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1

Acquisition system for the liquid helium L5 plant  

International Nuclear Information System (INIS)

The technology of low temperature at the beginning of this century, developed for the production of oxygen nitrogen and rare gases, was the basis for setting of the cryogenic technology. Engineering and construction of cryogenic plants appear today implied in: science, research and development, space technology, nuclear power techniques. An important component in this technologies is the helium liquefier of type L5. This fully automatic cryoliquefier operates for purification, liquefaction as well as reliquefaction of helium gas evaporated in cryostat systems. A helium production plant consists mainly of cold chamber with aluminium heat exchangers, two gas-lubricated turbo-expanders, instrumentation and a programmable controller as well an oil-injected screw-compressor. Cold helium with 4.5 K is transferred through a special vacuum and super insulated line to the tank. In liquefaction mode without LN2-precooling the performance data of this plant is 5 l/hour at 4.5 K. In the paper there are presented the work of designing and developing of a performing liquid helium delivery system corresponding with the basic equipment and accessories used in a L5 type helium liquefactor. The process software of LINDE L5 installation was updated and adapted to our technical conditions from our cryogenic laboratory. Therefore the new Lab-View based programme derived from the functions command protocol, allowed a reliable control on the technological process and induced as well severalogical process and induced as well several determinations on the performance of the process as following: - verification of the theoretical models of the cryogenic cycle energetic dimensions; - Increasing thermodynamic performances of different components of the cryogenic cycle by remodeling the geometrical flowing zones, based on gas dynamic studies, in concordance with the thermophysical characteristics of the gas; - study of the dynamic behavior of the installation by evaluation of the transient processes. (authors)

2

Heat transfer design and performance of a helium cryostat operating at 6.5 K  

International Nuclear Information System (INIS)

A liquid helium cryostat has been designed and operated for the purpose of testing visible light photon counter (VLPC) chips at 6.5 K. To achieve the desired operational characteristics for the VLPC devices their operating temperature is restricted to 6.5 K +/- 0.1 K. They will be used in a scintillating fiber tracker being proposed as part of an upgrade of the D(0) detector at Fermilab. The final version of the scintillating fiber tracker will contain roughly 100,000 VLPC channels. Two cryostats with identical thermal design (a 128 channel and a 3072 channel design) have been built to perform the initial VLPC testing. The heat transfer needed to maintain the VLPC at its operating temperature occurs by conduction across an annular helium gas gap to a liquid helium reservoir. Helium boiloff is used to intercept conduction heat leak to the liquid reservoir. ANSYS finite element heat transfer analysis was utilized in the thermal design of the cryostat. The cryostat design and thermal performance (predicted and measured) are presented

3

Interaction of positronium with helium atoms — the classical treatment of the 5-body collision system  

Science.gov (United States)

The interaction between positronium and a helium atom is studied using the 5-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for single ionization of the target, and ionization of the projectile, resulting from pure ionization and also from electron transfer (capture or loss) processes for 1-5.7 a.u. incident velocities of the positronium atom. Our results were compared with the calculated data using hydrogen projectiles having the same velocities as well as with the experimental data in collisions between H and He [R.D. DuBois, Á. Kövér, Phys. Rev. A 40, 3605 (1989)]. We analyze the similarities and deviations for ionization of helium atoms by positronium and hydrogen projectile impact. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.

T?kési, Károly; DuBois, Robert D.; Mukoyama, Takeshi

2014-09-01

4

Penetration Characteristics of Air, Carbon Dioxide and Helium Transverse Sonic Jets in Mach 5 Cross Flow  

Directory of Open Access Journals (Sweden)

Full Text Available An experimental investigation of sonic air, CO2 and Helium transverse jets in Mach 5 cross flow was carried out over a flat plate. The jet to freestream momentum flux ratio, J, was kept the same for all gases. The unsteady flow topology was examined using high speed schlieren visualisation and PIV. Schlieren visualisation provided information regarding oscillating jet shear layer structures and bow shock, Mach disc and barrel shocks. Two-component PIV measurements at the centreline, provided information regarding jet penetration trajectories. Barrel shocks and Mach disc forming the jet boundary were visualised/quantified also jet penetration boundaries were determined. Even though J is kept the same for all gases, the penetration patterns were found to be remarkably different both at the nearfield and the farfield. Air and CO2 jet resulted similar nearfield and farfield penetration pattern whereas Helium jet spread minimal in the nearfield.

Erinc Erdem

2014-12-01

5

Commissioning report of the MuCool 5 Tesla solenoid coupled with helium refrigerator  

Energy Technology Data Exchange (ETDEWEB)

MuCool 5T solenoid was successfully cooled down and operated coupled with MTA 'Brown' refrigerator. The system performed as designed with substantial performance margin. All process alarms and interlocks, as well as ODH and fire alarms, were active and performed as designed. The cooldown of the refrigerator started from warm conditions and took 44 hours to accumulate liquid helium level and solenoid temperature below 5K. Average liquid nitrogen consumption for the refrigerator precool and solenoid shield was measured as 20 gal/hr (including boil-off). Helium losses were small (below 30 scfh). The system was stable and with sufficient margin of performance and ran stably without wet expansion engine. Quench response demonstrated proper operation of the relieving devices and pointed to necessity of improving tightness of the relieving manifolds. Boil-off test demonstrated average heat load of 3 Watts for the unpowered solenoid. The solenoid can stay up to 48 hours cold and minimally filled if the nitrogen shield is maintained. A list of improvements includes commencing into operations the second helium compressor and completion of improvements and tune-ups for system efficiency.

Geynisman, Michael; /Fermilab

2010-05-01

6

FLOATING PRESSURE CONVERSION AND EQUIPMENT UPGRADES OF TWO 3.5KW, 20K, HELIUM REFRIGERATORS  

Energy Technology Data Exchange (ETDEWEB)

Two helium refrigerators, each rated for 3.5 KW at 20 K, are used at NASA's Johnson Space Center (JSC) in Building No. 32 to provide cryogenic-pumping within two large thermal-vacuum chambers. These refrigerators were originally commissioned in 1996. New changes to the controls of these refrigerators were recently completed. This paper describes some of the control issues that necessitated the controls change-over. It will describe the modifications and the new process control which allows the refrigerators to take advantage of the Ganni Cycle “floating pressure” control technology. The controls philosophy change-over to the floating pressure control technology was the first application on a helium gas refrigeration system. Previous implementations of the floating pressure technology have been on 4 K liquefaction and refrigeration systems, which have stored liquid helium volumes that have level indications used for varying the pressure levels (charge) in the system for capacity modulation. The upgrades have greatly improved the performance, stability, and efficiency of these two refrigerators. The upgrades have also given the operators more information and details about the operational status of the main components (compressors, expanders etc.) of the refrigerators at all operating conditions (i.e. at various loads in the vacuum chambers). The performance data of the two systems, pre and post upgrading are presented.

J. Homan, V. Ganni, A. Sidi-Yekhlef, J. Creel, R. Norton, R. Linza, G. Vargas, J. Lauterbach, J. Urbin, D. Howe

2010-04-01

7

Floating Pressure Conversion of Two 3.5 KW, 20 K, Helium Refrigerators  

Science.gov (United States)

Two helium refrigerators, each rated for 3.5 KW at 20 K, are used at NASA's Johnson Space Center (JSC) in Building No. 32 to provide cryogenic-pumping within two large thermal-vacuum chambers. These refrigerators were originally commissioned in 1996. New changes to the controls of these refrigerators were recently completed. This paper describes some of the control issues that necessitated the controls change-over. It will describe the modifications and the new process control which allows the refrigerators to take advantage of the Ganni Cycle "floating pressure" control technology. The controls philosophy change-over to the floating pressure control technology was the first application on a helium gas refrigeration system. Previous implementations of the floating pressure technology have been on 4 K liquefaction and refrigeration systems, which have stored liquid helium volumes that have level indications used for varying the pressure levels (charge) in the system for capacity modulation. The upgrades have greatly improved the performance, stability, and efficiency of these two refrigerators. The upgrades have also given the operators more information and details about the operational status of the main components (compressors, expanders etc.) of the refrigerators at all operating conditions (i.e. at various loads in the vacuum chambers). The performance data of the two systems, pre and post upgrading are presented.

Homan, J.; Ganni, V.; Sidi-Yekhlef, A.; Creel, J.; Norton, R.; Linza, R.; Vargas, G.; Lauterbach, J.; Urbin, J.; Howe, D.

2010-04-01

8

Development efforts on helium vessel for 5 cell - 650 MHz SRF cavity at RRCAT  

International Nuclear Information System (INIS)

The work focuses on the development of helium vessel which houses a 5 cell - 650 MHz SRF niobium cavity and serves as a helium bath to maintain the cavity at 2 K. The vessel has provision for changing the axial length of the cavity for tuning purpose by using a tuning mechanism and a large bellow. Titanium has been chosen as a material of construction of the vessel due to its coefficient of thermal expansion being close to that of niobium. Efforts have been initiated to understand the functional requirements, design requirements, acceptance criteria for design and analysis, non-destructive examination requirements, inspection and testing requirements, manufacturing technology of the titanium vessel and its integration with the SRF cavity. The welding assumes a special significance as titanium is highly reactive and ductility of the weld joint is lost in the presence of air and other impurities. A trial vessel has been conceptualised having typical sizes and geometries. The manufacturing features of vessel are based on ASME B and PV Code, Section VIII Division-1 and manufacturing of this vessel has been started at an Indian industry. Quality assurance plan for this work is developed. The paper describes the work done at RRCAT on the functional and integration requirements, overall design requirements, design methodology to achieve code conformance, manufacturing technology and QAP being used in the development of helium vessel. (author) (author)

9

Properties of V-(8-9)Cr-(5-6)Ti alloys irradiated in the dynamic helium charging experiment  

Energy Technology Data Exchange (ETDEWEB)

In the Dynamic Helium Charging Experiment (DHCE), helium was produced uniformly in vanadium alloy specimens by the decay of tritium during irradiation to 18-31 dpa at 425-600{degrees}C in lithium-filled capsules in the Fast Flux Test Facility. This report presents results of postirradiation tests of tensile properties and density change in V-8Cr-6Ti and V-9Cr-5Ti. Compared to tensile properties of the alloys irradiated in the non-DHCE (helium generation negligible), the effect of helium on tensile strength and ductility of V-8Cr-6Ti and V-9Cr-5Ti was insignificant after irradiation and testing at 420, 500, and 600{degrees}C. Both alloys retained a total elongation of >11 % at these temperatures. Density change was <0.48% for both alloys.

Chung, H.M.; Nowicki, L.; Smith, D.L. [Argonne National Lab., IL (United States)

1996-10-01

10

Properties of V-(8-9)Cr-(5-6)Ti alloys irradiated in the dynamic helium charging experiment  

International Nuclear Information System (INIS)

In the Dynamic Helium Charging Experiment (DHCE), helium was produced uniformly in vanadium alloy specimens by the decay of tritium during irradiation to 18-31 dpa at 425-600 degrees C in lithium-filled capsules in the Fast Flux Test Facility. This report presents results of postirradiation tests of tensile properties and density change in V-8Cr-6Ti and V-9Cr-5Ti. Compared to tensile properties of the alloys irradiated in the non-DHCE (helium generation negligible), the effect of helium on tensile strength and ductility of V-8Cr-6Ti and V-9Cr-5Ti was insignificant after irradiation and testing at 420, 500, and 600 degrees C. Both alloys retained a total elongation of >11 % at these temperatures. Density change was <0.48% for both alloys

11

Thermal-hydraulic system study of a high pressure, high temperature helium loop using RELAP5-3D code  

International Nuclear Information System (INIS)

Highlights: ? A thermal-hydraulic system analysis for a high pressure, high temperature helium loop has been investigated. ? The loop belongs to the Helium Loop Karlsruhe (HELOKA) facility, which contains the European Helium Cooled Pebble Beds Test Blanket Module (HCPB TBM) as the test module. ? The loop including all components has been modeled using the system code REALP5-3D, and the main control strategy has been implemented as well. ? With this model, the loop dynamics in conditions relevant for blanket module operation have been demonstrated. - Abstract: The thermal-hydraulic system analysis for the Helium Loop Karlsruhe (HELOKA) facility, a high pressure, high temperature experimental helium loop having the European Helium Cooled Pebble Beds Test Blanket Module (HCPB TBM) as the test module, was investigated. Using the system code REALP5-3D, all components in the loop are modeled as well as the main control strategy. With this model, the loop dynamics in conditions relevant for blanket module operation are simulated and analyzed.

12

Helium localisation in tritides  

International Nuclear Information System (INIS)

Study of titanium and LaNi5 type alloys tritides lattice parameters evolution revealed that helium created by tritium decay remains in interstitial sites up to a limit material dependant concentration. Beyond this one exceeding helium precipites in voids

13

Swelling of CLAM steel irradiated by electron/helium to 17.5 dpa with 10 appm He/dpa  

International Nuclear Information System (INIS)

To investigate irradiation/helium effects on microstructure of China Low Activation Martensitic (CLAM) steel, single beam (e-) and dual-beam (e-/He+) irradiation to 17.5 dpa with 10 appm He/dpa at 400 deg. C and 450 deg. C on CLAM steel was carried out with high voltage electron microscope HVEM. Evolution of microstructure was in situ observed during irradiation and annealing procedure. Preliminary results showed that size and density of voids and helium bubbles increased with irradiation dose. And swellings of voids and bubbles are ?0.5% and 1-1.5%, respectively after irradiation.

14

Tensile and fracture properties of EBR-II-irradiated V-15Cr-5Ti containing helium  

International Nuclear Information System (INIS)

The alloy V-15Cr-5Ti was cyclotron-implanted with 80 appM He and subsequently irradiated in the Experimental Breeder Reactor (EBR-II) to 30 dpa. The same alloy was also irradiated in the 10, 20, and 30% cold-worked conditions. Irradiation temperatures ranged from 400 to 7000C. No significant effects of helium on mechanical properties were found in this temperature range although the neutron irradiation shifted the temperature of transition from cleavage to ductile fracture to about 6250C. Ten percent cold work was found to have a beneficial effect in reducing the tendency for cleavage fracture following irradiation, but high levels (20%) were observed to reduce ductility. Still higher levels (30%) improved ductility by inducing recovery during the elevated-temperature irradiation. Swelling was found to be negligible, but precipitates - titanium oxides or carbonitrides - contained substantial cavities

15

Tensile and fracture properties of EBR-II-irradiated V-15Cr-5Ti containing helium  

Energy Technology Data Exchange (ETDEWEB)

The alloy V-15Cr-5Ti was cyclotron-implanted with 80 appM He and subsequently irradiated in the Experimental Breeder Reactor (EBR-II) to 30 dpa. The same alloy was also irradiated in the 10, 20, and 30% cold-worked conditions. Irradiation temperatures ranged from 400 to 700/sup 0/C. No significant effects of helium on mechanical properties were found in this temperature range although the neutron irradiation shifted the temperature of transition from cleavage to ductile fracture to about 625/sup 0/C. Ten percent cold work was found to have a beneficial effect in reducing the tendency for cleavage fracture following irradiation, but high levels (20%) were observed to reduce ductility. Still higher levels (30%) improved ductility by inducing recovery during the elevated-temperature irradiation. Swelling was found to be negligible, but precipitates - titanium oxides or carbonitrides - contained substantial cavities.

Grossbeck, M.L.; Horak, J.A.

1986-01-01

16

Elevated-temperature tensile properties of V--15Cr--5Ti containing helium introduced by ion bombardment and tritium decay  

International Nuclear Information System (INIS)

The tensile properties of V-15 wt percent Cr-5 wt percent Ti containing 25-35 appm He have been investigated from 600 to 8000C. Helium charging was accomplished by the ''tritium trick'' and both thin-sheet and cylindrical specimens were tested. Specimens containing helium showed decreases in elongation at temperatures of 7000C and above, but the cylindrical specimens with or without helium exhibited considerably greater elongations than the sheet specimens under corresponding conditions. A comparison of the tensile properties of the sheet specimens charged by the ''tritium trick'' with the properties of Cyclotron-injected sheet specimens from a previous study indicates that the Cyclotron-injected specimens exhibited greater ductility than the specimens charged by the ''tritium trick.'' The onset of gross embrittlement occurred between 700 and 7500C in both cases

17

Preliminary Design of 3.5-MeV Helium RFQ for Fusion Materials Radiation Damage Study  

International Nuclear Information System (INIS)

This work briefly summarized a 3.5 MeV helium RFQ design for alpha irradiation study. We have studied a 3.5-MeV helium RFQ for the fusion material damage study, especially for the alpha particle effects produced by DT reaction. The total length is about 3.7 m, which is compact to be installed in a general experiment hall with a reasonable radiation shielding. For the ion source of He, we are considering a microwave ion source. KOMAC (KOrea Multi-purpose Accelerator Complex) has developed a 100-MeV proton linac which includes a 50-keV ion source, a 3-MeV RFQ (Radio Frequency Quadrupole), and a 100-MeV DTL (drift tube linac). The RFQ technology can be also used to MeV ion beam applications. Especially helium beam with the kinetic energy of 3.5 MeV can be used to study the alpha particle irradiation from DT nuclear fusion reaction on the first wall of the fusion reactor

18

The Greenwood-Foreman-Rimmer loop punching mechanism as applied to helium bubble growth in nickel implanted with 5 keV He+ ions at 273 K  

International Nuclear Information System (INIS)

It is shown that as a result of the Greenwood-Foreman-Rimmer loop punching mechanism applied for helium bubble growth in nickel implanted with 5 keV He+ ions at 273 K, a considerable amount of helium remains outside the bubbles which are visible in a transmission electron microscope (TEM). It is also shown that even when it is assumed that there is an energy barrier with an upper limit equal to the formation energy of a self-interstitial atom, not all implanted helium can be accumulated in the bubbles below the critical dose for blistering. The experimental observation of bubble growth in a helium pre-implanted nickel specimen during 1 MeV e- irradiation may demonstrate that indeed a significant amount of helium remains between the bubbles visible in TEM. (author)

19

Recoil and fast-particle spectrometers for the study of 5GeV pion-helium interactions  

International Nuclear Information System (INIS)

The instrumentation of an experiment, in which the recoil as well as the fast-particle is measured, is described. The principal aim of the experiment is to search for isobar configurations in the nuclear function of helium by studying 5GeV pion-helium interactions and one pion-proton interactions. In the both first reactions the object X is a pion-nucleon system, which may have been produced on one of the bound nucleons in helium or may have existed prior to the collision. The last one gives the production amplitude from free nucleons. The final-state pions which are scattered in a narrow forward half cone, are measured in a spectrometer consisting of multiwire proportional counters (MWPC) and a magnet. The residual slow nuclei are measured and identified in a recoil spectrometer with MWPC's, solid state detectors and scintillators as the basic components. With these spectrometers the nuclear and the hadron states can be specified up to very high energies as long as the missing mass resolution is sufficient to separate the different resonances in X from each other

20

Microstructural analysis of 9% Cr martensitic steels containing 0.5 at.% helium  

Science.gov (United States)

Microstructural examinations by transmission electron microscopy and small angle neutron scattering were performed on 100 ?m thick specimens of 9Cr-1Mo (EM10) and modified 9Cr-1Mo (T91) martensitic steels homogeneously implanted with 23 MeV ? particles to a concentration of 5000 appm. Two implantation temperatures were selected, 250 and 550 °C, which correspond respectively to the lower and higher bounds of the operation temperature range foreseen for the window of accelerator driven systems devoted to waste transmutation. 250 °C is also the maximum operating temperature of the European spallation source window. The TEM samples were punched out from implanted tensile specimens following testing, which revealed, as detailed in a companion paper [P. Jung et al., these Proceedings], drastic hardening and complete ductility loss for the specimens implanted at 250 °C. Helium bubbles were detected in both materials implanted at 250 and 550 °C and bubble size distributions as well as number densities were determined. Furthermore, it was found that the bubbles are at thermodynamic equilibrium. Based on the microstructural results, it is shown that the high degree of hardening of specimens implanted at 250 °C is due to the high density of tiny helium bubbles they contain. It is furthermore suggested that the brittle, intergranular fracture mode displayed by these specimens results from the combined effects of pronounced intragranular hardening and weakening of prior austenite grain boundaries due to helium.

Henry, J.; Mathon, M.-H.; Jung, P.

2003-05-01

 
 
 
 
21

Microstructural analysis of 9% Cr martensitic steels containing 0.5 at.% helium  

International Nuclear Information System (INIS)

Microstructural examinations by transmission electron microscopy and small angle neutron scattering were performed on 100 ?m thick specimens of 9Cr-1Mo (EM10) and modified 9Cr-1Mo (T91) martensitic steels homogeneously implanted with 23 MeV ? particles to a concentration of 5000 appm. Two implantation temperatures were selected, 250 and 550 deg. C, which correspond respectively to the lower and higher bounds of the operation temperature range foreseen for the window of accelerator driven systems devoted to waste transmutation. 250 deg. C is also the maximum operating temperature of the European spallation source window. The TEM samples were punched out from implanted tensile specimens following testing, which revealed, as detailed in a companion paper [P. Jung et al., these Proceedings], drastic hardening and complete ductility loss for the specimens implanted at 250 deg. C. Helium bubbles were detected in both materials implanted at 250 and 550 deg. C and bubble size distributions as well as number densities were determined. Furthermore, it was found that the bubbles are at thermodynamic equilibrium. Based on the microstructural results, it is shown that the high degree of hardening of specimens implanted at 250 deg. C is due to the high density of tiny helium bubbles they contain. It is furthermore suggested that the brittle, intergranular fracture mode displayed by these specimens results from the combined effects of pronounced intragranular hardening and weakeninced intragranular hardening and weakening of prior austenite grain boundaries due to helium

22

First principles assessment of helium trapping in Y{sub 2}TiO{sub 5} in nano-featured ferritic alloys  

Energy Technology Data Exchange (ETDEWEB)

Nano-scale Y{sub 2}Ti{sub 2}O{sub 7} and Y{sub 2}TiO{sub 5} oxides are the major features that provide high strength and irradiation tolerance in nano-structured ferritic alloys. Here, we employ density functional theory to study helium trapping in Y{sub 2}TiO{sub 5}. The results suggest that helium is more deeply trapped in Y{sub 2}TiO{sub 5} compared to Y{sub 2}Ti{sub 2}O{sub 7}. Helium occupies open channels in Y{sub 2}TiO{sub 5}, where it weakly chemically interacts with neighboring oxygen anions, and results in less volume expansion compared to Y{sub 2}Ti{sub 2}O{sub 7}, reducing strains in the iron matrix. The corresponding helium mobility in these channels is very high. While its ultimate fate is to form oxide/matrix interface bubbles, transient deep trapping of helium in oxides plays a major role in the ability of NFA to manage helium distribution.

Jin, Yanan [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Jiang, Yong, E-mail: yjiang@csu.edu.cn, E-mail: odette@engineering.ucsb.edu; Yang, Litong; Lan, Guoqiang [School of Materials Science and Engineering, Central South University, Changsha 410083 (China); Key Lab for Nonferrous Materials of Ministry of Education, Central South University, Changsha 410083 (China); Robert Odette, G., E-mail: yjiang@csu.edu.cn, E-mail: odette@engineering.ucsb.edu; Yamamoto, Takuya [Materials Department, University of California, Santa Barbara 93106 (United States); Shang, Jiacheng; Dang, Ying [National Key Lab for Reactor Fuels and Materials, Nuclear Power Institute of China, Chengdu 610041 (China)

2014-10-14

23

Observation of turbulent waves in a helium plasma by optical spectroscopy, ch. 5  

International Nuclear Information System (INIS)

From the combined Stark-Zeeman pattern of helium allowed and forbidden optical lines the frequency spectrum, the field strength and the dominant polarization of microfields were determined in a turbulent plasma. Two frequent domains of oscillations were found in a turbulent heating experiment: low-frequency oscillations with dominant polarization perpendicular to the current direction and high-frequency osillations (f approximately fsub(pe)) with random polarization. The r.m.s. field strength of the oscillations is between 2 kV/cm and 10 kV/cm. The energy density of turbulent microfields amounts to 1% of the thermal energy density. (Auth.)

24

Thermal–hydraulic system study of the HELOKA-LP helium loop using RELAP5-3D code  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Thermal–hydraulic system study for the HELOKA-LP using RELAP5-3D. • Validation of various experiments with corresponding simulations, and good comparison between the experiments and the simulations. • Simulation of the two most heated compartments of IFMIF HFTM in the modeled helium loop and prediction of the loop dynamic. -- Abstract: The thermal–hydraulic system analyses for the HELOKA-LP (Helium Loop Karlsruhe – Low Pressure) facility are presented. Typical operation ranges for the test section are mass flow rate between 12 and 120 g/s, inlet temperature between 10 and 250 °C and pressure level between 0.3 and 0.6 MPa. An orifice is used for the loop testing, for which different experiments are validated with appropriate simulations. Afterwards instead of the orifice, two most heated compartments of IFMIF (International Fusion Materials Irradiation Facility) HFTM (high flux test module) are simulated in HELOKA-LP. Using the system code REALP5-3D components in the loop are modeled as well as the main control strategy. With this model the loop dynamics in conditions relevant for the HFTM operation are analyzed and the thermal time constant of the compartment is estimated.

Jin, Xue Zhou, E-mail: jin@kit.edu; Schlindwein, Georg; Schlenker, Markus; Ghidersa, Bradut-Eugen; Chen, Yuming; Arbeiter, Frederik

2013-10-15

25

Thermal–hydraulic system study of the HELOKA-LP helium loop using RELAP5-3D code  

International Nuclear Information System (INIS)

Highlights: • Thermal–hydraulic system study for the HELOKA-LP using RELAP5-3D. • Validation of various experiments with corresponding simulations, and good comparison between the experiments and the simulations. • Simulation of the two most heated compartments of IFMIF HFTM in the modeled helium loop and prediction of the loop dynamic. -- Abstract: The thermal–hydraulic system analyses for the HELOKA-LP (Helium Loop Karlsruhe – Low Pressure) facility are presented. Typical operation ranges for the test section are mass flow rate between 12 and 120 g/s, inlet temperature between 10 and 250 °C and pressure level between 0.3 and 0.6 MPa. An orifice is used for the loop testing, for which different experiments are validated with appropriate simulations. Afterwards instead of the orifice, two most heated compartments of IFMIF (International Fusion Materials Irradiation Facility) HFTM (high flux test module) are simulated in HELOKA-LP. Using the system code REALP5-3D components in the loop are modeled as well as the main control strategy. With this model the loop dynamics in conditions relevant for the HFTM operation are analyzed and the thermal time constant of the compartment is estimated

26

?-Helium-4 scattering experiment at 5GeV/c. Data processing  

International Nuclear Information System (INIS)

The context of this work is an experiment realised at CERN, with the object to search pre-existing isobaric states in helium nucleus, by means of the study of scattering reactions of ?- with simultaneous observation of recoil nucleus (3He or 3H) and forward pion. In this work, only the study of recoil detectors is done. This one, described with many details consists of a set of four wire chamber planes, two planes of semiconductors and two scintillators planes. The performances of this set of detectors are presented in regard to identification of recoil particle, energy and recoil angle measurements. A 'missing mass' analysis of the events of the experiment is done. Preliminary results of elastic and inelastic scattering are given. For elastic scattering a qualitative comparison is done with the multiple scattering Glauber formalism

27

Chromosome aberrations induced in human lymphocytes by 8.7 MeV protons and 23.5 MeV helium-3 ions  

International Nuclear Information System (INIS)

This paper describes the irradiation of thin samples of blood with 8.7 MeV protons and 23.5 MeV helium-3 ions in the track segment mode. Chromosome aberrations in human lymphocytes have been scored. The relationship between dicentric yield and dose in Gy was Y = 0.044 D + 0.058 D2 for protons and Y = 0.394 D for helium ions. These results are compared with data from other laboratories using protons and an attempt is made to reconcile differences. An unexpected observation was that the ratio of the linear coefficients for helium ions and protons was about 9 whereas the ratio of the l.e.t. values was 4.5. This disagrees with current theory which predicts that the linear coefficients should be proportional to l.e.t. Possible sources of error in our experiments are discussed but do not adequately account for the discrepancies. (author)

28

Helium cryogenics  

CERN Document Server

Twenty five years have elapsed since the original publication of Helium Cryogenics. During this time, a considerable amount of research and development involving helium fluids has been carried out culminating in several large-scale projects. Furthermore, the field has matured through these efforts so that there is now a broad engineering base to assist the development of future projects. Helium Cryogenics, 2nd edition brings these advances in helium cryogenics together in an updated form. As in the original edition, the author's approach is to survey the field of cryogenics with emphasis on helium fluids. This approach is more specialized and fundamental than that contained in other cryogenics books, which treat the associated range of cryogenic fluids. As a result, the level of treatment is more advanced and assumes a certain knowledge of fundamental engineering and physics principles, including some quantum mechanics. The goal throughout the work is to bridge the gap between the physics and engineering aspe...

Van Sciver, Steven W

2012-01-01

29

Heat transfer from horizontal cylinder to subcooled liquid helium  

International Nuclear Information System (INIS)

Experiments were made on the heat transfer in subcooled liquid helium I and II from a horizontal copper cylinder which was 2.5 cm in diameter and 5 cm in length. The results for helium I indicated some difference between subcooled and saturated helium. The heat flux in subcooled helium was larger than that of saturated helium in the nucleate-boiling region. In the free-convection region, the heat flux of subcooled helium was smaller than that of saturated helium. In the experiments for helium II, it was found that the difference of heat transfer rate between subcooled and saturated helium were not significant. (author)

30

Single-electron detachment cross sections for 5--50-keV H- ions incident on helium, neon, and argon atoms  

International Nuclear Information System (INIS)

Absolute measurements of the total single-electron detachment (SED) cross sections ?-10 for 3--50-keV H- ions incident on helium atoms and for 5--50-keV H- ions incident on neon and argon atoms are reported in this paper. The present SED cross sections for helium and neon targets are of similar magnitude but have a different energy dependence. By contrast, the SED cross sections for argon targets are significantly larger than either of the other two target species reported in this paper. Comparisons are made with the previous measurements and calculations in the literature

31

Does One Need a 4.5 K Screen in Cryostats of Superconducting Accelerator Devices Operating in Superfluid Helium? Lessons from the LHC  

CERN Document Server

Superfluid helium is increasingly used as a coolant for superconducting devices in particle accelerators: the lower temperature enhances the performance of superconductors in high-field magnets and reduces BCS losses in RF acceleration cavities, while the excellent transport properties of superfluid helium can be put to work in efficient distributed cooling systems. The thermodynamic penalty of operating at lower temperature however requires careful management of the heat loads, achieved inter alia through proper design and construction of the cryostats. A recurrent question appears to be that of the need and practical feasibility of an additional screen cooled by normal helium at around 4.5 K surrounding the cold mass at about 2 K, in such cryostats equipped with a standard 80 K screen. We introduce the issue in terms of first principles applied to the configuration of the cryostats, discuss technical constraints and economical limitations, and illustrate the argumentation with examples taken from large proj...

Lebrun, Ph; Tavian, L

2014-01-01

32

RELAP5 and CATHARE2 benchmarking assessment on two LOFA transients conducted in HE-FUS3 helium facility  

International Nuclear Information System (INIS)

The qualification of numerical tools for the transient and safety analysis of High Temperature Gas Reactors (HTGR) is essential to demonstrate the fulfillment of the GEN IV safety requirements. The availability of experimental data from the ENEA HE-FUS3 facility (Brasimone (Italy)) has given the opportunity to organize a benchmark exercise to assess the capability of a number of transient analysis code to describe the T/H behavior of a helium cooled loop both in steady state and transients conditions. The paper presents the results obtained in the post-test analysis of experimental LOFA transients with two of the most widely used system codes: RELAP5 Mod3.3 applied by ENEA-ANSALDO and CATHARE 2 V2.5 applied by CEA-IRSN. The analysis of these results on the basis of a code-to-data comparison and a code-to-code benchmark allows to verify that both codes are able to qualitatively reproduce the gas system thermal-hydraulics and dynamics, as well as to provide recommendations on gas cooled system modeling for the development of consistent numerical models for the HTGR accident analysis. Moreover, highlighting the weakness in some aspects of the present modeling approach, it is possible to suggest the needs of the future code developments. (authors)

33

Patterning, characterization, and chemical sensing applications of graphene nanoribbon arrays down to 5 nm using helium ion beam lithography.  

Science.gov (United States)

Bandgap engineering of graphene is an essential step toward employing graphene in electronic and sensing applications. Recently, graphene nanoribbons (GNRs) were used to create a bandgap in graphene and function as a semiconducting switch. Although GNRs with widths of alignment, width control, uniformity, high aspect ratios, and edge roughness must be resolved in order to introduce GNRs as a robust alternative technology. Here we report patterning, characterization, and superior chemical sensing of ultranarrow aligned GNR arrays down to 5 nm width using helium ion beam lithography (HIBL) for the first time. The patterned GNR arrays possess narrow and adjustable widths, high aspect ratios, and relatively high quality. Field-effect transistors were fabricated on such GNR arrays and temperature-dependent transport measurements show the thermally activated carrier transport in the GNR array structure. Furthermore, we have demonstrated exceptional NO2 gas sensitivity of the 5 nm GNR array devices down to parts per billion (ppb) levels. The results show the potential of HIBL fabricated GNRs for the electronic and sensing applications. PMID:24467172

Abbas, Ahmad N; Liu, Gang; Liu, Bilu; Zhang, Luyao; Liu, He; Ohlberg, Douglas; Wu, Wei; Zhou, Chongwu

2014-02-25

34

Level indicator for liquid helium  

International Nuclear Information System (INIS)

A level indicator for liquid helium and its block diagram are described. A section of wire made of a superconductor serves as the level indicator for measuring liquid helium. A current flows along this wire, that a part of wire, which is in helium vapours, transfers to a normal state due to joule heat release and corresponding wire overheating, while the other part of wire, which is in liquid helium, remains superconductive due to better heat exchange in liquid, than in gas. Thus, indicator resistance linearly depends on the level of liquid helium, the zero resistance of the indicator corresponding to the maximal level. The indicator differs in simplicity, high sensitivity, linearity and convenience in operation. The indicator design, volt-ampere characteristics of the indicator made of Nb-Ti wire 0.05 mm in diameter at different levels of liquid helium and an electric block diagram are presented. The indicator error does not exceed 5 mm

35

Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for Theory. 5; Radiative Levitation Versus Helium Mixing  

Science.gov (United States)

Atmospheric parameters (T(sub eff), log g), masses and helium abundances are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC6752. For 19 stars we derive magnesium and iron abundances as well and find that iron is enriched by a factor of 50 on average with respect to the cluster abundance whereas the magnesium abundances are consistent with the cluster abundance. Radiation pressure may levitate heavy elements like iron to the surface of the star in a diffusive process. Taking into account the enrichment of heavy elements in our spectroscopic analyses we find that high iron abundances can explain part, but not all, of the problem of anomalously low gravities along the blue HB. The blue HB stars cooler than about 15,100 K and the sdB stars (T(sub eff) greater than or = 20,000 K) agree well with canonical theory when analysed with metal-rich ([M/H] = +0.5) model atmospheres, but the stars in between these two groups remain offset towards lower gravities and masses. Deep Mixing in the red giant progenitor phase is discussed as another mechanism that may influence the position of the blue HB stars in the (T(sub eff), log g)-plane but not their masses.

Moehler, S.; Sweigart, A. V.; Landsman, W. B.; Heber, U.

2000-01-01

36

Effect of dynamically charged helium on tensile properties of V-5Ti, V-4Cr-4Ti, and V-3Ti-1Si  

Energy Technology Data Exchange (ETDEWEB)

In the Dynamic Helium Charging Experiment (DHCE), helium was produced uniformly in the specimen at linear rates of {approx}0.4 to 4.2 appm He/dpa by the decay of tritium during irradiation to 18-31 dpa at 424-600{degrees}C in the lithium-filled DHCE capsules in the Fast Flux Test Facility. This report presents results of postirradiation tests of tensile properties of V-5Ti, V-4Cr-4Ti, V-3Ti-1Si. The effect of helium on tensile strength and ductility was insignificant after irradiation and testing at >420{degrees}C. Contrary to initial expectation, room temperature ductility of DHCE specimens was higher than that on non-DHCE specimens, whereas strength was lower, indicating that different types of hardening centers are produced during DHCE and non-DHCE irradiation. In strong contrast to results of tritium-trick experiments, in which dense coalescence of helium bubbles is produced on grain boundaries in the absence of displacement damage, no intergranular fracture was observed in any tensile specimens irradiated in the DHCE.

Chung, H.M.; Loomis, B.A.; Nowicki, L.; Smith, D.L. [Argonne National Laboratory, Chicago, IL (United States)

1996-04-01

37

High nuclear polarization of helium-3 at low and high pressure by metastability exchange optical pumping at 1.5 Tesla  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We perform metastability exchange optical pumping of helium-3 in a strong magnetic field of 1.5 T. The achieved nuclear polarization, from 80% at 1.33 mbar to 25% at 67 mbar, shows a substantial improvement at high pressures with respect to standard low-field optical pumping. The specific mechanisms of metastability exchange optical pumping at high field are investigated, advantages and intrinsic limitations are discussed. From a practical point of view, our results open the...

Abboud, Marie; Sinatra, Alice; Mai?tre, Xavier; Tastevin, Genevie?ve; Nacher, Pierre-jean

2004-01-01

38

Fast leak of a channel filled with helium at a pressure of 2 bars (channel H5)  

International Nuclear Information System (INIS)

The loss of seal of a helium-filled channel opening the entire cross section of the front part leads to a fast leak. The channel fills to the upper generatrix of the leak orifice and part of the helium contained in the channel escapes into the circuit. The pressure drop in the reflector can lead to reactor and main pump shutdown. On the other hand, the Cooling Circuit Shutdown Bar circuit pumps remain in operation. This paper evaluates the consequences of an incident of this nature for the reactor and the surrounding experimental zones

39

Helium heat transfer  

Energy Technology Data Exchange (ETDEWEB)

Publications of the NBS Cryogenic Division relating to helium heat transfer are summarized, and new results from this past year are given in full. In this latter category are included the following: (1) comprehensive review of thermal oscillations and instabilities, including recommendations for needed direction of study, (2) brief summary of the combination of refrigeration systems and cooling loops, (3) analytical study of superconductor stability under forced flow conditions, analogous to previous studies for pool boiling, (4) Kapitza conductance and thermal conductivity measurements on copper, niobium, and aluminum, and (5) tabular data on a variety of helium properties of importance to the cryogenic engineer. In addition, a brief outline is given of work in progress and/or planned for next year, including forced two-phase flow experiments, further Kapitza conductance measurements, possible superfluid forced flow studies, helium pump survey and evaluation, and thermal stability studies on a cryogenic power transmission line.

Arp, V.; Ballinger, E.R.; Giarratano, P.J.; Hess, R.C.; Jones, M.C.

1972-06-30

40

Gas porosity in bulk and at interfaces on annealing of nickel saturated with helium up to concentration ? < 0.5 at.%  

International Nuclear Information System (INIS)

In the temperature dependence of swelling degree for nickel, implanted with helium up to concentrations of 0.5 at.% the temperature of HeV THeVD type complexes dissociation (900-920 K) divides the temperature range of post-radiation annealing into regions where development of helium porosity obeys different laws which was exhibited by its sharp activation at Tanneal ? THeV. It is shown in the present paper that the above mentioned law is also valid for substantionally lower gas concentrations (cHe ? = 0.02 at.%), however a necessary condition in every case is a proximity of active vacancy sources. If on the contrary such sources are remote (blocked) then in wide range the secondary swelling growth is hindered even at Tanneal Thev which is due to some features of formation of primary gas bubbles at the cost of radiation vacancies, namely to their superequilibrium state

 
 
 
 
41

Disalignment rates of the neon 2p5 and 2p10 atoms due to helium atom collisions measured at temperatures between 77 and 294 K  

Science.gov (United States)

Using a positive column of helium-neon glow discharge plasma at several temperatures between 77 and 294 K, the disalignment rates of excited neon atoms in the 2p5 and 2p10 (in Paschen notation) levels are measured by a polarization-resolved laser-induced fluorescence technique. For the 2p10 case, the disalignment rate due to radiation reabsorption is evaluated from the optical thickness of the plasma measured by a self-absorption method, and then is subtracted from the disalignment rate measured. From the slope of the obtained disalignment rate plotted against the helium atom density we determine the rate coefficients due to helium atom collisions. These rate coefficients are compared with the results of quantum multi-channel close-coupling calculations using the modified long-range potentials proposed by Bahrim and Khadilkar (2009 Phys. Rev. A 79 042715) from the original potentials of Hennecart and Masnou-Seeuws (1985 J. Phys. B: At. Mol. Phys. 18 657). Our present experiment agrees excellently with the theory for the 2p5 level at any temperatures between 77 and 294 K, and for the 2p10 state only at 294 K. Below 294 K, the experimental rate coefficients for the 2p10 state show a more rapid decrease with the decrease in temperature than the theory predicts.

Matsukuma, H.; Shikama, T.; Hasuo, M.

2011-04-01

42

Small scale helium liquefaction systems  

International Nuclear Information System (INIS)

We have developed two small-scale helium liquefaction systems that provide solutions for liquid helium usage in laboratories. These helium liquefaction systems use two-stage pulse tube cryocoolers to provide cooling at 4 K. The cold head/liquefier resides inside of the neck of a dewar. The room temperature helium gas to be liquefied enters the neck of the dewar and is efficiently pre-cooled down to 5-6 K by means of the regenerators and pulse tubes of the cold head before being liquefied. Two models of liquefaction system, LHeP12 and LHeP18, produce liquid helium from room temperature gas with the rates of >12 L/day and 18 L/day.

43

Cavitation pressure in liquid helium  

CERN Document Server

Recent experiments have suggested that, at low enough temperature, the homogeneous nucleation of bubbles occurs in liquid helium near the calculated spinodal limit. This was done in pure superfluid helium 4 and in pure normal liquid helium 3. However, in such experiments, where the negative pressure is produced by focusing an acoustic wave in the bulk liquid, the local amplitude of the instantaneous pressure or density is not directly measurable. In this article, we present a series of measurements as a function of the static pressure in the experimental cell. They allowed us to obtain an upper bound for the cavitation pressure P_cav (at low temperature, P_cav -3.0 bar in helium 3, P_cav > - 10.4 bar in helium 4). In this article we thus present quantitative evidence that cavitation occurs at low temperature near the calculated spinodal limit (-3.1 bar in helium 3 and -9.5 bar in helium 4). Further information is also obtained on the comparison between the two helium isotopes. We finally discuss the magnitud...

Caupin, F; Caupin, Frederic; Balibar, Sebastien

2001-01-01

44

Helium behaviour in nuclear glasses  

International Nuclear Information System (INIS)

The present thesis focuses on the study of helium behavior in R7T7 nuclear waste glass. Helium is generated by the minor actinides alpha decays incorporated in the glass matrix. Therefore, four types of materials were used in this work. These are non radioactive R7T7 glasses saturated with helium under pressure, glasses implanted with 3He+ ions, glasses doped with curium and glasses irradiated in nuclear reactor. The study of helium solubility in saturated R7T7 glass has shown that helium atoms are inserted in the glass free volume. The results yielded a solubility of about 1016 at. cm-3 atm.-1. The incorporation limit of helium in this type of glass has been determined; its value amounted to about 2*1021 at. cm-3, corresponding to 2.5 at.%. Diffusion studies have shown that the helium migration is controlled by the single population dissolved in the glass free volume. An ideal diffusion model was used to simulate the helium release data which allowed to determine diffusion coefficients obeying to the following Arrhenius law: D = D0exp(-Ea/kBT), where D0 = 2.2*10-2 and 5.4*10-3 cm2 s-1 and Ea = 0.61 eV for the helium saturated and the curium doped glass respectively. These results reflect a thermally activated diffusion mechanism which seems to be not influenced by the glass radiation damage and helium concentrations studied in the present work (up to 8*1019 at. g-1, corresponding to 0.1 at.%). Characterizations of the macroscopic, structural and microstructural properties of glasses irradiated in nuclear reactor did not reveal any impact associated with the presence of helium at high concentrations. The observed modifications i.e. a swelling of 0.7 %, a decrease in hardness by 38 %, an increase between 8 and 34 % of the fracture toughness and a stabilization of the glass structure under irradiation, were attributed to the glass nuclear damage induced by the irradiation in reactor. Characterizations by SEM and TEM of R7T7 glasses implanted with helium at high concentrations, doped with curium and irradiated in nuclear reactor showed a homogeneous microstructure free of helium bubbles, pores or cracking. The results of the present work were used to develop a long-term diffusion model of helium in an industrial R7T7 nuclear waste glass. The model considers the thermal history, the fracturing and the alpha activity of the glass. (author)

45

Does one need a 4.5 K screen in cryostats of superconducting accelerator devices operating in superfluid helium? lessons from the LHL  

International Nuclear Information System (INIS)

Superfluid helium is increasingly used as a coolant for superconducting devices in particle accelerators: the lower temperature enhances the performance of superconductors in high-field magnets and reduces BCS losses in RF acceleration cavities, while the excellent transport properties of superfluid helium can be put to work in efficient distributed cooling systems. The thermodynamic penalty of operating at lower temperature however requires careful management of the heat loads, achieved inter alia through proper design and construction of the cryostats. A recurrent question appears to be that of the need and practical feasibility of an additional screen cooled by normal helium at around 4.5 K surrounding the cold mass at about 2 K, in such cryostats equipped with a standard 80 K screen. We introduce the issue in terms of first principles applied to the configuration of the cryostats, discuss technical constraints and economical limitations, and illustrate the argumentation with examples taken from large projects confronted with this issue, i.e. CEBAF, SPL, ESS, LHC, TESLA, European X-FEL, ILC

46

Characterization of helium surface-wave plasmas at intermediate pressures (5–50?Torr): temperatures and density of metastable atoms in the 23s level  

Science.gov (United States)

A stationary surface wave discharge is studied in helium gas at intermediate pressure. By optical emission spectroscopy, rotational temperatures derived from impurities molecular bands have been studied, as well as the excitation temperature from the Boltzmann plot method of helium lines, as a function of gas pressure, absorbed power and axial position. The rotational temperature of OH molecules is supposed to be in thermal equilibrium with the plasma gas and is used for determining its temperature. The influence of the tube diameter has also been studied; it was observed that the tubes with smaller diameter lead to higher gas temperature. By optical absorption spectroscopy, the density of metastable atoms (in 23s level) has been studied as a function of the parameters. An important dependence on the gas pressure has been observed. Indeed, a one order of magnitude reduction is obtained when the pressure increases from 5 to 50?Torr. The density of metastable atoms remains constant as a function of power and almost all along the plasma column. Finally, a collisional-radiative model was used to compare the experimental to the theoretical results of the density of metastable atoms providing at the same time estimations of the density and the temperature of the electrons as well as the density of helium (atomic and molecular) ions. Results showed a good agreement when the tube diameter is large, but for smaller tubes, the agreement was obtained only for the higher gas pressures.

Hamdan, Ahmad; Margot, Joëlle; Vidal, François; Matte, Jean-Pierre

2015-01-01

47

Calculation of the electron-impact coherence parameters for excitation of the 31D state of helium at 26.5 eV  

International Nuclear Information System (INIS)

The 19-state and 29-state R-matrix methods of Fon et al have been extended to calculate the differential cross section (DCS) and electron-impact coherence parameters (EICP) associated with excitation of the 3 1D state of helium for an incident electron energy of 26.5 eV at electron scattering angles ranging from 0-180o. The calculated EICP values are compared with the only experimental data reported recently by McLaughlin et al. The agreement is good. (Author)

48

Liquid hydrogen target cooled by circulating helium  

International Nuclear Information System (INIS)

Structure and characteristics of a liquid hydrogen target, where hydrogen is liquefied with liquid helium flow using evaporation heat of liquid helium and vapour cold, are described. Good thermal insulation of liquid helium supply line permits to remove out of the target the most volumetric and heavy component - helium tank - and to supply liquid helium along spreaded pipeline from the Dewar helium flask. It results in considerable reduction of dimensions and weight, the structure simplification and work facilitation with the target. The target having a working volume of 400 mm length and 60 mm diameter was tested. Vacuum casing of the working volume was made of foam plastic, heat flow to the working volume is equal to 1.5 W. Achieving mode of operation including structure cooling and hydrogen liquefaction took approximately 3 h, liquid helium flow rate for liquefaction of 1 l hydrogen is 2.7 l. Liquid helium flow rate in the mode of operation was equal to 0.7 l/h, i.e. target operation period without adding liquid helium to the Dewar flask is 4-5 days. The target described is notable for simplicity in fabrication, reliability in operation and is very suitable for using in experiment as compared to existing targets with hydrogen liquefaction with liquid helium. Unit structure of the target enables to easily change its configuration relative to problems of concrete physical experiment

49

Geomagnetically trapped energetic helium nuclei  

International Nuclear Information System (INIS)

Geomagnetically trapped helium nuclei, at high energy (?40 endash 100 MeV/nucleon), have been measured by the ONR-604 instrument during the 1990/1991 CRRES mission. The ONR-604 instrument resolved the isotopes of helium with a mass resolution of 0.1 amu. The energetic helium observed at L3He and 4He show two peaks at L=1.2 and 1.9. Each isotope close-quote s flux, in each peak, can be characterized by a power law energy spectrum. The energy spectrum of the 3He is different from that of 4He, indicating that the 3He/4He ratio is energy dependent. Over the energy range of 51 endash 86 MeV/nucleon, the 3He/4He ratio is 8.7±3.1 at L=1.1 endash 1.5 and is 2.4±0.6 at L=1.5 endash 2.3. The trapped helium counting rates decrease gradually with time during the CRRES mission, when the anomalous component is excluded from the inner heliosphere, indicating that these high energy ions were not injected by flares during this time period. The decrease in intensity is attributed mainly to the events around L=1.9. The helium around L=1.2, dominated by 3He, does not show a significant temporal evolution, which implies a long-term energetic trapped 3He population. Two possible origins of the geomagnetically trapped helium is the geomagnetically trapped helium isotopes are the interactions of energetic protons with the upper atmosphere and/or the inward diffusion and acceleration of helium ions due to electric-field fluctuations. copyright 1996 American Institute of Physics

50

Nonrelativistic contributions of order ?5m?c2 to the Lamb shift in muonic hydrogen and deuterium, and in the muonic helium ion  

International Nuclear Information System (INIS)

Contributions to the energy levels in light muonic atoms and, in particular, to the Lamb shift fall into a few well-distinguished classes. The related diagrams are calculated using different approaches. In particular, there is a specific type of nonrelativistic (NR) contribution. Here, we consider such corrections to the Lamb shift of order ?5m?. These contributions are due to free vacuum-polarization loops as well as to various effects of light-by-light scattering. The closed loop in the related diagrams is an electronic one, which allows an NR consideration of the muon. Both types of contributions have been known for some time, however, the results obtained to date are only partial results. We complete a calculation of the ?5m? contributions for muonic hydrogen. The results are also adjusted for muonic deuterium atom and helium ion.

51

Helium retention and early stages of helium-vacancy complexes formation in low energy helium-implanted tungsten  

Science.gov (United States)

Tungsten has been selected as the material of the divertor of the ITER fusion reactor. In operation, tungsten will be submitted to high alpha particles bombardment. The consequence of helium implantation is a major issue for the reliability of tungsten components. The aim of the study was to investigate the behavior of helium implanted in tungsten at low energy and low flux. 320 eV Helium ions were introduced by plasma immersion at the flux of 2.5 × 1018 ion/m-2/s-1. The helium behavior was investigated by Nuclear Reaction Analysis and the evolution of the tungsten lattice by Positron Annihilation Spectroscopy (PAS). Helium-implanted tungsten exhibits a low retention rate (13.6% at 9.4 × 1019 He m-2) which decreases with the implantation fluence. The desorption of helium starts at low temperature (clusters does not require the presence of pre-existing vacancy and thus proceed from the trap mutation phenomenon.

Lhuillier, P. E.; Belhabib, T.; Desgardin, P.; Courtois, B.; Sauvage, T.; Barthe, M. F.; Thomann, A. L.; Brault, P.; Tessier, Y.

2013-02-01

52

Helium retention and early stages of helium-vacancy complexes formation in low energy helium-implanted tungsten  

International Nuclear Information System (INIS)

Tungsten has been selected as the material of the divertor of the ITER fusion reactor. In operation, tungsten will be submitted to high alpha particles bombardment. The consequence of helium implantation is a major issue for the reliability of tungsten components. The aim of the study was to investigate the behavior of helium implanted in tungsten at low energy and low flux. 320 eV Helium ions were introduced by plasma immersion at the flux of 2.5 × 1018 ion/m?2/s?1. The helium behavior was investigated by Nuclear Reaction Analysis and the evolution of the tungsten lattice by Positron Annihilation Spectroscopy (PAS). Helium-implanted tungsten exhibits a low retention rate (13.6% at 9.4 × 1019 He m?2) which decreases with the implantation fluence. The desorption of helium starts at low temperature (<400 K). SEM analysis after annealing over 973 K shows sparse pores probably due to bubbles opening at the surface. The creation of helium-filled defects in the near surface layer (0.5 to ?20 nm) was followed by PAS. A low level of damages was introduced by 12 MeV proton irradiation, prior to He introduction and allowed to examine the influence of pre-existing defects on the helium trapping. The PAS results suggest that the early stage of the formation of helium-filled vacancy clusters does not require the presence of pre-existing vacancy and thus proceed from the trap mutation phenomenon

53

Standard Guide for Simulation of Helium Effects in Irradiated Metals  

CERN Document Server

1.1 This guide provides advice for conducting experiments to investigate the effects of helium on the properties of metals where the technique for introducing the helium differs in some way from the actual mechanism of introduction of helium in service. Simulation techniques considered for introducing helium shall include charged particle implantation, exposure to ?-emitting radioisotopes, and tritium decay techniques. Procedures for the analysis of helium content and helium distribution within the specimen are also recommended. 1.2 Two other methods for introducing helium into irradiated materials are not covered in this guide. They are the enhancement of helium production in nickel-bearing alloys by spectral tailoring in mixed-spectrum fission reactors, and isotopic tailoring in both fast and mixed-spectrum fission reactors. These techniques are described in Refs (1-5). Dual ion beam techniques (6) for simultaneously implanting helium and generating displacement damage are also not included here. This lat...

American Society for Testing and Materials. Philadelphia

1996-01-01

54

Spent Nuclear Fuel (SNF) Project Cask and MCO Helium Purge System Design Review Completion Report - Project A.5 and A.6  

International Nuclear Information System (INIS)

This report documents the results of the design verification performed on the Cask and Multiple Canister Over-pack (MCO) Helium Purge System. The helium purge system is part of the Spent Nuclear Fuel (SNF) Project Cask Loadout System (CLS) at 100K area. The design verification employed the ''Independent Review Method'' in accordance with Administrative Procedure (AP) EN-6-027-01

55

Supercritical helium heat transfer  

International Nuclear Information System (INIS)

This paper reports part of the National Bureau of Standards Cryogenics Division's program to provide helium heat transfer information to designers of helium cooling systems. An experiment on supercritical helium heat transfer is described, and its results are compared with various standard and modified correlation expressions. Extensive appendices give tables of helium viscosity, thermal conductivity, and Prandtl numbers from 3 to 3000K. (U.S.)

56

Subharmonic responses in liquid helium  

International Nuclear Information System (INIS)

We report measurements of the subharmonic responses of liquid helium to ultrasound in the temperature range 1.3 K< T<2.5 K at applied frequencies of 0.3, 1.0, 2.8, and 10 MHz. Experimental results are compared in detail to the oscillating bubble model of Eller and Flynn and to predictions based upon parametric amplification. We show that the subharmonic response in liquid helium, below the superfluid transition, is directly associated with bulk turbulence. Visualization of the subharmonic response by light diffraction demonstrates that it can be a sustained and coherent bulk effect

57

A helium regenerative compressor  

International Nuclear Information System (INIS)

This paper discusses the design and performance of a regenerative compressor that was developed primarily for use in cryogenic helium systems. The objectives for the development were to achieve acceptable efficiency in the machine using conventional motor and bearing technology while reducing the complexity of the system required to control contamination from the lubricants. A single stage compressor was built and tested. The compressor incorporates aerodynamically shaped blades on a 218 mm (8.6 inches) diameter impeller to achieve high efficiency. A gas-buffered non-contact shaft seal is used to oppose the diffusion of lubricant from the motor bearings into the cryogenic circuit. Since it is a rotating machine, the flow is continuous and steady, and the machine is very quiet. During performance testing with helium, the single stage machine has demonstrated a pressure ratio of 1.5 at a flow rate of 12 g/s with measured isothermal efficiencies in excess of 30%. This performance compares favorably with efficiencies generally achieved in oil flooded screw compressors

58

Paramagnetic Attraction of Impurity-Helium Solids  

Science.gov (United States)

Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

2003-01-01

59

Spent Nuclear Fuel (SNF) Project Cask and MCO Helium Purge System Design Review Completion Report Project A.5 and A.6  

Energy Technology Data Exchange (ETDEWEB)

This report documents the results of the design verification performed on the Cask and Multiple Canister Over-pack (MCO) Helium Purge System. The helium purge system is part of the Spent Nuclear Fuel (SNF) Project Cask Loadout System (CLS) at 100K area. The design verification employed the ''Independent Review Method'' in accordance with Administrative Procedure (AP) EN-6-027-01.

ARD, K.E.

2000-04-19

60

Cooling with Superfluid Helium  

CERN Document Server

The technical properties of helium II (‘superfluid’ helium) are presented in view of its applications to the cooling of superconducting devices, particularly in particle accelerators. Cooling schemes are discussed in terms of heat transfer performance and limitations. Large-capacity refrigeration techniques below 2 K are reviewed, with regard to thermodynamic cycles as well as process machinery. Examples drawn from existing or planned projects illustrate the presentation. Keywords: superfluid helium, cryogenics

Lebrun, P

2014-01-01

 
 
 
 
61

Flow cytometric immunofluorescence and DNA analysis: Using a 1.5 mW helium-neon laser (544 nm)  

Energy Technology Data Exchange (ETDEWEB)

We evaluate a 1.5 mW HeNe laser (544 nm) for use on an EPICS{reg_sign} Elite with a 76 {mu}m Sortsense flow cell. The two applications chosen were immunofluorescence and DNA analysis. We measured the fluorescence threshhold of phycoerytherin calibration beads to be approximately 336 MESF. Cell analysis with a HeNe laser and Argon laser correlated well for the CD4{sup PE}, CD56{sup PE}, CD19{sup PE} conjugates, with correlation coefficients of 0.98, 0.99, 0.94, respectively. The % positive and mean channel fluorescence were comparable to the results obtained with a 15 mW Argon laser. In addition, a three-color configuration PE yielded excellent results. Cell analysis of CD4{sup PE}, CD3{sup ECD} and CD19{sup Cy-Chrome} with the HeNe laser and Argon laser correlated well with correlation coefficients of 0.96, 0.95, and 0.92, respectively. The histograms showed good separation between the negative cells, the dimly staining cells and the brightly staining cells. Propidium Iodide was chosen for DNA analysis. Full CV values for whole blood DNA fluorescence using the green laser were good at 2.6%. These data indicate the low power 544 nm laser is sufficient to do immunophenotyping and DNA analysis. Results may be explained by higher quantum efficiency and lower background fluorescence. The wavelength of the 544 nm laser is much closer to the excitation peaks of PI, PE, and the tandem dyes ECD and Cy-Chrome. Also, the Raman scattering of water for the 544 nm laser has a longer wavelength maximum than the emission peaks of PI, PE, and ECD. The major advantages of this laser for the research laboratory are small size, no cooling fan, low power requirements and low cost. 16 refs., 5 figs., 3 tabs.

Hudson, J.C.; Porcelli, R.T.; Russell, T.R. [Coulter Corp., Miami, FL (United States)

1995-10-01

62

Helium diffusion in the sun  

Science.gov (United States)

We calculate improved standard solar models using the new Livermore (OPAL) opacity tables, an accurate (exportable) nuclear energy generation routine which takes account of recent measurements and analyses, and the recent Anders-Grevesse determination of heavy element abundances. We also evaluate directly the effect of the diffusion of helium with respect to hydrogen on the calculated neutrino fluxes, on the primordial solar helium abundance, and on the depth of the convective zone. Helium diffusion increases the predicted event rates by about 0.8 SNU, or 11 percent of the total rate, in the chlorine solar neutrino experiment, by about 3.5 SNU, or 3 percent, in the gallium solar neutrino experiments, and by about 12 percent in the Kamiokande and SNO solar neutrino experiments. The best standard solar model including helium diffusion and the most accurate nuclear parameters, element abundances, and radiative opacity predicts a value of 8.0 SNU +/- 3.0 SNU for the C1-37 experiment and 132 +21/-17 SNU for the Ga - 71 experiment, where the uncertainties include 3 sigma errors for all measured input parameters.

Bahcall, J. N.; Pinsonneault, M. H.

1992-01-01

63

Helium resources of Mare Tranquillitatis  

Science.gov (United States)

Wisconsin Center for Space Automation and Robotics, Univ. of Wisc., Madison, Wisc. Mare Tranquillitatis, about 300000 sq km in area, is currently the most promising lunar source of He-3 for fueling fusion power plants on Earth. About 60 pct. of the mare regolith consists of particles 100 microns or less in diameter. Helium and other gases derived from the solar wind are concentrated in the fine size fractions. Studies of very small craters indicate that the average regolith exceeds 3 m in areas away from larger craters and other mare features not amenable to mining. There is no evidence of decrease of helium content of regolith and depth. Helium is known to be enriched in regoliths that are high in TiO2 content. Remote sensing indicates that about 90 pct. of Mare Tranquillitatis is covered by regolith ranging from about 6 to +7.5 pct. TiO2; inferred He contents range from 20 to at least 45 wppm total helium (7 to 18 wppb He-3). Detailed studies of craters and inferred ejecta halos displayed on high resolution photographs of the Apollo 11 and Ranger 8 areas suggest that as much as 50 pct. of the mare regolith may be physically minable, on average, with appropriate mining equipment. Assuming that the average thickness of regolith is 3 m, and that 50 pct. of the mare area is minable, the He-3 content of minable regolith containing 20 to 45 wppm total He is estimated at about 94,000 tonnes.

Cameron, Eugene N.

1991-01-01

64

Low-temperature centrifugal helium compressor  

International Nuclear Information System (INIS)

A centrifugal helium compressor with gas bearings, which can be operated at the temperature of liquid nitrogen, has been investigated. This compressor has the advantages that the compression ratio should be higher than the room temperature operation and that the contamination of helium could be eliminated. The outer diameter of the rotor is 112 mm. The experimental result for helium gas at low temperature shows a flow rate of 47 g/s and a compression ratio of 1.2 when the inlet pressure was 1 ata and the rotational speed 550 rev/s. The investigation is now focused on obtaining a compression ratio of 1.5. (author)

65

Fermilab's Central Helium Liquefier capacity upgrade  

International Nuclear Information System (INIS)

Fermilab's Tevatron Superconducting Accelerator has begun operations of colliding beams of protons and antiprotons at 980 GeV. This has been accomplished by lowering the operating temperature of the Tevatron magnet system from 4.5K to 3.6K using cold compressors on the two-phase portion of the system. The heat of compression by the cold compressors produces a greater liquid helium demand from the Central Helium Liquefier (CHL). Various upgrades have been completed or are in progress to provide sufficient capacity and redundancy for the liquid helium supply. The maximum allowable pressure of the helium system has been raised from 1.31 MPa to 1.65 MPa, thus providing a measured 18% liquefaction capacity increase for same compressors flow. One of four reciprocating helium compressors has been modified for four-stage operations, thus providing 33% increased capacity and more reliable operations. Together with capacity control of individual compressors, the available choice of operation of two 3-stage and two 4-stage compressors will provide the flexibility to operate the Central Helium Liquefier system at the most economical power consumption relative to the liquid helium demand by the accelerator cryogenic system

66

ESCAR helium refrigeration system  

International Nuclear Information System (INIS)

The ESCAR cryogenic system, with its two distribution loops offers many advantages. The system models the kind of system that can and should be used in future accelerators. The refrigerator cold box, with its turbine expanders, and the helium screw compressor system represent a significant step in the development of reliable helium refrigeration systems. (auth)

67

Anti-irradiation performance against helium bombardment in bulk metallic glass (Cu47Zr45Al8)98.5Y1.5  

International Nuclear Information System (INIS)

Highlights: ? This paper used He2+ ion-irradiated metallic glass (Cu47Zr45Al8)98.5Y1.5 and the W metal with the energy of 500 keV. ? There was no significant irradiation damage phenomenon on the surface of metallic glass at different irradiation fluences. ? For irradiated W, the peeling, delamination and flaking appeared numerously at fluences of 1 × 1018 and 2 × 1018 ions/cm2. ? The resistance to He2+ irradiation of metallic glass (Cu47Zr45Al8)98.5Y1.5 was superior to the one in W metal. -- Abstract: In order to compare the resistance to He2+ ion induced irradiation between metallic glass and polycrystal W metal, this paper used different fluences of He2+ ion-irradiated metallic glass (Cu47Zr45Al8)98.5Y1.5 and polycrystal W with an energy of 500 keV. The SRIM simulation calculation results showed that the range (1.19 ?m) of He2+ in metallic glass was greater than the one (0.76 ?m) in polycrystal W. The SEM analysis showed that there was no significant irradiation damage phenomenon on the surface of metallic glass, and there was only a damage layer 1.45 ?m away from the surface when the fluence reached 2 × 1018 ions/cm2. For W, there were surface peeling, flaking and other surface damages at a fluence of 1 × 1018 ions/cm2; when the fluence increased to 2 × 1018 ions/cm2, multilayer detachment phenomenon appeared. The surface root mean square roughness of metallic glass (Cu47Zr45Al8)98.5Y1.5 first increased and then decreased with the increase of fluence. The surface reflectivity of (Cu47Zr45Al8)98.5Y1.5 decreased with the increase of fluence. Through detection by XRD, it was found that (Cu47Zr45Al8)98.5Y1.5 always maintained amorphous phase after different fluences of radiation. The resistance to He2+ irradiation of metallic glass (Cu47Zr45Al8)98.5Y1.5 was superior to the one in polycrystal W

68

Dynamic model of helium turbine cycle system  

International Nuclear Information System (INIS)

The one-dimension flow and heat transfer models are built to simulate the components of helium turbine system, including the helium turbine model, compressor model, heat exchanger model, valve model, pipe model and shaft velocity model. The transient simulation code is established in MATLAB. The accident of loss of load and the transient of decreasing heat transfer capacity of the main heat exchanger by 5% are simulated, and important parameters like helium flow rate, temperature, shaft velocity, power rate and compressor surge margin are analyzed. The calculated results agree with the analyzed results. This shows that the present model can be used to simulate the dynamic process of helium turbine closed-cycle system. (authors)

69

Studies of helium breakdown at low temperatures  

International Nuclear Information System (INIS)

For designing cryogenic installations the breakdown strength of helium at temperatures near absolute zero has to be known. Various breakdown strengths are reported in literature concerning liquid helium. It is the objective of these studies to find an explanation for the different breakdown strengths by suitable variation of parameters. Various electrode materials commonly used in low temperature techniques with different sample preparation are used to measure breakdown strength of liquid helium in the gap range from 0.5 mm to 3 mm. A substantial influence of roughness, oxide layer and microcracks on strength is revealed. These terms are summarized and defined as 'condition of the electrode surface'. Taking this into account the various breakdown strengths can be qualitatively explained. Based on these results breakdown strength in supercritical high density helium is examined. A Paschen-curve can be given for this thermodynamical region. (orig./WL)

70

Helium generation in fusion reactor materials  

Energy Technology Data Exchange (ETDEWEB)

During this report period a topical report entitled A Neutron Fluence Map for the Rotating Target Neutron Source, (AI-ERDA-13188) was completed and distributed. The report inluded new 14.8-MeV neutron cross section data for the Ni, Nb, and Au dosimetry reactions. These results are summarized. A description is given of the preliminary analysis of wire rings included in the irradiation capsule for helium accumulation fluence dosimetry. The results show non-uniformities in the neutron fluence distribution characterizing this irradiation, and point out the value of helium accumulation fluence dosimetry for characterizing high energy (approx. 5 to 30 MeV) neutron fields. The helium accumulation fluence data are being used to adjust the neutron fluence map for calculation of final helium generation cross sections from the other RTNS-irradiated pure element specimens.

Farrar, H IV; Kneff, D W

1977-01-01

71

Deuterium trapping in helium-implanted nickel  

International Nuclear Information System (INIS)

By means of ion-beam-analysis techniques, the trapping of deuterium implanted into nickel preimplanted with helium was investigated in the temperature range 100--500 K. Following room-temperature helium implantations and deuterium implantations at approx.100 K, linear-ramp annealing (1--2 K/min) was carried out, while the deuterium concentration within the near-surface region (0--0.5 ?m) was monitored by use of the nuclear reaction D(3He,?)1 H. The release curves were analyzed by solving a diffusion equation with the appropriate trapping terms. In addition to trapping by lattice defects, stronger helium-associated traps were found with a binding enthalpy of 0.55 +- 0.05 eV relative to a solution site. We propose that the responsible entities are small helium bubbles observed in the implanted material by transmission electron microscopy

72

Small size helium refrigerating systems  

International Nuclear Information System (INIS)

Recently, for cooling the superconducting magnets used for medical nuclear magnetic resonance diagnostic system and for cooling Josephson elements, the development of the small helium refrigerating system of low vibration and maintenance free has been advanced. As the refrigerating system satisfying this requirement, a compact helium refrigerator using super-small, superhigh speed expansion turbines and diffusion joined laminate heat exchangers and a single stage screw compressor were developed. As the results of having carried out the performance test by the combination of these, the efficiency of the first turbine was 41 %, and that of the second turbine was 60 %. Besides, the refrigerating capacity was about 70 W (at 77 K) + 5 W (at 4.5 K). Thus the prospect of putting it in practical use was able to be obtained. The small helium refrigerator is composed of a compressor unit and a cold box containing two expansion turbines, five heat exchangers and Joule Thompson valves. These components are described, and the results of experiment are reported. (Kako, I.)

73

Particle detection using superfluid helium  

International Nuclear Information System (INIS)

5 MeV ? particles were observed to be stopped in volumes up to two liters of liquid helium at 70 mK. A fraction of the kinetic energy of an ? particle is converted to elementary excitations (rotons and phonons), which propagate ballistically in isotopically pure 4He below 0.1 K. Most of these excitations have sufficient energy to evaporate helium atoms on hitting a free surface. The evaporated helium atoms can be detected calorimetrically when adsorbed on a thin silicon wafer (?1.7 g, 35 cm2) suspended above the liquid. Temperature changes of the silicon are measured with a NTD germanium bolometer. For the geometry studied the observed temperature change of the silicon resulting from an ? event in the liquid is approximately 5% of the temperature rise from an ? hitting the silicon directly. The implications of these measurements will be discussed as they relate to the possible construction of a large scale detector of solar neutrinos. (author) 14 refs.; 4 figs

74

Spectral measurements along the path of N ions impinged into dense helium gas (400 Torr and 5.2 K). II. Excimer reactions dependent on stopping power and large emission yields near the termination of the track  

International Nuclear Information System (INIS)

Emission spectra and their decay were measured along the path of 4 MeV/amu N ions impinged into dense helium gas near 5.2 K and 420 Torr. Specific scintillation, dL/dX, and scintillation efficiency, dL/dE, for each emission band were measured separately on total, fast initial-rise (-1 cm2: Some of the emissions increased abruptly as the stopping power exceeded this value, while the other emissions decreased or their rates of increase were suppressed. This bend point corresponds to the starting point of a rapidly decreasing yield of delta rays. The result shows that helium has a good scintillation response to high-density excitation occurring at the termination of tracks of N ions, in contrast to usual scintillators, where scintillation decreases abruptly with decreasing delta-ray yield. The large yields of emissions at high-density excitation are explained by the direct excitation, induced emission, and cyclic regeneration of excimers by bimolecular reactions between the nonradiative metastable state, a3, in addition to a very low probability of quenching in helium. Furthermore, it is shown that the present results support the tentative assignment made in part I of this report that theent made in part I of this report that the new triplet bands centered at 4587 A result from an excimer--dimer

75

Core helium flash  

International Nuclear Information System (INIS)

The role of convection in the core helium flash is simulated by two-dimensional eddies interacting with the thermonuclear runaway. These eddies are followed by the explicit solution of the 2D conservation laws with a 2D finite difference hydrodynamics code. Thus, no phenomenological theory of convection such as the local mixing length theory is required. The core helium flash is violent, producing a deflagration wave. This differs from the detonation wave (and subsequent disruption of the entire star) produced in previous spherically symmetric violent core helium flashes as the second dimension provides a degree of relief which allows the expansion wave to decouple itself from the burning front. Our results predict that a considerable amount of helium in the core will be burned before the horizontal branch is reached and that some envelope mass loss is likely

76

Nucleation of helium precipitates in nickel observed by HDS  

International Nuclear Information System (INIS)

Thermal Helium Desorption Spectrometry (HDS) has been used to study the room temperature nucleation of helium precipitates at point defects in Ni, notably HeV defects at depth approx.=20 nm below the crystal surface. Helium is injected into the crystal by 50 eV He ion-irradiation which causes no atomic displacements. It has been observed that Hesub(n)V defects with occupation from n=2 He to n=4 He bind helium equally strongly, but weaker than for HeV. For n>=5 He the binding increases rapidly. The observed behaviour is attributed to helium induced trap mutation and agrees qualitatively with results of atomistic calculations in nickel for this case. Helium precipitation at near surface trapping sites is held responsible for the observed increase of helium release temperatures with helium dose when an undamaged crystal is irradiated. Preliminary TEM observations of Ni specimens irradiated with 50 times higher helium doses than the maximum dose used in the HDS experiments indicated planar clustering of the helium. (orig.)

77

Closed cycle liquid helium refrigerators  

International Nuclear Information System (INIS)

We have developed closed cycle liquid helium refrigerators using a Joule Thomson circuit precooled by commercially available two staged Gifford Mac Mahon cryocoolers. The Joule Thomson counterflow heat exchangers are modular and have been thermo-hydraulically characterized. Fully automatic cool down and operation are achieved by two pneumatically driven by pass and expansion valves. Several apparatus have been built or are under assembly with cooling power ranging from 100 mW up to 5 Watt, for temperature ranging from 2.8 K up to 4.5 K. A trouble free operation with several warm up and cool down cycles has been proven over 7000 hours

78

THERMAL UNIFORMITY OF LIQUID HELIUM IN ELECTRON BUBBLE CHAMBER.  

Energy Technology Data Exchange (ETDEWEB)

A CRYOGENIC RESEARCH APPARATUS TO MEASURE THE MOVEMENT OF ELECTRONS UNDER A HIGH ELECTRIC FIELD IN A LIQUID HELIUM BATH WAS DESIGNED AND BUILT AT THE BROOKHAVEN NATIONAL LABORATORY AND THE NEVIS LABORATORY OF COLUMBIA UNIVERSITY. THE LIQUID HELIUM CHAMBER IS A DOUBLE WALLED CYLINDRICAL CONTAINER EQUIPPED WITH 5 OPTICS WINDOWS AND 10 HIGH VOLTAGE CABLES. TO SHIELD THE LIQUID HELIUM CHAMBER AGAINST THE EXTERNAL HEAT LOADS AND TO PROVIDE THE THERMAL UNIFORMITY IN THE LIQUID HELIUM CHAMBER, THE DOUBLE WALLED JACKET WAS COOLED BY A PUMPED HELIUM BATH. THE HELIUM CHAMBER WAS BUILT INTO A COMMERICAL LN2 / LHE CRYOSTAT. THIS PAPER PRESENTS THE DESIGN AND THE NUMERICAL SIMULATION ANALYSIS ON THERMAL UNIFORMITY OF THE ELECTRON BUBBLE CHAMBER.

WANG,L.; JIA,L.

2002-07-22

79

Observation of the R(0.5) 2?1/2 transition of15N 18 O in helium nanodroplets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract Using our diode-laser- helium cluster machine setup we were able to detect the R(0.5) 2?1/2 transition of15N 18 O in heliumnanodroplets at 1796.38 cm-1. The line is red-shifted by 1.55 cm-1 with respect to the gas-phase. The transition and has a FWHM of 0.050 cm-1, which agrees very well with the result for 14N 16 O , indicating rotational relaxation.

Metzelthin, Anja; Havenith-Newen, Martina

2007-01-01

80

Helium flooded cryopump with increased hydrogen and helium entrainment factor  

International Nuclear Information System (INIS)

Superhigh-vacuum helium condensation-sorption pump with H2 and H entrainment factors 1.7 and 3.1 times respectively exceeding those in the known design cryopumps with the same diameters of casings and connecting flange flow sections is described. The N2 pumping-out rate is 6m3/s, the H2 one is 21 m3/s, the H2 pumping-out rate constitutes 12m3/s, the casing diameter is 0.5, the height - 0.8m, mass-35 kg. The pump is fabricated of titanium and aluminium

 
 
 
 
81

High-temperature helium-loop facility  

International Nuclear Information System (INIS)

The high-temperature helium loop is a facility for materials testing in ultrapure helium gas at high temperatures. The closed loop system is capable of recirculating high-purity helium or helium with controlled impurities. The gas loop maximum operating conditions are as follows: 300 psi pressure, 500 lb/h flow rate, and 21000F temperature. The two test sections can accept samples up to 3.5 in. diameter and 5 ft long. The gas loop is fully instrumented to continuously monitor all parameters of loop operation as well as helium impurities. The loop is fully automated to operate continuously and requires only a daily servicing by a qualified operator to replenish recorder charts and helium makeup gas. Because of its versatility and high degree of parameter control, the helium loop is applicable to many types of materials research. This report describes the test apparatus, operating parameters, peripheral systems, and instrumentation system. The experimental capabilities and test conand presents the results that have been obtained. The study has been conducted using a four-phase approach. The first phase develops the solution to the steady-state radon-diffusion equation in one-dimensieered barriers; disposal charge analysis; analysis of spent fuel policy implementation; spent f water. Field measurements and observations are reported for each site. Analytical data and field measurements are presented in tables and maps. Uranium concentrations in the sediments which were above detection limits ranged from 0.10 t 51.2 ppM. The mean of the logarithms of the uranium concentrations was 0.53. A group of high uranium concentrations occurs near the junctions of quadrangles AB, AC, BB, a 200 mK. In case 2), x-ray studies of isotopic phase separation in 3He--4He bcc solids were carried out by B. A. Fraass

82

Superfluid helium acoustic microscopy  

International Nuclear Information System (INIS)

This dissertation describes the development of an acoustic microscope operating in superfluid helium at temperatures less than 0.1K. The acoustic microscope uses sound waves, brought to a focus in a liquid, to image a sample. The lateral resolution of the microscope is approximately equal to the wavelength of the sound in the liquid. Low temperature superfluid helium is the ultimate fluid for acoustic microscopy because of its extremely small acoustic attenuation, allowing short wavelength and high resolution imaging. The present resolution of the helium acoustic microscope is 200 A using 8 GHz sound waves. The wavelength in helium at this frequency is only 300 A, twenty times shorter than red light. Several images are presented, including biological and integrated circuit samples. Comparisons are made with other forms of high resolution microscopy, specifically the scanning and transmission electron microscopes. By virtue of its contrast mechanisms and high resolution, the helium acoustic microscope can image many sample features that cannot be seen in other ways

83

Tritium/Helium-3 Dating  

Science.gov (United States)

First, the USGS summarizes the use of tritium and helium-3 for dating geologically young groundwater (1). Researchers can find the conditions needed to solve the helium isotope mass balance as well as equations and corrections needed to obtain the age of water. The second website, provided by the Rosenstiel School of Marine and Atmospheric Sciences, discusses the presence of tritium and helium isotopes in the oceans (2). Users can find out about the Noble Gas Isotope Lab's research projects including the _Mantle 3He Distribution and Deep Circulation in the Indian Ocean_. Next, the University of Ottawa offers equations for helium and tritium concentrations and decay (3). Visitors can also learn how solubility of noble gases is affected by temperature. Fourth, the University of Waterloo describes the characteristics of the hydrogen radioisotope, tritium (4). The website explains how tritium was discovered through the work of Lord Rutherford, Sir John, Ernest Lawrence, Luis Alvarex, Willard Libby, and others. Next, the University of T'bingen furnishes a pdf file dealing with numerous dating techniques including fission track, radio carbon, and thermoluminescence dating (5). Beginning on page nine, individuals can learn about tritium formation and decay as well as its use in dating ground water. At the sixth website, the USGS describes the characteristics of the stable isotopes of helium (6). Visitors can discover how 3He is used to date geologically young ground water, whereas 4He is used to date older ground water. The seventh website, created by SAHRA (Sustainability of semi-Arid Hydrology and Riparian Areas) at the University of Arizona, illustrates the effectiveness of isotope hydrology in "understanding fundamental physical, chemical, biological, and climate forcing processes occurring in a watershed" (7). Along with the discussion of the fundamentals of age dating and sources of isotopes, visitors can learn the advantages to using tritium for water samples collected in the field. Lastly, the Victoria University of Manchester introduces its research using noble gas isotopes to better understand earth systems (8). Visitors can discover the decay rates of tritium to 3He and the rates of accumulation of 4He in older groundwater as well as many applications of dating water.

84

Helium transfer line installation details.  

CERN Multimedia

A particularity of the 32 m long four in one helium transfer line in between the cold box in USC55 and the cavern UX5 is the fact that the transfer line passes through a hole in the crane rail support beam. In order to ensure the alignment of the suspension rail in the interconnecting tunnel with the hole in the rail support as well as the connection points at both ends required precise measurements of the given geometries as well as the installation of a temporary target for the verification of the theoretical predictions.

G. Perinic

2007-01-01

85

Helium solubility and bubble growth in metals under high pressure  

International Nuclear Information System (INIS)

Helium solubility and bubble growth in metals under high pressure polycrystals and single crystals of gold were heated in helium at temperatures between 475 K and 1250 K in a pressure regime of 200 to 2700 bar to measure the solubility of helium in gold. After quenching to room temperature the helium content, measured by mass spectrometry, showed the following properties: 1) A linear dependence of the He solubility on pressure. 2) Thinning of the specimen reduces the helium content by a factor 10 to 100 but does not change the linear pressure dependence. 3) The thermal release of He from thinned polycrystals and single crystals occurs mainly in a single peak at 500 K. 4) The He concentration of the thinned single crystals was lower by a factor of 10 to 50 than that of the thinned polycrystals. 5) The He solubility in single crystals can be described by an enthalpy of solution Hsub(s)sup(f) = 0.85 +- 0.7 eV and a non-configurational entropy of Ssub(s)sup(f) between 0 k and 1 k (k: Boltzmann-constant). In order to measure the pressure dependence of helium bubble growth in nickel polycrystal Ni-foils were ?-implanted to a helium content of 130 appm. The evaluation of the size distribution of the helium bubbles after heat treatments shows 1) The helium content of the observable bubbles - assumed to be in equilibrium - equals the amount of helium implanted into the specimen. 2) The activation energy for the growth of helium bubbles is 1.25 +- 0.3 eV. The comparison of specimen which had been heated at low pressures up to 10 bar with others heated at 2500-2700 bar does not show an unequivocal pressure dependence for helium bubble growth. (orig./IHOE)

86

Charged particles over liquid helium  

International Nuclear Information System (INIS)

The analysis of dusty plasma properties at cryogenic temperatures shows that it is necessary to take into account the condensation of helium on the plasma particles. The micron particles in the saturated helium vapor are covered by a liquid helium film of 100 A thick. This leads to the limitation of electron charge of the particles, as the electrons can hardly penetrate such a film. The exceptions are Cs, Rb and K clusters as they are not wetted with helium.

87

Cavitation in flowing superfluid helium  

Science.gov (United States)

Flowing superfluid helium cavitates much more readily than normal liquid helium, and there is a marked difference in the cavitation behavior of the two fluids as the lambda point is traversed. Examples of cavitation in a turbine meter and centrifugal pump are given, together with measurements of the cavitation strength of flowing superfluid helium. The unusual cavitation behavior of superfluid helium is attributed to its immense thermal conductivity .

Daney, D. E.

1988-01-01

88

New experimental device for VHTR structural material testing and helium coolant chemistry investigation – High Temperature Helium Loop in NRI ?ež  

International Nuclear Information System (INIS)

The High Temperature Helium Loop (HTHL) is an experimental device for simulation of VHTR helium coolant conditions. The purpose of the HTHL is structural materials testing and helium coolant chemistry investigation. In the HTHL pure helium will be used as working medium and its main physical parameters are 7 MPa, max. temperature in the test section 900 °C and flow rate 37.8 kg/h. The HTHL consists of an active channel, the helium purification system, the system of impurities dosage (e.g. CO, CO2, H2, H2O, O2, N2, and CH4) and the helium chemistry monitoring system (sampling and on-line analysis and determination of impurities in the helium flow). The active channel is planned to be placed into the core of the experimental reactor LVR-15 which will serve as a neutron flux source (max. 2.5 × 1018 n/m2 s for fast neutrons). The HTHL is now under construction. Some of its main parts are finished, some are still being produced (active channel internals, etc.), some should be improved to work correctly (the helium circulatory compressor); certain sub-systems are planned to be integrated to the loop (systems for the determination of moisture and other impurities in helium, etc.). The start of the HTHL operation is expected during 2011 and the integration of the active channel into the LVR-15 core during 2012.

89

Broken symmetry makes helium  

CERN Multimedia

"The subatomic pion particle breaks the charge symmetry rule that governs both fusion and decay. In experiments performed at the Indiana University Cyclotron Laboratory, physicists forced heavy hydrogen (1 proton + 1 neutron) to fuse into helium in a controlled, measurable environment" (1 paragraph).

Gray, P L

2003-01-01

90

Helium leak finding plant  

International Nuclear Information System (INIS)

The invention concerns a helium leak finding plant with a mass spectrometer cell on the suction side of a molecular pump and a mechanical pre-pump, where a test sample or a test sensor is connected between the two pumps. The mechanical pre-pump consists of three successive stages. (orig./HP)

91

Superfluid helium as a dark matter detector  

International Nuclear Information System (INIS)

The properties of liquid helium-four at temperatures in the vicinity of 100 mK suggest that it might be a suitable medium from which to construct a detector for certain types of dark matter. Among these properties are freedom from contaminants producing background and a high multiplicity of carriers (rotons) produced in energy deposition. It is suggested that there are processes available in helium which may permit discrimination between recoil nuclei and electrons of equal energy deposit. 19 refs., 5 figs

92

Ab initio potential energy curve for the helium atom pair and thermophysical properties of the dilute helium gas. I. Helium-helium interatomic potential  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract A helium-helium interatomic potential energy curve was determined from quantum-mechanical \\textit{ab initio} calculations. Very large atom-centred basis sets including a newly developed d-aug-cc-pV8Z basis set supplemented with bond functions and \\textit{ab initio} methods up to Full CI were applied. The aug-cc-pV7Z basis set of Gdanitz (\\emph{J. Chem. Phys.}, \\textbf{113}, 5145 (2000)) was modified to be more consistent with the aug-cc-pV5Z and aug-cc-pV6Z basis set...

Vogel, Eckhard; Bich, Eckard; Hellmann, Robert

2007-01-01

93

Helium diffusion in curium-doped borosilicate waste glass  

Science.gov (United States)

The isothermal release of helium from 244Cm-doped borosilicate glass has been studied as a function of time at different annealing temperatures. Helium measurements were performed using a micro gas chromatograph coupled to a furnace installed in a hot cell at ATALANTE nuclear research facility. Plane-parallel glass samples were prepared from glass discs that had been stored for 5.1 years at room temperature, accumulating around 10 19 alpha decays per gram of glass, a level that will be reached in current nuclear glass packages several thousand years after disposal. The experimental helium release data were simulated using a 3D numerical model to determine the helium diffusion coefficients. The extracted diffusion coefficients follow the Arrhenius law with an activation energy of 0.61 ± 0.03 eV and a pre-exponential factor of (5.7 ± 1.6) × 10 -3 cm 2 s -1. The results were compared with literature data on damaged and undamaged glasses to assess the effect of glass damage on helium release. The helium release results are consistent with a thermal diffusion mechanism involving only one population of helium atoms. The helium diffusion coefficients were unaffected by the glass alpha damage.

Fares, T.; Peuget, S.; Bouty, O.; Deschanels, X.; Magnin, M.; Jégou, C.

2011-09-01

94

Helium diffusion in curium-doped borosilicate waste glass  

International Nuclear Information System (INIS)

The isothermal release of helium from 244Cm-doped borosilicate glass has been studied as a function of time at different annealing temperatures. Helium measurements were performed using a micro gas chromatograph coupled to a furnace installed in a hot cell at ATALANTE nuclear research facility. Plane-parallel glass samples were prepared from glass discs that had been stored for 5.1 years at room temperature, accumulating around 1019 alpha decays per gram of glass, a level that will be reached in current nuclear glass packages several thousand years after disposal. The experimental helium release data were simulated using a 3D numerical model to determine the helium diffusion coefficients. The extracted diffusion coefficients follow the Arrhenius law with an activation energy of 0.61 ± 0.03 eV and a pre-exponential factor of (5.7 ± 1.6) x 10-3 cm2 s-1. The results were compared with literature data on damaged and undamaged glasses to assess the effect of glass damage on helium release. The helium release results are consistent with a thermal diffusion mechanism involving only one population of helium atoms. The helium diffusion coefficients were unaffected by the glass alpha damage.

95

Elastic scattering of positrons by helium atom  

International Nuclear Information System (INIS)

Distorted wave method has been employed to calculate differential cross sections for elastic scattering of positrons by helium atom. A suitable form of polarization potential has been used which includes the effects of short-range and long-range correlations. The agreement between the present results and corresponding theoretical predictions and experimental results in the literature are fair. (author). 5 refs., 1 fig

96

Surface flashover in supercritical helium  

International Nuclear Information System (INIS)

The surface flashover voltage of spacer-type specimens was measured in supercritical helium. The measurement was performed at 4.3 - 7.0 K, and the pressure of 0.8 MPa. The cylindrical spacer-type epoxy specimens filled with silica were used for the measurement of the flashover voltage. The major findings obtained were as follows: (1) Assuming that the flashover voltage is proportional to the n-th power of spacer length, the values of n were 0.92 for direct current, and 0.8 for the standard impulse, respectively. (2) The time lag up to the flashover due to the standard impulse was less than 5 us in most of the cases, (3) When projected electrodes were put in the spacers to lower the electric field between the spacers, gas and the electrodes sufficiently, surface flashover did not occur until the electric field at the center of the spacers became the breakdown voltage of the supercritical helium. (4) When a very small (0.3 mm) projection was made at the contact point of the electrode with the spacer, the surface flashover voltage became significantly low, if the electrode was of negative polarity. Whereas, the change of the flashover voltage was not observed if the polarity was positive. (Aoki, K.)

97

Helium accumulation in groundwater. Pt. 3  

International Nuclear Information System (INIS)

The groundwaters of the Great Artesian Basin (Australia) have been previously shown to be accumulating in-situ production helium for groundwaters ages 100 kyr. New helium isotope measurements show that the observed in-situ production helium (3He/4He ? 1.6x10-8) is isotopically distinct from the crustal degassing helium flux (3He/4He ? 6.6x10-8). Furthermore, the crustal degassing helium isotope ratio is marginally in excess of the whole crustal production ratio (3He/4He = 3.5x10-8) and the production ratio in a variety of continental rock types. This suggests that the upper limit on volatile transport across the mantle-crust boundary beneath the (relatively) stable and 'complacent' Australian continent can be characterized by a 'conductive-diffusive' helium/heat flux ratio of 64He atoms mW-1s-1 which is two orders of magnitude less than the 'intrusive-volcanic' ratio of 2.9x1084He atoms mW-1s-1 measured at the Galapagos. These results constrain the transcrustal mantle degassing fluxes of 4He and 40Ar to be much less than the mid-ocean ridge degassing fluxes; which are much less than the degassing of 4He and 40Ar from contineup>He and 40Ar from continental crust. Thus, the degassing of the Earth's interior is dominated by magmatic processes but the dominant fluxes of 4He and 40Ar to the atosphere must come from the continental crust. (orig.)

98

Helium effect on mechanical property of fusion reactor structural materials  

International Nuclear Information System (INIS)

High-energy neutrons produced in fusion reactor core caused helium in the structural materials of fusion reactors, such as blankets. We injected alpha particles accelerated by the cyclotron to the samples of martensite steel (9Cr3WVTaB). Equivalent helium doses injected to the sample is estimated to be up to 300 ppm, which were estimated to be equivalent to helium accumulation after the 1-year reactor operation. Creep tests of the samples were made to investigate helium embrittlement. There were no appreciable changes in the relation between the stresses and the rupture time, the minimum creep rate and the applied stress. Grain boundary effect by helium was not observed in ruptured surfaces. Fatigue tests were made for SUS304 samples, which contain helium up to 150 ppm. After 0.05 Hz cyclic stress tests, it was shown that the fatigue lifetime (cycles to rupture and extension to failure) are 1/5 in 150 ppm helium samples compared with no helium samples. The experimental results suggest martensite steel is promising for structural materials of fusion reactors. (Y. Tanaka)

99

Cryosorption vacuum pumping of hydrogen and helium mixtures  

International Nuclear Information System (INIS)

Cryosorption vacuum pumps continue to be the principal type of pumping systems considered for power-producing fusion reactors. In this context, a compound-pump concept is generally employed in which the helium pump is placed behind the hydrogen pump so that hydrogen will not condense on and hence block the 4.2 K helium cryosorption surface. To obtain an optimal design for such a pump, the amount of hydrogen which can reach the helium panel has been determined. Catastrophic failure of a cryosorption pump was observed in previous work when a 95% hydrogen-5% helium mixture was tested. No such failure has occurred in our studies with 4, 10, and 20% hydrogen. However, significant changes in pumping speed have been noted when only 4% hydrogen is present. Both helium and hydrogen speeds are reduced to approximately one-half to one-third of the pure compound speed. Many of the qualitative aspects of the behavior of the pump for pure helium are also observed for the hydrogen-helium mixtures. Cyclic variation in pumping speed above a helium feed rate of approx. 6 x 10-6 torr-L/s.cm2 is one such similarity; however, at the 4% hydrogen level, the period between instabilities is longer for the mixtures

100

Excitations in confined helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We design models for helium in matrices like aerogel, Vycor or Geltech from a manifestly microscopic point of view. For that purpose, we calculate the dynamic structure function of 4He on Si substrates and between two Si walls as a function of energy, momentum transfer, and the scattering angle. The angle--averaged results are in good agreement with the neutron scattering data; the remaining differences can be attributed to the simplified model used here for the complex pore...

Apaja, V.; Krotscheck, E.

2003-01-01

 
 
 
 
101

Analysis of decomposition of impurity-helium solid phase  

Science.gov (United States)

The elemental composition of the impurity-helium solid phase (IHSP) grown by injecting of a gas jet containing Ne, Ar, Kr, and Xe atoms and N2 molecules into superfluid HeII is studied. The measured stoichiometric ratios S=NHe/NIm are much larger than the values predicted by the model of frozen together monolayer helium clusters. The theoretical possibility of freezing together of two-layered clusters is justified in the continual model of the helium subsystem of IHSP which fills the space between rigid impurity centers. Regularities of decomposition of "dry" samples (extracted from liquid helium) are analyzed in the temperature range 1.5-12 K under pressures from 10 to 500 torr. Two stages of sample decomposition are discovered: a slow stage accompanied by cooling and a rapid stage accompanied by heat release. These results suggest the presence of two types of helium in IHSP, viz., weakly bound and strongly bound helium which can be attributed respectively to the second and first coordination spheres of helium formed around heavy impurity particles. A tendency to elevation of the thermal stability of impurity-helium (IH) samples upon an increase in the mass of impurity center has been observed. An increase in the helium vapor pressure above the samples also increases their stability. It is found that the decomposition of IH samples containing nitrogen atoms in the temperature range 3-4.5 K is accompanied with luminescence induced by recombination of atoms. This indicates the possibility of a wide range of chemical reactions in solidified helium.

Boltnev, R. E.; Gordon, E. B.; Krushinskaya, I. N.; Martynenko, M. V.; Pelmenev, A. A.; Popov, E. A.; Khmelenko, V. V.; Shestakov, A. F.

1997-07-01

102

Helium emanometry as an indicator of deeply buried uranium deposits  

International Nuclear Information System (INIS)

Helium emanometry has considerable potential for locating deeply buried uranium deposits. In order to determine whether near surface helium-4 anomalies are present over and in close proximity to deeply buried uranium deposits, helium measurements were carried out at three sites having known uranium ore bodies: the Red Desert in Sweetwater County, Wyoming; Copper Mountain in Fremont County, Wyoming; and Spokane Mountain in Stevens Couty, Washington. At each research site, near surface soil and soil gas (probe) samples were collected. Borehole water and soil gas (collector) samples were also taken at selected locations. The samples were analyzed at the laboratory for their helium, light hydrocarbon, and nitrogen content. In most instances it was not necessary to correct the soil gas data. In determining the quantity of helium-4 present in the soil gas samples, the practical precision was +- 50 ppb. The reproducibility of the helium-4 analyses of the water samples varied from +- 5% to +- 20%. The total error in the calculated soil helium-4 levels ranged from 5% to 10% of the value. The calculated corrected soil, water and oil gas helium-4 results were analyzed employing statistical techniques in order to separate the background and anomalous populations. The anomalous population was divided into five subsets for purposes of data presentation. The data are then presented in the form of histograms, dot maps and anomaly contour density maps.One can conclude that the resultsity maps.One can conclude that the results from this study confirm that near surface helium anomalies are present in the gas of the soil micropores overlying three types of uranium deposits situated in widely differing geological environments. The data obtained from the soil gas (probe) helium samples are also encouraging in that anomalies were found to be present over portions of the known extent of each of the three deposits

103

Applications of Groundwater Helium  

Science.gov (United States)

Helium abundance and isotope variations have widespread application in groundwater-related studies. This stems from the inert nature of this noble gas and the fact that its two isotopes ? helium-3 and helium-4 ? have distinct origins and vary widely in different terrestrial reservoirs. These attributes allow He concentrations and 3He/4He isotope ratios to be used to recognize and quantify the influence of a number of potential contributors to the total He budget of a groundwater sample. These are atmospheric components, such as air-equilibrated and air-entrained He, as well as terrigenic components, including in situ (aquifer) He, deep crustal and/or mantle He and tritiogenic 3He. Each of these components can be exploited to reveal information on a number of topics, from groundwater chronology, through degassing of the Earth?s crust to the role of faults in the transfer of mantle-derived volatiles to the surface. In this review, we present a guide to how groundwater He is collected from aquifer systems and quantitatively measured in the laboratory. We then illustrate the approach of resolving the measured He characteristics into its component structures using assumptions of endmember compositions. This is followed by a discussion of the application of groundwater He to the types of topics mentioned above using case studies from aquifers in California and Australia. Finally, we present possible future research directions involving dissolved He in groundwater.

Kulongoski, Justin T.; Hilton, David R.

2011-01-01

104

Study of the TL response of LiF:Mg,Ti to 3 and 7.5 MeV helium ions: Measurements and interpretation in terms of the track interaction model  

International Nuclear Information System (INIS)

We have measured the LiF:Mg,Ti (TLD-100) thermoluminescent response, efficiency and supralinearity, to 3 and 7.5 MeV helium ions in the fluence interval between 6x107 to 1.5x1011 cm-2. Ion irradiations were performed using a flux of elastically scattered ions from a thin gold target. The measured efficiencies with respect to 60Co ?-rays are equal to 0.074 and 0.174 at 3 and 7.5 MeV, respectively, for the response of peak 5. The supralinearity functions for peaks 4, 5, 6a, 6b, 7, 8, 9 and the total TL signal indicate that supralinearity is an increasing function of energy and that it increases with peak temperature. The data for peaks 5, 8 and 9 have been successfully described by Monte Carlo simulations of the track interaction model. The fitted parameters show that peak 5 displays a special behaviour which requires the use of a much larger effective track radius than the higher temperature peaks

105

Ab initio study of helium behavior in titanium tritides  

Energy Technology Data Exchange (ETDEWEB)

Ab initio calculations based on density functional theory have been performed to investigate the relative stability of titanium tritides and the helium behavior in stable titanium tritides. The results show that the ?-phase TiT1.5 without two tritium along the [100] direction (TiT1.5[100]) is more stable than other possible structures. The stability of titanium tritides decrease with the increased generation of helium in TiT1.5[100]. In addition, helium generated by tritium decay prefers locating at a tetrahedral site, and favorably migrates between two neighbor vacant tetrahedral sites through an intermediate octahedral site in titanium tritides, with a migration energy of 0.23 eV. Furthermore, helium is easily accumulated on a (100) plane in ?-phase TiT1.5[100].

Liang, J. H.; Dai, Yunya; Yang, Li; Peng, SM; Fan, K. M.; Long, XG; Zhou, X. S.; Zu, Xiaotao; Gao, Fei

2013-03-01

106

Surface electrons of helium films  

International Nuclear Information System (INIS)

Theoretical calculations of some properties of two-dimensional electrons on a liquid helium film adsorbed on a solid substrate are reviewed. We describe the spectrum of electron bound states on bulk helium as well on helium films. The correlational properties, such as the structure factor and correlation energy, are determined as functions of the film thickness for different types of substrates in the framework of a Generalized Random-Phase Approximation. The collective excitations of this system are also described. The results for electrons on the surface of thin films and bulk helium are easily obtained. we examine the electron interaction with the excitations of the liquid helium surface resulting in a new polaron state, which was observed very recently. The ground state energy and the effective mass of this polaron are determined by using the path-integral formalism and unitary-transformation method. Recent speculations about the phase diagram of electrons on the helium film are also discussed. (Author)

107

Use of helium in uranium exploration, Grants district  

International Nuclear Information System (INIS)

The continuous generation of inert helium gas from uranium and its daughter products provides a potentially useful means for remote detection of uranium deposits. The practicality of conducting helium surveys in the atmosphere, soil gas, and ground water to explore for buried uranium deposits has been tested in the Grants district and in the Powder River Basin of Wyoming. No detectable helium anomalies related to buried or surface uranium deposits were found in the atmosphere. However, reproducible helium-in-soil-gas anomalies were detected spatially related to uranium deposits buried from 50 to 800 ft deep. Diurnal and atmospheric effects can cause helium content variations (noise) in soil gas that are as great as the anomalies observed from instantaneous soil-gas samples. Cumulative soil-gas helium analyses, such as those obtained from collecting undisturbed soil samples and degassing them in the laboratory, may reveal anomalies from 5 to 100 percent above background. Ground water samples from the Grants district, New Mexico, and the Powder River Basin, Wyoming, have distinctly anomalous helium values spatially related to buried uranium deposits. In the southern Powder River Basin, helium values 20 to 200 percent above background occur 2 to 18 mile down the ground-water flow path from known uranium roll-front deposits. In the Grants district, helium contents 40 to 700 percent above background levels are present in ground waters from the host sandstone in the viciniters from the host sandstone in the vicinity of uranium deposits and from aquifers up to 3,000 ft stratigraphically above the deep uranium deposits. The use of helium in soil and ground-water surveys, along with uranium and radon analyses of the same materials, is strongly recommended is expensive, deep, uranium-exploration programs such as those being conducted in the Grants district

108

Isolating electrons on superfluid helium  

Science.gov (United States)

Electrons floating on the surface of superfluid helium have been suggested as promising mobile spin quantum bits (qubits). Transferring electrons extremely efficiently in a narrow channel structure with underlying gates has been demonstrated, showing no transfer error while clocking 109 pixels in a 3-phase charge coupled device (CCD). While on average, one electron per channel was clocked, it is desirable to reliably obtain a single electron per channel. We have designed an electron turnstile consisting of a narrow (0.8?m) channel and narrow underlying gates (0.5?m) operating across seventy-eight parallel channels. Initially, we find that more than one electron can be held above the small gates. Underlying gates in the turnstile region allow us to repeatedly split these electron packets. Results show a plateau in the electron signal as a function of the applied gate voltages, indicating quantization of the number of electrons per pixel, simultaneously across the seventy-eight parallel channels.

Takita, Maika; Lyon, S. A.

2014-12-01

109

Neutral transport and helium pumping of ITER  

International Nuclear Information System (INIS)

A 2-D Monte-Carlo simulation of the neutral atom densities in the divertor, divertor throat and pump duct of ITER was made using the DEGAS code. Plasma conditions in the scrape-off layer and region near the separatrix were modeled using the B2 plasma transport code. Wall reflection coefficients including the effect of realistic surface roughness were determined by using the fractal TRIM code. The DEGAS and B2 coupling was iterated until a consistent recycling was predicted. Results were obtained for a helium and a deuterium/tritium mixture on 7 different ITER divertor throat geometries for both the physics phase reference base case and a technology phase case. The geometry with a larger structure on the midplane-side of the throat opening closing the divertor throat and a divertor plate which maintains a steep slope well into the throat removed helium 1.5 times better than the reference geometry for the physics phase case and 2.2 times better for the technology phase case. At the same time the helium to hydrogen pumping ratio shows a factor of 2.34 ± .41 enhancement over the ratio of helium to hydrogen incident on the divertor plate in the physics phase and an improvement of 1.61 ± .31 in the technology phase. If the helium flux profile on the divertor plate is moved outward by 20 cm with respect to the D/T flux profile for this particular geometry, the enhancement increases to 4.36 ± .90 in the physics phase and 5.10 ± .92 in the technology phase

110

Cavitation in liquid helium  

Energy Technology Data Exchange (ETDEWEB)

Ultrasonic cavitation was induced in liquid helium over the temperature range 1.2 to 2.3 deg K, using a pair of identical transducers. The transducers were calibrated using a reciprocity technique and the cavitation threshold was determined at 90 kc/s. It was found that this threshold has a sharp peak at the lambda point, but is, at all temperatures quite low, with an approximate range of 0.001 to 0.01 atm. The significance of the results is discussed. (auth)

Finch, R. D.; Kagiwada, R.; Barmatz, M.; Rudnick, I.

1963-11-15

111

Simulation of liquid helium  

International Nuclear Information System (INIS)

The author discusses simulation methods for quantum mechanical systems at finite temperatures. Recently it has been shown that static properties of some quantum systems can be obtained by simulation in a straightforward manner using path integrals, albeit with an order of magnitude more computing effort needed than for the corresponding classical systems. Some dynamical information can be gleaned from these simulations as will be discussed below. But this is very limited - there is no quantum version of the molecular dynamics method. The path integral method is illustrated by discussing the application to liquid helium. 12 refs., 8 figs

112

Ultralow temperature helium compressor for Japan Atomic Energy Research Institute  

International Nuclear Information System (INIS)

Ishikawajima Harima Heavy Industries Co., Ltd. started the development of an ultralow temperature helium compressor for helium liquefaction in 1984 jointly with Japan Atomic Energy Research Institute, and has delivered the first practical machine to the Superconductive Magnet Laboratory of JAERI. For a large superconductive magnet to be used in the stable state for a fusion reactor, conventional superconductive materials (NbTi, NbTi3Sn, etc.) must be used, being cooled forcibly with supercritical helium. The supercritical helium which is compressed above the critical pressure of 228 kPa has a stable cooling effect since the thermal conductivity does not change due to the evaporation of liquid helium. In order to maintain the temperature of the supercritical helium below 4 K before it enters a magnet, a heat exchanger is used. The compressor that IHI has developed has the ability to reduce the vapor pressure of liquid helium from atmospheric pressure to 50.7 kPa, and can attain the temperature of 3.5 K. The specification of this single stage centrifugal compressor is: mass flow rate 25 - 64 g/s, speed 80,000 rpm, adiabatic efficiency 62 - 69 %. The structure and the performance are reported. (K.I.)

113

Helium exhaust studies in the DIII-D tokamak  

International Nuclear Information System (INIS)

Significant exhaust of thermal helium in a diverted, H-mode deuterium plasma has been demonstrated for the first time on the DIII-D tokamak using an in-vessel cryopump conditioned with an argon frost. The helium, introduced via gas puffing, is observed to reach the plasma core and then is readily removed from the plasma with a time constant of ?8-15 energy confinement times. Detailed analysis of the helium profile evolution indicates that the exhaust rate is limited by the exhaust efficiency of the pump (?5%) and not by the intrinsic helium transport properties of the plasma. Additional studies focusing on the recycling properties of helium relative to deuterium in the divertor region indicate some dependence of the helium concentration in the divertor pumping plenum on the divertor outer strike-point (OSP) position in Ohmic discharges. However, the helium concentration in the plenum appears to have little dependence on OSP position in beam-heated, ELMing H-mode discharges

114

Tensile behavior of helium-implanted and neutron-irradiated  

International Nuclear Information System (INIS)

Vanadium alloys are being considered for use for first-wall and blanket structures in fusion reactors due to their high melting points and low neutron activation. The alloy reported on here, V-15 Cr-5 Ti, was prepared by the Westinghouse Advanced Reactors Division (Heat HSV-307). Since the fusion environment produces helium in all common structural alloys including vanadium, the effect of helium in irradiated alloys was investigated. In a fusion reactor spectrum, ? 5 at. ppm He/dpa is expected. Ideally, the helium should be produced concurrently with displacement damage. However, since this is difficult or impossible in vanadium without a source of high-energy neutrons, cyclotron implantation of helium followed by fission reactor irradiation was chosen. By this method, it was hoped to scope qualitatively the effect of helium alone and the synergistic effect of helium in conjunction with neutron irradiation. Results show that: (1) cyclotron injection of 80 at. ppm He has little effect on mechanical properties of V-15 Cr-5 Ti at 700 and 6250C and causes a factor of ? 2 reduction in elongation at 4000C; and (2) neutron irradiation to 24 to 32 dpa increases the strength of annealed V-15 Cr-5 Ti by a factor of ? 2 and decreases ductility by a factor of about 10

115

Helium diffusion behavior and its retention in LaNiAl alloy from molecular dynamic simulations  

International Nuclear Information System (INIS)

Molecular dynamic method has been used to investigate the diffusion behavior of helium atom in the LaNiAl alloy system. The results have shown that diffusion coefficient of helium atom increases as the temperature increases from 300 to 1500 K, which indicates that helium atom gets more active via thermal desorption. The diffusion coefficient in LaNi5 and LaNi4Al are about 1.5 x 10-5 and 1.1 x 10-6 cm2/s at 1300 K, respectively, and the diffusion barrier of He are 1.45 and 0.52 eV, respectively. The helium diffusion is shown to be enhanced with temperature increasing. Compared with metallic La, Ni, Al and Pd, the simulation result implies that helium atom is more stable and difficult to diffuse in LaNi5 and LaNi4Al alloys, which are the most promising materials for helium retention in experiments. Our results indicate the correlation between diffusion behavior of helium atom and capacity of materials for helium retention. Therefore, it can be considered as a feasible method to evaluate the helium retention capacity of materials via determining the diffusion properties of interstitial helium atom.

116

Quantum cavitation in liquid helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using a functional-integral approach, we have determined the temperature below which cavitation in liquid helium is driven by thermally assisted quantum tunneling. For both helium isotopes, we have obtained the crossover temperature in the whole range of allowed negative p essures. Our results are compatible with recent experimental results on 4He.

Guilleumas, Montserrat; Barranco Go?mez, Manuel; Jezek, Dora M.; Lombard, Roland J.; Pi Pericay, Marti?

1996-01-01

117

CERN Technical Training 2002: Learning for the LHC! HEREF-2002 : HELIUM REFRIGERATION TECHNIQUES  

CERN Multimedia

Theory, Technology, Maintenance and Control of Helium Refrigerators HeREF-2002 is a new course, in the framework of the 2002 Technical Training Programme, that will provide a complete introduction to Helium refrigeration, with a practical approach to theory, technology, maintenance and control of Helium refrigeration installations. Theoretical aspects and equations will be limited to a minimum. HeREF-2002 targets an audience of technicians and operators of Helium refrigeration plants at CERN, as well as physicists and engineers needing an overview of current Helium refrigeration techniques. HeREF-2002 will address, among other, issues related to component technology, installation maintenance, process control and Helium purity. A commented visit to a couple of CERN Helium refrigeration or liquefaction plants will also take place. Duration: 7 half days (5 mornings and 2 afternoons), 21-25 October, 2002. Estimated cost: 300.- CHF Language: Bilingual English-French. The course support will be in English, the ...

Davide Vitè

2002-01-01

118

CERN Technical Training 2002: Learning for the LHC ! HeREF-2002 : Helium Refrigeration Techniques  

CERN Multimedia

Theory, Technology, Maintenance and Control of Helium Refrigerators HeREF-2002 is a new course, in the framework of the 2002 Technical Training Programme, that will provide a complete introduction to Helium refrigeration, with a practical approach to theory, technology, maintenance and control of Helium refrigeration installations. Theoretical aspects and equations will be limited to a minimum. HeREF-2002 targets an audience of technicians and operators of Helium refrigeration plants at CERN, as well as physicists and engineers needing an overview of current Helium refrigeration techniques. HeREF-2002 will address, among other, issues related to component technology, installation maintenance, process control and Helium purity. A commented visit to a couple of CERN Helium refrigeration or liquefaction plants will also take place. Duration: 7 half days (5 mornings and 2 afternoons), 21-25 October 2002. Estimated cost: 300.- CHF Language: Bilingual English-French. The course support will be in English, the...

Davide Vitè

2002-01-01

119

Helium in near Earth orbit  

CERN Document Server

The helium spectrum from 0.1 to 100 GeV/nucleon was measured by the Alpha Magnetic Spectrometer (AMS) during space shuttle flight STS-91 at altitudes near 380 km. Above the geomagnetic cutoff the spectrum is parameterized by a power law. Below the geomagnetic cutoff a second helium spectrum was observed. In the second helium spectra over the energy range 0.1 to 1.2 GeV/nucleon the flux was measured to be (6.3+or-0.9)*10/sup -3/ (m/sup 2/ sec sr)/sup -1/ and more than ninety percent of the helium was determined to be /sup 3/He (at the 90% CL). Tracing helium from the second spectrum shows that about half of the /sup 3/He travel for an extended period of time in the geomagnetic field and that they originate from restricted geographic regions similar to protons and positrons. (22 refs).

Alcaraz, J; Ambrosi, G; Anderhub, H; Ao, L; Arefev, A; Azzarello, P; Babucci, E; Baldini, L; Basile, M; Barancourt, D; Barão, F; Barbier, G; Barreira, G; Battiston, R; Becker, R; Becker, U; Bellagamba, L; Béné, P; Berdugo, J; Berges, P; Bertucci, B; Biland, A; Bizzaglia, S; Blasko, S; Bölla, G; Boschini, M; Bourquin, Maurice; Brocco, L; Bruni, G; Buénerd, M; Burger, J D; Burger, W J; Cai, X D; Camps, C; Cannarsa, P; Capell, M; Casadei, D; Casaus, J; Castellini, G; Cecchi, C; Chang, Y H; Chen, H F; Chen, H S; Chen, Z G; Chernoplekov, N A; Tzi Hong Chiueh; Chuang, Y L; Cindolo, F; Commichau, V; Contin, A; Cristinziani, M; Da Cunha, J P; Dai, T S; Deus, J D; Dinu, N; Djambazov, L; D'Antone, I; Dong, Z R; Emonet, P; Engelberg, J; Eppling, F J; Eronen, T; Esposito, G; Extermann, Pierre; Favier, Jean; Fiandrini, E; Fisher, P H; Flügge, G; Fouque, N; Galaktionov, Yu; Gervasi, M; Giusti, P; Grandi, D; Grimm, O; Gu, W Q; Hangarter, K; Hasan, A; Hermel, V; Hofer, H; Huang, M A; Hungerford, W; Ionica, M; Ionica, R; Jongmanns, M; Karlamaa, K; Karpinski, W; Kenney, G; Kenny, J; Kim, W; Klimentov, A; Kossakowski, R; Koutsenko, V F; Kräber, M H; Laborie, G; Laitinen, T; Lamanna, G; Laurenti, G; Lebedev, A; Lee, S C; Levi, G; Levchenko, P M; Liu, C L; Liu Hong Tao; Lopes, I; Lu, G; Lü, Y S; Lübelsmeyer, K; Luckey, D; Lustermann, W; Maña, C; Margotti, A; Mayet, F; McNeil, R R; Meillon, B; Menichelli, M; Mihul, A; Mourão, A M; Mujunen, A; Palmonari, F; Papi, A; Park, I H; Pauluzzi, M; Pauss, Felicitas; Perrin, E; Pesci, A; Pevsner, A; Pimenta, M; Plyaskin, V; Pozhidaev, V; Pohl, M; Postolache, V; Produit, N; Rancoita, P G; Rapin, D; Raupach, F; Ren, D; Ren, Z; Ribordy, M; Richeux, J P; Riihonen, E; Ritakari, J; Röser, U; Roissin, C; Sagdeev, R; Sartorelli, G; Schultz von Dratzig, A; Schwering, G; Scolieri, G; Seo, E S; Shoutko, V; Shoumilov, E; Siedling, R; Son, D; Song, T; Steuer, M; Sun, G S; Suter, H; Tang, X W; Ting, Samuel C C; Ting, S M; Tornikoski, M; Torsti, J; Trümper, J E; Ulbricht, J; Urpo, S; Usoskin, I; Valtonen, E; Van den Hirtz, J; Velcea, F; Velikhov, E P; Verlaat, B; Vetlitskii, I; Vezzu, F; Vialle, J P; Viertel, Gert M; Vitè, Davide F; Von Gunten, H P; Waldmeier-Wicki, S; Wallraff, W; Wang, B C; Wang, J Z; Wang, Y H; Wiik, K; Williams, C; Wu, S X; Xia, P C; Yan, J L; Yan Lu Guang; Yang, C G; Yang, M; Ye Shu Wei; Yeh, P; Xu, Z Z; Zhang, H Y; Zhang, Z P; Zhao, D X; Zhu, G Y; Zhu, W Z; Zhuang, H L; Zichichi, A; Zimmermann, B; Zuccon, P

2000-01-01

120

Ultrasensitive leak testing: helium accumulation  

International Nuclear Information System (INIS)

An investigation was carried out to develop a technique for detecting leak rates of less than 1 x 10-11 atm cm3/sec in order to measure the helium leak rate of radioisotopic heat sources. These heat sources consist of 238PuO2 triply sealed in welded containers under a helium atmosphere. A static accumulation method was developed to perform leakage measurements in the range of 10-10 to 10-13 atm cm3/sec since commercially available heliium leak detectors cannot measure dynamic helium leak rates of less than about 10-10 atm cm3/sec. It has been experimentally determined that the accumulation system can measure helium leakages in the range of 10-10 to 10-13 atm cm3/sec. Random system errors of +-10 percent were found which are well within the limits of accuracy of +-20 percent given for the calibrated helium leak rate standards

 
 
 
 
121

Determining carbon dioxide in helium by adsorption accumulation  

International Nuclear Information System (INIS)

A combined isotopic, chromatographic, and spectral method has been developed for determining CO2 in helium by the use of adsorption accumulation and chromatography at reduced pressures. The lower limit to the measurable contents is 5 x 10-6 mol%. The method does not require the use of reference specimens. The scope for reducing abundant isotope content is related to increased accuracy in the spectroscopic determination of CO2 isotope compositions and increasing the volume of helium used

122

Correlation of Helium Solubility in Liquid Nitrogen  

Science.gov (United States)

A correlation has been developed for the equilibrium mole fraction of soluble gaseous helium in liquid nitrogen as a function of temperature and pressure. Experimental solubility data was compiled and provided by National Institute of Standards and Technology (NIST). Data from six sources was used to develop a correlation within the range of 0.5 to 9.9 MPa and 72.0 to 119.6 K. The relative standard deviation of the correlation is 6.9 percent.

VanDresar, Neil T.; Zimmerli, Gregory A.

2012-01-01

123

Phase and density dependence of the delayed annihilation of metastable antiprotonic helium atoms in gas, liquid and solid helium  

International Nuclear Information System (INIS)

Systematic studies of the phase and density dependence of the delayed annihilation time spectra of antiprotons (DATS) in gaseous, liquid and solid helium have been performed using the Low Energy Antiproton Ring (LEAR) at CERN. The results show a small but significant dependence of DATS on the phase and density of the helium medium. The average lifetime of antiprotons (Tav) in gas at 10-30 K was found to be 4.03 ± 0.02 ?s. In liquid helium Tav decreases with density from 3.0 ?s at 1 bar to 2.5 ?s at 60 bar, while in solid helium its value is 2.14 ± 0.03 ?s, 20% shorter than that in liquid helium of the same density. There is no change of DATS between normal 1-bar liquid and superfluid helium. An isotope effect between 4He and 3He similar to the one previously observed in the gas phase has also been found for liquid helium. All the data can be fitted fairly well with a simple three-level chain decay model which describes the general structure of DATS, characterized by downward curving behavior on a logarithmic scale at later times and by the presence of a short-lived component. No delayed annihilation was observed in lithium. (author)

124

Effect of radiation damage in thermal desorption of helium from the ferritic-martensitic steel EP-450  

International Nuclear Information System (INIS)

The results of the study of helium thermal desorption from polycrystalline samples of steel EP-450 implanted helium ions with energy of 12 keV to doses (5 - 10 1016 cm-2 are given. The effect of precreated damage to the spectra of helium is considered. A comparison of temperature intervals of helium desorption from the ferriticmartensitic steel EP-450, nickel and iron are conducted.

125

Photoionization of helium dimers  

International Nuclear Information System (INIS)

The helium dimer is one of the most weakly bound systems in the universe. This makes it an interesting quantum mechanical object for investigation. These Van der Waals Clusters can be produced in an expansion of a cryogenic gas jet through a small nozzle into vacuum. In the present experiment we examine the interaction of He dimers with synchrotron radiation at an energy range from 64 to 78 eV. We observed different pathways leading to single ionization of both He atoms of the dimer compound. This two close standing ions begin now to dissociate in cause of their coulomb potential. All charged fragments were detected in coincidence with a COLTRIMS system. Especially Interatomic Coulombic Decay (ICD) and the two step process (TS1) were clearly identified. Furthermore a distribution of the internuclear distance was obtained from the measured Kinetic Energy Release (KER). (orig.)

126

Experimental loop for tests of helium cooled high heat flux components at 600 deg C/10 MPa helium inlet  

International Nuclear Information System (INIS)

Helium loop is a tool for tests of divertor design options which meet the requirements for He -cooled fusion DEMO reactor. These tests include: divertor materials and joining technology selection, cooling regimes optimization, mockups thermal cycling for lifetime estimation. It is also possible to use loop in other areas of high temperature helium nuclear technology (blanket/ first wall mock-ups tests, fission helium reactors relevant experiments). Also as results of systematic mock-ups tests it is planned to create data base for validation of gas dynamic and thermal mechanic codes, used for simulation of processes in high heat flux components. Helium loop is able to test mock-ups at nominal helium inlet temperature 600 deg C and pressure 10 MPa. Possible pressure losses in mock-up are up to 0.5 MPa. First stage of such helium loop creation using tank-to-tank principle has finished at Efremov Institute in collaboration with FZK. At this stage stationery flow rate 24 g/s, which is provided by oil-free membrane compressor, was achieved. One more possible loop regime - gas pulses at 50 g/s and duration up to 120 s. Diagnostic system provides measuring more then 40 parameters such as pressure, flow rate and temperature. Mock-up heat loading is provided by e-beam of TSEFEY facility with applied power up to 60 kW at 27 keV beam energy. Results of finger like mock-ups of DEMO helium cooled divertor vertical target testing are presented. At next stage helium loop will be able to reach flow rate of 600 g/s (using helium circulating pump) that will provide heat removal from mock-ups up to 120 kW. The design solutions and R-and-D results of activity at this stage of loop creation are also presented. (author)

127

Exotic helium molecules  

International Nuclear Information System (INIS)

We study the photo-association of an ultracold cloud of magnetically trapped helium atoms: pairs of colliding atoms interact with one or two laser fields to produce a purely long range 4He2(23S1-23P0) molecule, or a 4He2(23S1-23S1) long range molecule. Light shifts in one photon photo-association spectra are measured and studied as a function of the laser polarization and intensity, and the vibrational state of the excited molecule. They result from the light-induced coupling between the excited molecule, and bound and scattering states of the interaction between two metastable atoms. Their analysis leads to the determination of the scattering length a = (7.2 ± 0.6) ruling collisions between spin polarized atoms. The two photon photo-association spectra show evidence of the production of polarized, long-range 4He2(23S1-23S1) molecules. They are said to be exotic as they are made of two metastable atoms, each one carrying a enough energy to ionize the other. The corresponding lineshapes are calculated and decomposed in sums and products of Breit-Wigner and Fano profiles associated to one and two photon processes. The experimental spectra are fit, and an intrinsic lifetime ? = (1.4 ± 0.3) ?s is deduced. It is checked whether this lifetime could be limited by spin-dipole induced Penning autoionization. This interpretation requires that there is a quasi-bound state close to the dissociation threshold in the singlet interaction potential between metastable helium atoms for the theory to match the experiment. (author)

128

(3) He NMR studies on helium-pyrrole, helium-indole, and helium-carbazole systems: a new tool for following chemistry of heterocyclic compounds.  

Science.gov (United States)

The (3) He nuclear magnetic shieldings were calculated for free helium atom and He-pyrrole, He-indole, and He-carbazole complexes. Several levels of theory, including Hartree-Fock (HF), Second-order Møller-Plesset Perturbation Theory (MP2), and Density Functional Theory (DFT) (VSXC, M062X, APFD, BHandHLYP, and mPW1PW91), combined with polarization-consistent pcS-2 and aug-pcS-2 basis sets were employed. Gauge-including atomic orbital (GIAO) calculated (3) He nuclear magnetic shieldings reproduced accurately previously reported theoretical values for helium gas. (3) He nuclear magnetic shieldings and energy changes as result of single helium atom approaching to the five-membered ring of pyrrole, indole, and carbazole were tested. It was observed that (3) He NMR parameters of single helium atom, calculated at various levels of theory (HF, MP2, and DFT) are sensitive to the presence of heteroatomic rings. The helium atom was insensitive to the studied molecules at distances above 5?Å. Our results, obtained with BHandHLYP method, predicted fairly accurately the He-pyrrole plane separation of 3.15?Å (close to 3.24?Å, calculated by MP2) and yielded a sizable (3) He NMR chemical shift (about -1.5?ppm). The changes of calculated nucleus-independent chemical shifts (NICS) with the distance above the rings showed a very similar pattern to helium-3 NMR chemical shift. The ring currents above the five-membered rings were seen by helium magnetic probe to about 5?Å above the ring planes verified by the calculated NICS index. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25228253

Radula-Janik, Klaudia; Kupka, Teobald

2014-09-16

129

Overview of Helium Cooled System Applications with RELAP at ENEA  

International Nuclear Information System (INIS)

Some years ago, within the framework of the study for the International Thermonuclear Experimental Reactor (ITER), ENEA assessed the RELAP5 code capability to simulate Helium cooled systems on the experimental data provided by the helium facility HEFUS3 (Brasimone, Italy). This activity allowed acquiring a certain experience on the limits and capabilities of the code that, in the following years, was used for a wide range of applications concerning transient and accident analysis of helium cooled systems. At first the paper summarizes the results of the assessment activity, then describes the accident analyses performed for the conceptual study of the Fusion Power Reactor with Helium-Cooled Pebble Bed Blanket (HCPBB) and the studies to support the safety design of the gas cooled Accelerator Driven System (ADS) concept. The paper concludes highlighting the RELAP adaptations to realize within the framework of the feasibility studies for a combined cycle concept of the Very High Temperature Reactor (VHTR). (authors)

130

Thermal conductivity of the helium-argon system  

International Nuclear Information System (INIS)

A semiempirical relation for the thermal conductivity of helium--argon gas mixtures is suggested. The analyses used in support of the proposed conductivity relations are based on low-temperature (T 0C) thermal conductivity data for helium, argon and helium--argon mixtures. The report is a compilation of available data and theories, and does not contain any new experimental results. With the approach presented here, one should be able to predict thermal conductivities of helium--argon mixtures to within 5% of their true values for temperatures up to 1200 K. The recommended equations are best estimates and should be treated as such. A definite need exists for experimental data to verify or modify the recommendation

131

Alkali-helium snowball complexes formed on helium nanodroplets  

CERN Document Server

We systematically investigate the formation and stability of snowballs formed by femtosecond photo-ionization of small alkali clusters bound to helium nanodroplets. For all studied alkali species Ak=(Na, K, Rb, Cs) we observe the formation of snowballs (AkHe_N)^+ when multiply doping the droplets. Fragmentation of clusters Ak_N upon ionization appears to enhance snowball formation. In the case of Na and Cs we also detect snowballs (Ak_2He_N)^+ formed around Ak dimer ions. While the snowball progression for Na and K is limited to less than 11 helium atoms, the heavier atoms Rb and Cs feature wide distributions at least up to (AkHe_41)^+. Characteristic steps in the mass spectra of Cs-doped helium droplets are found at positions consistent with predictions on the closure of the 1st shell of helium atoms around the Ak^+ ion based on variational Monte Carlo simulations.

Müller, S; Stienkemeier, F

2009-01-01

132

A pool type liquid helium cryopump  

International Nuclear Information System (INIS)

Design and fabrication details of a pool type Liquid Helium Cryopump are described. It has got a liquid helium capacity of 5 litres and a/ pumping surface area of about 450 sq. cms. Three types of baffles having different geometries are used for radiation shield. Effect on pumping speed for argon, carbon dioxide and nitrogen gas using the baffles is determined at various pressures. The circular array baffle geometry provides the maximum pumping speed. Using circular array type baffle the maximum pumping speed for nitrogen, argon and carbon dioxide are 2700 1/s, 3600 1/s, 2550 1/s respectively at a pressure of 6.0 x 10-4 torr. The ultimate pressure obtained is 3.0 x 10-8 torr. (author)

133

Discrete liquid helium level indicator  

International Nuclear Information System (INIS)

Characteristics of liquid helium level indicators produced according to different procedUres from carbon-resistors of the ''Allen-Bredly'' company are presented. A change in the pick-up signal by 104% is attained during the vapour-liquid interface transition at heat release in liquid Wsub(liq.)not equal to 4.9 mW. The accuracy of the level determination is ?H<=2 mm. A six-position liquid helium level indicator enabling to reliably determine the liquid helium level under different operation conditions of the cryostat is described

134

Electronic properties of physisorbed helium  

Energy Technology Data Exchange (ETDEWEB)

This thesis deals with electronic excitations of helium physisorbed on metal substrates. It is studied to what extent the electronic properties change compared to the gas phase due to the increased helium density and the proximity of the metal. Furthermore, the influence of different substrate materials is investigated systematically. To this end, up to two helium layers were adsorbed onto Ru (001), Pt (111), Cu (111), and Ag (111) surfaces in a custom-made cryostat. These samples were studied spectroscopically using synchrotron radiation and a time-of-flight detector. The experimental results were then analyzed in comparison with extensive theoretical model calculations.

Kossler, Sarah

2011-09-22

135

Electronic properties of physisorbed helium  

International Nuclear Information System (INIS)

This thesis deals with electronic excitations of helium physisorbed on metal substrates. It is studied to what extent the electronic properties change compared to the gas phase due to the increased helium density and the proximity of the metal. Furthermore, the influence of different substrate materials is investigated systematically. To this end, up to two helium layers were adsorbed onto Ru (001), Pt (111), Cu (111), and Ag (111) surfaces in a custom-made cryostat. These samples were studied spectroscopically using synchrotron radiation and a time-of-flight detector. The experimental results were then analyzed in comparison with extensive theoretical model calculations.

136

Energy of helium dissolved in metals  

International Nuclear Information System (INIS)

An explanation for the large negative heat of solution of helium in metals, in terms of the strong repulsive helium pseudopotential interacting with the metal conduction electrons is proposed. Calculations for helium in aluminium and magnesium show that this mechanism indeed generates the expected negative heats. It is expected that the helium atoms will always seek out the site of lowest charge density. (author)

137

Implanting helium into nanocrystalline hydrogen storage alloy  

International Nuclear Information System (INIS)

The possibility of implanting helium into LaNixAly alloy by high energy ball milling is explored. By analyzing the sample after ball milling, it is shown that Helium can be implanted into the material. Helium lies in the interfacial free volume rather than the crystal lattice. The implanted helium has high thermal stability. Quantity of Helium implanted by this method is very little

138

Numerical study of helium solubility and helium bubble stability in mercury  

International Nuclear Information System (INIS)

Highlights: • Helium solubility in mercury was numerically evaluated and its small value was experimentally confirmed. • Mass-diffusion dominated bubble evolution is simulated and the bubbles were shown to be stable. • The study indicates that small bubble injection into the mercury target for cavitation damage mitigation is feasible. - Abstract: Dispersing small helium bubbles in the liquid mercury target of the high-power spallation neutron sources was proposed to add compressibility to the target made of liquid mercury. The pressure rise from proton beam deposition is reduced due to added compressibility, which in turn mitigates cavitation damage to the target boundary. A gas volume fraction of ?0.5% with a nominal bubble diameter of ?30 ?m is desired for optimal pressure pulse relaxation at the beam power of >1 MW. Initial gas injection experiments performed in the Oak Ridge National Laboratory encountered difficulty in obtaining the required volume fraction in mercury. Gas dissolution and diffusion in mercury were candidate mechanisms for this behavior. To clarify this, the solubility of helium in mercury is evaluated in this study and compared to the available experimental data. The results indicate that helium has very small solubility in mercury and that the solubility increases with system temperature. Based on the predicted solubility values, bubble size evolution due to mass diffusion is simulated numerically. Mass diffusion induced bubble size evolution does not significantly affect bubble behavior for conditions expected in high power spallation targets

139

Helium doped hydrogen or deuterium beam as cost effective and simple tool for plasma spectroscopy  

International Nuclear Information System (INIS)

Energetic neutral particles from neutral hydrogenic beam heating systems are widely used for active spectroscopic measurements of key plasma parameters in fusion experiments. Helium beams are used in dedicated diagnostic beamlines offering deeper penetration and resonant double charge exchange with alpha particles. Neutral beam systems using pure helium either require specialised helium gas pumping with a pumping speed in excess of 1000 m3/h or are restricted to short pulses (normally less than 1 s). A doped hydrogen/helium beam combines the requirements for plasma heating and diagnostics without the need for sophisticated helium pumping. A small flow of helium gas is injected into the plasma source for the time helium particles are required. The helium current is typically 10% of the total extracted current. The reduction in heating power of the doped beam can be kept below 5%. Doped deuterium/helium beams have been successfully tested and routinely used at JET. HeI beam emission spectra obtained with a doped deuterium/helium beam offer sufficiently strong visible lines for spectroscopic applications

140

ITER helium ash accumulation  

International Nuclear Information System (INIS)

Many studies have shown the importance of the ratio ?He/?E in determining the level of He ash accumulation in future reactor systems. Results of the first tokamak He removal experiments have been analysed, and a first estimate of the ratio ?He/?E to be expected for future reactor systems has been made. The experiments were carried out for neutral beam heated plasmas in the TEXTOR tokamak, at KFA/Julich. Helium was injected both as a short puff and continuously, and subsequently extracted with the Advanced Limiter Test-II pump limiter. The rate at which the He density decays has been determined with absolutely calibrated charge exchange spectroscopy, and compared with theoretical models, using the Multiple Impurity Species Transport (MIST) code. An analysis of energy confinement has been made with PPPL TRANSP code, to distinguish beam from thermal confinement, especially for low density cases. The ALT-II pump limiter system is found to exhaust the He with maximum exhaust efficiency (8 pumps) of ?8%. We find 1He/?E<3.3 for the database of cases analysed to date. Analysis with the ITER TETRA systems code shows that these values would be adequate to achieve the required He concentration with the present ITER divertor He extraction system

 
 
 
 
141

Hydrogen Production Using the Modular Helium Reactor  

Energy Technology Data Exchange (ETDEWEB)

The high-temperature characteristics of the Modular Helium Reactor (MHR) make it a strong candidate for the production of hydrogen using either thermochemical or high-temperature electrolysis (HTE) processes. Using heat from the MHR to drive a Sulfur-Iodine (S-I) thermochemical hydrogen process has been the subject of a DOE sponsored Nuclear Engineering Research Initiative (NERI) project lead by General Atomics, with participation from the Idaho National Engineering and Environmental Laboratory (INEEL) and Texas A&M University. While the focus of much of the initial work was on the S-I thermochemical production of hydrogen, recent activities have also included development of a preconceptual design for an integral HTE hydrogen production plant driven by the process heat and electricity produced by a 600 MWt MHR. This paper describes RELAP5-3D analyses performed to evaluate alternative primary system cooling configurations for the MHR to minimize peak reactor vessel and core temperatures while achieving core helium outlet temperatures in the range of 900 oC to 1000 oC, needed for the efficient production of hydrogen using either the S-I thermochemical or HTE process. The cooling schemes investigated are intended to ensure peak fuel temperatures do not exceed specified limits under normal or transient upset conditions, and that reactor vessel temperatures do not exceed ASME code limits for steady-state or transient conditions using standard LWR vessel materials. Preconceptual designs for both an S-I thermochemical and HTE hydrogen production plant driven by a 600 MWt MHR at helium outlet temperatures in the range of 900 oC to 1000 oC are described and compared. An initial SAPHIRE model to evaluate the reliability, maintainablility, and availability of the S-I hydrogen production plant is also discussed, and plans for future assessments of conceptual designs for both a S-I thermochemical and HTE hydrogen production plant coupled to a 600 MWt modular helium reactor are described.

E. A. Harvego; S. M. Reza; M. Richards; A. Shenoy

2005-05-01

142

Computer simulation of range and damage distributions of 0.5 to 8 keV helium ions in crystalline and amorphous niobium  

International Nuclear Information System (INIS)

The binary collision cascade simulation program MARLOWE is used to study the influence of the crystal lattice, electronic energy loss and crystal temperature on the range and damage distributions of 0.5 to 8 keV He ions penetrating into a Nb target. If the ions enter the crystal parallel to the close-packed direction, the penetration depth profiles show temperature dependent channeling and dechanneling effects. The range distributions in amorphous Nb agree generally with Lindhard's transport theory if surface effects are taken into account. The damage distributions are nearly independent of the electronic energy loss models. The number of vacancies per incident ion increases linearly with the mean nuclear energy loss of the ion in amorphous as well as in crystalline Nb. (orig./GSCH)

143

Swelling and structure of vanadium-base alloys irradiated in the dynamic helium charging experiment  

International Nuclear Information System (INIS)

Combined effects of dynamically charged helium and neutron damage on density change, void distribution, and microstructural evolution of V-4Cr-4Ti alloy have been determined after irradiation to 18--31 dpa at 425--600 C in the Dynamic Helium Charging Experiment (DHCE), and the results were compared with those from a non-DHCE in which helium generation and negligible. For specimens irradiated to ?18-31 dpa at 500--600 with a helium generation rate of 0.4--4.2 appm He/dpa, only a few helium bubbles were observed at the interface of grain matrices and some of the Ti(O,N,C) precipitates, and no microvoids or helium bubbles were observed either in grain matrices or near grain boundaries. Under these conditions, dynamically produced helium atoms seem to be trapped in the grain matrix without significant bubble nucleation or growth, and in accordance with this, density changes from DHCE and non-DHCE (negligible helium generation) were similar for comparable fluence and irradiation temperature. Only for specimens irradiated to ?31 dpa at 425 C, when helium was generated at a rage of 0.4--0.8 appm helium/dpa, were diffuse helium bubbles observed in limited regions of grain matrices and near ?15% of the grain boundaries in densities significantly lower than those in the extensive coalescences of helium bubbles typical of other alloys irradiated in tritium-trick experiments. Density changes of specimens irradiated at 425 C in the DHCE were significantly higher than those from non-DHCE irradiation. Microstructural evolution in V-4Cr-4Ti was similar for DHCE and non-DHCE except for helium bubble number density and distribution. As in non-DHCE, the irradiation-induced precipitation of ultrafine Ti5Si3 was observed for DHCE at >500 C but not at 425 C

144

Asteroseismic estimate of helium abundance of a solar analog binary system  

CERN Document Server

16 Cyg A and B are among the brightest stars observed by Kepler. What makes these stars more interesting is that they are solar analogs. 16 Cyg A and B exhibit solar-like oscillations. In this work we use oscillation frequencies obtained using 2.5 years of Kepler data to determine the current helium abundance of these stars. For this we use the fact that the helium ionization zone leaves a signature on the oscillation frequencies and that this signature can be calibrated to determine the helium abundance of that layer. By calibrating the signature of the helium ionization zone against models of known helium abundance, the helium abundance in the envelope of 16 Cyg A is found to lie in the range 0.231 to 0.251 and that of 16 Cyg B lies in the range 0.218 to 0.266.

Verma, Kuldeep; Antia, H M; Basu, Sarbani; Mazumdar, Anwesh; Monteiro, Mario J P F G; Appourchaux, Thierry; Chaplin, William J; Garcia, Rafael A; Metcalfe, Travis S

2014-01-01

145

High temperature creep of a helium-implanted titanium aluminide alloy  

Energy Technology Data Exchange (ETDEWEB)

The creep properties of an intermetallic alloy Ti-46Al-2W-0.5Si (at%) including strain rate and time to fracture were investigated in vacuum using helium-implanted and non-implanted samples, at a temperature of 1073 K and a stress of 200 MPa. The implantation was performed using 24 MeV He-ions, homogeneously implanting the samples with up to 1333 appm (atomic parts per million) helium. The size and location of helium bubbles were determined with transmission electron microscopy (TEM). Samples implanted with helium content above 10 appm exhibited strong helium embrittlement, reducing both the time to fracture and the elongation at fracture. The corresponding critical helium bubble size r{sub c} was determined to 10 nm.

Magnusson, Per, E-mail: per.magnusson@psi.ch [Paul Scherrer Institut, Nuclear Energy and Safety, 5232 Villigen PSI (Switzerland); Chen Jiachao; Hoffelner, Wolfgang [Paul Scherrer Institut, Nuclear Energy and Safety, 5232 Villigen PSI (Switzerland)

2011-09-01

146

High temperature creep of a helium-implanted titanium aluminide alloy  

Science.gov (United States)

The creep properties of an intermetallic alloy Ti-46Al-2W-0.5Si (at%) including strain rate and time to fracture were investigated in vacuum using helium-implanted and non-implanted samples, at a temperature of 1073 K and a stress of 200 MPa. The implantation was performed using 24 MeV He-ions, homogeneously implanting the samples with up to 1333 appm (atomic parts per million) helium. The size and location of helium bubbles were determined with transmission electron microscopy (TEM). Samples implanted with helium content above 10 appm exhibited strong helium embrittlement, reducing both the time to fracture and the elongation at fracture. The corresponding critical helium bubble size r c was determined to 10 nm.

Magnusson, Per; Chen, Jiachao; Hoffelner, Wolfgang

2011-09-01

147

Helium superfluidity. Shapes and vorticities of superfluid helium nanodroplets.  

Science.gov (United States)

Helium nanodroplets are considered ideal model systems to explore quantum hydrodynamics in self-contained, isolated superfluids. However, exploring the dynamic properties of individual droplets is experimentally challenging. In this work, we used single-shot femtosecond x-ray coherent diffractive imaging to investigate the rotation of single, isolated superfluid helium-4 droplets containing ~10(8) to 10(11) atoms. The formation of quantum vortex lattices inside the droplets is confirmed by observing characteristic Bragg patterns from xenon clusters trapped in the vortex cores. The vortex densities are up to five orders of magnitude larger than those observed in bulk liquid helium. The droplets exhibit large centrifugal deformations but retain axially symmetric shapes at angular velocities well beyond the stability range of viscous classical droplets. PMID:25146284

Gomez, Luis F; Ferguson, Ken R; Cryan, James P; Bacellar, Camila; Tanyag, Rico Mayro P; Jones, Curtis; Schorb, Sebastian; Anielski, Denis; Belkacem, Ali; Bernando, Charles; Boll, Rebecca; Bozek, John; Carron, Sebastian; Chen, Gang; Delmas, Tjark; Englert, Lars; Epp, Sascha W; Erk, Benjamin; Foucar, Lutz; Hartmann, Robert; Hexemer, Alexander; Huth, Martin; Kwok, Justin; Leone, Stephen R; Ma, Jonathan H S; Maia, Filipe R N C; Malmerberg, Erik; Marchesini, Stefano; Neumark, Daniel M; Poon, Billy; Prell, James; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Seifrid, Martin; Siefermann, Katrin R; Sturm, Felix P; Swiggers, Michele; Ullrich, Joachim; Weise, Fabian; Zwart, Petrus; Bostedt, Christoph; Gessner, Oliver; Vilesov, Andrey F

2014-08-22

148

Studying the structure and mechanical properties of the steel-0Kh16N15M3B irradiated with helium ions  

International Nuclear Information System (INIS)

The effect of helium on the mechanical properties and structure of the 0Kh16N15M3B-stainless steel has been studied depending on the testing temperature, deforma,.ion rate, grain size, and helium concentration. Samples for destructive testing have been uniformly (volumetrically) saturated with helium up to 10-5 to 10-2 at. % at a cyclot?n by irradiation with a 36 MeV helium ion beam. The helium ion-implanted material exhibits embrittlement at temperatures above 700 deg C, the embrittlement growing with the helium concentration increase

149

Cavity morphology in a Ni based superalloy under heavy ion irradiation with hot pre-injected helium. II  

Science.gov (United States)

In the current investigation, TEM in-situ heavy ion (1 MeV Kr2+) irradiation with helium pre-injected at elevated temperature (400 °C) was conducted to simulate in-reactor neutron irradiation induced damage in CANDU spacer material Inconel X-750, in an effort to understand the effects of helium on irradiation induced cavity microstructures. Three different quantities of helium, 400 appm, 1000 appm, and 5000 appm, were pre-injected directly into TEM foils at 400 °C. The samples containing helium were then irradiated in-situ with 1 MeV Kr2+ at 400 °C to a final dose of 5.4 dpa (displacement per atom). Cavities were formed from the helium injection solely and the cavity density and size increased with increasing helium dosage. In contrast to previous heavy ion irradiations with cold pre-injected helium, heterogeneous nucleation of cavities was observed. During the ensuing heavy ion irradiation, dynamical observation showed noticeable size increase in cavities which nucleated close to the grain boundaries. A "bubble-void" transformation was observed after Kr2+ irradiation to high dose (5.4 dpa) in samples containing 1000 appm and 5000 appm helium. Cavity distribution was found to be consistent with in-reactor neutron irradiation induced cavity microstructures. This implies that the distribution of helium is greatly dependent on the injection temperature, and helium pre-injection at high temperature is preferred for simulating the migration of the transmutation produced helium.

Zhang, He; Yao, Zhongwen; Daymond, Mark R.; Kirk, Marquis A.

2014-03-01

150

Cavity morphology in a Ni based superalloy under heavy ion irradiation with hot pre-injected helium. II  

Energy Technology Data Exchange (ETDEWEB)

In the current investigation, TEM in-situ heavy ion (1?MeV Kr{sup 2+}) irradiation with helium pre-injected at elevated temperature (400?°C) was conducted to simulate in-reactor neutron irradiation induced damage in CANDU spacer material Inconel X-750, in an effort to understand the effects of helium on irradiation induced cavity microstructures. Three different quantities of helium, 400 appm, 1000 appm, and 5000 appm, were pre-injected directly into TEM foils at 400?°C. The samples containing helium were then irradiated in-situ with 1?MeV Kr{sup 2+} at 400?°C to a final dose of 5.4 dpa (displacement per atom). Cavities were formed from the helium injection solely and the cavity density and size increased with increasing helium dosage. In contrast to previous heavy ion irradiations with cold pre-injected helium, heterogeneous nucleation of cavities was observed. During the ensuing heavy ion irradiation, dynamical observation showed noticeable size increase in cavities which nucleated close to the grain boundaries. A “bubble-void” transformation was observed after Kr{sup 2+} irradiation to high dose (5.4?dpa) in samples containing 1000 appm and 5000 appm helium. Cavity distribution was found to be consistent with in-reactor neutron irradiation induced cavity microstructures. This implies that the distribution of helium is greatly dependent on the injection temperature, and helium pre-injection at high temperature is preferred for simulating the migration of the transmutation produced helium.

Zhang, He; Yao, Zhongwen, E-mail: yaoz@me.queensu.ca; Daymond, Mark R. [Department of Mechanical and Materials Engineering, Queen' s University Kingston, Ontario K7L 3N6 (Canada); Kirk, Marquis A. [Material Science Division, Argonne National Laboratory Argonne, Illinois 60439 (United States)

2014-03-14

151

Recombination of positive helium ions in gaseous helium  

International Nuclear Information System (INIS)

The Wigner-Keck Monte Carlo trajectory method and the resonance complex theory are employed to calculate the rate coefficient k for He+ ions recombining in gaseous helium in the temperature range 80 2+ is obtained from a Morse potential and a long range ion-induced dipole interaction term. The three body He3+ interaction is represented by an approximate expression which, for practical purpose, depends on the same parameters that determine the two body interaction. Russell had employed the Wigner-Keck Monte Carlo trajectory method to the same reaction. Unlike his calculation, in which the final quasibound states are treated as continuous, we apply the JWKB approximation to quantize those quasibound states. Both the values of k, calculated from two different quasibound state treatments, are found to be very close and give good agreement with experimental results obtained by Biondi, although they are still 10% to 20% lower than the experimental results. The resonance complex theory, developed by Roberts et al, is then employed to investigated de-excitation from the highest quasibound state, which can be populated by inward tunneling through the rotational (centrifugal) barrier. It is found that this strongly supports a suggestion proposed by Russell. He had suggested that the remaining difference between the Wigner-Keck method and experiment might be larer-Keck method and experiment might be largely due to the formation of highly excited quasibound states. The statistical errors of the rate constants, which is the sun of results obtained from both methods, are kept less then 5% by running 2500 trajectories in the first method and 500 in the second

152

CEMS at low temperature with a gas mixture of helium and neon  

International Nuclear Information System (INIS)

Operational techniques of a gas-filled proportional counter for CEMS measurements was improved at temperatures between 20 and 45 K. The best CEMS spectrum was obtained when 0.2-0.5 atm neon and helium is filled in the counter under the conditions that the total pressure of neon and helium is 1 atm. (orig.)

153

The effect of primordial hydrogen/helium fractionation on the solar neutrino flux  

Science.gov (United States)

If hydrogen and helium are immiscible below some critical temperature, gravitational separation could occur in the proto-sun, resulting in a nearly pure helium core and a nearly pure hydrogen shell. We have constructed solar models according to this scenario and find the neutrino flux reduced to 1.5-3 SNU.

Wheeler, J. C.; Cameron, A. G. W.

1975-01-01

154

Cryogenic turbomachines for helium refrigeration system  

International Nuclear Information System (INIS)

A helium refrigeration system is indispensable for large superconducting magnets used in large-scale particle accelerators, nuclear fusion reactors, superconducting generators, etc. Cryogenic turbomachines in the refrigeration system are key components upon deciding on reliability and performance. This paper describes its role in the system, construction, and performance of 3.5 K/80 K cold compressor, SHE circulation pump, and SHE turbine that have been developed by IHI. Each machine has superior characteristics that is perfectly oil-free and also has a unique heat insulation device, achieving a remarkable performance. Now IHI's cryogenic turbomachines hold a top position in the world for the field of cryogenic application. (author)

155

Violent phase of the core helium flash  

International Nuclear Information System (INIS)

The calculations described previously by Cole and Deupree were continued until the core helium flash reached a violent phase. Suitable alterations were made to the input physics, and the violent phase followed for about 5 seconds. We find a deflagration wave, not a detonation wave as previous investigators of violent core flashes have found. We attribute this difference primarily to the nonspherical nature of the burning in our two-dimensional code. Velocities of core material reach 2000 km s-1, well below either the sound speed or the escape speed. It is highly likely that some mass loss will occur, but complete disruption of the star does not occur

156

Determination of low levels of krypton in helium by gas chromatography  

International Nuclear Information System (INIS)

Krypton-helium mixture was used as an adsorbate for surface area measurement--. The surface area measurements depend on the accuracy with which the krypton concentration is known. Generally gas tanks supplied by Union Carbide provide a nominal value of 0.1% krypton in helium. The surface area measurements require, however, that the krypton concentraion be known to +- 0.001% or better. A standard plot of krypton volume in microliters vs the area under the curve as measured by a planimeter using the helium detector and Molecular Sieve 5A column was obtained. Results with a thermal conductivity detector using Molecular Sieve 5A and Carbon Molecular Sieve are also given. Low levels of krypton in helium can be measured with precision using either a helium or a thermal conductivity detector with Molecular Sieve 5A or Carbon Molecular Sieve columns. 2 figures, 1 table

157

Reexamination of helium fine structure  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In order to explain discrepancies between theoretical predictions and experimental data for the helium fine structure, we check and recalculate all theoretical contributions up to orders m\\alpha^7 and m^2/M\\alpha^6. The previous result for the m\\alpha^7 correction is improved by a much more accurate calculation of relativistic corrections to the Bethe logarithm. The theoretical values of the 2^3P_0-2^3P_1 and 2^3P_1-2^3P_2 fine structure intervals in helium are, correspondin...

Pachucki, K.; Yerokhin, V. A.

2009-01-01

158

Energy Levels of Helium Nucleus  

Directory of Open Access Journals (Sweden)

Full Text Available The Helium-4 nucleus is more similar to the Hydrogen atom of atomic physics. In the case of hydrogen atom, there are many energy levels which were experimentally seen and theoretically explained using non-relativistic quantum mechanics. In this note, we use a central potential to derive the energy levels of Helium-4 nucleus. The ground state and the first few energy levels agree pretty well with experiment. The same potential can be used with nuclei like Oxygen-17 and many more nuclei.

Cvavb Chandra Raju

2013-04-01

159

Evolution of defects in silicon carbide implanted with helium ions  

Science.gov (United States)

Effects of accumulation of radiation damage in silicon carbide are important concerns for the use of silicon carbide in advanced nuclear energy systems. In the present work lattice damage in silicon carbide crystal (4H type) implanted with 100 keV 4He+ ions was investigated with Rutherford backscattering spectrometry in channeling geometry (RBS/c) and positron beam Doppler broadening spectrometry (PBDB). Helium implantation was performed at the specimen temperature of 510 K to avoid amorphization of the SiC crystal. Fluences of helium ions were selected to be in the range from 1 × 1016 to 3 × 1016 ions cm-2, around the dose threshold for the formation of observable helium bubbles under transmission electron microscopes (TEM). The RBS/c measurements show distinctly different annealing behavior of displaced Si atoms at doses below or above the threshold for helium bubble formation. The RBS/c yield in the peak damage region of the specimen implanted to 3 × 1016 He-ions cm-2 shows an increase on the subsequently thermal annealing above 873 K, which is readily ascribed to the extra displacement of Si atoms due to helium bubble growth. The RBS/c yield in the specimen implanted to a lower ion fluence of 1.5 × 1016 He-ions cm-2 decreases monotonously on annealing from ambient temperatures up to 1273 K. The PBDB measurements supply evidence of clustering of vacancies at temperatures from 510 to 1173 K, and dissociation of vacancy clusters above 1273 K. The similarity of annealing behavior in PBDB profiles for helium implantation to 1 × 1016 and 3 × 1016 ions cm-2 is ascribed to the saturation of trapping of positrons in vacancy type defects in the damaged layers in the specimens helium-implanted to the two dose levels.

Zhang, Chonghong; Song, Yin; Yang, Yitao; Zhou, Chunlan; Wei, Long; Ma, Hongji

2014-05-01

160

Helium transport and exhaust studies in enhanced confinement regimes in DIII-D  

Energy Technology Data Exchange (ETDEWEB)

A better understanding of helium transport in the plasma core and edge in enhanced confinement regimes is now emerging from recent experimental studies on DIII-D. Overall, the results are encouraging. Significant helium exhaust ({tau}*{sub He}/{tau}{sub E} {approximately} 11) has been obtained in a diverted, ELMing H-mode plasma simultaneous with a central source of helium. Detailed analysis of the helium profile evolution indicates that the exhaust rate is limited by the exhaust efficiency of the pump ({approximately}5%) and not by the intrinsic helium transport properties of the plasma. Perturbative helium transport studies using gas puffing have shown that D{sub He}/X{sub eff}{approximately}1 in all confinement regimes studied to date (including H-mode and VH-mode). Furthermore, there is no evidence of preferential accumulation of helium in any of these regimes. However, measurements in the core and pumping plenum show a significant dilution of helium as it flows from the plasma core to the pumping plenum. Such dilution could be the limiting factor in the overall removal rate of helium in a reactor system.

Wade, M.R.; Hillis, D.L.; Hogan, J.T.; Mahdavi, M.A.; Maingi, R.; West, W.P.; Burrell, K.H.; Finkenthal, D.F.; Gohil, P.; Groebner, R.J. [and others

1995-02-01

 
 
 
 
161

Helium retention properties of plasma facing materials  

Science.gov (United States)

In a fusion reactor, the continuous removal of helium from the core plasma is needed in order to sustain the ignition condition. For this purpose, it has been proposed to place helium selective pumping metals, which can trap more helium than hydrogen, in the vicinity of the divertor. In this study, the helium and hydrogen trapping properties of nickel, tungsten, molybdenum, SS 304 and Inconel 625 were examined. Namely, the dependencies of irradiation temperature on the amount of trapped helium and hydrogen were obtained by thermal desorption spectroscopy (TDS), after helium or hydrogen plasma irradiation. In those metals, nickel showed the most suitable selective pumping capability. Nickel had the helium selective pumping property above 100°C. The maximum amount of trapped helium was (2-3) × 10 16He/ cm2 at an irradiation temperature of 200°C and 600°C. The optimum temperature becomes about 600°C when nickel is used for a selective pumping material.

Yanagihara, H.; Yamauchi, Y.; Hino, T.; Hirohata, Y.; Yamashina, T.

1997-02-01

162

Pierre Gorce working on a helium pump.  

CERN Multimedia

This type of pump was designed by Mario Morpurgo, to circulate liquid helium in superconducting magnets wound with hollow conductors. M. Morpurgo, Design and construction of a pump for liquid helium, CRYIOGENICS, February 1977, p. 91

1975-01-01

163

Calcium fluoride crystal coloring initiated by helium  

International Nuclear Information System (INIS)

The work is devoted to ascertaining the mechanism of alkaline-earth fluoride thermostimulated luminescence (TSL) amplification and the role of helium in improving radiation defect formation efficiency. CaF2 monocrystals saturated with helium are used for measurements. It is shown that the crystal radiation colouring efficiency increases under CaF2 monocrystal saturation with helium for which a new optical center (?=535 mm) linked with helium is responsible

164

Study of the hadron-helium and helium-helium scattering at high energy  

International Nuclear Information System (INIS)

Multiple scattering Glauber's theory is used to calculate the hadron-helium and helium-helium elastic differential cross-section. The theory is very sensitive to the 4He wave functions. We use better 4He wave functions than experimental ones. These wave functions have correct asymptotic shape. In some calculations, we take into account the spin effects and the 4He, S, S' and D states contribution. At high energy, we use inelastic corrections, to complete the differential cross-section. A study of the diffractive and coherent p-4He ? 4He-X dissociation is developed. We use Humble's amplitudes with a peripherical character and an helicity structure. The agreement with experimental results is good for 24 to 400 GeV

165

Helium distribution functions in tokamak plasmas  

International Nuclear Information System (INIS)

Two different methods are used to obtain information on the helium distribution. The first method is a machine that measures the velocity distribution of neutral helium particles escaping from the plasma (NPA). The second method is charge exchange spectroscopy that measures the helium density and temperature as a function of time and place from the Doppler broadened intensity of He lines. (orig./HP)

166

Helium line detections from ELDWIM at 1.4 GHz  

CERN Document Server

Helium line observations towards 11 Galactic positions using Westerbork Synthesis Radio Telescope(WSRT) have been reported. These observations were made towards nearby positions where already hydrogen lines were detected at sufficiently high intensity($\\geq$50mK) at 1.4 GHz. This approach gave a fair chance for the detection of helium line as well, keeping in mind the relative abundance(10%) of helium with respect to hydrogen. Care was also taken to avoid the presence of HII regions along the line of sight so that the line emission originates from the extended diffuse low density ionized component, ELDWIM of the Galaxy. The observations have resulted in the detection of helium line towards 5 positions out of 11 with signal to noise ratio(snr) $>$ 4$\\sigma$. An attempt has been made to associate detection/non-detection of helium line to the presence of surrounding HII regions. A weighting scheme that accounts for nearby($<$ 500pc) HII regions, their distances and other factors produces favourable results. I...

Baddi, Raju

2012-01-01

167

Positron helium scattering using CCA  

International Nuclear Information System (INIS)

Calculations have been carried out to investigate e+-He scattering using close coupling method with various basis sets. The n=2 excitation cross section and positronium cross section are reported at medium energies. Two dynamically active electrons have been considered on same footing and realistic wavefunctions of helium target have been used. (author). 20 refs., 3 figs

168

Helium embrittlement of RAFM steels  

International Nuclear Information System (INIS)

Full text of publication follows: Transmutation product helium generated in the structure materials of future fusion reactors is believed to strongly influence material embrittlement behaviour. To simulate helium effects in reduced activation ferritic/martensitic (RAFM) steels, experimental heats ADS2 (OPTIFER-VIII), ADS3 and ADS4 with the basic composition of EUROFER97 (9%Cr-WVTa) were doped with different contents of natural boron and separated 10B-isotope and irradiated in HFR Petten up to 16.3 dpa at multiple temperatures of 250-450 deg. C (irradiation programme HFR IIb - SPCICE). For comparative purpose and in order to exclude significant differences in the microstructure, ADS2 and ADS3 were doped with 82 wppm nat. B and 83 wppm separated 10B isotope, respectively. ADS4 was doped with 1120 wppm 10B isotope. The embrittlement behaviour and hardening are investigated by instrumented Charpy-V tests with sub-size specimens. Boron-to-helium transformation lead to generation of 84, 432 and 5580 appm He in ADS2, ADS3 and ADS4 steels, respectively. At low irradiation temperatures Tirr?350 deg. C the boron doped steels show progressive embrittlement and reduction of toughness with increasing helium amount. The analysis of the hardening vs. embrittlement behaviour at Tirr=250 deg. C indicates that 84 appm helium produced in ADS2 leads to the extra embrittlement beyond that of reference EUROFER97 steel mainly due to eeference EUROFER97 steel mainly due to extra, helium induced hardening. For ADS3, however, generated helium amount of 432 appm contributes to additional embrittlement mechanisms beyond that of hardening embrittlement. At Tirr=450 deg. C, ADS2 does not exhibit extra embrittlement beyond that of reference EUROFER97 steel. ADS3 in contrast exhibits non-vanishing extra embrittlement also at this high irradiation temperature. Irradiation induced DBTT shift of EUROFER97 steel doped with 1120 wppm separated 10B isotope could not be quantified due to large embrittlement found in the investigated temperature range. (authors)

169

A design for a pinhole scanning helium microscope  

Science.gov (United States)

We present a simplified design for a scanning helium microscope (SHeM) which utilises almost entirely off the shelf components. The SHeM produces images by detecting scattered neutral helium atoms from a surface, forming an entirely surface sensitive and non-destructive imaging technique. This particular prototype instrument avoids the complexities of existing neutral atom optics by replacing them with an aperture in the form of an ion beam milled pinhole, resulting in a resolution of around 5 microns. Using the images so far produced, an initial investigation of topological contrast has been performed.

Barr, M.; Fahy, A.; Jardine, A.; Ellis, J.; Ward, D.; MacLaren, D. A.; Allison, W.; Dastoor, P. C.

2014-12-01

170

A transient modeling of a helium turbine power system  

International Nuclear Information System (INIS)

In this study, a transient performance simulation model of an indirect helium turbine cycle system is developed. One-dimension models are built to simulate the components, including helium turbine model, compressor model, heat exchanger model, valve model, duct model and shaft rotation model. The simulation code is established on MATLAB and the ordinary differential equations derived from component model are solved by the ode15s solvers of MATLAB. The accident of loss of load and the transient of decreasing heat transfer capacity of intermediate heat exchanger by 5% are simulated and analyzed. The analysis of calculated results validates the present model. (author)

171

Scintillation of Liquid Helium for Low-Energy Nuclear Recoils  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The scintillation properties of liquid helium upon the recoil of a low energy helium atom are discussed in the context of the possible use of this medium as a detector of dark matter. It is found that the prompt scintillation yield in the range of recoil energies from a few keV to 100 keV is somewhat higher than that obtained by a linear extrapolation from the measured yield for an 5 MeV alpha particle. A comparison is made of both the scintillation yield and the charge sepa...

Ito, T. M.; Seidel, G. M.

2013-01-01

172

The impact of transmutant helium on weldability of austenitic steel  

Science.gov (United States)

The results of the investigation of 0.05-0.15 dpa neutron irradiation impact on the Cr16Ni11Mo3Ti austenitic steel weldability are presented. Samples were irradiated to doses of 10 20 n/cm 2 and 3 × 10 20 n/cm 2 ( E > 0.1 MeV) in the RBT-10 reactor, thus providing helium accumulation of 1 appm and 2.5 appm, respectively. Flat samples, 1 mm in thickness, were welded by an automatic device for argon arc welding in a hot chamber. Low-cycle fatigue (LCF) testing in bending was used to assess impact of helium on the degradation of welded joint properties. LCF tests showed that the transmutant helium accumulation resulted in a decrease in the number of cycles to failure at Ttest = 20°C and 350°C. It is concluded that repeated welding will present in the repair of ITER materials.

Fabritsiev, S. A.; Pokrovsky, A. S.; Brovko, V. A.

1996-10-01

173

Effect of helium on tensile properties of vanadium alloys  

Energy Technology Data Exchange (ETDEWEB)

Tensile properties of V-4Cr-4Ti (Heat BL-47), 3Ti-1Si (BL-45), and V-5Ti (BL-46) alloys after irradiation in a conventional irradiation experiment and in the Dynamic Helium Charging Experiment (DHCE) were reported previously. This paper presents revised tensile properties of these alloys, with a focus on the effects of dynamically generated helium of ductility and work-hardening capability at <500{degrees}C. After conventional irradiation (negligible helium generation) at {approx}427{degrees}C, a 30-kg heat of V-4Cr-4Ti (BL-47) exhibited very low uniform elongation, manifesting a strong susceptibility to loss of work-hardening capability. In contrast, a 15-kg heat of V-3Ti-1Si (BL -45) exhibited relatively high uniform elongation ({approx}4%) during conventional irradiation at {approx}427{degrees}C, showing that the heat is resistant to loss of work-hardening capability.

Chung, H.M.; Billone, M.C.; Smith, D.L. [Argonne National Lab., IL (United States)

1997-08-01

174

Helium Refrigeration System for BNL Colliding-Beam Accelerator  

Energy Technology Data Exchange (ETDEWEB)

A Helium Refrigeration System which will supply the cooling required for the Colliding Beam Accelerator at Brookhaven National Laboratory is under construction. Testing of the compressor system is scheduled for late 1983 and will be followed by refrigerator acceptance tests in 1984. The refrigerator has a design capacity of 24.8 kW at a temperature level near 4% while simultaneously producing 55 kW for heat shield loads at 55K. When completed, the helium refrigerator will be the world's largest. Twenty-five oil-injected screw compressors with an installed total of 23,250 horsepower will supply the gas required. One of the unique features of the cycle is the application of three centrifugal compressors used at liquid helium temperature to produce the low temperatures (2.5K) and high flow rates (4154 g/s) required for this service.

Brown, D.P.; Farah, Y.; Gibbs, R.J.; Schlafke, A.P.; Schneider, W.J.; Sondericker, J.H.; Wu, K.C.

1983-01-01

175

Helium Refrigeration System for BNL Colliding-Beam Accelerator  

International Nuclear Information System (INIS)

A Helium Refrigeration System which will supply the cooling required for the Colliding Beam Accelerator at Brookhaven National Laboratory is under construction. Testing of the compressor system is scheduled for late 1983 and will be followed by refrigerator acceptance tests in 1984. The refrigerator has a design capacity of 24.8 kW at a temperature level near 4% while simultaneously producing 55 kW for heat shield loads at 55K. When completed, the helium refrigerator will be the world's largest. Twenty-five oil-injected screw compressors with an installed total of 23,250 horsepower will supply the gas required. One of the unique features of the cycle is the application of three centrifugal compressors used at liquid helium temperature to produce the low temperatures (2.5K) and high flow rates (4154 g/s) required for this service

176

Kapitza resistance between liquid and solid helium  

International Nuclear Information System (INIS)

The results of a study of the Kapitza resistance (R/sub K/ between liquid and solid helium-4 are presented. In the first chapter the recent proposal by Andreev and Parshin that, because of quantum delocalization of surface defects, the boundary between liquid and solid helium-4 would be in a special state is discussed. This state may be regarded as a quantum analog of an atomically rough interface. This particular interface is able to impede the passage of phonons because it can melt or freeze without dissipation as a response to an external non-equilibrium situation, i.e., pressure waves (phonons). In the second chapter two calculations of R/sub K/ are presented. One of them, the Acoustic-Mismatch calculation, is based on a model of the interface where no melting or freezing can occur. In this model the interface behaves as classical (non-rough). The usual T-3 temperature dependence is obtained. The other calculation is based on the model of the rough interface of Andreev and Parshin. R/sub K/ has a T-5 temperature dependence at low temperatures. At high temperatures (T > 0.5K) the two theories give approximately the same result for R/sub K/. In the third and fourth chapter experimental results for the phonon transmission coefficient across the interface are presented. These measurements are consistent with the rough interface theory of the Kapitza resistance

177

Neutron studies of liquid and solid helium  

International Nuclear Information System (INIS)

The progress made during 5/1/86--4/31/87 under contract No. F902- 34ER45082 is reported. The validity of the Impulse Approximation (IA) to the dynamic form factor, S(Q,?), has been investigated using realistic models of solid helium. The calculations suggest that the IA can be used to obtain the momentum distribution, n(p), within 1% at Q ? 30 Angstrom -1, if S(Q,?) is first symmetrized about the recoil frequency, ?R. For solid helium under pressure (e.g. 5 kbar) a Q approx-gt 50 Angstrom -1 is required. The S(Q,?) in liquid 3He and 4He in the wave vector transfer range 3 ? Q ? 10 Angstrom -1 has been evaluated, beginning from the pair potential. The general shape and width of S(Q,?) obtained agrees well with existing experiment. The width of S(Q,?) is found to oscillate as a function of Q in 4He but not in 3He. The dynamics of atoms adsorbed in solid layers on surfaces has been studied using self-consistent methods

178

Helium embrittlement of a lamellar titanium aluminide  

Energy Technology Data Exchange (ETDEWEB)

Embrittlement by helium was investigated in a lamellar TiAl alloy under two conditions: (a)Specimens were implanted to various amounts of helium up to 762 appm at temperatures from 630 °C to 1000 °C and some of them subsequently creep-tested at the same temperature under stresses from 150 to 300 MPa. The microstructure and fracture surfaces of creep-deformed and non-creep-deformed specimens were then studied by transmission electron microscopy (TEM) and by scanning electron microscopy (SEM), respectively. (b)Specimens were implanted to various amounts of helium at a low temperature (150 °C) and post-implantation annealed at elevated temperatures for TEM studies. Embrittlement was revealed by reduction in time- and strain-to-rupture and by a transition in fracture surface from ductile to an inter-lamellar appearance. Embrittlement occurred above a critical He concentration, which decreased from about 10 appm at 700 °C to below 6 appm at 900 °C. TEM showed that embrittlement could be associated to reaching a critical bubble diameter of about 5 nm. Bubble diameters increased with increasing temperature ranging in high-temperature implanted specimens from about 3 nm (630 °C) to 20 nm (1000 °C) and in post-implantation annealed ones from 1.2 nm (600 °C) to 2.2 nm (900 °C), respectively. With increasing temperature, the bubble distribution grew less homogenous with a lower density of larger bubbles situated preferentially at interfaces and sinks. This was ascribed to a change in bubble nucleation mode from homogeneous di-atomic nucleation at lower temperatures to multi-atomic nucleation at sinks at higher temperature.

Magnusson, P. [Department of Nuclear Energy and Safety, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Chen, J., E-mail: jiachao.chen@psi.ch [Department of Nuclear Energy and Safety, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Jung, P. [Department of Nuclear Energy and Safety, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Sauvage, T. [CEMHTI/CNRS, Université d’Orléans, 3A rue de la Férollerie, 45071 Orléans CEDEX 2 (France); Hoffelner, W. [Department of Nuclear Energy and Safety, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Spätig, Ph. [Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association Euratom – Confédération Suisse, 5232 Villigen PSI (Switzerland)

2013-03-15

179

Helium embrittlement of a lamellar titanium aluminide  

Science.gov (United States)

Embrittlement by helium was investigated in a lamellar TiAl alloy under two conditions: Specimens were implanted to various amounts of helium up to 762 appm at temperatures from 630 °C to 1000 °C and some of them subsequently creep-tested at the same temperature under stresses from 150 to 300 MPa. The microstructure and fracture surfaces of creep-deformed and non-creep-deformed specimens were then studied by transmission electron microscopy (TEM) and by scanning electron microscopy (SEM), respectively. Specimens were implanted to various amounts of helium at a low temperature (150 °C) and post-implantation annealed at elevated temperatures for TEM studies. Embrittlement was revealed by reduction in time- and strain-to-rupture and by a transition in fracture surface from ductile to an inter-lamellar appearance. Embrittlement occurred above a critical He concentration, which decreased from about 10 appm at 700 °C to below 6 appm at 900 °C. TEM showed that embrittlement could be associated to reaching a critical bubble diameter of about 5 nm. Bubble diameters increased with increasing temperature ranging in high-temperature implanted specimens from about 3 nm (630 °C) to 20 nm (1000 °C) and in post-implantation annealed ones from 1.2 nm (600 °C) to 2.2 nm (900 °C), respectively. With increasing temperature, the bubble distribution grew less homogenous with a lower density of larger bubbles situated preferentially at interfaces and sinks. This was ascribed to a change in bubble nucleation mode from homogeneous di-atomic nucleation at lower temperatures to multi-atomic nucleation at sinks at higher temperature.

Magnusson, P.; Chen, J.; Jung, P.; Sauvage, T.; Hoffelner, W.; Spätig, Ph.

2013-03-01

180

Helium embrittlement of a lamellar titanium aluminide  

International Nuclear Information System (INIS)

Embrittlement by helium was investigated in a lamellar TiAl alloy under two conditions: (a)Specimens were implanted to various amounts of helium up to 762 appm at temperatures from 630 °C to 1000 °C and some of them subsequently creep-tested at the same temperature under stresses from 150 to 300 MPa. The microstructure and fracture surfaces of creep-deformed and non-creep-deformed specimens were then studied by transmission electron microscopy (TEM) and by scanning electron microscopy (SEM), respectively. (b)Specimens were implanted to various amounts of helium at a low temperature (150 °C) and post-implantation annealed at elevated temperatures for TEM studies. Embrittlement was revealed by reduction in time- and strain-to-rupture and by a transition in fracture surface from ductile to an inter-lamellar appearance. Embrittlement occurred above a critical He concentration, which decreased from about 10 appm at 700 °C to below 6 appm at 900 °C. TEM showed that embrittlement could be associated to reaching a critical bubble diameter of about 5 nm. Bubble diameters increased with increasing temperature ranging in high-temperature implanted specimens from about 3 nm (630 °C) to 20 nm (1000 °C) and in post-implantation annealed ones from 1.2 nm (600 °C) to 2.2 nm (900 °C), respectively. With increasing temperature, the bubble distribution grew less homogenous with a lower density of larger bubbles situated preferentially at interfaces and sinks. This was ascribed to a change in bubble nucleation mode from homogeneous di-atomic nucleation at lower temperatures to multi-atomic nucleation at sinks at higher temperature

 
 
 
 
181

Ceramic helium-cooled blanket test module  

International Nuclear Information System (INIS)

The design of RF DEMO-relevant ceramic helium cooled blanket test module (CHC BTM) for testing in international thermonuclear experimental reactor (ITER) is under consideration. The RF concept of DEMO BTM is based upon the breeder inside tube (BIT)-concept. This concept suggests the use of solid breeding ceramic material, helium as coolant and tritium purge-gas, ferrite-martensite steel as structural material, and beryllium as neutron multiplier. The parameters of the primary circuit coolant are the following, pressure -8 MPa, inlet/outlet temperature -300/550 deg. C, respectively. Helium (0.1 MPa pressure) is used for tritium removal from ceramic breeder. The ITER water coolant is the secondary circuit coolant of DEMO BTM cooling system. Lithium orthosilicate (Li4SiO4) is used as tritium breeding material (pebbles-bed of diameter 0.5-1 mm spheres). It is planned to use the beryllium as neutron multiplier (spheres diameter 1 mm pebbles-bed or the porous beryllium). The 3-D neutronic calculations on Monte Carlo method, in accordance with FENDL-1 library of the nuclear data, have been performed for CHC BTM. To validate the CHC BTM concept, the thermal hydraulic analysis has been performed for the design elements and cooling system equipment. The preliminary stress analysis for BTM design elements has been carried out on the ASME-code and RF strength regulations. The four types of LOFA and LOCA accidents have been investigated. The parameters of cooe been investigated. The parameters of cooling, coolant purification and tritium extraction systems have been determined

182

Gravitational and radiative effects on the escape of helium from the moon  

Science.gov (United States)

On the moon, and probably on Mercury and other similar regolith-covered bodies with tenuous atmosphere, the dominant gas is He-4. It arises as the radiogenic product of the decay of uranium and thorium within any planet, but its major source appears to be the alpha particle flux of the solar wind. The moon intercepts solar wind helium at an average rate of 1.1 times 10 to the 24th atom/sec, and loses it at the same rate. Some helium may escape directly as the result of the process of solar wind soil bombardment which may release previously trapped helium at superthermal speeds. Atmospheric models have been calculated with the total helium influx as source. Subsequent comparison of model and measured helium concentrations indicates that the fraction of helium escaping via the atmosphere may range from 20% to 100% of the solar wind influx. Of the escaping atmosphere, most of the helium (about 93%) becomes trapped in earth orbit, while about 5% gets trapped in satellite orbits about the moon. Owing to a 6 month lifetime for helium in solar radiation, the satellite atoms form a lunar corona that exceeds the lunar atmosphere in total abundance by a factor of 4 to 5.

Hodges, R. R., Jr.

1978-01-01

183

Internally-cooled cabled superconductors cooled with helium II  

International Nuclear Information System (INIS)

Niobium-titanium superconductors maintained at sublambda temperatures provide an alternative to helium cooled niobium-3-tin superconductors operating in the 4.2 to 5 K temperature range. The subject paper examines the replacement of supercritical HeI with subcooled HeII in a slightly modified MIT-12 T test coil. Both steady-state and transient heat loads are considered

184

Imprints from the solar cycle on the helium atom and helium pickup ion distributions  

Directory of Open Access Journals (Sweden)

Full Text Available Neutral interstellar helium atoms penetrate into the solar system almost unaffected by gas–plasma interactions in the heliospheric interface region, and thus can be considered as carriers of original information on the basic parameters (like density, temperature, bulk velocity of the Very Local Interstellar Medium (VLISM. Such information can nowadays be derived from analysis of data obtained from different experimental methods: in situ measurements of He atoms (Ulysses, observations of the solar backscattered He 584 A radiation (EUVE, in situ measurements of He + pickup ions (AMPTE, Ulysses, Wind, SOHO, ACE. In view of the current coordinated international ISSI campaign devoted to the study of the helium focusing cone structure and its evolution, we analyze expected variations of neutral He density, of He + pickup fluxes and of their phase space distributions at various phases of the solar activity cycle based on a realistic time-dependent modelling of the neutral helium and He + pickup ion distributions, which reflect solar cycle-induced variations of the photoionization rate. We show that the neutral helium density values are generally anticorrelated with the solar activity phase and in extreme cases (near the downwind axis the maximum-to-minimum density ratio may even exceed factors of ~ 3 at 1 AU. We also demonstrate that in the upwind hemisphere (at 1 AU and beyond the He + fluxes are correlated with the solar cycle activity, whereas on the downwind side the maximum of the expected flux up to distances of ~ 3 AU occurs around solar minimum epoch, and only further away does the correlation with solar activity become positive. Finally, we present the response of the phase space distribution spectra of He + pickup ions (in the solar wind frame for different epochs of the solar cycle and heliocentric distances from 1 to 5 AU covering the range of Ulysses, Wind and ACE observations.

Key words. Solar physics, astrophysics and astronomy (ultraviolet emissions – Space plasma physics (ionization processes; numerical simulation studies

D. Rucinski

185

Formation of Triplet Positron-helium Bound State by Stripping of Positronium Atoms in Collision with Ground State Helium  

Science.gov (United States)

Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.

Drachman, Richard J.

2006-01-01

186

HeREF-2003: Helium Refrigeration Techniques  

CERN Multimedia

CERN Technical Training 2003: Learning for the LHC ! Theory, Technology, Maintenance and Control of Helium Refrigerators HeREF-2003 is a course in the framework of the 2002 Technical Training Programme, that will provide a complete introduction to Helium refrigeration, with a practical approach to theory, technology, maintenance and control of Helium refrigeration installations. Theoretical aspects and equations will be limited to a minimum. HeREF-2003 targets an audience of technicians and operators of Helium refrigeration plants at CERN, as well as physicists and engineers needing an overview of current Helium refrigeration techniques. HeREF-2003 will address, among other, issues related to component technology, installation maintenance, process control and Helium purity. A commented visit to a couple of CERN Helium refrigeration or liquefaction plants will also take place. Duration: 7 half days (4 mornings and 3 afternoons), 6-10 October, 2003 Cost per participant: 500.- CHF Language: Bilingual English...

2003-01-01

187

HeREF-2003 : Helium Refrigeration Techniques  

CERN Multimedia

CERN Technical Training 2003: Learning for the LHC ! Theory, Technology, Maintenance and Control of Helium Refrigerators HeREF-2003 is a course in the framework of the 2002 Technical Training Programme, that will provide a complete introduction to Helium refrigeration, with a practical approach to theory, technology, maintenance and control of Helium refrigeration installations. Theoretical aspects and equations will be limited to a minimum. HeREF-2003 targets an audience of technicians and operators of Helium refrigeration plants at CERN, as well as physicists and engineers needing an overview of current Helium refrigeration techniques. HeREF-2003 will address, among other, issues related to component technology, installation maintenance, process control and Helium purity. A commented visit to a couple of CERN Helium refrigeration or liquefaction plants will also take place. ? Duration: 7 half days (4 mornings and 3 afternoons), 6-10 October, 2003 ? Cost per participant: 500.- CHF ...

2003-01-01

188

Helium production in natural gas reservoirs  

International Nuclear Information System (INIS)

About 11,000 published natural gas analyses of helium are used in the estimation of the average global scale accumulation and concentration of radiogenic helium in sediments. Simple lognormal statistics is employed to derive a net accumulation rate between 1dagger105 to 6.7dagger105 helium atoms per cubic meter of reservoir rock per second. This acccumulation rate permitted to infer an average helium concentration of nonreservoir sediments of about 67 ppm. By assuming a simple closed system model it is shown that deep seated sources of helium are not necessary to explain the present regime of helium in sediments on a global scale. Helium accumulation rates and concentrations obtained by this method are in close agreement with existing fundamental geochemical estimates of uranium and thorium in rather average type sediments

189

Mixed helium-3 - helium-4 calorimeter. Very low temperature calorimetry  

International Nuclear Information System (INIS)

A description is given of a double-racket calorimeter using helium-4 and helium-3 as the cryogenic fluids and making it possible to vary the temperature continuously from 0.35 K to 4.2 K. By using an electric thermal regulator together with liquid hydrogen it is possible to extend this range up to about 30 K. In the second part, a review is made of the various, methods available for measuring specific heats. The method actually used in the apparatus previously described is described in detail. The difficulties arising from the use of an exchange gas for the thermal contact have been solved by the use of adsorption pumps. (author)

190

Vanadium alloys with improved resistance to helium embrittlement  

International Nuclear Information System (INIS)

A series of experimental vanadium alloys have been designed with small MC-type carbides in their microstructures to trap helium produced during neutron irradiation, thereby reducing helium embrittlement. The tensile properties and fabricability of the alloys were strongly influenced by the amounts of MC-forming-elements, especially carbon. Alloys with 0.05 and 0.10 wt % carbon exhibited slightly lower yield strengths at 420 to 600 degree C than vanadium alloys such as V-5Cr-5Ti, Vanstar-7, V-3Ti-1Si, and V-15Cr-5Ti. However, this characteristic may actually be an asset from the standpoint of resistance to irradiation hardening. After implantation with 300 appm 3He, both the V-Ti-C and V-Ti-Zr-C alloys exhibited less ductility losses at 600 degree C than the other vanadium alloys tested under comparable conditions. Examination of the experimental alloy microstructures by AEM showed that the small MC-type carbides did, in fact, trap helium and that they were responsible for the increased resistance to helium embrittlement of these alloys. 16 refs., 12 figs., 2 tabs

191

Diffusion and retention of helium in graphite and silicon carbide  

International Nuclear Information System (INIS)

?-particles of constant energies (5-28 MeV) and current densities from 0.8 to 40 x 1014 He/(m2s) were implanted to doses of typically 1017 m-2 at temperatures up to 1100 K into high purity pyrolytic graphite and silicon carbide. Helium release during and after implantation was monitored by mass spectrometry. Helium release from graphite during implantation strongly depends on specimen orientation and is highest for specimens implanted parallel to the basal plane. The corresponding diffusion coefficients are D[m2/s] = 5 x 10-5exp(- 1.17/kT) for 750 ? T [K] ? 1050. Helium release from SiC during implantation decreases strongly with increasing implantation depth. The diffusion coefficients are given by D [m2/s]=1.1 x 10-6exp(- 1.14/kT) for 800 ? T [K] ? 1050. In both materials a fraction of the implanted helium, which increases with increasing implantation depth and decreases with temperature, is retained and desorbs slowly. (orig.)

192

Effect of helium on separation performance of cryogenic distillation column cascade for fusion reactor  

International Nuclear Information System (INIS)

The effect of helium in the feed stream on separation performance of the cryogenic distillation columns was discussed in a probable case. The column cascade at Los Alamos National Laboratory was chosen in the present study. The new data for solubility of helium in liquid hydrogen isotopes was used in the present study. Column (2) is mainly affected by the presence of helium in the fuel stream. If the helium percentage in the feed stream is 1%, the column performance can be assured by increasing the condenser load: a larger inner diameter of the column; larger flow rate of the refrigerant gas; and larger heat transfer area at the condenser should be considered. If the percentage is 5%, both the column pressure and condenser load must be doubled in the steady-state operation. These results qualitatively agreed with the simulation results by Kinoshita in which the old data for solubility of helium were used. (author)

193

Helium bubble growth in 316 stainless steel  

International Nuclear Information System (INIS)

A systematic TEM investigation has been made of helium bubble growth in type 316 stainless steel. Commercial stainless steel samples have been vacuum annealed following room temperature helium implantation to a concentration of 5 x 1026 He.m-3. The bubble growth kinetics have been determined by measuring the mean bubble radius at annealing times in the range 1 to 200 h for temperatures of 873, 923 and 1023 K. At the lower two temperatures the bubble growth mechanism is believed to be migration and coalescence, with the migration limited by volume diffusion of the metal atoms. Four additional anneals for 2 h at temperatures in the range 923 to 973 K have been made to determine the activation energy for diffusion. This is found to be 4.9 eV. At 1023 K and for annealing times of less than 8 h, bubble growth appears to occur mainly by the acquisition of thermal vacancies from the sample surface. At longer annealing times the bubble migration becomes limited by the nucleation of atomic ledges on the bubble facet and the rate of bubble growth is reduced. The ledge energy is estimated to be 1 x 10-11 J.m-1. (author)

194

Helium circulator design and testing  

International Nuclear Information System (INIS)

The helium circulator is a key component of the 10 MW high temperature gas-cooled reactor (HTR-10), which assures the thermal energy transfer from the reactor core to the steam generator and operates at 3.0 MPa, 250 deg. C helium condition. At the rated condition, the mass flow rate is 4.32 kg s-1 and the pressure rise can reach 51.7 kPa at the rotational speed of 5000 rpm. In fact, the pressure rise required for the HTR-10 is only 14.7 kPa with a rotational speed of 3052 rpm. Thus, the layout of the blower contains a considerable margin. This paper presents the design procedures of the circulator during its development. Test results both in the factory and in the HTR-10 are given. Furthermore, the circulator design features and aerodynamic performance are highlighted

195

Absolute calibration of TFTR helium proportional counters  

Energy Technology Data Exchange (ETDEWEB)

The TFTR helium proportional counters are located in the central five (5) channels of the TFTR multichannel neutron collimator. These detectors were absolutely calibrated using a 14 MeV neutron generator positioned at the horizontal midplane of the TFTR vacuum vessel. The neutron generator position was scanned in centimeter steps to determine the collimator aperture width to 14 MeV neutrons and the absolute sensitivity of each channel. Neutron profiles were measured for TFTR plasmas with time resolution between 5 msec and 50 msec depending upon count rates. The He detectors were used to measure the burnup of 1 MeV tritons in deuterium plasmas, the transport of tritium in trace tritium experiments, and the residual tritium levels in plasmas following 50:50 DT experiments.

Strachan, J.D.; Diesso, M.; Jassby, D.; Johnson, L.; McCauley, S.; Munsat, T.; Roquemore, A.L. [Princeton Univ., NJ (United States). Plasma Physics Lab.; Barnes, C.W. [Princeton Univ., NJ (United States). Plasma Physics Lab.]|[Los Alamos National Lab., NM (United States); Loughlin, M. [Princeton Univ., NJ (United States). Plasma Physics Lab.]|[JET Joint Undertaking, Abingdon (United Kingdom)

1995-06-01

196

Absolute calibration of TFTR helium proportional counters  

International Nuclear Information System (INIS)

The TFTR helium proportional counters are located in the central five (5) channels of the TFTR multichannel neutron collimator. These detectors were absolutely calibrated using a 14 MeV neutron generator positioned at the horizontal midplane of the TFTR vacuum vessel. The neutron generator position was scanned in centimeter steps to determine the collimator aperture width to 14 MeV neutrons and the absolute sensitivity of each channel. Neutron profiles were measured for TFTR plasmas with time resolution between 5 msec and 50 msec depending upon count rates. The He detectors were used to measure the burnup of 1 MeV tritons in deuterium plasmas, the transport of tritium in trace tritium experiments, and the residual tritium levels in plasmas following 50:50 DT experiments

197

Contribution to the experimental study of the polarized liquid helium-3; Contributions a l'etude experimentale de l'helium-3 liquide polarise  

Energy Technology Data Exchange (ETDEWEB)

Spin-polarized liquid helium-3 is prepared by laser optical pumping in low magnetic field and at room temperature, prior to fast liquefaction of the polarized sample. The use of a new helium-3 cryostat enabled us to obtain liquid helium-3 with polarization rates up to 25 % at well-stabilized temperatures (around 0.5 K). We could thereby study the effect of nuclear polarization on liquid-vapour equilibrium, and particularly on the saturated vapour pressure. Very sensitive capacitive gauges were developed. We estimated (to first order in M{sup 2}) the expected effects when the polarization M is suddenly destroyed. These effects were experimentally observed in helium-3/helium-4 mixtures, in pure helium-3, only a transient increase in pressure has been recorded. We then describe in a third part a preliminary experiment which aimed at determining the longitudinal relaxation time T1 in mixtures. Relaxation on the walls is efficiently reduced by a cesium coating and T1s of order 20 minutes were observed. A careful determination of the helium-3 concentration in the liquid phase was made. Finally we studied the effects of dipolar field on transverse polarisation decay in our strongly polarized samples. We observed the free precession of polarization after a NMR pulse, and analysed in detail its decay time constant as a function of different parameters. This time constant drastically varied with the tipping angle, an effect which could be linked to NMR dynamical instabilities. (author)

Villard, B

1999-07-15

198

Superfluid Helium Tanker (SFHT) study  

Science.gov (United States)

Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997.

Eberhardt, Ralph N.; Dominick, Sam M.; Anderson, John E.; Gille, John P.; Martin, Tim A.; Marino, John S.; Paynter, Howard L.; Traill, R. Eric; Herzl, Alfred; Gotlib, Sam

1988-01-01

199

Acoustic streaming in superfluid helium  

International Nuclear Information System (INIS)

Quantitative measurements of acoustic streaming velocity in liquid helium as a function of sound intensity (up to the cavitation threshold), frequency (1, 3, and 10 MHz), and temperature (1.43 K< or =T< or =2.19 K) are reported. A transition to superfluid turbulence, several flow regions and flow fluctuations are observed. Comparison with the predictions of the second-order Khalatnikov two- fluid hydrodynamic equations indicates good functional and quantitative agreement

200

Detecting scintillations in liquid helium  

International Nuclear Information System (INIS)

We review our work in developing a tetraphenyl butadiene (TPB)-based detection system for a measurement of the neutron lifetime using magnetically confined ultracold neutrons (UCN). As part of the development of the detection system for this experiment, we studied the scintillation properties of liquid helium itself, characterized the fluorescent efficiencies of different fluors, and built and tested three detector geometries. We provide an overview of the results from these studies as well as references for additional information

 
 
 
 
201

On positron annihilation in helium  

International Nuclear Information System (INIS)

Numerical calculations of the positron annihilation decay rate in helium gas have been made over a wide range of electric (0-50 Vcm-1) and magnetic (0-20 KG) fields at various temperatures. Two models of positron-atom interaction have been considered. The computations indicate that the positron life-time decreases with the magnetic field at given electric/temperature fields. When the electric field is zero, magnetic field has no effect on the life-time. (Auth.)

202

Development of a Mass Flowmeter based on the Coriolis Acceleration for Liquid, Supercritical and Superfluid Helium  

CERN Document Server

Beginning in the 1980's, Coriolis meters have gained generalised acceptance in liquid applications with a worldwide installed base of over 300,000 units. To meet the demands of cryogenic applications below 20 K, off-the-shelf Coriolis meters have been used, with minor design modifications and operational changes. The meters were originally calibrated on water and tested on liquid helium at 4.5 K, supercritical helium around 5 K and superfluid helium below 2 K. The meters maintain their intrinsic robustness and accuracy of better than 1% of measured value; accuracy is independent of density and temperature.

De Jonge, T; Rivetti, A; Serio, L

2002-01-01

203

Vorticity matching in superfluid helium  

Science.gov (United States)

Recent experiments have rekindled interest in high Reynolds number flows using superfluid helium. In a continuing series of experiments, the flow of helium II through various devices (smooth pipes, corrugated pipes, valves, venturies, turbine flowmeters, and coanda flowmeters for example) was investigated. In all cases, the measured values (typically, mass flow rates and pressure drops) were found to be well described by classical relations for high Reynolds flows. This is unexpected since helium II consists of two interpenetrating fluids; one fluid with nonzero viscosity (the normal fluid) and one with zero viscosity (the superfluid). Only the normal fluid component should directly obey classical relations. Since the experiments listed above only measure the external behavior of the flow (i.e., pressure drops over devices), there is a great deal of room for interpretation of their results. One possible interpretation is that in turbulent flows the normal fluid and the superfluid velocity fields are somehow 'locked' together, presumably by the mutual friction force between the superfluid vortex filaments and the normal fluid. We refer to this locking together of the two fluids as 'vorticity matching.'

Samuels, David C.

1991-12-01

204

Vorticity matching in superfluid helium  

International Nuclear Information System (INIS)

Recent experiments have rekindled interest in high Reynolds number flows using superfluid helium. In a continuing series of experiments, the flow of helium II through various devices (smooth pipes, corrugated pipes, valves, venturies, turbine flowmeters, and coanda flowmeters for example) was investigated. In all cases, the measured values (typically, mass flow rates and pressure drops) were found to be well described by classical relations for high Reynolds flows. This is unexpected since helium II consists of two interpenetrating fluids; one fluid with nonzero viscosity (the normal fluid) and one with zero viscosity (the superfluid). Only the normal fluid component should directly obey classical relations. Since the experiments listed above only measure the external behavior of the flow (i.e., pressure drops over devices), there is a great deal of room for interpretation of their results. One possible interpretation is that in turbulent flows the normal fluid and the superfluid velocity fields are somehow 'locked' together, presumably by the mutual friction force between the superfluid vortex filaments and the normal fluid. We refer to this locking together of the two fluids as 'vorticity matching.'

205

Tritium-helium effects in metals  

International Nuclear Information System (INIS)

Investigations of helium effects in metals at the Savannah River Laboratory have been carried out by introducing helium by radioactive decay of tritium. This process does not create concurrent radiation damage, such as accompanies ion implantation and (n,?) reactions. The process has its own peculiarities, however, which partially mask and interact with the helium effect of interest. The distribution and local concentration of helium and tritium, which are responsible for changes in mechanical properties and fracture mode, are controlled by the large difference in solubility and diffusivity between the two atoms and by their differing interaction energies with lattice defects, impurities, and internal boundaries. Furthermore, in all investigations with helium generated from tritium decay, some tritium and deuterium are always present. Consequently, property changes include tritium-helium interaction effects to some extent. Results of investigations with several austenitic stainless steels, Armco iron, and niobium single crystals illustrate the variety of phenomena and some of the complex interactions that can be encountered

206

Helium damage in metal-tritium systems  

International Nuclear Information System (INIS)

The time evolution of Debye-Scherrer lines was investigated in metal-tritium-helium systems by neutron-scattering techniques. Polycrystalline samples of TaTx, YTx, and ScTx were measured over a period of three years. The results show that helium damage is governed by the behavior of self-interstitial atoms and dislocation loops created by helium clustering and bubble formation. The self-interstitials and loops induce a lattice expansion in the early stages of helium formation. For higher helium concentrations the self-interstitials and loops produced are completely incorporated into an evolving dislocation network. In hexagonal rare-earth systems a preferential condensation of loops into a dislocation network lying in basal planes is observed. Additional small-angle-scattering experiments show that platelike helium cavities are formed in the hexagonal systems

207

Density shift and broadening of dipole transitions in antiprotonic helium  

Energy Technology Data Exchange (ETDEWEB)

We present the numerical values of the density shift and broadening slopes of laser-stimulated dipole transitions in antiprotonic helium atoms at temperature 1.5 Degree-Sign K and 5.4 Degree-Sign K, evaluated in the semiclassical approach with a realistic interatomic potential calculated ab initio. Compared to our 2000 paper, the present results cover the much wider set of transition lines that have been subject of precision spectroscopy since then.

Bakalov, Dimitar, E-mail: dbakalov@inrne.bas.bg [Bulgarian Academy of sciences, Institute for Nuclear Research and Nuclear Energy (Bulgaria)

2012-05-15

208

Helium: Problematic primordial signals  

International Nuclear Information System (INIS)

Various lines of evidence suggest that pre-eruptive degassing of basalts is not only important but may dominate the He flux from the mantle to the oceans and atmosphere. These include: 1. correlations between U/4He ratios and M? in volcanic suites, which suggest that U/4He increases as differentiation proceeds; 2. the observation that U/4He ratios in MORB average about a factor of 400 lower than those from Loihi Seamount, although 3He/4He ratios suggest that Loihi is derived from a source with a lower U/4He ratio than is appropriate for the MORB source; and 3. the 3He budget of the oceans which, as defined by Craig and Lupton, requires that MORB is on average 70-90% outgassed in He. These observations suggest, as noted, that mantle 3He/4He ratios may be subject to perturbation due to radiogenic accumulation of 4He in systems where U/4He has been increased by pre-eruptive degassing. Models involving continuous diffusive loss (CDL) of He from a magma chamber and exhalative loss (EL) via solution of He in a CO2-rich gas or fluid phase are investigated. Low U/4He ratios in MORBs preclude significant pre-eruptive reduction of 3He/4He ratios; however, OIBs with U/4He>106 may be subject to significant reduction of 3He/4He (?10%) with pre-eruptive aging over time periods ranging from 1x103 to 5x105 years. (orig.)

209

Solid lubrication technology of HTGR under helium  

International Nuclear Information System (INIS)

Because Helium is used as coolant in High Temperature Gas-cooled Reactor (HTGR), the change of tribological properties of HTGR structure component under Helium is a big problem. Under Helium, tribological properties of material becomes worse and fluid lubrication can not be used. Bonded solid lubrication film and fusion sintering solid film are used in control rod and can solve the tribological problem well. Methods of replenishment solid lubricant are discussed for continuously operating friction components. The necessity and possibility for solid lubrication film used in Helium fan is also discussed

210

Low evaporation helium cryostat with a refrigerator  

International Nuclear Information System (INIS)

Improvement of a helium cryostat for a superconducting magnet is reported. A small refrigerator pre-cools the magnet and removes heat load. A gas filled thermal switch cools a helium vessel and thermally insulates the vessel when the refrigerator stops. Nb3Sn wires are used in the helium vessel to avoid resistive heating. The evaporation rate of the liquid helium is 1.0 - 1.7 1/day (with external current of 28A), when a magnet (maximum field 7T in 25mm bore) is set in the cryostat. (author)

211

Helium transport studies on DIII-D  

International Nuclear Information System (INIS)

The measurement of Helium density profiles in tokamak plasmas is necessary for helium transport studies. These studies are important in predicting the helium ash transport properties for ITER and win have important implications for the design. Poor helium transport in reactors could lead to a buildup of fusion ash, causing fuel dilution and increased radiation that will result in degraded fusion power and possibly quench ignition altogether. Present estimates indicate that He concentrations in the core must be kept below 10% in order to maintain continuous reactor operation. Helium transport studies have begun on the DM-D tokamak using charge exchange recombination (CER) spectroscopy for helium density measurements. Helium transport behavior has been observed by injecting helium gas puffs into DM-D plasmas and measuring the He density profile evolution. The profiles are used to calculate the relevant helium transport properties. This paper covers the results obtained from puffing He gas into L-mode plasmas of various electron densities. The results obtained in DIII-D L-mode plasmas are similar to measurements made at TEXTOR and JT-60

212

Helium turbo-expander with an alternator  

International Nuclear Information System (INIS)

Study was made on a helium turbo-expander, the heart of helium refrigerator systems, in order to develop a system which satisfies the required conditions. A helium turbo-expander with externally pressurized helium gas bearings at the temperature of liquid nitrogen and an alternator as a brake have been employed. The essential difference between a helium turbo-expander and a nitrogen turbo-expander was clarified. The gas bearing lubricated with nitrogen at room temperature and the gas bearing lubricated with helium at low temperature were tested. The flow rate of helium in a helium refrigerator for a large superconducting magnet is comparatively small, therefore a helium turbine must be small, but the standard for large turbine design can be applied to such small turbine. Using the alternator as a brake, the turbo-expander was easily controllable electrically. The prototype turbo-expander was made, and the liquefaction test with it and MHD power generation test were carried out. (Kako, I.)

213

Helium supply demand in future years  

International Nuclear Information System (INIS)

Adequate helium will be available to the year 2000 AD to meet anticipated helium demands for present day applications and the development of new superconducting technologies of potential importance to the nation. It is almost certain that there will not be enough helium at acceptable financial and energy cost after the turn of the century to meet the needs of the many promising helium based technologies now under development. Serious consideration should be given to establishing priorities in development and application based upon their relative value to the country. In the first half of the next century, three ways of estimating helium demand lead to cumulative ranges of from 75 to 125 Gcf (economic study), 89 to 470 Gcf (projected national energy growth rates) and 154 to 328 Gcf (needs for new technologies). These needs contrast with estimated helium resources in natural gas after 2000 AD which may be as low as 10 or 126 Gcf depending upon how the federal helium program is managed and the nation's natural gas resources are utilized. The technological and financial return on a modest national investment in further helium storage and a rational long term helium program promises to be considerable

214

Operational experience with the supercritical helium during the TF coils tests campaign of SST-1  

Science.gov (United States)

Under the 'SST-1 mission mandate' recently, all the sixteen Steady State Superconducting Tokamak (SST-1) Toroidal Field (TF) magnets have been successfully tested at their nominal currents of 10000 A in cold under supercritical helium (SHe) flow conditions. The TF magnets test campaign have begun in an experimental cryostat since June 2010 with the SST-1 Helium cryogenics facility, which is a 1.3 kW at 4.5 K helium refrigerator-cum-liquefier (HRL) system. The HRL provides ~300 g-s-1supercritical helium (SHe) with cold circulator (CC) as well as ~ 60 g-s-1 without cold circulator to fulfill the forced flow cooling requirements of SST- 1 magnets. In case of single TF coil tests, we can adjust HRL process parameters such that an adequate amount of required supercritical helium is available without the cold circulator. In this paper, the complete process is describing the Process Flow Diagram (PFD) of 1.3 kW at 4.5 K HRL, techniques to generate supercritical helium without using the cold-circulator and the results of the cooldown, steady state characteristics and experience of supercritical helium operations during the TF coils test campaign have been discussed.

Panchal, Rohitkumar Natvarlal; Patel, Rakesh; Tank, Jignesh; Mahesuria, Gaurang; Sonara, Dashrath; Tanna, Vipul; Patel, Jayant; Srikanth, G. L. N.; Singh, Manoj; Patel, Ketan; Christian, Dikens; Garg, Atul; Bairagi, Nitn; Gupta, Manoj Kumar; Nimavat, Hiren; Shah, Pankil; Sharma, Rajiv; Pradhan, Subrata

2012-06-01

215

Helium dilution for ram accelerator operation  

Science.gov (United States)

Experimental detonation characteristics (detonability limits and detonation velocities) of methane-oxygen-helium mixtures at initial pressures of up to 5 MPa were measured in a 90 mm caliber, 11.7 m long (130 calibers) smooth-bore detonation tube. Stoichiometric as well as fuel-rich mixtures were investigated in order to provide performance data for ram accelerator applications. The experimental results were used to adjust and validate calculations of the Chapman-Jouguet detonation characteristics by means of a thermochemical code based on various real gas equations of state. On the basis of the detonation velocity data, a series of intermolecular parameters involved in the thermochemical code was determined. Furthermore, the investigation enabled to determine of the upper detonable area of these dense ternary mixtures under the present experimental conditions.

Legendre, J. F.; Bauer, P.; Giraud, M.

216

Helium distribution system for the Large Coil Test Facility (LCTF)  

International Nuclear Information System (INIS)

The helium distribution system of the Large Coil Test Facility is designed to establish and maintain the thermal environment of the toroidal array of superconducting magnets throughout the initial test and evaluation period of the test program. The refrigeration and liquefaction requirements for the LCTF will be discussed including both the usual cooldown, lead cooling, thermal conduction and radiation and joule heating losses, and the unusual losses due to simulated nuclear heating, magnetic coupling losses due to the transient fields of the driving magnets, and pumping losses due to fluid resistance and pump inefficiency. The flow system is designed with separate cooldown and steady-state flow systems, and to simultaneously circulate helium understeady-state conditions through coils cooled by boiling liquid or supercritical helium at approximately 4.0 K and >2.5-atm pressure. Separate helium storage dewars are utilized for vapor cooling of the current leads to the magnets with the effluent gas being stored after compression in high pressure storage tanks. The flow diagram will be presented in simplified form to show the salient features of the cryogenic system

217

Helium distribution system for the Large Coil Test Facility (LCTF)  

Energy Technology Data Exchange (ETDEWEB)

The helium distribution system of the Large Coil Test Facility is designed to establish and maintain the thermal environment of the toroidal array of superconducting magnets throughout the initial test and evaluation period of the test program. The refrigeration and liquefaction requirements for the LCTF will be discussed including both the usual cooldown, lead cooling, thermal conduction and radiation and joule heating losses, and the unusual losses due to simulated nuclear heating, magnetic coupling losses due to the transient fields of the driving magnets, and pumping losses due to fluid resistance and pump inefficiency. The flow system is designed with separate cooldown and steady-state flow systems, and to simultaneously circulate helium understeady-state conditions through coils cooled by boiling liquid or supercritical helium at approximately 4.0 K and >2.5-atm pressure. Separate helium storage dewars are utilized for vapor cooling of the current leads to the magnets with the effluent gas being stored after compression in high pressure storage tanks. The flow diagram will be presented in simplified form to show the salient features of the cryogenic system.

Lawson, C.G.; May, J.R.

1977-01-01

218

The Liquefaction of Hydrogen and Helium Using Small Coolers  

International Nuclear Information System (INIS)

This report discusses the history of the liquefaction of hydrogen and helium using small coolers. This history dates form the 1960's when two stage GM coolers capable of reaching 7 K were used to liquefy helium and hydrogen by suing an added compressor and J-T circuit. Liquefaction using the added circuit failed to become mainstream because the J-T valve and heat exchanger clogged because of impurities in the gas being liquefied. Liquefaction using a GM cooler without an added J-T circuit proved to be difficult because the first stage was not used to pre-cool the gas coming to the second stage of the cooler. Once the gas being liquefied was pre-cooled using the cooler first stage, improvements in the liquefaction rates were noted. The advent of low temperature pulse tube cooler (down to 2.5 K) permitted one to achieve dramatic improvement is the liquefactions rates for helium. Similar but less dramatic improvements are expected for hydrogen as well. Using the PT-415 cooler, one can expect liquefaction rates of 15 to 20 liters per day for helium or hydrogen provided the heat leak into the cooler and the storage vessel is low. A hydrogen liquefier for MICE is presented at the end of this report

219

Helium stratification in HD 145792: a new Helium strong star  

CERN Document Server

In this paper we report on the real nature of the star HD 145792, classified as He weak in {\\it ``The General Catalogue of Ap and Am stars''}. By means of FEROS@ESO1.52m high resolution spectroscopic data, we refined the atmospheric parameters of the star, obtaining: T$_{\\rm eff}$ = 14400 $\\pm$ 400 K, $\\log g$ = 4.06 $\\pm$ 0.08 and $\\xi$ = 0 $^{+0.6}$ km s$^{-1}$. These values resulted always lower than those derived by different authors with pure photometric approaches. Using our values we undertook an abundance analysis with the aim to derive, for the first time, the chemical pattern of the star's atmosphere. For metals a pure LTE synthesis (ATLAS9 and SYNTHE) has been used, while for helium a hybrid approach has been preferred (ATLAS9 and SYNSPEC). The principal result of our study is that HD 145792 belongs to He strong class contrary to the previous classification. Moreover, helium seems to be vertically stratified in the atmosphere, decreasing toward deepest layers. For what that concerns metals abundanc...

Catanzaro, G

2007-01-01

220

A small and light weight heat exchanger for on-board helium refrigerator  

Science.gov (United States)

A small and light weight heat exchanger used for small helium refrigerator has been developed by Sumitomo Heavy Industries, Ltd. This heat exchanger is a laminated metal heat exchanger which consists of perforated aluminum metal plates and glassfiber reinforced plastic separators. The size is from 100 mm to 28 mm in diameter and about 300 mm in length. The weight is from 2.5 kg to 0.6 kg. Also it can be used between room temperature and liquid helium temperature. The thermal efficiency obtained has been more than 96%. The heat exchanger has been practically used for on-board helium refrigerator in Japanese National Railways' superconducting magnetic levitated trains.

Koizumi, T.; Takahashi, M.; Uchida, T.; Kanazawa, Y.; Suzuki, M.

1983-12-01

 
 
 
 
221

Helium refrigerator maintenance and reliability at the OPAL cold neutron source  

Science.gov (United States)

Australia's first Cold Neutron Source (CNS) is a major asset to its nuclear research program. The CNS, and associated helium refrigerator, was commissioned in 2006 and is operated at the Open Pool Light Water nuclear Reactor (OPAL). The OPAL CNS operates a 20K, 5 kW Brayton cycle helium refrigerator. In this paper relevant experiences from helium refrigerator operation, maintenance and repair are presented along with the lessons learnt from a series of technical investigations. Turbine failure, due to volatile organic species, is discussed along with the related compressor oil degradation and oil separation efficiency.

Thiering, Russell; Taylor, David; Lu, Weijian

2012-06-01

222

Helium bubble bursting in tungsten  

International Nuclear Information System (INIS)

Molecular dynamics simulations have been used to systematically study the pressure evolution and bursting behavior of sub-surface helium bubbles and the resulting tungsten surface morphology. This study specifically investigates how bubble shape and size, temperature, tungsten surface orientation, and ligament thickness above the bubble influence bubble stability and surface evolution. The tungsten surface is roughened by a combination of adatom “islands,” craters, and pinholes. The present study provides insight into the mechanisms and conditions leading to various tungsten topology changes, which we believe are the initial stages of surface evolution leading to the formation of nanoscale fuzz

223

Helium bubble bursting in tungsten  

Energy Technology Data Exchange (ETDEWEB)

Molecular dynamics simulations have been used to systematically study the pressure evolution and bursting behavior of sub-surface helium bubbles and the resulting tungsten surface morphology. This study specifically investigates how bubble shape and size, temperature, tungsten surface orientation, and ligament thickness above the bubble influence bubble stability and surface evolution. The tungsten surface is roughened by a combination of adatom “islands,” craters, and pinholes. The present study provides insight into the mechanisms and conditions leading to various tungsten topology changes, which we believe are the initial stages of surface evolution leading to the formation of nanoscale fuzz.

Sefta, Faiza [University of California, Berkeley, California 94720 (United States); Juslin, Niklas [University of Tennessee, Knoxville, Tennessee 37996 (United States); Wirth, Brian D., E-mail: bdwirth@utk.edu [University of Tennessee, Oak Ridge National Laboratory, Knoxville, Tennessee 37996 (United States)

2013-12-28

224

Helium irradiation of alkali halides  

International Nuclear Information System (INIS)

An investigation has been made of radiation damage in alkali halide crystals induced by heavy bombardment of 1 MeV helium ions. The channeling technique has been employed and three processes have been monitored simultaneously to explain the apparent reduction of damage at high doses. It is shown that the initial rise and fall of the back-scattered yield from different alkali halides can be related to the Pooley mechanism coupled with the aggregation of interstitials to form dislocation loops through the intermediate stage of clusters

225

Design of subcooled helium II refrigerator with helium-3 cold compressor  

International Nuclear Information System (INIS)

This paper will study the possibility of a He II refrigerator made up of three cold compressors by making use of helium-3 characteristics. This system is compact enough to fit inside a small cold box, so it can be easily connected with an existing helium-4 refrigerator. The authors designed the compressors, calculated the He II cooling capacity, 4.4 K refrigeration load, required inventory of helium-3, and Carnot efficiency. Though helium-3 is expensive, the required inventory of helium-3 to be filled inside this He II refrigerator was calculated to be small enough to prove practicality of constructing this refrigerator

226

Experimental loop for tests of helium-cooled HHF components at 600 C/10 MPA input  

International Nuclear Information System (INIS)

The Efremov Institute has completed the 1st stage of helium loop construction. This work has been carried out in collaboration with FZK. The helium loop is intended for tests of divertor design options, which meet the requirements for the DEMO helium-cooled fusion reactor. These tests include selection of divertor materials and joining technology, optimization of the cooling regimes, thermal cycling of mockups to estimate the divertor component lifetime. It is also possible to use the loop in other areas of high-temperature helium nuclear technology (tests of first wall mock-ups, fission helium reactors relevant experiments). On the basis of the results of the systematic mock-ups tests it is planned to create the database for validation of the gas-dynamic and thermal mechanic codes used for simulation of processes in high-heat-flux components. The helium loop is capable of testing the mock-ups at a nominal helium input temperature of 600 C and a pressure of 10 MPa. Maximum possible pressure losses in mock-ups amount to 0.5 MPa. At this stage of works a stationary helium flow rate of 24 g/s is provided by oil-free membrane compressor. One more possible loop regime is by periodic gas pulses at 50 g/s and duration up to 120 s. The diagnostic system provides measurement of more than 40 gas and mock-up parameters such as pressure, flow rate and temperature, as well the surface temperature distribution by an infra-red camera. Mock-up heat loading is provided by the e-beam op heat loading is provided by the e-beam of the TSEFEY facility with an applied power of 60 kW. The testing results of singlefinger mock-ups of the vertical target for the DEMO helium-cooled divertor are presented. At the next stage the helium loop will be capable of attaining a flow rate of 150 g/s (using a helium circulating pump), which is sufficient for tests of nine-finger modules of the DEMO helium-cooled divertor. Some preliminary design simulations have been made in order to assess the hot pump performance for different pump types. As result of these simulations a vortex-type pump has been chosen and its design has been adapted to the helium loop requirements. Preliminary experiments have been carried out with a simplified model and drive in order to verify the accepted solutions. The design solutions and R and D results of the activities at this stage of loop development are also presented. (orig.)

227

Experimental loop for tests of helium-cooled HHF components at 600 C/10 MPA input  

Energy Technology Data Exchange (ETDEWEB)

The Efremov Institute has completed the 1st stage of helium loop construction. This work has been carried out in collaboration with FZK. The helium loop is intended for tests of divertor design options, which meet the requirements for the DEMO helium-cooled fusion reactor. These tests include selection of divertor materials and joining technology, optimization of the cooling regimes, thermal cycling of mockups to estimate the divertor component lifetime. It is also possible to use the loop in other areas of high-temperature helium nuclear technology (tests of first wall mock-ups, fission helium reactors relevant experiments). On the basis of the results of the systematic mock-ups tests it is planned to create the database for validation of the gas-dynamic and thermal mechanic codes used for simulation of processes in high-heat-flux components. The helium loop is capable of testing the mock-ups at a nominal helium input temperature of 600 C and a pressure of 10 MPa. Maximum possible pressure losses in mock-ups amount to 0.5 MPa. At this stage of works a stationary helium flow rate of 24 g/s is provided by oil-free membrane compressor. One more possible loop regime is by periodic gas pulses at 50 g/s and duration up to 120 s. The diagnostic system provides measurement of more than 40 gas and mock-up parameters such as pressure, flow rate and temperature, as well the surface temperature distribution by an infra-red camera. Mock-up heat loading is provided by the e-beam of the TSEFEY facility with an applied power of 60 kW. The testing results of singlefinger mock-ups of the vertical target for the DEMO helium-cooled divertor are presented. At the next stage the helium loop will be capable of attaining a flow rate of 150 g/s (using a helium circulating pump), which is sufficient for tests of nine-finger modules of the DEMO helium-cooled divertor. Some preliminary design simulations have been made in order to assess the hot pump performance for different pump types. As result of these simulations a vortex-type pump has been chosen and its design has been adapted to the helium loop requirements. Preliminary experiments have been carried out with a simplified model and drive in order to verify the accepted solutions. The design solutions and R and D results of the activities at this stage of loop development are also presented. (orig.)

Kuznetsov, V.; Kokoulin, A.; Mazul, I.; Ovchinnikov, I. [Efremov SRI (Russian Federation); Krauss, W.; Norajitra, P. [FZK, Karlsruhe (Germany)

2007-07-01

228

Bichromatic Slowing of Metastable Helium  

CERN Document Server

We examine two approaches for significantly extending the velocity range of the optical bichromatic force (BCF), to make it useful for laser deceleration of atomic and molecular beams. First, we present experimental results and calculations for BCF deceleration of metastable helium using very large BCF detunings, and discuss the limitations of this approach. We consider in detail the constraints, both inherent and practical, that set the usable upper limit of the BCF. We then show that a more promising approach is to utilize a BCF profile with a relatively small velocity range in conjunction with chirped Doppler shifts, to keep the force resonant with the atoms as they are slowed. In an initial experimental test of this chirped BCF method, helium atoms are slowed by $\\sim 370$ m/s using a BCF profile with a velocity width of $\\lesssim 125$ m/s. Straightforward scaling of the present results indicates that a decelerator for He* capable of loading a magneto-optical trap (MOT) can yield a brightness comparable t...

Chieda, M A

2012-01-01

229

Helium-heated steam reformer  

International Nuclear Information System (INIS)

Catalyst action and the supply of high-temperature heat generating energy cause a steam reforming reaction on light hydrocarbons, which produces the reducing gas. The reactor, which permits this reaction to take place, is a steam reformer, the conventional type of which is a flame heating furnace. A heat-exchanger type steam reformer was newly developed for the National Research and Development Programme nuclear steel making project. Unlike conventional ones, this reactor is heated by high-temperature helium. A steam reforming process test plant was planned to test the performance and characteristics of this new steam reformer. Construction of the test plant was begun in 1975. It was completed at the end of May 1978. Subsequently, research and development passed on to the operating phase. The test plant has a nominal raw material treatment capacity of 100 kg/hr. The nominal quantity of heat exchanged is 310,000 Kcal/hr. The paper on the helium-heated steam reformer of this test plant is presented

230

Helium/radon precursory anomalies of Chamoli earthquake, Garhwal Himalaya, India  

Science.gov (United States)

In the Garhwal Himalaya, the Bhagirthi and Alaknanda valleys were rocked respectively by two major earthquakes; the Uttarkashi earthquake of magnitude mb=6.5, Ms= 7.0 on 20 October, 1991 and the Chamoli earthquake of mb =6.8, Ms=6.5 on 29 March 1999, during this decade only. Both these seismic events are associated with ongoing deformation along the main central thrust (MCT) of the Himalayas. The helium and radon anomalies on 24 and 27 March 1999, respectively, were recorded at Palampur which is about 393 km from the Chamoli earthquake epicentre. A helium/radon ratio anomaly was recorded on 20 March, 9 days before the Chamoli earthquake. The precursory nature of radon and helium anomalies is a strong indicator of the physical basis of earthquake prediction and a preliminary test for the proposed conceptual helium/radon ratio model.

Singh Virk, Hardev; Walia, Vivek; Kumar, Naresh

2001-03-01

231

On the problem of cryovacuum hydrogen adsorption by birch activated carbon in the presence of helium  

International Nuclear Information System (INIS)

The effects of activated cryovacuum adsorption of hydrogen from a mixture with helium are described. (Isotherms of adsorption of pure hydrogen and of hydrogen from a mixture with 10-4 volume % helium on activated birch charcoal at 20.4 K and the effect of heating to 70 K with subsequent cooling to 20.4 K were studied.) It was shown that, despite the high heat of adsorption, hydrogen does not displace helium from pores with inlet dimensions smaller than 4 to 4.5 A. This results in a decrease in the volume of hydrogen adsorbed from a mixture with helium compared with adsorption of pure hydrogen. For hydrogen filling of pores with inlet dimensions smaller than 4 to 4.5 A it is necessary to use heating with subsequent cooling to the initial temperature

232

Helium and tritium in neutron-irradiated beryllium  

International Nuclear Information System (INIS)

Beryllium is considered as a potential neutron multiplier in a Helium cooled pebble bed tritium breeding blanket for future fusion power reactors. Under neutron irradiation, helium and tritium are produced in beryllium. The formation of helium bubbles induces swelling; tritium retention is a safety and waste handling issue. In-pile gas release should be sufficiently high to avoid the evacuation of the plant site in case of a serious accident leading to the abrupt release of all accumulated tritium. A reliable prediction of the behaviour of helium and tritium in beryllium, in-pile and during out-of-pile fast temperature transients, is necessary in order to prove the attractiveness of the blanket concept and to optimise design and materials. The lack of experimental data for beryllium pebbles, in the range of neutron fluence and temperature typical of the blanket module operation, imposes an extrapolation of models outside their validation range. A more sophisticated gas kinetics model and a more detailed validation of its single parts are necessary for beryllium in a fusion reactor blanket, than for uranium oxide in fission reactors. Since 1992 the code ANFIBE has been developed to predict the behaviour of helium and tritium in neutron-irradiated beryllium. The aim of the present work is to improve the code for both theoretical modelling and experimental validation, in order to increase confidence in its extrapolation to fusion reactor conditions. This requires to prod reactor conditions. This requires to produce a more detailed, comprehensive and relevant experimental database than the one which was available during the early development phase of the code. The following milestones have been reached: (1) experimental characterisation of all helium and tritium diffusion and release stages in neutron-irradiated beryllium, also from a microscopic point of view; (2) assessment of helium and tritium thermal diffusion coefficients; (3) improvement of the model for gas precipitation into bubbles on the basis of the experimental study; (4) definition and application of an integrated validation procedure for the analytical model, based on the changes in the material microstructure related to different gas release stages. The final result of this study is a new version of the ANFIBE code, which can better describe gas atomic diffusion and precipitation into bubbles and the corresponding gas release. The code has then been applied to approximately assess tritium retention in beryllium at the end-of-life of a blanket module in a fusion reactor of 1.5 GW electric power. On the basis of such assessment, tritium retention in beryllium appears to be a much less critical issue than it was believed in the past. (orig.)

233

The consequences of helium production on microstructural development in isotopically tailored ferritic alloys  

Energy Technology Data Exchange (ETDEWEB)

A series of alloys have been made adding various isotopes of nickel in order to vary the production of helium during irradiation by a two step nuclear reaction in a mixed spectrum reactor. The alloys use a base composition of Fe-12Cr with an addition of 1.5% nickel, either in the form of {sup 60}Ni which produces no helium, {sup 59}Ni which produces helium at a rate of about 10 appm He/dpa, or natural nickel ({sup Nat}Ni) which provides an intermediate level of helium due to delayed development of {sup 59}Ni. Specimens were irradiated in the HFIR at Oak Ridge, TN to {approx}7 dpa at 300 and 400{degrees}C. Microstructural examinations indicated that nickel additions promote precipitation in all alloys, but the effect appears to be much stronger at 400{degrees}C than at 300{degrees}C. There is sufficient dose by 7 dpa (and with 2 appm He) to initiate void swelling in ferritic/martensitic alloys. Little difference was found between response from {sup 59}Ni and {sup Nat}Ni. Also, helium bubble development for high helium generation conditions appeared to be very different at 300 and 400{degrees}C. At 300{degrees}C, it appeared that high densities of bubbles formed whereas at 400{degrees}C, bubbles could not be identified, possibly because of the complexity of the microstructure, but more likely because helium accumulated at precipitate interfaces.

Gelles, D.S. [Pacific Northwest Lab., Richland, WA (United States)

1996-10-01

234

Contribution to the experimental study of the polarized liquid helium-3  

International Nuclear Information System (INIS)

Spin-polarized liquid helium-3 is prepared by laser optical pumping in low magnetic field and at room temperature, prior to fast liquefaction of the polarized sample. The use of a new helium-3 cryostat enabled us to obtain liquid helium-3 with polarization rates up to 25 % at well-stabilized temperatures (around 0.5 K). We could thereby study the effect of nuclear polarization on liquid-vapour equilibrium, and particularly on the saturated vapour pressure. Very sensitive capacitive gauges were developed. We estimated (to first order in M2) the expected effects when the polarization M is suddenly destroyed. These effects were experimentally observed in helium-3/helium-4 mixtures, in pure helium-3, only a transient increase in pressure has been recorded. We then describe in a third part a preliminary experiment which aimed at determining the longitudinal relaxation time T1 in mixtures. Relaxation on the walls is efficiently reduced by a cesium coating and T1s of order 20 minutes were observed. A careful determination of the helium-3 concentration in the liquid phase was made. Finally we studied the effects of dipolar field on transverse polarisation decay in our strongly polarized samples. We observed the free precession of polarization after a NMR pulse, and analysed in detail its decay time constant as a function of different parameters. This time constant drastically varied with the tipping angle, an effect which could be linked to NMR dynamical instabilities. (author)

235

Helium effects on creep properties of Fe-14CrWTi ODS steel at 650 °C  

Science.gov (United States)

In the present paper, the effects of helium on creep properties of Fe-14CrWTi ODS steel were studied by in-beam and post He-implantation creep tests. In-situ creep was performed in an in-beam creep device under uniaxial tensile stresses from 350 to 370 MPa during homogeneous helium implantation. Helium ions of energies varying from 0 to 25 MeV were implanted at a rate of 6 × 10-3 appm/s (corresponding to a displacement dose rate of 1.5 × 10-6 dpa/s). The average temperature was controlled to 650 °C within ±2 °C. In addition, post He-implantation creep tests were conducted at 650 °C as well. Subsequently, fracture surfaces and helium bubble evolution were studied in detail by SEM and TEM observations, respectively. Preliminary creep results show that helium slightly shortens the creep life time of ODS steel at 650 °C. Fracture surfaces of reference as well as implanted specimens, show areas with various grades of deformation. Areas of highest deformation can be interpreted as necking, while areas of low deformation show in helium implanted specimens a more granular structure. The results are discussed in terms of possible embrittlement of ODS steels by helium.

Chen, J.; Jung, P.; Rebac, T.; Duval, F.; Sauvage, T.; de Carlan, Y.; Barthe, M. F.

2014-10-01

236

Vibrations of charged liquid helium surface  

International Nuclear Information System (INIS)

Investigated is the application of metallic approximation for the problem of oscillations of liquid helium charged surface. It is shown that such approximation is true not only for a vapour-liquid surface charged by free electrons, but also for an application limit for He3-He4 boundary at which two-dimensional system of helium ions can be formed

237

Nuclear fusion and the helium supply problem  

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? Fusion power plants will require helium as cryogenic medium and as coolant. ? High losses are expected: for a power plant like DEMO ? 2 t p.a. ? The same power plant is expected to produce only ?0.6 t p.a. ? Global helium resources are finite: fusion will therefore exacerbate an already difficult situation. ? The “back-stop” technology will be the extraction helium of helium from the atmosphere. -- Abstract: The natural resources required for the operation of fusion power plants are – with the possible exception of the neutron multiplier beryllium – readily available. On the other hand, the supply of helium, which is required as cryogenic medium and coolant, may be a problem due to losses during operation and decommissioning. Helium is a rare element obtained as a by-product in the extraction of natural gas. The danger exists that the natural gas will be used up without the helium being conserved. We estimate the helium demand for a global 30% base-load contribution of fusion to electricity supply and also calculate the amount produced by the power plants themselves.

Bradshaw, A.M., E-mail: alex.bradshaw@ipp.mpg.de [Max Planck Institute for Plasma Physics, Association IPP-Euratom, Boltzmannstr. 2, 85741 Garching (Germany); Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany); Hamacher, T. [Institute for Energy Economy and Application Technology, Technical University of Munich, Arcisstrasse 21, 80333 München (Germany)

2013-10-15

238

Nuclear fusion and the helium supply problem  

International Nuclear Information System (INIS)

Highlights: ? Fusion power plants will require helium as cryogenic medium and as coolant. ? High losses are expected: for a power plant like DEMO ? 2 t p.a. ? The same power plant is expected to produce only ?0.6 t p.a. ? Global helium resources are finite: fusion will therefore exacerbate an already difficult situation. ? The “back-stop” technology will be the extraction helium of helium from the atmosphere. -- Abstract: The natural resources required for the operation of fusion power plants are – with the possible exception of the neutron multiplier beryllium – readily available. On the other hand, the supply of helium, which is required as cryogenic medium and coolant, may be a problem due to losses during operation and decommissioning. Helium is a rare element obtained as a by-product in the extraction of natural gas. The danger exists that the natural gas will be used up without the helium being conserved. We estimate the helium demand for a global 30% base-load contribution of fusion to electricity supply and also calculate the amount produced by the power plants themselves

239

Post-giant evolution of helium stars  

International Nuclear Information System (INIS)

Extremely hydrogen deficient stars (helium stars and R Coronae Borealis variables) are considered to be remnants of double shell source stars (of the asymptotic giant branch). The evolution of stars with a condensed C/O-core and a helium envelope is followed numerically from the red giant stage to the white dwarf domain, crossing the regions of R CrB- and helium stars (so far analyzed). They have typically masses M/M(sun) = 0.7 and luminosities log L/L(sun) = 4.1. The time for crossing the helium star domain is some 103 years. The corresponding times in the R CrB-region amounts up to several 104 years. The lower limit of the death rate of helium stars is estimated to be 4 x 10-14pc-3yr-1. This value is only a factor of ten lower than the birth rate of all non-DA white dwarfs. It is therefore possible that the helium stars are the precursors of helium rich white dwarfs. As a consequence, a significant fraction of all stars which end their lives as white dwarfs should pass through the helium star phase. (orig.)

240

Helium abundances and the helium isotope anomaly of sdB stars  

CERN Document Server

Helium abundances and atmospheric parameters have been determined from high resolution spectra for a new sample of 46 bright hot subdwarf B (sdB) stars. The helium abundances have been measured with high accuracy. We confirm the correlation of helium abundance with temperature and the existence of two distinct sequences in helium abundance found previously. We focused on isotopic shifts of helium lines and found helium-3 to be strongly enriched in 8 of our programme stars. Most of these stars cluster in a small temperature range between 27000 K and 31000 K very similar to the known helium-3-rich main sequence B stars, which cluster at somewhat lower temperatures. This phenomenon is most probably related to diffusion processes in the atmosphere, but poses a challenge to diffusion models.

Geier, S; Edelmann, H; Morales-Rueda, L; Kilkenny, D; O'Donoghue, D; Marsh, T R; Copperwheat, C

2011-01-01

 
 
 
 
241

ACOUSTIC SIGNATURES OF THE HELIUM CORE FLASH  

Energy Technology Data Exchange (ETDEWEB)

All evolved stars with masses M {approx}< 2 M{sub Sun} undergo an initiating off-center helium core flash in their M{sub c} Almost-Equal-To 0.48 M{sub Sun} He core as they ascend the red giant branch (RGB). This off-center flash is the first of a few successive helium shell subflashes that remove the core electron degeneracy over 2 Myr, converting the object into a He-burning star. Though characterized by Thomas over 40 years ago, this core flash phase has yet to be observationally probed. Using the Modules for Experiments in Stellar Astrophysics (MESA) code, we show that red giant asteroseismology enabled by space-based photometry (i.e., Kepler and CoRoT) can probe these stars during the flash. The rapid ({approx}< 10{sup 5} yr) contraction of the red giant envelope after the initiating flash dramatically improves the coupling of the p-modes to the core g-modes, making the detection of l = 1 mixed modes possible for these 2 Myr. This duration implies that 1 in 35 stars near the red clump in the H-R diagram will be in their core flash phase. During this time, the star has a g-mode period spacing of {Delta}P{sub g} Almost-Equal-To 70-100 s, lower than the {Delta}P{sub g} Almost-Equal-To 250 s of He-burning stars in the red clump, but higher than the RGB stars at the same luminosity. This places them in an underpopulated part of the large frequency spacing ({Delta}{nu}) versus {Delta}P{sub g} diagram that should ease their identification among the thousands of observed red giants.

Bildsten, Lars; Paxton, Bill; Moore, Kevin; Macias, Phillip J. [Kavli Institute for Theoretical Physics and Department of Physics Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)

2012-01-15

242

Primordial helium and the cosmic background radiation  

International Nuclear Information System (INIS)

The products of primordial nucleosynthesis, along with the cosmic microwave background (CMB) photons, are relics from the early evolution of the Universe whose observations probe the standard model of cosmology and provide windows on new physics beyond the standard models of cosmology and of particle physics. According to the standard, hot big bang cosmology, long before any stars have formed a significant fraction ( ? 25%) of the baryonic mass in the Universe should be in the form of helium-4 nuclei. Since current observations of 4He are restricted to low redshift regions where stellar nucleosynthesis has occurred, an observation of high redshift, prestellar, truly primordial 4He would constitute a fundamental test of the hot, big bang cosmology. At recombination, long after big bang nucleosynthesis (BBN) has ended, the temperature anisotropy spectrum imprinted on the CMB depends on the 4He abundance through its connection to the electron density and the effect of the electron density on Silk damping. Since the relic abundance of 4He is relatively insensitive to the universal density of baryons, but is sensitive to a non-standard, early Universe expansion rate, the primordial mass fraction of 4He, Yp, offers a test of the consistency of the standard models of BBN and the CMB and, provides constraints on non-standard physics. Here, the WMAP seven year data (supplemented by other CMB experiments), which lead to an indirect determination of Yp at high redshift, are compared to the BBN predictions and to the independent, direct observations of 4He in low redshift, extragalactic HII regions. At present, given the very large uncertainties in the CMB-determined primordial 4He abundance (as well as for the helium abundances inferred from HII region observations), any differences between the BBN predictions and the CMB observations are small, at a level ?<1.5?

243

Helium/radon precursory signals of Chamoli Earthquake, India  

Energy Technology Data Exchange (ETDEWEB)

The Bhagirthi and Alaknanda valleys of Garhwal Himalaya, were rocked, respectively, by two major earthquakes: the Uttarkashi earthquake of magnitude m{sub b}=6.5, M{sub s}=7.0 on October 20, 1991 and the Chamoli earthquake of m{sub b}=6.8, M{sub s}=6.5 on March 29, 1999, during this decade. Both these seismic events are associated with ongoing deformation along the main central thrust of the Himalayas. Helium and radon anomalies on March 24 and March 27, 1999, respectively, were recorded at Palampur which is about 393 km from the Chamoli earthquake epicentre. A He/Rn ratio anomaly was recorded on March 20, 9 days before the Chamoli earthquake. The precursory nature of radon and helium anomalies is a strong indicator of the physical basis of earthquake prediction and a preliminary test for the proposed conceptual He/Rn ratio model.

Virk, H.S. E-mail: virkhs@yahoo.comhsvirk@excite.com; Walia, V

2001-06-01

244

Helium/radon precursory signals of Chamoli Earthquake, India  

International Nuclear Information System (INIS)

The Bhagirthi and Alaknanda valleys of Garhwal Himalaya, were rocked, respectively, by two major earthquakes: the Uttarkashi earthquake of magnitude mb=6.5, Ms=7.0 on October 20, 1991 and the Chamoli earthquake of mb=6.8, Ms=6.5 on March 29, 1999, during this decade. Both these seismic events are associated with ongoing deformation along the main central thrust of the Himalayas. Helium and radon anomalies on March 24 and March 27, 1999, respectively, were recorded at Palampur which is about 393 km from the Chamoli earthquake epicentre. A He/Rn ratio anomaly was recorded on March 20, 9 days before the Chamoli earthquake. The precursory nature of radon and helium anomalies is a strong indicator of the physical basis of earthquake prediction and a preliminary test for the proposed conceptual He/Rn ratio model

245

A GM cryocooler with cold helium circulation for remote cooling  

Science.gov (United States)

A GM cryocooler with new cold helium circulation system has been developed at Cryomech. A set of check valves connects to the cold heat exchanger to convert a small portion of AC oscillating flow in the cold head to a DC gas flow for circulating cold helium in the remote loop. A cold finger, which is used for remote cooling, is connected to the check valves through a pair of 5 m long vacuum insulated flexible lines. The GM cryocooler, Cryomech model AL125 having 120 W at 80 K, is employed in the testing. The cold finger can provide 50 W at 81 K for the power input of 4.1 kW and 70.5 W at 81.8 K for the power input of 6 kW. This simple and low cost design is very attractive for some applications in the near future.

Wang, Chao; Brown, Ethan

2014-01-01

246

Impurity condensation in liquid and solid helium  

Science.gov (United States)

It is shown from an analysis of x-ray structural and IR spectroscopic studies that when impurity particles are introduced into liquid or solid helium, the clusters formed in the cold part of a gas jet have a pronounced spatial separation of impurities with different volatility. In particular, in the condensation of partially dissociated diatomic molecules the atoms are highly concentrated near and on the surface of the clusters. Segregation of this kind is preserved in the condensate in liquid helium, which consists of clusters stuck together into a porous structure; in solid helium clusters are isolated. The presence of high concentrations of atoms in the surface layer at the boundary with condensed helium explains the specifics of condensate behavior observed by methods of optical spectroscopy, ESR, and thermometry. An experimental strategy is developed for detecting the formation of an impurity-helium solid.

Gordon, E. B.

2004-10-01

247

Spectrographic detection of nitrogen impurity in helium  

International Nuclear Information System (INIS)

A device to observe very small amount of nitrogen impurity in helium gas was developed for a liquefaction system of helium. The principle of detection is based on the optical spectroscopy of the discharge arc in the helium gas. The new detector uses 427.8 nm spectral line as the detection light source while the previous works in this type of detectors used 391.4 nm spectral line. The advantage of newly introduced spectral line is that there is no strong helium spectral line in the neighbor of the observed line. As a result, it became possible to build a simple and reliable impurity detector which can continuously observe very small amount of nitrogen in helium. (author)

248

Adsorption and desorption of helium in aerogels  

International Nuclear Information System (INIS)

We have studied the adsorption and desorption of helium in a 95% porosity aerogel. The helium density in the aerogel was directly measured with a capacitive technique, while the pressure and bulk helium density were measured with in situ capacitive gauges. Thermal response is slow in aerogels, so we used a thin sample to minimize the time constant. The combination of high resolution and rapid equilibration allowed us to study the capillary condensation of helium, which in aerogels occurs very close to the bulk saturation pressure. We saw hysteresis between filling and emptying of the pores, even for very slow rates. The hysteresis becomes smaller as the critical temperature is approached. We discuss whether true two phase coexistence can be observed in the helium-aerogel system

249

Isotopic-chromatographic-spectral determination of carbon dioxide in helium using adsorption preconcentration  

International Nuclear Information System (INIS)

A combined chromatographic-spectro-isotopic method has been developed for determination of CO2 in helium using absorption accumulation and chromatography at low pressure. Down to 5x10-6 mole % CO2 can be determined. The method does not require reference samples based on test gases. The possibility to determine lower CO2 contents is connected with a better reliability of spectroscopic determination of CO2 isotopic composition and with an increase of a helium sample to be analysed

250

Determination of helium in beryl minerals  

International Nuclear Information System (INIS)

In order to obtain the diffusion coefficients of helium in beryl and phenacite samples at various temperatures, helium leak rates were measured in these minerals at these temperatures. Mass spectrometry (MS) was used to obtain helium leak rates and the gas flow was plotted against time. The gas quantity determined by MS was first obtained at various temperatures until no helium leak rate was detected. After that, these samples were irradiated with fast neutrons to produce helium which was measured again. This procedure was used to estimate the experimental error. The quantity of helium produced by interaction of gamma radiation with beryl minerals was theoretically calculated from the amount of thorium-232 at the neighbourhood of the samples. The quantity of helium produced in the minerals due to uranium and thorium decay was calculated using the amount of these heavy elements, and the results were compared with the amounts determined by MS. The amount of potassium-40 was determined in order to derive the quantity of argonium-40, since some workers found argonium in excess in these minerals. The quantity of helium in the beryl samples (s) was determined in the center and in the surface of the samples in order to obtain informations about the effectiveness of the Be(?, ?) He reaction. Beryl and phenacite minerals were choosen in this research since they are opposite each other with respect to the helium contents. Both have beryllium in their compositon but beryl hold a large amount of helium while phenacite, in spite of having about three times more beryllium than beryl, do not hold the gas. (author)

251

Exotic helium molecules; Molecules exotiques d'helium  

Energy Technology Data Exchange (ETDEWEB)

We study the photo-association of an ultracold cloud of magnetically trapped helium atoms: pairs of colliding atoms interact with one or two laser fields to produce a purely long range {sup 4}He{sub 2}(2{sup 3}S{sub 1}-2{sup 3}P{sub 0}) molecule, or a {sup 4}He{sub 2}(2{sup 3}S{sub 1}-2{sup 3}S{sub 1}) long range molecule. Light shifts in one photon photo-association spectra are measured and studied as a function of the laser polarization and intensity, and the vibrational state of the excited molecule. They result from the light-induced coupling between the excited molecule, and bound and scattering states of the interaction between two metastable atoms. Their analysis leads to the determination of the scattering length a = (7.2 {+-} 0.6) ruling collisions between spin polarized atoms. The two photon photo-association spectra show evidence of the production of polarized, long-range {sup 4}He{sub 2}(2{sup 3}S{sub 1}-2{sup 3}S{sub 1}) molecules. They are said to be exotic as they are made of two metastable atoms, each one carrying a enough energy to ionize the other. The corresponding lineshapes are calculated and decomposed in sums and products of Breit-Wigner and Fano profiles associated to one and two photon processes. The experimental spectra are fit, and an intrinsic lifetime {tau} = (1.4 {+-} 0.3) {mu}s is deduced. It is checked whether this lifetime could be limited by spin-dipole induced Penning autoionization. This interpretation requires that there is a quasi-bound state close to the dissociation threshold in the singlet interaction potential between metastable helium atoms for the theory to match the experiment. (author)

Portier, M

2007-12-15

252

Coaxial electron gun. Working principles and excitation processes in helium  

International Nuclear Information System (INIS)

The coaxial electron gun has been used for investigation of excitation of n=2 levels of helium plasma with a monokinetic electron beam. The electron distribution function by energy was calculated for a wide range of current and pressure alterations, allowing to make comparison between calculated and measured values of n=2 levels populations. The saturation of all states' populations (except 23S at a current increase above 1.5-2 A) showed the importance of inelastic collisions with electrons

253

Transfer excitation reactions in fast proton-helium collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Continuing previous work, we have measured the projectile scattering-angle dependency for transfer excitation of fast protons (300-1200 keV/u) colliding with helium (p+He $\\rightarrow$ H + He$^{+ *}$). Our high-resolution fully differential data are accompanied by calculations, performed in the plane wave first Born approximation and the eikonal wave Born approximation. Experimentally we find a deep minimum in the differential cross section around 0.5 $mrad$. The comparison ...

Scho?ffler, M. S.; Kim, H. -k; Chuluunbaatar, O.; Houamer, S.; Galstyan, A. G.; Titze, J. N.; Jahnke, T.; Schmidt, L. Ph H.; Schmidt-b Ocking, H.; D Orner, R.; Popov, Yu V.; Bulychev, A. A.

2013-01-01

254

Features of metrological characteristics of helium chromatographs and estimation of their stability as applied to problems of impurities control in coolant of HTGR plants  

International Nuclear Information System (INIS)

Two models of helium chromatographs with complete automation of analysis, which can be installed and used independently, have been developed. They are used to determine contents of hydrogen, oxygen, methane, humidity, carbon oxide and dioxide impurities in concentration range of 5x10-5-10-1 vol.% in helium coolant. Helium chromatographs are used for control of impurity content in the HTGR plant coolant. 2 refs., 3 tabs

255

THE EFFECTS OF CURVATURE AND EXPANSION ON HELIUM DETONATIONS ON WHITE DWARF SURFACES  

Energy Technology Data Exchange (ETDEWEB)

Accreted helium layers on white dwarfs have been highlighted for many decades as a possible site for a detonation triggered by a thermonuclear runaway. In this paper, we find the minimum helium layer thickness that will sustain a steady laterally propagating detonation and show that it depends on the density and composition of the helium layer, specifically {sup 12}C and {sup 16}O. Detonations in these thin helium layers have speeds slower than the Chapman-Jouget (CJ) speed from complete helium burning, v{sub CJ} = 1.5 × 10{sup 9} cm s{sup –1}. Though gravitationally unbound, the ashes still have unburned helium (?80% in the thinnest cases) and only reach up to heavy elements such as {sup 40}Ca, {sup 44}Ti, {sup 48}Cr, and {sup 52}Fe. It is rare for these thin shells to generate large amounts of {sup 56}Ni. We also find a new set of solutions that can propagate in even thinner helium layers when {sup 16}O is present at a minimum mass fraction of ?0.07. Driven by energy release from ? captures on {sup 16}O and subsequent elements, these slow detonations only create ashes up to {sup 28}Si in the outer detonated He shell. We close by discussing how the unbound helium burning ashes may create faint and fast 'Ia' supernovae as well as events with virtually no radioactivity, and speculate on how the slower helium detonation velocities impact the off-center ignition of a carbon detonation that could cause a Type Ia supernova in the double detonation scenario.

Moore, Kevin; Bildsten, Lars [Department of Physics, University of California, Santa Barbara, CA (United States); Townsley, Dean M. [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL (United States)

2013-10-20

256

Helium gas bubble trapped in liquid helium in high magnetic field  

Energy Technology Data Exchange (ETDEWEB)

High magnetic field magnets are used widely in the area of the condensed matter physics, material science, chemistry, geochemistry, and biology at the National High Magnetic Field Laboratory. New high field magnets of state-of-the-art are being pursued and developed at the lab, such as the current developing 32?T, 32?mm bore fully superconducting magnet. Liquid Helium (LHe) is used as the coolant for superconducting magnets or samples tested in a high magnetic field. When the magnetic field reaches a relatively high value the boil-off helium gas bubble generated by heat losses in the cryostat can be trapped in the LHe bath in the region where BzdBz/dz is less than negative 2100 T{sup 2}/m, instead of floating up to the top of LHe. Then the magnet or sample in the trapped bubble region may lose efficient cooling. In the development of the 32?T magnet, a prototype Yttrium Barium Copper Oxide coil of 6 double pancakes with an inner diameter of 40?mm and an outer diameter of 140?mm was fabricated and tested in a resistive magnet providing a background field of 15?T. The trapped gas bubble was observed in the tests when the prototype coil was ramped up to 7.5?T at a current of 200?A. This letter reports the test results on the trapped gas bubble and the comparison with the analytical results which shows they are in a good agreement.

Bai, H., E-mail: bai@magnet.fsu.edu; Hannahs, S. T.; Markiewicz, W. D.; Weijers, H. W. [National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States)

2014-03-31

257

Helium gas bubble trapped in liquid helium in high magnetic field  

Science.gov (United States)

High magnetic field magnets are used widely in the area of the condensed matter physics, material science, chemistry, geochemistry, and biology at the National High Magnetic Field Laboratory. New high field magnets of state-of-the-art are being pursued and developed at the lab, such as the current developing 32 T, 32 mm bore fully superconducting magnet. Liquid Helium (LHe) is used as the coolant for superconducting magnets or samples tested in a high magnetic field. When the magnetic field reaches a relatively high value the boil-off helium gas bubble generated by heat losses in the cryostat can be trapped in the LHe bath in the region where BzdBz/dz is less than negative 2100 T2/m, instead of floating up to the top of LHe. Then the magnet or sample in the trapped bubble region may lose efficient cooling. In the development of the 32 T magnet, a prototype Yttrium Barium Copper Oxide coil of 6 double pancakes with an inner diameter of 40 mm and an outer diameter of 140 mm was fabricated and tested in a resistive magnet providing a background field of 15 T. The trapped gas bubble was observed in the tests when the prototype coil was ramped up to 7.5 T at a current of 200 A. This letter reports the test results on the trapped gas bubble and the comparison with the analytical results which shows they are in a good agreement.

Bai, H.; Hannahs, S. T.; Markiewicz, W. D.; Weijers, H. W.

2014-03-01

258

Compatibility of vanadium alloys with reactor-grade helium for fusion reactor applications  

International Nuclear Information System (INIS)

Tests were conducted to determine the compatibility of vanadium alloys with reactor-grade helium and to define the helium gas chemistry requirements for fusion reactors, miniature tensile specimens of V-5Cr-5Ti. V-10Cr-5Ti, and V-12.5Cr-5 Ti were exposed in a once-through system to helium with 70 vppm-H2 (measured oxygen partial pressures of 10-12 atm) and bottle helium (measured oxygen partial pressures of -4 atm) between 500 and 700 degree C for up to 1008 h. The weight changes in the specimens were recorded. The helium-exposed specimens were tensile tested, and the effects of exposure on mechanical properties were assessed. Exposure between 500 and 700 degree C for 1008 h in He+70 vppm-H2 resulted in complete embrittlement of all the alloys in room temperature tensile tests. The fracture mode was primarily cleavage, probably caused by a hydrogen-induced shift in the ductile to brittle transition temperature (DBTT). Weight gains increased with temperature and were largest for the V-5Cr-5Ti alloy. Specimens exposed for 531 h between 500 and 700 degree C in bottle He exhibited two distinct fracture morphologies on the fracture surfaces. Brittle cleavage around the edges of specimens gave way to ductile dimpling in the center of the specimens. The brittle region around the periphery of the specimen is most likely the highest vanadium oxide. V2O5

259

A nuclear physical method for determining helium in surface layers of materials  

International Nuclear Information System (INIS)

The method of recoil nuclei, which permits to obtain data on integral content, differential distribution, and in crystal structures - on location in lattice of helium impUrity atoms without sample destruction, has been considered. The method is based on impurity nuclei recording, which are knocked off the sample layer analyzed as a result of elastic cocollisions with accelerated ions. When heavy ions are used the method of recoil nuclei permits to determine helium impurities with the concentration above 5x1012 atom/cm2. The thickness of the layer analyzed can reach 1 ?m at the resolution approximately 40 nm. Determination of helium impurity implanted with the energy up to 200 keV is possible. Results of helium determination in the alloy Ti-Al-V made using a cyclotron with the energy of nitrogen accelerated ions 16 MeV are presented. The bunch current in the chamber constituted 0.05 ?A. To record recoil nuclei a silicon surface-barrier detector with the resolution 40 keV is used. A good separation of peaks corresponding to recoil nuclei of hydrogen and helium adsorbed on the surface sample, which are implanted with the energy 30 keV and dose 5X1017 and 1x1016 atom/cm2, is observed. Residual concentration of helium constitutes 2.45x1016 atom/cm2 for the introduced dose 5x1017 atom/cm2

260

Helium hammer in superfluid transfer  

Science.gov (United States)

Large transient pressure pulses, referred to as a helium hammer, which occurred in the transfer line of the main cryogenic tank during the development tests of the Infrared Astronomical Satellite, launched on January 25, 1983, are analyzed, and the measures taken to prevent a failure described. The modifications include an installation of a 2.3-liter surge tank upstream, and a back-up relief valve downstream, of a burst disk. The surge tank is designed to attenuate a 0.33-MPa pressure pulse at the inlet down to 0.092 MPa at the outlet. A mechanism of the pulse generation is suggested, which involves flashing and rapid recondensation of the small amount of liquid entering the warm section of a transition to room temperature.

Tward, E.; Mason, P. V.

 
 
 
 
261

Helium adsorption on intermediate binding substrates  

Science.gov (United States)

This work investigates the 2D phase diagram and wetting properties of helium adsorbed onto intermediate binding substrates, in particular that of lithium and sodium. Intermediate binding substrates are substrates that bind more strongly with helium than cesium or rubidium where there exists a wetting or prewetting transition but are weaker than conventional substrates such as gold or graphite for which the surface potential is so strong that solid-like layers will form. Unique equipment was required to study the adsorption phase diagram of helium on these materials including a cryostat to reach low temperatures while maintaining optical access to the experiment, a method of creating clean and reproducible films at cryogenic temperatures and extremely precise techniques able to measure sub-monolayer films of helium. My colleagues and I constructed a optical pulse tube closed cycle helium three cryostat. This cryostat is able to reach and maintain temperatures as low as 0.4K. The cryostat has large windows to allow clear optical access to the experiment. I developed a pulsed laser deposition system to grow films of any metal or material in a cryogenic environment. Helium coverage was detected with a quartz crystal microbalance (QCM) with a resolution of 1/20th of a statistical layer of helium. In this work I have performed helium adsorption isotherms to measure the thin film wetting properties and two dimensional phase diagram of helium on lithium and sodium substrates. Thin films of helium undergo the Kosterlitz-Thouless (KT) transition, which predicts the superfluid density of the film as a function of temperature; monolayer helium films may also undergo a 2D liquid-vapor phase transition below a critical temperature. Previous theoretical and experimental work has placed such a critical point to be at 0.8K, so isotherms were performed from 1.6K to 0.4K. The primary focus of this work is to explore the interplay of the second order KT phase transition and the first order liquid-vapor phase transition on lithium and sodium. Strong binding substrates have been used to explore the complete two dimensional phase diagram, but past experiments on superfluid onset had to be performed on the second or higher layers of helium because the first layer is localized solid on conventional substrates. These are the first experiments that explore superfluid onset of helium on a bare substrate in the monolayer region. For temperatures above 1K the pressure inside the cell can be measured. It was discovered that coverage of helium on lithium and sodium is linear in pressure below one layer indicating the adsorption of an ideal 2D bose gas with no formation of solid-like layers of helium. The slope of this line provides a measurement of the binding energy of helium to lithium, -13.77 +/- 0.98K, and sodium, -9.45 +/- 0.715K. In all cases helium was observed to wet both lithium and sodium and reverse isotherms were performed on sodium at temperatures of 0.7K and above with no indication of hysteresis, indicating that at no point did a first order phase transition occur on the sodium substrate. When the superfluid density of helium is plotted as a function of temperature in a strong binding substrate the intercept of the KT line at T = 0 will be a positive coverage, know as the "dead layer", however for lithium and sodium the intercept of the line at T = 0 corresponds to a physically impossible negative coverage, and in the case of sodium the jump in the superfluid density becomes a constant independent of temperature. Both observations indicate a strong deviation from KT theory, which says that the superfluid onset should have universal features independent of substrate with a superfluid density jump that is proportional to the temperature.

van Cleve, Eli

262

In Beam Tests of Implanted Helium Targets  

CERN Document Server

Targets consisting of 3,4He implanted into thin aluminum foils (approximately 100, 200 or 600 ug/cm^2) were prepared using intense (a few uA) helium beams at low energy (approximately 20, 40 or 100 keV). Uniformity of the implantation was achieved by a beam raster across a 12 mm diameter tantalum collimator at the rates of 0.1 Hz in the vertical direction and 1 Hz in the horizontal direction. Helium implantation into the very thin (approximately 80-100 ug/cm^2) aluminum foils failed to produce useful targets (with only approximately 10% of the helium retained) due to an under estimation of the range by the code SRIM. The range of low energy helium in aluminum predicted by Northcliffe and Shilling and the NIST online tabulation are observed on the other hand to over estimate the range of low energy helium ions in aluminum. An attempt to increase the amount of helium by implanting a second deeper layer was also carried out, but it did not significantly increase the helium content beyond the blistering limit (ap...

McDonald, J E; Ahmed, M W; Blackston, M A; Delbar, T; Gai, M; Kading, T J; Parpottas, Y; Perdue, B A; Prior, R M; Rubin, D A; Spraker, M C; Yeomans, J D; Weissman, L; Weller, H R; Delbar, Th.; Conn, LNS/U; Duke, TUNL/

2006-01-01

263

Simulation study on retention and reflection from tungsten carbide under high fluence of helium ions  

International Nuclear Information System (INIS)

We have studied, with a Monte Carlo simulation code ACAT-DIFFUSE, the fluence-dependence of the amount of helium atoms retained in tungsten carbide at room temperature under helium ion bombardment. The retention behavior may be understood qualitatively in terms of irradiation-dependent diffusion coefficient assumed and range. The re-emission, reflection and sputtering from tungsten carbide under helium ion irradiation were derived and compared with each other. We have discussed the retention curves for incident energy of 5 keV at incident angles of 0 deg. and 80 deg. and of 500 eV at 0 deg. The energy spectra of helium atoms reflected from tungsten carbide for incident energy of 500 eV at 0 deg. and 80 deg. were compared with those from graphite and tungsten

264

On the formation mechanism of impurity-helium solids: evidence for extensive clustering  

International Nuclear Information System (INIS)

Optical emission studies on a discharged nitrogen-helium gas jet injected into superfluid helium near 1.5 K are described. The analysis of atomic (a-group) and molecular Vegard-Kaplan transitions clearly indicates that the emitting species are embedded in the nitrogen clusters. The formation of the clusters is most efficient in the crater formed on the liquid surface. The model calculations based on the classical bubble model and density functional theory suggest that under the experimental conditions only clusters consisting of more than 1000 molecules have a kinetic energy sufficient for the stable cavity formation inside liquid helium. The results obtained suggest that the formation of impurity-helium solids is a consequence of extensive clustering in the gas jet

265

Effects of dislocations on thermal helium desorption from nickel and iron  

Science.gov (United States)

Helium atoms in metals have a strong tendency to accumulate at defects. Unfortunately, the experimental identification of the trapping sites of helium atoms is difficult. In this paper, the effects of dislocations on the trapping and desorption of helium atoms in nickel and iron were studied by thermal desorption spectroscopy. Defects were introduced in well-annealed high-purity metals by cold rolling. Positron annihilation spectroscopy was carried out to identify defects by measuring the positron lifetime before annihilation with various defects. The trapping and desorption of helium atoms at dislocations were investigated by implantation with low-energy He + ions, both without irradiation damage (0.1 keV or 0.15 keV) and with irradiation damage (5.0 keV).

Cao, X. Z.; Xu, Q.; Sato, K.; Yoshiie, T.

2011-10-01

266

The effect of helium accumulation and radiation damage on the weldability of 316-type steel  

Science.gov (United States)

The embrittlement simulated by helium accumulation, with the ITER components repaired by welding during maintenance, is one of the factors limiting the materials lifetime. This work presents the results of the investigations into the effect of neutron produced helium, 0.1 dpa Tirr - 80°C, (at a low He/dpa and cyclotron introduced helium, 5-430 appm He (at high He/dpa) on the quality and mechanical properties of the type 316 steel welds. The samples, both irradiated and controls, were welded by e-beam welding (cyclotron injection) or on the automatic argon-arc welding device in the hot cell SRIIAr (neutron irradiation). Low-cycle fatigue (LCF) testing in bending was used to assess impact of helium on the degradation of welded joint properties.

Fabritsiev, S. A.; Pokrovsky, A. S.

1998-10-01

267

Improved analyzer for determining helium-4 in parts-per-billion range. Report of Investigations/1986  

International Nuclear Information System (INIS)

The Bureu of Mines has modified its parts-per-billion helium-4 analyzer to improve the analytical capabilities of the instrument. The modifications resulted in the following improvements: (1) the analytical precision of the instrument for 10 consecutive analyses was improved to + or - ppb at the 5000 ppb helium-4 level, (2) the helium-4 sensitivity was increased almost tenfold, and (3) the minimum detectable limit for helium-4 was improved to 0.5 ppb. The modifications made to improve the instrument included replacing the ion-source control circuit with a direct-current solid-state design, controlling the temperature of the ion source, stabilizing and reducing the pumping rate of the vacuum system, and optimizing peak integration

268

Helium-cooled, solid breeder blanket design for a tokamak fusion reactor  

International Nuclear Information System (INIS)

A preliminary design for a helium-cooled, solid breeder blanket for a tokamak fusion reactor has been developed and its performance looks quite good. The design is capable of bearing a 4 MW/m2 neutron wall load and the ideal pumping power required for the whole primary helium loop including the steam generators is only 2.5% of the total thermal power. The coolant pressure is at the moderate level of 5 MPa. The integrated helium duct work results in a compact blanket having a maximum overall thickness of only 86 cm. The design work was mainly focused on the thermal-hydraulic aspects, which in fact represent the key problems associated with using helium as a coolant. The present work, however, demonstrates that several disadvantages of helium can be avoided or at least minimized by an appropriate design. Thus, a major part of the criticisms against gas cooling for tokamaks are effectively refuted by this design study. Based on the work presented here, the conceptual design for a helium-cooled, solid breeder blanket test module has been adapted and submitted for the INTOR Testing Program. (Auth.)

269

A system for measurement of sub-parts-per-trillion helium in solids  

International Nuclear Information System (INIS)

A system for measurement of less than 1 ppt (parts per trillion) of helium contained in a solid within the range of mass between 100 mg and 1 g has been developed for the primary purpose of measuring neutron-induced helium production cross sections. The system consists of an apparatus based on ultrahigh vacuum techniques, computer codes to estimate suitable parameters for the given experimental conditions and to control data acquisition parts, and an appropriate routine of operation of the system. The system apparatus consists of a gas releaser, a mass spectrometer, and a standard helium supply. A sample containing helium is evaporated in the gas releaser and the gas is analyzed with the mass spectrometer after purifying it for helium to decrease background gases. The background of helium for a dummy sample of silicon is measured to be 0.04 ppt. The total uncertainty of the apparatus is 4.4% in the range of (0.5 endash 5.0)x1010 He measurement. copyright 1996 American Institute of Physics

270

Buoyancy-Driven Natural Convection of Liquid Helium in an Electron Bubble Chamber  

International Nuclear Information System (INIS)

A small liquid helium test chamber with 1.5 L active volume has been designed and constructed, to make the fundamental measurements of physical properties of electron bubble transports in liquid helium, aimed at developing a new cryogenic neutrino detector, using liquid helium as the detecting medium, for the detection of solar neutrinos. The test chamber is a double-walled cylindrical container equipped with five optical windows and ten high voltage cables. A LN2/LHe cryostat and a needle valve for vapor helium cooling are used to provide a 1.7?4.5 K low temperature environments for the test chamber. One of key issues for the cryogenic design and experimental sensitivity of electron bubble tracking is that of keeping a thermally uniform liquid helium bath. The external heat loads to the chamber will generate a buoyancy-induced convection of liquid helium, which will carry the electron bubbles and accelerate or decelerate their transportation and therefore must be reduced to the minimum, so that the slow motion of the electron bubbles will not be confused by this effect. This paper will present the computational simulation and analysis on thermal convection and uniformity of the test chamber

271

Molecular dynamics simulations of the diffusion and coalescence of helium in tungsten  

International Nuclear Information System (INIS)

Molecular dynamics (MD) simulations are performed on the diffusion and coalescence of helium in tungsten. A new method for determining the effective capture radii (ECRs) and the dissociation energies of helium-related defects is proposed in this work. It is observed that the ECR of an interstitial helium atom trapping helium interstitials (denoted as He–Hen, n = 1–3) decreases with increasing temperature, except for He–He2 at T n for helium clusters are also investigated. He2 migrates more quickly than a single He atom does at T 2 changes at higher temperatures. Another counterintuitive observation is that D5 > D3 > D4 at T 5. The Arrhenius relation describes the diffusion of Hen well in the temperature range from 300 K to 550 K, whereas the diffusion is not a standard thermally activated process at higher temperatures. Taken together, these results help elucidate the initial stage of helium bubble formation in tungsten as well as the requirements of long-term evolution methods such as KMC or RT models

272

Genetic changes in Mammalian cells transformed by helium cells  

International Nuclear Information System (INIS)

Midterm Syrian Hamster embryo (SHE) cells were employed to study high LET-radiation induced tumorigenesis. Normal SHE cells (secondary passage) were irradiated with accelerated helium ions at an incident energy of 22 MeV/u (9--10 keV/?m). Transformed clones were isolated after growth in soft agar of cells obtained from the foci of the initial monolayer plated postirradiation. To study the progression process of malignant transformation, the transformed clones were followed by monolayer subculturing for prolonged periods of time. Subsequently, neoplasia tests in nude mice were done. In this work, however, we have focused on karyotypic changes in the banding patterns of the chromosomes during the early part of the progressive process of cell transformation for helium ion-induced transformed cells. 26 refs., 5 figs., 2 tabs

273

Erosion of the non metallic materials under helium irradiation  

International Nuclear Information System (INIS)

The character of processes occurring on helium ion implantation in silicon carbide-based materials and silicon single crystals the properties of which had been rather extensivvely studied providing for a ready interpretation and comparison of results was investigated using a comparative approach. The irradiation with helium ions was made using a linear accelerator in the energy range from 50 to 175 keV at dozes from 0.01 kl/cm2 to 6.5 kl/cm2 and temperatures from 120 to 600 deg C. It is stated that the main surface erosion mechanism in brittle materials irradiated with low-soluble gas ions is represented by spalling resulting in high effective erosion coefficient values. The erosion coefficient values have been found to decrease at high irradiation dozes. The dependence of erosion character on the structure of initial crystals has been studied

274

Direct nano-patterning of graphene with helium ion beams  

Science.gov (United States)

Helium ion microscopy (HIM) was used for direct nano-patterning of single-layer graphene (SLG) on SiO2/Si substrates. This technique involves irradiation of the sample with accelerated helium ions (He+). Doses of 2.0 × 1016 He+ cm-2 from a 30 kV beam induced a metal-insulator transition in the SLG. The resolution of HIM patterning on SLG was investigated by fabricating nanoribbons and nanostructures. Analysis of scanning capacitance microscopy measurements revealed that the spatial resolution of HIM patterning depended on the dosage of He+ in a non-monotonic fashion. Increasing the dose from 2.0 × 1016 to 5.0 × 1016 He+ cm-2 improved the spatial resolution to several tens of nanometers. However, doses greater than 1.0 × 1017 He+ cm-2 degraded the patterning characteristics. Direct patterning using HIM is a versatile approach to graphene fabrication and can be applied to graphene-based devices.

Naitou, Y.; Iijima, T.; Ogawa, S.

2015-01-01

275

Failure of choroidal melanoma to respond to helium ion therapy  

Energy Technology Data Exchange (ETDEWEB)

Helium ion irradiation is a promising alternative therapy for choroidal melanoma. In short-term follow-up (less than 5 years), more than 90% (18/19) of treated patients demonstrated tumor regression. Researchers had to enucleate five eyes after helium ion therapy either because of continued tumor growth (four patients) or other complications (one patient). Two melanomas continued to grow and seemed to be radioresistant. In two other tumors it retrospectively seemed that the entire lesion was not inside the radiation field. In one patient total retinal detachment and glaucoma developed; enucleation was performed because of a painful eye. Metastatic disease developed in no patients. The treatment failures emphasize that there are a number of unresolved issues regarding the use of charged-particle irradiation in the treatment of melanoma. Further studies must be performed to answer these questions and better delineate the use of these newer forms of therapy.

Char, D.H.; Crawford, J.B.; Castro, J.R.; Woodruff, K.H.

1983-02-01

276

Failure of choroidal melanoma to respond to helium ion therapy  

International Nuclear Information System (INIS)

Helium ion irradiation is a promising alternative therapy for choroidal melanoma. In short-term follow-up (less than 5 years), more than 90% (18/19) of treated patients demonstrated tumor regression. Researchers had to enucleate five eyes after helium ion therapy either because of continued tumor growth (four patients) or other complications (one patient). Two melanomas continued to grow and seemed to be radioresistant. In two other tumors it retrospectively seemed that the entire lesion was not inside the radiation field. In one patient total retinal detachment and glaucoma developed; enucleation was performed because of a painful eye. Metastatic disease developed in no patients. The treatment failures emphasize that there are a number of unresolved issues regarding the use of charged-particle irradiation in the treatment of melanoma. Further studies must be performed to answer these questions and better delineate the use of these newer forms of therapy

277

Helium thermodesorption mechanism from irradiated boron carbide  

International Nuclear Information System (INIS)

The boron carbide powder, the particle size whereof constitutes about 10 ?m, is used as the WWER-1000 reactor absorption core. The model of the helium atoms activation yield from the accumulation centers and their diffusion to the surface of the boron carbide powder spherical particle is proposed. The evaluation of the helium yield from the material in the process of annealing is obtained. The effect of the powder grains size and change in the material temperature velocity on the helium thermodesorption from the irradiated boron carbide is evaluated

278

Kilohertz laser ablation for doping helium nanodroplets  

International Nuclear Information System (INIS)

A new setup for doping helium nanodroplets by means of laser ablation at kilohertz repetition rate is presented. The doping process is characterized and two distinct regimes of laser ablation are identified. The setup is shown to be efficient and stable enough to be used for spectroscopy, as demonstrated on beam depletion spectra of lithium atoms attached to helium nanodroplets. For the first time, helium droplets are doped with high temperature refractory materials such as titanium and tantalum. Doping with the nonvolatile DNA basis guanine is found to be efficient and a number of oligomers are detected

279

Helium desorption from a (110) Mo crystal  

International Nuclear Information System (INIS)

Helium desorption measurements with a Mo-crystal show that during stage III annealing vacancies are removed but that vacancies containing helium (HeV), which are immobile, are not affected. Since interstitials injected at room temperature do recombine with HeV's, it seems that, in stage III, vacancies become mobile and interstitials remain trapped (in e.g. clusters). These observations are supported by atomistic calculations. Measured desorption energies of helium from vacancies in Mo show good agreement with the calculated energies. (author)

280

Kilohertz laser ablation for doping helium nanodroplets  

CERN Document Server

A new setup for doping helium nanodroplets by means of laser ablation at kilohertz repetition rate is presented. The doping process is characterized and two distinct regimes of laser ablation are identified. The setup is shown to be efficient and stable enough to be used for spectroscopy, as demonstrated on beam-depletion spectra of lithium atoms attached to helium nanodroplets. For the first time, helium droplets are doped with high temperature refractory materials such as titanium and tantalum. Doping with the non-volatile DNA basis Guanine is found to be efficient and a number of oligomers are detected.

Mudrich, M; Müller, S; Dvorak, M; Buenermann, O; Stienkemeier, F

2007-01-01

 
 
 
 
281

Evolution of dopant-induced helium nanoplasmas  

CERN Document Server

Two-component nanoplasmas generated by strong-field ionization of doped helium nanodroplets are studied in a pump-probe experiment using few-cycle laser pulses in combination with molecular dynamics simulations. High yields of helium ions and a pronounced, droplet size-dependent resonance structure in the pump-probe transients reveal the evolution of the dopant-induced helium nanoplasma. The pump-probe dynamics is interpreted in terms of strong inner ionization by the pump pulse and resonant heating by the probe pulse which controls the final charge states detected via the frustration of electron-ion recombination.

Krishnan, S R; Fechner, L; Sharma, V; Kremer, M; Fischer, B; Camus, N; Pfeifer, T; Jha, J; Krishnamurthy, M; Schroeter, C -D; Ullrich, J; Stienkemeier, F; Moshammer, R; Fennel, Th; Mudrich, M

2012-01-01

282

Molecular dynamics simulations of the diffusion and coalescence of helium in tungsten  

Energy Technology Data Exchange (ETDEWEB)

Molecular dynamics (MD) simulations are performed on the diffusion and coalescence of helium in tungsten. A new method for determining the effective capture radii (ECRs) and the dissociation energies of helium-related defects is proposed in this work. It is observed that the ECR of an interstitial helium atom trapping helium interstitials (denoted as He–He{sub n}, n = 1–3) decreases with increasing temperature, except for He–He{sub 2} at T < 400 K. The traditional view that the ECR is approximately equal to the lattice constant, which has been widely used in kinetic Monte Carlo (KMC) and rate theory (RT) models, is only valid in some cases. However, the ECR between an interstitial helium atom and a substitutional helium atom (denoted as He–HeV) always approximates the third nearest-neighbor tetrahedral positions of the HeV. The diffusion coefficients D{sub n} for helium clusters are also investigated. He{sub 2} migrates more quickly than a single He atom does at T < 400 K, whereas the diffusion path of He{sub 2} changes at higher temperatures. Another counterintuitive observation is that D{sub 5} > D{sub 3} > D{sub 4} at T < 500 K, which can be attributed to the disordered structure of He{sub 5}. The Arrhenius relation describes the diffusion of He{sub n} well in the temperature range from 300 K to 550 K, whereas the diffusion is not a standard thermally activated process at higher temperatures. Taken together, these results help elucidate the initial stage of helium bubble formation in tungsten as well as the requirements of long-term evolution methods such as KMC or RT models.

Zhou, Y.L. [Key Lab for Radiation Physics and Technology, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064 (China); Department of Physics, Guangxi University, Nanning 530004 (China); Wang, J. [Key Lab for Radiation Physics and Technology, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064 (China); Hou, Q., E-mail: qhou@scu.edu.cn [Key Lab for Radiation Physics and Technology, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064 (China); Deng, A.H. [Department of Physics, Sichuan University, Chengdu 610064 (China)

2014-03-15

283

Photoionization Energies and Oscillator Strengths of Helium and Helium-like Ions  

Science.gov (United States)

We first studied the resonant photoionization of helium-like ions, such as C4+, N5+, and O6+, and determined the wave functions, the excitation energies, and the partial and total widths of the autoionizing states of these ions lying under the n = 3 thresholds of the residual ion. For more detailed analysis of the theory, and a better comprehension of the internal dynamics of atomic resonances and electronic phenomena of correlation, we extended these calculations to other helium-like ions, under higher thresholds (n = 4 and 5) of the hydrogen ions H-, and of Li+, C4+, N5+, and O6+. We were also interested in oscillator strengths. These parameters are important for interpreting the spectra and diagnosing astrophysical and laboratory plasmas, as well as for analyzing the spectra coming from space and determining the composition and relative abundance from the various elements of the stellar and interstellar environment. We sought a better comprehension of the coupling between autoionizing and continuum states and of the phenomena of electronic correlations. We used the method of diagonalization that has been used below the n = 2 threshold of the residual ion. The results are important for astrophysicists and physicists studying matter-radiation interaction and for the invention of new laser systems. We also measured laser-induced chlorophyll fluorescence (LICF) emission spectra of the leaves of some tropical plants using a compact fiber-optic fluorosensor with a continuous-wave violet diode laser as the exciting source and an integrated digital spectrometer to analyze the state of stress of the plants.

Faye, N. A. B.; Ndao, A. S.; Konte, A.; Biaye, M.; Wague, A.

2005-10-01

284

Molecular dynamics simulations of cumulative helium bombardments on tungsten surfaces  

Science.gov (United States)

Molecular dynamics simulations were performed to study the cumulative bombardments of low-energy (60-200 eV) helium atoms on tungsten surfaces. The behaviour of helium and the response of tungsten surface were investigated. The helium incident energy and tungsten temperature play important roles on the formation and growth of helium clusters. The temperature can promote the coalescence of helium clusters and increase the size of the helium clusters. The rupture of the helium clusters has also been observed. During the formation of helium clusters, the interstitial tungsten atoms are produced and evolve into bundles of crowdions, which would be constrained around the helium clusters for a long time. However, they will finally move onto the top surface along the direction, which results in stacking the tungsten atoms on the surface. The complex combination effects of the helium clusters and the interstitial atoms result in the growth of the surfaces. Besides, several tungsten atoms were ejected from tungsten surfaces.

Li, Min; Cui, Jiechao; Wang, Jun; Hou, Qing

2014-10-01

285

Lightweight Liquid Helium Dewar for High-Altitude Balloon Payloads  

Science.gov (United States)

Astrophysical observations at millimeter wavelengths require large (2-to-5- meter diameter) telescopes carried to altitudes above 35 km by scientific research balloons. The scientific performance is greatly enhanced if the telescope is cooled to temperatures below 10 K with no emissive windows between the telescope and the sky. Standard liquid helium bucket dewars can contain a suitable telescope for telescope diameter less than two meters. However, the mass of a dewar large enough to hold a 3-to-5-meter diameter telescope would exceed the balloon lift capacity. The solution is to separate the functions of cryogen storage and in-flight thermal isolation, utilizing the unique physical conditions at balloon altitudes. Conventional dewars are launched cold: the vacuum walls necessary for thermal isolation must also withstand the pressure gradient at sea level and are correspondingly thick and heavy. The pressure at 40 km is less than 0.3% of sea level: a dewar designed for use only at 40 km can use ultra thin walls to achieve significant reductions in mass. This innovation concerns new construction and operational techniques to produce a lightweight liquid helium bucket dewar. The dewar is intended for use on high-altitude balloon payloads. The mass is low enough to allow a large (3-to-5-meter) diameter dewar to fly at altitudes above 35 km on conventional scientific research balloons without exceeding the lift capability of the balloon. The lightweight dewar has thin (250- micron) stainless steel walls. The walls are too thin to support the pressure gradient at sea level: the dewar launches warm with the vacuum space vented continuously during ascent to eliminate any pressure gradient across the walls. A commercial 500-liter storage dewar maintains a reservoir of liquid helium within a minimal (hence low mass) volume. Once a 40-km altitude is reached, the valve venting the vacuum space of the bucket dewar is closed to seal the vacuum space. A vacuum pump then evacuates the dewar vacuum space to provide the necessary thermal isolation. Liquid helium may then be transferred from the storage dewar into the bucket dewar to cool the telescope inside the bucket dewar. By splitting the functions of helium storage and in-flight thermal isolation, the parasitic mass associated with the dewar pressure vessel is eliminated to achieve factor-of-five or better reduction in mass. The lower mass allows flight on conventional scientific research balloons, even for telescopes 3 to 5 meters in diameter.

Kogut, Alan; James, Bryan; Fixsen, Dale

2013-01-01

286

Helium trapping and surface deformation of helium-ion-implanted aluminium  

International Nuclear Information System (INIS)

Helium ions accelerated to 20 keV were implanted into Al samples at room temperature. The formation of blisters and flakes at the surface was observed as a function of He+ irradiation fluence by scanning electron microscopy and the number of He trapped in the Al was also determined. To examine the influence of microstructure studies were carried out for 4000C, 2 h (well-annealed) samples, 3000C, 0.5 h (moderately-annealed) samples, and compared to previous results for as-received (cold-rolled) Al. The number of trapped He varies in a saw-toothed form with He ion fluence for the samples with flakes and the surface deformation is predominantly by flaking for the well-annealed samples. The moderately-annealed samples undergo blistering and flaking. Results are discussed from the viewpoint of a correlation between the predominant surface deformation mode and the near-surface microstructural condition. (orig.)

287

Helium abundance enhancements in the solar wind  

Science.gov (United States)

Evidence for a link between helium enhancements at 1 AU and transient coronal mass ejections is provided by the statistical analysis of 73 large helium abundance enhancement observations made by IMPs 6, 7 and 8 over 1972-1978. These events, in which helium abundance enhancement is greater than about 10%, are sporadic, sometimes clustered in time, occur approximately in phase with the solar cycle, and nearly 50% of them are associated with interplanetary shocks and/or geomagnetic activity sudden commencements. The plasma pattern associated with them is nevertheless independent of shock occurrence, and features high magnetic field strength, low alpha-proton velocity difference, and low proton temperature, suggesting that the enhancement is embedded in a closed, magnetically dominated structure that expands adiabatically. Evidence of an association between helium enhancement at 1 AU and type II and IV radio bursts in the corona is presented.

Borrini, G.; Gosling, J. T.; Bame, S. J.; Feldman, W. C.

1982-01-01

288

Development of charcoal sorbents for helium cryopumping  

International Nuclear Information System (INIS)

Testing of the cryogenically cooled charcoal using fusion-compatible binders for pumping helium has shown promising results. The program demonstrated comparable or improved performance with these binders compared to the charcoal (type and size) using an epoxy binder

289

Development of charcoal sorbents for helium cryopumping  

Energy Technology Data Exchange (ETDEWEB)

Testing of the cryogenically cooled charcoal using fusion-compatible binders for pumping helium has shown promising results. The program demonstrated comparable or improved performance with these binders compared to the charcoal (type and size) using an epoxy binder.

Sedgley, D.W.; Tobin, A.G.

1984-01-01

290

Study of processes of insulation vacuum failure in helium cryostats  

International Nuclear Information System (INIS)

A setup with a helium cryostat was constructed and processes of insulation vacuum failure in the cryostat were studied. In this case the types of insulation in a helium vessel, the pressure of opening a safety valve, hole for a helium injection into the insulation space and other parameters were changed. Maximum specific heat influxes to the liquid helium were determined for the cases typical for the operation with helium cryostats

291

Cosmogenic helium in a terrestrial igneous rock  

International Nuclear Information System (INIS)

The author presents new helium isotopic measurements on samples from the Kula formation of Haleakala volcano (Hawaii) that are best explained by an in situ cosmogenic origin for a significant fraction of the 3He. Results from crushing and stepwise heating experiments, and consideration of the exposure age of the sample at the surface and the cosmic-ray fluxes strongly support this hypothesis. Although crustal cosmogenic helium has been proposed previously, this represents its first unambiguous identification in a terrestrial sample. (author)

292

Explosive helium burst in thermal spring emanations  

International Nuclear Information System (INIS)

An observation has been made of an explosive helium burst showing an anomalous concentration of helium of ?61.6 vol% compared to the ?1.4 vol% normally present in the thermal spring gas emanations at Bakreswar, West Bengal. This elevated level, along with deuterium ?1.7 vol%, has been observed for the first time in a gas chromatograph. Attempts have been made to correlate the observations, as a precursory signal, with some recent major tectonic disturbances

293

Explosive helium burst in thermal spring emanations  

Energy Technology Data Exchange (ETDEWEB)

An observation has been made of an explosive helium burst showing an anomalous concentration of helium of {approx}61.6 vol% compared to the {approx}1.4 vol% normally present in the thermal spring gas emanations at Bakreswar, West Bengal. This elevated level, along with deuterium {approx}1.7 vol%, has been observed for the first time in a gas chromatograph. Attempts have been made to correlate the observations, as a precursory signal, with some recent major tectonic disturbances.

Das, Nisith K. [Variable Energy Cyclotron Center, 1/AF Bidhannagar, Kolkata 700064 (India)]. E-mail: nkdas@veccal.ernet.in; Bhandari, Rakesh K. [Variable Energy Cyclotron Center, 1/AF Bidhannagar, Kolkata 700064 (India); Ghose, Debasis [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Sen, Prasanta [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)]. E-mail: psen@anp.saha.ernet.in; Sinha, Bikash [Variable Energy Cyclotron Center, 1/AF Bidhannagar, Kolkata 700064 (India); Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)

2006-01-01

294

Electrons on the surface of liquid helium  

International Nuclear Information System (INIS)

Spectroscopic techniques were used to study transitions of electrons between bound states in the potential well near a helium surface. The charge density distribution of electrons on the surface was independently obtained from electrical measurements. From the measurements, information was obtained both about the interaction of the bound state electrons with the surface of liquid helium and about local disorder in the positions of electrons on the surface

295

Primary neutral helium in the heliosphere  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two years of neutral measurements by IBEX-Lo have yielded several direct observations of interstellar neutral helium and oxygen during preferred viewing seasons. Besides the interstellar signal, there are indications of the presence of secondary neutral helium and oxygen created in the heliosphere. Detailed modeling of these particle species is necessary to connect the measured fluxes to the pristine local interstellar medium while accounting for loss and production of neutr...

Mueller, Hans-reinhard; Cohen, Jill H.

2012-01-01

296

Cosmogenic helium in a terrestrial igneous rock  

Science.gov (United States)

New helium isotopic measurements on samples from the Kula formation of Haleakala volcano of Hawaii are presented that are best explained by an in situ cosmogenic origin for a significant fraction of the He-3. Results from crushing and stepwise heating experiments, and consideration of the exposure age of the sample at the surface and the cosmic ray fluxes strongly support this hypothesis. Although crustal cosmogenic helium has been proposed previously, this represents its first unambiguous identification in a terrestrial sample.

Kurz, M. D.

1986-01-01

297

Helium-propane as drift chamber gas  

International Nuclear Information System (INIS)

A light gas mixture, consisting of helium and propane (0.938 : 0.062) at atmospheric pressure has been tested in a large single-volume drift chamber. Contrary to the general belief that helium cannot be used as a drift gas due to its high ionisation potential, the above mixture was found to have stable operation with spatial resolution of 260+-40 ?m. (orig.)

298

Study of helium diffusion, implanted at a cyclotron, in face-centered cubic metals: Au, Ag and Al  

International Nuclear Information System (INIS)

Helium in metals is produced by nuclear reactions of energetic particles. In nuclear technology the interest on helium in metals is import, due to its production by (n, ?) reaction. Because helium has extremely low solubility in metals, the precipitation in the form of filled bubbles at elevated temperatures occurs, which have detrimental effects on mechanical properties and may limit the lifetime of structural components. One typical example is the high temperature embrittlement. The nucleation and growth of the bubbles strongly depends on the mobility of the helium. This work presents the study of helium diffusion in Au, Ag and Al at temperatures above room temperature. The helium created by (n, ?) reactions has been simulated by homogeneous alpha particles implantation in cyclotron, at room temperature, in specimens of thicknesses between 5 and 50 ?m and helium concentration between 10-3 to 10 ppm. After implantation, the specimens were dropped in a furnace in a UHV-chamber and the diffusion was measured by observing the He-release during linear and isothermal annealings. The occurence of free diffusion was comparing the dependence of release kinetics on helium concentration, sample thickness, time and heating rate to diffusion theory and is clearly separeted from agglomeration process. The diffusion constants of helium in Au, Ag and Al follow an Arrhenius behavior, with: Au:Do=10-1.0 cm2/s ?H=1.70eV Ag:D0=10-1.2cm2/s ?H=1.51eV Al:Do=10+0.5cm2/s ?H=1.40eV. The results are compared to self-diffusion and to the diffusion of other gases in these metals. Comparison with theoretical estimates favours the vacancy mechanism for helium diffusion in Au, Ag and Al. (author)

299

Separation of compressor oil from helium  

International Nuclear Information System (INIS)

Compression of helium by an oil-sealed rorary screw compressor entrains as much as 4000 parts per million by weight of liquid and vapor oil impurities in the gas. The reduction below about 0.1 ppm for cryogenic applications is discussed. Oil seperation equipment designed for compressed air must be modified significantly to produce the desired results with helium. The main differences between air and helium filtration are described. A description of the coalescers is given with the continuous coalescing of liquid mist from air or other gas illustrated. Oil vapor in helium is discussed in terms of typical compressor oils, experimental procedure for measuring oil vapor concentration, measured volatile hydrocarbons in the lubricants, and calculated concentration of oil vapor in Helium. Liquid oil contamination in helium gas can be reduced well below 0.1 ppm by a properly designed multiple state coalescing filter system containing graded efficiency filter elements. The oil vapor problem is best attached by efficiently treating the oil to remove most of the colatiles before charging the compressor

300

THE GREEN BANK TELESCOPE H II REGION DISCOVERY SURVEY. IV. HELIUM AND CARBON RECOMBINATION LINES  

Energy Technology Data Exchange (ETDEWEB)

The Green Bank Telescope H II Region Discovery Survey (GBT HRDS) found hundreds of previously unknown Galactic regions of massive star formation by detecting hydrogen radio recombination line (RRL) emission from candidate H II region targets. Since the HRDS nebulae lie at large distances from the Sun, they are located in previously unprobed zones of the Galactic disk. Here, we derive the properties of helium and carbon RRL emission from HRDS nebulae. Our target sample is the subset of the HRDS that has visible helium or carbon RRLs. This criterion gives a total of 84 velocity components (14% of the HRDS) with helium emission and 52 (9%) with carbon emission. For our highest quality sources, the average {sup 4}He{sup +}/H{sup +} abundance ratio by number, (y {sup +}), is 0.068 {+-} 0.023(1{sigma}). This is the same ratio as that measured for the sample of previously known Galactic H II regions. Nebulae without detected helium emission give robust y {sup +} upper limits. There are 5 RRL emission components with y {sup +} less than 0.04 and another 12 with upper limits below this value. These H II regions must have either a very low {sup 4}He abundance or contain a significant amount of neutral helium. The HRDS has 20 nebulae with carbon RRL emission but no helium emission at its sensitivity level. There is no correlation between the carbon RRL parameters and the 8 {mu}m mid-infrared morphology of these nebulae.

Wenger, Trey V.; Bania, T. M. [Astronomy Department, 725 Commonwealth Avenue, Boston University, Boston, MA 02215 (United States); Balser, Dana S. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA, 22903-2475 (United States); Anderson, L. D. [Department of Physics, West Virginia University, Morgantown, WV 26506 (United States)

2013-02-10

 
 
 
 
301

Cryogenic infrastructure for superfluid helium testing of LHC prototype superconducting magnets  

International Nuclear Information System (INIS)

The Large Hadron Collider (LHC) project at CERN will require about 1800 high-field superconducting magnets, operating below 1.9 K in pressurized helium II. All magnets will be reception-tested before their installation in the 26.7 km circumference ring tunnel. For this purpose, the authors have installed large-capacity cryogenic facilities, beginning to operate for tests of full-scale prototype magnets produced by European industry. Based around a 6 kW at sign 4.5 K helium refrigerator and a 25 m3 liquid helium storage, the system includes a low-pressure, 6 to 18 g/s helium pumping unit for 1.8 K refrigeration, a set of magnet cooldown and warmup units delivering each up to 120 kW of refrigeration at precisely controlled temperature, and a network of cryogenic lines for transferring liquid nitrogen, liquid helium and cold gaseous helium. All components are controlled by embedded PLCs, connected to a general supervision system for operator interface. The authors present the system layout and describe the design and performance of the main components

302

Cryogenic infrastructure for superfluid helium testing of LHC prototype superconducting magnets  

Energy Technology Data Exchange (ETDEWEB)

The Large Hadron Collider (LHC) project at CERN will require about 1800 high-field superconducting magnets, operating below 1.9 K in pressurized helium II. All magnets will be reception-tested before their installation in the 26.7 km circumference ring tunnel. For this purpose, the authors have installed large-capacity cryogenic facilities, beginning to operate for tests of full-scale prototype magnets produced by European industry. Based around a 6 kW@4.5 K helium refrigerator and a 25 m{sup 3} liquid helium storage, the system includes a low-pressure, 6 to 18 g/s helium pumping unit for 1.8 K refrigeration, a set of magnet cooldown and warmup units delivering each up to 120 kW of refrigeration at precisely controlled temperature, and a network of cryogenic lines for transferring liquid nitrogen, liquid helium and cold gaseous helium. All components are controlled by embedded PLCs, connected to a general supervision system for operator interface. The authors present the system layout and describe the design and performance of the main components.

Benda, V.; Duraffour, G.; Guiard-Marigny, A.; Lebrun, Ph.; Momal, F.; Saban, R.; Sergo, V.; Tavian, L.; Vullierme, B. [CERN, Geneva (Switzerland)

1994-12-31

303

Results of radon and helium surveys at three known uranium occurrences  

International Nuclear Information System (INIS)

Radon and helium measurements in near-surface soil were performed over detailed (1.5 km2) and subregional (40 km2) areas at three known uranium occurrences. The detailed survey results at these sites indicated anomalously high radon and helium concentrations which appeared to correspond to the known mineralization at depth. The radon and helium patterns for the subregional areas at two sites were different, and did not indicate the known mineralization. The radon patterns were controlled by lithology and the radium concentration of the soil. Anomalous helium areas were related to structure. At the third site, the radon and helium patterns over the subregional area, though different, were basically mapping lithology, and the known deposit appeared as a subtle anomaly for both radon and helium. Since radon located the deposit for both detailed and subregional sampling surveys at this site, core from the surface to the deposit was analyzed for extractable polonium-210, a long-lived decay product of radon. These measurements indicated that radon does not migrate very far from its source

304

Study of heat transfer in superconducting cable electrical insulation of accelerator magnet cooled by superfluid helium  

International Nuclear Information System (INIS)

Heat transfer studies of electrical cable insulation in superconducting winding are of major importance for stability studies in superconducting magnets. This work presents an experimental heat transfer study in superconducting cables of Large Hadron Collider dipoles cooled by superfluid helium and submitted to volume heat dissipation due to beam losses. For NbTi magnets cooled by superfluid helium the most severe heat barrier comes from the electrical insulation of the cables. Heat behaviour of a winding is approached through an experimental model in which insulation characteristics can be modified. Different tests on insulation patterns show that heat transfer is influenced by superfluid helium contained in insulation even for small volume of helium (2 % of cable volume). Electrical insulation can be considered as a composite material made of a solid matrix with a helium channels network which cannot be modelled easily. This network is characterised by another experimental apparatus which allows to study transverse and steady-state heat transfer through an elementary insulation pattern. Measurements in Landau regime (?T?10-5 to 10-3 K) and in Gorter-Mellink regime (?T>10-3 K) and using assumptions that helium thermal paths and conduction in the insulation are decoupled allow to determine an equivalent channel area (10-6 m2) and an equivalent channel diameter (25 ?). (author)

305

Helium exhaust studies with the ALT-II pump limiter in TEXTOR  

International Nuclear Information System (INIS)

In TEXTOR helium removal experiments with the pump-limiter ALT-1I have started. To simulate the presence of helium ash in the plasma, helium is injected into the discharge (e.g. at t=0.7 s) as a short pulse of ?t=20 ms. It is found that the He is removed from the discharge in an e-folding time of about half a second for neutral beam heated plasmas and in an e-folding time of about 1.5 s in an OH plasma. The exhaust efficiency of helium amounts to about 8% and is close to the one for deuterium. The fuelling efficiency for the injected helium is found to be in the range of 50-100%; the remaining part seems to be stored in the TEXTOR walls. An estimate of the surface density leads to a value of several times 1013 cm-2. This helium can easily be liberated in succeeding discharges and can be removed efficiently when ALT is pumping. (orig.)

306

Helium exhaust studies with the ALT-II pump limiter in TEXTOR  

Science.gov (United States)

In TEXTOR helium removal experiments with the pump-limiter ALT-II have started. To simulate the presence of helium ash in the plasma, helium is injected into the discharge (e.g. at t = 0.7s) as a short pulse of ? t = 20ms. It is found that the He is removed from the discharge in an e-folding time of about half a second for neutral beam heated plasmas and in an e-folding time of about 1.5 s in an OH plasma. The exhaust efficiency of helium amounts to about 8% and is close to the one for deuterium. The fuelling efficiency for the injected helium is found to be in the range of 50-100%; the remaining part seems to be stored in the TEXTOR walls. An estimate of the surface density leads to a value of several times 10 13 cm -2. This helium can easily be liberated in succeeding discharges and can be removed efficiently when ALT is pumping.

Finken, K. H.; Hillis, D. L.; Dippel, K. H.; Hardtke, A.; Hogan, J. T.; Moyer, R. A.; Pospieszczyk, A.; Rusbüldt, D.; Akaishi, K.; Conn, R. W.; Euringer, H.; Gray, D. S.; Horton, L. D.; Hulse, R. A.; Isler, R. C.; Klepper, C. C.; Mioduszewski, P. K.; Miyahara, A.; Sengoku, S.; Watkins, J. G.; Wolf, G. H.

1990-12-01

307

A Catalog of Helium Abundance Determinations from Globular Cluster Photometry  

Science.gov (United States)

We provide a comprehensive list of re-determinations of the values for the helium abundance indicators R =NHB/NRGB, A (the exponent of the mass-luminosity relation for RR Lyraes), and Delta (the magnitude difference between the HB and the main sequence at (B-V)0 = 0.7) for globular clusters in the Milky Way and Magellanic Clouds as well as nearby dwarf spheroidals. This study corrects a prevalent error in the determination of R, and provides a more comprehensive error analysis for all three indicators. We attempt to correlate the indicators to identify anomalous abundances in spite of shortcomings in each indicator. From the R determinations, we identify 6 clusters which show high values, possibly as a result of environmental factors --- each cluster has a galactocentric radius of less than 7 kpc, and 5 of the 6 appear to be post-core-collapse. From A values, all indications point toward a constant helium abundance of Y~0.23 for virtually all Oosterhoff class I clusters. In general, uncertainties in reddening determinations must be reduced in order to improve the worth of the Delta indicator, which is the most sensitive to helium.

Sandquist, E.

1997-12-01

308

Helium research in support of superconducting power transmission  

Energy Technology Data Exchange (ETDEWEB)

During FY 77, research for Superconducting Power Transmission Line (SPTL) development included the following four research tasks: preparation of computer codes for the computation of cooldown by either single stream or counterstream methods; experimental verification of cooldown computations with emphasis on counterstream cooling; thermal cycling of a length of lead-sheathed model cable destined for testing in the BNL 5th Avenue facility; and evaluation of heat flow sensors as a means of non-intrusive vacuum indication for power transmission line vacuum envelopes. A series of progress reports on these four tasks are presented, with 6 appendicies on: experimental observations of flow oscillations in a high aspect ratio heated tube with supercritical helium as coolant; the results of a study of friction factors measured in the same apparatus as was used in Appendix 1; results of a numerical study of the response of SPTL current leads to overload currents; the microwave cavity pressure transducer developed at NBS for SPTL application; a correlation of heat transfer data to supercritical helium in forced convection; and a pressure regulator designed and used in controlling the pressure of cryogenic helium at supercritical pressures.

Jones, M. C. [ed.

1979-04-01

309

Helium irradiation effects on deuterium retention in tungsten  

Energy Technology Data Exchange (ETDEWEB)

To investigate effects of helium irradiation on deuterium retention properties in tungsten, thermal desorption spectroscopy of deuterium from a specimen irradiated with a sequential irradiation of 3 keV helium and 1.5 keV deuterium ions at room temperature was measured and the related microstructure was observed by transmission electron microscopy. It was found that pre-irradiation of 3 keV He{sup +} ions to fluences of 1.0 × 10{sup 21}–1.0 × 10{sup 22} He{sup +}/m{sup 2} increased, while the retention of deuterium drastically decreased above the fluences of 1.0 × 10{sup 23} He{sup +}/m{sup 2}. A similar reduction of deuterium retention was also observed by the pre-exposure of the specimen to a very low energy (?10 eV) and high fluence helium plasma. The reduction effects on deuterium retention are discussed in terms of the formation of linked or interconnected structure of bubbles, which could create an easy release and diffusion path for deuterium desorption.

Sakoi, Yuki [Department of Material Science, Shimane University, Matsue, Shimane 690-8504 (Japan); Miyamoto, Mitsutaka, E-mail: miyamoto@riko.shimane-u.ac.jp [Department of Material Science, Shimane University, Matsue, Shimane 690-8504 (Japan); Ono, Kotaro [Department of Material Science, Shimane University, Matsue, Shimane 690-8504 (Japan); Sakamoto, Mizuki [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan)

2013-11-15

310

Hydrogen and helium in the spectra of Type Ia supernovae  

CERN Document Server

We present predictions for hydrogen and helium emission line luminosities from circumstellar matter around Type Ia supernovae (SNe Ia) using time dependent photoionization modeling. ESO/VLT optical echelle spectra of the SN Ia 2000cx were taken before and up to 70 days after maximum. We detect no hydrogen and helium lines, and place an upper limit on the mass loss rate for the putative wind of less than 1.3EE{-5} solar masses per year, assuming a speed of 10 km/s and solar abundances for the wind. In a helium-enriched case, the best line to constrain the mass loss would be He I 10,830 A. We confirm the details of interstellar Na I and Ca II absorption towards SN 2000cx as discussed by Patat et al., but also find evidence for 6613.56 A Diffuse Interstellar Band (DIB) absorption in the Milky Way. We discuss measurements of the X-ray emission from the interaction between the supernova ejecta and the wind and we re-evaluate observations of SN 1992A obtained 16 days after maximum by Schlegel & Petre. We find a...

Lundqvist, Peter; Sollerman, Jesper; Kozma, Cecilia; Baron, E; Cox, Nick L J; Fransson, Claes; Leibundgut, Bruno; Spyromilio, Jason

2013-01-01

311

Helium, hydrogen, and oxygen velocities observed in ISEE 3  

International Nuclear Information System (INIS)

The velocities of helium, oxygen, and hydrogen ions have been recorded over a full range of solar wind conditions by the ion composition instrument (ICI) and Los Alamos National Laboratory plasma instrument (LANLPI), respectively, aboard the ISEE 3 spacecraft between August 1978 and December 1979. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s-1 the velocity exceeded the hydrogen velocity by 5 km s-1 on the average. For solar wind velocities between 400 and 500 km s-1 the average difference was 14 km s-1; however, no evidence was found for a systematic nonzero average difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Helium-hydrogen velocity differences are generally bounded by the Alfven speed. Velocity differences show abrupt changes across interplanetary discontinuities, persumably tangential. Differences between the speeds of differently charged minor ions appear also to result from the electrostatic potential differences across the interplanetary shocks. The potential difference, calculated from the energy jump condition for a perpendicular hydromagnetic shock, is of the correct magnitude to produce the observed effects

312

Helium irradiation effects on deuterium retention in tungsten  

Science.gov (United States)

To investigate effects of helium irradiation on deuterium retention properties in tungsten, thermal desorption spectroscopy of deuterium from a specimen irradiated with a sequential irradiation of 3 keV helium and 1.5 keV deuterium ions at room temperature was measured and the related microstructure was observed by transmission electron microscopy. It was found that pre-irradiation of 3 keV He+ ions to fluences of 1.0 × 1021-1.0 × 1022 He+/m2 increased, while the retention of deuterium drastically decreased above the fluences of 1.0 × 1023 He+/m2. A similar reduction of deuterium retention was also observed by the pre-exposure of the specimen to a very low energy (˜10 eV) and high fluence helium plasma. The reduction effects on deuterium retention are discussed in terms of the formation of linked or interconnected structure of bubbles, which could create an easy release and diffusion path for deuterium desorption.

Sakoi, Yuki; Miyamoto, Mitsutaka; Ono, Kotaro; Sakamoto, Mizuki

2013-11-01

313

Photoionization rates for helium: update  

CERN Document Server

The NIS He gas has been observed at a few AU to the Sun almost from the beginning of the space age. To model its flow an estimate of the loss rates due to ionization by solar extreme-ultraviolet (EUV) flux is needed. The EUV irradiance has been measured directly from mid 1990-ties, but with high temporal and spectral resolution only from 2002. Beforehand only EUV proxies are available. A new method of reconstruction of the Carrington rotation averaged photoionization rates for neutral interstellar helium (NIS He) in the ecliptic at 1 AU to the Sun before 2002 is presented. We investigate the relation between the solar rotation averaged time series of the ionization rates for NIS He at 1 AU derived from TIMED measurements of EUV irradiance and the solar 10.7 cm flux (F10.7) only. We perform a weighted iterative fit of a nonlinear model to data split into sectors. The obtained formula allows to reconstruct the solar rotation averages of photoionization rates for He between ~1947 and 2002 with an uncertainty ran...

Sokó?, Justyna M

2014-01-01

314

Time characteristics of neon and helium spontaneous emission  

International Nuclear Information System (INIS)

Results of investigation are presented of time characteristics of neon and helium spontaneous emission at different pressures and component relations. A discharge tube of 12 mm internal diameter and of 100 cm discharge gap length was used. Gas was excited by current pulses of about 2 mks in duration and at repetition rate of 1 kHz. The spectral composition of the emission and its time characteristics were detected by a diffraction monochromator, a photomultiplier and an oscillograph. Under investigation was spontaneous emission only from those neon levels that were operating levels for laser transitions. In helium transitions on the level 23S were studied, as a result of which emitted wavelengths are 388.8; 706.5 and 1083.0 nm. The neon levels 2S and 2p at the pressure below 1 mm Hg are shown to be weanly polulated in the period of afterglow. During the excitation pulse the highest rate of population is observed in the level 2 P1. The helium levels 33P, 33S and 23P are densely populated during afterglow at the pressures below a 1 mm Hg. The level 33S during afterglow is populated more densely than during the excitation pulse due to the predominating role of recombination processes. When helium is added, the population of the neon levels 2S and 2p during afterglow increases, The inverse population on neon levels during the excitation is considerably affected by different rates of populating the 2S and 2Pifferent rates of populating the 2S and 2P neon levels, and during afterglow- by deactivation of of 2P levels

315

Investigation of Cellular Interactions of Nanoparticles by Helium Ion Microscopy  

Energy Technology Data Exchange (ETDEWEB)

The helium ion mircroscope (HIM) probes light elements (e.g. C, N, O, P) with high contrast due to the large variation in secondary electron yield, which minimizes the necessity of specimen staining. A defining characteristic of HIM is its remarkable capability to neutralize charge by the implementation of an electron flood gun, which eliminates the need for coating non-conductive specimens for imaging at high resolution. In addition, the small convergence angle in HeIM offers a large depth of field (~5x FE-SEM), enabling tall structures to be viewed in focus within a single image. Taking advantage of these capabilities, we investigate the interactions of engineered nanoparticles (NPs) at the surface of alveolar type II epithelial cells grown at the air-liquid interface (ALI). The increasing use of nanomaterials in a wide range of commercial applications has the potential to increase human exposure to these materials, but the impact of such exposure on human health is still unclear. One of the main routs of exposure is the respiratory tract, where alveolar epithelial cells present a vulnerable target at the interface with ambient air. Since the cellular interactions of NPs govern the cellular response and ultimately determine the impact on human health, our studies will help delineating relationships between particle properties and cellular interactions and response to better evaluate NP toxicity or biocompatibility. The Rutherford backscattered ion (RBI) is a helium ions imaging mode, which backscatters helium ions from every element except hydrogen, with a backscatter yield that depends on the atomic number of the target. Energy-sensitive backscatter analysis is being developed, which when combined with RBI image information, supports elemental identification at helium ion nanometer resolution. This capability will enable distinguishing NPs from cell surface structures with nanometer resolution.

Arey, Bruce W.; Shutthanandan, V.; Xie, Yumei; Tolic, Ana; Williams, Nolann G.; Orr, Galya

2011-06-01

316

Investigation of cellular interactions of nanoparticles by helium ion microscopy  

Science.gov (United States)

The helium ion microscope (HIM) probes light elements (e.g. C, N, O, P) with high contrast due to the large variation in secondary electron yield, which minimizes the necessity of specimen staining. A defining characteristic of HIM is its remarkable capability to neutralize charge by the implementation of an electron flood gun, which eliminates the need for coating non-conductive specimens for imaging at high resolution. In addition, the small convergence angle in HeIM offers a large depth of field (~5× FE-SEM), enabling tall structures to be viewed in focus within a single image. Taking advantage of these capabilities, we investigate the interactions of engineered nanoparticles (NPs) at the surface of alveolar type II epithelial cells grown at the airliquid interface (ALI). The increasing use of nanomaterials in a wide range of commercial applications has the potential to increase human exposure to these materials, but the impact of such exposure on human health is still unclear. One of the main routs of exposure is the respiratory tract, where alveolar epithelial cells present a vulnerable target at the interface with ambient air. Since the cellular interactions of NPs govern the cellular response and ultimately determine the impact on human health, our studies will help delineating relationships between particle properties and cellular interactions and response to better evaluate NP toxicity or biocompatibility. The Rutherford backscattered ion (RBI) is a helium ions imaging mode, which backscatters helium ions from every element except hydrogen, with a backscatter yield that depends on the atomic number of the target. Energy-sensitive backscatter analysis is being developed, which when combined with RBI image information, supports elemental identification at helium ion nanometer resolution. This capability will enable distinguishing NPs from cell surface structures with nanometer resolution.

Arey, B. W.; Shutthanandan, V.; Xie, Y.; Tolic, A.; Williams, N.; Orr, G.

2011-06-01

317

COSMIC-RAY PROTON AND HELIUM SPECTRA FROM THE FIRST CREAM FLIGHT  

International Nuclear Information System (INIS)

Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ?38.5 km with an average atmospheric overburden of ?3.9 g cm-2. Individual elements are clearly separated with a charge resolution of ?0.15 e (in charge units) and ?0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 ± 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 ± 0.02 for helium nuclei from 630 GeV nucleon-1 to 63 TeV nucleon-1. They are harder than previous measurements at a few tens of GeV nucleon-1. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 ± 0.5 for the range from 2.5 TeV nucleon-1 to 63 TeV nucleon-1. This ratio is considerably smaller than the previous measurements at a few tens of GeV nucleon-1.

318

Cosmic-Ray Proton and Helium Spectra from the First CREAM Flight  

CERN Document Server

Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ~38.5 km with an average atmospheric overburden of ~3.9 g cm$^{-2}$. Individual elements are clearly separated with a charge resolution of ~0.15 e (in charge units) and ~0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 $\\pm$ 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 $\\pm$ 0.02 for helium nuclei from 630 GeV/nucleon to 63 TeV/nucleon. They are harder than previous measurements at a few tens of GeV/nucleon. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 $\\pm$ 0.5 for the range from 2.5 TeV/nucleon to 63 TeV/...

Yoon, Y S; Allison, P S; Bagliesi, M G; Beatty, J J; Bigongiari, G; Boyle, P J; Childers, J T; Conklin, N B; Coutu, S; DuVernois, M A; Ganel, O; Han, J H; Jeon, J A; Kim, K C; Lee, M H; Lutz, L; Maestro, P; Malinine, A; Marrocchesi, P S; Minnick, S A; Mognet, S I; Nam, S; Nutter, S; Park, I H; Park, N H; Seo, E S; Sina, R; Swordy, S; Wakely, S P; Wu, J; Yang, J; Zei, R; Zinn, S Y; 10.1088/0004-637X/728/2/122

2011-01-01

319

Tritium and helium behavior in irradiated beryllium  

International Nuclear Information System (INIS)

Large quantities of Be (> 100 metric tons) are planned for use in the ITER blanket design to enhance tritium breeding and to act as a thermal barrier between coolant and breeder. Tritium retention/release and He-induced swelling are important issues in blanket design. The data base on tritium and helium behavior in Be is reviewed. New data on tritium retention/release and He bubble growth are presented for Be irradiated to 5 x 1022 n(E > 1 MeV)/cm2 at ?75 degree C and postirradiation-annealed for 700 hours at 500 degree C. A model (diffusion/desorption) is proposed and tested against the data base to determine tritium diffusivity and the desorption rate constant. Similarly a model for He-induced swelling is developed and tested against the data base. The dependence of tritium retention and release on He content and impurities (e.g. BeO) is also explored. 11 refs., 6 figs

320

The Kapitza resistance at the solid helium-copper boundary under heavy thermal loads  

International Nuclear Information System (INIS)

Results are presented of three sets of measurement of the heat conduction at the interface between solid helium and a copper cold conductor in 0.45-1.5 K temperature range. The heat flux through the boundary can be satisfactorily described by Q=A(Tsub(He4)-Tsub(Cu4), where the parameter A weakly depends on the temperature, i.e. the temperature dependence of the Kapitza resistance Rsub(K)=(1/4AT3) is close to the cubic dependence predicted by the acoustic detuning theory. On the other hand the Rsub(K) quantity is by one or two orders of magnitude smaller than that predicted by the theory and, in contrast to the theory, does not depend on the density or sound velosity in helium. A comparison of the resistances at the boundaries between helium and a copper monocrystal or a polycrystalline copper sample shows that the quality of the crystal structure of the copper sample also does not affect Rsub(K). The resistance at the helium-copper boundary is primarily determined by the properties of the surface layer of the copper sample. It unambiguously follows from the fact that Rsub(K) is independent of the helium impedance, which increases 5 times on transition from He 2 to solid helium at 185 atm., and of the degree of perfection of the bulk structure of the copper sample and helium crystals, and also from the considerable change (up to 5 times) of Rsub(K) on substitution of the cold conductor. Plots of the heat conductivity of He4 a the heat conductivity of He4 and He3 crystals prepared from technically pure gases at pressures between 40 and 150 atm. are presented

 
 
 
 
321

Helium diffraction from the GaAs(110) surface and the generation of helium-surface potentials  

Science.gov (United States)

A theoretical analysis of the helium diffraction experiments performed on the GaAs(110) surface by Cardillo, Becker, Sibener, and Miller is presented. Dynamic scattering calculations for several model potentials approximating that of the surface are presented. These suggest that the surface is a smoothly corrugated soft wall with a peak-to-trough distance along the [001] direction of ~ 1 Å and an attractive well depth of ~ 7 meV. Existing methods for generating van der Waals potentials are reviewed and an explanation is suggested for their poor performance in the case of helium. New semiempirical rules fit to the known helium rare-gas potentials and consistent with the recent results of Esjberg and Nørskov are proposed. These are used to construct an approximate potential for GaAs(110), which we show to agree qualitatively with the empirically fit potential. The classical turning-point surface of this potential lies 3.5 Å above the As nucleus. Scattering calculations performed on this potential are shown to agree poorly with experiment. We conclude from this that the scattering is very sensitive to nuances in the potential, and that very accurate surface charge densities will be required before a potential capable of scattering in agreement with experiment can be constructed.

Laughlin, R. B.

1982-02-01

322

Helium diffraction from the GaAs(110) surface and the generation of helium-surface potentials  

International Nuclear Information System (INIS)

A theoretical analysis of the helium diffraction experiments performed on the GaAs(110) surface by Cardillo, Becker, Sibener, and Miller is presented. Dynamic scattering calculations for several model potentials approximating that of the surface are presented. These suggest that the surface is a smoothly corrugated soft wall with a peak-to-trough distance along the [001] direction of approx.1 A and an attractive well depth of approx. 7 meV. Existing methods for generating van der Waals potentials are reviewed and an explanation is suggested for their poor performance in the case of helium. New semiempirical rules fit to the known helium rare-gas potentials and consistent with the recent results of Esjberg and Norskov are proposed. These are used to construct an approximate potential for GaAs(110), which we show to agree qualitatively with the empirically fit potential. The classical turning-point surface of this potential lies 3.5 A above the As nucleus. Scattering calculations performed on this potential are shown to agree poorly with experiment. We conclude from this that the scattering is very sensitive to nuances in the potential and that very accurate surface charge densities will be required before a potential capable of scattering in agreement with experiment can be constructed

323

Accuracy of helium accumulation fluence monitor  

International Nuclear Information System (INIS)

A He accumulation fluence monitor (HAFM) has been developed for neutron dosimetry and the direct measurement of He production in structural component materials used for fast reactors. As to accuracy of measuring helium atoms by the HAFM measurement system, previous study using He ions implanted samples shows that this system could measure He atoms within 5% error. In order to confirm the measurement accuracy of neutron fluence in the fast reactor, the HAFM samples were irradiated to a total fluence of 1015 - 1017 n/cm2 in the standard fast neutron spectrum field of the Fast Neutron Source Reactor 'YAYOI' at University of Tokyo. Irradiated samples were measured by the HAFM measurement system and the He Atoms Measurement System (HAMS) at Kyushu University, and the measured values were compared with the calculated He productions. The principle results are summarized as follows: (1) It was confirmed that He production in 10B could be measured within 5% error by the HAFM system at the reactor core center or the experimental hole through the blanket where He were produced by neutron of 10 keV - 1 MeV and at Fast Column where He were produced by neutron less than 10 keV. (2) It was also found that He production in 9Be could be measured within 5% at the experimental hole through the blanket. Thus it is expected that Be could be applied to measurements of fast neutron of its energy over 1 MeV. (3) The differences between the measured values by the HAFM measurement system and those by HAMS were less than the experimental error, therefore it was confirmed that the measured values was reliable. (author)

324

Thermal evolution of helium in magnetron sputtered titanium films  

Science.gov (United States)

Helium-containing titanium films synthesized by magnetron sputtering method were investigated using thermal desorption spectrometry (TDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Helium evolution behaviors under thermal treatment from room temperature to 1500 °C were characterized. Four peaks appeared in TDS at around 100, 420, 700, and 1250 °C were identified and attributed to helium desorption from the specimen surface, substitutional helium (helium atom in a vacancy), small HemVn clusters with different helium-to-vacancy ratios, and helium bubbles or voids, respectively. The helium evolution under thermal treatment composed of two coexisting and competing processes, where the faster process dominated in relevant temperature range, i.e. helium diffusion and release at low temperatures, and bubble or void formation at high temperatures. Three characteristic temperatures in TDS were identified in description of the phenomenon.

Zhang, Jinchao; Cheng, Chun; Wu, Erdong; Xiong, Liangyin; Liu, Shi

2014-10-01

325

Helium Exhaust Studies in H-Mode Discharges in the DIII-D Tokamak Using an Argon-Frosted Divertor Cryopump  

International Nuclear Information System (INIS)

The first experiments demonstrating exhaust of thermal helium in a diverted, H-mode deuterium plasma have been performed on the DIII-D tokamak. The helium, introduced via gas puffing, is observed to reach the plasma core, and then is readily removed from the plasma with a time constant of ?10--20 energy-confinement times by an in-vessel cryopump conditioned with argon frosting. Detailed analysis of the helium profile evolution suggests that the exhaust rate is limited by the exhaust efficiency of the pump (?5%) and not by the intrinsic helium-transport properties of the plasma

326

Application of gas chromatographic method in simultaneous measurements of helium, argon and neon concentration in groundwaters  

Science.gov (United States)

Helium concentration in groundwater is a fine indicator in water dating in a range from a hundred to tens of thousands of years. Gas chromatography (GC) measurements of helium can be used as an alternative to mass spectrometry (MS) determinations of 4He for groundwater dating [1]. Argon and neon concentrations mainly serve for determining the temperature of recharge and the air excess which is needed to correct measured values of helium concentration [2] . A chromatographic measurement system of helium, argon and neon concentration in groundwater is presented [3]. Water samples are taken from groundwater with a precise procedure without contamination with air in a special stainless steel vessels of volume equal to 2900 cm3. Helium is extracted from water samples using the head-space method. After enrichment by cryotrap method helium is analyzed in the gas chromatograph equipped with the thermal conductivity detector (TCD) with detection limit of about 2.8 ng He. The helium limit of detection of presented method is 1,2·10-8 cm3STP/gH2O [4]. We are currently working on adapting the method of cryogenic enrichment of helium concentration for simultaneous measurements of the concentration of helium, argon and neon using single sample of groundwater. Neon will be measured with the thermal conductivity detector and capillary column filled with molecular sieve 5A. Argon will be analyzed also with the thermal conductivity detector and packed column filled with molecular sieve 5A. This work was supported by grant No. N N525 3488 38 from the polish National Science Centre. [1] A. Zuber, W. Ci??kowski, K. Ró?a?ski (red.), Tracer methods in hydrogeological studies - a methodological guide. Wroclaw University of Technology Publishing House, Wroclaw, 2007 (in polish). [2] P. Mochalski, Chromatographic method for the determination of Ar, Ne and N2 in water, Ph.D. thesis, Institute of Nuclear Physics Polish Academy of Sciences in Krakow, 2003 (in polish). [3] A. ?urek, P. Mochalski, Use of the gas chromatographic method for the denitrification process assessment in groundwater of the Triassic aquifer in Opole region (southern Poland), Geology, Quarterly, AGH, 36, z.1, 135-148, 2010 (in polish). [4] J. Najman, Development of chromatographic measurement method of helium concentration in groundwater for the purpose of dating in the hydrological issues, Ph.D. thesis, Institute of Nuclear Physics Polish Academy of Sciences in Krakow, 2008, http://www.ifj.edu.pl/SD/rozprawy_dr/rozpr_Najman.pdf?lang=pl(in polish).

Najman, J.; Bielewski, J.; Sliwka, I.

2012-04-01

327

Helium turbo-expander with an alternator: Large helium refrigerator-liquefier system  

Science.gov (United States)

The requirements for practical use of the large scale helium refrigerator system are considered. As a long continuous operation is required, the life time of the system should be approximately as long as that of other electrical machines. The refrigerator should be connected directly to the superconducting system by circulation of coolant (liquid or gaseous helium). In this case, an accident of the refrigerator system causes a fatal breakdown of the full system. The contamination in the circulating helium should be avoided. The efficiency of the refrigerator system should be as high as possible. The control method must be established so that the refrigerator can be operated for a long period by a few operators. A helium turbo-expander with externally pressurized helium gas bearings at the temperature of liquid nitrogen and an alternator as a brake was employed for the investigation.

Akiyama, Y.

1980-07-01

328

Helium-filled proportional counter for low-temperature operation (4.2--300 K) and its application to cryogenic resonance-electron Moessbauer spectroscopy  

International Nuclear Information System (INIS)

The operation of a proportional counter filled with helium gas has been investigated at low temperatures down to 5 K. It has been found for the first time that a helium-filled counter cooled at temperatures below 30 K works well in the proportional region, but with low gas gains (? 100). The operation at low temperatures (? 30 K) is attributed to the complete removal of impurities from helium gas as well as the extreme depression of the reaction frequency of metastable heliums. The absence of impurities results in eliminating the Penning effect, i.e., an ionization process of impurity atoms or molecules by collisions with metastable helium, which spreads electron avalanches in both space and time if helium gas contains a slight amount of impurities (1--103 ppm). Continuous discharges caused by the photoeffect of ultraviolet photons, which are mostly produced in decay channels of metastable helium, are thermally quenched at low temperatures below 30 K. The helium-filled counter provides us with a new method to detect nuclear radiations at very low temperatures. The present counter technique has been successfully applied to the resonance-electron Moessbauer spectroscopy near liquid-helium temperature (--5 K)

329

Cavity microstructure and kinetics during gas tungsten arc welding of helium-containing stainless steel  

International Nuclear Information System (INIS)

It is well known that energetic neutron irradiation produces significant physical damage to crystalline solids by the displacement of atoms from their normal lattice sites. In addition, transmutation reactions generate foreign elements of which helium is known to induce intergranular embrittlement. Degradation of material properties by these processes plays a decisive role in limiting the useful life of nuclear reactor components. It is reasonable, therefore, to anticipate that the repair and replacement of degraded reactor components will be required. Such repair procedures are likely to require the use of joining processes such as gas tungsten arc (GTA) welding. Helium was implanted in type 316 stainless steel, through tritium decay, to levels of 0.18, 2.5, 27, 105, and 256 atomic parts per million (appm). Bead-on-sheet welds were then made using the GTA process. Intergranular cracking occurred in the heat-affected zones (HAZs) of specimens with helium concentrations equal to or greater than 2.5 appm. No such cracking was observed in helium-free control specimens or in specimens containing the lowest helium concentrations. In addition to the HAZ cracking, brittle, centerline cracking occurred in the fusion zone of specimens containing 105 and 256 appm helium. Transmission and scanning electron microscopy results indicated that both the HAZ cracking and centerline cracking in the fusion zone resulted from the stress-induced growth and coalescence of cavities initiaterowth and coalescence of cavities initiated at helium bubbles on interfaces. For the HAZ case, the cavity growth rate is modeled and shown to predict the experimentally measured 1-second time lag between peak weld temperature and the onset of cracking

330

Special operations in the helium system, III-4  

International Nuclear Information System (INIS)

Special operations in the helium system are: pouring helium form the low pressure reservoir to the high pressure reservoir by compressor with membrane, measuring the percent of hydrogen-oxygen gas and percent of free deuterium by manual gas analyzer, measurement of deuterium content, adding helium into the cover gas system, adding oxygen into the helium system, control of hydrogen-oxygen gas increase rate bypassing the contact device, activating the automated analyzer of percent of hydrogen-oxygen gas in helium and activating the automated analyzer of percent of air in helium

331

Hydrodynamic simulations of the core helium flash  

CERN Document Server

We describe and discuss hydrodynamic simulations of the core helium flash using an initial model of a 1.25 M_sol star with a metallicity of 0.02 near at its peak. Past research concerned with the dynamics of the core helium flash is inconclusive. Its results range from a confirmation of the standard picture, where the star remains in hydrostatic equilibrium during the flash (Deupree 1996), to a disruption or a significant mass loss of the star (Edwards 1969; Cole & Deupree 1980). However, the most recent multidimensional hydrodynamic study (Dearborn 2006) suggests a quiescent behavior of the core helium flash and seems to rule out an explosive scenario. Here we present partial results of a new comprehensive study of the core helium flash, which seem to confirm this qualitative behavior and give a better insight into operation of the convection zone powered by helium burning during the flash. The hydrodynamic evolution is followed on a computational grid in spherical coordinates using our new version of th...

Mocak, M; Weiss, A; Kifonidis, K; 10.1017/S1743921308022813

2009-01-01

332

Liquid helium and the dilution refrigerator  

International Nuclear Information System (INIS)

Anomalies occure in the density and specific heat of helium at a very low temperature. Below the Lambda-transition temperature helium is a superfluid. Liquid helium also has enormous thermal conductivity. If two vessels containing superfluid helium are connected through a narrow capillary then a temperature difference gives rise to a corresponding pressure difference. 4He obeys Bose-Einstein statistics and 3He obeys Fermi-Dirac statistics. The operation of the helium refrigerator depends on a naturally occuring isotopic separation of a mixture of 4He and 3He below 1 Kelvin. At this temperature 3He can expand by being diluted with 4He. When mixtures containing more than 6% 3He are cooled below 0.86 Kelvin they separate out into a lighter quasi-liquid 3He rich phase floating on top of a denser quasi-gas 4He rich phase. The 4He in the lower phase is almost entirely superfluid with zero entropy and viscosity functioning as a background matrix through which the 3He moves. There is a latent heat of transition as 3He passes from the upper to the lower phase to produce a cooling similar to a liquid cooled by evaporation

333

Helium release from radioisotope heat sources  

Energy Technology Data Exchange (ETDEWEB)

Diffusion of helium in /sup 238/PuO/sub 2/ fuel was characterized as a function of the heating rate and the fuel microstructure. The samples were thermally ramped in an induction furnace and the helium release rates measured with an automated mass spectrometer. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metallographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release is controlled by movement of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles along grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranular bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel.

Peterson, D.E.; Early, J.W.; Starzynski, J.S.; Land, C.C.

1984-05-01

334

Helium release from radioisotope heat sources  

International Nuclear Information System (INIS)

Diffusion of helium in 238PuO2 fuel was characterized as a function of the heating rate and the fuel microstructure. The samples were thermally ramped in an induction furnace and the helium release rates measured with an automated mass spectrometer. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metallographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release is controlled by movement of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles along grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranular bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel

335

Hydrodynamic simulations of the core helium flash  

Science.gov (United States)

We desribe and discuss hydrodynamic simulations of the core helium flash using an initial model of a 1.25 M? star with a metallicity of 0.02 near at its peak. Past research concerned with the dynamics of the core helium flash is inconclusive. Its results range from a confirmation of the standard picture, where the star remains in hydrostatic equilibrium during the flash (Deupree 1996), to a disruption or a significant mass loss of the star (Edwards 1969; Cole & Deupree 1980). However, the most recent multidimensional hydrodynamic study (Dearborn et al. 2006) suggests a quiescent behavior of the core helium flash and seems to rule out an explosive scenario. Here we present partial results of a new comprehensive study of the core helium flash, which seem to confirm this qualitative behavior and give a better insight into operation of the convection zone powered by helium burning during the flash. The hydrodynamic evolution is followed on a computational grid in spherical coordinates using our new version of the multi-dimensional hydrodynamic code HERAKLES, which is based on a direct Eulerian implementation of the piecewise parabolic method.

Mocák, Miroslav; Müller, Ewald; Weiss, Achim; Kifonidis, Konstantinos

2008-10-01

336

Partial discharges in lapped polymer taped insulation impregnated with supercritical helium  

International Nuclear Information System (INIS)

Apparatus has been designed and constructed to evaluate the high-voltage parameters of lapped cable models impregnated with supercritical helium for pressures up to 1.5 MPa and for temperatures to 4.2K. The tape materials studied are as follows: high-density polythene, Valeron (cross-laminated polythene film), polypropylene, Nylon 11 and polysulphone with limited tests using polycarbonate. The variation of the maximum value of discharge with applied alternating voltage was obtained, and also the variation of inception stress (1 pC and 5 pC) with helium density and pressure. (author)

337

Development of small size Claude cycle helium refrigerator with micro turbo-expander  

International Nuclear Information System (INIS)

In the field of small size helium refrigerators, need for a maintenance free and vibration free system is rapidly increasing, especially for the application to cryoelectronic devices such as NMR-CT and Josephson computers. To meet this need, we have been developing a Claude cycle helium refrigerator (5W at 4.5 K) with two-stage expansion micro-turbines. Other than the micro-turbines, compact size perforatedplate heat exchangers and a single-stage screw type compressor have been developed for the system. This paper describes design and test results of the major components of the system with an emphasis on the microturbine performance

338

Cryogenic neutron detector comprising an InSb semiconductor detector and a supercritical helium-3 gas converter  

International Nuclear Information System (INIS)

We evaluated the neutron-detection characteristics of a proposed cryogenic neutron detector comprising an InSb semiconductor detector and a helium-3 gas converter. The neutron detector was operated at 4.2 K with helium-3 gas filling up to 1.5 atm, at which the density of the helium-3 nucleus corresponds to that at 160 atm at room temperature. The secondary particles generated by the 3He(n,p)T reaction were successfully detected by the InSb detector with a time response of ?80 ns at all tested gas pressures

339

Effect of helium on fatigue crack growth and life of reduced activation ferritic/martensitic steel  

International Nuclear Information System (INIS)

The effects of helium on the fatigue life, micro-crack growth behavior up to final fatigue failure, and fracture mode under fatigue in the reduced activation ferritic/martensitic steel, F82H IEA-heat, were investigated by low cycle fatigue tests at room temperature in air at a total strain range of 0.6–1.5%. Significant reduction of the fatigue life due to helium implantation was observed for a total strain range of 1.0–1.5%, which might be attributable to an increase in the micro-crack propagation rate. However, the reduction of fatigue life due to helium implantation was not significant for a total strain range of 0.6–0.8%. A brittle fracture surface (an original point of micro-crack initiation) and a cleavage fracture surface were observed in the helium-implanted region of fracture surface. A striation pattern was observed in the non-implanted region. These fracture modes of the helium-implanted specimen were independent of the strain range

340

Performance of a venturi flow meter in two-phase helium flow  

Science.gov (United States)

The performance of a venturi flow meter in vertical and horizontal two-phase helium flow is reported. In both flow configurations, tests were conducted by connecting two identical Venturis of 2.29 mm throat and 4.57 mm inlet diameters in series with a two-phase helium flow loop driven by a single-stroke bellows pump. With one venturi operating in single-phase liquid helium and one in two-phase helium, as controlled by an in-line heater, the ratio of the pressure drop across the two venturis is found to be well correlated with vapour quality. Vertical flow tests were performed under both forced flow and natural circulating flow conditions at 1.0 atm and at mass flow rates ranging from 1.0 to 2.5 g s -1. Horizontal flow tests were conducted at mass flow rates ranging from 0.5 to 2.0 g s -1 and under system pressures between 0.65 and 1.2 atm. Within the parameter range covered in the present study, the performance of the venturi flow meter in two-phase helium flows can be well described by the homogeneous model regardless of the flow orientation.

Huang, X.; Van Sciver, S. W.

 
 
 
 
341

Density decrease in vanadium-base alloys irradiated in the dynamic helium charging experiment  

Energy Technology Data Exchange (ETDEWEB)

Combined effects of dynamically charged helium and neutron damage on density decrease (swelling) of V-4Cr-4Ti, V-5Ti, V-3Ti-1Si, and V-8Cr-6Ti alloys have been determined after irradiation to 18-31 dpa at 425-600{degrees}C in the Dynamic helium Charging Experiment (DHCE). To ensure better accuracy in density measurement, broken pieces of tensile specimens {approx} 10 times heavier than a transmission electron microscopy (TEM) disk were used. Density increases of the four alloys irradiated in the DHCE were <0.5%. This small change seems to be consistent with the negligible number density of microcavities characterized by TEM. Most of the dynamically produced helium atoms seem to have been trapped in the grain matrix without significant cavity nucleation or growth.

Chung, H.M.; Galvin, T.M.; Smith, D.L. [Argonne National Laboratory, Chicago, IL (United States)

1996-04-01

342

Study of heat transfer in the gas-cooled necks of helium vessels and cryostats  

International Nuclear Information System (INIS)

This paper uses an experimental helium cryostat to measure heat flow along a neck cooled by gaseous helium. The test element took the form of an inset in the shape of a hollow cylinder made of steel Kh18N10T. The tests were conducted at warm boundary surface temperatures of 77-220 K and ratios L/D from 1.5 to 3.5. Tests were also conducted on serially produced helium cryostat KG-60/300, with a capacity of 60 liters and a neck diameter of 300 mm. Analysis of the test data shows that free convection has a substantial effect on heat transfer between the walls of the neck and the gas. It is expressed in an increase in heat transfer and a decrease in heat flow along the neck

343

Metastable helium density probe for remote plasmas  

International Nuclear Information System (INIS)

Helium metastable atom density was spatially determined by a modified electrostatic probe in a remote plasma. The probe structure was similar to that of a guard ring probe. Opposite polarity voltages were applied to the inner probe and the guard ring to shield both electrons and ions from the vicinity of the inner probe. Therefore, the inner probe current is due to secondary electrons generated by the de-exciting helium metastable atom flux. The photoelectron current was removed by shielding and orienting the probe 90 deg. to the direction of the plasma-generated photon flux. Helium metastable atom density on the order of 107 cm-3 was measured. Limitations on the use of this technique are revealed by comparisons with simulated metastable distributions.

344

Metastable helium density probe for remote plasmas  

Energy Technology Data Exchange (ETDEWEB)

Helium metastable atom density was spatially determined by a modified electrostatic probe in a remote plasma. The probe structure was similar to that of a guard ring probe. Opposite polarity voltages were applied to the inner probe and the guard ring to shield both electrons and ions from the vicinity of the inner probe. Therefore, the inner probe current is due to secondary electrons generated by the de-exciting helium metastable atom flux. The photoelectron current was removed by shielding and orienting the probe 90 deg. to the direction of the plasma-generated photon flux. Helium metastable atom density on the order of 10{sup 7} cm{sup -3} was measured. Limitations on the use of this technique are revealed by comparisons with simulated metastable distributions.

Miura, Naoto; Hopwood, Jeffrey [Department of Electrical and Computer Engineering, Tufts University, 161 College Ave., Medford, Massachusetts 02155 (United States)

2009-11-15

345

Metastable helium density probe for remote plasmas  

Science.gov (United States)

Helium metastable atom density was spatially determined by a modified electrostatic probe in a remote plasma. The probe structure was similar to that of a guard ring probe. Opposite polarity voltages were applied to the inner probe and the guard ring to shield both electrons and ions from the vicinity of the inner probe. Therefore, the inner probe current is due to secondary electrons generated by the de-exciting helium metastable atom flux. The photoelectron current was removed by shielding and orienting the probe 90° to the direction of the plasma-generated photon flux. Helium metastable atom density on the order of 107 cm-3 was measured. Limitations on the use of this technique are revealed by comparisons with simulated metastable distributions.

Miura, Naoto; Hopwood, Jeffrey

2009-11-01

346

Evolution of dopant-induced helium nanoplasmas  

International Nuclear Information System (INIS)

Two-component nanoplasmas generated by strong-field ionization of doped helium nanodroplets are studied in a pump-probe experiment using few-cycle laser pulses in combination with molecular dynamics simulations. High yields of helium ions and a pronounced resonance structure in the pump-probe transients which is droplet size dependent reveal the evolution of the dopant-induced helium nanoplasma with an active role for He shells in the ensuing dynamics. The pump-probe dynamics is interpreted in terms of strong inner ionization by the pump pulse and resonant heating by the probe pulse which controls the final charge states detected via the frustration of electron-ion recombination. (paper)

347

Molar volume of solid isotopic helium mixtures  

International Nuclear Information System (INIS)

Solid isotopic helium mixtures have been studied by path-integral Monte Carlo simulations in the isothermal-isobaric ensemble. This method allowed us to study the molar volume as a function of temperature, pressure, and isotopic composition. At 25 K and 0.2 GPa, the relative difference between molar volumes of isotopically pure crystals of 3He and 4He is found to be about 3%. This difference decreases under pressure, and for 12 GPa it is smaller than 1%. For isotopically mixed crystals, a linear relation between lattice parameters and concentrations of helium isotopes is found, in agreement with Vegard's law. The virtual crystal approximation, valid for isotopic mixtures of heavier atoms, does not give reliable results for solid solutions of helium isotopes

348

Helium behaviour in nuclear waste materials  

International Nuclear Information System (INIS)

Waste conditioning matrices like synthetic zirconolite (CaZrTi2O7) were fabricated and doped with either the short-lived alpha-emitters 238Pu or 244Cm, or with 239Pu to generate various amounts of helium and of alpha-damage. The samples were annealed in a Knudsen cell, and the helium desorption profiles interpreted in conjunction with parallel radiation damage and previous annealing behaviour studies. To understand the long term behaviour of spent nuclear fuel, UO2 samples doped with the alpha-emitters 233U, 238Pu have been investigated by transmission electron microscopy (TEM), by XRD and by thermal desorption spectroscopy. The release of helium has been explained by the recrystallization of amorphized zirconolite on one hand and partially during alpha-damage recovery in the case of the spent fuel. This study mostly highlights the correlation between restructuring of damaged materials and gas release

349

Helium corona-assisted air discharge  

Energy Technology Data Exchange (ETDEWEB)

Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb--for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

Jiang Nan; Gao Lei; Ji Ailing; Cao Zexian [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2011-10-15

350

Helium corona-assisted air discharge  

International Nuclear Information System (INIS)

Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb--for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

351

Helium corona-assisted air discharge  

Science.gov (United States)

Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb—for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

Jiang, Nan; Gao, Lei; Ji, Ailing; Cao, Zexian

2011-10-01

352

Simulating the tevatron liquid helium satellite refrigerators  

International Nuclear Information System (INIS)

A computer program to simulate the Fermilab Tevatron liquid helium satellite refrigeration system has been developed. The simulator program takes advantage of the Macintosh platform upon which it was developed to produce a unique, easy to use Macintosh interface to facilitate ease of cycle design and modification. The user can drag icons representing refrigerator components around on the screen and piece them together to form a variety of liquid helium refrigeration cycle configurations. Extensive use of the icons, windows, and pull-down menus of the Macintosh interface allows the user to easily alter refrigeration component configurations and parameters. Calculation accuracy is retained by using existing helium property subroutines and component models. The user interface, program output, and code details are described. Sample configurations and results are presented

353

Stress distribution in helium-ion implantations  

International Nuclear Information System (INIS)

The stress introduced into a material in a monoenergetic helium-ion implantation is calculated for an ion beam with a gaussian intensity distribution. An effective beam spot of the order of several millimeters was chosen as typical of blistering experiments. The sample is assumed to be semi-infinite and isotropic. The ion distribution is cylindrically symmetric with a gaussian depth profile. The parameters defining the distribution are consistent with incident ion energies of approximately 40 and approximately 400 keV in both nickel and niobium. The volume expansion caused by the implanted ions is assumed to be proportional to the local helium concentration; the validity of this assumption is discussed. The maximum shear stress is calculated as a function of depth, and the volume expansion per helium atom required to produce plastic deformation at the experimentally observed critical doses in niobium is found to be of the order of one atomic volume

354

Accuracy of helium accumulation fluence monitor for fast reactor dosimetry  

Energy Technology Data Exchange (ETDEWEB)

A helium (He) accumulation fluence monitor (HAFM) has been developed for fast reactor dosimetry. In order to evaluate the measurement accuracy of neutron fluence by the HAFM method, the HAFMs of enriched boron (B) and beryllium (Be) were irradiated in the Fast Neutron Source Reactor `YAYOI`. The number of He atoms produced in the HAFMs were measured and compared with the calculated values. As a result of this study, it was confirmed that the neutron fluence could be measured within 5 % by the HAFM method, and that met the required accuracy for fast reactor dosimetry. (author)

Ito, Chikara; Aoyama, Takafumi [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center

1998-03-01

355

Superfluidity of Grain Boundaries in Solid Helium-4  

CERN Document Server

By large-scale quantum Monte Carlo simulations we show that grain boundaries in Helium-4 crystals are generically superfluid at low temperature, with a transition temperature of the order of ~0.5K at the melting pressure; insulating grain boundaries are found only for special orientations of the grains. We also find that close vicinity to the melting line is not a necessary condition for superfluid grain boundaries, and a grain boundary in direct contact with the superfluid liquid at the melting curve is found to be mechanically stable and the grain boundary superfluidity observed by Sasaki et al. [Science 313, 1098 (2006)] is not just a crack filled with superfluid.

Pollet, L; Kuklov, A B; Prokofiev, N V; Svistunov, B V; Troyer, M

2007-01-01

356

Determination of the Fine Structure Constant Using Helium Fine Structure  

International Nuclear Information System (INIS)

We measure 31 908 131.25(30) kHz for the 23P J=0 to 2 fine structure interval in helium. The difference between this and theory to order m?7 (20 Hz numerical uncertainty) implies 0.22(30) kHz for uncalculated terms. The measurement is performed by using atomic beam and electro-optic laser techniques. Various checks include a 3He 23S hyperfine measurement. We can obtain an independent value for the fine structure constant ? with a 5 ppb experimental uncertainty. However, dominant m?8 terms (potentially 1.2 kHz) limit the overall uncertainty to a less competitive 20 ppb in ?.

357

The hall Effect in 2D Electrons on Liquid Helium  

International Nuclear Information System (INIS)

The a.c. Hall effect has been measured directly in a 2D sheet of free electrons above the surface of liquid helium at frequencies from 1.5. to 35 kHz in a magnetic field B up to 4 T. For small B the normal Hall effect is observed but at higher fields finite frequency effects occur as the 2D skin depth becomes less than the sample size. Calculations using the magnetoconductivity tensor for a 2D transmission line agree well with experiment, except in the high-field limit as quantum effects become significant

358

Several operational features of a cataphoresis helium-cadium laser  

Energy Technology Data Exchange (ETDEWEB)

By simultaneously measuring the lasing power and the discharge plasma parameters of a cataphoresic helium-cadium laser, it is established that as the discharge current changes, the cadium vapour pressure in the functional section of the tube does not remain constant despite the fact that the temperature of the cadium vapour source remains constant plus or minus .5/sup 0/ C. By applying an axial magnetic field to the active medium with single-frequency lasing conditions, an increase in lasing power may be achieved.

Andreeva, E.U.; Elagin, V.V.; Fotiadi, A.E.; Fridrikhov, S.A.; Terekhin, D.K.

1979-01-01

359

Two-photon laser spectroscopy of antiprotonic helium  

International Nuclear Information System (INIS)

The ASACUSA collaboration of CERN has recently carried out two-photon laser spectroscopy of antiprotonic helium atoms. Some nonlinear two-photon transitions of the antiproton at the deep UV wavelengths ? = 139.8–197.0 nm were excited by irradiating the atom with two counterpropagating laser beams. This reduced the thermal Doppler broadening in the observed spectral lines. Three transition frequencies were thus determined with fractional precisions of 2.3–5 parts in 109. By comparing the results with three-body quantum electrodynamics calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). In this paper, we briefly review these recent experimental results. (author)

360

Electron microscopic studies of tungsten films irradiated with helium ions  

International Nuclear Information System (INIS)

An investigation is presented of the generation and development of defects in 4.5? tungsten films bombarded by approximately 1 MeV helium ions (2.1016-7.1016cm-2.) at specimen temperatures Tsub(irra)=1000C and 10000C. The films irradiated at 1000C are annealed at Tsub(an)=1000 to 16000C. As the irradiation dose increases, the dislocation structure develops from ''black points'' to dislocation loops and dislocation network. On annealing up to 14000C, the appearance of gas bubbles is observed. When irradiated at elevated temperature the bubbles begin to form at 10000C

 
 
 
 
361

Subtask 12G1: Effects of dynamically charged helium on swelling and microstructure of vanadium-base alloys  

Energy Technology Data Exchange (ETDEWEB)

The objective of this work is to determine void structure, distribution, and density changes of several vanadium-base alloys irradiated in the Dynamic Helium Charging Experiment (DHCE). Combined effects of dynamically charged helium and neutron damage on density change, void distribution, and microstructural evolution of V-4Cr-4Ti alloy have been determined after irradiation to 18-31 dpa at 425-600{degrees}C in the DHCE, and the results compared with those from a non-DHCE in which helium generation was negligible. For specimens irradiated to {approx}18-31 dpa at 500-600{degrees}C with a helium generation rate of 0.4-4.2 appm He/dpa, only a few helium bubbles were observed at the interface of grain matrices and some of the Ti(O,N,C) precipitates, and no microvoids or helium bubbles were observed either in grain matrices or near grain boundaries. Under these conditions, dynamically produced helium atoms seem to be trapped in the grain matrix without significant bubble nucleation or growth, and in accordance with this, density changes from DHCE and non-DHCE (negligible helium generation) were similar for comparable fluence and irradiation temperature. Only for specimens irradiated to {approx}31 dpa at 425{degrees}C, when helium was generated at a rate of 0.4-0.8 appm helium/dpa, were diffuse helium bubbles observed in limited regions of grain matrices and near {approx}15% of the grain boundaries in densities significantly lower than those in the extensive coalescences of helium bubbles typical of other alloys irradiated in tritium-trick experiments. Density changes of specimens irradiated at 425{degrees}C in the DHCE were significantly higher than those from non-DHCE irradiation. Microstructural evolution in V-4Cr-4Ti was similar for DHCE and non-DHCE except for helium bubble number density and distribution. As in non-DHCE, the irradiation-induced precipitation of ultrafine Ti{sub 5}Si{sub 3} was observed for DHCE at >500{degrees}C but not at 425{degrees}C.

Chung, H.M.; Nowicki, L.; Gazda, J.; Smith, D.L. [Argonne National Lab., IL (United States)

1995-03-01

362

Ab Initio Simulations of Dense Helium Plasmas  

CERN Document Server

We study the thermophysical properties of dense helium plasmas by using quantum molecular dynamics and orbital-free molecular dynamics simulations, where densities are considered from 400 to 800 g/cm$^{3}$ and temperatures up to 800 electron-volt. Results are presented for the equation of state. From the Kubo-Greenwood formula, we derive the electrical conductivity and electronic thermal conductivity. In particular, with the increase of temperature, we discuss the change of Lorenz number, which indicates a transition from strong coupling and degenerate state to moderate coupling and partial degeneracy regime for dense helium.

Wang, Cong; Zhang, Ping

2010-01-01

363

Helium damage in austenitic stainless steels  

International Nuclear Information System (INIS)

Helium produced by tritium decay was first shown to embrittle austenitic stainless steel at ambient temperature in tensile specimens of Nitronic-40 steel (Armco, Inc.). A long-term study was initiated to study this form of helium damage in five austenitic alloys. Results from this study have been analyzed by the J-integral technique and show a decrease in ductile fracture toughness with increasing He-3 concentration. Sustained-load cracking tests indicate that the stress intensity required to initiate and propagate a crack also decreases with increasing He-3 concentration. 9 figures, 3 tables

364

Acoustic Signatures of the Helium Core Flash  

Digital Repository Infrastructure Vision for European Research (DRIVER)

All evolved stars with masses M <2 solar masses undergo an initiating off-center helium core flash in their 0.48 solar mass He core as they ascend the red giant branch (RGB). This off-center flash is the first of a few successive helium shell subflashes that remove the core electron degeneracy over 2 Myrs, converting the object into a He burning star. Though characterized by Thomas over 40 years ago, this core flash phase has yet to be observationally probed. Using the Modul...

Bildsten, Lars; Paxton, Bill; Moore, Kevin; Macias, Phillip J.

2011-01-01

365

In Beam Tests of Implanted Helium Targets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Targets consisting of 3,4He implanted into thin aluminum foils (approximately 100, 200 or 600 ug/cm^2) were prepared using intense (a few uA) helium beams at low energy (approximately 20, 40 or 100 keV). Uniformity of the implantation was achieved by a beam raster across a 12 mm diameter tantalum collimator at the rates of 0.1 Hz in the vertical direction and 1 Hz in the horizontal direction. Helium implantation into the very thin (approximately 80-100 ug/cm^2) aluminum foil...

Mcdonald, J. E.; France Iii, R. H.; Jarvis, R. A.; Ahmed, M. W.; Blackston, M. A.; Delbar, Th; Gai, M.; Kading, T. J.; Parpottas, Y.; Perdue, B. A.; Prior, R. M.; Rubin, D. A.; Spraker, M. C.; Yeomans, J. D.; Weissman, L.

2006-01-01

366

Properties of hydrogen/helium accretion plasmas  

International Nuclear Information System (INIS)

We study the properties of impulsively-heated plasmas initially composed of hydrogen and helium. We follow the time-dependent behavior of the ion and electron temperatures, the pair density, and the densities of hydrogen, helium, and nuclei formed in fusion and breakup reactions. We also consider neutron production and escape, and calculate the 0.431 and 0.478 MeV line luminosities from ?-? fusion reactions, and the 2.22 MeV line luminosity from neutron capture on protons. 13 refs., 3 figs., 1 tab

367

Bubble instability in overheated liquid Helium-3  

Science.gov (United States)

The generation and the growth of vapor bubbles in metastable liquid Helium-3 are studied. The finite diffuse layer of vapor bubble, the temperature dependence of the surface tension and the relaxation processes are taken into consideration. We show that the growth of bubble in overheated liquid Helium-3 is significantly influenced by the memory effects caused by the dynamic Fermi-surface distortions. In particular, the increase of bubble is strongly hindered and accompanied by the characteristic oscillations of the bubble radius. The oscillations of the bubble radius disappear in a short relaxation-time limit where the memory effects are negligible.

Kolomietz, V. M.

2014-11-01

368

Ab Initio Simulations of Dense Helium Plasmas  

International Nuclear Information System (INIS)

We study the thermophysical properties of dense helium plasmas by using quantum molecular dynamics and orbital-free molecular dynamics simulations, where densities are considered from 400 to 800 g/cm3 and temperatures up to 800 eV. Results are presented for the equation of state. From the Kubo-Greenwood formula, we derive the electrical conductivity and electronic thermal conductivity. In particular, with the increase in temperature, we discuss the change in the Lorenz number, which indicates a transition from strong coupling and degenerate state to moderate coupling and partial degeneracy regime for dense helium.

369

Excited state positronium collisions with helium  

International Nuclear Information System (INIS)

Calculations of the discrete positronium (Ps) transition Ps(2s) ? Ps(2p) in collisions with ground state helium are reported. Results are presented at total and single differential levels. Calculations are made within the first born approximation (FBA). The Hartley-Walters approximation is used to sum over all possible final excited atom states. In addition, impulse approximation (IA) calculations are reported for Ps(2s) and Ps(2p) fragmentation collisions with ground state helium, where the atom does not change state. Again, the FBA with the HWA is used to account for collisions in which the atom is excited or ionized

370

Level gauge for the liquid helium  

International Nuclear Information System (INIS)

Level gauge for liquid helium, which can be used as a level indicator and a gauge of limit level is described. An accuracy of the liquid level measurement is equal to +-1 mm. At constant feed, the gauge reaction on its passage from liquid helium into the gaseous one is equal to 0.2 s. Maximum electric imput power of the device produced on the PEhS-10 relay basis, operating under the regime of a low level gauge, does not exceed 0.11 W. Reading of the level gauge do not depend on steam pressure over the liquid surface

371

Excited state positronium collisions with helium  

Energy Technology Data Exchange (ETDEWEB)

Calculations of the discrete positronium (Ps) transition Ps(2s) {yields} Ps(2p) in collisions with ground state helium are reported. Results are presented at total and single differential levels. Calculations are made within the first born approximation (FBA). The Hartley-Walters approximation is used to sum over all possible final excited atom states. In addition, impulse approximation (IA) calculations are reported for Ps(2s) and Ps(2p) fragmentation collisions with ground state helium, where the atom does not change state. Again, the FBA with the HWA is used to account for collisions in which the atom is excited or ionized.

Starrett, C. [Department of Applied Mathematics and Theoretical Physics, Queen' s University, Belfast BT7 1NN (United Kingdom)], E-mail: c.starrett@qub.ac.uk; Walters, H.R.J. [Department of Applied Mathematics and Theoretical Physics, Queen' s University, Belfast BT7 1NN (United Kingdom); McAlinden, Mary T. [School of Computing and Mathematical Sciences, Oxford Brookes University, Wheatley Campus, Oxford OX33 1HX (United Kingdom)

2008-02-15

372

Helium damage in austenitic stainless steels  

Energy Technology Data Exchange (ETDEWEB)

Helium produced by tritium decay was first shown to embrittle austenitic stainless steel at ambient temperature in tensile specimens of Nitronic-40 steel (Armco, Inc.). A long-term study was initiated to study this form of helium damage in five austenitic alloys. Results from this study have been analyzed by the J-integral technique and show a decrease in ductile fracture toughness with increasing He-3 concentration. Sustained-load cracking tests indicate that the stress intensity required to initiate and propagate a crack also decreases with increasing He-3 concentration. 9 figures, 3 tables.

Caskey, G.R. Jr.; Mezzanotte, D.A. Jr.; Rawl, D.E. Jr.

1983-01-01

373

Experimental and numerical investigation of time evolution of discharge current and optical emission in helium–nitrogen cryoplasmas  

Science.gov (United States)

Cryoplasmas represent a class of non-equilibrium plasmas whose gas temperature can be controlled below room temperature. However, so far, the influence of the plasma gas temperature on the plasma chemical reactions has not yet been examined in detail. Here we investigated the time-dependent reaction dynamics related to optical emission in helium–nitrogen cryoplasmas. We acquired voltage and discharge current waveforms, optical emission spectra, and observed a temporal change of the emission intensity in helium–nitrogen cryoplasmas at two experimental conditions (temperatures of temperature detector: 5 K and plasma gas temperature: 28 K (condition A), 40 K and 54 K (condition B)). Two time-dependent phenomena were observed: the first was a longer duration of the discharge current compared to that of helium emission at both conditions A and B, and the second was nitrogen ion emission delayed by about 8 µs with respect to the emissions of atomic helium and helium dimers at 40 K. The experimental observations could be reproduced qualitatively by a global reaction model, which took into account the effect of the plasma gas temperature on the reaction rate constants and the diffusion coefficients. The simulations suggested that the reactions related to metastable helium atom were the key reactions, and that the long lifetimes of metastable helium atoms at cryogenic gas temperatures are crucial for the appearance of the time-dependent phenomena. These results imply that the plasma gas temperature is one of the key parameters in non-equilibrium plasma chemistry.

Muneoka, Hitoshi; Urabe, Keiichiro; Choi, Jai Hyuk; Stauss, Sven; Terashima, Kazuo

2014-12-01

374

Development of helium-cooled fusion applications: overview on major helium activities at the Forschungszentrum Karlsruhe  

International Nuclear Information System (INIS)

Helium cooled high temperature components and reactors from today's point of view are most likely to capture a major importance in the future energy market. Similar to the tendency in the development of future fission reactors the main emphasis in regard to future fusion reactors is on Helium cooled systems. Both European reference blanket concepts are completely Helium cooled and in addition, the development of a Helium cooled divertor is in progress. Also the third, alternative European blanket concept ''Dual-coolant lead lithium'' in regard to a DEMO fusion reactor relies on a Helium-cooled structure. In the International- Fusion-Material-Irradiation-Facility (IFMIF), again, Helium cooling is applied e.g. to the High Flux Test Module (HFTM). Against this background major Helium activities were launched at the Forschungszentrum Karlsruhe, including the design and construction of several Helium Test Facilities applicable to perform various experiments from single effect studies up to full component tests for the qualification of complete test modules to be operated in ITER. In addition a fundamental research Programme is under way to improve the local Helium cooling technologies applied in different applications and to improve the knowledge base on heat transfer, boundary layers, turbulence development and flow structures as well as the dynamic behaviour of large Helium cycles under unsteady boundary conditions. An important complementary activity is found in the arecomplementary activity is found in the area of computational fluid dynamics (CFD) were the most appropriate turbulence models are determined by code validation based on the obtained experimental data. In this paper an outline of the overall Helium cooling development strategy at Forschungszentrum Karlsruhe is given along with a brief description of the operated and planned Helium Test Facilities including the (i) ITHEX facility used for flow field studies in IFMIF-relevant transitional flows, (ii) the HEBLO facility used for example to test Blanket First Wall channels and divertor mock-ups, (iii) the HELOKA-HP/TBM facility used for TBM development and (iv) the HELOKA-LP facility used for IFMIF HFTM development. In addition an overview on the status of research on jet impingement cooling applied to the divertor, rib cooling for the First Wall of breeding blankets and convective heat transfer in minichannels of the IFMIF HFTM is given. (orig.)

375

Energy spectra of finite temperature superfluid helium-4 turbulence  

International Nuclear Information System (INIS)

A mesoscopic model of finite temperature superfluid helium-4 based on coupled Langevin-Navier-Stokes dynamics is proposed. Drawing upon scaling arguments and available numerical results, a numerical method for designing well resolved, mesoscopic calculations of finite temperature superfluid turbulence is developed. The application of model and numerical method to the problem of fully developed turbulence decay in helium II, indicates that the spectral structure of normal-fluid and superfluid turbulence is significantly more complex than that of turbulence in simple-fluids. Analysis based on a forced flow of helium-4 at 1.3 K, where viscous dissipation in the normal-fluid is compensated by the Lundgren force, indicate three scaling regimes in the normal-fluid, that include the inertial, low wavenumber, Kolmogorov k?5/3 regime, a sub-turbulence, low Reynolds number, fluctuating k?2.2 regime, and an intermediate, viscous k?6 range that connects the two. The k?2.2 regime is due to normal-fluid forcing by superfluid vortices at high wavenumbers. There are also three scaling regimes in the superfluid, that include a k?3 range that corresponds to the growth of superfluid vortex instabilities due to mutual-friction action, and an adjacent, low wavenumber, k?5/3 regime that emerges during the termination of this growth, as superfluid vortices agglomerate between intense normal-fluid vorticity regions, and weakly polarized bundles are formed. There is also evidence of a high wavenumber k?1 range that corresponds to the probing of individual-vortex velocity fields. The Kelvin waves cascade (the main dynamical effect in zero temperature superfluids) appears to be damped at the intervortex space scale

376

Direct modeling of neutral helium in the heliosphere  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several years of neutral particle measurements by the NASA/IBEX mission have yielded direct observations of interstellar neutral helium and oxygen. The data indicate the presence of secondary neutral helium and oxygen, which are created within the heliosphere by charge exchange involving helium or oxygen ions. This contribution describes a detailed conserving calculation method based on Keplerian orbits that has been developed to characterize helium distribution functions th...

Mueller, Hans-reinhard

2012-01-01

377

Helium in Nanoconfinement: Interplay Between Geometry and Wetting Behavior  

Science.gov (United States)

This paper reviews the most recent research of adsorption of finite helium systems, performed in the frame of Density Functional theory. These comprehend the deposition and spreading of helium droplets on flat alkali metal surfaces, the determination of isotherms, the construction of the phase diagram of helium on such substrates, the adsorption of helium on spherical and cylindrical surfaces, the filling of wedges and of infinite polygonal pores, and the adsorption on planar surfaces structured with an array of parabolic nanocavities.

Ancilotto, F.; Barranco, M.; Hernández, E. S.; Pi, M.

2009-11-01

378

Gearbox Scheme in High Temperature Reactor Helium Gas Turbine System  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Helium Turbine is used in High Temperature Reactor Helium Gas Turbine (HTR-GT) system, by which the direct helium circulation between the reactor and turbine generator system will come true. Between helium turbine and generator, there is gearbox device which reduces the turbine rotation speed to normal speed required by the generator. Three optional gearbox schemes are discussed. The first is single reduction cylindrical gearbox, which consists of one high speed gear and one low speed gear. I...

Sheng Liu; Xuanyu Sheng

2012-01-01

379

Helium sources and recovery processes - with special reference to India  

International Nuclear Information System (INIS)

Helium plays an important role in a variety of processes. Its only widely exploited source is natural gas with a helium content of 1-8%. Postulated, increased demand has stimulated interest in both novel sources and extraction techniques. Existing and new methods of helium recovery from natural gas are discussed with particular attention pair to pilot plants for helium extraction from monazite mineral and thermal springs in India. (author)

380

Energy harvesting in doped helium nano-droplets  

International Nuclear Information System (INIS)

We report the observation of sequential Penning ionization of dopants by metastable helium atoms in helium nano-droplets resulting in doubly charged ions. Strong charge induced dipole-interaction between the excited helium atom and the target ion provides a high probability for the transfer of the internal energy of the excited helium atom to the dopant ion. This process may also lead subsequently to a Coulomb explosion of molecular or cluster dopants.

 
 
 
 
381

Analysis of irradiated boron alloy pellets for entrapped helium  

International Nuclear Information System (INIS)

Helium gas trapped in the irradiated titanium boron samples was determined over a temperature range 1073-1923 K. It was observed that helium releases only above 1823 K and that helium content is more at peripheries compared to centre part of the pellets. (author)

382

Surface excitations in thin helium films on silica aerogel  

Digital Repository Infrastructure Vision for European Research (DRIVER)

First measurements are reported on pure surface excitations in thin superfluid 4He films on silica aerogel. The ripplon dispersion curve is found to be the same for helium on graphite and silica aerogel substrates. However, the layered roton line width in helium films on aerogel shows a pronounced broadening with respect to that found in helium films on graphite.

Lauter, Hans J.; Bogoyavlenskii, I. V.; Puchkov, Alexander V.; Godfrin, Henri; Skomorokhov, Andrei; Klier, Ju?rgen; Leiderer, Paul

2002-01-01

383

Physiological response of rats to delivery of helium and xenon: implications for hyperpolarized noble gas imaging  

Science.gov (United States)

The physiological effects of various hyperpolarized helium and xenon MRI-compatible breathing protocols were investigated in 17 Sprague-Dawley rats, by continuous monitoring of blood oxygen saturation, heart rate, EKG, temperature and endotracheal pressure. The protocols included alternating breaths of pure noble gas and oxygen, continuous breaths of pure noble gas, breath-holds of pure noble gas for varying durations, and helium breath-holds preceded by two helium rinses. Alternate-breath protocols up to 128 breaths caused a decrease in oxygen saturation level of less than 5% for either helium or xenon, whereas 16 continuous-breaths caused a 31.5% +/- 2.3% decrease in oxygen saturation for helium and a 30.7% +/- 1. 3% decrease for xenon. Breath-hold protocols up to 25 s did not cause the oxygen saturation to fall below 90% for either of the noble gases. Oxygen saturation values below 90% are considered pathological. At 30 s of breath-hold, the blood oxygen saturation dropped precipitously to 82% +/- 0.6% for helium, and to 76.5% +/- 7. 4% for xenon. Breath-holds longer than 10 s preceded by pre-rinses caused oxygen saturation to drop below 90%. These findings demonstrate the need for standardized noble gas inhalation procedures that have been carefully tested, and for continuous physiological monitoring to ensure the safety of the subject. We find short breath-hold and alternate-breath protocols to be safe procedures for use in hyperpolarized noble gas MRI experiments. Copyright 2000 John Wiley & Sons, Ltd.

Ramirez, M. P.; Sigaloff, K. C.; Kubatina, L. V.; Donahue, M. A.; Venkatesh, A. K.; Albert, M. S.; ALbert, M. S. (Principal Investigator)

2000-01-01

384

Superfluid Onset and 2D phase transitions of Helium-4 on Lithium and Sodium  

Science.gov (United States)

We have fabricated lithium and sodium films on quartz crystal microbalances (QCM) using in situ low temperature pulsed laser deposition. The frequency shift and dissipation of the QCM was measured as a function of helium pressure and chemical potential and used to construct the phase diagram of helium films on these substrates. Pressure measurement techniques based on an RGA mass spectrometer, which provides accurate measurement below 10-8 Torr will be described. Lithium and sodium are predicted to be intermediate strength substrates which are strong enough to be wetted by He-4 but weak enough that solid-like layers do not form, so they are candidates for observing sub-monolayer superfluidity in direct contact with a metallic surface. Helium adsorption isotherms and quenches between 0.5K and 1.6K on both lithium and sodium indicated continuous, sub-monolayer helium film growth and superfluid onsets in sub-monolayer films. Features below 1K indicate a collision between a classical 2D liquid/vapor phase transition and the Kosterlitz-Thouless superfluid phase transition. We see no evidence for the pre-wetting step instability predicted for helium on sodium.

Velasco, Angel; Huisman, Fawn; van Cleve, Eli; Taborek, Peter

2012-02-01

385

Engineering Sensitivity Improvement of Helium Mass Spectrometer Leak Detection System by Means Global Hard Vacuum Test  

International Nuclear Information System (INIS)

The engineering sensitivity improvement of Helium mass spectrometer leak detection using global hard vacuum test configuration has been done. The purpose of this work is to enhance the sensitivity of the current leak detection of pressurized method (sniffer method) with the sensitivity of 10-3 ? 10-5 std cm3/s, to the global hard vacuum test configuration method which can be achieved of up to 10-8 std cm3/s. The goal of this research and development is to obtain a Helium leak test configuration which is suitable and can be used as routine bases in the quality control tests of FPM capsule and AgInCd safety control rod products. The result is an additional instrumented vacuum tube connected with conventional Helium mass spectrometer. The pressure and temperature of the test object during the leak measurement are simulated by means of a 4.1 kW capacity heater and Helium injection to test object, respectively. The addition of auxiliary mechanical vacuum pump of 2.4 l/s pumping speed which is directly connected to the vacuum tube, will reduce 86 % of evacuation time. The reduction of the measured sensitivity due to the auxiliary mechanical vacuum pump can be overcome by shutting off the pump soon after Helium mass spectrometer reaches its operating pressure condition. (author)

386

Control of radio-frequency atmospheric pressure argon plasma characteristics by helium gas mixing  

International Nuclear Information System (INIS)

The control of plasma characteristics is one of the important issues in many atmospheric pressure plasma applications. In order to accomplish this control, a feasibility study was performed by investigating the role of helium gas in an argon glow plasma that were produced in ambient air by 13.56 MHz radio-frequency power. Optical emission spectroscopy was used to measure rotational temperature and emission spectra acquired between 300 and 840 nm. Based on electrical and optical measurements, parameters such as gas temperature, breakdown voltage, power coupling efficiency, spatial uniformity of rotational temperature, and the sum of the emission intensity were controlled by varying the argon and helium gas mixing ratio. The addition of helium gas (from 0 to 10 lpm) to the argon flow (of 10 lpm) lowered the breakdown voltage (from 430 to 300 Vpk) and the rotational temperature (from 465 to 360 K). However, an excessive addition of helium resulted in a reduction of the spatial uniformity and efficiency of power coupling. When the ratio of helium to argon flow was between 0.3 and 0.5, a high spatial uniformity with a relatively low gas temperature and breakdown voltage was achieved. This suggests that mixing of the supply gas is a useful way of controlling the plasma characteristics that may be utilized for applications with specific required discharge conditions

387

Microwave spectroscopic study of the hyperfine structure of antiprotonic helium-3  

CERN Document Server

In this work we describe the latest results for the measurements of the hyperfine structure of antiprotonic helium-3. Two out of four measurable super-super-hyperfine SSHF transition lines of the (n,L)=(36,34) state of antiprotonic helium-3 were observed. The measured frequencies of the individual transitions are 11.12548(08) GHz and 11.15793(13) GHz, with an increased precision of about 43% and 25% respectively compared to our first measurements with antiprotonic helium-3 [S. Friedreich et al., Phys. Lett. B 700 (2011) 1--6]. They are less than 0.5 MHz higher with respect to the most recent theoretical values, still within their estimated errors. Although the experimental uncertainty for the difference of 0.03245(15) GHz between these frequencies is large as compared to that of theory, its measured value also agrees with theoretical calculations. The rates for collisions between antiprotonic helium and helium atoms have been assessed through comparison with simulations, resulting in an elastic collision rate...

Friedreich, Susanne; Caspers, Fritz; Dax, Andreas; Hayano, Ryugo S; Hori, Masaki; Horváth, Dezs?; Juhász, Bertalan; Kobayashi, Takumi; Massiczek, Oswald; Sótér, Anna; Todoroki, Koichi; Widmann, Eberhard; Zmeskal, Johann

2013-01-01

388

Helium release and microstructural changes in Er(D,T)2-x3Hex films).  

Energy Technology Data Exchange (ETDEWEB)

Er(D,T){sub 2-x} {sup 3}He{sub x}, erbium di-tritide, films of thicknesses 500 nm, 400 nm, 300 nm, 200 nm, and 100 nm were grown and analyzed by Transmission Electron Microscopy, X-Ray Diffraction, and Ion Beam Analysis to determine variations in film microstructure as a function of film thickness and age, due to the time-dependent build-up of {sup 3}He in the film from the radioactive decay of tritium. Several interesting features were observed: One, the amount of helium released as a function of film thickness is relatively constant. This suggests that the helium is being released only from the near surface region and that the helium is not diffusing to the surface from the bulk of the film. Two, lenticular helium bubbles are observed as a result of the radioactive decay of tritium into {sup 3}He. These bubbles grow along the [111] crystallographic direction. Three, a helium bubble free zone, or 'denuded zone' is observed near the surface. The size of this region is independent of film thickness. Four, an analysis of secondary diffraction spots in the Transmission Electron Microscopy study indicate that small erbium oxide precipitates, 5-10 nm in size, exist throughout the film. Further, all of the films had large erbium oxide inclusions, in many cases these inclusions span the depth of the film.

Gelles, D. S. (Pacific Northwest National Laboratory, Richland, WA); Browning, James Frederick; Snow, Clark Sheldon; Banks, James Clifford; Mangan, Michael A.; Rodriguez, Mark Andrew; Brewer, Luke N.; Kotula, Paul Gabriel

2007-12-01

389

Positron and deuteron depth profiling in helium-3-implanted electrum-like alloy  

International Nuclear Information System (INIS)

In spite of previous extensive studies, the helium behavior in metals still remains an issue in microelectronics as well as in nuclear technology. A gold-silver solid solution (Au60Ag40: synthetic gold-rich electrum) was chosen as a relevant model to study helium irradiation of heavy metals. After helium-3 ion implantation at an energy ranging from 4.2 to 5.6 MeV, nuclear reaction analysis (NRA) based on the 3He(d,p)4He reaction, was performed in order to study the thermal diffusion of helium atoms. At room temperature, NRA data reveal that a single Gaussian can fit the He-distribution, which remains unchanged after annealing at temperatures below 0.45 of the melting point. Slow positron implantation spectroscopy, used to monitor the fluence dependence of induced defects unveils a positron saturation trapping, which occurs for He contents of the order of 50-100 appm, whereas concentrations larger than 500 appm seem to favor an increase in the S-parameter of Doppler broadening. Moreover, at high temperature, NRA results clearly show that helium long range diffusion occurs, though, without following a simple Fick law

390

Positron and deuteron depth profiling in helium-3-implanted electrum-like alloy  

Science.gov (United States)

In spite of previous extensive studies, the helium behavior in metals still remains an issue in microelectronics as well as in nuclear technology. A gold-silver solid solution (Au 60Ag 40: synthetic gold-rich electrum) was chosen as a relevant model to study helium irradiation of heavy metals. After helium-3 ion implantation at an energy ranging from 4.2 to 5.6 MeV, nuclear reaction analysis (NRA) based on the 3He(d,p) 4He reaction, was performed in order to study the thermal diffusion of helium atoms. At room temperature, NRA data reveal that a single Gaussian can fit the He-distribution, which remains unchanged after annealing at temperatures below 0.45 of the melting point. Slow positron implantation spectroscopy, used to monitor the fluence dependence of induced defects unveils a positron saturation trapping, which occurs for He contents of the order of 50-100 appm, whereas concentrations larger than 500 appm seem to favor an increase in the S-parameter of Doppler broadening. Moreover, at high temperature, NRA results clearly show that helium long range diffusion occurs, though, without following a simple Fick law.

Grynszpan, R. I.; Baclet, N.; Darque, A.; Flament, J. L.; Zielinski, F.; Anwand, W.; Brauer, G.

2006-02-01

391

Experimental determination of the effect of helium on the fracture toughness of steel  

International Nuclear Information System (INIS)

A fundamental issue with the use of structural steels for fusion applications is the effect of helium on mechanical properties. This concern has been difficult to address due to the limited neutron energies, hence limited helium production, of the fission reactor facilities used to simulate the effects of irradiation on properties such as fracture toughness. This paper will compare results from identical pre-cracked DCT fracture toughness samples irradiated using spallation and fission neutrons at ?60-90 deg. C. Materials studied were 304L and 316L stainless steel. The spallation neutron irradiated specimens were irradiated over a dose range up to ?10 dpa with a helium and hydrogen-to-dpa ratio of ?60 and 400, resp. Fracture toughness was seen to rapidly decreased from a value of ?250 to ?150 MPa m1/2 by the 1 dpa level. Following fission irradiation in the 1-1.5 dpa range, fracture toughness results were indistinguishable from those irradiated in the spallation neutron. The helium and hydrogen concentration for the fission neutron irradiated materials was ?6 appm and ?30 appm, respectively. It is concluded that, within the measurement uncertainty, increasing the helium and hydrogen concentration by more than an order of magnitude has had little influence on the fracture toughness of 304L and 316L stainless steel irradiated to similar displacement doses of a few dpa in the temperature range of 60-90 deg. C

392

Recondensation performance of liquid helium cryostat for a 28 GHz electron cyclotron resonance ion source  

Science.gov (United States)

Cryostat performance is essential for the stable operation of a superconducting magnet. A closed-cycle liquid helium cryostat was adopted for use for a superconducting electron cyclotron resonance (ECR) ion source by recondensing liquid helium vapor. The goal was to maintain the liquid helium filled reservoir at a constant level without transferring any liquid helium during the normal operation of the ECR ion source. To accomplish this, Gifford-McMahon (GM) refrigerators, which have two cold heads, were installed on the top of the cryostat. The cooling power of the GM cryocooler is 1.5 W at the second stage and 50 W at the first stage. Each stage was connected to the liquid helium reservoir, a radiation shield including high-Tc current lead, and related items. Before commissioning the ECR ion source, a preliminary evaluation of the recondensation performance was carried out with the magnet in partial operation. The design of the cryostat, its fabrication, and the experimental results are reported.

Choi, Seyong; Lee, Byoung-Seob; Park, Jin Yong; Ok, Jung-Woo; Shin, Chang Seouk; Yoon, Jang-Hee; Won, Mi-Sook; Kim, Byoung-Chul

2014-02-01

393

Conceptual design of helium experimental loop  

International Nuclear Information System (INIS)

In a future demonstration fusion power station (DEMO), helium is envisaged as coolant for plasma facing components, such as blanket and dive,or. All these components have a very complex geometry, with many parallel cooling channels, involving a complex helium flow distribution. Test blanket modules (TBM) of this concept will under go various tests in the experimental reactor ITER. For the qualification of TBM, it is indispensable to test mock-ups in a helium loop under realistic pressure and temperature profiles, in order to validate design codes, especially regarding mass flow and heat transition processes in narrow cooling channels. Similar testing must be performed for DEMO blanket, currently under development. A Helium Experimental Loop (HELOOP) is planed to be built for TBM tests. The design parameter of temperature, pressure, flow rate is 550 degree C, 10 MPa, l kg/s respectively. In particular, HELOOP is able to: perform full-scale tests of TBM under realistic conditions; test other components of the He-cooling system in ITER; qualify the purification circuit; obtain information for the design of the ITER cooling system. The main requirements and characteristics of the HELOOP facility and a preliminary conceptual design are described in the paper. (authors)

394

Potential applications of high temperature helium  

International Nuclear Information System (INIS)

This paper discusses the DOE MHTGR-SC program's recent activity to improve the economics of the MHTGR without sacrificing safety performance and two potential applications of high temperature helium, the MHTGR gas turbine plant and a process heat application for methanol production from coal

395

Messer to provide helium for LHC  

CERN Multimedia

Over the course of the next few years, industrial gas specialist The Messer Group, through its Swiss subsidiary Messer Schweiz AG, is to provide a 160,000kg supply of helium to the European Organisation for Nuclear Research (CERN) for the operation of the world's largest particle accelerator.

2008-01-01

396

Messer to provide helium for LHC project  

CERN Multimedia

Over the course of the next few years, industrial gas specialist The Messer Group, through its Swiss subsidiary Messer Schweiz AG, is to provide a 160,000kg supply of helium to the European Organisation for Nuclear Research (CERN) for the operation of the world's largest particle accelerator.

2008-01-01

397

Forbidden transitions in the helium atom  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nonrelativistically forbidden, single-photon transition rates between low lying states of the helium atom are rigorously derived within quantum electrodynamics theory. Equivalence of velocity and length gauges, including relativistic corrections is explicitly demonstrated. Numerical calculations of matrix elements are performed with the use of high precision variational wave functions and compared to former results.

Lach, Grzegorz; Pachucki, Krzysztof

2001-01-01

398

Acoustic streaming in helium-II  

International Nuclear Information System (INIS)

The first quantitative measurements of acoustic streaming velocity in helium-II as a function of sound intensity and temperature are presented. Comparison with theoretical calculations to second order shows detailed agreement in the temperature range examined, 1.4 K <= T <= 2.0 K. The coefficient of second viscosity appears to be the dominant hydrodynamic parameter. (orig.)

399

Potential applications of high temperature helium  

Energy Technology Data Exchange (ETDEWEB)

This paper discusses the DOE MHTGR-SC program`s recent activity to improve the economics of the MHTGR without sacrificing safety performance and two potential applications of high temperature helium, the MHTGR gas turbine plant and a process heat application for methanol production from coal.

Schleicher, R.W. Jr.; Kennedy, A.J.

1992-09-01

400

Potential applications of high temperature helium  

Energy Technology Data Exchange (ETDEWEB)

This paper discusses the DOE MHTGR-SC program's recent activity to improve the economics of the MHTGR without sacrificing safety performance and two potential applications of high temperature helium, the MHTGR gas turbine plant and a process heat application for methanol production from coal.

Schleicher, R.W. Jr.; Kennedy, A.J.

1992-09-01

 
 
 
 
401

Low-energy Antiproton Interaction with Helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An ab initio potential for the interaction of the neutral helium atom with antiprotons and protons is calculated using the Born-Oppenheimer approximation. Using this potential, the annihilation cross section for antiprotons in the energy range 0.01 microvolt to 1 eV is calculated.

Gibbs, W. R.

1997-01-01

402

Development of helium isotopic database in Japan  

International Nuclear Information System (INIS)

We constructed “Helium Isotopic Database in Japan”, which includes isotope ratios of noble gases and chemical compositions of gas samples collected from hot springs and drinking water wells. The helium isotopes are excellent natural tracers for indicating the presence of mantle derived volatiles, because they are chemically inert and thus conserved in crustal rock-water systems. It is common knowledge that mantle degassing does not occur homogeneously over the Earth's surface. The 3He/4He ratios higher than the typical crustal values are interpreted to indicate that transfer of mantle volatiles into the crust by processes or mechanisms such as magmatic intrusion, faulting. In particular the spatial variation of helium isotope ratios could provide a valuable information to identify volcanic regions and tectonically active areas. The database was compiled geochemical data of hot spring gas etc. from 108 published papers. As a result of the data compiling, the database has 1728 helium isotopic data. A CD-ROM is attached as an appendix. (author)

403

Polarizability and dielectric properties of helium  

International Nuclear Information System (INIS)

A precise measurement of the dielectric second virial coefficient of helium gives a value which compares very favorably with the previously determined experimental value of Orcutt and Cole. The dielectric third virial coefficient agrees reasonably well with the calculation of Heller and Gelbart based on the Hartree--Fock theory

404

Development of a helium cryostat for laser spectroscopy of atoms with unstable nuclei in superfluid helium  

Energy Technology Data Exchange (ETDEWEB)

We are developing a new nuclear laser spectroscopic technique for the study of nuclear structure that can be applied to short-lived low-yield atoms with unstable nuclei. The method utilizes superfluid helium (He II) as a trapping medium for high-energy ion beams. A liquid helium cryostat with optical windows is a key apparatus for this type of experiment. We describe the design and the performance of the cryostat which is developed for the present project.

Imamura, Kei, E-mail: kimamura@riken.jp [Department of Physics, Meiji University, 1-1-1 Higashi-Mita, Tama, Kawasaki, Kanagawa 214-8571 (Japan); Furukawa, Takeshi [Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397 (Japan); RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Wakui, Takashi [Cyclotron and Radioisotope Center, Tohoku University, 6-3 Aoba, Aramaki, Aoba, Sendai, Miyagi 980-8578 (Japan); Yang, Xiaofei [RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); School of Physics, Peking University, Chengfu Road, Haidian District, Beijing 100871 (China); Yamaguchi, Yasuhiro [Department of Physics, Meiji University, 1-1-1 Higashi-Mita, Tama, Kawasaki, Kanagawa 214-8571 (Japan); Tetsuka, Hiroki [Department of Physics, Tokyo Gakugei University, 4-1-1 Nukuikitamachi, Koganei, Tokyo 184-8501 (Japan); Mitsuya, Yosuke [Department of Physics, Meiji University, 1-1-1 Higashi-Mita, Tama, Kawasaki, Kanagawa 214-8571 (Japan); Tsutsui, Yoshiki [Department of Physics, Tokyo Gakugei University, 4-1-1 Nukuikitamachi, Koganei, Tokyo 184-8501 (Japan); Fujita, Tomomi [Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Ebara, Yuta; Hayasaka, Miki [Department of Physics, Tokyo Gakugei University, 4-1-1 Nukuikitamachi, Koganei, Tokyo 184-8501 (Japan); Arai, Shino; Muramoto, Sosuke [Department of Physics, Meiji University, 1-1-1 Higashi-Mita, Tama, Kawasaki, Kanagawa 214-8571 (Japan); Ichikawa, Yuichi [RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Department of Physics, Tokyo Instutute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551 (Japan); Ishibashi, Yoko [RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Department of Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); and others

2013-12-15

405

Cryogenic system with GM cryocooler for krypton, xenon separation from hydrogen-helium purge gas  

International Nuclear Information System (INIS)

In the thorium molten salt reactor (TMSR), fission products such as krypton, xenon and tritium will be produced continuously in the process of nuclear fission reaction. A cryogenic system with a two stage GM cryocooler was designed to separate Kr, Xe, and H2 from helium purge gas. The temperatures of two stage heat exchanger condensation tanks were maintained at about 38 K and 4.5 K, respectively. The main fluid parameters of heat transfer were confirmed, and the structural heat exchanger equipment and cold box were designed. Designed concentrations after cryogenic separation of Kr, Xe and H2 in helium recycle gas are less than 1 ppb

406

Data on trapping and re-emission of energetic hydrogen isotopes and helium in materials  

International Nuclear Information System (INIS)

This report presents a compilation of the experimental data on trapping and re-emission of energetic hydrogen isotopes and helium in materials. A survey has been made of the literatures up to end of 1980, by dividing it into following seven sections: 1) Dose Dependence, 2) Target Material Dependence, 3) Time Dependence, 4) Target Temperature Dependence, 5) Incident Energy Dependence, 6) Damage Effects, 7) Ion-Induced Release. The experimental data for helium, however, is cited only in limited cases, because of the lack of experiments. (author)

407

Control of two-photon double ionization of helium with intense chirped attosecond laser pulses  

Science.gov (United States)

We study the two-photon double-ionization process of the helium atom by solving numerically the nonrelativistic, time-dependent Schrödinger equation in its full dimensionality. We investigate with intense chirped attosecond laser pulses of 23.5-nm wavelength the two-photon absorption near and above the sequential threshold. We show how it is possible by adjusting the chirp parameter to control the electronic transitions inside the atom, thereby reinforcing or weakening the ionization process. Attosecond chirped laser pulses offer a promising way to probe and control the two-photon double ionization of helium when compared with attosecond transform-limited pulses.

Barmaki, S.; Lanteigne, P.; Laulan, S.

2014-06-01

408

Electron yield of glow discharge cathode materials under helium ion bombardment  

Science.gov (United States)

The secondary electron emission coefficient of materials for helium ion bombardment in the energy range 0.5-20 keV was measured for the surface conditions of cathodes in high voltage glow discharges. The materials studied are oxidized aluminum, oxidized magnesium, a molybdenum-aluminum oxide sintered composite, molybdenum, stainless steel, copper, gold, and graphite. Each sample was surface conditioned by operating it as cathode of a helium glow discharge shortly before the electron yield measurement. The results are relevant to the modeling of glow discharges and the design of cold cathode electron guns.

Szapiro, B.; Rocca, J. J.; Prabhuram, T.

1988-08-01

409

Application of laser resonance fluorescence for investigations of helium in a near-wall plasma  

International Nuclear Information System (INIS)

Use of laser resonance fluorescence (LRF) method for solution of problems related to the presence of helium in plasma is considered. Investigations were carried on at T-10 tokamak. General principles of measurements consist in optical pumping of one of transitions in HeI with the subsequent observation of responses in different lines. In optical pumping of the 23P ? D3D transition 33P ? 23S(?=388.9 nm) and 33S ? 23P(?=706.5 nm) lines were observed. Observed evaluations of elementary process rates in helium atom agree well with theoretical evaluations

410

Application of JLab 12GeV helium refrigeration system for the FRIB accelerator at MSU  

Energy Technology Data Exchange (ETDEWEB)

The planned approach to have a turnkey helium refrigeration system for the MSU-FRIB accelerator system, encompassing the design, fabrication, installation and commissioning of the 4.5-K refrigerator cold box(es), cold compression system, warm compression system, gas management, oil removal and utility/ancillary systems, was found to be cost prohibitive. Following JLab’s suggestion, MSU-FRIB accelerator management made a formal request to evaluate the applicability of the recently designed 12GeV JLab cryogenic system for this application. The following paper will outline the findings and the planned approach for the FRIB helium refrigeration system.

Ganni, V.; Knudsen, P.; Arenius, D. [Thomas Jefferson National Accelerator Facility, Newport News, VA 23606 (United States); Casagrande, F. [MSU-FRIB, East Lansing, MI 48824 (United States)

2014-01-29

411

Fine structure of the 2 3P state in helium-like sulfur and chlorine  

International Nuclear Information System (INIS)

We present precision measurements of the 1s2p (3P2 - 3P0) fine structure energies in the helium-like ions S14+ and Cl15+. The fine structures are obtained from spectroscopic measurements of the 1s2s 3S1 - 1s2p 3P0,2 transition wavelengths. These results represent the most precise experimental determinations of the helium-like J=2 - 0 intervals for Z>5. They establish the magnitude of missing higher order relativistic contributions in previous high-Z calculations of this fine structure, and they are in excellent agreement with new relativistic many-body calculations

412

Experimental observations of flow boiling of liquid helium I in vertical channels  

International Nuclear Information System (INIS)

Results are reported of the flow structure and pressure drop of helium 1 flowing upwards in a vertical heated circular glass tube. The experiments covered heat fluxes from 4.5 to 600 Wm-2, mass fluxes from 2 to 12 kg m-2s-1 and pressures between 1 and 1.2 atm. For the bubble flow regime the shape, size and drag coefficient of the observed bubbles are reported. Slip velocity, void fraction and pressure drop measurements are compared with generally accepted two-phase flow theories. A void fraction correlation for two-phase helium flow is proposed. (author)

413

An efficient cooling loop for connecting cryocooler to a helium reservoir  

International Nuclear Information System (INIS)

The magnet system of the VENUS ECR Ion Source at LBNL has two 1.5-watt cryocoolers suspended in the cryostat vacuum. Helium vapor from the liquid reservoir is admitted to a finned condenser bolted to the cryocooler 2nd stage and returns as liquid via gravity. Small-diameter flexible tubes allow the cryocoolers to be located remotely from the reservoir. With 3.1 watts load, the helium reservoir is maintained at 4.35 K, 0.05K above the cryocooler temperature. Design, analysis, and performance are presented

414

Cryogenic system with GM cryocooler for krypton, xenon separation from hydrogen-helium purge gas  

Science.gov (United States)

In the thorium molten salt reactor (TMSR), fission products such as krypton, xenon and tritium will be produced continuously in the process of nuclear fission reaction. A cryogenic system with a two stage GM cryocooler was designed to separate Kr, Xe, and H2 from helium purge gas. The temperatures of two stage heat exchanger condensation tanks were maintained at about 38 K and 4.5 K, respectively. The main fluid parameters of heat transfer were confirmed, and the structural heat exchanger equipment and cold box were designed. Designed concentrations after cryogenic separation of Kr, Xe and H2 in helium recycle gas are less than 1 ppb.

Chu, X. X.; Zhang, M. M.; Zhang, D. X.; Xu, D.; Qian, Y.; Liu, W.

2014-01-01

415

Cryogenic system with GM cryocooler for krypton, xenon separation from hydrogen-helium purge gas  

Energy Technology Data Exchange (ETDEWEB)

In the thorium molten salt reactor (TMSR), fission products such as krypton, xenon and tritium will be produced continuously in the process of nuclear fission reaction. A cryogenic system with a two stage GM cryocooler was designed to separate Kr, Xe, and H{sub 2} from helium purge gas. The temperatures of two stage heat exchanger condensation tanks were maintained at about 38 K and 4.5 K, respectively. The main fluid parameters of heat transfer were confirmed, and the structural heat exchanger equipment and cold box were designed. Designed concentrations after cryogenic separation of Kr, Xe and H{sub 2} in helium recycle gas are less than 1 ppb.

Chu, X. X.; Zhang, D. X.; Qian, Y.; Liu, W. [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201800 (China); Zhang, M. M.; Xu, D. [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190 (China)

2014-01-29

416

Nanometer-scale tunnel formation in metallic glass by helium ion irradiation  

Science.gov (United States)

We have shown that upon high fluence helium ion irradiation, metallic glass Cu50Zr45Ti5 becomes highly porous at the depth of the helium projected range. The resulting porous region is characterized by the formation of a tunnel like structure and self-linkage of nanometer size gas bubbles. Furthermore, the irradiation leads to the formation of nanometer size CuxZry crystals that are randomly distributed. The results of this study indicate that the He-filled bubbles have attractive interactions and experience considerable mobility. Movement of the bubbles is believed to be assisted by ballistic collisions.

Shao, Lin; Gorman, Brian P.; Aitkaliyeva, Assel; David Theodore, N.; Xie, Guoqiang

2012-07-01

417

Nanometer-scale tunnel formation in metallic glass by helium ion irradiation  

Energy Technology Data Exchange (ETDEWEB)

We have shown that upon high fluence helium ion irradiation, metallic glass Cu{sub 50}Zr{sub 45}Ti{sub 5} becomes highly porous at the depth of the helium projected range. The resulting porous region is characterized by the formation of a tunnel like structure and self-linkage of nanometer size gas bubbles. Furthermore, the irradiation leads to the formation of nanometer size Cu{sub x}Zr{sub y} crystals that are randomly distributed. The results of this study indicate that the He-filled bubbles have attractive interactions and experience considerable mobility. Movement of the bubbles is believed to be assisted by ballistic collisions.

Shao Lin [Department of Nuclear Engineering, Texas A and M University, College Station, Texas 77843 (United States); Materials Science and Engineering Program, Texas A and M University, College Station, Texas 77843 (United States); Gorman, Brian P. [Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado 80401 (United States); Aitkaliyeva, Assel [Materials Science and Engineering Program, Texas A and M University, College Station, Texas 77843 (United States); David Theodore, N. [CHD-Fab, Freescale Semiconductor, Inc., Chandler, Arizona 85224 (United States); Xie Guoqiang [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

2012-07-23

418

A Study on the Heat Transfer Properties of Pressurized Helium II through Fine Channels  

Science.gov (United States)

An experimental study was carried out on the heat transfer properties of pressurized superfluid helium in the Gorter-Mellink heat transfer region. By using channels of hydraulic diameter from 5.6 × 10- through 4.81 × 10-3 m, the heat transfer properties of pressurized superfluid helium were measured in the experiment. The temperature dependence of Gorter-Mellink parameter, AGM, is revealed from the experimental results. It is also proven that AGM depend only on temperature, and not on the channel size and shape. The effect of quantized vortices on heat transfer of pressurized superfluid helium is discussed in comparison of the channel diameter with the mean vortex line spacing.

Kimura, N.; Nakai, H.; Murakami, M.; Yamamoto, A.; Shintomi, T.

2006-04-01

419

Adsorption purification of helium coolant of high-temperature gas-cooled reactors of carbon dioxide  

International Nuclear Information System (INIS)

A series experiments on adsorption purification of helium of CO2 using national adsorbent under the conditions characteristic of HTGR type reactors cleanup system is performed. The experimnts have been conducted under the dynamic mode with immobile adsorbent layer (CaA zeolite) at gas flow rates from 0,02 to 0,055 m/s in the pressure range from 0,8 to 5 MPa at the temperature of 273 and 293 K. It is shown that the adsorption grows with the decrease of gas rate, i.e. with increase of contact time with adsorbent. The helium pressure, growth noticeably whereas the temperature decrease from 293 to 273 K results in adsorption 2,6 times increase. The conclusion is drawn that it is advisable drying and purification of helium of CO2 to perform separately using different zeolites: NaA - for water. CaA - for CO2. Estimations of purification unit parameters are realized

420

Effect of the physical properties of the overburden on helium emanometry. National Uranium Resource Evaluation  

International Nuclear Information System (INIS)

During the period of 1977 to 1978, a detailed soil helium study (40 samples per square kilometer) was carried out over three known mineralized areas, each being approximately 2.5 square kilometers in extent. These areas were: the Red Desert and Copper Mountain research sites in Wyoming, and the Spokane Mountain research site in Washington State. The result of the detailed study indicated that there was an association between the soil helium anomalies and the known uranium orebodies. This study was carried out in order to determine whether the technique could be used on a semi-reconnaissance basis (10 samples per square kilometer) and to determine if the helium anomalies truly indicate the presence of uranium deposits or reflect the variations in the physical properties of the overburden. The physical properties studied were the porosity and permeability of the rocks. This study was carried out at the Red Desert research site and at the Copper Mountain research site

 
 
 
 
421

Deuteron and helium ion irradiation of ceramic coatings on Nb-1% Zr  

International Nuclear Information System (INIS)

The surface damage to insulating barium alumino-silicate glass coatings due to irradiation by 100- and 250-keV deuterons and helium ions at room temperature and at 3000C has been studied. Blisters are observed after irradiation at room temperature with both deuterons and helium ions with energies of 100 keV and 250 keV. For deuteron irradiation a large fraction of the blisters have diameters which are approximately 3 to 5 times larger than the diameter observed with helium ions for identical irradiation conditions, but the density of blisters is nearly an order of magnitude lower. For irradiation at 3000C, no blisters are observed with either type of particle. The sharp rise in permeation rate with temperature is thought to be responsible for this behavior. The blister skin thicknesses have been measured and correlated with calculated projected-range values. (Auth.)

422

Influence of MHD effects and edge conditions on ITER helium ash accumulation and sustained ignition  

International Nuclear Information System (INIS)

Dilution of reacting species by build-up of helium ash and its effect on ignition in the ITER tokamak have been studies in a series of simulations with the one-dimensional BALDUR transport code. Thermal diffusivities, obtained from ITER scaling laws and with radial variations observed in JET, gave ?E ? 2--4 sec. Refueling of deuterium and tritium maintained constant electron density, while carbon recycling was 100% and the helium ash recycling was varied from 1.0 to 0.5. Including MHD effects, specifically sawteeth and beta limits, we find that ignition can be sustained for 200 seconds with Rhelium = 0.95. These simulations, the only non-zero-dimensional, time-dependent simulations thus far made for ITER plasmas, emphasize that edge plasma conditions, MHD behavior, and helium particle transport are critical synergistic issues for sustained ignition. 27 refs., 2 figs., 1 tab

423

Degradation of optical properties in Mo mirrors under irradiation with low energy helium and deuterium ions  

International Nuclear Information System (INIS)

Degradation of the optical properties in polycrystalline Mo mirrors irradiated with 1-5 keV helium or deuterium ions has been studied by in situ reflectivity measurement, SEM, TEM and spectroscopic ellipsometry. It has been shown that the reflectivity in these specimens at a wavelength range of (320-850) nm decreases with increase in the fluence and the energy of the ions, and that the degradation in helium irradiated specimens is greater than that in deuterium irradiated specimens. It has been demonstrated that optical constants vary due to formation of a damaged layer in the surface and subsurface region. Particularly in a helium irradiated specimens, the real part of the dielectric constant changes from negative to positive values and its imaginary part considerably decreases due to the bubble formation. These results suggest that penetration of the laser light is facilitated by the formation of damage such as bubbles and results in the degradation of reflectivity.

424

Creep rupture properties of some high temperature reactor circuit materials in helium  

International Nuclear Information System (INIS)

Creep rupture tests in air and in helium containing nominally 500:500:50:50 ppM of H2:CO:H2O:CH4 have been carried out on three ferritic and three austenitic steels for durations of up to 10,000 h at temperatures ranging from 400 to 8000C. The helium environment was found to reduce the creep and rupture strengths of the austenitic steels at 650 to 7500C by 5 to 15 percent whereas a smaller environmental effect was observed on a 1 percent Cr steel at 5000C and a 21/4 percent Cr steel at 5500C. No effect of environment was detected on mild steel at 4000C. The creep and rupture behavior is shown to be consistent with the metallographic findings which indicated that specimens tested in helium often contained deeper surface cracks and in all cases showed differences in the oxidation behavior

425

Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets  

Science.gov (United States)

Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (?? > 100 cm-1) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.

Pentlehner, D.; Slenczka, A.

2015-01-01

426

Spectrophotometry of extreme helium stars - Ultraviolet fluxes and effective temperatures  

Science.gov (United States)

Ultraviolet flux distributions are presented for the extremely helium rich stars BD +10 deg 2179, HD 124448, LSS 3378, BD -9 deg 4395, LSE 78, HD 160641, LSIV -1 deg 2, BD 1 deg 3438, HD 168476, MV Sgr, LS IV-14 deg 109 (CD -35 deg 11760), LSII +33 deg 5 and BD +1 deg 4381 (LSIV +2 deg 13) obtained with the International Ultraviolet Explorer (IUE). Broadband photometry and a newly computed grid of line blanketed model atmospheres were used to determine accurate angular diameters and total stellar fluxes. The resultant effective temperatures are in most cases in satisfactory agreement with those based on broadband photometry and/or high resolution spectroscopy in the visible. For two objects, LSII +33 deg 5 and LSE 78, disagreement was found between the IUE observations and broadband photometry: the colors predict temperatures around 20,000 K, whereas the UV spectra indicate much lower photospheric temperatures of 14,000 to 15,000 K. The new temperature scale for extreme helium stars extends to lower effective temperatures than that of Heber and Schoenberner (1981) and covers the range from 8,500 K to 32,000 K. Previously announced in STAR as N83-24433

Heber, U.; Drilling, J. S.; Schoenberner, D.; Lynas-Gray, A. E.

1984-01-01

427

Helium retention and diffusivity in flowing liquid lithium  

International Nuclear Information System (INIS)

The flowing liquid surface retention experiment (FLIRE) has been designed to provide fundamental data on the retention and pumping of He, H and other species in flowing liquid surfaces. The FLIRE facility currently uses an ion beam source, which injects ions into a flowing stream of liquid lithium. Its design allows the liquid lithium to flow between two vacuum chambers that become isolated from each other when the lithium flows. Flow velocities between 0.5 and 3.0 m/s down two ramps inside the upper vacuum chamber can be achieved. The ramps and lines where the liquid lithium flows are heated to temperatures ranging from 250 to 500 deg. C to prevent any possible freezing. A dual residual gas analyzer system monitors the partial pressure of the implanted species in both vacuum chambers. The release rate of gas atoms in the second chamber is directly related to the mechanisms of transport within the metal bulk and also the process of desorption from the surface. For the case of helium, the diffusion coefficient was calculated to be 4.5x10-3 cm2/s at 250 deg. C, with an uncertainty of ±2x10-3 cm2/s. Helium retention coefficients on the order of 10-4 were obtained based on the experimental data

428

Helium-Cooled Refractory Alloys First Wall and Blanket Evaluation  

International Nuclear Information System (INIS)

Under the APEX program the He-cooled system design task is to evaluate and recommend high power density refractory alloy first wall and blanket designs and to recommend and initiate tests to address critical issues. We completed the preliminary design of a helium-cooled, W-5Re alloy, lithium breeder design and the results are reported in this paper. Many areas of the design were assessed, including material selection, helium impurity control, and mechanical, nuclear and thermal hydraulics design, and waste disposal, tritium and safety design. System study results show that at a closed cycle gas turbine (CCGT) gross thermal efficiency of 57.5%, a superconducting coil tokamak reactor, with an aspect ratio of 4, and an output power of 2 GWe, can be projected to have a cost of electricity at 54.6 mill/kWh. Critical issues were identified and we plan to continue the design on some of the critical issues during the next phase of the APEX design study

429

Reliability study of sheathed thermocouples in helium environment  

International Nuclear Information System (INIS)

This paper describes reliability of sheathed thermocouples in helium environment in the temperature range of 1000 - 12000C in contact with graphite. Thermocouple wires of K, R and WRe 5 - 26%, and sheath materials of Inconel 600, Hastelloy X, PR 10% alloy and tantalum were tested at 1000 and 12000C for 1000 hours. Al2O3 and ZrO2 coating with plasma spray method on sheath materials improved compatibility with graphite at 12000C. Vaporization of alloy elements of Inconel 600 sheath caused deterioration of K and R thermocouple wires at 12000C. R wires reacted with MgO insulator at 12000C, and this reaction was enhanced in tantalum sheath. Stability of electric potential of thermocouples was acceptable for K-Inconel 600 sheath at 10000C, and R-PR 10% sheath and WRe 5 - 26%-tantalum sheath at 12000C. Finally, reaction of sheath materials with CO (500 ppm in helium) was investigated at 12000C. Tantalum was severely reacted after 100 hours, whereas PR 10% sheath was sound even after 500 hours. (author)

430

Helium measurements of pore-fluids obtained from SAFOD drillcore  

Energy Technology Data Exchange (ETDEWEB)

{sup 4}He accumulated in fluids is a well established geochemical tracer used to study crustal fluid dynamics. Direct fluid samples are not always collectable; therefore, a method to extract rare gases from matrix fluids of whole rocks by diffusion has been adapted. Helium was measured on matrix fluids extracted from sandstones and mudstones recovered during the San Andreas Fault Observatory at Depth (SAFOD) drilling in California, USA. Samples were typically collected as subcores or from drillcore fragments. Helium concentration and isotope ratios were measured 4-6 times on each sample, and indicate a bulk {sup 4}He diffusion coefficient of 3.5 {+-} 1.3 x 10{sup -8} cm{sup 2}s{sup -1} at 21 C, compared to previously published diffusion coefficients of 1.2 x 10{sup -18} cm{sup 2}s{sup -1} (21 C) to 3.0 x 10{sup -15} cm{sup 2}s{sup -1} (150 C) in the sands and clays. Correcting the diffusion coefficient of {sup 4}He{sub water} for matrix porosity ({approx}3%) and tortuosity ({approx}6-13) produces effective diffusion coefficients of 1 x 10{sup -8} cm{sup 2}s{sup -1} (21 C) and 1 x 10{sup -7} (120 C), effectively isolating pore fluid {sup 4}He from the {sup 4}He contained in the rock matrix. Model calculations indicate that <6% of helium initially dissolved in pore fluids was lost during the sampling process. Complete and quantitative extraction of the pore fluids provide minimum in situ porosity values for sandstones 2.8 {+-} 0.4% (SD, n=4) and mudstones 3.1 {+-} 0.8% (SD, n=4).

Ali, S.; Stute, M.; Torgersen, T.; Winckler, G.; Kennedy, B.M.

2010-04-15