the Rayleigh-Taylor instability. The instability is not present for wave numbers along the field lines, which may explain why the striations are long and uniform in that direction. The E field develops inside the ablation cloud as a result of cold electron return currents which are induced to cancel the incoming hot plasma electron current streaming along the field lines

Intense ion beam transport in magnetic quadrupoles: Experiments on electron and gas effects

International Nuclear Information System (INIS)

Seidl, P.A.; Molvik, A.W.; Bieniosek, F.M.; Cohen, R.H.; Faltens, A.; Friedman, A.; Kireef Covo, M.; Lund, S.M.; Prost, L.; Vay, J-L.

2004-01-01

Heavy-ion induction linacs for inertial fusion energy and high-energy density physics have an economic incentive to minimize the clearance between the beam edge and the aperture wall. This increases the risk from electron clouds and gas desorbed from walls. We have measured electron and gas emission from 1 MeV K + incident on surfaces near grazing incidence on the High-Current Experiment (HCX) at LBNL. Electron emission coefficients reach values >100, whereas gas desorption coefficients are near 10 4 . Mitigation techniques are being studied: A bead-blasted rough surface reduces electron emission by a factor of 10 and gas desorption by a factor of 2. We also discuss the results of beam transport (of 0.03-0.18 A K + ) through four pulsed room-temperature magnetic quadrupoles in the HCX at LBNL. Diagnostics are installed on HCX, between and within quadrupole magnets, to measure the beam halo loss, net charge and expelled ions, from which we infer gas density, electron trapping, and the effects of mitigation techniques. A coordinated theory and computational effort has made significant progress towards a self-consistent model of positive-ion beam and electron dynamics. We are beginning to compare experimental and theoretical results

Status of the experimental studies of the electron cloud at the Los Alamos proton storage ring

International Nuclear Information System (INIS)

Macek, R.J.; Browman, A.A.; Borden, M.J.; Fitzgerald, D.H.; McCrady, R.C.; Spickermann, T.J.; Zaugg, T.J.

2003-01-01

The electron cloud (EC) at the Los Alamos Proton Storage Ring (PSR) has been studied extensively for the past several years with an overall aim to identify and measure its important characteristics, the factors that influence these characteristics, and to relate these to the two-stream (e-p) transverse instability long observed at PSR. Some new results since PAC2001 are presented.

Compression of Antiproton Clouds for Antihydrogen Trapping

CERN Document Server

Andresen, G B; Bowe, P D; Bray, C C; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Fajans, J; Fujiwara, M C; Funakoshi, R; Gill, D R; Hangst, J S; Hardy, W N; Hayano, R S; Hayden, M E; Hydomako, R; Jenkins, M J; Jørgensen, L V; Kurchaninov, L; Lambo, R; Madsen, N; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Robicheaux, F; Sarid, E; Seif El Nasr, S; Silveira, D M; Storey, J W; Thompson, R I; Van der Werf, D P; Wurtele, J S; Yamazaki, Y

2008-01-01

Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report the first detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile and its relation to that of the electron plasma.

Rigid-body rotation of an electron cloud in divergent magnetic fields

International Nuclear Information System (INIS)

Fruchtman, A.; Gueroult, R.; Fisch, N. J.

2013-01-01

For a given voltage across a divergent poloidal magnetic field, two electric potential distributions, each supported by a rigid-rotor electron cloud rotating with a different frequency, are found analytically. The two rotation frequencies correspond to the slow and fast rotation frequencies known in uniform plasma. Due to the centrifugal force, the equipotential surfaces, that correspond to the two electric potential distributions, diverge more than the magnetic surfaces do, the equipotential surfaces in the fast mode diverge largely in particular. The departure of the equipotential surfaces from the magnetic field surfaces may have a significant focusing effect on the ions accelerated by the electric field. The focusing effect could be important for laboratory plasma accelerators as well as for collimation of astrophysical jets

Implementation of Carbon Thin Film Coatings in the Super Proton Synchrotron (SPS) for Electron Cloud Mitigation

CERN Document Server

Costa Pinto, P; Basso, T; Edwards, P; Mensi, M; Sublet, A; Taborelli, M

2014-01-01

Low Secondary Electron Yield (SEY) carbon thin films eradicate electron multipacting in accelerator beam pipes. Two magnetic cells of the SPS were coated with such material and installed. In total more than forty vacuum vessels and magnet interconnections were treated. The feasibility of the coating process was validated. The performance of the carbon thin film will be tested with LHC nominal beams after the end of the long shutdown 1. Particular attention will be drawn to the long term behaviour. This paper presents the sputtering techniques used to coat the different components; their characterization (SEY measurements on coupons, RF multipacting tests and pump down curves); and the technology to etch the carbon film in case of a faulty coating. The strategy to coat the entire SPS will also be described.

Cloud based, Open Source Software Application for Mitigating Herbicide Drift

Science.gov (United States)

Saraswat, D.; Scott, B.

2014-12-01

The spread of herbicide resistant weeds has resulted in the need for clearly marked fields. In response to this need, the University of Arkansas Cooperative Extension Service launched a program named Flag the Technology in 2011. This program uses color-coded flags as a visual alert of the herbicide trait technology within a farm field. The flag based program also serves to help avoid herbicide misapplication and prevent herbicide drift damage between fields with differing crop technologies. This program has been endorsed by Southern Weed Science Society of America and is attracting interest from across the USA, Canada, and Australia. However, flags have risk of misplacement or disappearance due to mischief or severe windstorms/thunderstorms, respectively. This presentation will discuss the design and development of a cloud-based, free application utilizing open-source technologies, called Flag the Technology Cloud (FTTCloud), for allowing agricultural stakeholders to color code their farm fields for indicating herbicide resistant technologies. The developed software utilizes modern web development practices, widely used design technologies, and basic geographic information system (GIS) based interactive interfaces for representing, color-coding, searching, and visualizing fields. This program has also been made compatible for a wider usability on different size devices- smartphones, tablets, desktops and laptops.

Physical conditions in CaFe interstellar clouds

OpenAIRE

Gnacinski, P.; Krogulec, M.

2007-01-01

Interstellar clouds that exhibit strong Ca I and Fe I lines were called CaFe clouds. The ionisation equilibrium equations were used to model the column densities of Ca II, Ca I, K I, Na I, Fe I and Ti II in CaFe clouds. The chemical composition of CaFe clouds is that of the Solar System and no depletion of elements onto dust grains is seen. The CaFe clouds have high electron densities n=1 cm^-3 that leads to high column densities of neutral Ca and Fe.

Plume trajectory validation study: Brown cloud support project overview

International Nuclear Information System (INIS)

Brown-Strattan, M.A.; Smith, M.L.

1991-01-01

The brown cloud is an air pollution phenomenon of great concern to the Denver metropolitan area. Regulatory agencies, academia, and research organizations are involved in characterizing the development and transport of the brown cloud and identifying mitigation approaches. In support of this effort, NOAA conducted releases of small (one cubic meter) constant density balloons from sites in Denver and along the South Platte Valley. These balloons, called ''tetroons'' because of their tetrahedral shape, carried five-ounce transponders and were tracked by radar as they rose to predetermined altitudes and followed airflow patterns at those altitudes. The data gathered from these releases included the geographic position and altitude of each tetroon over time. These data will aid efforts to understand brown cloud development, structure, and transport

ECONOMIC DENIAL OF SUSTAINABILITY (EDOS ATTACK ON CLOUD – A SURVEY

Directory of Open Access Journals (Sweden)

A. Somasundaram

2016-12-01

Full Text Available Cloud computing is a promising technology aims to provide reliable, customized and quality of service computation environments for cloud users in terms of Software as a Service-SaaS , Plat- form as a Service-PaaS and Infrastructure as Service-IaaS, which is provided on the pay per use basis. Cloud computing enables services to be deployed and accessed globally on demand with little maintenance by providing QoS as per service level agreement (SLA of customer. However, due to elasticity of resources, cloud systems are facing severe security problems. One of the most serious threats to cloud computing is EDoS (economic Distributed Denial of Service aims to consume the cloud resource by attacker and impose financial burden to the legitimate user, where integrity, availability and confidentiality of the cloud services are never compromised but affects the accountability which leads to inaccurate billing. Since the billing models of cloud services may not be mature enough to properly account for an EDoS attack. These paper surveys, the different techniques that generate, detect and mitigate the EDoS Attack on Cloud.

Simulations of Neon Pellets for Plasma Disruption Mitigation in Tokamaks

Science.gov (United States)

Bosviel, Nicolas; Samulyak, Roman; Parks, Paul

2017-10-01

Numerical studies of the ablation of neon pellets in tokamaks in the plasma disruption mitigation parameter space have been performed using a time-dependent pellet ablation model based on the front tracking code FronTier-MHD. The main features of the model include the explicit tracking of the solid pellet/ablated gas interface, a self-consistent evolving potential distribution in the ablation cloud, JxB forces, atomic processes, and an improved electrical conductivity model. The equation of state model accounts for atomic processes in the ablation cloud as well as deviations from the ideal gas law in the dense, cold layers of neon gas near the pellet surface. Simulations predict processes in the ablation cloud and pellet ablation rates and address the sensitivity of pellet ablation processes to details of physics models, in particular the equation of state.

Charging dynamics and strong localization of a two-dimensional electron cloud

International Nuclear Information System (INIS)

Dianoux, R; Smilde, H J H; Marchi, F; Buffet, N; Mur, P; Comin, F; Chevrier, J

2007-01-01

The dynamics of charge injection in silicon nanocrystals embedded in a silicon dioxide matrix is studied using electrostatic force microscopy. We show that the presence of silicon nanocrystals with a density of 10 11 cm -2 is essential for strong localization of charges, and results in exceptional charge retention properties compared to nanocrystal-free SiO 2 samples. In both systems, a logarithmic dependence of the diameter of the charged area on the injection time is experimentally observed on a timescale between 0.1 and 10 s (voltage≤10 V). A field-emission injection, limited by Coulomb blockade and a lateral charge spreading due to a repulsive radial electric field are used to model the sample charging. Once the tip is retracted, the electron cloud is strongly confined in the nanocrystals and remains static

Study on FPGA SEU Mitigation for the Readout Electronics of DAMPE BGO Calorimeter in Space

Science.gov (United States)

Shen, Zhongtao; Feng, Changqing; Gao, Shanshan; Zhang, Deliang; Jiang, Di; Liu, Shubin; An, Qi

2015-06-01

The BGO calorimeter, which provides a wide measurement range of the primary cosmic ray spectrum, is a key sub-detector of the Dark Matter Particle Explorer (DAMPE). The readout electronics of calorimeter consists of 16 pieces of Actel ProASIC Plus FLASH-based field-programmable gate array (FPGA), of which the design-level flip-flops and embedded block random access memories (RAM) are single event upset (SEU) sensitive in the harsh space environment. To comply with radiation hardness assurance (RHA), SEU mitigation methods, including partial triple modular redundancy (TMR), CRC checksum, and multi-domain reset are analyzed and tested by the heavy-ion beam test. Composed of multi-level redundancy, a FPGA design with the characteristics of SEU tolerance and low resource consumption is implemented for the readout electronics.

Considerations on comprehensive risk assessment and mitigation planning of volcanic ash-fall

International Nuclear Information System (INIS)

Toshida, Kiyoshi

2010-01-01

Volcanic ash-fall is inevitable hazard throughout Japan, and causes wide range of effects due to its physical and chemical properties. Nuclear power plants in Japan face the necessity to assess the risk from volcanic ash-fall. Risk assessment of the volcanic ash-fall should include engineering solution and mitigation planning as well as the ash-fall hazard. This report points out the characteristics for reducing the various effects of volcanic ash-fall as follows. Large-scale eruptions produce prominent volcanic ash-falls that can approach power plants at a great distance. Aftermath hazards of ash-fall events, such as remobilization of fine ash particles and generation of lahars, require further assessments. The kind and extent of damages becomes greater whenever ash is wet. Wet ash requires separate assessments in contrast to dry ash. The mitigation and recovery measures at power plants involve quick cleanup operations of volcanic ash. Those operations should be prepared through comprehensive risk assessment, and by cooperation with authorities, during pre-eruption repose period. The comprehensive assessment for volcanic ash-fall hazards, however, has yet to be conducted. Development of risk communication method may result in increased implementation mitigation planning. Numerical analysis of the ash-fall hazards provides quantitative data on particle motions that can be used in the risk assessment. In order to implement the quantitative assessment method, the verification on the effect of ambient air condition to the altitude of volcanic ash cloud is necessary. We need to develop a three-dimensional model of volcanic ash cloud, and calculate motions of ash clouds under multiple conditions of ambient air. (author)

How to build a cloud chamber?

International Nuclear Information System (INIS)

Mariaud, C.

2012-01-01

The cloud chamber had its heyday in the first half of last century and allowed the discovery of new particles such as the anti-electron, the muon and the neutral and the charged kaon. The bubble chamber replaced it in the mid fifties. This article recalls the principle of the cloud chamber and shows, in a detailed way, how to proceed to build one with on-the-shelf materials. This design is based on the use of isopropanol whose liquefaction through the form of droplets materializes the track of the particle and on the use of combined Peltier cells (instead of CO 2 snow) to cool the chamber. This cloud chamber has been successfully used in schools to observe particles mainly electrons, alphas and muons generated by cosmic rays. (A.C.)

Electron cloud effects in intense, ion beam linacs theory and experimental planning for heavy-ion fusion

International Nuclear Information System (INIS)

Molvik, A.W.; Cohen, R.H.; Lund, S.M.; Bieniosek, F.M.; Lee, E.P.; Prost, L.R.; Seidl, P.A.; Vay, Jean-Luc

2002-01-01

Heavy-ion accelerators for HIF will operate at high aperture-fill factors with high beam current and long pulses. This will lead to beam ions impacting walls: liberating gas molecules and secondary electrons. Without special preparation a large fractional electron population ((ge)1%) is predicted in the High-Current Experiment (HCX), but wall conditioning and other mitigation techniques should result in substantial reduction. Theory and particle-in-cell simulations suggest that electrons, from ionization of residual and desorbed gas and secondary electrons from vacuum walls, will be radially trapped in the ∼4 kV ion beam potential. Trapped electrons can modify the beam space charge, vacuum pressure, ion transport dynamics, and halo generation, and can potentially cause ion-electron instabilities. Within quadrupole (and dipole) magnets, the longitudinal electron flow is limited to drift velocities (E x B and (del)B) and the electron density can vary azimuthally, radially, and longitudinally. These variations can cause centroid misalignment, emittance growth and halo growth. Diagnostics are being developed to measure the energy and flux of electrons and gas evolved from walls, and the net charge and gas density within magnetic quadrupoles, as well as the their effect on the ion beam

Electron Cloud in Steel Beam Pipe vs Titanium Nitride Coated and Amorphous Carbon Coated Beam Pipes in Fermilab's Main Injector

Energy Technology Data Exchange (ETDEWEB)

Backfish, Michael

2013-04-01

This paper documents the use of four retarding field analyzers (RFAs) to measure electron cloud signals created in Fermilab’s Main Injector during 120 GeV operations. The first data set was taken from September 11, 2009 to July 4, 2010. This data set is used to compare two different types of beam pipe that were installed in the accelerator. Two RFAs were installed in a normal steel beam pipe like the rest of the Main Injector while another two were installed in a one meter section of beam pipe that was coated on the inside with titanium nitride (TiN). A second data run started on August 23, 2010 and ended on January 10, 2011 when Main Injector beam intensities were reduced thus eliminating the electron cloud. This second run uses the same RFA setup but the TiN coated beam pipe was replaced by a one meter section coated with amorphous carbon (aC). This section of beam pipe was provided by CERN in an effort to better understand how an aC coating will perform over time in an accelerator. The research consists of three basic parts: (a) continuously monitoring the conditioning of the three different types of beam pipe over both time and absorbed electrons (b) measurement of the characteristics of the surrounding magnetic fields in the Main Injector in order to better relate actual data observed in the Main Injector with that of simulations (c) measurement of the energy spectrum of the electron cloud signals using retarding field analyzers in all three types of beam pipe.

Scheduling multimedia services in cloud computing environment

Science.gov (United States)

Liu, Yunchang; Li, Chunlin; Luo, Youlong; Shao, Yanling; Zhang, Jing

2018-02-01

Currently, security is a critical factor for multimedia services running in the cloud computing environment. As an effective mechanism, trust can improve security level and mitigate attacks within cloud computing environments. Unfortunately, existing scheduling strategy for multimedia service in the cloud computing environment do not integrate trust mechanism when making scheduling decisions. In this paper, we propose a scheduling scheme for multimedia services in multi clouds. At first, a novel scheduling architecture is presented. Then, We build a trust model including both subjective trust and objective trust to evaluate the trust degree of multimedia service providers. By employing Bayesian theory, the subjective trust degree between multimedia service providers and users is obtained. According to the attributes of QoS, the objective trust degree of multimedia service providers is calculated. Finally, a scheduling algorithm integrating trust of entities is proposed by considering the deadline, cost and trust requirements of multimedia services. The scheduling algorithm heuristically hunts for reasonable resource allocations and satisfies the requirement of trust and meets deadlines for the multimedia services. Detailed simulated experiments demonstrate the effectiveness and feasibility of the proposed trust scheduling scheme.

Simulation studies on the electron cloud build-up in the elements of the LHC Arcs at 6.5 TeV

CERN Document Server

Dijkstal, Philipp; Mether, Lotta; Rumolo, Giovanni; CERN. Geneva. ATS Department

2017-01-01

The formation of electron clouds in the arcs of the Large Hadron Collider (LHC) has been identified as one of the main limitations for the performance of the machine. In particular, the impacting electrons can deposit a significant power on the cold beam screens of the LHC superconducting magnets, which translates into a significant heat load for the cryogenic system. A detailed model of the e-cloud formation in the different elements of the LHC arc half-cell has been developed using the PyECLOUD simulation code. The model includes the main dipole and quadrupole magnets, shorter corrector magnets and drift spaces. Particular care was taken to correctly model the impact of the hotoelectrons produced by the beam synchrotron radiation. For this purpose, we reviewed the available literature on the characterization of the LHC beam screen surface in terms of reflectivity and photoelectron yield and we defined the necessary steps to obtain the photoemission model in the format required in input by t...

The Electronic Forensics Process under Cloud Environment%云环境下电子取证方式与流程

Institute of Scientific and Technical Information of China (English)

骆智森

2015-01-01

in recent years, with the continuous development of cloud computing technology, our life also because cloud computing function has been a lot of convenience, convenient our daily some important information preservation. But the network also ap⁃peared a lot of for cloud computing or cloud computing to steal the target of cyber crime, both at the technical level or in law, cloud computing is gaining achievements is still not big enough, it also gives the cloud computing network security left a loophole. Rising trend of cyber crime, for a criminal record has been unable to use traditional methods of electronic evidence for forensic evidence, which for the evidence is a difficult challenge. Therefore, this paper will be electronic evidence of cloud computing research and analysis. At first, this paper analyzes the difficulty of obtaining evidence under the environment of cloud computing, then pointed out that the cloud computing environment of the primary collection objects, in the end, this article presents a new kind of cloud fo⁃rensics forensic methods. The final result of this article will evidence to bring a lot of convenience, can also provide some reference for the cloud forensics forensic investigators.%近年来，随着云计算技术的不断发展，我们的生活也因为云计算功能得到了很多的便利，方便我们日常的一些重要信息保存。可是网络上也出现了大量的针对云计算或以云计算为窃取目标的网络犯罪，无论是在技术层面还是在法律方面，云计算取得的成就还是不够大，这也给云计算的网络安全留下了一个漏洞。网络犯罪的趋势不断上涨，对犯罪记录进行取证的人员已经无法用传统的电子取证方法为案件取证，这对取证人员来说，是一个困难的挑战。因此，该文将会对云计算的电子取证进行探究和分析。该文首先分析了云计算环境下取证的困难，之后便点明了云计算环境下的首要取证对象，在最后，文章会提出一种新的有关云取证的取证方法。本篇文章的最终研究成果会给取证人员带来很多的便利，也可以为进行云取证的取证人员提供一些参考。

A comparison and benchmark of two electron cloud packages

Energy Technology Data Exchange (ETDEWEB)

Lebrun, Paul L.G.; Amundson, James F; Spentzouris, Panagiotis G; Veitzer, Seth A

2012-01-01

We present results from precision simulations of the electron cloud (EC) problem in the Fermilab Main Injector using two distinct codes. These two codes are (i)POSINST, a F90 2D+ code, and (ii)VORPAL, a 2D/3D electrostatic and electromagnetic code used for self-consistent simulations of plasma and particle beam problems. A specific benchmark has been designed to demonstrate the strengths of both codes that are relevant to the EC problem in the Main Injector. As differences between results obtained from these two codes were bigger than the anticipated model uncertainties, a set of changes to the POSINST code were implemented. These changes are documented in this note. This new version of POSINST now gives EC densities that agree with those predicted by VORPAL, within {approx}20%, in the beam region. The root cause of remaining differences are most likely due to differences in the electrostatic Poisson solvers. From a software engineering perspective, these two codes are very different. We comment on the pros and cons of both approaches. The design(s) for a new EC package are briefly discussed.

Effect of the LHC Beam Screen Baffle on the Electron Cloud Buildup

CERN Document Server

Romano, Annalisa; Li, Kevin; Rumolo, Giovanni

2016-01-01

Electron Cloud (EC) has been identified as one of the major intensity-limiting factors in the CERN Large Hadron Collider (LHC). Due to the EC, an additional heat load is deposited on the perforated LHC beam screen, for which only a small cooling capacity is available. In order to preserve the superconducting state of the magnets, pumping slots shields were added on the outer side of the beam screens. In the framework of the design of the beam screens of the new HL-LHC triplets, the impact of these shields on the multipacting process was studied with macroparticle simulations. For this purpose multiple new features had to be introduced in the PyECLOUD code. This contribution will describe the implemented simulation model and summarize the outcome of this study.

A State-of-the-Art Experimental Laboratory for Cloud and Cloud-Aerosol Interaction Research

Science.gov (United States)

Fremaux, Charles M.; Bushnell, Dennis M.

2011-01-01

The state of the art for predicting climate changes due to increasing greenhouse gasses in the atmosphere with high accuracy is problematic. Confidence intervals on current long-term predictions (on the order of 100 years) are so large that the ability to make informed decisions with regard to optimum strategies for mitigating both the causes of climate change and its effects is in doubt. There is ample evidence in the literature that large sources of uncertainty in current climate models are various aerosol effects. One approach to furthering discovery as well as modeling, and verification and validation (V&V) for cloud-aerosol interactions is use of a large "cloud chamber" in a complimentary role to in-situ and remote sensing measurement approaches. Reproducing all of the complex interactions is not feasible, but it is suggested that the physics of certain key processes can be established in a laboratory setting so that relevant fluid-dynamic and cloud-aerosol phenomena can be experimentally simulated and studied in a controlled environment. This report presents a high-level argument for significantly improved laboratory capability, and is meant to serve as a starting point for stimulating discussion within the climate science and other interested communities.

Streaming support for data intensive cloud-based sequence analysis.

Science.gov (United States)

Issa, Shadi A; Kienzler, Romeo; El-Kalioby, Mohamed; Tonellato, Peter J; Wall, Dennis; Bruggmann, Rémy; Abouelhoda, Mohamed

2013-01-01

Cloud computing provides a promising solution to the genomics data deluge problem resulting from the advent of next-generation sequencing (NGS) technology. Based on the concepts of "resources-on-demand" and "pay-as-you-go", scientists with no or limited infrastructure can have access to scalable and cost-effective computational resources. However, the large size of NGS data causes a significant data transfer latency from the client's site to the cloud, which presents a bottleneck for using cloud computing services. In this paper, we provide a streaming-based scheme to overcome this problem, where the NGS data is processed while being transferred to the cloud. Our scheme targets the wide class of NGS data analysis tasks, where the NGS sequences can be processed independently from one another. We also provide the elastream package that supports the use of this scheme with individual analysis programs or with workflow systems. Experiments presented in this paper show that our solution mitigates the effect of data transfer latency and saves both time and cost of computation.

Streaming Support for Data Intensive Cloud-Based Sequence Analysis

Directory of Open Access Journals (Sweden)

Shadi A. Issa

2013-01-01

Full Text Available Cloud computing provides a promising solution to the genomics data deluge problem resulting from the advent of next-generation sequencing (NGS technology. Based on the concepts of “resources-on-demand” and “pay-as-you-go”, scientists with no or limited infrastructure can have access to scalable and cost-effective computational resources. However, the large size of NGS data causes a significant data transfer latency from the client’s site to the cloud, which presents a bottleneck for using cloud computing services. In this paper, we provide a streaming-based scheme to overcome this problem, where the NGS data is processed while being transferred to the cloud. Our scheme targets the wide class of NGS data analysis tasks, where the NGS sequences can be processed independently from one another. We also provide the elastream package that supports the use of this scheme with individual analysis programs or with workflow systems. Experiments presented in this paper show that our solution mitigates the effect of data transfer latency and saves both time and cost of computation.

Streaming Support for Data Intensive Cloud-Based Sequence Analysis

Science.gov (United States)

Issa, Shadi A.; Kienzler, Romeo; El-Kalioby, Mohamed; Tonellato, Peter J.; Wall, Dennis; Bruggmann, Rémy; Abouelhoda, Mohamed

2013-01-01

Cloud computing provides a promising solution to the genomics data deluge problem resulting from the advent of next-generation sequencing (NGS) technology. Based on the concepts of “resources-on-demand” and “pay-as-you-go”, scientists with no or limited infrastructure can have access to scalable and cost-effective computational resources. However, the large size of NGS data causes a significant data transfer latency from the client's site to the cloud, which presents a bottleneck for using cloud computing services. In this paper, we provide a streaming-based scheme to overcome this problem, where the NGS data is processed while being transferred to the cloud. Our scheme targets the wide class of NGS data analysis tasks, where the NGS sequences can be processed independently from one another. We also provide the elastream package that supports the use of this scheme with individual analysis programs or with workflow systems. Experiments presented in this paper show that our solution mitigates the effect of data transfer latency and saves both time and cost of computation. PMID:23710461

Model of E-Cloud Instability in the Fermilab Recycler

Energy Technology Data Exchange (ETDEWEB)

Balbekov, V. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

2015-06-24

Simple model of electron cloud is developed in the paper to explain e-cloud instability of bunched proton beam in the Fermilab Recycler. The cloud is presented as an immobile snake in strong vertical magnetic field. The instability is treated as an amplification of the bunch injection errors from the batch head to its tail. Nonlinearity of the e-cloud field is taken into account. Results of calculations are compared with experimental data demonstrating good correlation.

Ku/Ka/W-band Antenna for Electronically-Scanned Cloud and Precipitation Radar

Data.gov (United States)

National Aeronautics and Space Administration — Previously, cloud radars such as CloudSat have been separated from precipitation radars such as TRMM (Tropical Rainfall Measurement Mission) and GPM (Global...

Cost-benefit analysis of alternative LNG vapor-mitigation measures. Topical report, September 14, 1987-January 15, 1991

International Nuclear Information System (INIS)

Atallah, S.

1992-01-01

A generalized methodology is presented for comparing the costs and safety benefits of alternative hazard mitigation measures for a large LNG vapor release. The procedure involves the quantification of the risk to the public before and after the application of LNG vapor mitigation measures. In the study, risk was defined as the product of the annual accident frequency, estimated from a fault tree analysis, and the severity of the accident. Severity was measured in terms of the number of people who may be exposed to 2.5% or higher concentration. The ratios of the annual costs of the various mitigation measures to their safety benefits (as determined by the differences between the risk before and after mitigation measure implementation), were then used to identify the most cost-effective approaches to vapor cloud mitigation

Direct Numerical Modeling of E-Cloud Driven Instability of a Bunch Train in the CERN SPS

International Nuclear Information System (INIS)

Vay, J.-L.; Furman, M.A.; Venturini, M.

2011-01-01

The simulation package WARP-POSINST was recently upgraded for handling multiple bunches and modeling concurrently the electron cloud buildup and its effect on the beam, allowing for direct self-consistent simulation of bunch trains generating, and interacting with, electron clouds. We have used the WARP-POSINST package on massively parallel supercomputers to study the buildup and interaction of electron clouds with a proton bunch train in the CERN SPS accelerator. Results suggest that a positive feedback mechanism exists between the electron buildup and the e-cloud driven transverse instability, leading to a net increase in predicted electron density. Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS and other accelerators. So far, simulations of electron cloud buildup and their effects on beam dynamics have been performed separately. This is a consequence of the large computational cost of the combined calculation due to large space and time scale disparities between the two processes. We have presented the latest improvements of the simulation package WARP-POSINST for the simulation of self-consistent ecloud effects, including mesh refinement, and generation of electrons from gas ionization and impact at the pipe walls. We also presented simulations of two consecutive bunches interacting with electrons clouds in the SPS, which included generation of secondary electrons. The distribution of electrons in front of the first beam was initialized from a dump taken from a preceding buildup calculation using the POSINST code. In this paper, we present an extension of this work where one full batch of 72 bunches is simulated in the SPS, including the entire buildup calculation and the self-consistent interaction between the bunches and the electrons.

Simulation and experimental studies on electron cloud effects in particle accelerators

CERN Document Server

Romano, Annalisa; Cimino, Roberto; Iadarola, Giovanni; Rumolo, Giovanni

Electron Cloud (EC) effects represent a serious limitation for particle accelerators operating with intense beams of positively charged particles. This Master thesis work presents simulation and experimental studies on EC effects carried out in collaboration with the European Organization for Nuclear Research (CERN) in Geneva and with the INFN-LNF laboratories in Frascati. During the Long Shut- down 1 (LS1, 2013-2014), a new detector for EC measurements has been installed in one of the main magnets of the CERN Proton Synchrotron (PS) to study the EC formation in presence of a strong magnetic field. The aim is to develop a reli- able EC model of the PS vacuum chamber in order to identify possible limitation for the future high intensity and high brightness beams foreseen by Large Hadron Collider (LHC) Injectors Upgrade (LIU) project. Numerical simulations with the new PyECLOUD code were performed in order to quantify the expected signal at the detector under different beam conditions. The experimental activity...

A Generic Software Development Process Refined from Best Practices for Cloud Computing

Directory of Open Access Journals (Sweden)

Soojin Park

2015-04-01

Full Text Available Cloud computing has emerged as more than just a piece of technology, it is rather a new IT paradigm. The philosophy behind cloud computing shares its view with green computing where computing environments and resources are not as subjects to own but as subjects of sustained use. However, converting currently used IT services to Software as a Service (SaaS cloud computing environments introduces several new risks. To mitigate such risks, existing software development processes must undergo significant remodeling. This study analyzes actual cases of SaaS cloud computing environment adoption as a way to derive four new best practices for software development and incorporates the identified best practices for currently-in-use processes. Furthermore, this study presents a design for generic software development processes that implement the proposed best practices. The design for the generic process has been applied to reinforce the weak points found in SaaS cloud service development practices used by eight enterprises currently developing or operating actual SaaS cloud computing services. Lastly, this study evaluates the applicability of the proposed SaaS cloud oriented development process through analyzing the feedback data collected from actual application to the development of a SaaS cloud service Astation.

Status report on the 'Merging' of the Electron-Cloud Code POSINST with the 3-D Accelerator PIC CODE WARP

International Nuclear Information System (INIS)

Vay, J.-L.; Furman, M.A.; Azevedo, A.W.; Cohen, R.H.; Friedman, A.; Grote, D.P.; Stoltz, P.H.

2004-01-01

We have integrated the electron-cloud code POSINST [1] with WARP [2]--a 3-D parallel Particle-In-Cell accelerator code developed for Heavy Ion Inertial Fusion--so that the two can interoperate. Both codes are run in the same process, communicate through a Python interpreter (already used in WARP), and share certain key arrays (so far, particle positions and velocities). Currently, POSINST provides primary and secondary sources of electrons, beam bunch kicks, a particle mover, and diagnostics. WARP provides the field solvers and diagnostics. Secondary emission routines are provided by the Tech-X package CMEE

Making the most of cloud storage - a toolkit for exploitation by WLCG experiments

Science.gov (United States)

Alvarez Ayllon, Alejandro; Arsuaga Rios, Maria; Bitzes, Georgios; Furano, Fabrizio; Keeble, Oliver; Manzi, Andrea

2017-10-01

Understanding how cloud storage can be effectively used, either standalone or in support of its associated compute, is now an important consideration for WLCG. We report on a suite of extensions to familiar tools targeted at enabling the integration of cloud object stores into traditional grid infrastructures and workflows. Notable updates include support for a number of object store flavours in FTS3, Davix and gfal2, including mitigations for lack of vector reads; the extension of Dynafed to operate as a bridge between grid and cloud domains; protocol translation in FTS3; the implementation of extensions to DPM (also implemented by the dCache project) to allow 3rd party transfers over HTTP. The result is a toolkit which facilitates data movement and access between grid and cloud infrastructures, broadening the range of workflows suitable for cloud. We report on deployment scenarios and prototype experience, explaining how, for example, an Amazon S3 or Azure allocation can be exploited by grid workflows.

Confidentiality Protection of Digital Health Records in Cloud Computing.

Science.gov (United States)

Chen, Shyh-Wei; Chiang, Dai Lun; Liu, Chia-Hui; Chen, Tzer-Shyong; Lai, Feipei; Wang, Huihui; Wei, Wei

2016-05-01

Electronic medical records containing confidential information were uploaded to the cloud. The cloud allows medical crews to access and manage the data and integration of medical records easily. This data system provides relevant information to medical personnel and facilitates and improve electronic medical record management and data transmission. A structure of cloud-based and patient-centered personal health record (PHR) is proposed in this study. This technique helps patients to manage their health information, such as appointment date with doctor, health reports, and a completed understanding of their own health conditions. It will create patients a positive attitudes to maintain the health. The patients make decision on their own for those whom has access to their records over a specific span of time specified by the patients. Storing data in the cloud environment can reduce costs and enhance the share of information, but the potential threat of information security should be taken into consideration. This study is proposing the cloud-based secure transmission mechanism is suitable for multiple users (like nurse aides, patients, and family members).

Risk mitigation of shared electronic records system in campus institutions: medical social work practice in singapore.

Science.gov (United States)

Ow Yong, Lai Meng; Tan, Amanda Wei Li; Loo, Cecilia Lay Keng; Lim, Esther Li Ping

2014-10-01

In 2013, the Singapore General Hospital (SGH) Campus initiated a shared electronic system where patient records and documentations were standardized and shared across institutions within the Campus. The project was initiated to enhance quality of health care, improve accessibility, and ensure integrated (as opposed to fragmented) care for best outcomes in our patients. In mitigating the risks of ICT, it was found that familiarity with guiding ethical principles, and ensuring adherence to regulatory and technical competencies in medical social work were important. The need to negotiate and maneuver in a large environment within the Campus to ensure proactive integrative process helped.

Workshop on Electron-Cloud Simulations for Proton and Positron Beams (ECLOUD'02) organized by the SL Accelerator Physics Group at CERN.

CERN Multimedia

Patrice Loïez

2002-01-01

This workshop was organized by the SL Accelerator Physics group at CERN from 15 to 18 April 2002. More than 60 participants from 17 institutes reflect the great worldwide interest in the electron-cloud phenomenon, which presently limits the performance of several storage rings and has become a concern for the LHC.

Self-Consistant Numerical Modeling of E-Cloud Driven Instability of a Bunch Train in the CERN SPS

International Nuclear Information System (INIS)

Vay, J.-L.; Furman, M.A.; Secondo, R.; Venturini, M.; Fox, J.D.; Rivetta, C.H.

2010-01-01

The simulation package WARP-POSINST was recently upgraded for handling multiple bunches and modeling concurrently the electron cloud buildup and its effect on the beam, allowing for direct self-consistent simulation of bunch trains generating, and interacting with, electron clouds. We have used the WARP-POSINST package on massively parallel supercomputers to study the growth rate and frequency patterns in space-time of the electron cloud driven transverse instability for a proton bunch train in the CERN SPS accelerator. Results suggest that a positive feedback mechanism exists between the electron buildup and the e-cloud driven transverse instability, leading to a net increase in predicted electron density. Comparisons to selected experimental data are also given. Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS and other accelerators. So far, simulations of electron cloud buildup and their effects on beam dynamics have been performed separately. This is a consequence of the large computational cost of the combined calculation due to large space and time scale disparities between the two processes. We have presented the latest improvements of the simulation package WARP-POSINST for the simulation of self-consistent ecloud effects, including mesh refinement, and generation of electrons from gas ionization and impact at the pipe walls. We also presented simulations of two consecutive bunches interacting with electrons clouds in the SPS, which included generation of secondary electrons. The distribution of electrons in front of the first beam was initialized from a dump taken from a preceding buildup calculation using the POSINST code. In this paper, we present an extension of this work where one full batch of 72 bunches is simulated in the SPS, including the entire buildup calculation and the self-consistent interaction between the bunches and the electrons. Comparisons to experimental data are also given.

Aircraft Weather Mitigation for the Next Generation Air Transportation System

Science.gov (United States)

Stough, H. Paul, III

2007-01-01

Atmospheric effects on aviation are described by Mahapatra (1999) as including (1) atmospheric phenomena involving air motion - wind shear and turbulence; (2) hydrometeorological phenomena - rain, snow and hail; (3) aircraft icing; (4) low visibility; and (5) atmospheric electrical phenomena. Aircraft Weather Mitigation includes aircraft systems (e.g. airframe, propulsion, avionics, controls) that can be enacted (by a pilot, automation or hybrid systems) to suppress and/or prepare for the effects of encountered or unavoidable weather or to facilitate a crew operational decision-making process relative to weather. Aircraft weather mitigation can be thought of as a continuum (Figure 1) with the need to avoid all adverse weather at one extreme and the ability to safely operate in all weather conditions at the other extreme. Realistic aircraft capabilities fall somewhere between these two extremes. The capabilities of small general aviation aircraft would be expected to fall closer to the "Avoid All Adverse Weather" point, and the capabilities of large commercial jet transports would fall closer to the "Operate in All Weather Conditions" point. The ability to safely operate in adverse weather conditions is dependent upon the pilot s capabilities (training, total experience and recent experience), the airspace in which the operation is taking place (terrain, navigational aids, traffic separation), the capabilities of the airport (approach guidance, runway and taxiway lighting, availability of air traffic control), as well as the capabilities of the airplane. The level of mitigation may vary depending upon the type of adverse weather. For example, a small general aviation airplane may be equipped to operate "in the clouds" without outside visual references, but not be equipped to prevent airframe ice that could be accreted in those clouds.

Collisional Damping of Electron Bernstein Waves and its Mitigation by Evaporated Lithium Conditioning in Spherical-Tokamak Plasmas

International Nuclear Information System (INIS)

Diem, S. J.; Caughman, J. B.; Taylor, G.; Efthimion, P. C.; Kugel, H.; LeBlanc, B. P.; Phillips, C. K.; Preinhaelter, J.; Urban, J.; Sabbagh, S. A.

2009-01-01

The first experimental verification of electron Bernstein wave (EBW) collisional damping, and its mitigation by evaporated Li conditioning, in an overdense spherical-tokamak plasma has been observed in the National Spherical Torus Experiment (NSTX). Initial measurements of EBW emission, coupled from NSTX plasmas via double-mode conversion to O-mode waves, exhibited <10% transmission efficiencies. Simulations show 80% of the EBW energy is dissipated by collisions in the edge plasma. Li conditioning reduced the edge collision frequency by a factor of 3 and increased the fundamental EBW transmission to 60%.

Plasma cloud expansion in the ionosphere: Three-dimensional simulation

International Nuclear Information System (INIS)

Ma, T.Z.; Schunk, R.W.

1991-01-01

A three-dimensional time-dependent model was developed to study the characteristics of a plasma cloud expansion in the ionosphere. The electrostatic potential is solved in three dimensions taking into account the large parallel-to-perpendicular conductivity ratio. Three sample simulations are presented: a plasma expansion of a nearly spherical 1 km Ba + cloud, both with and without a background neutral wind, and a long thin Ba + cloudlet. With or without the neutral wind the effective potential, which is different from the electrostatic potential if the electron temperature is included, is constant along the magnetic field for typical cloud sizes. The expanding plasma clouds become elongated in the magnetic field direction. The released Ba + ions push the background O + ions away along the magnetic field as they expand. Consequently, a hole develops in the background O + distribution at the cloud location and on the two sides of the cloud O + bumps form. The entire three-dimensional structure, composed of the plasma cloud and the background plasma embedded in the cloud, slowly rotates about the magnetic field, with the ions and electrons rotating in opposite directions. The cloud configuration takes the shape of a rotating ellipsoid with a major axis that expands with time. Perpendicular to the magnetic field, in the absence of the neutral wind the motion is insignificant compared to the parallel motion. With a neutral wind the motion along the magnetic field and the rotational motion are qualitatively unchanged, but the cloud and the perturbed background structure move in the direction of the wind, with a speed less than the wind speed. Perpendicular to the magnetic field the deformation of the cloud indiced by the wind is characterized by steepening of the backside

The International Symposium on Grids and Clouds

Science.gov (United States)

The International Symposium on Grids and Clouds (ISGC) 2012 will be held at Academia Sinica in Taipei from 26 February to 2 March 2012, with co-located events and workshops. The conference is hosted by the Academia Sinica Grid Computing Centre (ASGC). 2012 is the decennium anniversary of the ISGC which over the last decade has tracked the convergence, collaboration and innovation of individual researchers across the Asia Pacific region to a coherent community. With the continuous support and dedication from the delegates, ISGC has provided the primary international distributed computing platform where distinguished researchers and collaboration partners from around the world share their knowledge and experiences. The last decade has seen the wide-scale emergence of e-Infrastructure as a critical asset for the modern e-Scientist. The emergence of large-scale research infrastructures and instruments that has produced a torrent of electronic data is forcing a generational change in the scientific process and the mechanisms used to analyse the resulting data deluge. No longer can the processing of these vast amounts of data and production of relevant scientific results be undertaken by a single scientist. Virtual Research Communities that span organisations around the world, through an integrated digital infrastructure that connects the trust and administrative domains of multiple resource providers, have become critical in supporting these analyses. Topics covered in ISGC 2012 include: High Energy Physics, Biomedicine & Life Sciences, Earth Science, Environmental Changes and Natural Disaster Mitigation, Humanities & Social Sciences, Operations & Management, Middleware & Interoperability, Security and Networking, Infrastructure Clouds & Virtualisation, Business Models & Sustainability, Data Management, Distributed Volunteer & Desktop Grid Computing, High Throughput Computing, and High Performance, Manycore & GPU Computing.

Cloud Infrastructure & Applications - CloudIA

Science.gov (United States)

Sulistio, Anthony; Reich, Christoph; Doelitzscher, Frank

The idea behind Cloud Computing is to deliver Infrastructure-as-a-Services and Software-as-a-Service over the Internet on an easy pay-per-use business model. To harness the potentials of Cloud Computing for e-Learning and research purposes, and to small- and medium-sized enterprises, the Hochschule Furtwangen University establishes a new project, called Cloud Infrastructure & Applications (CloudIA). The CloudIA project is a market-oriented cloud infrastructure that leverages different virtualization technologies, by supporting Service-Level Agreements for various service offerings. This paper describes the CloudIA project in details and mentions our early experiences in building a private cloud using an existing infrastructure.

Manifestations of electric currents in interstellar molecular clouds

International Nuclear Information System (INIS)

Carlqvist, P.; Gahm, G.F.

1991-12-01

We draw the attention to filamentary structures in molecular clouds and point out the existence of subfilaments of sinusoidal shape and also of helix-like structures. For two dark clouds, the Lynds 204 complex and the Sandqvist 187-188 complex (The Norma 'sword') we make a detailed study of such shapes and in addition we find the possible existence of helices wound around the main filaments. All these features are highly reminiscent of morphologies encountered in solar ascending prominences and in experiments in plasma physics and suggest the existence of electric currents and magnetic fields in these clouds. On the basis of a generalization of the Bennett pinch model, we derive the magnitudes of the currents expected to flow in the filaments. Values of column densities, magnetic field strengths, and direction of the fields are derived from observations. Magnetic fields with both toroidal and axial components are considered. This study shows that axial currents of the order of a few times 10 13 A are necessary for the clouds to be in equilibrium. The corresponding mean current densities are very small and even at the very low values of the fractional abundance of electrons encountered in these clouds, the mean electron velocities are of the order of 10 -2 -10 -5 m s -1 , much lower than the thermal velocities in the clouds. We suggest that helical structures may evolve as a result of various instabilities in the pinched clouds. We also call the attention to the kink intability in connection with the sinusoidal shapes. The existence of electromagnetically controlled features in the interstellar clouds can be tested by further observations. (au)

Government Cloud Computing Policies: Potential Opportunities for Advancing Military Biomedical Research.

Science.gov (United States)

Lebeda, Frank J; Zalatoris, Jeffrey J; Scheerer, Julia B

2018-02-07

This position paper summarizes the development and the present status of Department of Defense (DoD) and other government policies and guidances regarding cloud computing services. Due to the heterogeneous and growing biomedical big datasets, cloud computing services offer an opportunity to mitigate the associated storage and analysis requirements. Having on-demand network access to a shared pool of flexible computing resources creates a consolidated system that should reduce potential duplications of effort in military biomedical research. Interactive, online literature searches were performed with Google, at the Defense Technical Information Center, and at two National Institutes of Health research portfolio information sites. References cited within some of the collected documents also served as literature resources. We gathered, selected, and reviewed DoD and other government cloud computing policies and guidances published from 2009 to 2017. These policies were intended to consolidate computer resources within the government and reduce costs by decreasing the number of federal data centers and by migrating electronic data to cloud systems. Initial White House Office of Management and Budget information technology guidelines were developed for cloud usage, followed by policies and other documents from the DoD, the Defense Health Agency, and the Armed Services. Security standards from the National Institute of Standards and Technology, the Government Services Administration, the DoD, and the Army were also developed. Government Services Administration and DoD Inspectors General monitored cloud usage by the DoD. A 2016 Government Accountability Office report characterized cloud computing as being economical, flexible and fast. A congressionally mandated independent study reported that the DoD was active in offering a wide selection of commercial cloud services in addition to its milCloud system. Our findings from the Department of Health and Human Services

A study of shock mitigating materials in a split Hopkinson bar configuration

International Nuclear Information System (INIS)

Bateman, V.I.; Bell, R.G. III; Brown, F.A.; Hansen, N.R.

1996-01-01

Sandia National Laboratories (SNL) designs mechanical systems with electronics that must survive high shock environments. These mechanical systems include penetrators that must survive soil, rock, and ice penetration, nuclear transportation casks that must survive transportation environments, and laydown weapons that must survive delivery impact of 125-fps. These mechanical systems contain electronics that may operate during and after the high shock environment and that must be protected from the high shock environments. A study has been started to improve the packaging techniques for the advanced electronics utilized in these mechanical systems because current packaging techniques are inadequate for these more sensitive electronics. In many cases, it has been found that the packaging techniques currently used not only do not mitigate the shock environment but actually amplify the shock environment. An ambitious goal for this packaging study is to avoid amplification and possibly attenuate the shock environment before it reaches the electronics contained in the various mechanical system. As part of the investigation of packaging techniques, a two part study of shock mitigating materials is being conducted. This paper reports the first part of the shock mitigating materials study. A study to compare three thicknesses (0.125, 0.250, and 0.500 in.) of seventeen, unconfined materials for their shock mitigating characteristics has been completed with a split Hopkinson bar configuration. The nominal input as measured by strain gages on the incident Hopkinson bar is 50 fps at sign 100 micros for these tests. It is hypothesized that a shock mitigating material has four purposes: to lengthen the shock pulse, to attenuate the shock pulse, to mitigate high frequency content in the shock pulse, and to absorb energy. Both time domain and frequency domain analyses of the split Hopkinson bar data have been performed to compare the materials' achievement of these purposes

Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

Science.gov (United States)

Gobbin, M.; Li, L.; Liu, Y. Q.; Marrelli, L.; Nocente, M.; Papp, G.; Pautasso, G.; Piovesan, P.; Valisa, M.; Carnevale, D.; Esposito, B.; Giacomelli, L.; Gospodarczyk, M.; McCarthy, P. J.; Martin, P.; Suttrop, W.; Tardocchi, M.; Teschke, M.; the ASDEX Upgrade Team; the EUROfusion MST1 Team

2018-01-01

Disruption-generated runaway electron (RE) beams represent a severe threat for tokamak plasma-facing components in high current devices like ITER, thus motivating the search of mitigation techniques. The application of 3D fields might aid this purpose and recently was investigated also in the ASDEX Upgrade experiment by using the internal active saddle coils (termed B-coils). Resonant magnetic perturbations (RMPs) with dominant toroidal mode number n = 1 have been applied by the B-coils, in a RE specific scenario, before and during disruptions, which are deliberately created via massive gas injection. The application of RMPs affects the electron temperature profile and seemingly changes the dynamics of the disruption; this results in a significantly reduced current and lifetime of the generated RE beam. A similar effect is observed also in the hard-x-ray (HXR) spectrum, associated to RE emission, characterized by a partial decrease of the energy content below 1 MeV when RMPs are applied. The strength of the observed effects strongly depends on the upper-to-lower B-coil phasing, i.e. on the poloidal spectrum of the applied RMPs, which has been reconstructed including the plasma response by the code MARS-F. A crude vacuum approximation fails in the interpretation of the experimental findings: despite the relatively low β (< 0.5 % ) of these discharges, a modest amplification (factor of 2) of the edge kink response occurs, which has to be considered to explain the observed suppression effects.

Cosmic rays, clouds and climate

Energy Technology Data Exchange (ETDEWEB)

Svensmark, Henrik [Danish Space Research Institute, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark)

2007-07-01

Changes in the intensity of galactic cosmic rays seems alter the Earth's cloudiness. A recent experiment has shown how electrons liberated by cosmic rays assist in making aerosols, the building blocks of cloud condensation nuclei, while anomalous climatic trends in Antarctica confirm the role of clouds in helping to drive climate change. Variations in the cosmic-ray influx due to solar magnetic activity account well for climatic fluctuations on decadal, centennial and millennial timescales. Over longer intervals, the changing galactic environment of the Solar System has had dramatic consequences, including Snowball Earth episodes.

Formation of Massive Molecular Cloud Cores by Cloud-cloud Collision

OpenAIRE

Inoue, Tsuyoshi; Fukui, Yasuo

2013-01-01

Recent observations of molecular clouds around rich massive star clusters including NGC3603, Westerlund 2, and M20 revealed that the formation of massive stars could be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we demonstrate that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by the cloud-cloud collision. We find that the massive mol...

LS1 Report: the clouds are lifting

CERN Multimedia

Anaïs Schaeffer

2014-01-01

To combat the problem of electron clouds, which perturbate the environment of the particle beams in our accelerators, the Vacuum team have turned to amorphous carbon. This material is being applied to the interior of 16 magnets in the SPS during LS1 and will help prevent the formation of the secondary particles which are responsible for these clouds.   This photo shows the familiar coils of an SPS dipole magnet in brown. The vacuum chamber is the metallic rectangular part in the centre. The small wheeled device you can see in the vacuum chamber carries the hollow cathodes  along the length of the chamber. When a particle beam circulates at high energy in a vacuum chamber, it unavoidably generates secondary particles. These include electrons produced by the ionisation of residual molecules in the vacuum or indirectly generated by synchrotron radiation. When these electrons hit the surface of the vacuum chamber, they produce other electrons which, through an avalanche-like process, re...

High-performance scientific computing in the cloud

Science.gov (United States)

Jorissen, Kevin; Vila, Fernando; Rehr, John

2011-03-01

Cloud computing has the potential to open up high-performance computational science to a much broader class of researchers, owing to its ability to provide on-demand, virtualized computational resources. However, before such approaches can become commonplace, user-friendly tools must be developed that hide the unfamiliar cloud environment and streamline the management of cloud resources for many scientific applications. We have recently shown that high-performance cloud computing is feasible for parallelized x-ray spectroscopy calculations. We now present benchmark results for a wider selection of scientific applications focusing on electronic structure and spectroscopic simulation software in condensed matter physics. These applications are driven by an improved portable interface that can manage virtual clusters and run various applications in the cloud. We also describe a next generation of cluster tools, aimed at improved performance and a more robust cluster deployment. Supported by NSF grant OCI-1048052.

Examination and Mitigation of Electron Interception Processes in Dye-sensitized Solar Cells through Redox Shuttle and Photoelectrode Modification

Science.gov (United States)

Hoffeditz, William Lawrence

With the dual challenges of meeting global energy demand and mitigating anthropogenic climate change, significant effort is being applied to generating power from renewable sources. The dye-sensitized solar cell (DSC) is a photovoltaic technology capable of generating electricity from sunlight, but suffers losses in efficiency due to deleterious electron transfer processes. Controlling these processes is essential if DSCs are to continue to advance, and this dissertation focuses on isolation, interrogation, and mitigation of these processes via controllable inorganic redox/coordination chemistry and atomic layer deposition (ALD). The redox shuttle is often the subject of innovation in DSCs, the goal being to increase obtainable photovoltage without sacrificing photocurrent. A copper redox shuttle with a favorable (II/I) redox potential for DSC use and intriguing inner-sphere reorganization energy was investigated. The shuttle completely replaces its tetradentate coordinating ligand upon oxidation with multiple pyridine molecules. This new species displays markedly slower electron interception, necessitating fabrication of a new counter electrode in order for the shuttle to function. Upon reduction, the tetradentate ligand re-coordinates, creating a dual-species shuttle that outperforms either species as a Cu(II/I) shuttle in isolation. Photoelectrode modification is also the subject of innovation in DSCs. ALD is ideally suited for this type of innovation as it can coat high aspect surfaces with metal-oxide films of uniform thickness. The ALD post-treatment technique is described and used to deposit Al2O3 around a TiO2 adsorbed zinc-porphyrin dye. This technique is shown to prevent dye degradation from ambient air and/or light. Additionally, the architecture allows the study of dye-influenced electron interception processes. It was found that the presence of dye increased interception, which was attributed to dye-mediated electron hopping and/or superexchange

Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

OpenAIRE

Y. Liu; W. Wu; M. P. Jensen; T. Toto

2011-01-01

This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surfaced-based approach for measuring cloud albedo; (3) multiscale (diurnal, annual and inter-annual) variations and covariations of surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo. An analytical expression is first derived to quantify the relationship between cloud radiative forcing, cloud fractio...

Virtual Machine Replication on Achieving Energy-Efficiency in a Cloud

Directory of Open Access Journals (Sweden)

Subrota K. Mondal

2016-07-01

Full Text Available The rapid growth in cloud service demand has led to the establishment of large-scale virtualized data centers in which virtual machines (VMs are used to handle user requests for service. A user’s request cannot be completed if the VM fails. Replication mechanisms can be used to mitigate the impact of failures. Further, data centers consume a large amount of energy resulting in high operating costs and contributing to significant greenhouse gas (GHG emissions. In this paper, we focus on Infrastructure as a Service (IaaS cloud where user job requests are processed by VMs and analyze the effectiveness of VM replications in terms of job completion time performance as well as energy consumption. Three different schemes: cold, warm, and hot replications are considered. The trade-offs between job completion time and energy consumption in different replication schemes are characterized through comprehensive analytical models which capture VM state transitions and associated power consumption patterns. The effectiveness of replication schemes are demonstrated through experimental results. To verify the validity of the proposed analytical models, we extend the widely used cloud simulator CloudSim and compare the simulation results with analytical solutions.

Simultaneous observations of solar MeV particles in a magnetic cloud and in the earth's northern tail lobe - Implications for the global field line topology of magnetic clouds and for the entry of solar particles into the magnetosphere during cloud passage

Science.gov (United States)

Farrugia, C. J.; Richardson, I. G.; Burlaga, L. F.; Lepping, R. P.; Osherovich, V. A.

1993-01-01

Simultaneous ISEE 3 and IMP 8 spacecraft observations of magnetic fields and flow anisotropies of solar energetic protons and electrons during the passage of an interplanetary magnetic cloud show various particle signature differences at the two spacecraft. These differences are interpretable in terms of the magnetic line topology of the cloud, the connectivity of the cloud field lines to the solar surface, and the interconnection between the magnetic fields of the magnetic clouds and of the earth. These observations are consistent with a magnetic cloud model in which these mesoscale configurations are curved magnetic flux ropes attached at both ends to the sun's surface, extending out to 1 AU.

The dynamics of low-β plasma clouds as simulated by a three-dimensional, electromagnetic particle code

International Nuclear Information System (INIS)

Neubert, T.; Miller, R.H.; Buneman, O.; Nishikawa, K.I.

1992-01-01

The dynamics of low-β plasma clouds moving perpendicular to an ambient magnetic field in vacuum and in a background plasma is simulated by means of a three-dimensional, electromagnetic, and relativistic particle simulation code. The simulations show the formation of the space charge sheaths at the sides of the cloud with the associated polarization electric field which facilitate the cross-field propagation, as well as the sheaths at the front and rear end of the cloud caused by the larger ion Larmor radius, which allows ions to move ahead and lag behind the electrons as they gyrate. Results on the cloud dynamics and electromagnetic radiation include the following: (1) In a background plasma, electron and ion sheaths expand along the magnetic field at the same rate, whereas in vacuum the electron sheath expands much faster than the ion sheath. (2) Sheath electrons are accelerated up to relativistic energies. This result indicates that artificial plasma clouds released in the ionosphere or magnetosphere may generate optical emissions (aurora) as energetic sheath electrons scatter in the upper atmosphere. (3) The expansion of the electron sheaths is analogous to the ejection of high-intensity electron beams from spacecraft. (4) Second-order and higher-order sheaths are formed which extend out into the ambient plasma. (5) Formation of the sheaths and the polarization field reduces the forward momentum of the cloud. (6) The coherent component of the particle gyromotion is damped in time as the particles establish a forward directed drift velocity. (7) The coherent particle gyrations generate electromagnetic radiation

Status report on the 'Merging' of the Electron-Cloud Code POSINST with the 3-D Accelerator PIC CODE WARP

Energy Technology Data Exchange (ETDEWEB)

Vay, J.-L.; Furman, M.A.; Azevedo, A.W.; Cohen, R.H.; Friedman, A.; Grote, D.P.; Stoltz, P.H.

2004-04-19

We have integrated the electron-cloud code POSINST [1] with WARP [2]--a 3-D parallel Particle-In-Cell accelerator code developed for Heavy Ion Inertial Fusion--so that the two can interoperate. Both codes are run in the same process, communicate through a Python interpreter (already used in WARP), and share certain key arrays (so far, particle positions and velocities). Currently, POSINST provides primary and secondary sources of electrons, beam bunch kicks, a particle mover, and diagnostics. WARP provides the field solvers and diagnostics. Secondary emission routines are provided by the Tech-X package CMEE.

Integrated Geo Hazard Management System in Cloud Computing Technology

Science.gov (United States)

Hanifah, M. I. M.; Omar, R. C.; Khalid, N. H. N.; Ismail, A.; Mustapha, I. S.; Baharuddin, I. N. Z.; Roslan, R.; Zalam, W. M. Z.

2016-11-01

Geo hazard can result in reducing of environmental health and huge economic losses especially in mountainous area. In order to mitigate geo-hazard effectively, cloud computer technology are introduce for managing geo hazard database. Cloud computing technology and it services capable to provide stakeholder's with geo hazards information in near to real time for an effective environmental management and decision-making. UNITEN Integrated Geo Hazard Management System consist of the network management and operation to monitor geo-hazard disaster especially landslide in our study area at Kelantan River Basin and boundary between Hulu Kelantan and Hulu Terengganu. The system will provide easily manage flexible measuring system with data management operates autonomously and can be controlled by commands to collects and controls remotely by using “cloud” system computing. This paper aims to document the above relationship by identifying the special features and needs associated with effective geohazard database management using “cloud system”. This system later will use as part of the development activities and result in minimizing the frequency of the geo-hazard and risk at that research area.

Interaction of plasma cloud with external electric field in lower ionosphere

Directory of Open Access Journals (Sweden)

Y. S. Dimant

2010-03-01

Full Text Available In the auroral lower-E and upper-D region of the ionosphere, plasma clouds, such as sporadic-E layers and meteor plasma trails, occur daily. Large-scale electric fields, created by the magnetospheric dynamo, will polarize these highly conducting clouds, redistributing the electrostatic potential and generating anisotropic currents both within and around the cloud. Using a simplified model of the cloud and the background ionosphere, we develop the first self-consistent three-dimensional analytical theory of these phenomena. For dense clouds, this theory predicts highly amplified electric fields around the cloud, along with strong currents collected from the ionosphere and circulated through the cloud. This has implications for the generation of plasma instabilities, electron heating, and global MHD modeling of magnetosphere-ionosphere coupling via modifications of conductances induced by sporadic-E clouds.

Cloud screening Coastal Zone Color Scanner images using channel 5

Science.gov (United States)

Eckstein, B. A.; Simpson, J. J.

1991-01-01

Clouds are removed from Coastal Zone Color Scanner (CZCS) data using channel 5. Instrumentation problems require pre-processing of channel 5 before an intelligent cloud-screening algorithm can be used. For example, at intervals of about 16 lines, the sensor records anomalously low radiances. Moreover, the calibration equation yields negative radiances when the sensor records zero counts, and pixels corrupted by electronic overshoot must also be excluded. The remaining pixels may then be used in conjunction with the procedure of Simpson and Humphrey to determine the CZCS cloud mask. These results plus in situ observations of phytoplankton pigment concentration show that pre-processing and proper cloud-screening of CZCS data are necessary for accurate satellite-derived pigment concentrations. This is especially true in the coastal margins, where pigment content is high and image distortion associated with electronic overshoot is also present. The pre-processing algorithm is critical to obtaining accurate global estimates of pigment from spacecraft data.

Clean Energy Use for Cloud Computing Federation Workloads

Directory of Open Access Journals (Sweden)

Yahav Biran

2017-08-01

Full Text Available Cloud providers seek to maximize their market share. Traditionally, they deploy datacenters with sufficient capacity to accommodate their entire computing demand while maintaining geographical affinity to its customers. Achieving these goals by a single cloud provider is increasingly unrealistic from a cost of ownership perspective. Moreover, the carbon emissions from underutilized datacenters place an increasing demand on electricity and is a growing factor in the cost of cloud provider datacenters. Cloud-based systems may be classified into two categories: serving systems and analytical systems. We studied two primary workload types, on-demand video streaming as a serving system and MapReduce jobs as an analytical systems and suggested two unique energy mix usage for processing that workloads. The recognition that on-demand video streaming now constitutes the bulk portion of traffic to Internet consumers provides a path to mitigate rising energy demand. On-demand video is usually served through Content Delivery Networks (CDN, often scheduled in backend and edge datacenters. This publication describes a CDN deployment solution that utilizes green energy to supply on-demand streaming workload. A cross-cloud provider collaboration will allow cloud providers to both operate near their customers and reduce operational costs, primarily by lowering the datacenter deployments per provider ratio. Our approach optimizes cross-datacenters deployment. Specifically, we model an optimized CDN-edge instance allocation system that maximizes, under a set of realistic constraints, green energy utilization. The architecture of this cross-cloud coordinator service is based on Ubernetes, an open source container cluster manager that is a federation of Kubernetes clusters. It is shown how, under reasonable constraints, it can reduce the projected datacenter’s carbon emissions growth by 22% from the currently reported consumption. We also suggest operating

Achieving Payoffs from an Industry Cloud Ecosystem at BankID

DEFF Research Database (Denmark)

Eaton, Ben; Hallingby, Hanne Kristine; Nesse, Per-Jonny

2014-01-01

BankID is an industry cloud owned by Norwegian banks. It provides electronic identity, authentication and electronic signing capabilities for banking, merchant and government services. More than 60% of the population uses BankID services. As the broader ecosystem around BankID evolved, challenges......—arising from tensions between different parts of the ecosystem—had to be resolved. The four lessons learned from the BankID case will help others to build an industry cloud and establish a healthy ecosystem to service a broad user base....

Secure system for personal finances on the cloud

OpenAIRE

Quintana i Vidal, Xavier

2015-01-01

Este documento contiene la memoria de la realización del Trabajo Final de Máster que tiene como objetivo la creación de un Cloud para el almacenamiento de forma segura de las facturas electrónicas. This document contains the memory of the accomplishment of the final Project, which aims to create a Cloud for secure storage of the electronic invoices. Aquest document conté la memòria de la realització del Treball Final de Màster que té com a objectiu la creació d'un Cloud per a l'emmagatz...

Mitigating tin whisker risks theory and practice

CERN Document Server

Handwerker, Carol A; Bath, Jasbir

2016-01-01

Discusses the growth mechanisms of tin whiskers and the effective mitigation strategies necessary to reduce whisker growth risks. This book covers key tin whisker topics, ranging from fundamental science to practical mitigation strategies. The text begins with a review of the characteristic properties of local microstructures around whisker and hillock grains to identify why these particular grains and locations become predisposed to forming whiskers and hillocks. The book discusses the basic properties of tin-based alloy finishes and the effects of various alloying elements on whisker formation, with a focus on potential mechanisms for whisker suppression or enhancement for each element. Tin whisker risk mitigation strategies for each tier of the supply chain for high reliability electronic systems are also described.

Cloud-Top Entrainment in Stratocumulus Clouds

Science.gov (United States)

Mellado, Juan Pedro

2017-01-01

Cloud entrainment, the mixing between cloudy and clear air at the boundary of clouds, constitutes one paradigm for the relevance of small scales in the Earth system: By regulating cloud lifetimes, meter- and submeter-scale processes at cloud boundaries can influence planetary-scale properties. Understanding cloud entrainment is difficult given the complexity and diversity of the associated phenomena, which include turbulence entrainment within a stratified medium, convective instabilities driven by radiative and evaporative cooling, shear instabilities, and cloud microphysics. Obtaining accurate data at the required small scales is also challenging, for both simulations and measurements. During the past few decades, however, high-resolution simulations and measurements have greatly advanced our understanding of the main mechanisms controlling cloud entrainment. This article reviews some of these advances, focusing on stratocumulus clouds, and indicates remaining challenges.

Cloud type comparisons of AIRS, CloudSat, and CALIPSO cloud height and amount

Directory of Open Access Journals (Sweden)

B. H. Kahn

2008-03-01

Full Text Available The precision of the two-layer cloud height fields derived from the Atmospheric Infrared Sounder (AIRS is explored and quantified for a five-day set of observations. Coincident profiles of vertical cloud structure by CloudSat, a 94 GHz profiling radar, and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO, are compared to AIRS for a wide range of cloud types. Bias and variability in cloud height differences are shown to have dependence on cloud type, height, and amount, as well as whether CloudSat or CALIPSO is used as the comparison standard. The CloudSat-AIRS biases and variability range from −4.3 to 0.5±1.2–3.6 km for all cloud types. Likewise, the CALIPSO-AIRS biases range from 0.6–3.0±1.2–3.6 km (−5.8 to −0.2±0.5–2.7 km for clouds ≥7 km (<7 km. The upper layer of AIRS has the greatest sensitivity to Altocumulus, Altostratus, Cirrus, Cumulonimbus, and Nimbostratus, whereas the lower layer has the greatest sensitivity to Cumulus and Stratocumulus. Although the bias and variability generally decrease with increasing cloud amount, the ability of AIRS to constrain cloud occurrence, height, and amount is demonstrated across all cloud types for many geophysical conditions. In particular, skill is demonstrated for thin Cirrus, as well as some Cumulus and Stratocumulus, cloud types infrared sounders typically struggle to quantify. Furthermore, some improvements in the AIRS Version 5 operational retrieval algorithm are demonstrated. However, limitations in AIRS cloud retrievals are also revealed, including the existence of spurious Cirrus near the tropopause and low cloud layers within Cumulonimbus and Nimbostratus clouds. Likely causes of spurious clouds are identified and the potential for further improvement is discussed.

A comparison of shock-cloud and wind-cloud interactions: effect of increased cloud density contrast on cloud evolution

Science.gov (United States)

Goldsmith, K. J. A.; Pittard, J. M.

2018-05-01

The similarities, or otherwise, of a shock or wind interacting with a cloud of density contrast χ = 10 were explored in a previous paper. Here, we investigate such interactions with clouds of higher density contrast. We compare the adiabatic hydrodynamic interaction of a Mach 10 shock with a spherical cloud of χ = 103 with that of a cloud embedded in a wind with identical parameters to the post-shock flow. We find that initially there are only minor morphological differences between the shock-cloud and wind-cloud interactions, compared to when χ = 10. However, once the transmitted shock exits the cloud, the development of a turbulent wake and fragmentation of the cloud differs between the two simulations. On increasing the wind Mach number, we note the development of a thin, smooth tail of cloud material, which is then disrupted by the fragmentation of the cloud core and subsequent `mass-loading' of the flow. We find that the normalized cloud mixing time (tmix) is shorter at higher χ. However, a strong Mach number dependence on tmix and the normalized cloud drag time, t_{drag}^' }, is not observed. Mach-number-dependent values of tmix and t_{drag}^' } from comparable shock-cloud interactions converge towards the Mach-number-independent time-scales of the wind-cloud simulations. We find that high χ clouds can be accelerated up to 80-90 per cent of the wind velocity and travel large distances before being significantly mixed. However, complete mixing is not achieved in our simulations and at late times the flow remains perturbed.

Cloud Computing, Tieto Cloud Server Model

OpenAIRE

Suikkanen, Saara

2013-01-01

The purpose of this study is to find out what is cloud computing. To be able to make wise decisions when moving to cloud or considering it, companies need to understand what cloud is consists of. Which model suits best to they company, what should be taken into account before moving to cloud, what is the cloud broker role and also SWOT analysis of cloud? To be able to answer customer requirements and business demands, IT companies should develop and produce new service models. IT house T...

Phosphate Changes Effect of Humic Acids on TiO2 Photocatalysis: From Inhibition to Mitigation of Electron-Hole Recombination.

Science.gov (United States)

Long, Mingce; Brame, Jonathon; Qin, Fan; Bao, Jiming; Li, Qilin; Alvarez, Pedro J J

2017-01-03

A major challenge for photocatalytic water purification with TiO 2 is the strong inhibitory effect of natural organic matter (NOM), which can scavenge photogenerated holes and radicals and occlude ROS generation sites upon adsorption. This study shows that phosphate counteracts the inhibitory effect of humic acids (HA) by decreasing HA adsorption and mitigating electron-hole recombination. As a measure of the inhibitory effect of HA, the ratios of first-order reaction rate constants between photocatalytic phenol degradation in the absence versus presence of HA were calculated. This ratio was very high, up to 5.72 at 30 mg/L HA and pH 4.8 without phosphate, but was decreased to 0.76 (5 mg/L HA, pH 8.4) with 2 mM phosphate. The latter ratio indicates a surprising favorable effect of HA on TiO 2 photocatalysis. FTIR analyses suggest that this favorable effect is likely due to a change in the conformation of adsorbed HA, from a multiligand exchange arrangement to a complexation predominantly between COOH groups in HA and the TiO 2 surface in the presence of phosphate. This configuration can reduce hole consumption and facilitate electron transfer to O 2 by the adsorbed HA (indicated by linear sweep voltammetry), which mitigates electron-hole recombination and enhances contaminant degradation. A decrease in HA surface adsorption and hole scavenging (the predominant inhibitory mechanisms of HA) by phosphate (2 mM) was indicated by a 50% decrease in the photocatalytic degradation rate of HA and 80% decrease in the decay rate coefficient of interfacial-related photooxidation in photocurrent transients. These results, which were validated with other compounds (FFA and cimetidine), indicate that anchoring phosphate - or anions that exert similar effects on the TiO 2 surface - might be a feasible strategy to counteract the inhibitory effect of NOM during photocatalytic water treatment.

Cloud residues and interstitial aerosols from non-precipitating clouds over an industrial and urban area in northern China

Science.gov (United States)

Li, Weijun; Li, Peiren; Sun, Guode; Zhou, Shengzhen; Yuan, Qi; Wang, Wenxing

2011-05-01

Most studies of aerosol-cloud interactions have been conducted in remote locations; few have investigated the characterization of cloud condensation nuclei (CCN) over highly polluted urban and industrial areas. The present work, based on samples collected at Mt. Tai, a site in northern China affected by nearby urban and industrial air pollutant emissions, illuminates CCN properties in a polluted atmosphere. High-resolution transmission electron microscopy (TEM) was used to obtain the size, composition, and mixing state of individual cloud residues and interstitial aerosols. Most of the cloud residues displayed distinct rims which were found to consist of soluble organic matter (OM). Nearly all (91.7%) cloud residues were attributed to sulfate-related salts (the remainder was mostly coarse crustal dust particles with nitrate coatings). Half the salt particles were internally mixed with two or more refractory particles (e.g., soot, fly ash, crustal dust, CaSO 4, and OM). A comparison between cloud residues and interstitial particles shows that the former contained more salts and were of larger particle size than the latter. In addition, a somewhat high number scavenging ratio of 0.54 was observed during cloud formation. Therefore, the mixtures of salts with OMs account for most of the cloud-nucleating ability of the entire aerosol population in the polluted air of northern China. We advocate that both size and composition - the two influential, controlling factors for aerosol activation - should be built into all regional climate models of China.

+Cloud: An Agent-Based Cloud Computing Platform

OpenAIRE

González, Roberto; Hernández de la Iglesia, Daniel; de la Prieta Pintado, Fernando; Gil González, Ana Belén

2017-01-01

Cloud computing is revolutionizing the services provided through the Internet, and is continually adapting itself in order to maintain the quality of its services. This study presents the platform +Cloud, which proposes a cloud environment for storing information and files by following the cloud paradigm. This study also presents Warehouse 3.0, a cloud-based application that has been developed to validate the services provided by +Cloud.

The interaction of fast alpha particles with pellet ablation clouds

International Nuclear Information System (INIS)

McChesney, J.M.; Parks, P.B.; Fisher, R.K.; Olson, R.E.

1997-01-01

The energy spectra of energetic confined alpha particles are being measured using the pellet charge exchange method [R. K. Fisher, J. S. Leffler, A. M. Howald, and P. B. Parks, Fusion Technol. 13, 536 (1988)]. The technique uses the dense ablation cloud surrounding an injected impurity pellet to neutralize a fraction of the incident alpha particles, allowing them to escape from the plasma where their energy spectrum can be measured using a neutral particle analyzer. The signal calculations given in the above-mentioned reference disregarded the effects of the alpha particles' helical Larmor orbits, which causes the alphas to make multiple passes through the cloud. Other effects such as electron ionization by plasma and ablation cloud electrons and the effect of the charge state composition of the cloud, were also neglected. This report considers these issues, reformulates the signal level calculation, and uses a Monte-Carlo approach to calculate the neutralization fractions. The possible effects of energy loss and pitch angle scattering of the alphas are also considered. copyright 1997 American Institute of Physics

Silicon Photonics Cloud (SiCloud)

DEFF Research Database (Denmark)

DeVore, P. T. S.; Jiang, Y.; Lynch, M.

2015-01-01

Silicon Photonics Cloud (SiCloud.org) is the first silicon photonics interactive web tool. Here we report new features of this tool including mode propagation parameters and mode distribution galleries for user specified waveguide dimensions and wavelengths.......Silicon Photonics Cloud (SiCloud.org) is the first silicon photonics interactive web tool. Here we report new features of this tool including mode propagation parameters and mode distribution galleries for user specified waveguide dimensions and wavelengths....

Kinetics of laser irradiated nanoparticles cloud

Science.gov (United States)

Mishra, S. K.; Upadhyay Kahaly, M.; Misra, Shikha

2018-02-01

A comprehensive kinetic model describing the complex kinetics of a laser irradiated nanoparticle ensemble has been developed. The absorbed laser radiation here serves dual purpose, viz., photoenhanced thermionic emission via rise in its temperature and direct photoemission of electrons. On the basis of mean charge theory along with the equations for particle (electron) and energy flux balance over the nanoparticles, the transient processes of charge/temperature evolution over its surface and mass diminution on account of the sublimation (phase change) process have been elucidated. Using this formulation phenomenon of nanoparticle charging, its temperature rise to the sublimation point, mass ablation, and cloud disintegration have been investigated; afterwards, typical timescales of disintegration, sublimation and complete evaporation in reference to a graphite nanoparticle cloud (as an illustrative case) have been parametrically investigated. Based on a numerical analysis, an adequate parameter space describing the nanoparticle operation below the sublimation temperature, in terms of laser intensity, wavelength and nanoparticle material work function, has been identified. The cloud disintegration is found to be sensitive to the nanoparticle charging through photoemission; as a consequence, it illustrates that radiation operating below the photoemission threshold causes disintegration in the phase change state, while above the threshold, it occurs with the onset of surface heating.

An Efficient Searchable Encryption Against Keyword Guessing Attacks for Sharable Electronic Medical Records in Cloud-based System.

Science.gov (United States)

Wu, Yilun; Lu, Xicheng; Su, Jinshu; Chen, Peixin

2016-12-01

Preserving the privacy of electronic medical records (EMRs) is extremely important especially when medical systems adopt cloud services to store patients' electronic medical records. Considering both the privacy and the utilization of EMRs, some medical systems apply searchable encryption to encrypt EMRs and enable authorized users to search over these encrypted records. Since individuals would like to share their EMRs with multiple persons, how to design an efficient searchable encryption for sharable EMRs is still a very challenge work. In this paper, we propose a cost-efficient secure channel free searchable encryption (SCF-PEKS) scheme for sharable EMRs. Comparing with existing SCF-PEKS solutions, our scheme reduces the storage overhead and achieves better computation performance. Moreover, our scheme can guard against keyword guessing attack, which is neglected by most of the existing schemes. Finally, we implement both our scheme and a latest medical-based scheme to evaluate the performance. The evaluation results show that our scheme performs much better performance than the latest one for sharable EMRs.

Cloud Processed CCN Suppress Stratus Cloud Drizzle

Science.gov (United States)

Hudson, J. G.; Noble, S. R., Jr.

2017-12-01

Conversion of sulfur dioxide to sulfate within cloud droplets increases the sizes and decreases the critical supersaturation, Sc, of cloud residual particles that had nucleated the droplets. Since other particles remain at the same sizes and Sc a size and Sc gap is often observed. Hudson et al. (2015) showed higher cloud droplet concentrations (Nc) in stratus clouds associated with bimodal high-resolution CCN spectra from the DRI CCN spectrometer compared to clouds associated with unimodal CCN spectra (not cloud processed). Here we show that CCN spectral shape (bimodal or unimodal) affects all aspects of stratus cloud microphysics and drizzle. Panel A shows mean differential cloud droplet spectra that have been divided according to traditional slopes, k, of the 131 measured CCN spectra in the Marine Stratus/Stratocumulus Experiment (MASE) off the Central California coast. K is generally high within the supersaturation, S, range of stratus clouds (< 0.5%). Because cloud processing decreases Sc of some particles, it reduces k. Panel A shows higher concentrations of small cloud droplets apparently grown on lower k CCN than clouds grown on higher k CCN. At small droplet sizes the concentrations follow the k order of the legend, black, red, green, blue (lowest to highest k). Above 13 µm diameter the lines cross and the hierarchy reverses so that blue (highest k) has the highest concentrations followed by green, red and black (lowest k). This reversed hierarchy continues into the drizzle size range (panel B) where the most drizzle drops, Nd, are in clouds grown on the least cloud-processed CCN (blue), while clouds grown on the most processed CCN (black) have the lowest Nd. Suppression of stratus cloud drizzle by cloud processing is an additional 2nd indirect aerosol effect (IAE) that along with the enhancement of 1st IAE by higher Nc (panel A) are above and beyond original IAE. However, further similar analysis is needed in other cloud regimes to determine if MASE was

MODIS Snow Cover Mapping Decision Tree Technique: Snow and Cloud Discrimination

Science.gov (United States)

Riggs, George A.; Hall, Dorothy K.

2010-01-01

Accurate mapping of snow cover continues to challenge cryospheric scientists and modelers. The Moderate-Resolution Imaging Spectroradiometer (MODIS) snow data products have been used since 2000 by many investigators to map and monitor snow cover extent for various applications. Users have reported on the utility of the products and also on problems encountered. Three problems or hindrances in the use of the MODIS snow data products that have been reported in the literature are: cloud obscuration, snow/cloud confusion, and snow omission errors in thin or sparse snow cover conditions. Implementation of the MODIS snow algorithm in a decision tree technique using surface reflectance input to mitigate those problems is being investigated. The objective of this work is to use a decision tree structure for the snow algorithm. This should alleviate snow/cloud confusion and omission errors and provide a snow map with classes that convey information on how snow was detected, e.g. snow under clear sky, snow tinder cloud, to enable users' flexibility in interpreting and deriving a snow map. Results of a snow cover decision tree algorithm are compared to the standard MODIS snow map and found to exhibit improved ability to alleviate snow/cloud confusion in some situations allowing up to about 5% increase in mapped snow cover extent, thus accuracy, in some scenes.

A Technique for Mitigating Thermal Stress and Extending Life Cycle of Power Electronic Converters Used for Wind Turbines

Directory of Open Access Journals (Sweden)

Canras Batunlu

2015-11-01

Full Text Available Over the last two decades, various models have been developed to assess and improve the reliability of power electronic conversion systems (PECs with a focus on those used for wind turbines. However, only few studies have dealt with mitigating the PECs thermo-mechanical effects on their reliability taking into account variations in wind characteristics. This work critically investigates this issue and attempts to offer a mitigating technique by, first, developing realistic full scale (FS and partial scale (PS induction generator models combined with two level back-to-back PECs. Subsequently, deriving a driving algorithm, which reduces PEC’s operating temperature by controlling its switching patterns. The developed switching procedure ensures minimum temperature fluctuations by adapting the variable DC link and system’s frequency of operation. It was found for both FS and PS topologies, that the generator side converters have higher mean junction temperatures where the grid side ones have more fluctuations on their thermal profile. The FS and PS cycling temperatures were reduced by 12 °C and 5 °C, respectively. Moreover, this led to a significant improvement in stress; approximately 27 MPa stress reduction for the FS induction generator PEC.

Considerations about Cloud Services: Learning

Directory of Open Access Journals (Sweden)

Riccardo Cognini

2013-05-01

Full Text Available Cloud services are ubiquitous: for small to large companies the phenomenon of cloud service is nowadays a standard business practice. This paper would compile an analysis over a possible implementation of a cloud system, treating especially the legal aspect of this theme. In the Italian market has a large number of issues arise form cloud computing. First of all, this paper investigates the legal issues associated to cloud computing, specific contractual scheme that is able to define rights a duties both of user (private and/or public body and cloud provider. On one side there is all the EU legislative production related to privacy over electronic communication and, furthermore, the Privacy Directive is under a revision process to be more adaptable to new challenges of decentralized data treatment, but concretely there are no any structured and well defined legal instruments. Objectives: we present a possible solution to address the uncertainty of this area, starting from the EU legislative production with the help of the specific Italian scenario that could offer an operative solution. Indeed the Italian legal system is particularly adaptable to changing technologies and it could use as better as possible to adapt the already existing legal tools to this new technological era. Prior work: after an introduction to the state of the art, we show the main issues and their critical points that must be solved. Approach: observation of the state of the art to propose a new approach to find the suitable disciple

Improved cloud parameterization for Arctic climate simulations based on satellite data

Science.gov (United States)

Klaus, Daniel; Dethloff, Klaus; Dorn, Wolfgang; Rinke, Annette

2015-04-01

The defective representation of Arctic cloud processes and properties remains a crucial problem in climate modelling and in reanalysis products. Satellite-based cloud observations (MODIS and CPR/CALIOP) and single-column model simulations (HIRHAM5-SCM) were exploited to evaluate and improve the simulated Arctic cloud cover of the atmospheric regional climate model HIRHAM5. The ECMWF reanalysis dataset 'ERA-Interim' (ERAint) was used for the model initialization, the lateral boundary forcing as well as the dynamical relaxation inside the pan-Arctic domain. HIRHAM5 has a horizontal resolution of 0.25° and uses 40 pressure-based and terrain-following vertical levels. In comparison with the satellite observations, the HIRHAM5 control run (HH5ctrl) systematically overestimates total cloud cover, but to a lesser extent than ERAint. The underestimation of high- and mid-level clouds is strongly outweighed by the overestimation of low-level clouds. Numerous sensitivity studies with HIRHAM5-SCM suggest (1) the parameter tuning, enabling a more efficient Bergeron-Findeisen process, combined with (2) an extension of the prognostic-statistical (PS) cloud scheme, enabling the use of negatively skewed beta distributions. This improved model setup was then used in a corresponding HIRHAM5 sensitivity run (HH5sens). While the simulated high- and mid-level cloud cover is improved only to a limited extent, the large overestimation of low-level clouds can be systematically and significantly reduced, especially over sea ice. Consequently, the multi-year annual mean area average of total cloud cover with respect to sea ice is almost 14% lower than in HH5ctrl. Overall, HH5sens slightly underestimates the observed total cloud cover but shows a halved multi-year annual mean bias of 2.2% relative to CPR/CALIOP at all latitudes north of 60° N. Importantly, HH5sens produces a more realistic ratio between the cloud water and ice content. The considerably improved cloud simulation manifests in

Cloud vertical profiles derived from CALIPSO and CloudSat and a comparison with MODIS derived clouds

Science.gov (United States)

Kato, S.; Sun-Mack, S.; Miller, W. F.; Rose, F. G.; Minnis, P.; Wielicki, B. A.; Winker, D. M.; Stephens, G. L.; Charlock, T. P.; Collins, W. D.; Loeb, N. G.; Stackhouse, P. W.; Xu, K.

2008-05-01

CALIPSO and CloudSat from the a-train provide detailed information of vertical distribution of clouds and aerosols. The vertical distribution of cloud occurrence is derived from one month of CALIPSO and CloudSat data as a part of the effort of merging CALIPSO, CloudSat and MODIS with CERES data. This newly derived cloud profile is compared with the distribution of cloud top height derived from MODIS on Aqua from cloud algorithms used in the CERES project. The cloud base from MODIS is also estimated using an empirical formula based on the cloud top height and optical thickness, which is used in CERES processes. While MODIS detects mid and low level clouds over the Arctic in April fairly well when they are the topmost cloud layer, it underestimates high- level clouds. In addition, because the CERES-MODIS cloud algorithm is not able to detect multi-layer clouds and the empirical formula significantly underestimates the depth of high clouds, the occurrence of mid and low-level clouds is underestimated. This comparison does not consider sensitivity difference to thin clouds but we will impose an optical thickness threshold to CALIPSO derived clouds for a further comparison. The effect of such differences in the cloud profile to flux computations will also be discussed. In addition, the effect of cloud cover to the top-of-atmosphere flux over the Arctic using CERES SSF and FLASHFLUX products will be discussed.

CLOUD EDUCATIONAL RESOURCES FOR PHYSICS LEARNING RESEARCHES SUPPORT

Directory of Open Access Journals (Sweden)

Oleksandr V. Merzlykin

2015-10-01

Full Text Available The definition of cloud educational resource is given in paper. Its program and information components are characterized. The virtualization as the technological ground of transforming from traditional electronic educational resources to cloud ones is reviewed. Such levels of virtualization are described: data storage device virtualization (Data as Service, hardware virtualization (Hardware as Service, computer virtualization (Infrastructure as Service, software system virtualization (Platform as Service, «desktop» virtualization (Desktop as Service, software user interface virtualization (Software as Service. Possibilities of designing the cloud educational resources system for physics learning researches support taking into account standards of learning objects metadata (accessing via OAI-PMH protocol and standards of learning tools interoperability (LTI are shown. The example of integration cloud educational resources into Moodle learning management system with use of OAI-PMH and LTI is given.

Secondary Electron Yield on Cryogenic Surfaces as a Function of Physisorbed Gases

CERN Document Server

Kuzucan, Asena; Taborelli, Mauro

2011-01-01

In LHC the electron cloud induced by photoelectrons, gas ionization and secondary electrons emitted from the beam pipe walls could be a limitation of the performance. The electron cloud induce heat load on the cryogenic system, cause pressure rise, emittance growth and beam instabilities, which in the end will limit the beam’s lifetime. Beam- induced multipacting, which can arise through oscillatory motion of photoelectrons and low-energy secondary electrons bouncing back and forth between opposite walls of the vacuum chamber during successive passage of proton bunches, represent therefore a potential problem for the machine. The secondary electron yield (SEY) is one of the key parameters for the electron cloud build up and multipacting phenomenon. An electron cloud occurs if the metal surface secondary electron yield is high enough for electron multiplication. This parameter has been extensively studied on room temperature samples but uncertainties remain for samples at cryogenic temperature. Indeed, at l...

Virtual machine migration in an over-committed cloud

KAUST Repository

Zhang, Xiangliang

2012-04-01

While early emphasis of Infrastructure as a Service (IaaS) clouds was on providing resource elasticity to end users, providers are increasingly interested in over-committing their resources to maximize the utilization and returns of their capital investments. In principle, over-committing resources hedges that users - on average - only need a small portion of their leased resources. When such hedge fails (i.e., resource demand far exceeds available physical capacity), providers must mitigate this provider-induced overload, typically by migrating virtual machines (VMs) to underutilized physical machines. Recent works on VM placement and migration assume the availability of target physical machines [1], [2]. However, in an over-committed cloud data center, this is not the case. VM migration can even trigger cascading overloads if performed haphazardly. In this paper, we design a new VM migration algorithm (called Scattered) that minimizes VM migrations in over-committed data centers. Compared to a traditional implementation, our algorithm can balance host utilization across all time epochs. Using real-world data traces from an enterprise cloud, we show that our migration algorithm reduces the risk of overload, minimizes the number of needed migrations, and has minimal impact on communication cost between VMs. © 2012 IEEE.

Rough surface mitigates electron and gas emission

International Nuclear Information System (INIS)

Molvik, A.

2004-01-01

Heavy-ion beams impinging on surfaces near grazing incidence (to simulate the loss of halo ions) generate copious amounts of electrons and gas that can degrade the beam. We measured emission coefficients of η e (le) 130 and η 0 ∼ 10 4 respectively, with 1 MeV K + incident on stainless steel. Electron emission scales as η e ∝ 1/cos(θ), where θ is the ion angle of incidence relative to normal. If we were to roughen a surface by blasting it with glass beads, then ions that were near grazing incidence (90 o ) on smooth surface would strike the rims of the micro-craters at angles closer to normal incidence. This should reduce the electron emission: the factor of 10 reduction, Fig. 1(a), implies an average angle of incidence of 62 o . Gas desorption varies more slowly with θ (Fig. 1(b)) decreasing a factor of ∼2, and along with the electron emission is independent of the angle of incidence on a rough surface. In a quadrupole magnet, electrons emitted by lost primary ions are trapped near the wall by the magnetic field, but grazing incidence ions can backscatter and strike the wall a second time at an azimuth where magnetic field lines intercept the beam. Then, electrons can exist throughout the beam (see the simulations of Cohen, HIF News 1-2/04). The SRIM (TRIM) Monte Carlo code predicts that 60-70% of 1 MeV K + ions backscatter when incident at 88-89 o from normal on a smooth surface. The scattered ions are mostly within ∼10 o of the initial direction but a few scatter by up to 90 o . Ion scattering decreases rapidly away from grazing incidence, Fig. 1(c ). At 62 deg. the predicted ion backscattering (from a rough surface) is 3%, down a factor of 20 from the peak, which should significantly reduce electrons in the beam from lost halo ions. These results are published in Phys. Rev. ST - Accelerators and Beams

A study of shock mitigating materials in a split Hopkinson bar configuration. Phase 1

International Nuclear Information System (INIS)

Bateman, V.I.; Brown, F.A.; Hansen, N.R.

1998-06-01

Sandia National Laboratories (SNL) designs mechanical systems with electronics that must survive high shock environments. These mechanical systems include penetrators that must survive soil, rock, and ice penetration, nuclear transportation casks that must survive transportation environments, and laydown weapons that must survive delivery impact of 125 fps. These mechanical systems contain electronics that may operate during and after the high shock environment and that must be protected from the high shock environments. A study has been started to improve the packaging techniques for the advanced electronics utilized in these mechanical systems because current packaging techniques are inadequate for these more sensitive electronics. In many cases, it has been found that the packaging techniques currently used not only do not mitigate the shock environment but actually amplify the shock environment. An ambitious goal for this packaging study is to avoid amplification and possibly attenuate the shock environment before it reaches the electronics contained in the various mechanical systems. As part of the investigation of packaging techniques, a two phase study of shock mitigating materials is being conducted. The purpose of the first phase reported here is to examine the performance of a joint that consists of shock mitigating material sandwiched in between steel and to compare the performance of the shock mitigating materials. A split Hopkinson bar experimental configuration simulates this joint and has been used to study the shock mitigating characteristics of seventeen, unconfined materials. The nominal input for these tests is an incident compressive wave with 50 fps peak (1,500 micro var-epsilon peak) amplitude and a 100 micros duration (measured at 10% amplitude)

A Survey of Denial-of-Service and Distributed Denial of Service Attacks and Defenses in Cloud Computing

Directory of Open Access Journals (Sweden)

Adrien Bonguet

2017-08-01

Full Text Available Cloud Computing is a computing model that allows ubiquitous, convenient and on-demand access to a shared pool of highly configurable resources (e.g., networks, servers, storage, applications and services. Denial-of-Service (DoS and Distributed Denial-of-Service (DDoS attacks are serious threats to the Cloud services’ availability due to numerous new vulnerabilities introduced by the nature of the Cloud, such as multi-tenancy and resource sharing. In this paper, new types of DoS and DDoS attacks in Cloud Computing are explored, especially the XML-DoS and HTTP-DoS attacks, and some possible detection and mitigation techniques are examined. This survey also provides an overview of the existing defense solutions and investigates the experiments and metrics that are usually designed and used to evaluate their performance, which is helpful for the future research in the domain.

iMAGE cloud: medical image processing as a service for regional healthcare in a hybrid cloud environment.

Science.gov (United States)

Liu, Li; Chen, Weiping; Nie, Min; Zhang, Fengjuan; Wang, Yu; He, Ailing; Wang, Xiaonan; Yan, Gen

2016-11-01

To handle the emergence of the regional healthcare ecosystem, physicians and surgeons in various departments and healthcare institutions must process medical images securely, conveniently, and efficiently, and must integrate them with electronic medical records (EMRs). In this manuscript, we propose a software as a service (SaaS) cloud called the iMAGE cloud. A three-layer hybrid cloud was created to provide medical image processing services in the smart city of Wuxi, China, in April 2015. In the first step, medical images and EMR data were received and integrated via the hybrid regional healthcare network. Then, traditional and advanced image processing functions were proposed and computed in a unified manner in the high-performance cloud units. Finally, the image processing results were delivered to regional users using the virtual desktop infrastructure (VDI) technology. Security infrastructure was also taken into consideration. Integrated information query and many advanced medical image processing functions-such as coronary extraction, pulmonary reconstruction, vascular extraction, intelligent detection of pulmonary nodules, image fusion, and 3D printing-were available to local physicians and surgeons in various departments and healthcare institutions. Implementation results indicate that the iMAGE cloud can provide convenient, efficient, compatible, and secure medical image processing services in regional healthcare networks. The iMAGE cloud has been proven to be valuable in applications in the regional healthcare system, and it could have a promising future in the healthcare system worldwide.

Measuring agreement between decision support reminders: the cloud vs. the local expert

OpenAIRE

Dixon, Brian Edward; Simonaitis, Linas; Perkins, Susan M; Wright, Adam; Middleton, Blackford

2014-01-01

Background: A cloud-based clinical decision support system (CDSS) was implemented to remotely provide evidence-based guideline reminders in support of preventative health. Following implementation, we measured the agreement between preventive care reminders generated by an existing, local CDSS and the new, cloud-based CDSS operating on the same patient visit data. Methods: Electronic health record data for the same set of patients seen in primary care were sent to both the cloud-based web ser...

Stratocumulus Cloud Top Radiative Cooling and Cloud Base Updraft Speeds

Science.gov (United States)

Kazil, J.; Feingold, G.; Balsells, J.; Klinger, C.

2017-12-01

Cloud top radiative cooling is a primary driver of turbulence in the stratocumulus-topped marine boundary. A functional relationship between cloud top cooling and cloud base updraft speeds may therefore exist. A correlation of cloud top radiative cooling and cloud base updraft speeds has been recently identified empirically, providing a basis for satellite retrieval of cloud base updraft speeds. Such retrievals may enable analysis of aerosol-cloud interactions using satellite observations: Updraft speeds at cloud base co-determine supersaturation and therefore the activation of cloud condensation nuclei, which in turn co-determine cloud properties and precipitation formation. We use large eddy simulation and an off-line radiative transfer model to explore the relationship between cloud-top radiative cooling and cloud base updraft speeds in a marine stratocumulus cloud over the course of the diurnal cycle. We find that during daytime, at low cloud water path (CWP correlated, in agreement with the reported empirical relationship. During the night, in the absence of short-wave heating, CWP builds up (CWP > 50 g m-2) and long-wave emissions from cloud top saturate, while cloud base heating increases. In combination, cloud top cooling and cloud base updrafts become weakly anti-correlated. A functional relationship between cloud top cooling and cloud base updraft speed can hence be expected for stratocumulus clouds with a sufficiently low CWP and sub-saturated long-wave emissions, in particular during daytime. At higher CWPs, in particular at night, the relationship breaks down due to saturation of long-wave emissions from cloud top.

Cloud networking understanding cloud-based data center networks

CERN Document Server

Lee, Gary

2014-01-01

Cloud Networking: Understanding Cloud-Based Data Center Networks explains the evolution of established networking technologies into distributed, cloud-based networks. Starting with an overview of cloud technologies, the book explains how cloud data center networks leverage distributed systems for network virtualization, storage networking, and software-defined networking. The author offers insider perspective to key components that make a cloud network possible such as switch fabric technology and data center networking standards. The final chapters look ahead to developments in architectures

Importance of including ammonium sulfate ((NH42SO4 aerosols for ice cloud parameterization in GCMs

Directory of Open Access Journals (Sweden)

P. S. Bhattacharjee

2010-02-01

Full Text Available A common deficiency of many cloud-physics parameterizations including the NASA's microphysics of clouds with aerosol-cloud interactions (hereafter called McRAS-AC is that they simulate lesser (larger than the observed ice cloud particle number (size. A single column model (SCM of McRAS-AC physics of the GEOS4 Global Circulation Model (GCM together with an adiabatic parcel model (APM for ice-cloud nucleation (IN of aerosols were used to systematically examine the influence of introducing ammonium sulfate (NH42SO4 aerosols in McRAS-AC and its influence on the optical properties of both liquid and ice clouds. First an (NH42SO4 parameterization was included in the APM to assess its effect on clouds vis-à-vis that of the other aerosols. Subsequently, several evaluation tests were conducted over the ARM Southern Great Plain (SGP and thirteen other locations (sorted into pristine and polluted conditions distributed over marine and continental sites with the SCM. The statistics of the simulated cloud climatology were evaluated against the available ground and satellite data. The results showed that inclusion of (NH42SO4 into McRAS-AC of the SCM made a remarkable improvement in the simulated effective radius of ice cloud particulates. However, the corresponding ice-cloud optical thickness increased even more than the observed. This can be caused by lack of horizontal cloud advection not performed in the SCM. Adjusting the other tunable parameters such as precipitation efficiency can mitigate this deficiency. Inclusion of ice cloud particle splintering invoked empirically further reduced simulation biases. Overall, these changes make a substantial improvement in simulated cloud optical properties and cloud distribution particularly over the Intertropical Convergence Zone (ITCZ in the GCM.

How to build a cloud chamber?; Comment realiser une chambre a bouillard?

Energy Technology Data Exchange (ETDEWEB)

Mariaud, C. [Lycee Rene Descartes, 37000 Tours (France)

2012-01-15

The cloud chamber had its heyday in the first half of last century and allowed the discovery of new particles such as the anti-electron, the muon and the neutral and the charged kaon. The bubble chamber replaced it in the mid fifties. This article recalls the principle of the cloud chamber and shows, in a detailed way, how to proceed to build one with on-the-shelf materials. This design is based on the use of isopropanol whose liquefaction through the form of droplets materializes the track of the particle and on the use of combined Peltier cells (instead of CO{sub 2} snow) to cool the chamber. This cloud chamber has been successfully used in schools to observe particles mainly electrons, alphas and muons generated by cosmic rays. (A.C.)

Mobile healthcare information management utilizing Cloud Computing and Android OS.

Science.gov (United States)

Doukas, Charalampos; Pliakas, Thomas; Maglogiannis, Ilias

2010-01-01

Cloud Computing provides functionality for managing information data in a distributed, ubiquitous and pervasive manner supporting several platforms, systems and applications. This work presents the implementation of a mobile system that enables electronic healthcare data storage, update and retrieval using Cloud Computing. The mobile application is developed using Google's Android operating system and provides management of patient health records and medical images (supporting DICOM format and JPEG2000 coding). The developed system has been evaluated using the Amazon's S3 cloud service. This article summarizes the implementation details and presents initial results of the system in practice.

Cybersecurity and privacy issues for socially integrated mobile healthcare applications operating in a multi-cloud environment.

Science.gov (United States)

Al-Muhtadi, Jalal; Shahzad, Basit; Saleem, Kashif; Jameel, Wasif; Orgun, Mehmet A

2017-05-01

Social media has enabled information-sharing across massively large networks of people without spending much financial resources and time that are otherwise required in the print and electronic media. Mobile-based social media applications have overwhelmingly changed the information-sharing perspective. However, with the advent of such applications at an unprecedented scale, the privacy of the information is compromised to a larger extent if breach mitigation is not adequate. Since healthcare applications are also being developed for mobile devices so that they also benefit from the power of social media, cybersecurity privacy concerns for such sensitive applications have become critical. This article discusses the architecture of a typical mobile healthcare application, in which customized privacy levels are defined for the individuals participating in the system. It then elaborates on how the communication across a social network in a multi-cloud environment can be made more secure and private, especially for healthcare applications.

A new privacy preserving technique for cloud service user endorsement using multi-agents

Directory of Open Access Journals (Sweden)

D. Chandramohan

2016-01-01

Full Text Available In data analysis the present focus on storage services are leveraged to attain its crucial part while user data get compromised. In the recent years service user’s valuable information has been utilized by unauthorized users and service providers. This paper examines the privacy awareness and importance of user’s secrecy preserving in the current cloud computing era. Gradually the information kept under the cloud environment gets increased due to its elasticity and availability. However, highly sensitive information is in a serious attack from various sources. Once private information gets misused, the probability of privacy breaching increases which thereby reduces user’s trust on cloud providers. In the modern internet world, information management and maintenance is one among the most decisive tasks. Information stored in the cloud by the finance, healthcare, government sectors, etc. makes it all the more challenging since such tasks are to be handled globally. The present scenario therefore demands a new Petri-net Privacy Preserving Framework (PPPF for safeguarding user’s privacy and, providing consistent and breach-less services from the cloud. This paper illustrates the design of PPPF and mitigates the cloud provider’s trust among users. The proposed technique conveys and collaborates with Privacy Preserving Cohesion Technique (PPCT, to develop validate, promote, adapt and also increase the need for data privacy. Moreover, this paper focuses on clinching and verification of unknown user intervention into the confidential data present in storage area and ensuring the performance of the cloud services. It also acts as an information preserving guard for high secrecy data storage areas.

Securing services in the cloud: an investigation of the threats and the mitigations

Science.gov (United States)

Farroha, Bassam S.; Farroha, Deborah L.

2012-05-01

The stakeholder's security concerns over data in the clouds (Voice, Video and Text) are a real concern to DoD, the IC and private sector. This is primarily due to the lack of physical isolation of data when migrating to shared infrastructure platforms. The security concerns are related to privacy and regulatory compliance required in many industries (healthcare, financial, law enforcement, DoD, etc) and the corporate knowledge databases. The new paradigm depends on the service provider to ensure that the customer's information is continuously monitored and is kept available, secure, access controlled and isolated from potential adversaries.

Time evolution of artificial plasma cloud in atmospheric environment

International Nuclear Information System (INIS)

Lu Qiming; Yang Weihong; Liu Wandong

2004-01-01

By analyzing the time evolution of artificial plasma cloud in the high altitude of atmospheric environment, the authors found that there are two zones, an exponential attenuation zone and a linearly attenuating zone, existing in the spatial distribution of electron density of the artificial plasma clouds. The plasma generator's particle flux density only contributes to the exponential attenuation zone, and has no effect on the linear attenuation zone. The average electron density in the linear attenuation zone is about 10 -5 of neutral particle density, and can diffuse over a wider area. The conclusion will supply some valuable references to the research of electromagnetic wave and artificial plasma interaction, the plasma invisibleness research of missile and special aerocraft, and the design of artificial plasma source. (authors)

Formation of giant molecular clouds in global spiral structures: the role of orbital dynamics and cloud-cloud collisions

International Nuclear Information System (INIS)

Roberts, W.W. Jr.; Stewart, G.R.

1987-01-01

The different roles played by orbital dynamics and dissipative cloud-cloud collisions in the formation of giant molecular clouds (GMCs) in a global spiral structure are investigated. The interstellar medium (ISM) is simulated by a system of particles, representing clouds, which orbit in a spiral-perturbed, galactic gravitational field. The overall magnitude and width of the global cloud density distribution in spiral arms is very similar in the collisional and collisionless simulations. The results suggest that the assumed number density and size distribution of clouds and the details of individual cloud-cloud collisions have relatively little effect on these features. Dissipative cloud-cloud collisions play an important steadying role for the cloud system's global spiral structure. Dissipative cloud-cloud collisions also damp the relative velocity dispersion of clouds in massive associations and thereby aid in the effective assembling of GMC-like complexes

Evaluation of Passive Multilayer Cloud Detection Using Preliminary CloudSat and CALIPSO Cloud Profiles

Science.gov (United States)

Minnis, P.; Sun-Mack, S.; Chang, F.; Huang, J.; Nguyen, L.; Ayers, J. K.; Spangenberg, D. A.; Yi, Y.; Trepte, C. R.

2006-12-01

During the last few years, several algorithms have been developed to detect and retrieve multilayered clouds using passive satellite data. Assessing these techniques has been difficult due to the need for active sensors such as cloud radars and lidars that can "see" through different layers of clouds. Such sensors have been available only at a few surface sites and on aircraft during field programs. With the launch of the CALIPSO and CloudSat satellites on April 28, 2006, it is now possible to observe multilayered systems all over the globe using collocated cloud radar and lidar data. As part of the A- Train, these new active sensors are also matched in time ad space with passive measurements from the Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer - EOS (AMSR-E). The Clouds and the Earth's Radiant Energy System (CERES) has been developing and testing algorithms to detect ice-over-water overlapping cloud systems and to retrieve the cloud liquid path (LWP) and ice water path (IWP) for those systems. One technique uses a combination of the CERES cloud retrieval algorithm applied to MODIS data and a microwave retrieval method applied to AMSR-E data. The combination of a CO2-slicing cloud retireval technique with the CERES algorithms applied to MODIS data (Chang et al., 2005) is used to detect and analyze such overlapped systems that contain thin ice clouds. A third technique uses brightness temperature differences and the CERES algorithms to detect similar overlapped methods. This paper uses preliminary CloudSat and CALIPSO data to begin a global scale assessment of these different methods. The long-term goals are to assess and refine the algorithms to aid the development of an optimal combination of the techniques to better monitor ice 9and liquid water clouds in overlapped conditions.

The electromagnetic virtual cloud of the ground-state hydrogen atom - a quantum field theory approach

International Nuclear Information System (INIS)

Radozycki, T.

1990-01-01

The properties of the virtual cloud around the hydrogen atom in the ground state are studied with the use of quantum field theory methods. The relativistic expression for the electromagnetic energy density around the atom, with the electron spin taken into account, is obtained. The distribution of the angular momentum contained in the cloud and the self-interaction kernel for the electrons bound in atom are also investigated. (author)

Web-based Tsunami Early Warning System with instant Tsunami Propagation Calculations in the GPU Cloud

Science.gov (United States)

Hammitzsch, M.; Spazier, J.; Reißland, S.

2014-12-01

Usually, tsunami early warning and mitigation systems (TWS or TEWS) are based on several software components deployed in a client-server based infrastructure. The vast majority of systems importantly include desktop-based clients with a graphical user interface (GUI) for the operators in early warning centers. However, in times of cloud computing and ubiquitous computing the use of concepts and paradigms, introduced by continuously evolving approaches in information and communications technology (ICT), have to be considered even for early warning systems (EWS). Based on the experiences and the knowledge gained in three research projects - 'German Indonesian Tsunami Early Warning System' (GITEWS), 'Distant Early Warning System' (DEWS), and 'Collaborative, Complex, and Critical Decision-Support in Evolving Crises' (TRIDEC) - new technologies are exploited to implement a cloud-based and web-based prototype to open up new prospects for EWS. This prototype, named 'TRIDEC Cloud', merges several complementary external and in-house cloud-based services into one platform for automated background computation with graphics processing units (GPU), for web-mapping of hazard specific geospatial data, and for serving relevant functionality to handle, share, and communicate threat specific information in a collaborative and distributed environment. The prototype in its current version addresses tsunami early warning and mitigation. The integration of GPU accelerated tsunami simulation computations have been an integral part of this prototype to foster early warning with on-demand tsunami predictions based on actual source parameters. However, the platform is meant for researchers around the world to make use of the cloud-based GPU computation to analyze other types of geohazards and natural hazards and react upon the computed situation picture with a web-based GUI in a web browser at remote sites. The current website is an early alpha version for demonstration purposes to give the

HIGH-ENERGY PARTICLES FLUX ORIGIN IN THE CLOUDS, DARK LIGHTNING

Directory of Open Access Journals (Sweden)

Kuznetsov, V.V.

2016-11-01

Full Text Available Problem of high-energy particles flux origin in clouds is discussed. Conditions in which dark lightning preceding the ordinary one and creating additional ionization, fluxes of fast electrons with MeV energy prior to the earthquake detected among lightning initiating ball-lightning, glow, sprites are considered. All above phenomena appear to be of general nature founded on quantum entanglement of hydrogen bonds protons in water clasters inside clouds.

Examination of Icing Induced Loss of Control and Its Mitigations

Science.gov (United States)

Reehorst, Andrew L.; Addy, Harold E., Jr.; Colantonio, Renato O.

2010-01-01

Factors external to the aircraft are often a significant causal factor in loss of control (LOC) accidents. In today s aviation world, very few accidents stem from a single cause and typically have a number of causal factors that culminate in a LOC accident. Very often the "trigger" that initiates an accident sequence is an external environment factor. In a recent NASA statistical analysis of LOC accidents, aircraft icing was shown to be the most common external environmental LOC causal factor for scheduled operations. When investigating LOC accident or incidents aircraft icing causal factors can be categorized into groups of 1) in-flight encounter with super-cooled liquid water clouds, 2) take-off with ice contamination, or 3) in-flight encounter with high concentrations of ice crystals. As with other flight hazards, icing induced LOC accidents can be prevented through avoidance, detection, and recovery mitigations. For icing hazards, avoidance can take the form of avoiding flight into icing conditions or avoiding the hazard of icing by making the aircraft tolerant to icing conditions. Icing detection mitigations can take the form of detecting icing conditions or detecting early performance degradation caused by icing. Recovery from icing induced LOC requires flight crew or automated systems capable of accounting for reduced aircraft performance and degraded control authority during the recovery maneuvers. In this report we review the icing induced LOC accident mitigations defined in a recent LOC study and for each mitigation describe a research topic required to enable or strengthen the mitigation. Many of these research topics are already included in ongoing or planned NASA icing research activities or are being addressed by members of the icing research community. These research activities are described and the status of the ongoing or planned research to address the technology needs is discussed

Cloud Computing Fundamentals

Science.gov (United States)

Furht, Borko

In the introductory chapter we define the concept of cloud computing and cloud services, and we introduce layers and types of cloud computing. We discuss the differences between cloud computing and cloud services. New technologies that enabled cloud computing are presented next. We also discuss cloud computing features, standards, and security issues. We introduce the key cloud computing platforms, their vendors, and their offerings. We discuss cloud computing challenges and the future of cloud computing.

ELECTRON TRAPPING IN WIGGLER AND QUADRUPOLE MAGNETS OF CESRTA

International Nuclear Information System (INIS)

Wang, Lanfa

2010-01-01

The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R and D (1). One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in the wiggler and quadrupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with long lifetime in a quadrupole magnet due to the mirror field trapping mechanism and photoelectrons produced in the wiggler zero field zone have long lifetime due to their complicated trajectory.

Software Defined Networking challenges and future direction: A case study of implementing SDN features on OpenStack private cloud

International Nuclear Information System (INIS)

Shamugam, Veeramani; Murray, I; Leong, J A; Sidhu, Amandeep S

2016-01-01

Cloud computing provides services on demand instantly, such as access to network infrastructure consisting of computing hardware, operating systems, network storage, database and applications. Network usage and demands are growing at a very fast rate and to meet the current requirements, there is a need for automatic infrastructure scaling. Traditional networks are difficult to automate because of the distributed nature of their decision making process for switching or routing which are collocated on the same device. Managing complex environments using traditional networks is time-consuming and expensive, especially in the case of generating virtual machines, migration and network configuration. To mitigate the challenges, network operations require efficient, flexible, agile and scalable software defined networks (SDN). This paper discuss various issues in SDN and suggests how to mitigate the network management related issues. A private cloud prototype test bed was setup to implement the SDN on the OpenStack platform to test and evaluate the various network performances provided by the various configurations. (paper)

Software Defined Networking challenges and future direction: A case study of implementing SDN features on OpenStack private cloud

Science.gov (United States)

Shamugam, Veeramani; Murray, I.; Leong, J. A.; Sidhu, Amandeep S.

2016-03-01

Cloud computing provides services on demand instantly, such as access to network infrastructure consisting of computing hardware, operating systems, network storage, database and applications. Network usage and demands are growing at a very fast rate and to meet the current requirements, there is a need for automatic infrastructure scaling. Traditional networks are difficult to automate because of the distributed nature of their decision making process for switching or routing which are collocated on the same device. Managing complex environments using traditional networks is time-consuming and expensive, especially in the case of generating virtual machines, migration and network configuration. To mitigate the challenges, network operations require efficient, flexible, agile and scalable software defined networks (SDN). This paper discuss various issues in SDN and suggests how to mitigate the network management related issues. A private cloud prototype test bed was setup to implement the SDN on the OpenStack platform to test and evaluate the various network performances provided by the various configurations.

Open Source Cloud-Based Technologies for Bim

Science.gov (United States)

Logothetis, S.; Karachaliou, E.; Valari, E.; Stylianidis, E.

2018-05-01

This paper presents a Cloud-based open source system for storing and processing data from a 3D survey approach. More specifically, we provide an online service for viewing, storing and analysing BIM. Cloud technologies were used to develop a web interface as a BIM data centre, which can handle large BIM data using a server. The server can be accessed by many users through various electronic devices anytime and anywhere so they can view online 3D models using browsers. Nowadays, the Cloud computing is engaged progressively in facilitating BIM-based collaboration between the multiple stakeholders and disciplinary groups for complicated Architectural, Engineering and Construction (AEC) projects. Besides, the development of Open Source Software (OSS) has been rapidly growing and their use tends to be united. Although BIM and Cloud technologies are extensively known and used, there is a lack of integrated open source Cloud-based platforms able to support all stages of BIM processes. The present research aims to create an open source Cloud-based BIM system that is able to handle geospatial data. In this effort, only open source tools will be used; from the starting point of creating the 3D model with FreeCAD to its online presentation through BIMserver. Python plug-ins will be developed to link the two software which will be distributed and freely available to a large community of professional for their use. The research work will be completed by benchmarking four Cloud-based BIM systems: Autodesk BIM 360, BIMserver, Graphisoft BIMcloud and Onuma System, which present remarkable results.

OPEN SOURCE CLOUD-BASED TECHNOLOGIES FOR BIM

Directory of Open Access Journals (Sweden)

S. Logothetis

2018-05-01

Full Text Available This paper presents a Cloud-based open source system for storing and processing data from a 3D survey approach. More specifically, we provide an online service for viewing, storing and analysing BIM. Cloud technologies were used to develop a web interface as a BIM data centre, which can handle large BIM data using a server. The server can be accessed by many users through various electronic devices anytime and anywhere so they can view online 3D models using browsers. Nowadays, the Cloud computing is engaged progressively in facilitating BIM-based collaboration between the multiple stakeholders and disciplinary groups for complicated Architectural, Engineering and Construction (AEC projects. Besides, the development of Open Source Software (OSS has been rapidly growing and their use tends to be united. Although BIM and Cloud technologies are extensively known and used, there is a lack of integrated open source Cloud-based platforms able to support all stages of BIM processes. The present research aims to create an open source Cloud-based BIM system that is able to handle geospatial data. In this effort, only open source tools will be used; from the starting point of creating the 3D model with FreeCAD to its online presentation through BIMserver. Python plug-ins will be developed to link the two software which will be distributed and freely available to a large community of professional for their use. The research work will be completed by benchmarking four Cloud-based BIM systems: Autodesk BIM 360, BIMserver, Graphisoft BIMcloud and Onuma System, which present remarkable results.

Toward real-time Monte Carlo simulation using a commercial cloud computing infrastructure.

Science.gov (United States)

Wang, Henry; Ma, Yunzhi; Pratx, Guillem; Xing, Lei

2011-09-07

Monte Carlo (MC) methods are the gold standard for modeling photon and electron transport in a heterogeneous medium; however, their computational cost prohibits their routine use in the clinic. Cloud computing, wherein computing resources are allocated on-demand from a third party, is a new approach for high performance computing and is implemented to perform ultra-fast MC calculation in radiation therapy. We deployed the EGS5 MC package in a commercial cloud environment. Launched from a single local computer with Internet access, a Python script allocates a remote virtual cluster. A handshaking protocol designates master and worker nodes. The EGS5 binaries and the simulation data are initially loaded onto the master node. The simulation is then distributed among independent worker nodes via the message passing interface, and the results aggregated on the local computer for display and data analysis. The described approach is evaluated for pencil beams and broad beams of high-energy electrons and photons. The output of cloud-based MC simulation is identical to that produced by single-threaded implementation. For 1 million electrons, a simulation that takes 2.58 h on a local computer can be executed in 3.3 min on the cloud with 100 nodes, a 47× speed-up. Simulation time scales inversely with the number of parallel nodes. The parallelization overhead is also negligible for large simulations. Cloud computing represents one of the most important recent advances in supercomputing technology and provides a promising platform for substantially improved MC simulation. In addition to the significant speed up, cloud computing builds a layer of abstraction for high performance parallel computing, which may change the way dose calculations are performed and radiation treatment plans are completed.

Toward real-time Monte Carlo simulation using a commercial cloud computing infrastructure

International Nuclear Information System (INIS)

Wang, Henry; Ma Yunzhi; Pratx, Guillem; Xing Lei

2011-01-01

Monte Carlo (MC) methods are the gold standard for modeling photon and electron transport in a heterogeneous medium; however, their computational cost prohibits their routine use in the clinic. Cloud computing, wherein computing resources are allocated on-demand from a third party, is a new approach for high performance computing and is implemented to perform ultra-fast MC calculation in radiation therapy. We deployed the EGS5 MC package in a commercial cloud environment. Launched from a single local computer with Internet access, a Python script allocates a remote virtual cluster. A handshaking protocol designates master and worker nodes. The EGS5 binaries and the simulation data are initially loaded onto the master node. The simulation is then distributed among independent worker nodes via the message passing interface, and the results aggregated on the local computer for display and data analysis. The described approach is evaluated for pencil beams and broad beams of high-energy electrons and photons. The output of cloud-based MC simulation is identical to that produced by single-threaded implementation. For 1 million electrons, a simulation that takes 2.58 h on a local computer can be executed in 3.3 min on the cloud with 100 nodes, a 47x speed-up. Simulation time scales inversely with the number of parallel nodes. The parallelization overhead is also negligible for large simulations. Cloud computing represents one of the most important recent advances in supercomputing technology and provides a promising platform for substantially improved MC simulation. In addition to the significant speed up, cloud computing builds a layer of abstraction for high performance parallel computing, which may change the way dose calculations are performed and radiation treatment plans are completed. (note)

Toward real-time Monte Carlo simulation using a commercial cloud computing infrastructure

Energy Technology Data Exchange (ETDEWEB)

Wang, Henry [Department of Electrical Engineering, Stanford University, Stanford, CA 94305 (United States); Ma Yunzhi; Pratx, Guillem; Xing Lei, E-mail: hwang41@stanford.edu [Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305-5847 (United States)

2011-09-07

Monte Carlo (MC) methods are the gold standard for modeling photon and electron transport in a heterogeneous medium; however, their computational cost prohibits their routine use in the clinic. Cloud computing, wherein computing resources are allocated on-demand from a third party, is a new approach for high performance computing and is implemented to perform ultra-fast MC calculation in radiation therapy. We deployed the EGS5 MC package in a commercial cloud environment. Launched from a single local computer with Internet access, a Python script allocates a remote virtual cluster. A handshaking protocol designates master and worker nodes. The EGS5 binaries and the simulation data are initially loaded onto the master node. The simulation is then distributed among independent worker nodes via the message passing interface, and the results aggregated on the local computer for display and data analysis. The described approach is evaluated for pencil beams and broad beams of high-energy electrons and photons. The output of cloud-based MC simulation is identical to that produced by single-threaded implementation. For 1 million electrons, a simulation that takes 2.58 h on a local computer can be executed in 3.3 min on the cloud with 100 nodes, a 47x speed-up. Simulation time scales inversely with the number of parallel nodes. The parallelization overhead is also negligible for large simulations. Cloud computing represents one of the most important recent advances in supercomputing technology and provides a promising platform for substantially improved MC simulation. In addition to the significant speed up, cloud computing builds a layer of abstraction for high performance parallel computing, which may change the way dose calculations are performed and radiation treatment plans are completed. (note)

Relationships among cloud occurrence frequency, overlap, and effective thickness derived from CALIPSO and CloudSat merged cloud vertical profiles

Science.gov (United States)

Kato, Seiji; Sun-Mack, Sunny; Miller, Walter F.; Rose, Fred G.; Chen, Yan; Minnis, Patrick; Wielicki, Bruce A.

2010-01-01

A cloud frequency of occurrence matrix is generated using merged cloud vertical profiles derived from the satellite-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and cloud profiling radar. The matrix contains vertical profiles of cloud occurrence frequency as a function of the uppermost cloud top. It is shown that the cloud fraction and uppermost cloud top vertical profiles can be related by a cloud overlap matrix when the correlation length of cloud occurrence, which is interpreted as an effective cloud thickness, is introduced. The underlying assumption in establishing the above relation is that cloud overlap approaches random overlap with increasing distance separating cloud layers and that the probability of deviating from random overlap decreases exponentially with distance. One month of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat data (July 2006) support these assumptions, although the correlation length sometimes increases with separation distance when the cloud top height is large. The data also show that the correlation length depends on cloud top hight and the maximum occurs when the cloud top height is 8 to 10 km. The cloud correlation length is equivalent to the decorrelation distance introduced by Hogan and Illingworth (2000) when cloud fractions of both layers in a two-cloud layer system are the same. The simple relationships derived in this study can be used to estimate the top-of-atmosphere irradiance difference caused by cloud fraction, uppermost cloud top, and cloud thickness vertical profile differences.

Structure, shape, and evolution of radiatively accelerated QSO emission-line clouds

International Nuclear Information System (INIS)

Blumenthal, G.R.; Mathews, W.G.

1979-01-01

The possibility that the broad emission-line regions of QSOs and active galactic nuclei are formed by a multitude of small clouds which are radiatively accelerated is discussed. Although this model is by no means certain at present, it has four virtues: (1) Observed emission-line widths can be produced with observationally allowed electron densities, UV luminosities, and ionization levels. (2) The acceleration force is coherent in each cloud are found. (3) Reasonable line profiles can result for all emission lines. (4) Photoionization of hydrogen accounts for both heating and acceleration of the emission-line gas. A self-consistent model is developed for the structure, shape, and evolution of radiatively accelerated clouds. The shape varies with cloud mass, and two distinct types of clouds. Fully ionized clouds of very low mass approach a nearly spherical shape. However, all clouds having masses greater than some critical mass adopt a ''pancake'' shape. The condition for constant cloud mass in the cloud frame is shown to be equivalent to the equation of motion of a cloud in the rest frame of the QSO. The emission-line profiles can be sensitive to radial variations in the properties of the intercloud medium, and those properties that correspond to observed profiles are discussed. Finally, the covering factor of a system of pancake clouds is estimated along with the total number of clouds required--approximately 10 14 clouds in each QSO

Risk mitigation strategy for the ITER electron cyclotron upper port launcher

NARCIS (Netherlands)

Goede, A. P. H.; Bongers, W. A.; Elzendoorn, B. S. Q.; M. F. Graswinckel,; M.R. de Baar,

2010-01-01

A basic requirement for ITER equipment to meet is a high level of reliability, because ITER operation time is precious and radioactive operation leaves limited scope for repair. In order to reduce the risk of failure during ITER operation an effective risk mitigation strategy is necessary. This

Incorporating changes in albedo in estimating the climate mitigation benefits of land use change projects

Science.gov (United States)

Bird, D. N.; Kunda, M.; Mayer, A.; Schlamadinger, B.; Canella, L.; Johnston, M.

2008-04-01

Some climate scientists are questioning whether the practice of converting of non-forest lands to forest land (afforestation or reforestation) is an effective climate change mitigation option. The discussion focuses particularly on areas where the new forest is primarily coniferous and there is significant amount of snow since the increased climate forcing due to the change in albedo may counteract the decreased climate forcing due to carbon dioxide removal. In this paper, we develop a stand-based model that combines changes in surface albedo, solar radiation, latitude, cloud cover and carbon sequestration. As well, we develop a procedure to convert carbon stock changes to equivalent climatic forcing or climatic forcing to equivalent carbon stock changes. Using the model, we investigate the sensitivity of combined affects of changes in surface albedo and carbon stock changes to model parameters. The model is sensitive to amount of cloud, atmospheric absorption, timing of canopy closure, carbon sequestration rate among other factors. The sensitivity of the model is investigated at one Canadian site, and then the model is tested at numerous sites across Canada. In general, we find that the change in albedo reduces the carbon sequestration benefits by approximately 30% over 100 years, but this is not drastic enough to suggest that one should not use afforestation or reforestation as a climate change mitigation option. This occurs because the forests grow in places where there is significant amount of cloud in winter. As well, variations in sequestration rate seem to be counterbalanced by the amount and timing of canopy closure. We close by speculating that the effects of albedo may also be significant in locations at lower latitudes, where there are less clouds, and where there are extended dry seasons. These conditions make grasses light coloured and when irrigated crops, dark forests or other vegetation such as biofuels replace the grasses, the change in carbon

Electron cloud buildup driving spontaneous vertical instabilities of stored beams in the Large Hadron Collider

Directory of Open Access Journals (Sweden)

Annalisa Romano

2018-06-01

Full Text Available At the beginning of the 2016 run, an anomalous beam instability was systematically observed at the CERN Large Hadron Collider (LHC. Its main characteristic was that it spontaneously appeared after beams had been stored for several hours in collision at 6.5 TeV to provide data for the experiments, despite large chromaticity values and high strength of the Landau-damping octupole magnet. The instability exhibited several features characteristic of those induced by the electron cloud (EC. Indeed, when LHC operates with 25 ns bunch spacing, an EC builds up in a large fraction of the beam chambers, as revealed by several independent indicators. Numerical simulations have been carried out in order to investigate the role of the EC in the observed instabilities. It has been found that the beam intensity decay is unfavorable for the beam stability when LHC operates in a strong EC regime.

Proposing Hybrid Architecture to Implement Cloud Computing in Higher Education Institutions Using a Meta-synthesis Appro

Directory of Open Access Journals (Sweden)

hamid reza bazi

2017-12-01

Full Text Available Cloud computing is a new technology that considerably helps Higher Education Institutions (HEIs to develop and create competitive advantage with inherent characteristics such as flexibility, scalability, accessibility, reliability, fault tolerant and economic efficiency. Due to the numerous advantages of cloud computing, and in order to take advantage of cloud computing infrastructure, services of universities and HEIs need to migrate to the cloud. However, this transition involves many challenges, one of which is lack or shortage of appropriate architecture for migration to the technology. Using a reliable architecture for migration ensures managers to mitigate risks in the cloud computing technology. Therefore, organizations always search for suitable cloud computing architecture. In previous studies, these important features have received less attention and have not been achieved in a comprehensive way. The aim of this study is to use a meta-synthesis method for the first time to analyze the previously published studies and to suggest appropriate hybrid cloud migration architecture (IUHEC. We reviewed many papers from relevant journals and conference proceedings. The concepts extracted from these papers are classified to related categories and sub-categories. Then, we developed our proposed hybrid architecture based on these concepts and categories. The proposed architecture was validated by a panel of experts and Lawshe’s model was used to determine the content validity. Due to its innovative yet user-friendly nature, comprehensiveness, and high security, this architecture can help HEIs have an effective migration to cloud computing environment.

Clustering, randomness, and regularity in cloud fields: 2. Cumulus cloud fields

Science.gov (United States)

Zhu, T.; Lee, J.; Weger, R. C.; Welch, R. M.

1992-12-01

During the last decade a major controversy has been brewing concerning the proper characterization of cumulus convection. The prevailing view has been that cumulus clouds form in clusters, in which cloud spacing is closer than that found for the overall cloud field and which maintains its identity over many cloud lifetimes. This "mutual protection hypothesis" of Randall and Huffman (1980) has been challenged by the "inhibition hypothesis" of Ramirez et al. (1990) which strongly suggests that the spatial distribution of cumuli must tend toward a regular distribution. A dilemma has resulted because observations have been reported to support both hypotheses. The present work reports a detailed analysis of cumulus cloud field spatial distributions based upon Landsat, Advanced Very High Resolution Radiometer, and Skylab data. Both nearest-neighbor and point-to-cloud cumulative distribution function statistics are investigated. The results show unequivocally that when both large and small clouds are included in the cloud field distribution, the cloud field always has a strong clustering signal. The strength of clustering is largest at cloud diameters of about 200-300 m, diminishing with increasing cloud diameter. In many cases, clusters of small clouds are found which are not closely associated with large clouds. As the small clouds are eliminated from consideration, the cloud field typically tends towards regularity. Thus it would appear that the "inhibition hypothesis" of Ramirez and Bras (1990) has been verified for the large clouds. However, these results are based upon the analysis of point processes. A more exact analysis also is made which takes into account the cloud size distributions. Since distinct clouds are by definition nonoverlapping, cloud size effects place a restriction upon the possible locations of clouds in the cloud field. The net effect of this analysis is that the large clouds appear to be randomly distributed, with only weak tendencies towards

Self-Similar Spin Images for Point Cloud Matching

Science.gov (United States)

Pulido, Daniel

The rapid growth of Light Detection And Ranging (Lidar) technologies that collect, process, and disseminate 3D point clouds have allowed for increasingly accurate spatial modeling and analysis of the real world. Lidar sensors can generate massive 3D point clouds of a collection area that provide highly detailed spatial and radiometric information. However, a Lidar collection can be expensive and time consuming. Simultaneously, the growth of crowdsourced Web 2.0 data (e.g., Flickr, OpenStreetMap) have provided researchers with a wealth of freely available data sources that cover a variety of geographic areas. Crowdsourced data can be of varying quality and density. In addition, since it is typically not collected as part of a dedicated experiment but rather volunteered, when and where the data is collected is arbitrary. The integration of these two sources of geoinformation can provide researchers the ability to generate products and derive intelligence that mitigate their respective disadvantages and combine their advantages. Therefore, this research will address the problem of fusing two point clouds from potentially different sources. Specifically, we will consider two problems: scale matching and feature matching. Scale matching consists of computing feature metrics of each point cloud and analyzing their distributions to determine scale differences. Feature matching consists of defining local descriptors that are invariant to common dataset distortions (e.g., rotation and translation). Additionally, after matching the point clouds they can be registered and processed further (e.g., change detection). The objective of this research is to develop novel methods to fuse and enhance two point clouds from potentially disparate sources (e.g., Lidar and crowdsourced Web 2.0 datasets). The scope of this research is to investigate both scale and feature matching between two point clouds. The specific focus of this research will be in developing a novel local descriptor

Individual aerosol particles in and below clouds along a Mt. Fuji slope: Modification of sea-salt-containing particles by in-cloud processing

Science.gov (United States)

Ueda, S.; Hirose, Y.; Miura, K.; Okochi, H.

2014-02-01

Sizes and compositions of atmospheric aerosol particles can be altered by in-cloud processing by absorption/adsorption of gaseous and particulate materials and drying of aerosol particles that were formerly activated as cloud condensation nuclei. To elucidate differences of aerosol particles before and after in-cloud processing, aerosols were observed along a slope of Mt. Fuji, Japan (3776 m a.s.l.) during the summer in 2011 and 2012 using a portable laser particle counter (LPC) and an aerosol sampler. Aerosol samples for analyses of elemental compositions were obtained using a cascade impactor at top-of-cloud, in-cloud, and below-cloud altitudes. To investigate composition changes via in-cloud processing, individual particles (0.5-2 μm diameter) of samples from five cases (days) collected at different altitudes under similar backward air mass trajectory conditions were analyzed using a transmission electron microscope (TEM) equipped with an energy dispersive X-ray analyzer. For most cases (four cases), most particles at all altitudes mainly comprised sea salts: mainly Na with some S and/or Cl. Of those, in two cases, sea-salt-containing particles with Cl were found in below-cloud samples, although sea-salt-containing particles in top-of-cloud samples did not contain Cl. This result suggests that Cl in the sea salt was displaced by other cloud components. In the other two cases, sea-salt-containing particles on samples at all altitudes were without Cl. However, molar ratios of S to Na (S/Na) of the sea-salt-containing particles of top-of-cloud samples were higher than those of below-cloud samples, suggesting that sulfuric acid or sulfate was added to sea-salt-containing particles after complete displacement of Cl by absorption of SO2 or coagulation with sulfate. The additional volume of sulfuric acid in clouds for the two cases was estimated using the observed S/Na values of sea-salt-containing particles. The estimation revealed that size changes by in-cloud

Spectroscopic diagnostics for ablation cloud of tracer-encapsulated solid pellet in LHD

International Nuclear Information System (INIS)

Tamura, N.; Kalinina, D. V.; Sato, K.; Sudo, S.; Sergeev, V. Yu.; Miroshnikov, I. V.; Sharov, I. A.; Bakhareva, O. A.; Ivanova, D. M.; Timokhin, V. M.; Kuteev, B. V.

2008-01-01

In the Large Helical Device (LHD), various spectroscopic diagnostics have been applied to study the ablation process of an advanced impurity pellet, tracer-encapsulated solid pellet (TESPEL). The total light emission from the ablation cloud of TESPEL is measured by photomultipliers equipped with individual interference filters, which provide information about the TESPEL penetration depth. The spectra emitted from the TESPEL ablation cloud are measured with a 250 mm Czerny-Turner spectrometer equipped with an intensified charge coupled device detector, which is operated in the fast kinetic mode. This diagnostic allows us to evaluate the temporal evolution of the electron density in the TESPEL ablation cloud. In order to gain information about the spatial distribution of the cloud parameters, a nine image optical system that can simultaneously acquire nine images of the TESPEL ablation cloud has recently been developed. Several images of the TESPEL ablation cloud in different spectral domains will give us the spatial distribution of the TESPEL cloud density and temperature.

A review on the state-of-the-art privacy-preserving approaches in the e-health clouds.

Science.gov (United States)

Abbas, Assad; Khan, Samee U

2014-07-01

Cloud computing is emerging as a new computing paradigm in the healthcare sector besides other business domains. Large numbers of health organizations have started shifting the electronic health information to the cloud environment. Introducing the cloud services in the health sector not only facilitates the exchange of electronic medical records among the hospitals and clinics, but also enables the cloud to act as a medical record storage center. Moreover, shifting to the cloud environment relieves the healthcare organizations of the tedious tasks of infrastructure management and also minimizes development and maintenance costs. Nonetheless, storing the patient health data in the third-party servers also entails serious threats to data privacy. Because of probable disclosure of medical records stored and exchanged in the cloud, the patients' privacy concerns should essentially be considered when designing the security and privacy mechanisms. Various approaches have been used to preserve the privacy of the health information in the cloud environment. This survey aims to encompass the state-of-the-art privacy-preserving approaches employed in the e-Health clouds. Moreover, the privacy-preserving approaches are classified into cryptographic and noncryptographic approaches and taxonomy of the approaches is also presented. Furthermore, the strengths and weaknesses of the presented approaches are reported and some open issues are highlighted.

Enhanced machine learning scheme for energy efficient resource allocation in 5G heterogeneous cloud radio access networks

KAUST Repository

Alqerm, Ismail

2018-02-15

Heterogeneous cloud radio access networks (H-CRAN) is a new trend of 5G that aims to leverage the heterogeneous and cloud radio access networks advantages. Low power remote radio heads (RRHs) are exploited to provide high data rates for users with high quality of service requirements (QoS), while high power macro base stations (BSs) are deployed for coverage maintenance and low QoS users support. However, the inter-tier interference between the macro BS and RRHs and energy efficiency are critical challenges that accompany resource allocation in H-CRAN. Therefore, we propose a centralized resource allocation scheme using online learning, which guarantees interference mitigation and maximizes energy efficiency while maintaining QoS requirements for all users. To foster the performance of such scheme with a model-free learning, we consider users\\' priority in resource blocks (RBs) allocation and compact state representation based learning methodology to enhance the learning process. Simulation results confirm that the proposed resource allocation solution can mitigate interference, increase energy and spectral efficiencies significantly, and maintain users\\' QoS requirements.

Cloud occurrences and cloud radiative effects (CREs) from CERES-CALIPSO-CloudSat-MODIS (CCCM) and CloudSat radar-lidar (RL) products

Science.gov (United States)

Ham, Seung-Hee; Kato, Seiji; Rose, Fred G.; Winker, David; L'Ecuyer, Tristan; Mace, Gerald G.; Painemal, David; Sun-Mack, Sunny; Chen, Yan; Miller, Walter F.

2017-08-01

Two kinds of cloud products obtained from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, and Moderate Resolution Imaging Spectroradiometer (MODIS) are compared and analyzed in this study: Clouds and the Earth's Radiant Energy System (CERES)-CALIPSO-CloudSat-MODIS (CCCM) product and CloudSat radar-lidar products such as GEOPROF-LIDAR and FLXHR-LIDAR. Compared to GEOPROF-LIDAR, low-level (40°). The difference occurs when hydrometeors are detected by CALIPSO lidar but are undetected by CloudSat radar. In the comparison of cloud radiative effects (CREs), global mean differences between CCCM and FLXHR-LIDAR are mostly smaller than 5 W m-2, while noticeable regional differences are found. For example, CCCM shortwave (SW) and longwave (LW) CREs are larger than FXLHR-LIDAR along the west coasts of Africa and America because the GEOPROF-LIDAR algorithm misses shallow marine boundary layer clouds. In addition, FLXHR-LIDAR SW CREs are larger than the CCCM counterpart over tropical oceans away from the west coasts of America. Over midlatitude storm-track regions, CCCM SW and LW CREs are larger than the FLXHR-LIDAR counterpart.

Simulation of E-Cloud Driven Instability And Its Attenuation Using a Feedback System in the CERN SPS

International Nuclear Information System (INIS)

Vay, Jean-Luc

2012-01-01

Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS, and a feedback system to control the instabilities is under active development. We present the latest improvements to the Warp-Posinst simulation framework and feedback model, and its application to the self-consistent simulations of two consecutive bunches interacting with an electron cloud in the SPS.

Relation of Cloud Occurrence Frequency, Overlap, and Effective Thickness Derived from CALIPSO and CloudSat Merged Cloud Vertical Profiles

Science.gov (United States)

Kato, Seiji; Sun-Mack, Sunny; Miller, Walter F.; Rose, Fred G.; Chen, Yan; Minnis, Patrick; Wielicki, Bruce A.

2009-01-01

A cloud frequency of occurrence matrix is generated using merged cloud vertical profile derived from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR). The matrix contains vertical profiles of cloud occurrence frequency as a function of the uppermost cloud top. It is shown that the cloud fraction and uppermost cloud top vertical pro les can be related by a set of equations when the correlation distance of cloud occurrence, which is interpreted as an effective cloud thickness, is introduced. The underlying assumption in establishing the above relation is that cloud overlap approaches the random overlap with increasing distance separating cloud layers and that the probability of deviating from the random overlap decreases exponentially with distance. One month of CALIPSO and CloudSat data support these assumptions. However, the correlation distance sometimes becomes large, which might be an indication of precipitation. The cloud correlation distance is equivalent to the de-correlation distance introduced by Hogan and Illingworth [2000] when cloud fractions of both layers in a two-cloud layer system are the same.

Global cloud condensation nuclei influenced by carbonaceous combustion aerosol

Directory of Open Access Journals (Sweden)

D. V. Spracklen

2011-09-01

Full Text Available Black carbon in carbonaceous combustion aerosol warms the climate by absorbing solar radiation, meaning reductions in black carbon emissions are often perceived as an attractive global warming mitigation option. However, carbonaceous combustion aerosol can also act as cloud condensation nuclei (CCN so they also cool the climate by increasing cloud albedo. The net radiative effect of carbonaceous combustion aerosol is uncertain because their contribution to CCN has not been evaluated on the global scale. By combining extensive observations of CCN concentrations with the GLOMAP global aerosol model, we find that the model is biased low (normalised mean bias = −77 % unless carbonaceous combustion aerosol act as CCN. We show that carbonaceous combustion aerosol accounts for more than half (52–64 % of global CCN with the range due to uncertainty in the emitted size distribution of carbonaceous combustion particles. The model predicts that wildfire and pollution (fossil fuel and biofuel carbonaceous combustion aerosol causes a global mean cloud albedo aerosol indirect effect of −0.34 W m⁻², with stronger cooling if we assume smaller particle emission size. We calculate that carbonaceous combustion aerosol from pollution sources cause a global mean aerosol indirect effect of −0.23 W m⁻². The small size of carbonaceous combustion particles from fossil fuel sources means that whilst pollution sources account for only one-third of the emitted mass they cause two-thirds of the cloud albedo aerosol indirect effect that is due to carbonaceous combustion aerosol. This cooling effect must be accounted for, along with other cloud effects not studied here, to ensure that black carbon emissions controls that reduce the high number concentrations of fossil fuel particles have the desired net effect on climate.

A simple model for the initial phase of a water plasma cloud about a large structure in space

International Nuclear Information System (INIS)

Hastings, D.E.; Gatsonis, N.A.; Mogstad, T.

1988-01-01

Large structures in the ionosphere will outgas or eject neutral water and perturb the ambient neutral environment. This water can undergo charge exchange with the ambient oxygen ions and form a water plasma cloud. Additionally, water dumps or thruster firings can create a water plasma cloud. A simple model for the evolution of a water plasma cloud about a large space structure is obtained. It is shown that if the electron density around a large space structure is substantially enhanced above the ambient density then the plasma cloud will move away from the structure. As the cloud moves away, it will become unstable and will eventually break up into filaments. A true steady state will exist only if the total electron density is unperturbed from the ambient density. When the water density is taken to be consistent with shuttle-based observations, the cloud is found to slowly drift away on a time scale of many tens of milliseconds. This time is consistent with the shuttle observations

Contrasting Cloud Composition Between Coupled and Decoupled Marine Boundary Layer Clouds

Science.gov (United States)

WANG, Z.; Mora, M.; Dadashazar, H.; MacDonald, A.; Crosbie, E.; Bates, K. H.; Coggon, M. M.; Craven, J. S.; Xian, P.; Campbell, J. R.; AzadiAghdam, M.; Woods, R. K.; Jonsson, H.; Flagan, R. C.; Seinfeld, J.; Sorooshian, A.

2016-12-01

Marine stratocumulus clouds often become decoupled from the vertical layer immediately above the ocean surface. This study contrasts cloud chemical composition between coupled and decoupled marine stratocumulus clouds. Cloud water and droplet residual particle composition were measured in clouds off the California coast during three airborne experiments in July-August of separate years (E-PEACE 2011, NiCE 2013, BOAS 2015). Decoupled clouds exhibited significantly lower overall mass concentrations in both cloud water and droplet residual particles, consistent with reduced cloud droplet number concentration and sub-cloud aerosol (Dp > 100 nm) number concentration, owing to detachment from surface sources. Non-refractory sub-micrometer aerosol measurements show that coupled clouds exhibit higher sulfate mass fractions in droplet residual particles, owing to more abundant precursor emissions from the ocean and ships. Consequently, decoupled clouds exhibited higher mass fractions of organics, nitrate, and ammonium in droplet residual particles, owing to effects of long-range transport from more distant sources. Total cloud water mass concentration in coupled clouds was dominated by sodium and chloride, and their mass fractions and concentrations exceeded those in decoupled clouds. Conversely, with the exception of sea salt constituents (e.g., Cl, Na, Mg, K), cloud water mass fractions of all species examined were higher in decoupled clouds relative to coupled clouds. These results suggest that an important variable is the extent to which clouds are coupled to the surface layer when interpreting microphysical data relevant to clouds and aerosol particles.

Security Attacks and Solutions in Electronic Health (E-health) Systems.

Science.gov (United States)

Zeadally, Sherali; Isaac, Jesús Téllez; Baig, Zubair

2016-12-01

For centuries, healthcare has been a basic service provided by many governments to their citizens. Over the past few decades, we have witnessed a significant transformation in the quality of healthcare services provided by healthcare organizations and professionals. Recent advances have led to the emergence of Electronic Health (E-health), largely made possible by the massive deployment and adoption of information and communication technologies (ICTs). However, cybercriminals and attackers are exploiting vulnerabilities associated primarily with ICTs, causing data breaches of patients' confidential digital health information records. Here, we review recent security attacks reported for E-healthcare and discuss the solutions proposed to mitigate them. We also identify security challenges that must be addressed by E-health system designers and implementers in the future, to respond to threats that could arise as E-health systems become integrated with technologies such as cloud computing, the Internet of Things, and smart cities.

Context-aware distributed cloud computing using CloudScheduler

Science.gov (United States)

Seuster, R.; Leavett-Brown, CR; Casteels, K.; Driemel, C.; Paterson, M.; Ring, D.; Sobie, RJ; Taylor, RP; Weldon, J.

2017-10-01

The distributed cloud using the CloudScheduler VM provisioning service is one of the longest running systems for HEP workloads. It has run millions of jobs for ATLAS and Belle II over the past few years using private and commercial clouds around the world. Our goal is to scale the distributed cloud to the 10,000-core level, with the ability to run any type of application (low I/O, high I/O and high memory) on any cloud. To achieve this goal, we have been implementing changes that utilize context-aware computing designs that are currently employed in the mobile communication industry. Context-awareness makes use of real-time and archived data to respond to user or system requirements. In our distributed cloud, we have many opportunistic clouds with no local HEP services, software or storage repositories. A context-aware design significantly improves the reliability and performance of our system by locating the nearest location of the required services. We describe how we are collecting and managing contextual information from our workload management systems, the clouds, the virtual machines and our services. This information is used not only to monitor the system but also to carry out automated corrective actions. We are incrementally adding new alerting and response services to our distributed cloud. This will enable us to scale the number of clouds and virtual machines. Further, a context-aware design will enable us to run analysis or high I/O application on opportunistic clouds. We envisage an open-source HTTP data federation (for example, the DynaFed system at CERN) as a service that would provide us access to existing storage elements used by the HEP experiments.

AceCloud: Molecular Dynamics Simulations in the Cloud.

Science.gov (United States)

Harvey, M J; De Fabritiis, G

2015-05-26

We present AceCloud, an on-demand service for molecular dynamics simulations. AceCloud is designed to facilitate the secure execution of large ensembles of simulations on an external cloud computing service (currently Amazon Web Services). The AceCloud client, integrated into the ACEMD molecular dynamics package, provides an easy-to-use interface that abstracts all aspects of interaction with the cloud services. This gives the user the experience that all simulations are running on their local machine, minimizing the learning curve typically associated with the transition to using high performance computing services.

VMware private cloud computing with vCloud director

CERN Document Server

Gallagher, Simon

2013-01-01

It's All About Delivering Service with vCloud Director Empowered by virtualization, companies are not just moving into the cloud, they're moving into private clouds for greater security, flexibility, and cost savings. However, this move involves more than just infrastructure. It also represents a different business model and a new way to provide services. In this detailed book, VMware vExpert Simon Gallagher makes sense of private cloud computing for IT administrators. From basic cloud theory and strategies for adoption to practical implementation, he covers all the issues. You'll lea

SIMULATION OF E-CLOUD DRIVEN INSTABILITY AND ITS ATTENUATION USING A FEEDBACK SYSTEM IN THE CERN SPS

International Nuclear Information System (INIS)

Vay, J.-L.; Byrd, J.M.; Furman, M.A.; Secondo, R.; Venturini, M.; Fox, J.D.; Rivetta, C.H.; Hofle, W.

2010-01-01

Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS (1), and a feedback system to control the instabilities is under active development (2). We present the latest improvements to the Warp-Posinst simulation framework and feedback model, and its application to the self-consistent simulations of two consecutive bunches interacting with an electron cloud in the SPS.

Elongated dust clouds in a uniform DC positive column of low pressure gas discharge

International Nuclear Information System (INIS)

Usachev, A D; Zobnin, A V; Petrov, O F; Fortov, V E; Thoma, M H; Pustylnik, M Y; Fink, M A; Morfill, G E

2016-01-01

Experimental investigations of the formation of elongated dust clouds and their influence on the plasma glow intensity of the uniform direct current (DC) positive column (PC) have been performed under microgravity conditions. For the axial stabilization of the dust cloud position a polarity switching DC gas discharge with a switching frequency of 250 Hz was used. During the experiment, a spontaneous division of one elongated dust cloud into two smaller steady state dust clouds has been observed. Quantitative data on the dust cloud shape, size and dust number density distribution were obtained. Axial and radial distributions of plasma emission within the 585.2 nm and 703.2 nm neon spectral lines were measured over the whole discharge volume. It has been found that both spectral line intensities at the dust cloud region grew 1.7 times with respect to the undisturbed positive column region; in this the 585.2 nm line intensity increased by 10% compared to the 703.2 nm line intensity. For a semi-quantitative explanation of the observed phenomena the Schottky approach based on the equation of diffusion was used. The model reasonably explains the observed glow enhancement as an increasing of the ionization rate in the discharge with dust cloud, which compensates ion-electron recombination on the dust grain surfaces. In this, the ionization rate increases due to the growing of the DC axial electric field, and the glow grows directly proportional to the electric field. It is shown that the fundamental condition of the radial stability of the dusty plasma cloud is equal to the ionization and recombination rates within the cloud volume that is possible only when the electron density is constant and the radial electric field is absent within the dust cloud. (paper)

Creating cloud-free Landsat ETM+ data sets in tropical landscapes: cloud and cloud-shadow removal

Science.gov (United States)

Sebastián Martinuzzi; William A. Gould; Olga M. Ramos Gonzalez

2007-01-01

Clouds and cloud shadows are common features of visible and infrared remotelysensed images collected from many parts of the world, particularly in humid and tropical regions. We have developed a simple and semiautomated method to mask clouds and shadows in Landsat ETM+ imagery, and have developed a recent cloud-free composite of multitemporal images for Puerto Rico and...

Mitigation of Voltage Sags in CIGRE Low Voltage Distribution Network

DEFF Research Database (Denmark)

Mustafa, Ghullam; Bak-Jensen, Birgitte; Mahat, Pukar

2013-01-01

Any problem in voltage in a power network is undesirable as it aggravates the quality of the power. Power electronic devices such as Voltage Source Converter (VSC) based Static Synchronous Compensator (STATCOM), Dynamic Voltage Restorer (DVR) etc. are commonly used for the mitigation of voltage p....... The compensation of voltage sags in the different parts of CIGRE distribution network is done by using the four STATCOM compensators already existing in the test grid. The simulations are carried out in DIgSILENT power factory software version 15.0.......Any problem in voltage in a power network is undesirable as it aggravates the quality of the power. Power electronic devices such as Voltage Source Converter (VSC) based Static Synchronous Compensator (STATCOM), Dynamic Voltage Restorer (DVR) etc. are commonly used for the mitigation of voltage...... problems in the distribution system. The voltage problems dealt with in this paper are to show how to mitigate voltage sags in the CIGRE Low Voltage (LV) test network and networks like this. The voltage sags, for the tested cases in the CIGRE LV test network are mainly due to three phase faults...

Mobility and Cloud: Operating in Intermittent, Austere Network Conditions

Science.gov (United States)

2014-09-01

limited DSC Digital Selective Calling EC2 Elastic Compute Cloud ECM electronic countermeasure EMIO Expanded Maritime Interdiction Operations ENDA...to a theoretical range of approximately 300 nautical miles (nm). The downside is that it is not electronic countermeasure (ECM)-resistant. 7 4...operator. For CMG, the streaming of video using the commercial video conferencing software Skype was used. High frame rate is important for good gaming

Collisionless scattering of plasma cloud in a dipole magnetic field

International Nuclear Information System (INIS)

Osipyan, D.A.

2006-01-01

Results of numerical simulation of dense plasma cloud scattering dynamics in a magnetized background and MHD indignations generation are presented. The magnetic field has dipole structure. The initial system of equations includes the Vlasov equations for ionic components of plasma, hydrodynamic approach for electrons and Maxwell's system of equations. The method of solution is based on the use of the method of particles in cells and finite difference splitting schemes. Quantitative characteristics of dependence of scattering cloud parameters from the Mach-Alfven number and parameter of magnetic laminar interaction are observed. In particular, a condition of more effective deformation of a cloud is large values of the Mach-Alfven numbers and small parameters of the magnetic laminar interaction

A robust method to forecast volcanic ash clouds

Science.gov (United States)

Denlinger, Roger P.; Pavolonis, Mike; Sieglaff, Justin

2012-01-01

Ash clouds emanating from volcanic eruption columns often form trails of ash extending thousands of kilometers through the Earth's atmosphere, disrupting air traffic and posing a significant hazard to air travel. To mitigate such hazards, the community charged with reducing flight risk must accurately assess risk of ash ingestion for any flight path and provide robust forecasts of volcanic ash dispersal. In response to this need, a number of different transport models have been developed for this purpose and applied to recent eruptions, providing a means to assess uncertainty in forecasts. Here we provide a framework for optimal forecasts and their uncertainties given any model and any observational data. This involves random sampling of the probability distributions of input (source) parameters to a transport model and iteratively running the model with different inputs, each time assessing the predictions that the model makes about ash dispersal by direct comparison with satellite data. The results of these comparisons are embodied in a likelihood function whose maximum corresponds to the minimum misfit between model output and observations. Bayes theorem is then used to determine a normalized posterior probability distribution and from that a forecast of future uncertainty in ash dispersal. The nature of ash clouds in heterogeneous wind fields creates a strong maximum likelihood estimate in which most of the probability is localized to narrow ranges of model source parameters. This property is used here to accelerate probability assessment, producing a method to rapidly generate a prediction of future ash concentrations and their distribution based upon assimilation of satellite data as well as model and data uncertainties. Applying this method to the recent eruption of Eyjafjallajökull in Iceland, we show that the 3 and 6 h forecasts of ash cloud location probability encompassed the location of observed satellite-determined ash cloud loads, providing an

Zen of cloud learning cloud computing by examples on Microsoft Azure

CERN Document Server

Bai, Haishi

2014-01-01

Zen of Cloud: Learning Cloud Computing by Examples on Microsoft Azure provides comprehensive coverage of the essential theories behind cloud computing and the Windows Azure cloud platform. Sharing the author's insights gained while working at Microsoft's headquarters, it presents nearly 70 end-to-end examples with step-by-step guidance on implementing typical cloud-based scenarios.The book is organized into four sections: cloud service fundamentals, cloud solutions, devices and cloud, and system integration and project management. Each chapter contains detailed exercises that provide readers w

A new type of coating to chase the clouds away

CERN Multimedia

Stefania Pandolfi

2016-01-01

The electron cloud problem needs to be addressed with innovative solutions, particularly in view of the rapidly approaching HL-LHC upgrade. CERN’s Vacuum, Surfaces and Coatings group has greatly improved its amorphous carbon coating technique, which is an alternative to the scrubbing process used so far. This technique is now fully mature and is being used for the vacuum chambers of the SPS magnets and the delicate beam screens of the LHC’s quadrupole triplets.   The violet light is produced by the argon plasma used when sputtering the amorphous carbon. The beam screen is coated in this case using the magnetic field of the quadrupole itself. (Image: Pedro Costa Pinto) We know that conditioning (or “scrubbing”) the beam pipe reduces the avalanche-like creation of secondary electrons from the tube’s walls, thus preventing the formation of unwanted electron clouds. But it has also been observed that scrubbing natur...

Local clouds ionization, temperatures, electron densities and interfaces, from GHRS and IMAPS spectra of epsilon Canis Majoris

CERN Document Server

Gry, C; Gry, Cecile; Jenkins, Edward B.

2001-01-01

The composition and physical properties of several local clouds, including the Local Interstellar Cloud (LIC) in which the Sun is embedded, are derived from absorption features in the UV spectrum of the star epsilon CMa. We derive temperatures and densities for three components by combining our interpretations of the ionization balance of magnesium and the relative population of C II in an excited fine-structure level. We find that for the LIC n(e) = 0.12 +/-0.05 cm-3 and T = 7000 +/-1200 K. We derive the ionization fractions of hydrogen and discuss the ionizing processes. In particular the hydrogen and helium ionizations in the LIC are compatible with photoionization by the local EUV radiation fields from the hot stars and the cloud interface with the hot gas. We confirm the detection of high ionization species : Si III is detected in all clouds and C IV in two of them, including the LIC, suggesting the presence of ionized interfaces around the local clouds.

TURBULENCE DECAY AND CLOUD CORE RELAXATION IN MOLECULAR CLOUDS

International Nuclear Information System (INIS)

Gao, Yang; Law, Chung K.; Xu, Haitao

2015-01-01

The turbulent motion within molecular clouds is a key factor controlling star formation. Turbulence supports molecular cloud cores from evolving to gravitational collapse and hence sets a lower bound on the size of molecular cloud cores in which star formation can occur. On the other hand, without a continuous external energy source maintaining the turbulence, such as in molecular clouds, the turbulence decays with an energy dissipation time comparable to the dynamic timescale of clouds, which could change the size limits obtained from Jean's criterion by assuming constant turbulence intensities. Here we adopt scaling relations of physical variables in decaying turbulence to analyze its specific effects on the formation of stars. We find that the decay of turbulence provides an additional approach for Jeans' criterion to be achieved, after which gravitational infall governs the motion of the cloud core. This epoch of turbulence decay is defined as cloud core relaxation. The existence of cloud core relaxation provides a more complete understanding of the effect of the competition between turbulence and gravity on the dynamics of molecular cloud cores and star formation

COMPARATIVE STUDY OF CLOUD COMPUTING AND MOBILE CLOUD COMPUTING

OpenAIRE

Nidhi Rajak*, Diwakar Shukla

2018-01-01

Present era is of Information and Communication Technology (ICT) and there are number of researches are going on Cloud Computing and Mobile Cloud Computing such security issues, data management, load balancing and so on. Cloud computing provides the services to the end user over Internet and the primary objectives of this computing are resource sharing and pooling among the end users. Mobile Cloud Computing is a combination of Cloud Computing and Mobile Computing. Here, data is stored in...

Strategies for mitigating the ionization-induced beam head erosion problem in an electron-beam-driven plasma wakefield accelerator

Directory of Open Access Journals (Sweden)

W. An

2013-10-01

Full Text Available Strategies for mitigating ionization-induced beam head erosion in an electron-beam-driven plasma wakefield accelerator (PWFA are explored when the plasma and the wake are both formed by the transverse electric field of the beam itself. Beam head erosion can occur in a preformed plasma because of a lack of focusing force from the wake at the rising edge (head of the beam due to the finite inertia of the electrons. When the plasma is produced by field ionization from the space charge field of the beam, the head erosion is significantly exacerbated due to the gradual recession (in the beam frame of the 100% ionization contour. Beam particles in front of the ionization front cannot be focused (guided causing them to expand as in vacuum. When they expand, the location of the ionization front recedes such that even more beam particles are completely unguided. Eventually this process terminates the wake formation prematurely, i.e., well before the beam is depleted of its energy. Ionization-induced head erosion can be mitigated by controlling the beam parameters (emittance, charge, and energy and/or the plasma conditions. In this paper we explore how the latter can be optimized so as to extend the beam propagation distance and thereby increase the energy gain. In particular we show that, by using a combination of the alkali atoms of the lowest practical ionization potential (Cs for plasma formation and a precursor laser pulse to generate a narrow plasma filament in front of the beam, the head erosion rate can be dramatically reduced. Simulation results show that in the upcoming “two-bunch PWFA experiments” on the FACET facility at SLAC national accelerator laboratory the energy gain of the trailing beam can be up to 10 times larger for the given parameters when employing these techniques. Comparison of the effect of beam head erosion in preformed and ionization produced plasmas is also presented.

Analysis of the Metal Oxide Space Clouds (MOSC) HF Propagation Environment

Science.gov (United States)

Jackson-Booth, N.; Selzer, L.

2015-12-01

Artificial Ionospheric Modification (AIM) attempts to modify the ionosphere in order to alter the high frequency (HF) propagation environment. It can be achieved through injections of aerosols, chemicals or radio (RF) signals into the ionosphere. The Metal Oxide Space Clouds (MOSC) experiment was undertaken in April/May 2013 to investigate chemical AIM. Two sounding rockets were launched from the Kwajalein Atoll (part of the Marshall Islands) and each released a cloud of vaporized samarium (Sm). The samarium created a localized plasma cloud, with increased electron density, which formed an additional ionospheric layer. The ionospheric effects were measured by a wide range of ground based instrumentation which included a network of high frequency (HF) sounders. Chirp transmissions were made from three atolls and received at five sites within the Marshall Islands. One of the receive sites consisted of an 18 antenna phased array, which was used for direction finding. The ionograms have shown that as well as generating a new layer the clouds created anomalous RF propagation paths, which interact with both the cloud and the F-layer, resulting in 'ghost traces'. To fully understand the propagation environment a 3D numerical ray trace has been undertaken, using a variety of background ionospheric and cloud models, to find the paths through the electron density grid for a given fan of elevation and azimuth firing angles. Synthetic ionograms were then produced using the ratio of ray path length to speed of light as an estimation of the delay between transmission and observation for a given frequency of radio wave. This paper reports on the latest analysis of the MOSC propagation environment, comparing theory with observations, to further understanding of AIM.

Review of Cloud Computing and existing Frameworks for Cloud adoption

OpenAIRE

Chang, Victor; Walters, Robert John; Wills, Gary

2014-01-01

This paper presents a selected review for Cloud Computing and explains the benefits and risks of adopting Cloud Computing in a business environment. Although all the risks identified may be associated with two major Cloud adoption challenges, a framework is required to support organisations as they begin to use Cloud and minimise risks of Cloud adoption. Eleven Cloud Computing frameworks are investigated and a comparison of their strengths and limitations is made; the result of the comparison...

Cloud CCN feedback

International Nuclear Information System (INIS)

Hudson, J.G.

1992-01-01

Cloud microphysics affects cloud albedo precipitation efficiency and the extent of cloud feedback in response to global warming. Compared to other cloud parameters, microphysics is unique in its large range of variability and the fact that much of the variability is anthropogenic. Probably the most important determinant of cloud microphysics is the spectra of cloud condensation nuclei (CCN) which display considerable variability and have a large anthropogenic component. When analyzed in combination three field observation projects display the interrelationship between CCN and cloud microphysics. CCN were measured with the Desert Research Institute (DRI) instantaneous CCN spectrometer. Cloud microphysical measurements were obtained with the National Center for Atmospheric Research Lockheed Electra. Since CCN and cloud microphysics each affect the other a positive feedback mechanism can result

Health Records and the Cloud Computing Paradigm from a Privacy Perspective

OpenAIRE

Stingl, Christian; Slamanig, Daniel

2011-01-01

With the advent of cloud computing, the realization of highly available electronic health records providing location-independent access seems to be very promising. However, cloud computing raises major security issues that need to be addressed particularly within the health care domain. The protection of the privacy of individuals often seems to be left on the sidelines. For instance, common protection against malicious insiders, i.e., non-disclosure agreements, is purely organizational. Clea...

Radon mitigation experience in difficult-to-mitigate schools

International Nuclear Information System (INIS)

Leovic, K.W.; Craig, A.B.

1990-01-01

Initial radon mitigation experience in schools has shown sub-slab depressurization (SSD) to be generally effective in reducing elevated levels of radon in schools that have a continuous layer of clean, coarse aggregate underneath the slab. However, mitigation experience is limited in schools without sub-slab aggregate and in schools with characteristics such as return-air ductwork underneath the slab or unducted return-air plenums in the drop ceiling that are open to the sub-slab area (via open tops of block walls). Mitigation of schools with utility tunnels and of schools constructed over crawl spaces is also limited. Three Maryland schools exhibiting some of the above characteristics are being researched to help understand the mechanisms that control radon entry and mitigation in schools where standard SSD systems are not effective. This paper discusses specific characteristics of potentially difficult-to-mitigate schools and, where applicable, details examples from the three Maryland schools

Analytical treatment of the nonlinear electron cloud effect and the combined effects with beam-beam and space charge nonlinear forces in storage rings

International Nuclear Information System (INIS)

Gao Jie

2009-01-01

In this paper we treat first some nonlinear beam dynamics problems in storage rings, such as beam dynamic apertures due to magnetic multipoles, wiggles, beam-beam effects, nonlinear space charge effect, and then nonlinear electron cloud effect combined with beam-beam and space charge effects, analytically. This analytical treatment is applied to BEPC II. The corresponding analytical expressions developed in this paper are useful both in understanding the physics behind these problems and also in making practical quick hand estimations. (author)

Disruption mitigation with high-pressure helium gas injection on EAST tokamak

Science.gov (United States)

Chen, D. L.; Shen, B.; Granetz, R. S.; Qian, J. P.; Zhuang, H. D.; Zeng, L.; Duan, Y.; Shi, T.; Wang, H.; Sun, Y.; Xiao, B. J.

2018-03-01

High pressure noble gas injection is a promising technique to mitigate the effect of disruptions in tokamaks. In this paper, results of mitigation experiments with low-Z massive gas injection (helium) on the EAST tokamak are reported. A fast valve has been developed and successfully implemented on EAST, with valve response time  ⩽150 μs, capable of injecting up to 7 × 1022 particles, corresponding to 300 times the plasma inventory. Different amounts of helium gas were injected into stable plasmas in the preliminary experiments. It is seen that a small amount of helium gas (N_He≃ N_plasma ) can not terminate a discharge, but can trigger MHD activity. Injection of 40 times the plasma inventory impurity (N_He≃ 40× N_plasma ) can effectively radiate away part of the thermal energy and make the electron density increase rapidly. The mitigation result is that the current quench time and vertical displacement can both be reduced significantly, without resulting in significantly higher loop voltage. This also reduces the risk of runaway electron generation. As the amount of injected impurity gas increases, the gas penetration time decreases slowly and asymptotes to (˜7 ms). In addition, the impurity gas jet has also been injected into VDEs, which are more challenging to mitigate that stable plasmas.

Cloud Governance

DEFF Research Database (Denmark)

Berthing, Hans Henrik

Denne præsentation beskriver fordele og værdier ved anvendelse af Cloud Computing. Endvidere inddrager resultater fra en række internationale analyser fra ISACA om Cloud Computing.......Denne præsentation beskriver fordele og værdier ved anvendelse af Cloud Computing. Endvidere inddrager resultater fra en række internationale analyser fra ISACA om Cloud Computing....

CesrTA Retarding Field Analyzer Measurements in Drifts, Dipoles, Quadrupoles and Wigglers

International Nuclear Information System (INIS)

Calvey, J.R.; Li, Y.; Livezey, J.A.; Makita, J.; Meller, R.E.; Palmer, M.A.; Schwartz, R.M.; Strohman, C.R.; Harkay, K.; Calatroni, S.; Rumolo, G.; Kanazawa, K.; Suetsugu, Y.; Pivi, M.; Wang, L.

2010-01-01

Over the course of the CesrTA program, the Cornell Electron Storage Ring (CESR) has been instrumented with several retarding field analyzers (RFAs), which measure the local density and energy distribution of the electron cloud. These RFAs have been installed in drifts, dipoles, quadrupoles, and wigglers; and data have been taken in a variety of beam conditions and bunch configurations. This paper will provide an overview of these results, and give a preliminary evaluation of the efficacy of cloud mitigation techniques implemented in the instrumented vacuum chambers.

A Lightweight Distributed Framework for Computational Offloading in Mobile Cloud Computing

Science.gov (United States)

Shiraz, Muhammad; Gani, Abdullah; Ahmad, Raja Wasim; Adeel Ali Shah, Syed; Karim, Ahmad; Rahman, Zulkanain Abdul

2014-01-01

The latest developments in mobile computing technology have enabled intensive applications on the modern Smartphones. However, such applications are still constrained by limitations in processing potentials, storage capacity and battery lifetime of the Smart Mobile Devices (SMDs). Therefore, Mobile Cloud Computing (MCC) leverages the application processing services of computational clouds for mitigating resources limitations in SMDs. Currently, a number of computational offloading frameworks are proposed for MCC wherein the intensive components of the application are outsourced to computational clouds. Nevertheless, such frameworks focus on runtime partitioning of the application for computational offloading, which is time consuming and resources intensive. The resource constraint nature of SMDs require lightweight procedures for leveraging computational clouds. Therefore, this paper presents a lightweight framework which focuses on minimizing additional resources utilization in computational offloading for MCC. The framework employs features of centralized monitoring, high availability and on demand access services of computational clouds for computational offloading. As a result, the turnaround time and execution cost of the application are reduced. The framework is evaluated by testing prototype application in the real MCC environment. The lightweight nature of the proposed framework is validated by employing computational offloading for the proposed framework and the latest existing frameworks. Analysis shows that by employing the proposed framework for computational offloading, the size of data transmission is reduced by 91%, energy consumption cost is minimized by 81% and turnaround time of the application is decreased by 83.5% as compared to the existing offloading frameworks. Hence, the proposed framework minimizes additional resources utilization and therefore offers lightweight solution for computational offloading in MCC. PMID:25127245

A lightweight distributed framework for computational offloading in mobile cloud computing.

Directory of Open Access Journals (Sweden)

Muhammad Shiraz

Full Text Available The latest developments in mobile computing technology have enabled intensive applications on the modern Smartphones. However, such applications are still constrained by limitations in processing potentials, storage capacity and battery lifetime of the Smart Mobile Devices (SMDs. Therefore, Mobile Cloud Computing (MCC leverages the application processing services of computational clouds for mitigating resources limitations in SMDs. Currently, a number of computational offloading frameworks are proposed for MCC wherein the intensive components of the application are outsourced to computational clouds. Nevertheless, such frameworks focus on runtime partitioning of the application for computational offloading, which is time consuming and resources intensive. The resource constraint nature of SMDs require lightweight procedures for leveraging computational clouds. Therefore, this paper presents a lightweight framework which focuses on minimizing additional resources utilization in computational offloading for MCC. The framework employs features of centralized monitoring, high availability and on demand access services of computational clouds for computational offloading. As a result, the turnaround time and execution cost of the application are reduced. The framework is evaluated by testing prototype application in the real MCC environment. The lightweight nature of the proposed framework is validated by employing computational offloading for the proposed framework and the latest existing frameworks. Analysis shows that by employing the proposed framework for computational offloading, the size of data transmission is reduced by 91%, energy consumption cost is minimized by 81% and turnaround time of the application is decreased by 83.5% as compared to the existing offloading frameworks. Hence, the proposed framework minimizes additional resources utilization and therefore offers lightweight solution for computational offloading in MCC.

Development of an ITER prototype disruption mitigation valve

Energy Technology Data Exchange (ETDEWEB)

Czymek, G., E-mail: g.czymek@fz-juelich.de [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, D52425 Jülich (Germany); Giesen, B., E-mail: ingenieurbuero.giesen@gmx.de [IBG, Sibertstr. 22, D-52525 Heinsberg (Germany); Charl, A.; Panin, A.; Hiller, A.; Nicolai, D.; Neubauer, O.; Koslowski, H.R.; Sandri, N. [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, D52425 Jülich (Germany)

2015-10-15

Highlights: • An ITER-DMV prototype for 100 bar, D = 80 mm, opening time 3.5 ms, is ready for fabrication. • The vacuum part is sealed against the working gas by stainless steel bellows for 110 bar. • The conical Laval gas outlet allows maximal mass flow rate. • The eddy current drive turn ratio was optimized for low tilting moment. • Polyimide is used for the head sealing, the decelerator and for the bearing of the guide tube. - Abstract: Disruptions in tokamaks seem to be unavoidable. Consequences of disruptions are (i) high heat loads on plasma-facing components, (ii) large forces on the vacuum vessel, and (iii) the generation of runaway electron beams. In ITER, the thermal energy of the plasma needs to be evenly distributed on the first wall in order to prevent melting, forces from vertical displacement events have to be minimized, and the generation of runaway electrons suppressed. Massive gas injection using fast valves is a concept for disruption mitigation which is presently being explored in many tokamaks. Fast disruption mitigation valves based on an electromagnetic eddy current drive have been developed in Jülich since the 1990s and models of various sizes have been built and are in operation in the TEXTOR, MAST, and JET tokamaks. A disruption mitigation valve for ITER is of necessity larger with an estimated injected gas volume of ∼20 kPa m{sup 3}[7] for runaway electron suppression and all materials used have to be resistant to much higher levels of neutron and gamma radiation than in existing tokamaks. During the last 5 years, the concept for an ITER prototype disruption mitigation valve has been developed up to the stage that a fully functional valve could be built and tested. Special emphasis was given to the development and functional testing of some critical items: (i) the injection chamber seal, (ii) the piston seal, (iii) the eddy current drive, and (iv) a braking mechanism to avoid too fast closure of the valve, which could damage

Comparisons of Satellite-Deduced Overlapping Cloud Properties and CALIPSO CloudSat Data

Science.gov (United States)

Chang, Fu-Lung; Minnis, Patrick; Lin, Bing; Sun-Mack, Sunny

2010-01-01

Introduction to the overlapped cloud properties derived from polar-orbiting (MODIS) and geostationary (GOES-12, -13, Meteosat-8, -9, etc.) meteorological satellites, which are produced at the NASA Langley Research Center (LaRC) cloud research & development team (NASA lead scientist: Dr. Patrick Minnis). Comparison of the LaRC CERES MODIS Edition-3 overlapped cloud properties to the CALIPSO and the CloudSat active sensing data. High clouds and overlapped clouds occur frequently as deduced by CALIPSO (44 & 25%), CloudSat (25 & 4%), and MODIS (37 & 6%). Large fractions of optically-thin cirrus and overlapped clouds are deduced from CALIPSO, but much smaller fractions are from CloudSat and MODIS. For overlapped clouds, the averaged upper-layer CTHs are about 12.8 (CALIPSO), 10.9 (CloudSat) and 10 km (MODIS), and the averaged lower-layer CTHs are about 3.6 (CALIPSO), 3.2 (CloudSat) and 3.9 km (MODIS). Based on comparisons of upper and lower-layer cloud properties as deduced from the MODIS, CALIPSO and CloudSat data, more enhanced passive satellite methods for retrieving thin cirrus and overlapped cloud properties are needed and are under development.

Securing the Cloud Cloud Computer Security Techniques and Tactics

CERN Document Server

Winkler, Vic (JR)

2011-01-01

As companies turn to cloud computing technology to streamline and save money, security is a fundamental concern. Loss of certain control and lack of trust make this transition difficult unless you know how to handle it. Securing the Cloud discusses making the move to the cloud while securing your peice of it! The cloud offers felxibility, adaptability, scalability, and in the case of security-resilience. This book details the strengths and weaknesses of securing your company's information with different cloud approaches. Attacks can focus on your infrastructure, communications network, data, o

Electron Production and Collective Field Generation in Intense Particle Beams

International Nuclear Information System (INIS)

Molvik, A W; Vay, J; Cohen, R; Friedman, A; Lee, E; Verboncoeur, J; Covo, M K

2006-01-01

Electron cloud effects (ECEs) are increasingly recognized as important, but incompletely understood, dynamical phenomena, which can severely limit the performance of present electron colliders, the next generation of high-intensity rings, such as PEP-II upgrade, LHC, and the SNS, the SIS 100/200, or future high-intensity heavy ion accelerators such as envisioned in Heavy Ion Inertial Fusion (HIF). Deleterious effects include ion-electron instabilities, emittance growth, particle loss, increase in vacuum pressure, added heat load at the vacuum chamber walls, and interference with certain beam diagnostics. Extrapolation of present experience to significantly higher beam intensities is uncertain given the present level of understanding. With coordinated LDRD projects at LLNL and LBNL, we undertook a comprehensive R and D program including experiments, theory and simulations to better understand the phenomena, establish the essential parameters, and develop mitigating mechanisms. This LDRD project laid the essential groundwork for such a program. We developed insights into the essential processes, modeled the relevant physics, and implemented these models in computational production tools that can be used for self-consistent study of the effect on ion beams. We validated the models and tools through comparison with experimental data, including data from new diagnostics that we developed as part of this work and validated on the High-Current Experiment (HCX) at LBNL. We applied these models to High-Energy Physics (HEP) and other advanced accelerators. This project was highly successful, as evidenced by the two paragraphs above, and six paragraphs following that are taken from our 2003 proposal with minor editing that mostly consisted of changing the tense. Further benchmarks of outstanding performance are: we had 13 publications with 8 of them in refereed journals, our work was recognized by the accelerator and plasma physics communities by 8 invited papers and we have

Cloud management and security

CERN Document Server

Abbadi, Imad M

2014-01-01

Written by an expert with over 15 years' experience in the field, this book establishes the foundations of Cloud computing, building an in-depth and diverse understanding of the technologies behind Cloud computing. In this book, the author begins with an introduction to Cloud computing, presenting fundamental concepts such as analyzing Cloud definitions, Cloud evolution, Cloud services, Cloud deployment types and highlighting the main challenges. Following on from the introduction, the book is divided into three parts: Cloud management, Cloud security, and practical examples. Part one presents the main components constituting the Cloud and federated Cloud infrastructure(e.g., interactions and deployment), discusses management platforms (resources and services), identifies and analyzes the main properties of the Cloud infrastructure, and presents Cloud automated management services: virtual and application resource management services. Part two analyzes the problem of establishing trustworthy Cloud, discuss...

Cloud computing patterns fundamentals to design, build, and manage cloud applications

CERN Document Server

Fehling, Christoph; Retter, Ralph; Schupeck, Walter; Arbitter, Peter

2014-01-01

The current work provides CIOs, software architects, project managers, developers, and cloud strategy initiatives with a set of architectural patterns that offer nuggets of advice on how to achieve common cloud computing-related goals. The cloud computing patterns capture knowledge and experience in an abstract format that is independent of concrete vendor products. Readers are provided with a toolbox to structure cloud computing strategies and design cloud application architectures. By using this book cloud-native applications can be implemented and best suited cloud vendors and tooling for i

Progress in Near Real-Time Volcanic Cloud Observations Using Satellite UV Instruments

Science.gov (United States)

Krotkov, N. A.; Yang, K.; Vicente, G.; Hughes, E. J.; Carn, S. A.; Krueger, A. J.

2011-12-01

Volcanic clouds from explosive eruptions can wreak havoc in many parts of the world, as exemplified by the 2010 eruption at the Eyjafjöll volcano in Iceland, which caused widespread disruption to air traffic and resulted in economic impacts across the globe. A suite of satellite-based systems offer the most effective means to monitor active volcanoes and to track the movement of volcanic clouds globally, providing critical information for aviation hazard mitigation. Satellite UV sensors, as part of this suite, have a long history of making unique near-real time (NRT) measurements of sulfur dioxide (SO2) and ash (aerosol Index) in volcanic clouds to supplement operational volcanic ash monitoring. Recently a NASA application project has shown that the use of near real-time (NRT,i.e., not older than 3 h) Aura/OMI satellite data produces a marked improvement in volcanic cloud detection using SO2 combined with Aerosol Index (AI) as a marker for ash. An operational online NRT OMI AI and SO2 image and data product distribution system was developed in collaboration with the NOAA Office of Satellite Data Processing and Distribution. Automated volcanic eruption alarms, and the production of volcanic cloud subsets for multiple regions are provided through the NOAA website. The data provide valuable information in support of the U.S. Federal Aviation Administration goal of a safe and efficient National Air Space. In this presentation, we will highlight the advantages of UV techniques and describe the advances in volcanic SO2 plume height estimation and enhanced volcanic ash detection using hyper-spectral UV measurements, illustrated with Aura/OMI observations of recent eruptions. We will share our plan to provide near-real-time volcanic cloud monitoring service using the Ozone Mapping and Profiler Suite (OMPS) on the Joint Polar Satellite System (JPSS).

Military clouds: utilization of cloud computing systems at the battlefield

Science.gov (United States)

Süleyman, Sarıkürk; Volkan, Karaca; İbrahim, Kocaman; Ahmet, Şirzai

2012-05-01

Cloud computing is known as a novel information technology (IT) concept, which involves facilitated and rapid access to networks, servers, data saving media, applications and services via Internet with minimum hardware requirements. Use of information systems and technologies at the battlefield is not new. Information superiority is a force multiplier and is crucial to mission success. Recent advances in information systems and technologies provide new means to decision makers and users in order to gain information superiority. These developments in information technologies lead to a new term, which is known as network centric capability. Similar to network centric capable systems, cloud computing systems are operational today. In the near future extensive use of military clouds at the battlefield is predicted. Integrating cloud computing logic to network centric applications will increase the flexibility, cost-effectiveness, efficiency and accessibility of network-centric capabilities. In this paper, cloud computing and network centric capability concepts are defined. Some commercial cloud computing products and applications are mentioned. Network centric capable applications are covered. Cloud computing supported battlefield applications are analyzed. The effects of cloud computing systems on network centric capability and on the information domain in future warfare are discussed. Battlefield opportunities and novelties which might be introduced to network centric capability by cloud computing systems are researched. The role of military clouds in future warfare is proposed in this paper. It was concluded that military clouds will be indispensible components of the future battlefield. Military clouds have the potential of improving network centric capabilities, increasing situational awareness at the battlefield and facilitating the settlement of information superiority.

Clustering, randomness, and regularity in cloud fields. 4: Stratocumulus cloud fields

Science.gov (United States)

Lee, J.; Chou, J.; Weger, R. C.; Welch, R. M.

1994-01-01

To complete the analysis of the spatial distribution of boundary layer cloudiness, the present study focuses on nine stratocumulus Landsat scenes. The results indicate many similarities between stratocumulus and cumulus spatial distributions. Most notably, at full spatial resolution all scenes exhibit a decidedly clustered distribution. The strength of the clustering signal decreases with increasing cloud size; the clusters themselves consist of a few clouds (less than 10), occupy a small percentage of the cloud field area (less than 5%), contain between 20% and 60% of the cloud field population, and are randomly located within the scene. In contrast, stratocumulus in almost every respect are more strongly clustered than are cumulus cloud fields. For instance, stratocumulus clusters contain more clouds per cluster, occupy a larger percentage of the total area, and have a larger percentage of clouds participating in clusters than the corresponding cumulus examples. To investigate clustering at intermediate spatial scales, the local dimensionality statistic is introduced. Results obtained from this statistic provide the first direct evidence for regularity among large (more than 900 m in diameter) clouds in stratocumulus and cumulus cloud fields, in support of the inhibition hypothesis of Ramirez and Bras (1990). Also, the size compensated point-to-cloud cumulative distribution function statistic is found to be necessary to obtain a consistent description of stratocumulus cloud distributions. A hypothesis regarding the underlying physical mechanisms responsible for cloud clustering is presented. It is suggested that cloud clusters often arise from 4 to 10 triggering events localized within regions less than 2 km in diameter and randomly distributed within the cloud field. As the size of the cloud surpasses the scale of the triggering region, the clustering signal weakens and the larger cloud locations become more random.

Clustering, randomness, and regularity in cloud fields. 4. Stratocumulus cloud fields

Science.gov (United States)

Lee, J.; Chou, J.; Weger, R. C.; Welch, R. M.

1994-07-01

To complete the analysis of the spatial distribution of boundary layer cloudiness, the present study focuses on nine stratocumulus Landsat scenes. The results indicate many similarities between stratocumulus and cumulus spatial distributions. Most notably, at full spatial resolution all scenes exhibit a decidedly clustered distribution. The strength of the clustering signal decreases with increasing cloud size; the clusters themselves consist of a few clouds (less than 10), occupy a small percentage of the cloud field area (less than 5%), contain between 20% and 60% of the cloud field population, and are randomly located within the scene. In contrast, stratocumulus in almost every respect are more strongly clustered than are cumulus cloud fields. For instance, stratocumulus clusters contain more clouds per cluster, occupy a larger percentage of the total area, and have a larger percentage of clouds participating in clusters than the corresponding cumulus examples. To investigate clustering at intermediate spatial scales, the local dimensionality statistic is introduced. Results obtained from this statistic provide the first direct evidence for regularity among large (>900 m in diameter) clouds in stratocumulus and cumulus cloud fields, in support of the inhibition hypothesis of Ramirez and Bras (1990). Also, the size compensated point-to-cloud cumulative distribution function statistic is found to be necessary to obtain a consistent description of stratocumulus cloud distributions. A hypothesis regarding the underlying physical mechanisms responsible for cloud clustering is presented. It is suggested that cloud clusters often arise from 4 to 10 triggering events localized within regions less than 2 km in diameter and randomly distributed within the cloud field. As the size of the cloud surpasses the scale of the triggering region, the clustering signal weakens and the larger cloud locations become more random.