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1

Liquid Helium  

Science.gov (United States)

Preface; 1. Introduction; 2. Equilibrium properties; 3. Theories; 4. The new thermodynamics; 5. First and second sound; 6. Further aspects of the thermodynamics; 7. Helium films; 8. Helium three; 9. He3-He4 mixtures; References; Index.

Atkins, K. R.

2014-06-01

2

First principles assessment of helium trapping in Y2TiO5 in nano-featured ferritic alloys  

Science.gov (United States)

Nano-scale Y2Ti2O7 and Y2TiO5 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 Y2TiO5. The results suggest that helium is more deeply trapped in Y2TiO5 compared to Y2Ti2O7. Helium occupies open channels in Y2TiO5, where it weakly chemically interacts with neighboring oxygen anions, and results in less volume expansion compared to Y2Ti2O7, 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; Jiang, Yong; Yang, Litong; Lan, Guoqiang; Robert Odette, G.; Yamamoto, Takuya; Shang, Jiacheng; Dang, Ying

2014-10-01

3

Solar flare accelerated isotopes of hydrogen and helium. [observed by IMP-4 and IMP-5  

Science.gov (United States)

Measurements of solar flare hydrogen, deuterium, tritium, helium-3, and helium-4 in the energy range approximately 10 to 50 MeV per nucleon obtained with instrumentation on the IMP-4 and IMP-5 satellites are reported and studies based on these results which place several constraints on theories of solar flare particle acceleration are discussed. A brief review of previous work and the difficulties in studying the rare isotopes of hydrogen and helium is also included. Particular emphasis is placed on the fact that the information to be obtained from the solar flare products of high energy interactions is not available through either solar wind observations where both the acceleration mechanism and the coronal source of the nuclear species are different, or optical measurements of solar active regions.

Anglin, J. D.; Dietrich, W. F.; Simpson, J. A.

1973-01-01

4

Kapitza conductance between Gd3Ga5O12 and superfluid helium  

International Nuclear Information System (INIS)

The thermal conductance at the interface between Gd3Ga5O12 and superfluid helium (Kapitza conductance), is a fundamental data for magnetic cooling applications using this material. It has been observed that the heat flux over the interface can be increased by a factor of 2 when the surface is polished

5

Detailed design and transport properties of a helium droplet nozzle from 5 to 50 K  

Science.gov (United States)

This paper reports our efforts to engineer a robust, user-friendly, and broadly tunable helium droplet nozzle, and to quantitatively measure its thermal and mass transport performance. In addition to describing the physical design in detail, we report helium throughput measurements for a 6.4 ?m diameter nozzle over stagnation conditions ranging from 5 to 50 K and 10 to 100 bar. The measured flow rates were in excellent agreement with those predicted by a simple effusive flow model for nozzle temperatures above 20 K, but were systematically lower for both sub-critical and super-critical jets as the temperature was lowered. The helium flow through a 500 ?m skimmer was also measured, and the skimmed fraction was found to vary by two orders of magnitude over the range of stagnation conditions investigated. These results indicate a substantial narrowing of the total jet angle spread from ˜90° to 5° at temperatures below 10 K. Efforts to image the low temperature jet with Schlieren and shadowgraph techniques were unsuccessful. These details combined with previously reported theory and experiments on the droplet size distributions provide the necessary foundation to predict cluster production rates and to customize nozzle/pump designs for specific applications.

Cleaver, Rebecca M.; Lindsay, C. Michael

2012-07-01

6

Antiprotonic helium  

CERN Multimedia

An exotic atom in w hich an electron and an antiproton orbit a helium nucleus could reveal if there are any differences between matter and antimatter. The author describes this unusual mirror on the antiworld (5 pages)

Eades, John

2005-01-01

7

Specification of Four New Large 4.5 K Helium Refrigerators for the LHC  

CERN Document Server

The cooling capacity for the superconducting magnets in the Large Hadron Collider (LHC) at the European Laboratory for Particle Physics, CERN will be provided by eight helium refrigerators serving the eight 3.3 km long machine sectors. Of these eight refrigerators, four are already existing and are currently used for the Large Electron Positron Collider (LEP) project. These existing refrigerators have to be modified to serve the requirements for the LHC. Four new refrigerators providing cooling capacity down to 4.5 K will be added. All eight 4.5 K refrigerators will be completed by 1.8 K cooling stages. This presentation recalls the cryogenic architecture of the LHC, the constraints in process design resulting from it and from the desired capacity for steady state and transient operation. It then describes how these requirements were expressed in the technical specification for the four new 4.5 K refrigerators to be delivered between the years 2000 and 2002.

Claudet, S; Wagner, U

1999-01-01

8

Investigation of accident cases for high pressure, high temperature experimental helium loop using RELAP5-3D code  

International Nuclear Information System (INIS)

Accident cases are investigated for the Helium Loop Karlsruhe (HELOKA) facility, a high pressure and high temperature experimental helium loop having the European Helium Cooled Pebble Beds (HCPB) Test Blanket Module (TBM) as test module. Two typical operation modes for the loop operation have been numerically modeled using RELAP5-3D code: a pulsed operation (ITER-like situation) and a steady state operation (very long pulse). In both situations a maximum heat load on the first wall of 500 kW/m2 has been considered. Using the generated RELAP-model for these two operating modes three accident cases are studied: failure of helium pressure control system (PCS), loss of helium flow and loss of cooling water flow. Simulation results show that the most critical case is the loss of helium flow. In this case failure of the TBM box is possible. By the loss of cooling water the integrity of the TBM box could be assured, if actions are taken in time. By the failure of the PCS the integrity of pressure barriers are not affected.

9

Tensile properties of helium-injected V-15Cr-5Ti after irradiation in EBR-II  

International Nuclear Information System (INIS)

Miniature specimens of V-15Cr-5Ti were prepared in the annealed condition and with 10, 20, and 30% cold work. The annealed specimens were cyclotron injected with helium and irradiated in sodium in EBR-II. The cold-worked specimens were irradiated in EBR-II but not helium injected. The specimens were irradiated at 400, 525, 625, and 7000C and received a fluence of 4.1 to 5.5 x 1026 neutrons/m2 (E > 0.1 meV). Tensile testing revealed very significant embrittlement as a result of the neutron irradiation but a much smaller change, mostly at 4000C, resulting from helium injection. 5 references, 9 figures, 2 tables

10

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

11

Floating Pressure Conversion and Equipment Upgrades of Two 3.5kw, 20k, Helium Refrigerators  

Science.gov (United States)

Two helium refrigerators, each rated for 3.5KW at 20K, are used at NASA s Johnson Space Center (JSC) in Building No. 32 to provide cryo-pumping within two large thermal-vacuum chambers. These refrigerators were originally commissioned in 1996. Equipment refurbishment and upgrades to the controls of these refrigerators were recently completed. This paper describes some of the mechanical and control issues that necessitated the equipment refurbishment and 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 upgrades -- the controls philosophy change-over to the floating pressure control technology and the newly refurbished equipment -- 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). Capabilities, configuration, and performance data pre, and post, upgrading will be presented.

Homan, Jonathan; Linza, Robert; Garcia, Sam; Vargas, Gerardo; Lauterbach, John; Ganni, Venkatarao (Rao); Sidi-Yekhlef, Ahmed; Creel, Jonathan; Norton, Robert; Urbin, John; Howe, Don

2008-01-01

12

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

13

Neutron Small Angle Scattering on Liquid Helium in the temperature Range 1.5-4.2 K  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The small angle neutron scattering from liquid helium at saturated vapour pressure in the temperature range from 1.5 to 4.2 K was measured with the instrument D22 of the ILL Grenoble at a wavelength of 4.6 angstrom. The zero angle cross section is monotonically decreasing with decreasing temperature and does not show any singularity at the lambda-point. On the other handd, we observe a change of the slope of the temperature dependence of thw second momentum of the pair corre...

Tsipenyuk, Yu M.; May, R. P.

2002-01-01

14

Development of analytical procedure for the design of 1.5 Mwt helium gas intermediate heat exchanger  

International Nuclear Information System (INIS)

This paper reports the structural integrity study of 1.5 Mwt helium gas intermediate heat exchanger performed as a part of 'Research and Development of Direct Steel Making Technology Utilizing High Temperature Reducing Gas' which is one of the National Research and Development Programs by Agency of Industrial Science and Technology, Ministry of International Trade and Industry, Japan. The normal operation temperature of the heat exchanger exceeds 10000C which is beyond the scope covered by the existing design code, e.g. ASME Code Case 1592. Therefore, a special analytical and experimental procedure should be developed to establish design rules of unprecedented components operating at extremely high temperature. (orig.)

15

A 6 kW at 4.5 K helium refrigerator for CERN's Cryogenic Test Station  

International Nuclear Information System (INIS)

For purposes of testing the present LEP superconducting resonant cavities and the future LHC magnets, CERN built a test station the cryogenic power of which is presently supplied by a dedicated 6 kW at 4.5 K helium refrigerator. The thermodynamic cycle is discussed and special emphasis is put on a new cryogenic expansion turbine operating in the liquid phase. Information is given about: the cycle screw compressors' performances, the general performance of the refrigerator, the expected efficiency enhancement due to the liquid turbine, an off-design turn down operation

16

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.)

17

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

18

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

19

?-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

20

Correlation between hydrogen and helium retentions in stainless steel irradiated with helium and hydrogen  

International Nuclear Information System (INIS)

Helium depth profiles have been measured for stainless steel pre-irradiated with 10 keV helium and post-irradiated with 5 keV hydrogen. Helium profiles observed as a function of helium fluence are similar to the hydrogen profiles previously measured using the 1H(15N, ? ?)12C reaction. The difference in helium retention observed with and without post-irradiation of hydrogen has revealed an obvious reduction of helium by hydrogen post-irradiation. (orig.)

 
 
 
 
21

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

CERN Document Server

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 way to alternative technological solutions for polarized helium-3 applications and in particular for magnetic resonance imaging of human lungs.

Abboud, M; Maitre, X; Tastevin, G; Nacher, P J; Abboud, Marie; Sinatra, Alice; Maitre, Xavier; Tastevin, Genevieve; Nacher, Pierre-Jean

2003-01-01

22

Relativistic helium fragments emitted in 24 Mg and 22 Ne-emulsion interactions at nearly 4.5 A GeV/c  

International Nuclear Information System (INIS)

Experimental data of 4.5 A GeV/c 24 Mg and 4.1 A GeV/c 22 Ne interactions in nuclear emulsion have, been investigated. The multiplicity distributions of the projectile helium fragments exhibit a K NO scaling. The values of C2, C3 and C4 moments are found to be independent of masses and energies of the projectiles. The average multiplicities for the projectile helium fragments for different projectiles at various incident energies can be parametrized in terms of the projectile mass number

23

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

24

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 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

25

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)

26

Metastability Exchange Optical Pumping of Helium-3 at High Pressures and 1.5 T: Comparison of two Optical Pumping Transitions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

At low magnetic field, metastability exchange optical pumping of helium-3 is known to provide high nuclear polarizations for pressures around 1 mbar. In a recent paper, we demonstrated that operating at 1.5 T can significantly improve the results of metastability exchange optical pumping at high pressures. Here, we compare the performances of two different optical pumping lines at 1.5 T, and show that either the achieved nuclear polarization or the production rate can be opt...

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

2005-01-01

27

Influence of boron-generated helium on the swelling of neutron irradiated V, V-5Cr and V-5Fe  

International Nuclear Information System (INIS)

The effect of He on dimensional stability of V, V-5Cr and V-5Fe alloys has been studied using the B doping technique. The addition of 5 wt% Cr to pure V leads to a significant increase in neutron-induced swelling at 600 C. Although the swelling of V-5Cr increases strongly with irradiation temperature, the influence of Cr is reversed at lower temperatures, with pure V swelling more than V-5Cr. The use of B additions to generate relatively large amounts of He in V, V-5Cr and V-5Fe leads to a very complex swelling response, depending on the B level and the irradiation temperature. At 520 C, B addition is found to increase the cavity density. However, the most pronounced response occurs in V-5Cr at 600 C, where B levels of 100 appm or greater cause a significant reduction in swelling. The complexity of swelling response is thought to result from the competition between He effects and the separate chemical effects of B and Li, each of which may exhibit its own dependence on irradiation temperature. (orig.)

28

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

29

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 way to alternativ...

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

2004-01-01

30

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; Maitre, Xavier; Tastevin, Genevieve; Nacher, Pierre-jean

2003-01-01

31

Helium bubble growth during 1 MeV electron irradiation at 300 K in 5 keV-He+ pre-implanted nickel and an amorphous Fe-Ni-Mo-B alloy  

International Nuclear Information System (INIS)

The influence of 1 MeV electron irradiation at 300 K on the diameter distribution of helium bubbles after 5 keV He+ implantation in nickel and in Metglas 2826 MB (Fe40 Ni38 Mo4 B18) is investigated. Electron irradiation induces additional bubble growth in both materials. Helium bubble growth in nickel as function of damage dose (2 to 18 dpa) is as effective during e- irradiation of a He+ pre-implanted specimen as it is the case during further He+ implantation. This indicates that a significant proportion of the implanted helium resides outside the bubbles after He+ implantation and that this helium precipitates into the bubbles during electron irradiation. In the amorphous alloy, the helium bubbles grow less during electron irradiation than during further He+ implantation. (author)

32

Helium effect on the structure of Fe-0.6C-16Cr-15Ni-3Mo-0.5Nb steel  

International Nuclear Information System (INIS)

The microstructure of Fe-0.6C-16Cr-15Ni-3Mo-0.5Nb stainless steel was studied by transmission electron microscopy (TEM) after helium implantation to 0.5-1000 appm at temperature 5 appm and at temperatures of 600-900 C. Change in the aging temperature leads to changes in particle morphology caused by the evolution of interstitial type dislocation loops. Plate-shaped particles are formed in the matrix as a result of impurity segregation at the stacking faults of Frank loops, whereas globular particles are produced in the region of dislocation cores of unfaulted loops. (orig.)

33

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

Energy Technology Data Exchange (ETDEWEB)

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.

Lebrun, Philippe [DG unit, CERN, CH-1211 Geneva 23 (Switzerland); Parma, Vittorio; Tavian, Laurent [TE department, CERN, CH-1211 Geneva 23 (Switzerland)

2014-01-29

34

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

35

Differential cross sections for ejection of electrons and dissociative ionisation cross sections for 5-20 keV H2+ and H3+ impacts on helium  

International Nuclear Information System (INIS)

The absolute electron-production cross sections for 5-20 keV H2+ and 5-20 keV H3+ impacts on helium, differential in angle and energy of the ejected electrons, have been measured for electron energies of 2-50 eV at ejection angles of 300, 600, 900 and 1200. The dissociative ionisation cross sections are derived from the present differential cross sections for electron production and compared with the results of direct measurement by Guidini (C.R. Acad. Sci., Paris 253: 829 (1961)). (author)

36

ISABELLE forced circulation cooling system: proposed method of producing and distributing helium refrigerant for 4.5 K superconducting magnets  

International Nuclear Information System (INIS)

A report is given of the refrigeration system proposed for ISABELLE. The system features a single refrigerator of about 25 kW capacity. The refrigerant helium is supplied to the 960 ISABELLE Magnets at a pressure of 15 atm and a temperature of 2.80K. The return to the refrigerator is at 14.3 atm and a 6.20K. As many as 60 magnets will be cooled in series. The steady-state design temperature for the warmest magnet is 4.30K. This temperature will rise to 4.50K during the acceleration cycle

37

Nanoparticle dispersion in superfluid helium  

Science.gov (United States)

Cryogenic fluid flows including liquid nitrogen and superfluid helium are a rich environment for novel scientific discovery. Flows can be measured optically and dynamically when faithful tracer particles are dispersed in the liquid. We present a reliable technique for dispersing commercially available fluorescent nanoparticles into cryogenic fluids using ultrasound. Five types of fluorescent nanoparticles ranging in size from 5 nm to 1 ?m were imaged in liquid nitrogen and superfluid helium, and were tracked at frame rates up to 100 Hz.

Meichle, David P.; Lathrop, Daniel P.

2014-07-01

38

Helium cooled nuclear reactors  

International Nuclear Information System (INIS)

A closed loop coolant circuit for a helium cooled high temperature reactor is described. The circuit has a conventional purification by-pass loop including an oxidizing bed for impurities and an absorption bed for the oxidized impurities. A recycle pipe line is provided whereby a fraction of wet gas leaving the oxidizing bed is returned to the main coolant circuit. 8 claims, 5 drawing figures

39

Helium production cross section measurement by helium atoms measurement system  

International Nuclear Information System (INIS)

Proton-induced helium production cross sections for nickel at proton energies up to 16 MeV have been measured with a helium accumulation method. A sample is a nickel sheet (chemical purity 99.98%, sizes 12x9x0.119 mm3) sandwiched between two gold foils (chemical purity 99.99%, size 12x9x0.051 mm3) which are collectors for the emitted ?-particles from the nickel surfaces. Nine nickel samples were irradiated by protons ranging from 8.8 to 17.5 MeV at Kyushu University Tandem Accelerator Laboratory. The number of helium atoms produced and accumulated in the nickel foil and two gold collectors was measured using the helium atoms measurement system. (author)

40

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.

 
 
 
 
41

Counting Individual Electrons on Liquid Helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show that small numbers of electrons, including a single electron, can be held in a novel electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 micron diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor (SET) as an electrometer. A Coulomb staircase is observ...

Papageorgiou, G.; Glasson, P.; Harrabi, K.; Antonov, V.; Collin, E.; Fozooni, P.; Frayne, P. G.; Lea, M. J.; Mukharsky, Y.; Rees, D. G.; van der

2004-01-01

42

Helium removal and recycling  

International Nuclear Information System (INIS)

This paper deals with two, on first sight only loosely related topics: Firstly, with the issue of helium removal from a stationary burning D-T fusion device, and secondly, with the so called 'recycling process' in the plasma near exposed first wall components. The strong interrelation of these two issues will be a major point in the discussion. It is observed that the helium removal for steady plasma burn is apparently very closely connected with the details of plasma recycling via the neutral particle channel. Firstly because only neutral ash particles can be channeled into pumping stations, but secondly also because of the effects of neutral particle recycling on the edge plasma flow, and thus on the forces acting on the ionized helium particles. Various conflicting requirements have to be met simultaneously such as: good confinement (for energy balance); poor confinement (for particle throughput); strong pumping (for ash removal); and weak pumping (for favorable high recycling conditions). The search for a plasma edge configuration compatible with all these constraints, both experimentally and by computer simulations, is one of the key design issues to be solved before a reliable plasma surface interaction concept for ITER (and a future reactor) can be developed. 9 refs., 5 figs

43

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

44

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 (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.

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

2013-02-01

45

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

46

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

47

Influence of helium I layer formation on the copper-helium-4 Kapitza resistance at helium II bath temperatures  

International Nuclear Information System (INIS)

The transient Kapitza resistance between copper and helium II caused by a step input in power has been studied near 2 K. The resistance is affected by formation of a helium I layer whose thickness, of the order 10-4--10-5 cm, is evaluated as a function of the heat flux density

48

Thermal-Hydraulic System Study of the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) for ITER Using System Code RELAP5  

Science.gov (United States)

The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The thermal-hydraulic effect of the TBM-combined cooling circuit during a cyclic operation in ITER has been studied using the system code RELAP5. The RELAP5 is based on an one-dimensional, transient two-fluid model for the flow of a two-phase steam-water mixture that can contain noncondensable components like Helium. The RELAP5-models are modified to take the cyclic operation of the circulator, heat exchanger, bypass, valves etc in to account. A sequence of operational phases is investigated, starting from the cold state through the heating phase that brings the system to a stand-by condition, followed by typical power cycles applied in ITER. The results show that the implemented control mechanisms keep the inlet temperature to the TBM and the total mass flow rate at the required values through all phases.

Jin, Xuezhou; R, Meyder

2005-04-01

49

Thermal-hydraulic system study of the helium cooled pebble bed (HCPB) test blanket module (TBM) for ITER using system code RELAP5  

International Nuclear Information System (INIS)

The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The thermal-hydraulic effect of the TBM-combined cooling circuit during a cyclic operation in ITER has been studied using the system code RELAP5. The RELAP5 is based on an one-dimensional, transient two-fluid model for the flow of a two-phase steam-water mixture that can contain noncondensable components like Helium. The RELAP5-models are modified to take the cyclic operation of the circulator, heat exchanger, bypass, valves etc in to account. A sequence of operational phases is investigated, starting from the cold state through the heating phase that brings the system to a stand-by condition, followed by typical power cycles applied in ITER. The results show that the implemented control mechanisms keep the inlet temperature to the TBM and the total mass flow rate at the required values through all phases. (authors)

50

Dynamics and helium distribution in hydrogen-helium fluid planets  

International Nuclear Information System (INIS)

A semiquantitative analysis of the thermal and compositional history of an evolving hydrogen-helium planet such as Jupiter or Saturn is presented. First, the evolution of a homogeneous planet with no first-order phase transitions or immiscibilities is considered. Adiabatic, evolutionary models are discussed. The times taken for Jupiter and Saturn to reach their observed luminosities are about 4 x 109 and 2 x 109 years, respectively, essentially independent of formation details. The result for Saturn appears to be inconsistent with its actual age, assumed to be approx.4.5 x 109 years.Next, the effects of a first-order molecular-metallic hydrogen transition are discussed for a pure hydrogen planet: A well-defined interface between the phases persists, despite the presence of convection. The temperature is continuous at the interface and the entropy is discontinuous, the charge in entropy being equal to the latent heat of transition. Consequently, the heat content and derived ''age'' differ from the determined for a purely adiabatic model (by a factor between 1 and 2, depending on the unknown latent heat). Convection in the presense of a composition gradient is discussed, and the importance of overstable modes and diffusive-convective equilibria established. The convective transport of helium away from a localized helium source is shown to be inefficient because helium diffusivity is much less than heat diffusivity. Evolutions with helium immiscibility are discussed

51

The cosmic helium abundance  

Science.gov (United States)

Cosmic helium abundance was studied through the interior structure of young stars, profiles of helium absorption lines in the photospheric spectra of hot young stars, and emission-line spectrum of ionized gas. It is concluded that helium occurred before galaxies were formed. Inconsistencies found in the quasar spectra are briefly mentioned.

Searle, L.

1971-01-01

52

Liquid helium target  

International Nuclear Information System (INIS)

A liquid helium target system has been built and used for the experiment on the reaction 4He(?, p). The target system has worked satisfactorily; the consumption rate of liquid helium is 360 ml/h and the cryogenic system retains liquid helium for about ten hours. The structure, operation and performance of the target system are reported. (author)

53

Mobility of ? particles in helium  

International Nuclear Information System (INIS)

The mobility of ? particles in helium gas is calculated using the zeroth-order Viehland-Mason theory with interaction potentials recently computed by Cohen and Bardsley. The results show a dependence on field strength similar to the measurements of Johnsen and Biondi but are lower in magnitude by about 5%

54

Theoretical description of the ejected-electron spectrum in collisions of 1.5-MeV/u F9+ with helium  

International Nuclear Information System (INIS)

We present the results of an extensive classical trajectory Monte Carlo (CTMC) simulation of the ejected electron spectrum in collisions of 1.5-MeV/u F9+ with helium. Excellent agreement is found with the measurements of Lee et al. [Phys. Rev. A 41, 4816 (1990)] for ejection to 0 degree. In particular, the simulation reproduces extremely well the shape and magnitude of the electron-capture-to-the-continuum and binary peaks. We contrast this agreement with calculations utilizing various quantum-mechanical perturbation theories. Also, a continuum-distorted-wave--eikonal-initial-state approach, which describes the interaction between the outgoing electron and the residual target ion through a model potential, has been utilized. This approach is shown to be an improvement over conventional calculations based on the use of effective charges. We draw conclusions regarding the proper representation of the collision dynamics leading to electron ejection in the low-energy, electron-capture-to-the-continuum, and binary peak regimes. Calculations of the doubly differential ionization cross section for non-0 degree ejection are displayed as well

55

Trapping single electrons on liquid helium  

Science.gov (United States)

Surface-state electrons on liquid helium, localised in quantum dots, have been proposed as condensed matter qubits. We now demonstrate experimentally that small numbers of electrons, including a single isolated electron, can be held in a novel electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 ?m diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor (SET) as an electrometer. A Coulomb staircase is observed as electrons leave the trap one-by-one until the trap is empty. A design for a prototype quantum information processor using an array of electron traps on liquid helium is presented.

Glasson, P.; Papageorgiou, G.; Harrabi, K.; Rees, D. G.; Antonov, V.; Collin, E.; Fozooni, P.; Frayne, P. G.; Mukharsky, Y.; Lea, M. J.

2005-08-01

56

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

57

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

58

Space helium refrigerator  

Science.gov (United States)

Design studies and flight tests of an automatic closed-cycle three-cascade helium refrigerator are presented. Intended for cooling submillimeter telescope detectors to 4.4 K on the orbital station Salyut-6, the cryogenic system is based on the Joule-Thomson cooling effect, with two gas cooling machines operating under the Stirling cycle for preliminary cooling levels of 80 K and 20 K. Power requirements are less than 1.5 kW, while providing useful refrigeration of 0.5 W. Results of two years of flight tests indicate successful operation, including the merits of high accuracy and stability in maintaining operation temperature, short cool-down period, high efficiency, reliability and simplicity of operation.

Salomonovich, A. E.; Sidiakina, T. M.; Khaikin, A. S.; Bakun, V. N.; Nikonov, A. A.; Maslakov, V. A.; Klimenko, E. I.; Kurkin, V. N.

1981-08-01

59

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

60

Helium bubble kinetics during laser welding of helium-doped stainless steel  

International Nuclear Information System (INIS)

Helium is generated within neutron-irradiated reactor components and entrapped in the stainless steel components. The repair of the components using conventional GTA welding practices is then exceedingly difficult, because of the creation of helium bubbles and weld cracking. In this research, the behavior of helium bubbles in austenitic stainless steel weldments was investigated using stainless steel helium ion-implanted and then welded using YAG Laser apparatus. Helium ion implanting of the sample was carried out using 8MeV implantation apparatus, the sample being doped 2.45?1019/m2 at 6MeV and then doped 1?1019/m2 at 5MeV. Helium bubbles are present at the bond region, heat-affected zone and weld metal. An increase of weld heat input causes the growth of helium bubbles and produce toe cracks and cracks along the dendrite cell boundary in the weld metal. The helium bubble phenomena can be simulated in the weld metal and in the heat-affected zone during repair welding using helium ion implanting technique. (author)

 
 
 
 
61

Behavior of helium bubble in helium-doped stainless steel weldment for nuclear power plant  

International Nuclear Information System (INIS)

The behavior of helium bubble in helium-doped austenitic stainless steel weldment was investigated using scanning electron microscopy, transmission electron microscopy and numerical calculation technique. The stainless steel was helium ion-implanted and welded by YAG laser apparatus. Helium ion implanting to the sample was carried out using 8 MeV implantation apparatus. The sample was doped 1.0x1019 atoms/m2 at 5 MeV and then doped 2.45x1019 atoms/m2 at 6 MeV. The region where helium bubbles formed in the heat-affected zone increased with increasing laser power. For low laser power, the helium concentration was above 10 appm in the weld metal and many large helium bubbles larger than 3 ?m in diameter were observed at the bond region. The volume of weld metal increased and the size of helium bubble decreased with increasing laser power respectively. Number of fine helium bubbles below 0.1 ?m in diameter were observed along the dendrite cell boundary in the weld metal. The increases of laser power and travel speed led to the initiation of cracking at the dendrite cell boundary in the weld metal, even at 2.9 appmHe. (author)

62

Helium diffusion in carbonates  

Science.gov (United States)

The abundance and large grain size of carbonate minerals make them a potentially attractive target for 4He thermochronology and 3He cosmogenic dating, although the diffusive properties of helium in carbonates remain poorly understood. This work characterizes helium diffusion in calcite and dolomite to better understand the crystal-chemical factors controlling He transport and retentivity. Slabs of cleaved natural calcite and dolomite, and polished sections of calcite cut parallel or normal to c, were implanted with 3He at 3 MeV with a dose of 5x1015/cm2. Implanted carbonates were heated in 1-atm furnaces, and 3He distributions following diffusion anneals were profiled with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For 3He transport normal to cleavage surfaces in calcite, we obtain the following Arrhenius relation over the temperature range 78-300°C: Dcalcite = 9.0x10-9exp(-55 × 6 kJ mol-1/RT) m2sec-1. Diffusion in calcite exhibits marked anisotropy, with diffusion parallel to c about two orders of magnitude slower than diffusion normal to cleavage faces. He diffusivities for transport normal to the c-axis are similar in value to those normal to cleavage surfaces. Our findings are broadly consistent with helium diffusivities from step-heating measurements of calcite by Copeland et al. (2007); these bulk degassing data may reflect varying effects of diffusional anisotropy. Helium diffusion normal to cleavage surfaces in dolomite is significantly slower than diffusion in calcite, and has a much higher activation energy for diffusion. For dolomite, we obtain the following Arrhenius relation for He diffusion over the temperature range 150-400°C: Ddolomite = 9.0x10-8exp(-92 × 9 kJ mol-1/RT) m2sec-1. The role of crystallographic structure in influencing these differences among diffusivities was evaluated using the maximum aperture approach of Cherniak and Watson (2011), in which crystallographic structures are sectioned along possible diffusion directions and the maximum interstitial apertures in each 'slice' in the structure are identified. Preliminary results show that observed differences in diffusivities are consistent with the size of the smallest maximum aperture along each diffusion direction. In calcite, the smallest maximum apertures are ~0.92 and ~0.66 angstroms for cleavage-normal and c-axis parallel directions respectively. In dolomite, the smallest maximum aperture is ~0.78 angstroms for the cleavage normal direction. Work is in progress on characterizing helium diffusion for other orientations in dolomite, and in other carbonates, including aragonite and magnesite, and in implementing these diffusion findings in the interpretation and modeling of bulk volume diffusion in heterogeneous calcite crystals common in many geologic applications. Copeland et al. (2007) GCA 71, 4488-4511 Cherniak and Watson, (2011) Chem. Geo. 288, 149-161

Amidon, W. H.; Cherniak, D. J.; Watson, E. B.; Hobbs, D.

2013-12-01

63

Chemistry in liquid helium  

International Nuclear Information System (INIS)

Helium is well known as a typical quantum liquid and a quantum solid. Because of very peculiar properties originating from quantum character, liquid and solid helium have been attracting many scientists. However, the studies are mostly focused on the physical aspects. Recent development using laser sputtering technique to introduce metal ions or neutral atoms into the liquid helium accelerated the spectroscopic investigation of bubble, snowball and cluster formed in the superfluid helium from chemical point of view. Compared with the rapid progress of spectroscopy of impurities in the liquid helium, no attempt has been carried out to observe chemical reaction in the liquid helium medium. The author has been trying to observe the chemical reaction of hydrogen isotopes in the liquid helium. In the present article, behavior of impurity ions, atoms in the liquid helium is reviewed from chemical point of view and the recent experimental results of tunneling abstraction reaction of tritium atom with H2 and D2 in super- and normalfluid helium are introduced. (author). 52 refs

64

Classical Helium Model  

Science.gov (United States)

The EJS Classical Helium Model is an example of a three-body problem that is similar to the gravitational three-body problem of a heavy sun and two light planets. The important difference is that the helium atom's two electrons repel one another, unlike the planetary case where the intraplanetary interaction is attractive. The EJS Classical Helium Model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_mech_orbits_ClassicalHelium.jar file will run the program if Java is installed.

Christian, Wolfgang

2009-03-14

65

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

66

Helium refrigeration considerations for cryomodule design  

Science.gov (United States)

Many of the present day accelerators are based on superconducting radio frequency (SRF) cavities, packaged in cryo-modules (CM), which depend on helium refrigeration at sub-atmospheric pressures, nominally 2 K. These specialized helium refrigeration systems are quite cost intensive to produce and operate. Particularly as there is typically no work extraction below the 4.5-K supply, it is important that the exergy loss between this temperature level and the CM load temperature(s) be minimized by the process configuration choices. This paper will present, compare and discuss several possible helium distribution process arrangements to support the CM loads.

Ganni, V.; Knudsen, P.

2014-01-01

67

Counting Individual Trapped Electrons on Liquid Helium  

Science.gov (United States)

We show that small numbers of electrons, including a single isolated electron, can be held in an electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 ?m diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor as an electrometer. A Coulomb staircase is observed as electrons leave the trap one-by-one until the trap is empty. A design for a scalable quantum information processor using an array of electron traps is presented.

Papageorgiou, G.; Glasson, P.; Harrabi, K.; Antonov, V.; Collin, E.; Fozooni, P.; Frayne, P. G.; Lea, M. J.; Rees, D. G.; Mukharsky, Y.

2005-04-01

68

Counting Individual Electrons on Liquid Helium  

CERN Document Server

We show that small numbers of electrons, including a single electron, can be held in a novel electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 micron diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor (SET) as an electrometer. A Coulomb staircase is observed as electrons leave the trap one-by-one until the trap is empty. A design for a scalable quantum information processor using arrays of electron traps is presented

Papageorgiou, G

2004-01-01

69

Helium refrigeration considerations for cryomodule design  

International Nuclear Information System (INIS)

Many of the present day accelerators are based on superconducting radio frequency (SRF) cavities, packaged in cryo-modules (CM), which depend on helium refrigeration at sub-atmospheric pressures, nominally 2 K. These specialized helium refrigeration systems are quite cost intensive to produce and operate. Particularly as there is typically no work extraction below the 4.5-K supply, it is important that the exergy loss between this temperature level and the CM load temperature(s) be minimized by the process configuration choices. This paper will present, compare and discuss several possible helium distribution process arrangements to support the CM loads

70

Helium refrigeration considerations for cryomodule design  

Energy Technology Data Exchange (ETDEWEB)

Many of the present day accelerators are based on superconducting radio frequency (SRF) cavities, packaged in cryo-modules (CM), which depend on helium refrigeration at sub-atmospheric pressures, nominally 2 K. These specialized helium refrigeration systems are quite cost intensive to produce and operate. Particularly as there is typically no work extraction below the 4.5-K supply, it is important that the exergy loss between this temperature level and the CM load temperature(s) be minimized by the process configuration choices. This paper will present, compare and discuss several possible helium distribution process arrangements to support the CM loads.

Ganni, V.; Knudsen, P. [Thomas Jefferson National Accelerator Facility (JLab), Newport News, VA 23606 (United States)

2014-01-29

71

Metal tritides helium emission  

International Nuclear Information System (INIS)

Over the past several years, we have been measuring the release of helium from metal tritides (primarily erbium tritide). We find that qualitatively all tritides of interest to us behave the same. When they are first formed, the helium is released at a low rate that appears to be related to the amount of surface area which has access to the outside of the material (either film or bulk). For example, erbium tritide films initially release about 0.3% of the helium generated. Most tritide films emit helium at about this rate initially. At some later time, which depends upon the amount of helium generated, the parent occluding element and the degree of tritium saturation of the dihydride phase the helium emission changes to a new mode in which it is released at approximately the rate at which it is generated (for example, we measure this value to be approx. = .31 He/Er for ErT1.9 films). If erbium ditritide is saturated beyond 1.9 T/Er, the critical helium/metal ratio decreases. For example, in bulk powders ErT2.15 reaches critical release concentration at approx. = 0.03. Moderate elevation of temperature above room temperature has little impact on the helium release rate. It appears that the process may have approx. = 2 kcal/mol activation energy. The first helium formed is well bound. As the tritide ages, the helium is found in higher energy sites. Similar but less extensive measurements on scandium, titanium, and zirconium tritides are also described. Finally, the thermal desorption of erbium tritides of various ages from 50 days to 3154 days is discussed. Significant helium is desorbed along with the tritium in all but the youngest samples during thermodesorption

72

Disalignment rates of the neon 2p{sub 5} and 2p{sub 10} atoms due to helium atom collisions measured at temperatures between 77 and 294 K  

Energy Technology Data Exchange (ETDEWEB)

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 2p{sub 5} and 2p{sub 10} (in Paschen notation) levels are measured by a polarization-resolved laser-induced fluorescence technique. For the 2p{sub 10} 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 2p{sub 5} level at any temperatures between 77 and 294 K, and for the 2p{sub 10} state only at 294 K. Below 294 K, the experimental rate coefficients for the 2p{sub 10} state show a more rapid decrease with the decrease in temperature than the theory predicts.

Matsukuma, H; Shikama, T; Hasuo, M, E-mail: hiraku@t04.mbox.media.kyoto-u.ac.jp [Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Yoshida Hon-machi, Sakyo, Kyoto, 606-8501 (Japan)

2011-04-14

73

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)

74

In beam tests of implanted helium targets  

Science.gov (United States)

Targets of 3,4He implanted into thin aluminum foils (approximately 100, 200 or 600 ?g/cm2) were prepared using intense helium beams at low energy (20, 40 or 100 keV). Uniformity was achieved by a beam raster across a tantalum collimator at the rates of 0.1 Hz (vertical) and 1 Hz (horizontal). Helium implantation into the very thin (80-100 ?g/cm2) aluminum foils failed to produce useful targets due to an under estimation of the range by SRIM code. The range in aluminum predicted by Northcliffe and Shilling and the NIST online tabulation, on the other hand, over estimate this range. An attempt to implant a second layer was also carried out, but did not significantly increase the helium content beyond the blistering limit. Rutherford Back Scattering of 1.0 and 2.5 MeV proton beams and recoil helium from 15.0 MeV oxygen beams were used to study the helium content and profile. The helium content and profile were very stable even after a prolonged bombardment (two days) with moderately intense beams of 16O or 4He. Helium implanted into thin foils is a good choice, for example, for a measurement of the 3He(?,?)7Be reaction and the associated S34 astrophysical cross section factor (S-factor).

McDonald, J. E.; France, R. H., III; 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. F.; Spraker, M. C.; Yeomans, J. D.; Weissman, L.; Weller, H. R.; Wilds, E. L., Jr.

2006-09-01

75

In beam tests of implanted helium targets  

Energy Technology Data Exchange (ETDEWEB)

Targets of {sup 3,4}He implanted into thin aluminum foils (approximately 100, 200 or 600 {mu}g/cm{sup 2}) were prepared using intense helium beams at low energy (20, 40 or 100 keV). Uniformity was achieved by a beam raster across a tantalum collimator at the rates of 0.1 Hz (vertical) and 1 Hz (horizontal). Helium implantation into the very thin (80-100 {mu}g/cm{sup 2}) aluminum foils failed to produce useful targets due to an under estimation of the range by SRIM code. The range in aluminum predicted by Northcliffe and Shilling and the NIST online tabulation, on the other hand, over estimate this range. An attempt to implant a second layer was also carried out, but did not significantly increase the helium content beyond the blistering limit. Rutherford Back Scattering of 1.0 and 2.5 MeV proton beams and recoil helium from 15.0 MeV oxygen beams were used to study the helium content and profile. The helium content and profile were very stable even after a prolonged bombardment (two days) with moderately intense beams of {sup 16}O or {sup 4}He. Helium implanted into thin foils is a good choice, for example, for a measurement of the {sup 3}He({alpha},{gamma}){sup 7}Be reaction and the associated S{sub 34} astrophysical cross section factor (S-factor)

McDonald, J E [Department of Physics, University of Hartford, 200 Bloomfield Ave, West Hartford, CT 06117-1599 (United States); France, R H III [Department of Chemistry and Physics, Georgia College and State University, Campus Box 82, Milledgeville, GA 31061-0490 (United States); Jarvis, R A [Laboratory for Nuclear Science at Avery Point, University of Connecticut, 1084 Shennecossett Rd, Groton, CT 06340-6097 (United States)] (and others)

2006-09-15

76

In beam tests of implanted helium targets  

International Nuclear Information System (INIS)

Targets of 3,4He implanted into thin aluminum foils (approximately 100, 200 or 600 ?g/cm2) were prepared using intense helium beams at low energy (20, 40 or 100 keV). Uniformity was achieved by a beam raster across a tantalum collimator at the rates of 0.1 Hz (vertical) and 1 Hz (horizontal). Helium implantation into the very thin (80-100 ?g/cm2) aluminum foils failed to produce useful targets due to an under estimation of the range by SRIM code. The range in aluminum predicted by Northcliffe and Shilling and the NIST online tabulation, on the other hand, over estimate this range. An attempt to implant a second layer was also carried out, but did not significantly increase the helium content beyond the blistering limit. Rutherford Back Scattering of 1.0 and 2.5 MeV proton beams and recoil helium from 15.0 MeV oxygen beams were used to study the helium content and profile. The helium content and profile were very stable even after a prolonged bombardment (two days) with moderately intense beams of 16O or 4He. Helium implanted into thin foils is a good choice, for example, for a measurement of the 3He(?,?)7Be reaction and the associated S34 astrophysical cross section factor (S-factor)

77

Experiments on solid Helium-4  

Science.gov (United States)

This thesis presents data on experiments done with hcp 4He. The main focus is on the possibility of superfluidity inside solid 4He. The presence of superfluidity inside the solid should be manifested by a flow through the solid. The aim of these experiments was to search for a D.C. flow, characterize it and determine if the flow is due to superfluidity. A cell was designed that exploits the properties of helium in confined geometries to provide an interface between superfluid liquid helium, and hcp solid helium at pressures greater than the bulk melting curve. This interface allowed for a direct injection of atoms into the solid from the superfluid. With this cell, two different methods can be used to induce flow. In the first method, mass is injected directly into one side of the solid, while the pressure of the other side is monitored for a response. In the second method, flow is induced by changing the temperature of liquid reservoirs connected to the solid through porous Vycor glass. In addition to observing flow, it is also seen that a fountain pressure exists between the two liquid reservoirs connected to each other through the Vycor, and solid helium. Using this same design, the growth of solid helium was also studied at pressure higher than the bulk melting curve. Here, the solid cannot grow along a free surface, since off the melting curve the cell is supposed to be completely filled with solid. Near the melting curve, transients of 1--5 mK are seen in the temperature along with pressure drops ? 160 mbar. These transients are shown to probably be due to the solidification of metastable liquid regions imbedded in the solid. Off the melting curve, growth of the solid continues, and this growth is studied in the context of, "isochoric compressibility."

Ray, Michael William

78

Helium retention and surface morphology of oxidized vanadium alloy  

Energy Technology Data Exchange (ETDEWEB)

The effects of the surface oxidation on the helium desorption and retention behaviors of vanadium alloy were investigated. V-4Cr-4Ti alloy, which was thermally oxidized at 873 K for 15 min with 0.05 Pa, was irradiated by helium ions with energy of 5 keV at room temperature. Then, the helium desorption and retention behaviors were evaluated using a technique of thermal desorption spectroscopy. The changes in surface structures by the irradiation were also evaluated. Helium desorption behavior in low temperature region were significantly changed by the oxidation. Helium desorption around 700 K became large for the oxidized sample. The amount of retained helium and the blister size in the oxidized sample were smaller than of those in the non-oxidized one. These results indicate that the surface oxidation significantly affects the helium retention and desorption behaviors of the vanadium alloy.

Yamauchi, Y., E-mail: yamauchi@qe.eng.hokudai.ac.jp [Laboratory of Plasma Physics and Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan); Oku, D.; Hino, T. [Laboratory of Plasma Physics and Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan); Shibayama, T. [Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan); Nobuta, Y. [Laboratory of Plasma Physics and Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628 (Japan); Nagasaka, T.; Muroga, T. [National Institute for Fusion Science, 322-6, Oroshi-cho, Toki, Gifu 509-5292 (Japan)

2011-10-01

79

Intense pulsed helium droplet beams  

CERN Document Server

Pulsed (30 - 100 microseconds) nozzle beams have been used to generate helium droplets ( = 10^4-10^5). The dependence of the beam intensity and the mean droplet size on the source stagnation pressure and temperature are studied via mass spectroscopy and laser induced fluorescence of embedded phthalocyanine molecules. In comparison to a cw beam the pulsed source for the same pressure and temperature has a factor of 100 higher flux and the droplet sizes are an order of a magnitude larger.

Slipchenko, M N; Momose, T; Vilesov, A F; Slipchenko, Mikhail N.; Kuma, Susumu; Momose, Takamasa; Vilesov, Andrey F.

2002-01-01

80

Co-pumping of deuterium-helium and tritium-helium mixtures at TSTA  

International Nuclear Information System (INIS)

Future fusion experimental devices and power reactors will pump continuously large amounts of helium, and deuterium and tritium (DT). DT to helium ratios greater than 10:1 are projected. Cryopumps are the logical choice to pump gases in the 100 cubic meter per second range. Compound cryopumps, although complex, have been indicated as the preferred method: these pumps will separately pump helium and DT and will provide to the fuel clean-up system relatively helium free DT gas. Recent study however, shows that helium can be proceeded in the fuel cleanup system, negating the need for separate regeneration. A test program undertaken at Los Alamos evaluated the capability of co-pumping the fusion exhaust gases on a liquid helium cooled surface of activated carbon (coconut charcoal). A compound cryopump installed in the VAC system of the Tritium Systems Test Assembly was used as the test article. In the test program, co-pumping of helium and deuterium and helium-3 and tritium was undertaken. Test results show that co-pumping is practical and that compound pumps may not be required for fusion applications. 5 refs., 7 figs

 
 
 
 
81

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)

82

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)

83

An Introduction to the Helium Ion Microscope  

Science.gov (United States)

A new microscope has been developed that uses a beam of helium ions which is focused and scanned across the sample. In principle, and in its applications, it is similar to a traditional scanning electron microscope (SEM). However, the source technology, the sample interaction, and the contrast mechanisms are distinctly different. The helium ion source offers high brightness (4×109 A/cm2sr) and a small energy spread (?E/E˜3×10-5), and hence allows the beam to be focused to small probe sizes (as small as 0.25 nm). As the beam interacts with the sample, the beam penetrates relatively deeply before it diverges and hence there is a narrow sample interaction region near the surface. The helium beam generates secondary electrons, scattered helium atoms (ions and neutrals), and other detectable particles from which images can be generated or analysis can be performed.

Notte, John; Ward, Bill; Economou, Nick; Hill, Ray; Percival, Randy; Farkas, Lou; McVey, Shawn

2007-09-01

84

KSTAR Helium Refrigeration System Design and Manufacturing  

International Nuclear Information System (INIS)

The tokamak developed in the KSTAR (Korean Superconducting Tokamak Advanced Research) project makes intensive use of superconducting magnets operated at 4.5 K. The cold components of the KSTAR tokamak require forced flow of supercritical helium for magnets/structure, boiling liquid helium for current leads, and gaseous helium for thermal shields. The cryogenic system will provide stable operation and full automatic control. A three-pressure helium cycle composed of six turbines has been customised design for this project. The '' design '' operating mode results with a system composed of a 9 kW refrigerator (including safety margin) and using gas and liquid storages for mass balancing. During Shot/Standby mode, the heat loads are highly time-dependent. A thermal damper is used to smooth these variations and will allow stable operation. (author)

85

A proton polarimeter using liquid helium target  

Science.gov (United States)

The design, the calibration and the performance of a high efficiency proton polarimeter for double scattering experiments are described. The polarimeter target is liquid helium held in a conical cell. Protons scattered by helium are detected by two phototubes with CsI(Tl) scintillator, having a diameter of 50 mm and a thickness of 2 mm, and placed at a scattering angle of 60° in the left and right at a distance of 130 mm from the 4He target. The effective analyzing power is about -0.5 and the detection efficiency is about 2×10-4 between 12 and 22 MeV. Once liquid helium is filled in the 6l reservoir tank, the liquid helium target works stably at least for three days.

Mukouhara, Y.; Nakagawa, S.; Kishita, H.; Katabuchi, T.; Hirota, K.; Masaki, M.; Aoki, Y.; Tagishi, Y.

1995-09-01

86

The diffusion of helium in bcc and hexagonal metals  

International Nuclear Information System (INIS)

Foil specimens (2.5-85.0 ?m) of V, Fe (bcc) and Ti, Co and Mg (hcp) were homogenously implanted with helium to final concentrations between 0.001 ppm and 5 ppm. By subsequent thermal desorption measurements three regimes of different desorption behaviour were identified: 1) Free diffusion determined the helium-release as long as the mean distance between a helium atom and the surface was small compared to the mean distance between the helium atoms. For titanium a substitutional mechanismen was proposed, while in all the other metals helium diffuses by a dissociative mechanism with recapture at thermal vacancies (Mg, Co) and implantation-induced vacancies (V, Fe), respectively. 2) Free diffusion was reduced by the agglomeration of helium atoms. The amount of helium released during free diffusion depended on the thickness d and the helium-concentration c0 as 1/d ?c0. This dependence was explained by a simple agglomeration-model. 3) After the formation of helium-bubbles a small helium-release persisted. This could be explained by two different coarsening mechanismens: Bubble-migration and -coalescence (e.g. Mg) and Ostwald-ripening (e.g. Ti). (orig.)

87

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.)

88

Helium analysis of subsurface waters as a uranium exploration tool  

International Nuclear Information System (INIS)

Field studies conducted in areas of known uranium deposits are described. In Weld County, Colorado, 18 samples were collected in an 80 square kilometer area around a roll-type uranium deposit approximately 70 meters deep. Stock supply wells and domestic wells, ranging from 5 to 25 meters deep, were sampled and analyzed for helium. The wells located down the ground water gradient with respect to the ore body had helium concentrations 30 to 50 times greater than those values expected from atmospheric equilibrium. The shallow wells had less helium than the deeper domestic wells. At the Schwartzwalder mine in Jefferson County, Colorado, mine water, pond water, springs and streams were sampled and analyzed for helium. The mine water and springs had helium concentrations 5 to 15 times greater than atmospheric equilibrium, but the ponds and streams, into which the mine water drained, showed no excess helium. The equilibrium values of helium found in the ponds and streams were expected because even minor turbulence effectively removes excess helium from water. Therefore, streams and standing bodies of water are not good candidates for helium analysis. Mine water was also sampled from several uranium mines at the Ambrosia Lake deposits near Grants, New Mexico. The samples were taken at the surface discharge pipes and the helium values were 2 to 7 times that of atmospheric equilibrated waters. Because of both the short residence time of the water with the ore and the great amount of turbulence from pumping, the helium values were relatively low. The large geographic area in the vicinity of a uranium deposit in which subsurface water samples show helium anomalies indicates that helium analyses can be used as a reconnaissance exploration tool

89

The Descending Helium Balloon  

Science.gov (United States)

I describe a simple and fascinating experiment wherein helium leaks out of a rubber balloon, thereby causing it to descend. An estimate of the volumetric leakage rate is made by measuring its rate of descent.

Helseth, Lars Egil

2014-01-01

90

Noncavitating Pump For Liquid Helium  

Science.gov (United States)

Immersion pump features high efficiency in cryogenic service. Simple and reliable centrifugal pump transfers liquid helium with mass-transfer efficiency of 99 percent. Liquid helium drawn into pump by helical inducer, which pressurizes helium slightly to prevent cavitation when liquid enters impeller. Impeller then pressurizes liquid. Purpose of pump to transfer liquid helium from supply to receiver vessel, or to provide liquid helium flow for testing and experimentation.

Hasenbein, Robert; Izenson, Michael; Swift, Walter; Sixsmith, Herbert

1996-01-01

91

Superfluidity of Helium-3  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This article presents a phenomenological dynamic phase transition theory -- modeling and analysis -- for liquid helium-3. We derived two new models, for liquid helium-3 with or without applied field, by introducing three wave functions and using a unified dynamical Ginzburg-Landau model. The analysis of these new models leads to predictions of existence of 1) a unstable region, 2) a new phase C in a narrow region, and 3) switch points of transition types on the coexistence c...

Ma, Tian; Wang, Shouhong

2008-01-01

92

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

93

Charged Hydrogenic, Helium and Helium-Hydrogenic Molecular Chains in a Strong Magnetic Field  

CERN Document Server

A non-relativistic classification of charged molecular hydrogenic, helium and mixed helium-hydrogenic chains with one or two electrons which can exist in a strong magnetic field $B \\lesssim 10^{16} $G is given. It is shown that for both $1e-2e$ cases at the strongest studied magnetic fields the longest hydrogenic chain contains at most five protons indicating to the existence of the $\\rm{H}_5^{4+}$ and $\\rm{H}_5^{3+}$ ions, respectively. In the case of the helium chains the longest chains can exist at the strongest studied magnetic fields with three and four $\\al-$particles for $1e-2e$ cases, respectively. For mixed helium-hydrogenic chains the number of heavy centers can reach five for highest magnetic fields studied. In general, for a fixed magnetic field two-electron chains are more bound than one-electron ones.

Turbiner, A V; Vieyra, J C Lopez

2009-01-01

94

Radiation enhanced diffusion and redistribution of helium in LiNbO3  

International Nuclear Information System (INIS)

Effects of ionizing radiation on helium diffusion and desorption from LiNbO3 previously implanted with helium have been evaluated. The study has been performed for 45 keV helium implanted samples for doses from 2 × 1015 up to 2 × 1017 ions/cm2. The results show that the temperature for helium desorption decreases as the implantation dose increases. In order to study ionizing radiation effects, samples previously implanted with helium were irradiated with 1.8 MeV electrons and the radiation-enhanced helium desorption was measured during irradiation at 500 Gy/s. Ionizing-radiation-enhanced diffusion and redistribution of helium were observed to occur during electron irradiation. The helium-release behavior after 45 keV implantation and after 1.5 keV helium bombardment were compared

95

Helium cooled Flibe blanket  

International Nuclear Information System (INIS)

The blanket design uses a pressure vessel to contain the 50 atmosphere helium gas. Helium cools the first wall and blanket internals. The internals consist of a bed of beryllium balls nominally 1 cm diameter in which neutrons are multiplied and later captured, breeding adequate (even excess) amounts of tritium and releasing energy in exothermic nuclear reactions. Tritium is bred in the molten flibe salt which flows slowly (0.1m/sec) in steel tubes. The salt is kept reducing by periodic reacting with beryllium so the tritium will be in the T2 form, however with somewhat enhanced corrosion rate the salt could be kept oxidizing in which case the tritium would be in the TF form. To prevent the tritium from permitting too much into the helium stream, a tungsten coating on the inside of the tubes is proposed. Tritium is removed from the salt and helium by processing both. Because the solubility of tritium in Flibe is so low, there will be a strong driving force for tritium permeation and this places a great burden on a high integrity tungsten permeation barrier. The tritium in the helium is prevented from permeating excessively into the steam system by jacketing the steel steam generator tubes with a 1 mm aluminum jacket. Clearly, tritium containment and barrier development are the most important feasibility issues for this design

96

Formation of Helium-Cluster Ions CO2Hen+ (n?15) in a Drift Tube Cooled by Liquid Helium  

Science.gov (United States)

The formation of helium-cluster ion CO2Hen+ (n?15) has been observed when CO2+ ions are injected into a drift tube filled with helium gas cooled by liquid helium. The cluster sizes n = 5 and 14 are found to be magic numbers based on the drift-field dependence of the cluster size distribution. The structure of CO2He14+ cannot be considered as the icosahedron, which is proposed as the structure of the cluster ions having twelve helium atoms surrounding the ionic core in our previous papers.

Tanuma, H.; Sakamoto, M.; Kobayashi, N.

97

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.

98

Variation in Atmospheric Helium Isotopes  

Science.gov (United States)

Anthropogenic activity such as oil and gas exploitation releases crustal helium, which has excess 4He compared to atmospheric helium. This may give rise to both spatial and temporal variations in the atmospheric 3He/4He. Helium is present in trace quantities in the air (5 ppm) and has a very low ratio (3He/4Heair = 1.38 x 10-6), consequently high precision measurements of atmospheric He presents a significant analytical challenge. Recent work by Sano et al. [1] has endeavored to experimentally quantify these potential variations in the atmospheric 3He/4He by measuring the helium isotopes from air samples collected around the globe and from samples of ancient trapped atmosphere. Their results indicate an increase in the atmospheric 3He/4He from northern to southern latitudes of the order 2 - 4 ‰, which they attribute to greater use of fossil fuels in the northern hemisphere. However, since most of their data points overlap at the 2-3 ‰ (2?) level, additional measurements (with increased precision if possible) are needed. We have constructed an automated extraction line dedicated to measuring He in samples of air which can rapidly switch between measuring aliquots of sample with standards. It additionally features an adjustable bellows on the sample aliquot volume that enables us to adjust the size of a sample aliquot to precisely match the standard, eliminating biases arising from nonlinear pressure effects in the mass spectrometer. The measurements are made using a Helix SFT multi-collector mass spectrometer. At present, repeat measurements of 3He/4He from our standard (purified air) have a reproducibility of 2‰ (2?), while measurements of local (Nancy, France) air samples have a reproducibility of 3He/4He of 3‰ (2?), which are at a similar level to the uncertainties reported by Sano. Modifications are underway to improve 3He measurements which are the principal source of error. We have collected atmospheric samples from around the globe over a wide range of latitudes to search for spatial variations. In addition to samples from France and Iceland, we have samples collected over a two week period in January 2010 from north to south of the South American continent with a sampling interval of 500km. We also have samples collected from ships sailing between Hobart, Tasmania and Antarctica and then further samples collected into the interior of Antarctica to the Dome C station. [1] Sano, Y., Furukawa, Y. & Takahata, N. Atmospheric helium isotope ratio: Possible temporal and spatial variations. Geochimica et Cosmochimica Acta 74, 4893-4901 (2010).

Mabry, J. C.; Marty, B.; Burnard, P.; Blard, P.

2010-12-01

99

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

100

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)

 
 
 
 
101

Helium Production and Possible Projection  

Directory of Open Access Journals (Sweden)

Full Text Available The future availability of helium has been raised as an issue in the literature. However, a disaggregated projection of helium production has not been attempted, presumably due to the difficult nature of accessing disaggregated historic production data to test the accuracy of this issue. This paper presents collated and estimated historic helium production statistics from 1921 to 2012 for each helium producing country in the world and by U.S. state. A high and regular growth projection of helium has been created. It is found that helium resources are sufficient for the near future, with the projected production plateauing in 2060–2075 and 2090–2100 for the high and regular growth scenarios, respectively. As long as natural gas deposits with helium are appropriately managed, there is little likelihood for helium shortages to occur in the short term due to geologic constraints.

Steve Mohr

2014-03-01

102

Onset Properties of Supersolid Helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Supersolid helium has a rather low transition temperature and a small critical velocity, compared with liquid helium. These properties could be explained in terms of helium's spectrum structure and quantum jumps involving large momentum transfer. A grain in the solid helium possess valleys (local minima) in its many-body dispersion curve, and an exchange of large momenta with the grain's surroundings occurs in a jump between a level in one valley and another level in the nei...

Yu, Yongle

2010-01-01

103

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.

104

Liquid helium level detector  

International Nuclear Information System (INIS)

Means generally used for liquid helium level measurement are the capacitive or superconductive probes. The signal, generally electric, is collected and treated by electronic means operating at ambiant temperature; they operate the pneumatic or electric command of a control valve; the cold active element of this valve controls the necessary alimentation flow

105

Helium Neon Laser  

Science.gov (United States)

This resource, part of the Spectroscopy Lab Suite, illustrates the physics of a Helium-Neon Laser. Students can create energy levels for both the He and Ne atoms. The basic processes for light emission, including collisions and level transitions, are shown. The atomic energy levels and the pumping energy can be adjusted to achieve an output spectrum similar to the measured physical spectrum.

Zollman, Dean

2010-08-13

106

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)

107

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

108

The pulsating extreme helium star BD + 1303224  

International Nuclear Information System (INIS)

Ultraviolet flux variations are reported for the pulsating extreme helium star BD + 1303224 (V652 Her). Effective temperature and angular radius variations over a cycle are determined from static plane-parallel LTE model atmospheres. When compared with radius changes derived from ground-based spectroscopy, the angular radius variations indicate radial pulsations and correspond to a distance of 1.5 +- 0.1 kpc. BD + 1303224 is thought to be a helium-burning star of 0.7 Msolar masses, which has an envelope contracting as the helium-burning core grows; it is similar to HD 144941 and these two stars may constitute a new sub-class of the hydrogen-deficient stars. (author)

109

Helium stars as supernova progenitors  

CERN Document Server

We follow the evolution of helium stars of initial mass $(2.2 - 2.5) M_\\odot$, and show that they undergo off-center carbon burning, which leaves behind ${\\mathbf \\sim 0.01 M_\\odot}$ of unburnt carbon in the inner part of the core. When the carbon-oxygen core grows to Chandrasekhar mass, the amount of left-over carbon is sufficient to ignite thermonuclear runaway. At the moment of explosion, the star will possess an envelope of several $0.1 M_{\\odot}$, consisting of He, C, and possibly some H, perhaps producing a kind of peculiar SN. Based on the results of Waldman and Barkat (2007) for accreting white dwarfs, we expect to get thermonuclear runaway at a broad range of $\\rho_c \\approx (1 - 6) \\times 10^9 \\mathrm{g cm^{-3}}$, depending on the amount of residual carbon. We verified the feasibility of this scenario by showing that in a close binary system with initial masses $(8.5 + 7.7) M_{\\odot}$ and initial period of 150 day the primary produces a helium remnant of $2.3 M_{\\odot}$ that evolves further like the...

Waldman, Roni; Barkat, Zalman

2007-01-01

110

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

111

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.

112

Helium diffusion in curium-doped borosilicate waste glass  

Energy Technology Data Exchange (ETDEWEB)

The isothermal release of helium from {sup 244}Cm-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{sup 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) x 10{sup -3} cm{sup 2} s{sup -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., E-mail: toby.fares@cea.fr [CEA Marcoule, DEN/DTCD/SECM, 30207 Bagnols-sur-Ceze Cedex (France); Peuget, S.; Bouty, O. [CEA Marcoule, DEN/DTCD/SECM, 30207 Bagnols-sur-Ceze Cedex (France); Deschanels, X. [Institut de Chimie Separative de Marcoule, 30207 Bagnols-sur-Ceze Cedex (France); Magnin, M.; Jegou, C. [CEA Marcoule, DEN/DTCD/SECM, 30207 Bagnols-sur-Ceze Cedex (France)

2011-09-01

113

The cryogenic helium cooling system for the Tokamak physics experiment  

International Nuclear Information System (INIS)

The Tokamak Physics Experiment (TPX) will use supercritical helium to cool all the magnets and supply helium to the Vacuum cryopumping subsystem. The heat loads will come from the standard steady state conduction and thermal radiation sources and from the pulsed loads of the nuclear and eddy currents caused by the Central Solenoid Coils and the plasma positioning coils. The operations of the TPX will begin with pulses of up to 1000 seconds in duration every 75 minutes. The helium system utilizes a pulse load leveling scheme to buffer out the effects of the pulse load and maintain a constant cryogenic plant operation. The pulse load leveling scheme utilizes the thermal mass of liquid and gaseous helium stored in a remote dewar to absorb the pulses of the tokamak loads. The mass of the stored helium will buffer out the temperature pulses allowing 5 K helium to be delivered to the magnets throughout the length of the pulse. The temperature of the dewar will remain below 5 K with all the energy of the pulse absorbed. This paper will present the details of the heat load sources, of the pulse load leveling scheme operations, a partial helium schematic, dewar temperature as a function of time, the heat load sources as a function of time and the helium temperature as a function of length along the various components that will be cooled

114

Metastable states of antiprotonic helium atoms  

International Nuclear Information System (INIS)

We discuss the latest theoretical achievements in calculations of energy transitions in the antiprotonic helium He+p-0304; atoms. New variational calculations of the nonrelativistic energies with precision of ?10-10 a.u. and relativistic and QED corrections to the energy levels of m?5 order are presented

115

The Weakest Link: Bonding between Helium Atoms  

Science.gov (United States)

A highly simplified model for helium dimers that reproduces their essential features without the need for elaborate computation is presented. The He-He potential is predicted to have minimum of 10.9 K at a nuclear separation of 5.61 bohrs.

Lohr, Lawrence L.; Blinder, S. M.

2007-01-01

116

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

117

Helium behavior in vanadium-based alloys irradiated in the dynamic helium charging experiments  

International Nuclear Information System (INIS)

Helium effect of neutron irradiated vanadium alloys, containing titanium, has been studied using Dynamic Helium Charging Experiment (DHCE) in FFTF. Cavity formation was observed only in pure vanadium irradiated at 430 to 600 C and in V-5Ti irradiated at 600 C. No apparent cavity formation was obtained in V-3Ti-1Si and V-4Cr-4Ti. The precipitation of titanium oxide in V-5Ti, V-3Ti-1Si and V-4Cr-4Ti occurred in all irradiation conditions in this study and the precipitates of Ti5Si3 only appeared in V-3Ti-1Si irradiated at 600 C up to 15 dpa with helium generation rate of 4 appmHe/dpa. It is suggested that titanium oxide plays an important role for suppression of cavity formation and swelling from early stage of irradiation. Detail characterization of precipitates and He effect for neutron damages in vanadium alloys are discussed here

118

Scattering angle-integrated (total) and magnetic sublevel cross-sections and degree of linear polarization for electron and proton induced excitation [HeI (1snp) 1P0 (n=2-5)] of helium  

International Nuclear Information System (INIS)

Experimental scattering-angle-integrated (total) cross-sections ?-bar, (scattering) angle-integrated magnetic sublevel cross-sections ?-barML, and degree of linear polarization data have been measured in the extreme ultraviolet (EUV) wavelength region following decay of HeI (1snp) 1P0 (n=2-5) states induced by electron and proton impact on a neutral helium target. These measurements are compared with a first Born approach as well as more sophisticated theoretical calculations. Specifically, theoretical values for electron impact include convergent close-coupling (CCC) and R-matrix with pseudo states (RMPS) methods in addition to first Born (Born 1) approximation while proton induced excitation cross-sections are compared with atomic-orbital close-coupling (AOCC) and first Born predictions

119

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.)

120

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.)

 
 
 
 
121

Helium removal from Tokamaks  

International Nuclear Information System (INIS)

Helium, as the ash of burning D-T plasma, is an unavoidable impurity component necessarily present already in near future tokamak experiments with significant alpha particle heating. Its efficient removal from the burning zone of a D-T fusion reactor (or lack thereof) will play a key role in the path towards achievement of economic fusion power production. A survey is given of the issues related to this question. Since there is as yet no experimental experience with thermonuclear plasmas significantly heated by fusion products, this review is based on results from simulation experiments of helium injection into hydrogen or deuterium tokamak plasmas, and from numerical transport code work. Both kinds of results are discussed with reference to handy ignition criteria obtained for steady D-T burning, which have been reformulated in terms relevant for the ash removal problem. (author)

122

Techniques of helium content measurement in irradiated structural materials  

International Nuclear Information System (INIS)

Helium effect on radiation damage of structural materials governs the necessity of the detailed study in the field of helium accumulation in these materials under different operating conditions. Helium interaction with different defects of the structure is one of the factors, which influence on the change of the structure, porosity evolution and material embrittlement during irradiation and finally can be a reason of service life shortening or even damage of structural components in nuclear reactors. The paper presents a pilot facility to measure helium content in the irradiated structural materials having a melting temperature up to 2000 deg C. The range of absolute helium quantity measurement inside the specimen is (10-12 to 10-5) mole and it allows the molar fraction of helium to be measured in the range of (1- 10 000) appm according to the specimen matrix mass and material. Mass-spectrometer techniques of helium content measurement using isotopic dilution and volumetric quasistatic methods were developed and certified. The confidence bounds of relative measurement errors depend on the measured values and are in the range of 6 to 9% for the method employing isotopic dilution and of 7 to 19% for the volumetric quasistatic method. The results of comparative certification of two measurement procedures using the same standard specimens demonstrate a good agreement of helium measurement results, which were obtained with the help of the two techniques

123

Classical Helium Program  

Science.gov (United States)

The classical-physics model of helium is a simple example of a three body problem and is similar to gravitational problem of a heavy sun and two light planets. It consists of two electrons moving in a 2/r potential well and interacting through a 1/r potential. Initial conditions can be set to show phenomena such as autoionization or braided orbits. These conditions are stored in an xml document.

Christian, Wolfgang; Gould, Harvey; Tobochnik, Jan

2008-05-21

124

Education in Helium Refrigeration  

International Nuclear Information System (INIS)

On the one hand, at the end of the time I was active in helium refrigeration, I noticed that cryogenics was stepping into places where it was not yet used. For example, a conventional accelerator, operating at room temperature, was to be upgraded to reach higher particle energy. On the other hand, I was a little bit worried to let what I had so passionately learned during these years to be lost. Retirement made time available, and I came gradually to the idea to teach about what was my basic job. I thought also about other kinds of people who could be interested in such lessons: operators of refrigerators or liquefiers who, often by lack of time, did not get a proper introduction to their job when they started, young engineers who begin to work in cryogenics... and so on.Consequently, I have assembled a series of lessons about helium refrigeration. As the audiences have different levels of knowledge in the field of cryogenics, I looked for a way of teaching that is acceptable for all of them. The course is split into theory of heat exchangers, refrigeration cycles, technology and operation of main components, process control, and helium purity

125

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

126

Antiprotonic helium atomcules  

Directory of Open Access Journals (Sweden)

Full Text Available About 3% of antiprotons ( stopped in helium are long-lived with microsecond lifetimes, against picoseconds in all other materials. This unusual longevity has been ascribed to the trapping of on metastable bound states in He+ helium atom-molecules thus named atomcules. Apart from their unique dual structure investigated by laser spectroscopy – a near-circular quasi-classical Rydberg atom with l ~ n – 1 ~ 37 or a special diatomic molecule with a negatively charged nucleus in high rotational state with J = l – the chemical physics aspects of their interaction with other atoms or molecules constitute an interesting topic for molecular physics. While atomcules may resist to million collisions in helium, molecular contaminants such as H2 are likely to destroy them in a single one, down to very low temperatures. In the Born-Oppenheimer framework, we interpret the molecular interaction obtained by ab initio quantum chemical calculations in terms of classical reactive channels, with activation barriers accounting for the experiments carried out in He and H2. From classical trajectory Monte Carlo simulations, we show that the thermalization stage strongly quenches initial populations, thus reduced to a recovered 3 % trapping fraction. This work illustrates the pertinence of chemical physics concepts to the study of exotic processes involving antimatter. New insights into the physico-chemistry of cold interstellar radicals are anticipated.

Sauge Sébastien

2012-10-01

127

Feasibility of lunar Helium-3 mining  

Science.gov (United States)

With fossil fuels running out and global energy demand increasing, the need for alternative energy sources is apparent. Nuclear fusion using Helium-3 may be a solution. Helium-3 is a rare isotope on Earth, but it is abundant on the Moon. Throughout the space community lunar Helium-3 is often cited as a major reason to return to the Moon. Despite the potential of lunar Helium-3 mining, little research has been conducted on a full end-to-end mission. This abstract presents the results of a feasibility study conducted by students from Delft University of Technology. The goal of the study was to assess whether a continuous end-to-end mission to mine Helium-3 on the Moon and return it to Earth is a viable option for the future energy market. The set requirements for the representative end-to-end mission were to provide 10% of the global energy demand in the year 2040. The mission elements have been selected with multiple trade-offs among both conservative and novel concepts. A mission architecture with multiple decoupled elements for each transportation segment (LEO, transfer, lunar surface) was found to be the best option. It was found that the most critical element is the lunar mining operation itself. To supply 10% of the global energy demand in 2040, 200 tons of Helium-3 would be required per year. The resulting regolith mining rate would be 630 tons per second, based on an optimistic concentration of 20 ppb Helium-3 in lunar regolith. Between 1,700 to 2,000 Helium-3 mining vehicles would be required, if using University of Wisconsin’s Mark III miner. The required heating power, if mining both day and night, would add up to 39 GW. The resulting power system mass for the lunar operations would be in the order of 60,000 to 200,000 tons. A fleet of three lunar ascent/descent vehicles and 22 continuous-thrust vehicles for orbit transfer would be required. The costs of the mission elements have been spread out over expected lifetimes. The resulting profits from Helium-3 fusion were calculated using a predicted minimum energy price in 2040 of 30.4 Euro/MWh. Annual costs are between 427.7 to 1,347.9 billion Euro, with annual expected profit ranging from -724.0 to 260.0 billion Euro. Due to the large scale of the mission, it has also been evaluated for providing 0.1% and 1% of the global energy demand in 2040. For 1%, the annual costs are 45.6 to 140.3 billion Euro and the expected annual profits are -78.0 to 23.1 billion Euro. For 0.1%, the annual costs are 7.7 to 20.5 billion Euro. The annual expected profits are -14.3 to -0.8 billion Euro. Feasibility has been addressed in three aspects. Technically, the mission is extremely challenging and complex. However, most required technologies exist or could be developed within a reasonable time span. From a political and legal perspective, the current international treaties hardly provide any framework for a lunar mining operation. Financially, the mission only produces a net profit in the best case, and only for medium- to large-scale operations, which require a very large initial investment. To make lunar Helium-3 usage possible, further research should concentrate on the mining operation and costs of fusion plants, as their impact by far outranks all other mission elements. Different transportation concepts may be investigated nevertheless. Many - not only technical - challenges concerning Helium-3 mining are still to be addressed. Although only a starting point for further investigations, this study shows that, despite popular claims, lunar Helium-3 is unsuitable to provide a significant percentage of the global energy demand in 2040.

Kleinschneider, Andreas; Van Overstraeten, Dmitry; Van der Reijnst, Roy; Van Hoorn, Niels; Lamers, Marvin; Hubert, Laurent; Dijk, Bert; Blangé, Joey; Hogeveen, Joel; De Boer, Lennaert; Noomen, Ron

128

A reexamination of quenches in Helium 4 and Helium 3  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the light of recent difficulties in observing vortices in quenches of liquid helium 4 to its superfluid state we re-examine the Zurek scenario for their production. We argue that experiments in helium 4 are unlikely to produce true vortices in the numbers originally anticipated, if at all, because of the wide Ginzberg regime and the slowness of the mechanical quenches. On the other hand, the observed production of unambiguous vortices in neutron-bombarded helium 3, with i...

Karra, G.; Rivers, R. J.

1998-01-01

129

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)

130

Cavitation pressure in liquid helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Caupin, Frederic; Balibar, Sebastien

2001-01-01

131

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 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

132

Effect of weld thermal cycle on helium bubble formation in stainless steel  

International Nuclear Information System (INIS)

Helium bubble structure was examined on a helium-implanted stainless steel after applying two kinds of heat input. Helium ions were implanted on type 304 stainless steel at 573 K from 2 to 200 appm to a peak depth of 0.5 ?m from the surface. After that, weld thermal history was applied by an electron beam. The cooling rates were selected to be 370 and 680 K/s from 1023 to 773 K. TEM observation revealed that nucleation and growth of helium bubbles were strongly dependent on the cooling rate after welding and the helium concentration. (orig.)

133

Effect of weld thermal cycle on helium bubble formation in stainless steel  

Science.gov (United States)

Helium bubble structure was examined on a helium-implanted stainless steel after applying two kinds of heat input. Helium ions were implanted on Type 304 stainless steel at 573 K from 2 to 200 appm to a peak depth of 0.5 ?m from the surface. After that, weld thermal history was applied by an electron beam. The cooling rates were selected to be 370 and 680 K/s from 1023 to 773 K. TEM observation revealed that nucleation and growth of helium bubbles were strongly dependent on the cooling rate after welding and the helium concentration.

Kano, F.; Nakahigashi, S.; Nakamura, H.; Uesugi, N.; Mitamura, T.; Terasawa, M.; Irie, H.; Fukuya, K.

1998-10-01

134

Leak detection with liquid helium  

Science.gov (United States)

A method for approximately locating ultra-small leaks in a superconducting cyclotron magnet cryostat has been developed using liquid helium. A method for locating ultra-small leaks using cold helium gas (refrigerator. The main part of the MSU cryostat is inaccessible to temperature variations due to gas flow changes, which primarily occur at the top of the cryostat. In the main body of the cryostat there is the option of raising and lowering the liquid helium level, and it has been discovered that the location of the leak is clearly defined as it is covered (uncovered) by liquid helium.

Mallory, M. L.; Laumer, H. W.

1980-11-01

135

Onset Properties of Supersolid Helium  

International Nuclear Information System (INIS)

Supersolid helium has a rather low transition temperature and a small critical velocity, compared with liquid helium. These properties could be explained in terms of helium's spectrum structure and quantum jumps involving large momentum transfer. A grain in the solid helium possess valleys (local minima) in its many-body dispersion curve, and an exchange of large momenta with the grain's surroundings occurs in a jump between a level in one valley and another level in the neighboring valley. Such jump process also naturally causes dissipation accompanying the onset of supersolidity.

136

Photodissociation of alkyl iodides in helium nanodroplets. II. Solvation dynamics  

Science.gov (United States)

The solvation dynamics of nonthermal species in liquid helium has been investigated by photolyzing alkyl iodide molecules, CH3I, C2H5I, and CF3I, embedded in helium nanodroplets. Iodine and CH3 fragments are found to leave the droplets solvated by a finite number of helium atoms, this in contrast to C2H5 and CF3 fragments. The speed distributions of the IHeN and CH3HeN complexes show a prominent correlation with the degree of solvation N. It is argued that this correlation is caused by a dynamical adjustment of the solvation structure size to the relative speed of the traveling fragments as they pass through the helium bath. The absence of C2H5HeN and CF3HeN complexes is attributed to the large internal energy of these alkyl fragments which leads to a rapid destruction of any possibly formed complexes.

Braun, Andreas; Drabbels, Marcel

2007-09-01

137

Helium ion implanted waveguide lasers  

International Nuclear Information System (INIS)

High energy ion implantation may be used to modify the refractive index of surfaces of insulators to form optical waveguides and waveguide lasers. Bombardment with MeV helium ions normally reduces the crystalline indices at the end of the ion range. This low index region provides an optical barrier and so defines a waveguide. The method has been demonstrated in more than 30 crystalline targets. Possible factors which influence the refractive index profile are discussed. A successful approach to form waveguide lasers is to use the implantation damage method to construct a waveguide in a predoped crystal. After annealing the optical losses are reduced and planar waveguide lasers have so far been demonstrated in Nd doped YAG, YAP, LiNbO3, Gd3Ga5O12 and Bi4Ge3O12. (orig.)

138

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

139

Reciprocating magnetic refrigerator for helium liquefaction  

International Nuclear Information System (INIS)

We have developed a reciprocating magnetic refigerator for liquefying helium from a temperature in the 15 K region. The working material (gadolinium-gallium-garnet (GGG) single crystal, 30 mm in diameter and 40 mm in length) is placed at the end of the piston. When GGG is placed in a high-intensity magnetic field (4.5 T), its temperature rises to 15 K. The inner surface of the cylinder is cooled by an auxiliary refrigerator; the generated heat is removed through the narrow gap between GGG and cylinder (less than 50 um in the 15 K region) filled with gaseous helium. When the magnetic field in the GGG is eliminated by moving the piston, the GGG temperature falls below 4.2 K and the refrigeration occurs by condensing the helium on the GGG surface. Technical emphasis was placed on the realization of a high heat exchange rate between GGG and gaseous helium. A sufficient heat transfer rate was achieved after several component level experiments. Sources of inefficiency to the refrigeration power has been also discussed. Finally a refrigeration power of 0.95 W at 4.2 K was achieved in 0.38 Hz operation by a reciprocating magnetic refrigerator equiped with two pistons

140

Diffusion of helium in the sun  

International Nuclear Information System (INIS)

I have reduced the set of diffusion and flow equations developed by Burgers for a multi-component gas to a workable scheme for the actual evaluation of the relative diffusion of hydrogen and helium in stars. Previous analyses have used the Aller and Chapman equations, which apply only to trace constitutents and whose coefficients are not believed to be as accurate as Burgers'. Furthermore, the resulting equations have been combined consistently with Paczynski's stellar evolution code to demonstrate small but significant effects in the Sun, from the thermal and gravitational settling of Helium. The core helium content of a 1 M star goes up about 0.04 and the surface helium content down by about -0.03 in 4.5 109 years. The results are still somewhat uncertain because of uncertainties in the underlying plasma physics, and further research is suggested. In any case, the diffusion process speeds up with time, due to increased temperature gradient, and it will be of interest to follow the process in older stars and in later stellar evolution. (orig.)

 
 
 
 
141

Vacancies in solid helium  

International Nuclear Information System (INIS)

Some theoretical and experimental properties of thermally excited Schottky type vacancies in solid helium are reviewed: the mechanism for creation of a vacancy and the possibility for the latter to tunnel from one lattice site to a neighbouring one are considered. This tunnelling is compared with Pauli exchange interactions in solid 3He. The possibility of vacancy waves is studied and the difference between the cases of 3He and 4He pointed out. X ray scattering in body centered cubic helium three yields the energy of formation of vacancies without ambiguity in principle, although with a so far limited accuracy. Vacancy induced diffusion of magnetization in body centered cubic 3He is studied by the method of moments and existing experimental data are recalled. Spin lattice relaxation is recalled with some detail, both the Zeeman-vacancies relaxation due to the modulation of the dipole-dipole interactions by the motion of the vacancies and the exchange-lattice relaxation through the vacancies. The Zeeman-vacancies relaxation is studied by the method of moments, in parallel with the theory of diffusion. The exchange-lattice relaxation is calculated by the method of strong collisions of Ailion and Slichter. The various published experiments are reviewed. In the case of body centered cubic helium three, it can be concluded to the tunnelling of vacancies by comparison of NMR activation energies with the energies of formation measured by X ray scattering. The case of the 3He impurities in hexagonal close packed 4He is also studied as it also reveals the existence of vacancies in 4He. Finally the possibility of inelastic scattering of either neutrons or light by vacancies is noted. It is not possible to detect directly by such an experiment the vacancy waves

142

Estimation of helium in gas mixture using helium leak detector  

International Nuclear Information System (INIS)

A method is described for using helium leak detector for determining the helium content in gas mixtures. Details of various attachments for sample handling and other modifications needed are outlined. Sources of error and the respective corrections are indicated. Procedure for the analysis of samples in percentage, ppm and sub ppm has been standardised. Precision of analysis for these concentrations is mentioned. (auth.)

143

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

144

Magical helium clusters  

International Nuclear Information System (INIS)

Physicists are well acquainted with the concept of 'magic numbers'. In nuclear physics, for example, a nucleus is more stable if it contains a magic number (e.g. 2, 8, 20, 28,...) of protons or neutrons. Similar patterns are seen in small atomic systems, such as the closed shells of valence electrons in metal clusters. Theory predicts, however, that such numbers -- which are related to an enhanced stability of the ground state -- should not occur for clusters of helium-4 atoms. Rather, the ground-state properties of the cluster should change smoothly as the number of atoms it contains increases. Now, astonishingly, Peter Toennies of the Max Planck Institute for Flow Research in Goettingen, Germany, and co-workers have observed magic numbers in helium-4 clusters (R Bruehl et al. 2004 Phys. Rev. Lett. 92 185301). To create the helium clusters, Toennies and colleagues in Spain and the US allowed fluid helium to expand at cryogenic temperatures and form a collimated beam. The researchers then directed this beam through a transmission grating that had a period of 100nm, which diffracted the clusters into a mass spectrometer. Since the de Broglie wavelength of a cluster is inversely proportional to its mass, clusters of different sizes were diffracted at different angles. By plotting the signal from the mass spectrometer as a function of the diffraction angle, the team was therefore able to plot the size distributions of the clusters with excellent resolution. Contrary to ws with excellent resolution. Contrary to what is expected, certain cluster sizes appear to be favoured more than others. Toennies and co-workers carried out several tests to check that the peaks in the size distribution were independent of conditions in the source region and in the detector. They also varied the angle of the diffraction grating relative to the incident beam of clusters, and concluded that the peaks definitely indicated magic numbers corresponding to cluster sizes of 10/11, 14, 22, 26/27 and 44 atoms. (U.K.)

145

Compressibility of solid helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The compressibility of solid helium (3He and 4He) in the hcp and fcc phases has been studied by path-integral Monte Carlo. Simulations were carried out in both canonical (NVT) and isothermal-isobaric (NPT) ensembles at temperatures between 10 and 300 K, showing consistent results in both ensembles. For pressures between 4 and 10 GPa, the bulk modulus B is found to decrease by about 10 %, when temperature increases from the low-temperature limit to the melting temperature. Th...

Herrero, Carlos P.

2008-01-01

146

Dynamic sparger for measuring low helium concentrations in liquid sodium  

International Nuclear Information System (INIS)

In a novel type of LMFBR steam generator presently being developed, detection of incipient leaks is possible from the appearance of helium in the sodium coolant. A dynamic sparger to detect helium at low concentrations in sodium was designed, built, and tested. Bubble velocities, radii, and mass transfer coefficients were delineated from static mode tests. A successful automatic sodium level control system was included in the demonstration of feasibility of the overall dynamic sparger concept. In the dynamic mode the sparger could detect 0.04 ppB helium in sodium. Sparging efficiency was 0.2 to 0.5 over a workable range of operating conditions

147

First principles calculations of shock compressed fluid helium.  

Science.gov (United States)

The properties of hot dense helium at megabar pressures are studied with two first principles computer simulation techniques: path integral Monte Carlo simulation and density functional molecular dynamics. The simulations predict that the compressibility of helium is substantially increased by electronic excitations that are present in the hot fluid at thermodynamic equilibrium. A maximum compression ratio of 5.24(4)-fold the initial density was predicted for 360 GPa and 150,000 K. This result distinguishes helium from deuterium, for which simulations predicted a maximum compression ratio of 4.3(1). Hugoniot curves for statically precompressed samples are also discussed. PMID:17155480

Militzer, B

2006-10-27

148

Scintillation of Liquid Helium for Low-Energy Nuclear Recoils  

CERN Document Server

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 separation by an electric field for nuclear recoils and for electrons stopped in helium.

Ito, T M

2013-01-01

149

Neon-helium refrigerator  

International Nuclear Information System (INIS)

To construct economical facilities of preliminary cooling a neon-helium refrigerator is designed and produced in Which a generator gas (helium) is successively cooled at three temperature levels - 78 K, 64 K and 28 K. The first two levels are ensUred by liquid nitrogen, and the third one by a throttle neon refrigerator of 400 W cooling capacity at the 28 K level, at the 45 m3/h neon compressor capacity. The rig trials of the refrigerator were carried out. Its real cooling capacity was 270 W while working with a compressor at the 31 m3/h capacity. This fact is in good agreement with the calculations taking into account that the practical neon compressor capacity is less than the calculated one. The refrigerator efficiency depending on the cooling object temperature is calculated. The optimal cooling conditions are determined from the power point of view. The dynamics of object cooling is considered. It is shown that when utilizing multi-stage cooling of cryogenic objects it is necessary to determine optimal temperatures of transition from one cooling stage to another, that permits to minimize expenditure of energy during cooling process

150

Helium dilution refrigeration system  

Science.gov (United States)

A helium dilution refrigeration system operable over a limited time period, and recyclable for a next period of operation. The refrigeration system is compact with a self-contained pumping system and heaters for operation of the system. A mixing chamber contains .sup.3 He and .sup.4 He liquids which are precooled by a coupled container containing .sup.3 He liquid, enabling the phase separation of a .sup.3 He rich liquid phase from a dilute .sup.3 He-.sup.4 He liquid phase which leads to the final stage of a dilution cooling process for obtaining low temperatures. The mixing chamber and a still are coupled by a fluid line and are maintained at substantially the same level with the still cross sectional area being smaller than that of the mixing chamber. This configuration provides maximum cooling power and efficiency by the cooling period ending when the .sup.3 He liquid is depleted from the mixing chamber with the mixing chamber nearly empty of liquid helium, thus avoiding unnecessary and inefficient cooling of a large amount of the dilute .sup.3 He-.sup.4 He liquid phase.

Roach, Patrick R. (Darien, IL); Gray, Kenneth E. (Naperville, IL)

1988-01-01

151

Ionization curves of C4+ and N5+ helium-like ions in a range of O (<=) Esub(e) (<=) 30 keV  

International Nuclear Information System (INIS)

Ionization curves of C4+ and N5+ have been calculated in the energy range of ionizing electons Esub(e) = (0-30) keV. For this purpose the matrix element squares of dipole tr tions Msub(i)2(C4+ ? C5+)=(24.5ansi+-6) x10sup(-)3 and Msub(i)2(N5+ ? N6+)=(17.0+-4) x10-3 have been found by means of the graphic integration method. From the data obtained it follows that the ionization cross sections of C4+ and N5+ measured earlier correspond to the points in the vicinity of sigmasub(max). In order to check completely the calculated values, the cross sections sigmasub(i) should be measured at several points by Esub(e)

152

Flow and Supersolidity in Helium  

Science.gov (United States)

Recent torsional oscillator measurements showed evidence of non-classical rotational inertia in solid helium at temperatures below 200 mK and generated a great deal of interest in a possible supersolid state. The nature and properties of such a state are still unclear, although experiments involving 3He impurities and crystal annealing may provide clues. It would be very interesting to know whether supersolids share any of the other unusual properties of superfluids: superleaks, persistent currents, second sound and quantized vortices. We have studied the response of solid helium to pressure differences, in order to look for unusual flow properties that might be associated with supersolidity. Our measurements involved both helium confined in the nanometer pores of Vycor glass and bulk solid helium, at temperatures as low as 30 mK. Near melting, solid helium flows very easily but we did not see any evidence of superflow at low temperatures. If helium does become a supersolid at low temperatures, then its response to pressure gradients must be very different from that of liquid helium. We describe these and other experiments and discuss the role that defects may play in the low temperature behavior of solid helium.

Day, James; Beamish, John

2007-09-01

153

Quantum cavitation in liquid helium  

CERN Document Server

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, M; Jezek, D M; Lombard, R J; Pi, M

1996-01-01

154

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.)

155

The Hall D solenoid helium refrigeration system at JLab  

Science.gov (United States)

Hall D, the new Jefferson Lab experimental facility built for the 12GeV upgrade, features a LASS 1.85 m bore solenoid magnet supported by a 4.5 K helium refrigerator system. This system consists of a CTI 2800 4.5 K refrigerator cold box, three 150 hp screw compressors, helium gas management and storage, and liquid helium and nitrogen storage for stand-alone operation. The magnet interfaces with the cryo refrigeration system through an LN2-shielded distribution box and transfer line system, both designed and fabricated by JLab. The distribution box uses a thermo siphon design to respectively cool four magnet coils and shields with liquid helium and nitrogen. We describe the salient design features of the cryo system and discuss our recent commissioning experience.

Laverdure, N.; Creel, J.; Dixon, K.; Ganni, V.; Martin, F.; Norton, R.; Radovic, S.

2014-01-01

156

Evaluation of helium cooling for fusion divertors  

International Nuclear Information System (INIS)

The divertors of future fusion reactors will have a power throughput of several hundred MW. The peak heat flux on the diverter surface is estimated to be 5 to 15 MW/m2 at an average heat flux of 2 MW/m2. The divertors have a requirement of both minimum temperature (100 degrees C) and maximum temperature. The minimum temperature is dictated by the requirement to reduce the absorption of plasma, and the maximum temperature is determined by the thermo-mechanical properties of the plasma facing materials. Coolants that have been considered for fusion reactors are water, liquid metals and helium. Helium cooling has been shown to be very attractive from safety and other considerations. Helium is chemically and neutronically inert and is suitable for power conversion. The challenges associated with helium cooling are: (1) Manifold sizes; (2) Pumping power; and (3) Leak prevention. In this paper the first two of the above design issues are addressed. A variety of heat transfer enhancement techniques are considered to demonstrate that the manifold sizes and the pumping power can be reduced to acceptable levels. A helium-cooled diverter module was designed and fabricated by GA for steady-state heat flux of 10 MW/m2. This module was recently tested at Sandia National Laboratories. At an inlet pressure of 4 MPa, the module was tested at a steady-state heat flux of 10 MW/m2. The pumping power required was less than 1% of the power removed. These results verified the design prediction

157

Effect of heat treatment on helium trapping in vanadium alloy at high ion implantation fluence  

International Nuclear Information System (INIS)

Helium was implanted into a V-4Ti alloy by using a 5 keV helium ion beam with a flux of 1014 He/cm2 s, and then helium retention was analyzed by a technique of thermal desorption spectroscopy (TDS). The influence of heat treatment on helium trapping was studied by pre-annealing of the samples before ion irradiation. The annealing temperature was 973, 1223 and 1373 K, respectively. Results indicated that pre-annealing treatments did not influence significantly the helium retention and release behavior in vanadium alloy on the present experimental conditions where the helium ion implantation fluence is in the region of 1017-1018 He/cm2, which shows a different tendency from the situation at a low fluence region (1013-1014 He/cm2). The reason could be due to different trap mechanisms of helium at different ion fluences

158

The Application and Improvement of Helium Turbines in the EAST Cryogenic System  

Science.gov (United States)

The helium cryogenic system supplies supercritical helium cooling capacity at 4.5 K for the superconducting magnets in the EAST superconducting tokamak. Four low-temperature helium turbines are used in the 2 kW helium refrigeration system, and their performance and reliability are critical for the continuous operation of the tokamak. The turbines were made by the Helium Mechanics Company in Russia. The start-up process is very unstable, easily broken, and thus testing and improvements are needed. In this paper, we analyze the structure of the helium turbine, make improvements, and describe the testing process and results of the improved helium turbines. Some of the operational experiences during the start-up process and tests are also presented.

Fu, Bao; Zhang, Qiyong; Zhu, Ping; Cheng, Anyi

2014-05-01

159

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

160

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

 
 
 
 
161

Leak detection with liquid helium  

International Nuclear Information System (INIS)

A method for approximately locating ultra-small leaks in a superconducting cyclotron magnet cryostat has been developed using liquid helium. A method for locating ultra-small leaks using cold helium gas (<,m 205K) has been reported. The cold gas method requires a means of varying the return path of the liquid helium boil-off gas to refrigerator. The main part of the MSU cryostat is inaccessible to temperature variations due to gas flow changes, which primarily occur at the top of the cryostat. In the main body of the cryostat there is the option of raising and lowering the liquid helium level, and it has been discovered that the location of the leak is clearly defined as it is covered (uncovered) by liquid helium. (orig.)

162

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

163

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

164

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

165

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 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 bars, 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 betweeen 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 with describes the general structure of DATS, characterized by downaward 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

166

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)

167

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

168

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.)

169

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)

170

Study on the hydrogen and helium isotope yields from Ni58, Ni64 targets at the interaction with 7.5 GeV protons  

International Nuclear Information System (INIS)

To find isotope effects studied are the yield of p,d,t, 3He and 4He secondary slow light particles from the 58Ni and 64Ni isotopes while bombarding them by protons with the 7.5 GeV energy. Proton beam intensity reached 5x209 particles in one acceleration cycle outler. The outlet temporal extending was equal to 300 ms. 58Ni and 64Ni tangets were metal foils with the width of 8 mg/cm2.; the main isotopote amount was equal to 95 and 90%, respectively. Shortly described is the block diagram of electronics operating on-line with the BESM-4 computer. Secondary particles spectra are obtained in the following ranges: protons - from 4 to 18.5 Mev, deuterons - from 4.0 to 26 MeV, tritons - from 4.0 to 28 MeV, 3He, 4He - from 11 to 58 MeV. The process the psectra the simpliest variant of the nuclear particle evaporation statistical theory is used, i.e. evaporation approximation. It is found out from the comparison with the experimental results while using bombariding proton energy of 660 MeV, that at the proton energy of 7.5 GeV relative deuteron and triton yield are approximately two times higher; for 3He they almost coincide. The differences observed in relative yields of d and t are connected perhaps with the differences in secondary particle initiation processes at the transition of bombarding particle energy from 0.66 ot 7.5 GeV. The relation between neut0.66 ot 7.5 GeV. The relation between neutron exceesses of nucleus-target and nucleus-product is noted, i.e. relative proton yield form 64Ni is decreased, whereas that of tritons is increased in comparison whith 58Ni target. In energy spectra the isotope effect exhibits itself in the fact that spectra of p, d, t, 3He secondary particles are not more harder for 64Ni target

171

Phase separation in hydrogen-helium mixtures at Mbar pressures  

Science.gov (United States)

The properties of hydrogen-helium mixtures at Mbar pressures and intermediate temperatures (4000 to 10000 K) are calculated with first-principles molecular dynamics simulations. We determine the equation of state as a function of density, temperature, and composition and, using thermodynamic integration, we estimate the Gibbs free energy of mixing, thereby determining the temperature, at a given pressure, when helium becomes insoluble in dense metallic hydrogen. These results are directly relevant to models of the interior structure and evolution of Jovian planets. We find that the temperatures for the demixing of helium and hydrogen are sufficiently high to cross the planetary adiabat of Saturn at pressures ?5 Mbar; helium is partially miscible throughout a significant portion of the interior of Saturn, and to a lesser extent in Jupiter.

Morales, Miguel A.; Schwegler, Eric; Ceperley, David; Pierleoni, Carlo; Hamel, Sebastien; Caspersen, Kyle

2009-02-01

172

Laser Spectroscopy of Hydrogen Peroxide Embedded in Helium Nanodroplets  

Science.gov (United States)

Helium nanodroplets provide a gentle matrix in which to isolate reactive species for spectroscopic investigations. In our ongoing effort to generate radical species in helium nanodroplets, we have recently focused our attention on the highly reactive hydrogen peroxide (H_2O_2) molecule, a potential precursor for the hydroxyl radical. The infrared spectrum of hydrogen peroxide was measured in helium nanodroplets using a cw OPO infrared laser in the OH stretching region. Several rovibrational transitions in the v_5 band of hydrogen peroxide (and HOOD) were recorded and assigned. Intensities, shapes, and assignments of lines will be discussed, as will prospects for the use of hydrogen peroxide in the production of hydroxyl radicals in helium droplets using laser photolysis.

Knapp, Chrissy J.; Raston, Paul L.; Jäger, Wolfgang

2011-06-01

173

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

174

Electron-helium scattering in Debye plasmas  

Energy Technology Data Exchange (ETDEWEB)

Electron-helium scattering in weakly coupled hot-dense (Debye) plasma has been investigated using the convergent close-coupling method. The Yukawa-type Debye-Hueckel potential has been used to describe plasma Coulomb screening effects. Benchmark results are presented for momentum transfer cross sections, excitation, ionization, and total cross sections for scattering from the ground and metastable states of helium. Calculations cover the entire energy range up to 1000 eV for the no screening case and various Debye lengths (5-100 a{sub 0}). We find that as the screening interaction increases, the excitation and total cross sections decrease, while the total ionization cross sections increase.

Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor [ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, WA 6845 (Australia); Janev, R. K. [Macedonian Academy of Sciences and Arts, P.O. Box 428, 1000 Skopje (Macedonia, The Former Yugoslav Republic of)

2011-11-15

175

Cycle design for the ISABELLE helium refrigerator  

International Nuclear Information System (INIS)

The superconducting magnets for the ISABELLE storage ring/accelerator are designed to be operated at 3.80K using a forced-flow supercritical helium cooling system. The ISABELLE refrigerator has been designed subject to these special requirements. The design output is 13.65 KW of refrigeration below 4.20K (for cooling the magnet and distribution system), 55 KW at 550K (to cool heat shields for the whole system) and 100 g/s of liquefaction (for magnet power leads cooling). The system incorporates a subcooler section that produces liquid helium at 5.3 atm and 2.6 K and circulates it through the loads, and a Claude-type main refrigerator section. The main refrigerator section has five stages of cooling, with four of them below liquid nitrogen temperature. Liquid nitrogen precooling is not used. With 60% isothermal compressors the efficiency of the refrigerator system will be about 26% of Carnot

176

The History and Morphology of Helium Reionization  

CERN Document Server

A variety of observations now indicate that intergalactic helium was fully ionized by z~3. The most recent measurements of the high-redshift quasar luminosity function imply that these sources had produced ~2.5 ionizing photons per helium atom by that time, consistent with a picture in which the known quasar population drives HeII reionization. Here we describe the distribution of ionized and neutral helium gas during this era. Because the sources were rare and bright (with the photon budget dominated by quasars with luminosities L>L_\\star), random fluctuations in the quasar population determined the morphology of ionized gas when the global ionized fraction x_i was small, with the typical radius R_c of a HeIII bubble ~15-20 comoving Mpc. Only when x_i>0.5 did the large-scale clustering of the quasars drive the characteristic size of ionized regions above this value. Still later, when x_i>0.75, most ionizing photons were consumed by dense, recombining systems before they reached the edge of their source's ion...

Furlanetto, Steven

2007-01-01

177

Two-photon spectroscopy of antiprotonic helium  

Science.gov (United States)

The precision of laser spectroscopy of antiprotonic helium (a helium atom with one of its electrons replaced by an antiproton) has improved by almost 4 orders of magnitude over its 20 years of history. Experimental transition frequencies can be compared to 3-body QED calculations to derive the antiproton-electron mass ratio. In the latest measurements of the Asacusa experiment at CERN, two-photon transitions of antiprotonic helium were excited using two counter-propagating laser beams. This method reduces the Doppler-broadening caused by the thermal motion of the atoms, and allowed us to measure the transition frequencies with a fractional precision of 2.5-5 parts in 109. From these frequencies, we derived an antiproton-electron mass ratio of 1836.1526736(23). Our precision approaches that of the experimental value of the proton-electron mass ratio, and agrees with the latter within errors. Assuming CPT symmetry (i.e. mp=m_{overline {p}}), we further derived the electron's atomic mass as m e = 0.0005485799091(7)u from the more accurately known atomic mass of the proton.

Barna, Dániel

2014-04-01

178

Images in the rocket ultraviolet - The initial helium abundance and distance modulus of the globular cluster M5 from photometry of horizontal-branch stars  

Science.gov (United States)

A natural laboratory for the study of postmain-sequence evolution of low-mass (less than one solar mass) metal-poor stars is provided by globular clusters. These clusters are, therefore, a critical aid for developing an understanding of advanced stages of stellar evolution and of the chemical evolution of the Galaxy. Bohlin et al. (1983) have described a study of the postasymptotic branch star near the center of M5. The present investigation is concerned with the fainter horizontal-branch stars. The observations were made with the aid of a rocket-borne 38 cm f/9.0 Ritchey-Chretien telescope. Attention is given to payload and flight data, preflight bandpass calibration, the reduction of flight data, star selection, position measurement, photometry, the minimum observed horizontal-branch mass and inferences on mass loss, and individual UV-bright stars.

Bohlin, R. C.; Cornett, R. H.; Hill, J. K.; Smith, A. M.; Stecher, T. P.

1985-01-01

179

Embrittlement of vanadium alloys doped with helium  

International Nuclear Information System (INIS)

Helium embrittlement in serval binary vanadium alloys together with pure vanadium has been studied by tensile tests between room temperature and 800deg C after helium doping by the tritium trick technique. Although all the alloys without helium doping showed good ductility in the full temperature range studied, all the alloys doped with helium became brittle at 800deg C. Helium release during tensile deformation has been measured simultaneously with the load-displacement signal. A good correlation has been found between the helium release during deformation and embrittlement. Another correlation has been found between the helium release and atomic size factor; that is, the smaller solute atoms result in lower helium release. This study has also proved that the measurement of helium release during deformation provides valuable information on the behavior of helium during deformation. (orig.)

180

Laser spectroscopy of antiprotonic helium  

CERN Document Server

When antiprotons (i.e. the antimatter counterpart of protons) are stopped in helium gas, 97% of them annihilate within picoseconds by reacting with the helium nuclei; a 3% fraction, however, survive with an anomalously long lifetime of several microseconds. This longevity is due to the formation of antiprotonic helium, which is a three-body Rydberg atom composed of an antiproton, electron, and helium nucleus. The ASACUSA experimental collaboration has recently synthesized large numbers of these atoms using CERN's Antiproton Decelerator facility, and measured the atom's transition frequencies to 60 parts per billion by laser spectroscopy. By comparing the experimental results with recent three-body QED calculations and the known antiproton cyclotron frequency, we were able to show that the antiproton mass and charge are the same as the corresponding proton values to a precision of 10 parts per billion. Ongoing and future series of experiments will further improve the experimental precision by using chirp-compe...

Hori, M

2005-01-01

 
 
 
 
181

Low temperature uses of helium  

Science.gov (United States)

Helium is used for purging and pressurizing cryogenic rocket propellants, welding, atmosphere control, leak detection, and refrigeration. It provides the lowest possible liquid-bath temperature and produces superconductivity in certain materials. Its superfluid effects are used in superconducting magnets.

Brown, G. V.

1970-01-01

182

Microcellular Injection Molding Using Helium  

International Nuclear Information System (INIS)

In comparison with conventional foaming process microcellular injection molding process has advantages such as small bubble size, the removal of sink mark, scale reliability, and weight lightening. So microcellular injection molded parts are applied to electrical product and automobile part. Conventional microcellular foaming process used carbon dioxide and nitrogen as a foaming agent. And it has been never researched and applied about microcellular injection molding process using helium. In this paper, we did a microcellular injection molding process using helium based on previous research result and made samples. From this we can certificate the possibility of microcellular continuous process using helium. Helium is lighter and faster in diffusion than carbon dioxide or nitrogen so through this technique, it can be solved the problem such as spray or labeling

183

Behavior of weld defects in laser weldment of helium-doped stainless steel  

International Nuclear Information System (INIS)

Helium is generated within neutron-irradiated reactor components and entrapped in the stainless steel components. The repair of the components using conventional GTA welding practices is exceedingly difficult by entrapped helium, because of the initiation of helium bubbles and weld cracking. In this research, the behavior of helium bubble in the austenitic stainless steel weldment was investigated by utilizing stainless steels ion-implanted with helium and then welded by YAG laser apparatus. Helium ion implanting to the sample was carried out using 8MeV implantation apparatus, and the sample was doped with 2.45 x 1019 atoms/m2 dose at 6MeV and then doped with 1 x 1019 atoms/m2 dose at 5MeV. Helium bubbles are present at the bond region, heat-affected zone and weld metal. The increase of laser power causes the growth of helium bubble, toe cracks and cracks along the dendrite cell boundary in the weld metal. The helium bubble phenomena can be reproduced in the weld metal and in the heat-affected zone during repair welding using helium ion implanting technique. (author)

184

Optical traps for ultracold metastable helium atoms  

Energy Technology Data Exchange (ETDEWEB)

One of the main characteristics of metastable helium atoms is their high internal energy (20 eV). This energy can be released when a metastable atom hits a surface, ejecting one electron. Therefore, using a Channeltron Electron Multiplier (CEM), one can detect atoms with a time resolution of up to 5 ns. However, this high internal energy raises the problem of inelastic Penning ionizations, following: He{sup *}+He{sup *}{yields}He+He{sup +}+e{sup *}. This process has a rate of the order of 10 x 10 cm{sup 3} cot s{sup -}1 but is reduced by four orders of magnitude if the atoms are spin polarized due to total spin conservation. We report on the progress of the set up of a dipole trap for ultracold metastable helium using a red detuned fiber laser at 1560 nm. One of the aims of this optical trap is to release the constraint on the magnetic field value. We plan to measure the magnetic field dependance of inelastic collision rates for temperatures smaller than 10 {mu}K. In a spin polarized gas of helium, the spin-spin interaction produces spin relaxation and relaxation induced Penning ionization if the polarization condition is no longer maintained. We also present the development of a optical lattices in 1D and later in 3D. We intend to monitor the Penning ionization rate in order to follow the real-time dynamics of the superfluid-Mott insulator quantum phase transition.

Simonet, Juliette [LKB ENS, Paris (France)

2009-07-01

185

Hydrogen Production Using the Modular Helium Reactor  

International Nuclear Information System (INIS)

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 and 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 C to 1000 C, 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 C to 1000 C are described and compared. An initial SAPHIRE model to evaluate the reliability, maintainability, 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

186

Review of Liquid Helium Level Sensors  

Energy Technology Data Exchange (ETDEWEB)

Reliability of liquid helium level sensors becomes critical whenever a cryostat needs to be completely welded and accessibility becomes limited. This paper presents a review of the currently available continuous LHe level sensors from the viewpoint of reliability and wide operating temperature range (1.5 - 5.0 K). The only in limited temperature segments 3.0 - 4.6 K and below the lambda-point. Specifications of a new, simple and wide temperature range level sensor which dissipates very low power (~ 6 mW) into the cryogenic system and that can measure level of any cryogenic liquid are also presented here.

Myneni, Ganapati; Rao Myneni, Ganapati

1991-01-01

187

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

188

Effect of carbon content and helium gas environment on creep crack growth properties of Ni-26 pct Cr-17 pct W-0.5 pct Mo alloy at 1,273 K  

International Nuclear Information System (INIS)

Nickel-base superalloys are the most promising candidate structural materials for very high temperature use, e.g., as structural components of piping and heat exchangers in high-temperature gas-cooled reactors (HTGRs) and turbine discs in advanced aircraft engines. They can maintain good creep resistance in a very high temperature range of 1,273 K or higher. Here, creep crack growth tests were conducted on Ni-26 pct Cr-17 pct W-0.5 pct Mo alloys with different carbon contents in air and in helium gas environment at 1273 K using the compact-type (CT) specimen, and the effects of carbon content and environment on creep crack growth rate are discussed. Creep crack growth rate da/dt is evaluated by the C* parameters. The da/dt is faster in higher-carbon alloys than in lower-carbon alloys in each environment. This effect of carbon content is attributed to the lower creep ductility due to the increase of fine trans-granular carbides in higher-carbon alloys. The environmental effect on the da/dt vs C* relations is scarcely observed in higher-carbon alloys. In the 0.003 pct C alloy, however, da/dt is much lower in the He gas environment than in air. Carburization is observed ahead of the crack tip in the He gas environment at 1,273 K. The intergranular carbides precipitated due to carburization have a granular configuration and are considered to prevent the grain boundary sliding in lower-carbon alloys

189

The generation of particles to observe quantized vortex dynamics in superfluid helium  

Science.gov (United States)

We describe a method to prepare a sample of superfluid helium-4 with hydrogen particles suspended within it. The method is to dilute hydrogen gas with helium at room temperature, and bubble the mixture through liquid helium at a temperature above the superfluid phase transition temperature, T? ? 2.17 K. The procedure yields a suspension of micron-sized particles whose total volume is about 10 5 times smaller than the fluid volume. The fluid and suspension are then cooled to a temperature below T?. We show that the particles, so prepared in superfluid helium, are useful for studying superfluid flows and, in particular, the dynamics of quantized vortices. In addition, the particle-superfluid helium system is rich in not yet fully explained interactions. We review preliminary investigations that include observing the vortex lattice in rotating helium, vortex reconnection in quantized vortex turbulence, and vortex ring decay. These data illustrate the basic mechanisms of dissipation in superfluid turbulence.

Bewley, Gregory P.

2009-10-01

190

Thermal desorption of helium from graphite irradiated by He+ ions  

International Nuclear Information System (INIS)

Thermal desorption of helium from graphite irradiated with 20 keV He+ ions and surface erosion caused by ion irradiation have been studied. After He+ ion irradiation, localized protrusions and uniform domed surface uplifting were observed on isotropic graphite irradiation doses of 5.0x1017 ions/cm2 and 5.0x1018 ions/cm2, respectively. The peak temperatures in thermal desorption curves have a tendency to rise with irradiation dose, and become constant at about 3300C for irradiation doses above 5.0x1017 ions/cm2. Thermal desorption of helium considerably depends on the structure of graphite samples studied here. Glassy carbon and graphitized paper (PAPYEX) retained only 22% and 12% of the helium retention of isotropic graphite, respectively. (orig.)

191

Measurement of helium generated in V-B alloys irradiated in FFTF/MOTA  

International Nuclear Information System (INIS)

V-B and V-5Cr-B alloys have been irradiated in FFTF to assess the impact of helium generation rate on microstructural evolution of vanadium-base alloys. Using this method it is somewhat difficult to separate the various effects of the original boron as well as the lithium and helium products of the 10B (n, ?) reaction. Post-irradiation measurements of helium concentrations have been completed for two sets of V-B alloys, one irradiated in-core and one below core. It appears that the boron doping technique used to produce the various alloys was reasonably successful in reaching the desired helium/dpa variations

192

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

193

Performance of the Helium Circulation System on a Commercialized MEG  

International Nuclear Information System (INIS)

We report the performance of a helium circulation system (HCS) mounted on a MEG (Magnetoencephalography) at Nagoya University, Japan. This instrument is the first commercialized version of an HCS. The HCS collects warm helium gas at approximately 300 K and then cools it to approximately 40 K. The gas is returned to the neck tube of a Dewar of the MEG to keep it cold. It also collects helium gas in the region just above the liquid helium surface while it is still cold, re-liquefies the gas and returns it to the Dewar. A special transfer tube (TT) of approximately 3 m length was developed to allow for dual helium streams. This tube separates the HCS using a MEG to reduce magnetic noise. A refiner was incorporated to effectively collect contaminating gases by freezing them. The refiner was equipped with an electric heater to remove the frozen contaminants as gases into the air. A gas flow controller was also developed, which automatically controlled the heater and electric valves to clean up contamination. The developed TT exhibited a very low heat inflow of less than 0.1 W/m to the liquid helium, ensuring efficient operation. The insert tube diameter, which was 1.5 in. was reduced to a standard 0.5 in. size. This dimensional change enabled the HCS to mount onto any commercialized MEG without any modifications to the MEG. The HCS can increase liquid helium in the Dewar by at least 3 liters/Day using two GM cryocoolers (SRDK-415D, Sumitomo Heavy Industries, Ltd.). The noise levels were virtually the same as before this installation.

194

Performance of the Helium Circulation System on a Commercialized MEG  

Science.gov (United States)

We report the performance of a helium circulation system (HCS) mounted on a MEG (Magnetoencephalography) at Nagoya University, Japan. This instrument is the first commercialized version of an HCS. The HCS collects warm helium gas at approximately 300 K and then cools it to approximately 40 K. The gas is returned to the neck tube of a Dewar of the MEG to keep it cold. It also collects helium gas in the region just above the liquid helium surface while it is still cold, re-liquefies the gas and returns it to the Dewar. A special transfer tube (TT) of approximately 3 m length was developed to allow for dual helium streams. This tube separates the HCS using a MEG to reduce magnetic noise. A refiner was incorporated to effectively collect contaminating gases by freezing them. The refiner was equipped with an electric heater to remove the frozen contaminants as gases into the air. A gas flow controller was also developed, which automatically controlled the heater and electric valves to clean up contamination. The developed TT exhibited a very low heat inflow of less than 0.1 W/m to the liquid helium, ensuring efficient operation. The insert tube diameter, which was 1.5 in. was reduced to a standard 0.5 in. size. This dimensional change enabled the HCS to mount onto any commercialized MEG without any modifications to the MEG. The HCS can increase liquid helium in the Dewar by at least 3 liters/Day using two GM cryocoolers (SRDK-415D, Sumitomo Heavy Industries, Ltd.). The noise levels were virtually the same as before this installation.

T, Takeda; M, Okamoto; T, Miyazaki; K, Katagiri

2012-12-01

195

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

International Nuclear Information System (INIS)

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

196

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

197

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

198

Precision spectroscopy of antiprotonic helium  

CERN Document Server

Antiprotonic helium, a neutral exotic three-body system consisting of a helium nucleus, an electron and an antiproton, is being studied at the Antiproton Decelerator of CERN by the ASAUCSA collaboration. Using laser spectroscopy of the energy levels of the antiproton in this system and comparison to theory, a value of the antiproton-to-electron mass ratio with an error of 3 ppb could be obtained. This result agrees with the most precise measurement of the value of the proton and allows us to extract a limit of the equality of the proton and antiproton charge and mass of 2 ppb. Using microwave spectroscopy, the hyperfine structure of antiprotonic helium has been measured to 30 ppm. Experimental improvements are expected to soon provide a new value for the magnetic moment of the antiproton.

Widmann, E

2007-01-01

199

Analysis of flow instability of supercritical helium in curved tubing  

International Nuclear Information System (INIS)

Flow instability of supercritical helium in curved stainless steel tubing is studied to obtain engineering data applicable to forced cooled superconducting magnets. The tubing is wound in a ten turn coil of 100 mm in radius, the length and inner diameter of the tubing are 3 m and 2.88 mm respectively. The supercritical helium studied is at a temperature from 5 to 11 K, the pressure is 0.5 to 1.2 MPa and the mass flow rate from 0.3 to 0.7 g/s. The results obtained from the experiments are: (1) Wall temperature along the cooling channel under pulsive thermal input is strongly dependent on flow velocity, heat flux, and heating time. (2) Inverse flow has been observed under heat flux high enough for the helium to reach the pseudo-critical line. (3) A linear relation between the energy per oscillation period and the helium pressure has been derived under a DC thermal input to flowing supercritical helium

200

Diffusion and retention of helium in titanium carbide  

Science.gov (United States)

The knowledge of helium migration in TiC is an important issue due to its possible use as fuel coating in fission reactors and as first wall material coating in fusion reactors. Helium release measurements and diffusion coefficient calculations of helium in polycrystalline TiC have been carried out in the temperature range (1000-1600 °C) for the time period of 2 h. Polished bars of TiC were implanted with 3 MeV 3He+ ions in normal incidence at a dose of 5 × 1020 at./m2 at room temperature. Helium depth profile was measured at each step using the 3He(d, p0)4He nuclear reaction by varying the incident deuteron energy from 900 to 1800 keV. Effective diffusion coefficients vary from 4.20 × 10-18 to 2.59 × 10-17 m2 s-1 and activation energy values obtained are in the range 0.8-2.5 eV. Due to scarce availability of stoichiometric TiC, challenges in this study came from native vacancies present in the samples. The helium distribution and its release were affected by the presence of grain boundaries. He is considered to undergo two distinct populations into the sample and different values of diffusion coefficient have been determined for each population.

Agarwal, S.; Trocellier, P.; Vaubaillon, S.; Miro, S.

2014-05-01

 
 
 
 
201

Helium reionization and the thermal proximity effect  

CERN Document Server

We examine the temperature structure of the intergalactic medium IGM) surounding a hard radiation source, such as a Quasi-Stellar Object (QSO), as it responds to the onset of helium reionization by the source. We model the reionization using a radiative transfer (RT) code coupled to a particle-mesh (PM) N-body code. Neutral hydrogen and helium are initially ionized by a starburst spectrum, which is allowed to gradually evolve into a power law spectrum (fnu ~ nu^(-0.5)). Multiple simulations were performed with different times for the onset and dominance of the hard spectrum, with onset redshifts ranging from z = 3.5 to 5.5. The source is placed in a high-density region to mimic the expected local environment of a QSO. Simulations with the source placed in a low-density environment were also performed as control cases to explore the role of the environment on the properties of the surrounding IGM. We find in both cases that the IGM temperature within the HeIII region produced exceeds the IGM temperature before...

Meiksin, Avery; Brown, Calum K; 10.1111/j.1365-2966.2009.15667.x

2010-01-01

202

Long flexible transfer lines for gaseous and liquid helium  

International Nuclear Information System (INIS)

Screened flexible four-fold coaxial transfer lines for gaseous and liquid helium with lengths of 5 to 50 m have been successfully built and tested. The lines for gaseous helium have to supply and return a mass flow of 5 to 10g s-1 at temperatures ranging between 350 and 20 K for cooldown or warmup of superconducting magnets. The lines for liquid helium have to supply up to 100 lh-1 for final cooldown or up to 25 lh-1 for normal operation of superconducting magnets. The hydrodynamic and thermal performance characteristics of the lines have been measured. The results are encouraging and the use of these lines for superconducting magnets in high energy accelerators can be envisaged. (author)

203

Helium bubble growth in nickel at temperatures below vacancy migration  

International Nuclear Information System (INIS)

It is shown that bubble growth in nickel during 5 keV He+-implantation in the temperature range 200 K-600 K and dose range 5x1020 He+/m2-1022 He+/m2 can fairly well be described by a loop-punching mechanism. The results indicate that not all helium that remains in the matrix has precipitated into visible bubbles. With increasing dose, however, the percentage of helium in the bubbles increases. It is also shown that at 2x1021 He+/m2 the helium bubble distribution changes from a random distribution to a partially ordered distribution. The bubbles are ordered in some planes of the fcc nickel matrix, but ordering is lacking in other planes. (orig.)

204

Electron Bubbles in Liquid Helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

When an electron (or positronium atom) is injected into liquid helium with nearly zero energy, a bubble quickly forms around it. This phenomenon (which also occurs in liquid hydrogen, liquid neon and possibly in solid helium) lowers the mobility of the electron to a value similar to that for a positive ion. We estimate the radius of the bubble at zero pressure and temperature based on the zero point energy of the electron. If the liquid is held in a state of negative pressur...

Mcdonald, Kirk T.

2003-01-01

205

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

206

Direct current insulation breakdown characteristics of supercritical helium  

International Nuclear Information System (INIS)

The insulation breakdown characteristics of helium around a pseudo-critical line were experimentally studied, and their correspondence with the other physical characteristics was obtained. The breakdown voltage was measured in the following ranges of parameters; temperature 4.6 - 8.8 K, pressure 2.5 - 11 atm, density 20 - 146 mg/cm3. Voltage was raised at the rate of 1 kV/sec. The tested electrodes were a stainless steel plate vs. a tangsten needle (1mm diameter, 30 deg vertical angle) or a stainless steel ball (25 mm diameter) vs. the plate. The measured D.C. breakdown voltage was plotted in relation to the helium density. The effect of the electrode polarity was also investigated. The breakdown characteristics in the regions of pseudo-liquid, pseudo-gas, and across the pseudo-critical line are discussed, based on the experimental data with the needle having negative polarity. The effects of electrode distance and temperature were also investigated. The following major findings were obtained from the present study. (1) The breakdown characteristics changed at the pseudo-critical line, (2) The breakdown voltage in the pseudo-liquid region coincided with that of liquid helium. (3) It was suggested that gas bubbles did not play an important role also in the breakdown mechanism of liquid helium, because there can not be bubbles in pseudo-liquid supercritical helium. (4) In the case of steel ball and plate electrodes, the breakdown voltage of the pseudo-liquid he breakdown voltage of the pseudo-liquid helium did not coincide with that of liquid helium, but a tendency of changing toward coincidence was observed when the surfaces of the electrodes were roughened. (Aoki, K.)

207

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

208

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

209

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

International Nuclear Information System (INIS)

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 (?*He/?E ? 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 (?5%) and not by the intrinsic helium transport properties of the plasma. Perturbative helium transport studies using gas puffing have shown that DHe/Xeff?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

210

Thermal annealing behaviour and defect evolution of helium in fully stabilised zirconia  

International Nuclear Information System (INIS)

Helium implantations in fully stabilised zirconia have been performed with 30 keV ions with high doses (5.1 x 1016 and 2.6 x 1016 cm-2) and low doses (6.3 x 1015 and 1.7 x 1015 cm-2). The retained amount of helium and depth profiles have been monitored with neutron depth profiling and the damage distribution with positron beam analysis (PBA) after several annealing steps. The temperature dependent helium release was investigated by thermal helium desorption spectrometry. In the low dose samples, helium is released through diffusion as seen by a broadening of the helium distribution peak. PBA, performed with a two-layer model, shows shrinkage of the damage layer during annealing. For the high dose samples the helium peak does not broaden after annealing. Helium is retained up to high temperatures which is ascribed to bubble formation during thermal annealing. Fitting of the PBA results to a three-layer model shows that the ion implanted layer gets narrower after annealing at 600 K, up to 1000 K the S-parameter is increasing because helium is released from the bubbles, whereby vacancy clusters are left behind

211

The Effects of Curvature and Expansion on Helium Detonations on White Dwarf Surfaces  

Science.gov (United States)

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 12C and 16O. Detonations in these thin helium layers have speeds slower than the Chapman-Jouget (CJ) speed from complete helium burning, v CJ = 1.5 × 109 cm s-1. Though gravitationally unbound, the ashes still have unburned helium (?80% in the thinnest cases) and only reach up to heavy elements such as 40Ca, 44Ti, 48Cr, and 52Fe. It is rare for these thin shells to generate large amounts of 56Ni. We also find a new set of solutions that can propagate in even thinner helium layers when 16O is present at a minimum mass fraction of ?0.07. Driven by energy release from ? captures on 16O and subsequent elements, these slow detonations only create ashes up to 28Si 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; Townsley, Dean M.; Bildsten, Lars

2013-10-01

212

Prodigious degassing of a billion years of accumulated radiogenic helium at Yellowstone  

Science.gov (United States)

Helium is used as a critical tracer throughout the Earth sciences, where its relatively simple isotopic systematics is used to trace degassing from the mantle, to date groundwater and to time the rise of continents1. The hydrothermal system at Yellowstone National Park is famous for its high helium-3/helium-4 isotope ratio, commonly cited as evidence for a deep mantle source for the Yellowstone hotspot2. However, much of the helium emitted from this region is actually radiogenic helium-4 produced within the crust by ?-decay of uranium and thorium. Here we show, by combining gas emission rates with chemistry and isotopic analyses, that crustal helium-4 emission rates from Yellowstone exceed (by orders of magnitude) any conceivable rate of generation within the crust. It seems that helium has accumulated for (at least) many hundreds of millions of years in Archaean (more than 2.5 billion years old) cratonic rocks beneath Yellowstone, only to be liberated over the past two million years by intense crustal metamorphism induced by the Yellowstone hotspot. Our results demonstrate the extremes in variability of crustal helium efflux on geologic timescales and imply crustal-scale open-system behaviour of helium in tectonically and magmatically active regions.

Lowenstern, J.B.; Evans, W.C.; Bergfeld, D.; Hunt, A.G.

2014-01-01

213

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

International Nuclear Information System (INIS)

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 12C and 16O. Detonations in these thin helium layers have speeds slower than the Chapman-Jouget (CJ) speed from complete helium burning, vCJ = 1.5 × 109 cm s–1. Though gravitationally unbound, the ashes still have unburned helium (?80% in the thinnest cases) and only reach up to heavy elements such as 40Ca, 44Ti, 48Cr, and 52Fe. It is rare for these thin shells to generate large amounts of 56Ni. We also find a new set of solutions that can propagate in even thinner helium layers when 16O is present at a minimum mass fraction of ?0.07. Driven by energy release from ? captures on 16O and subsequent elements, these slow detonations only create ashes up to 28Si 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

214

48 CFR 52.208-8 - Required Sources for Helium and Helium Usage Data.  

Science.gov (United States)

...2010-10-01 2010-10-01 false Required Sources for Helium and Helium Usage Data. 52.208-8 Section 52.208-8...Provisions and Clauses 52.208-8 Required Sources for Helium and Helium Usage Data. As prescribed in...

2010-10-01

215

The epoch of helium reionization  

Science.gov (United States)

We study the reionization of Heii by quasars using a numerical approach that combines 3D radiative transfer calculations with cosmological hydrodynamical simulations. Sources producing the ionizing radiation are selected according to an empirical quasar luminosity function, and are assigned luminosities according to their intrinsic masses. The free parameters associated with this procedure are (1) a universal source lifetime, (2) a minimum mass cut-off, (3) a minimum luminosity cut-off, (4) a solid angle specifying the extent to which radiation is beamed, and (5) a tail-end spectral index for the radiative energy distribution of the sources. We present models in which these parameters are varied, and examine characteristics of the resultant reionization process that distinguish the various cases. In addition, we extract artificial spectra from the simulations and quantify statistical properties of the spectral features in each model. We find that the most important factor affecting the evolution of Heii reionization is the cumulative number of ionizing photons that are produced by the sources. Comparisons between Heii opacities measured observationally and those obtained by our analysis reveal that the available ranges in plausible values for the parameters provide enough leeway to provide a satisfactory match. However, one property common to all our calculations is that the epoch of Heii reionization must have occurred at a redshift in the range 3<~z <~4. If so, future observational programmes will be able to directly trace the details of the ionization history of helium and to probe the low-density phase of the intergalactic medium during this phase of the evolution of the Universe.

Sokasian, Aaron; Abel, Tom; Hernquist, Lars

2002-05-01

216

Automatic Refilling System For Liquid Helium  

Science.gov (United States)

Cryogenic experiments left unattended for days. System automatically replenishes liquid helium in cryogenic experimental apparatus as liquid evaporates. Automatic filling system transfers liquid helium from storage vessel to experimental apparatus under computer control. Gaseous helium from cylinder supplies pumping pressure. Circuit senses level of liquid helium by sensing voltage across measuring resistors in series with silicon resistance thermometers (SRT's). Low voltage indicates SRT covered, while high voltage indicates uncovered.

Serlemitsos, Aristides; Sansebastian, Mark; Geagen, Jay; Warner, Brent

1990-01-01

217

Atomic spectra in a helium bubble  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Density functional theory (DFT) is applied to atomic spectra under perturbations of superfluid liquid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of the D1 and D2 absorption lines are quite well reproduced by theory, suggesting that the DFT may be useful for describin...

Nakatsukasa, Takashi; Yabana, Kazuhiro; Bertsch, George F.

2002-01-01

218

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)

219

Multipurpose top for liquid helium Dewar  

Science.gov (United States)

Multipurpose top was fabricated for liquid helium Dewar flask which guards against flash vaporization of liquid helium and allows boiling temperature of liquid helium to be lowered by reduction of ambient pressure in Dewar flask. Device is rugged and simple, and does not require frequent calibrations or adjustments.

Murphy, R. S.; Anderholm, J. R.

1972-01-01

220

30 CFR 256.11 - Helium.  

Science.gov (United States)

...2010-07-01 2010-07-01 false Helium. 256.11 Section 256.11 Mineral...Sulphur Management, General § 256.11 Helium. (a) Each lease issued or continued...the ownership of and the right to extract helium from all gas produced from the...

2010-07-01

 
 
 
 
221

Explosive helium burning in white dwarf stars  

International Nuclear Information System (INIS)

Helium burning kinetics in white dwarfs has been considered at constant temperatures T >= 109 K and densities rho >105 g/cm3. It is found, that helium detonation in white dwarfs does not lead to formation of light (A < 56) elements. Thus, helium white dwarf model for supernova 1 is inconsistent with observations

222

Metastable states of antiprotonic helium  

Energy Technology Data Exchange (ETDEWEB)

New theoretical results on energy structure of metastable states of antiprotonic helium are reported. Among them are: highly accurate variational calculations of nonrelativistic energies; relativistic and QED corrections resulting on energy shifts; fine and hyperfine splitting; Auger transition rates. These newly obtained results for the transition wavelengths are in a few ppm agreement with experiment. (orig.).

Korobov, V.I. [Joint Inst. for Nuclear Research, Dubna (Russian Federation)

1997-06-01

223

Liquid helium fluid dynamics studies  

International Nuclear Information System (INIS)

The present report describes the work carried out under the sponsorship of the Division of High Energy Physics. The report is divided into sections according to the original grant proposal (hydrodynamic studies of single phase helium; two phase flow studies; component development studies; and new research areas). Following the text is a listing of publications which have resulted from work under the grant

224

Thermal compensator for helium refrigerators  

Science.gov (United States)

Closed-cycle helium refrigerator sensor generates negative-feedback control signals that drive heating diode to maintain temperature stability. Temperature-sensing diode and heating diode are mounted on heat sink that provides conductive path between load and cold tip. Method is applicable to other temperature-control applications, such as laser equipment, electronic instruments, and computer systems.

Hillman, J. J.; Jennings, D. E.

1978-01-01

225

Transferring superfluid helium in space  

International Nuclear Information System (INIS)

A preliminary concept of a system for resupplying superfluid helium in space has been developed at NASA Ames Research Center. Such a system would greatly enhance several planned scientific missions. These include the Space Infrared Telescope Facility (SIRTF), Large Deployable Reflector (LDR), Gravity Probe-B (GP-B), Hubble Space Telescope (HST), and Advanced X-ray Astrophysics Facility (AXAF). Resupplying helium in orbit would extend the lifetime for each of these missions without the difficulties, delays, and costs associated with retrieving the system, resupplying on the ground, and relaunching. This is especially true of systems such as the LDR that are assembled in space. A simple thermodynamic model of a transfer system is presented and discussed. The different thermodynamic regimes that can be expected in the transfer line are also discussed. The relations between these regimes are used to evaluate the relative efficiencies of different transfer techniques that could be used with the transfer system. The efficient transfer of liquid helium requires a low heat leak into the transfer line, particularly at point sources such as the coupling. It is also shown that the proper selection of supply tank temperature is critical during helium resupply

226

Cryopumping of hydrogen and helium  

International Nuclear Information System (INIS)

Results obtained in numerous tests on small (approx. 1000 l/S) and large (approx. 105 l/S) cryopumps cooled to 4.20K by LHe or between 10 to 200K by closed-cycle helium refrigerator are summarized. Then, measurements of the compound cryopump, designed to work on Tokamaks to handle the exhaust gases from the Torus are presented

227

Metastable states of antiprotonic helium  

International Nuclear Information System (INIS)

New theoretical results on energy structure of metastable states of antiprotonic helium are reported. Among them are: highly accurate variational calculations of nonrelativistic energies; relativistic and QED corrections resulting on energy shifts; fine and hyperfine splitting; Auger transition rates. These newly obtained results for the transition wavelengths are in a few ppm agreement with experiment. (orig.)

228

Helium loop for the HCPB Test Blanket Module  

Energy Technology Data Exchange (ETDEWEB)

The primary loop for the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) has been investigated with regard to layout definition, selection and dimensioning of components including piping and mechanical integration of the circuit into the different sections of ITER. The accommodation of the main components of the helium loop into the Torus Coolant Water System (TCWS) vault turned out as the most challenging point. Additionally operational states have been defined and the dynamic circuit behaviour has been investigated during transitions between operational states and accident situations with the RELAP5- code.

Neuberger, H. [Forschungszentrum Karlsruhe (FZK) Euratom Association, Postfach 3640, 76021 Karlsruhe (Germany)], E-mail: neuberger@irs.fzk.de; Jin, X.; Boccaccini, L.V.; Ghidersa, B.E.; Meyder, R. [Forschungszentrum Karlsruhe (FZK) Euratom Association, Postfach 3640, 76021 Karlsruhe (Germany)

2007-10-15

229

Helium loop for the HCPB Test Blanket Module  

International Nuclear Information System (INIS)

The primary loop for the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) has been investigated with regard to layout definition, selection and dimensioning of components including piping and mechanical integration of the circuit into the different sections of ITER. The accommodation of the main components of the helium loop into the Torus Coolant Water System (TCWS) vault turned out as the most challenging point. Additionally operational states have been defined and the dynamic circuit behaviour has been investigated during transitions between operational states and accident situations with the RELAP5- code

230

Superfluid plug as a control device for helium coolant  

Science.gov (United States)

New results are obtained on the characteristics of a superfluid plug as a nonmechanical control device for supplying cold helium vapor on demand from a superfluid-helium container. The data reported are for an Al2O3 ceramic plug having a nominal 5-micron pore size. A theoretical background and steady-state data are presented on mass flow rates and pressures as a function of liquid temperature. It is demonstrated that the superfluid plug can be employed as a flow control device in a control system designed to provide coolant on demand.

Karr, G. R.; Urban, E. W.

1980-01-01

231

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

232

Helium temperatures in a four-circle neutron diffractometer  

International Nuclear Information System (INIS)

The cooling of single-crystal samples to helium temperatures within a four-circle neutron diffractometer has been achieved by a novel continuous-flow system. The system relies solely on helium for its cooling power with two flow circuits being used. The first delivers liquid to a reservoir cryostat of capacity 1.4 l located close to the Eulerian cradle of the diffractometer and the second draws the refrigerant from this cryostat via a flexible transfer tube into the sample region of a compact cooling unit mounted off the cradle. This arrangement allows unhindered motion of the diffractometer circles for sample temperature operation in the range 3.9-300 K. The system requires a total helium flow of 1.0 l h-1 to maintain a temperature of 20 +- 0.1 K, decreasing to 0.5 l h-1 at higher temperatures. (Auth.)

233

Characterizing uniform discharge in atmospheric helium by numerical modelling  

International Nuclear Information System (INIS)

One-dimensional fluid model of dielectric barrier discharge (DBD) in helium at atmospheric pressure was established and the discharge was numerically simulated. It was found that not only the spatial distributions of the internal parameters such as the electric field, the electron density and ion density are similar to those in a low-pressure glow discharge, but also the visually apparent attribute (light emission) is exactly the same as the observable feature of a low-pressure glow discharge. This confirms that the uniform DBD in atmospheric helium is a glow type discharge. The fact that the thickness of the cathode fall layer is about 0.5 mm, much longer than that of a normal glow discharge in helium at atmospheric pressure, indicates the discharge being a sub-normal glow discharge close to normal one. The multipulse phenomenon was reproduced in the simulation and a much less complicated explanation for this phenomenon was given. (fluids, plasmas and electric discharges)

234

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 4K 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

235

Helium Isotopes in Geothermal Exploration  

Science.gov (United States)

Mantle volatiles, principally water and CO2, play an important role in the production of buoyant fluids that can be injected into the shallow crust. Regional and local trends in the crustal occurrence of mantle volatiles provide insight into the coupling between mantle-crust tectonics, heat and mass exchange between the mantle and crust, and the occurrence and distribution of economic resources such as ore minerals and oil, gas, and geothermal fluids. Mantle-derived volatiles in the crust are traceable through He isotopic compositions of hydrologic fluids. Once injected into a crustal-fluid system, mantle He will be continuously diluted with radiogenic helium-4 (4He) acquired from the U,Th-rich crust, and therefore in addition to providing information regarding the heat source, surface-fluid He isotopic compositions also provide a measure of the mantle He flux and the integrated permeability-fluid pressure gradient (flow rate) through the crust. The application of helium isotopes to geothermal exploration and reservoir characterization will be discussed for four cases: regional He isotope trends in amagmatic regions, He isotope trends at the local or basin scale with no evidence for recent crustal magmatism and two cases (Yellowstone Caldera and the Ohaaki Thermal Area, New Zealand) where helium isotope trends can be misleading. Regional trends across the northern Basin and Range show a correlation between helium isotopes and crustal extension rates and direction. The trends reflect changes in mantle fluid fluxes through the ductile lower crust and can be modeled as a proxy for deep crustal permeability. Local basin scale trends can be used to map the extent of a geothermal resource or its influence on the local hydrology. In some cases, the helium isotope trends can be misleading, in that high 3He/4He ratios (indicative of high mantle input or shallow magmatic activity) do not necessarily identify the location of a high temperature resource.

Kennedy, B. M.; Christenson, B. W.; van Soest, M. C.

2010-12-01

236

Simplicity works for superfluid helium  

International Nuclear Information System (INIS)

The famous philosopher Karl Popper once said that ''science is the art of systematic oversimplification''. Indeed, when faced with a new puzzle the trick is to simplify it without losing the essential physics - something that is easier said than done. However, this approach has paid off recently in low-temperature physics. Last year Richard Packard, Seamus Davis and co-workers at the University of California at Berkeley encountered a puzzling new phenomenon in superfluid helium-3, a quantum fluid that remains a liquid close to absolute zero and exhibits unusual properties such as the ability to flow without friction (A Machenkov et al. 1999 Phys. Rev. Lett. 83 3860). Previous experiments had revealed that certain effects in liquid helium are analogous to effects observed in superconductors, materials that lose all resistance to electric current at low temperatures. When the Berkeley researchers connected two reservoirs of superfluid helium-3, the superfluid flowed back and forth through apertures that formed a ''weak link'' between the two containers. This behaviour is similar to the oscillatory current of electrons that can flow across an insulating gap separating two superconductors - a device that is known as a Josephson junction. What was puzzling about the Berkeley results was that the helium-3 had two different stable configurations, both of which behaved in an unconventional way compared with a Josephson junction. This puzzle has now been solved independently by Sidney Yip at the National Center for Theoretical Sciences in Taiwan, and by Janne Viljas and Erkki Thuneberg at the Helsinki University of Technology in Finland (Phys. Rev. Lett. 1999 83 3864 and 3868). In this article the author describes the latest research on superfluid helium. (UK)

237

Chromatographic method of measurement of helium concentration in underground waters for dating in hydrological questions  

International Nuclear Information System (INIS)

Research methods which use natural environmental indicators are widely applied in hydrology. Different concentrations of indicators and their isotopic components in ground waters allow to determine the genesis of waters and are valuable source of information about the water flow dynamics. One of the significant indicator is helium. The concentration of 4He (helium) in ground water is a fine indicator in water dating in a range from a hundreds to millions of years (Aeschbach-Hertig i in., 1999; Andrews i in., 1989; Castro i in., 2000; Zuber i in., 2007). 4He is also used for dating young waters of age about 10 years (Solomon i in., 1996). Thesis consist the description of elaborated in IFJ PAN in Krakow chromatographic measurement method of helium concentration in ground waters in aim of dating. Chapter 1 contain short introduction about ground water dating and chapter 2 description of helium property and chosen applications of helium for example in technology and earthquake predictions. Helium sources in ground waters are described in chapter 3. Helium concentration in water after infiltration (originated from atmosphere) to the ground water system depends mainly on the helium concentration coming from the equilibration with the atmosphere increased by additional concentration from '' excess air ''. With the increasing resistance time of ground water during the flow, radiogenic, non-atmospheric component of helium dissolves also in water. In chapter 4 two measurement methods of helium concentration in ground waters were introduced: mass spectrometric and gas chromatographic method. Detailed description of elaborated chromatographic measurement method of helium concentration in ground water contain chapter 5. To verify developed method the concentration of helium in ground waters from the regions of Krakow and Busko Zdroj were measured. For this waters the concentrations of helium are known from the earlier mass spectrometric measurements. The results of verification are introduced in chapter 6. Described in chapter 5 chromatographic method was applied to measurements of helium concentration in ground waters from the regions of Zakopane, Raciborz and Torun. Obtained results of this measurements are shown in chapter 7. Appendixes A and B contain explanation of chromatographic system calibration and head-space method respectively. Detailed description of calculation of helium concentration in ground water using elaborated method and measurement deviations are introduced in Appendixes C and D. (author)

238

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

239

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

240

Precise laser spectroscopy of antiprotonic helium at CERN's Antiproton Decelerator  

International Nuclear Information System (INIS)

The ASACUSA collaboration of CERN has carried out several laser spectroscopy experiments of antiprotonic helium atoms. By comparing the results with three-body QED calculations, the antiproton-to-electron mass ratio was determined as Mp-bar/me=1836.152674(5). We are now developing some laser systems and detectors to further improve the experimental precision.

 
 
 
 
241

The parity violating rotation of the neutron spin in helium  

International Nuclear Information System (INIS)

The spin rotation angle for transversally polarized neutrons in liquid helium is calculated. The result is expressed in terms of a parity violating nucleon-nucleon interaction taken in the one-boson exchange approximation. For reasonable parameters of the interaction the spin rotation angle is equal to phi = (-0.1 +- 1.5) x 10-6 rad/m. (orig.)

242

Applicability of Henry's Law to helium solubility in olivine  

Science.gov (United States)

Applicability of Henry's Law to helium solubility in olivine We have experimentally determined helium solubility in San Carlos olivine across a range of helium partial pressures (PHe) with the goal of quantifying how noble gases behave during partial melting of peridotite. Helium solubility in olivine correlates linearly with PHe between 55 and 1680 bar. This linear relationship suggests Henry's Law is applicable to helium dissolution into olivine up to 1680 bar PHe, providing a basis for extrapolation of solubility relationships determined at high PHe to natural systems. This is the first demonstration of Henry's Law for helium dissolution into olivine. Averaging all the data of the PHe series yields a Henry's coefficient of 3.8(×3.1)×10-12 mol g-1 bar-1. However, the population of Henry's coefficients shows a positive skew (skewness = 1.17), i.e. the data are skewed to higher values. This skew is reflected in the large standard deviation of the population of Henry's coefficients. Averaging the median values from each experiment yields a lower Henry's coefficient and standard deviation: 3.2(× 2.3)×10-12 mol g-1 bar-1. Combining the presently determined helium Henry's coefficient for olivine with previous determinations of helium Henry's coefficients for basaltic melts (e.g. 1) yields a partition coefficient of ~10-4. This value is similar to previous determinations obtained at higher PHe (2). The applicability of Henry's Law here suggests helium is incorporated onto relatively abundant sites within olivine that are not saturated by 1680 bar PHe or ~5×10-9 mol g-1. Large radius vacancies, i.e. oxygen vacancies, are energetically favorable sites for noble gas dissolution (3). However, oxygen vacancies are not abundant enough in San Carlos olivine to account for this solubility (e.g. 4), suggesting the 3x10-12 mol g-1 bar-1 Henry's coefficient is associated with interstitial dissolution of helium. Helium was dissolved into olivine using an externally heated pressure vessel (Brown University). The starting materials were prepared by cutting gem-quality San Carlos olivine (~Fo90) into small blocks (~4×2×1 mm) using a diamond wafering blade saw and polishing with alumina slurries and colloidal silica. Analysis was completed by laser ablation-mass spectrometry using a 193 nm excimer laser and a MAP 215-50 specifically tuned for He (Open University, UK). Laser ablation pit depth varied from 2 to 40 ?m, and no correlation between pit depth and [He] is observed after accounting for variations PHe across the different experiments. This lack of correlation indicates a close approach to equilibrium was achieved over the experimental durations. Two analyses yielded spuriously high [He] (>3 std. dev. from the population mean, n = 85), and these analyses were not used to calculate Henry's coefficients. The two spuriously high analyses, in combination with the right skew of Henry's coefficients calculated from individual data points, suggests gem-quality San Carlos olivine contains volumes with anomalously high helium solubility. The nature of these volumes is currently under investigation. However, despite their presence, helium is still highly incompatible in olivine during partial melting. [1] Lux GCA 1987 [2] Heber et al. GCA 2007 [3] Shcheka & Keppler Nature 2012 [4] Walker et al. PEPI 2009

Jackson, C.; Parman, S. W.; Kelley, S. P.; Cooper, R. F.

2013-12-01

243

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

244

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

245

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

246

SCHe helium supply  

International Nuclear Information System (INIS)

The SCHe bottles are dedicated for safety use by CGI-SNF-D-13-2-P5-050. That CGI does not include the gas. The gas is important to the emergency MCO purge. The gas purity and pressure must be controlled items to satisfy the assumptions made in the safety analyses

247

Helium behaviour in Fe-base materials: thermal desorption and nuclear reaction analyses  

International Nuclear Information System (INIS)

Polycrystalline Fe 99.95 and 99.5 samples were implanted with helium at 8 keV and 3 MeV. Thermal Desorption Spectroscopy (TDS) and Nuclear Reaction Analysis (NRA) provided a complementary set of techniques to characterize helium-materials interactions within two different implantation depths, respectively close to the surface and in the bulk. Using TDS, it was possible to get information about the nature and the states of the structures where helium was trapped in radiation damaged Fe specimens. Activation energies for every trapping site (mono-vacancies, clusters) have been determined from conventional reaction model. The effect of interstitial carbon was also discussed, and compared with previous ab-initio studies. Moreover, the helium bulk diffusion constants in radiation damaged structures could be derived from non destructive 3He depth profiling. Preliminary observations highlighted that a few part of He remained trapped while helium bubbles migrated in the bulk. (authors)

248

Development of a process for recovery of helium from monazite sand  

International Nuclear Information System (INIS)

The pilot plant studies made to develop a process for helium recovery from monazite and its purification are described. The steps in the developed process are : (1) liberation of helium from monazite processing plant during caustic digestion of the ore, (2) collection of the crude gas (30-50% helium) after removal of condensables and drying, (3) removal of hydrogen by catalytic combination with oxygen to form water vapour using de-oxo catalyst bed, (4) removal of oxygen and nitrogen by condensation (helium content is raised 98% in this step) and (5) passing the gas over activated charcoal cooled by liquid nitrogen. In the final step, 99.995% pure helium is obtained. Trials have shown that the process is feasible. (M.G.B.)

249

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

Science.gov (United States)

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 D3 > D4 at T disordered structure of He5. 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.

Zhou, Y. L.; Wang, J.; Hou, Q.; Deng, A. H.

2014-03-01

250

Cycle design for the ISABELLE helium refrigerator  

Energy Technology Data Exchange (ETDEWEB)

The superconducting magnets for the ISABELLE storage ring/accelerator are designed to be operated at 3.8/sup 0/K using a forced-flow supercritical helium cooling system. The ISABELLE refrigerator has been designed subject to these special requirements. The design output is 13.65 KW of refrigeration below 4.2/sup 0/K (for cooling the magnet and distribution system), 55 KW at 55/sup 0/K (to cool heat shields for the whole system) and 100 g/s of liquefaction (for magnet power leads cooling). The system incorporates a subcooler section that produces liquid helium at 5.3 atm and 2.6 K and circulates it through the loads, and a Claude-type main refrigerator section. The main refrigerator section has five stages of cooling, with four of them below liquid nitrogen temperature. Liquid nitrogen precooling is not used. With 60% isothermal compressors the efficiency of the refrigerator system will be about 26% of Carnot.

Brown, D.P.; Schlafke, A.P.; Wu, K.C.; Moore, R.W.

1981-01-01

251

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)

252

Commissioning result of the KSTAR helium refrigeration system  

International Nuclear Information System (INIS)

To keep the SuperConducting (SC) magnet coils of KSTAR at proper operating conditions, not only the coils but also other cold components, such as Thermal Shields (TS), magnet structures, SC Bus-Lines (BL), and Current Leads (CL) must be maintained at their respective cryogenic temperatures. A Helium Refrigeration System (HRS) with an exergetic equivalent cooling power of 9 kW at 4.5 K without Liquid Nitrogen (LN2) pre-cooling has been manufactured and installed. The main components of the KSTAR Helium Refrigeration System (HRS) can be classified into the Warm Compression System (WCS) and the cryogenic devices according to the operating temperature levels. The process helium is compressed from 1 bar to 22 bar passing through the WCS and is supplied to cryogenic devices. The main components of cryogenic devices are consist of Cold Box (C/B) and Distribution Box (D/B). The C/B cool-down and make the various cryogenic helium for the KSTAR Tokamak and the various cryogenic helium is distributed by the D/B as per the KSTAR requirement. In this proceeding, we will present the commissioning results of the KSTAR HRS. Circuits which can simulate the thermal loads and pressure drops corresponding to the cooling channels of each cold component of KSTAR have been integrated into the helium distribution system of the HRS. Using those circuits, the performance and the capability of the HRS, to fulfill the mission of establishing the appropriate operating condition for the KSTAR SC magnet coils, have been successfully demonstrated

253

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

254

Hyperfine structure in muonic helium  

International Nuclear Information System (INIS)

A calculation of the ground-state hyperfine frequency in muonic helium is given. Perturbation theory is applied to the Schroedinger equation to obtain a series in m/sub e//m/sub ?/. The value obtained is 4462.6 +- 3 MHz, which is consistent with experiments at the Swiss Institute for Nuclear Research and the Los Alamos Meson Physics Facility. The theoretical value includes a -46-MHz contribution from excited states of the effective (??-)+ nucleus

255

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

256

The lifetime of the helium anion  

International Nuclear Information System (INIS)

We report the result of a correction-free measurement of the lifetime of the metastable atomic negative helium ion. For all previous experimental investigations of the lifetime of the most long lived level of the He? ion, 1s2s2p 4P5/2, it was necessary to correct for systematic effects of the experimental environment as magnetically induced mixing with more short-lived fine structure components and/or photo detachment by the thermal radiation. In the present experiment any such influence on the measured lifetime has been effectively eliminated by performing the measurement in a cryogenic electrostatic ion-beam trap. With this technique we have reached a higher accuracy than earlier obtained. Our result with one standard deviation error is ?5/2 = (359.0±0.7)?s.

257

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

258

Bichromatic Slowing of Metastable Helium  

Science.gov (United States)

This dissertation describes experiments to develop and realize an atomic decelerator (or "slower") for metastable helium using the optical bichromatic force (BCF). The research comprises two subtopics---using the bichromatic force at very large detunings, and developing a chirped BCF slower. There is experimental evidence that as bichromatic detunings approach 300 times the natural linewidth, the BCF breaks down. The likely cause is that large Doppler frequency shifts from the rapid deceleration result in cumulative dephasing of the Rabi cycling of the atom. To circumvent this and other problems, we have developed an alternate slower design in which the center frequency of a narrow BCF force profile is swept to stay resonant with the atoms as they are slowed. Results from a first-generation experiment show atomic slowing larger than has previously been possible with a large fixed detuning. Additional refinements will allow the design to be scaled up enough to slow metastable helium atoms to magneto-optical trapping velocities, with a brightness comparable to modern Zeeman slowers, but in a much smaller and considerably simplified configuration. I close with a discussion of prospects for direct laser slowing of molecules using the BCF. An estimate for CaF shows that a buffer-gas cooled beam can be slowed to rest, and proof-of-principle experiments in atomic helium yield very promising results.

Chieda, Michael Andrew

259

On the formation of (anionic) excited helium dimers in helium droplets.  

Science.gov (United States)

Metastable atomic and molecular helium anions exhibiting high-spin quartet configurations can be produced in helium droplets via electron impact. Their lifetimes allow detection in mass spectrometric experiments. Formation of atomic helium anions comprises collision-induced excitation of ground state helium and concomitant electron capture. Yet the formation of molecular helium anions in helium droplets has been an unresolved issue. In this work, we explore the interaction of excited helium atoms exhibiting high-spin triplet configurations with ground state helium using the equation-of-motion coupled-cluster method. Transition barriers in the energetically lowest He*-He and He*(-)-He interaction potentials prevent molecule formation at the extremely low temperatures present in helium droplets. In contrast, some excited states allow a barrier-free formation of molecular helium (anions). Moreover, we show that the necessary excitation energies pinpoint (higher) resonances in recently recorded mass spectra and emend the assignment of those resonances that have previously been assigned to electron-impact ionization of ground state helium necessitating subsequent double-electron capture. Embedding molecules or molecular clusters in helium droplets is a predestined experimental technique for the study of phenomena at very low temperatures. Profound knowledge about active processes in the helium environment is required for a proper assessment of experimental data. PMID:24866535

Huber, Stefan E; Mauracher, Andreas

2014-08-21

260

Helium diffusion in nickel at high temperatures  

International Nuclear Information System (INIS)

Helium has been implanted at certain temperatures between 800 and 12500C into single and polycrystalline Ni-samples with implantation depths between 15 and 90 ?m. Simultaneously the helium reemission from the sample is measured by a mass-spectrometer. It has been shown that the time dependence of the observed reemission rate is governed by volume diffusion of the helium. Measuring this time dependence as a function of temperature the helium diffusion constant has been determined. The He-diffusion is interpreted as a interstitial diffusion hindered by thermal vacancies. Depending on the implantation depth more or less of the implanted helium remains in the sample and forms large helium bubbles. (orig./GSCH)

 
 
 
 
261

Critical Landau velocity in helium nanodroplets.  

Science.gov (United States)

The best-known property of superfluid helium is the vanishing viscosity that objects experience while moving through the liquid with speeds below the so-called critical Landau velocity. This critical velocity is generally considered a macroscopic property as it is related to the collective excitations of the helium atoms in the liquid. In the present work we determine to what extent this concept can still be applied to nanometer-scale, finite size helium systems. To this end, atoms and molecules embedded in helium nanodroplets of various sizes are accelerated out of the droplets by means of optical excitation, and the speed distributions of the ejected particles are determined. The measurements reveal the existence of a critical velocity in these systems, even for nanodroplets consisting of only a thousand helium atoms. Accompanying theoretical simulations based on a time-dependent density functional description of the helium confirm and further elucidate this experimental finding. PMID:24160595

Brauer, Nils B; Smolarek, Szymon; Loginov, Evgeniy; Mateo, David; Hernando, Alberto; Pi, Marti; Barranco, Manuel; Buma, Wybren J; Drabbels, Marcel

2013-10-11

262

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

263

Muon transfer from deuterium to helium  

International Nuclear Information System (INIS)

We report on an experiment at the Paul Scherrer Institute, Villigen, Switzerland measuring x rays from muon transfer from deuterium to helium. Both the ground-state transfer via the exotic (d?3,4He)* molecules and the excited-state transfer from (?d)* were measured. The use of charge-coupled device detectors allowed x rays from 1.5 keV to 11 keV to be detected with sufficient energy resolution to separate the transitions to different final states in both deuterium and helium. The x-ray peaks of the (d?3He)* and (d?4He)* molecules were measured with good statistics. For the D2+3He mixture, the peak has its maximum at Ed?3He=6768±12 eV with full width at half maximum (FWHM) ?d?3He=863±10 eV. Furthermore, the radiative branching ratio was found to be ?d?3He=0.301±0.061. For the D2+4He mixture, the maximum of the peak lies at Ed?4He=6831±8 eV and the FWHM is ?d?4He=856±10 eV. The radiative branching ratio is ?d?4He=0.636±0.097. The excited-state transfer is limited by the probability to reach the deuterium ground state, q1s. This coefficient was determined for both mixtures: q1s3He=68.9±2.7% and q1s4He=90.1±1.5%±1.5%

264

The diffusion of helium through glass  

International Nuclear Information System (INIS)

Measurements have been made by mass spectrometry of the rates at which helium diffuses at different temperatures through two types of glass noted for their low helium permeation rate (Corning 1724 and GW glass from Glaswerk Wertheim). The lowest rate is for the Corning 1724 but it is shown that both types have helium adsorptions low enough to be suitable for storing the samples for the analysis of tritium by the 3He regrowth technique. (author)

265

Helium isotopic abundance variation in nature  

Energy Technology Data Exchange (ETDEWEB)

The isotopic abundance of helium in nature has been reviewed. This atomic weight value is based on the value of helium in the atmosphere, which is invariant around the world and up to a distance of 100,000 feet. Helium does vary in natural gas, volcanic rocks and gases, ocean floor sediments, waters of various types and in radioactive minerals and ores due to {alpha} particle decay of radioactive nuclides.

Holden, N.E.

1993-08-01

266

Qubits with electrons on liquid helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study dissipation effects for electrons on the surface of liquid helium, which may serve as qubits of a quantum computer. Each electron is localized in a 3D potential well formed by the image potential in helium and the potential from a submicron electrode submerged into helium. We estimate parameters of the confining potential and characterize the electron energy spectrum. Decay of the excited electron state is due to two-ripplon scattering and to scattering by phonons i...

Dykman, M. I.; Platzman, P. M.; Seddighrad, P.

2002-01-01

267

Kilohertz laser ablation for doping helium nanodroplets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ...

Mudrich, M.; Forkl, B.; Mueller, S.; Dvorak, M.; Buenermann, O.; Stienkemeier, F.

2007-01-01

268

Pair Correlations in Superfluid Helium 3  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In 1996 Lee, Osheroff and Richardson received the Nobel Prize for their 1971 discovery of superfluid helium 3 -- a discovery which opened the door to the most fascinating system known in condensed matter physics. The superfluid phases of helium 3, originating from pair condensation of helium 3 atoms, turned out to be the ideal test-system for many fundamental concepts of modern physics, such as macroscopic quantum phenomena, (gauge-)symmetries and their spontaneous breakdown...

Vollhardt, D.

1997-01-01

269

High voltage heavy current leads for liquid helium cryostats  

International Nuclear Information System (INIS)

Properties of insulation for high voltage cryoelectric equipment are considered. The results of investigations into surface dielectric strength under cryogenic conditions of bushing models made of monolithic teflon are discussed. New designs for heavy current leads for liquid helium cryostats, based on the obtained results, have been suggested and built. The current leads were tested at 80 and 100 kV with 5.5 kA current and the results are presented. (author)

270

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.)

271

Silicon Detectors For Helium Liquid And Vapor  

Science.gov (United States)

Simple electrical-resistance devices made of silicon indicate whether helium liquid or helium vapor present. Devices designed primarily for use in outer space, were tested and found to operate in normal Earth gravity. Silicon cubes supported by stainless-steel wires and strips. Voltage across each cube at fixed current indicates whether immersed in helium liquid or vapor. Liquid cools more than vapor does, resulting in greater electrical resistance. Such helium-liquid/vapor detectors incorporated into ducts or containers of laboratory equipment, and used to infer locations of liquid/vapor interfaces in order to measure quantities of liquid and vapor or to control refill operations.

Di Pirro, M. J.; Serlemitsos, A. T.

1990-01-01

272

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.)

273

Pulsation of high luminosity helium stars  

International Nuclear Information System (INIS)

Preliminary calculations are made on a systematic restudy of the linear and nonlinear pulsations of helium stars allowing for more recent and higher estimates of the effective temperature and for the high carbon abundance. Linear and nonlinear models are used. Results show qualitative agreement with earlier ones, models with sufficiently large L/M have a very hot blue edge for their instability strip, very large L/M values lead to dynamically unstable models which would appear to eject mass and therefore may not be realistic models for the pulsating RCrB stars, for the sequence studied a reasonable mass could be greater than or equal to 1.5 Msub solar. 12 references

274

Effect of Helium on Vycor Glass: Anomalous Thermal Conductivity Reduction  

Science.gov (United States)

There is a long history of studying helium adsorbed in Vycor. In this talk we present the results showing that helium can have a profound effect on the thermal conductivity property of Vycor glass. Although the thermal conductivity of liquid ^4He is four orders of magnitude higher than that of Vycor, the filling of liquid ^4He inside the Vycor pores brings about a three-fold reduction of the thermal conductivity as compared with empty Vycor between 0.06 and 0.5 K. By comparing these results with that of superfluid films, liquid ^3He and solid helium in the Vycor pores, we found that heat is conducted primarily through the silica network even when the pores are filled with solid or liquid helium. The dramatic reduction is brought about by the presence of slow sound mode in liquid ^4He that greatly facilitates the quantum tunneling of the two level systems (TLS) in the silica which enhances the scattering of the thermal phonons.

Cheng, Zhigang; Banavar, Samhita; Chan, Moses H. W.

2013-03-01

275

The Liquefaction of Hydrogen and Helium Using Small Coolers  

Energy Technology Data Exchange (ETDEWEB)

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.

Green, Michael A.

2006-02-12

276

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

277

Helium stratification in HD145792: a new helium strong star  

Science.gov (United States)

In this Letter, we report on the real nature of the star HD145792, classified as He weak in `The General Catalogue of Ap and Am stars'. By means of FEROS@ESO 1.52m high-resolution spectroscopic data, we refined the atmospheric parameters of the star, obtaining: Teff = 14400 +/- 400 K, logg =4.06 +/- 0.08 and ? =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 local thermodynamic equilibrium 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 HD145792 belongs to He-strong class contrary to the previous classification. Moreover, helium seems to be vertically stratified in the atmosphere, decreasing towards deepest layers. For what that concerns metal abundances, we found the following: overabundance of oxygen, neon, silicon, phosphorus, sulphur and calcium; carbon, nitrogen, magnesium, aluminum, titanium, chromium and nickel are normal, being the discrepancies from the solar values within the experimental errors; iron resulted to be slightly underabundant. Based on observations collected at the European Southern Observatory (ESO), La Silla, Chile, proposal ID 69.D-0537. E-mail: Giovanni.Catanzaro@oact.inaf.it

Catanzaro, G.

2008-03-01

278

Acoustic studies in liquid helium  

International Nuclear Information System (INIS)

Two acoustic studies in liquid helium recently carried out in the present group are reported. The first of these is the study of critical sound attenuation and dispersion associated with the critical phenomena near the superfluid transition temperature, where the validities of the dynamic scaling hypothesis and the universality precept are claimed. The second one is the study of dynamic properties of normal liquid 3He, a typical Fermi liquid, by the use of sound attenuation. A Landau parameter F2 and the lifetime of 3He quasiparticles have been obtained as functions of pressure. (author)

279

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

280

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

 
 
 
 
281

Helium in Earth's Early Core  

Science.gov (United States)

The high 3He/4He ratios for some ocean-island basalts, and more recent observations for solar components of the other rare gases (Ne, Ar and possibly Xe), continue to raise questions on primordial source reservoirs as well as on accretionary and incorporation processes of rare gases. A number of geochemical mantle models have been made to explain the observed 3He/4He ratios, the most popular of which has been an undegassed primordial reservoir. Isotope systematics of other radiogenic elements do not support such an isolated source and changes in the accepted models of mantle convection style have made it harder to rely on the deep mantle as a reservoir. The core has remained a particularly unfavourable location either because of difficulty in constructing a retention mechanism during planetary accretion or simply because of a lack of data: Partitioning studies at pressure are rare and complicated by the difficulty in reproducing not only absolute concentrations, but confinement of gas in high-pressure apparatus and post-run analysis. We present experiments on helium solubility and partitioning between molten silicates and Fe-rich metal liquids up to 16 GPa and 3000 K, with the laser-heated diamond-anvil cell, and the quenched run products analysed by ultra-violet laser ablation mass spectrometry (UVLAMP). Our results indicate a significantly higher partition coefficient for He between molten silicates and Fe-rich alloy liquids of about 10-2 at 16 GPa and 3000~K -- two orders of magnitude more helium is measured in the metal phase compared to the only previous data of Matsuda et al., (1993). The solubility mechanism is varied and involves a distinguishable bulk component and an apparent surface signature (that may be the result of the quench process). Whether surface effects are included or not, the early Earth's core would have incorporated non-negligible amounts of primordial helium if its segregation took place under mid-depth, magma-ocean conditions. The process of incorporation is determined at the atomic scale by the detailed composition and structure of silicate liquids that act as an important control of the level of incompatibility of noble gases under pressure. The time evolution of this core source of helium through to the present is yet another factor to be considered in making sense of 3He/4He ratios for the Earth, together with partitioning trends to higher pressure. Similar studies with other rare gases (and ultimately other isotopic systems) will help assess the level of consistency for the core as an active, present-day source of trace elements in the Earth, and the magnitudes of core- mantle chemical exchange.

Jephcoat, A. P.; Bouhifd, M. A.; Heber, V.; Kelley, S. P.

2006-12-01

282

Electromagnetic interactions in liquid helium  

International Nuclear Information System (INIS)

The Hamiltonian of interaction of liquid helium with the quantized electromagnetic field plays an important role in such phenomena as Raman scattering, excitons, and possible cooperative effects of exchange of virtual photons. This interaction has been derived from first principles by application of an appropriate unitary transformation to the second-quantized Hamiltonian of nuclei and electrons interacting with the quantized radiation field. The transformation is chosen so that the atomic bound states appear explicitly in the relevant scattering and reaction terms of the transformed Hamiltonian. (Auth.)

283

Energy-loss and straggling of hydrogen and helium ions in selenium  

International Nuclear Information System (INIS)

Using a transmission technique, the energy-loss and straggling of protons, deuterons and helium ions in Se were measured in the energy range between 0.3 and 2.5 MeV. The experimental stopping powers of the various ions are the same as the semiempirical values of Andersen and Ziegler, except in the vicinity of the stopping power maximum. The reduced straggling for the helium and hydrogen ions is energy independent above 0.25 MeV/amu with the helium values the same as predicted by Bohr but the hydrogen values are somewhat lower. (orig.)

284

Diffusion Coefficient of Helium in Mo-Assessed by the Internal Friction Technique  

International Nuclear Information System (INIS)

Diffusion behavior of helium in molybdenum was investigated by means of the internal friction method. An apparent relaxation internal friction peak associated with helium long-range diffusion was observed around 475 K at a resonant frequency of 56 Hz. In terms of the Gorsky relaxation model and the shift of the peak position with the measurement frequency, the activation energy and pre-exponential factor of the diffusion coefficient of the helium atoms in molybdenum were deduced as 0.63 eV and 6.5 cm2/s, respectively.

285

Energy and charge distribution of energetic helium ions in the outer radiation belt of the earth  

Science.gov (United States)

The first direct measurement of the charge states of helium at energies greater than 0.5 MeV/nucleon in the outer radiation belt, obtained aboard the ISEE-1 spacecraft in 1977, is reported. High abundances of singly ionized helium, with He(+)/He(2+) = 0.4 + or - 0.1 at L = 3.3 was found during one perigee pass, with a sudden decrease of that ratio by a factor of about 10 between L = 3.3 and 3.7. It is shown that nonstationary and/or nonadiabatic processes may play an important role for the distribution of helium ions in the outer radiation belt.

Klecker, B.; Hovestadt, D.; Scholer, M.; Gloeckler, G.; Ipavich, F. M.; Fan, C. Y.

1983-01-01

286

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

287

21 CFR 868.1640 - Helium gas analyzer.  

Science.gov (United States)

...2010-04-01 false Helium gas analyzer. 868.1640 Section...SERVICES (CONTINUED) MEDICAL DEVICES ANESTHESIOLOGY...868.1640 Helium gas analyzer. (a) Identification. A helium gas analyzer is a device...

2010-04-01

288

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

289

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.)

290

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

291

First principles simulations of hydrogen and helium at high pressures  

Science.gov (United States)

In this dissertation, a study of hydrogen and helium at high pressure is presented using state-of-the-art first-principles simulations using Quantum Monte Carlo (QMC) and Density Functional Theory (DFT). The Coupled Electron Ion Monte Carlo method, a novel QMC-based first-principles simulation method, is extensively used in order to produce the most accurate study of hydrogen at high pressure to date. The main motivation for this work comes from the study of giant planets, like Jupiter and Saturn. These planets are mainly composed of mixture of hydrogen and helium and the thermodynamic properties of the mixture is a basic ingredient to models of their evolution and interior structure. One of the main goals of our work is to produce an accurate parametrization of the free energy of hydrogen and helium from first principles simulations that can replace the Saumon-Chabrier-Van Horn model equations of state. We present a detail study of molecular dissociation in liquid hydrogen. We observe clear evidence of the plasma phase transition at low temperatures, through regions of (PARTP/PARTp)=0 and from discontinuities in the electronic conductivity. Both QMC-based and DFT-based simulation methods agree in the reported transition, although Monte Carlo methods predict higher transition pressures. Using the size of the discontinuity in the electronic conductivity, we estimate the critical point of the transition at temperatures slightly below 2000 K. We calculate the melting curve of solid molecular hydrogen up to pressures of 200 GPa using free energy integrations in the liquid and solid phases, and determine its intersection with the plasma phase transition. We also study the equation of state of hydrogen, helium and hydrogen-helium mixtures at pressures beyond 200 GPa. We find very good agreement between both simulation methodologies for pressures beyond 600 GPa. From the equation of state calculations, an analysis of the miscibility properties of the mixture is performed. We find that the temperatures for the dcmixing of helium and metallic hydrogen are sufficiently high to cross the planetary adiabat of Saturn at pressures around 5 Mbar. Helium is partially miscible throughout a significant portion of the interior of Saturn, and to a lesser extent in Jupiter. These results are directly relevant to models of the interior structure and evolution of Jovian planets.

Morales, Miguel Angel

292

Helium effects on displacement cascades in ?-iron  

International Nuclear Information System (INIS)

Molecular dynamics simulations have been performed to investigate the effects of helium on the displacement cascades in ?-iron. Besides conventional analysis tools, a new graphical representation of the data based on ternary plots has been introduced. Results show that the production of defects and their subsequent clustering appear to be greatly influenced by the presence of helium. Calculations reveal that the location of helium atoms, substitutional or interstitial, plays a major role. Compared to pure iron, interstitial helium atoms increase the amount of Frenkel pairs generated during the cascades. Conversely, substitutional helium atoms tend to decrease this production. However, in both cases, it is observed that helium atoms stabilize larger self-interstitial clusters, due to a strong binding energy. These simulations show that helium atoms trap self-interstitial clusters and would thus slow down their subsequent migration. Some helium-vacancy clusters are generated in the core of the displacement cascades but also grow at the periphery of self-interstitial clusters. It is shown that results greatly depend on the irradiation temperature.

293

Helium effects on displacement cascades in ?-iron  

Science.gov (United States)

Molecular dynamics simulations have been performed to investigate the effects of helium on the displacement cascades in ?-iron. Besides conventional analysis tools, a new graphical representation of the data based on ternary plots has been introduced. Results show that the production of defects and their subsequent clustering appear to be greatly influenced by the presence of helium. Calculations reveal that the location of helium atoms, substitutional or interstitial, plays a major role. Compared to pure iron, interstitial helium atoms increase the amount of Frenkel pairs generated during the cascades. Conversely, substitutional helium atoms tend to decrease this production. However, in both cases, it is observed that helium atoms stabilize larger self-interstitial clusters, due to a strong binding energy. These simulations show that helium atoms trap self-interstitial clusters and would thus slow down their subsequent migration. Some helium-vacancy clusters are generated in the core of the displacement cascades but also grow at the periphery of self-interstitial clusters. It is shown that results greatly depend on the irradiation temperature.

Lucas, G.; Schäublin, R.

2008-10-01

294

LOX Tank Helium Removal for Propellant Scavenging  

Science.gov (United States)

System studies have shown a significant advantage to reusing the hydrogen and oxygen left in these tanks after landing on the Moon in fuel cells to generate power and water for surface systems. However in the current lander concepts, the helium used to pressurize the oxygen tank can substantially degrade fuel cell power and water output by covering the reacting surface with inert gas. This presentation documents an experimental investigation of methods to remove the helium pressurant while minimizing the amount of the oxygen lost. This investigation demonstrated that significant quantities of Helium (greater than 90% mole fraction) remain in the tank after draining. Although a single vent cycle reduced the helium quantity, large amounts of helium remained. Cyclic venting appeared to be more effective. Three vent cycles were sufficient to reduce the helium to small (less than 0.2%) quantities. Two vent cycles may be sufficient since once the tank has been brought up to pressure after the second vent cycle the helium concentration has been reduced to the less than 0.2% level. The re-pressurization process seemed to contribute to diluting helium. This is as expected since in order to raise the pressure liquid oxygen must be evaporated. Estimated liquid oxygen loss is on the order of 82 pounds (assuming the third vent cycle is not required).

Chato, David J.

2009-01-01

295

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

296

Helium Speech: An Application of Standing Waves  

Science.gov (United States)

Taking a breath of helium gas and then speaking or singing to the class is a favorite demonstration for an introductory physics course, as it usually elicits appreciative laughter, which serves to energize the class session. Students will usually report that the helium speech "raises the frequency" of the voice. A more accurate description of the…

Wentworth, Christopher D.

2011-01-01

297

Pressure-driven Flow of Solid Helium  

Science.gov (United States)

Recent torsional oscillator measurements by Moses Chan's Penn State group showed evidence of ``non-classical rotational inertia'' for solid helium at temperatures below 200 mK. This discovery followed decades of theoretical speculation and experimental searches for ``supersolidity'' in helium. The experiments generated a great deal of interest but the origin and properties of such a state are still unclear. It would be very interesting to know whether supersolids share any of the other unusual properties of superfluids: persistent currents, second sound and quantized vortices. We have studied the response of solid helium to pressure changes in order to look for unusual flow properties that might be associated with supersolidity. The measurements involved both helium confined in the nanometer pores of Vycor glass and bulk solid helium, at temperatures as low as 30 mK. Pressure changes were generated with piezoelectrically driven diaphragm and flow was monitored with sensitive capacitive techniques. Near melting, solid helium flows very easily but we did not see any evidence of superflow at low temperatures. If helium does become a supersolid at low temperatures then its response to pressure gradients must be very different from that of liquid helium.

Beamish, John

2006-03-01

298

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

299

Explosive helium burning in white dwarfs  

International Nuclear Information System (INIS)

Analysis of the helium-burning kinetics at constant temperature and density (T> or =109 0K, rho> or =105 g/cm3) indicates that He4 detonation in white dwarfs cannot produce an appreciable quantity of light (A<56) elements. Hence type I supernova models relying on helium white dwarf detonation are not compatible with the observational evidence

300

The Effects of Curvature and Expansion on Helium Detonations on White Dwarf Surfaces  

CERN Document Server

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 C12 and O16. Detonations in these thin helium layers have speeds slower than the Chapman-Jouget (CJ) speed from complete helium burning, v_cj=1.5e9 cm/s. Though gravitationally unbound, the ashes still have unburned helium (~ 80% in the thinnest cases) and only reach up to heavy elements such as Ca40, Ti44, Cr48, and Fe52. It is rare for these thin shells to generate large amounts of Ni56. We also find a new set of solutions that can propagate in even thinner helium layers when O16 is present at a minimum mass fraction of ~0.07. Driven by energy release from alpha captures on O16 and subsequent elements, these slow detonations only create ashes up to Si28 ...

Moore, Kevin; Bildsten, Lars

2013-01-01

 
 
 
 
301

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

302

Properties of vanadium-base alloys irradiated in the dynamic helium charging experiment  

International Nuclear Information System (INIS)

One property of vanadium-base alloys that is not well understood in terms of their potential use as fusion reactor structural materials is the effect of simultaneous generation of helium and neutron damage. In the present Dynamic Helium Charging Experiment (DHCE), helium was produced uniformly in the specimen at linear rates of ? 0.4 to 4.2 appm helium/dpa by the decay of tritium during irradiation to 18--31 dpa at 425--600 C in Li-filled capsules in a sodium-cooled fast reactor. This paper presents results of postirradiation examination and tests of microstructure and mechanical properties of V-5Ti, V-3Ti-1Si, V-8Cr-6Ti, and V-4Cr-4Ti (the latter alloy has been identified as the most promising candidate vanadium alloy). Effects of helium on tensile strength and ductility were insignificant after irradiation and testing at > 420 C. However, postirradiation ductilities at -150 C in DHCE specimens. Predominantly brittle-cleavage fracture morphologies were observed only at -196 C in some specimens that were irradiated to 31 dpa at 425 C during the DHCE. For the helium generation rates in this experiment (? 0.4--4.2 appm He/dpa), grain-boundary coalescence of helium microcavities was negligible and intergranular fracture was not observed

303

Helium-3 blankets for tritium breeding in near-term fusion devices  

International Nuclear Information System (INIS)

The purpose of this paper is to propose a novel blanket concept for in-situ tritium breeding in a near-term device such as ITER. In this concept terrestrial supplies of helium-3, rather than lithium, are used for tritium breeding. In order to assess the key characteristics of this concept, a reference configuration was adopted based on minor modifications to the helium-cooled blanket concepts considered in the Blanket Comparison and Selection Study. The chosen configuration assumes a ferritic steel for structure and cladding and beryllium for neutron multiplication. The helium-3 is contained in a loop separate from the helium-4 coolant loop and flows within the beryllium. The helium-3 blanket exhibits good tritium breeding potential and low tritium inventories and leakage rates. The helium-3 requirements are 25-50 kg of inventory and 3.4-8.5 kg makeup/yr, 95% of which is due to burnup. It is estimated that there is sufficient helium-3 from decay of present military tritium stockpiles to meet this requirement. (orig.)

304

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)

305

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?

306

Helium Migration Mechanisms in Polycrystalline Uranium Dioxide  

International Nuclear Information System (INIS)

This study aims at identifying the release mechanisms of helium in uranium dioxide. Two sets of polycrystalline UO2 sintered samples presenting different microstructures were implanted with 3He ions at concentrations in the region of 0.1 at.%. Changes in helium concentrations were monitored using two Nuclear Reaction Analysis (NRA) techniques based on the 3He(d,?)1H reaction. 3He release is measured in-situ during sample annealing at temperatures ranging between 700 deg. C and 1000 deg. C. Accurate helium depth profiles are generated after each annealing stage. Results that provide data for further understanding helium release mechanisms are discussed. It is found that helium diffusion appears to be enhanced above 900 deg. C in the vicinity of grain boundaries possibly as a result of the presence of defects. (authors)

307

Solubility of helium in metallic hydrogen  

International Nuclear Information System (INIS)

In the low-pressure limit, a helium atom embedded in the electron gas appropriate to metallic hydrogen is only weakly perturbed from its free space structure, and its interaction with the electron gas can be represented by an energy-dependent pseudopotential. A calculation is made for the Gibbs energy of mixing for H-He, using an Austin pseudopotential and a fluid state model based on hard-sphere structure factors. A large orthogonalisation hole is predicted, which may crudely represent the gradual transition from a helium atom to a screened ?-particle as the electron density increases. The helium solubility is predominantly determined by the structure-independent interaction of the electron gas with the repulsive pseudopotential, and is probably least at the lowest pressures. In the hydrogen-helium planets (Jupiter, Saturn) the helium concentration may be at or close to saturation at the molecular-metallic hydrogen transition. (author)

308

Characteristics of a helium field ion gun  

International Nuclear Information System (INIS)

A helium field ion gun for a focused ion beam system was designed and constructed. The main feature of the ion gun structure is the use of a gas jet nozzle with a tungsten field emitter tip near the nozzle end. Since the helium gas jet is collimated towards the emitter tip, the local pressure in the vicinity of the tip is kept 110 times higher than the value for the location of the ion gauge which is about 20 cm away from the helium jet ion gun. Using this ion gun, current density of 1 ?A/sr was obtained although the helium gas flow rate ejected from the nozzle is as small as 1.6 x 10-3 Torr l/s. This result indicates high efficiency of the helium gas supply to the emitter tip surface

309

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

310

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)

311

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

312

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

313

The Hottest Horizontal-Branch Stars in Omega Centauri: Late Hot Flasher vs. Helium Enrichment  

Science.gov (United States)

UV observations of some massive globular clusters uncovered a significant population of very hot stars below the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario here stars experience the helium flash while on the white dwarf cooling curve or by the helium-rich sub-population recently postulated to exist in some clusters. Spectroscopic analyses of blue hook stars in omega Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified from existing data. We want to determine effective temperatures, surface gravities and abundances of He, C, N in blue hook and canonical extreme horizontal branch (EHB) star candidates. Moderately high resolution spectra of stars at the hot end of the blue horizontal branch in the globular cluster omega Cen were analysed for atmospheric parameters (T(sub eff), log g) and abundances using LTE and Non-LTE model atmospheres. In the temperature range 30,000 K to 50,000 K we find that 37% of our stars are helium-poor (log nHe/nH less than -2), 49% have solar helium abundance within a factor of 3 (-1.5 less than or equal to log nHe/nH less than or equal to -0.5) and 14% are helium rich (log nHe/nH greater than -0.4). We also find carbon enrichment in step with helium enrichment, with a maximum carbon enrichment of 3% by mass. At least 30% of the hottest HB stars in omega Centauri show helium abundances well above the predictions from the helium enrichment scenario (Y = 0.42 corresponding to log nHe/nH approximately equal to -0.74). In addition the most helium-rich stars show strong carbon enrichment as predicted by the late hot flasher scenario. We conclude that the helium-rich HB stars in omega Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

Moehler, S.; Dreizler, S.; Lanz, T.; Bono, G.; Sweigart, A V.; Calamida, A.; Monelli, M.; Nonino, M.

2007-01-01

314

Microanalysis by focused MeV helium ion beam  

International Nuclear Information System (INIS)

A microbeam line with 1.5 MeV helium ions for Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) measurements has been realized by piezo-driven objective slits and a magnetic quadrupole doublet. A minimum beam spot size of 1.3 ?m x 2.2 ?m was obtained. Secondary electron and Rutherford backscattering mapping images were demonstrated. (author)

315

Ground State Hyperfine Structure of Muonic Helium Atom  

CERN Document Server

The vacuum polarization and the nuclear structure corrections of orders alpha^5 and alpha^6 including the recoil effects are calculated in the hyperfine splitting of the ground state in muonic helium atom (mu e ^4_2He) by the perturbation theory. The obtained total numerical result Delta E^{hfs}=4464.539 MHz improves the previous calculations and is in the agreement with the experimental data.

Krutov, A A

2007-01-01

316

Atmospheric helium isotope ratio: Possible temporal and spatial variations  

Science.gov (United States)

The atmospheric 3He/ 4He ratio has been considered to be constant on a global scale, because the residence time of helium is significantly longer than the mixing time in the atmosphere. However, this ratio may be decreasing with time owing to the anthropogenic release of crustal helium from oil and natural gas wells, although this observation has been disputed. Here, we present the 3He/ 4He ratios of old air trapped in historical slags in Japan and of modern surface air samples collected at various sites around the world, measured with a newly developed analytical system. In air helium extracted from metallurgical slag found at refineries in operation between AD 1603 and 1907 in Japan, we determined a mean 3He/ 4He ratio of (5106 ± 108) × 10 -5 R HESJ (where R HESJ is the 3He/ 4He ratio of the Helium Standard of Japan), which is consistent with the previously reported value of (5077 ± 59) × 10 -5 R HESJ for historical slags in France and United Arab Emirates and about 4% higher than that of average modern air, (4901 ± 4) × 10 -5 R HESJ. This result implies that the air 3He/ 4He ratio has decreased with time as expected by anthropogenic causes. Our modern surface air samples revealed that the 3He/ 4He ratio increases from north to south at a rate of (0.16 ± 0.08) × 10 -5 R HESJ/degree of latitude, suggesting that the low 3He/ 4He ratio originates in high-latitude regions of the northern hemisphere, which is consistent with the fact that most fossil fuel is extracted and consumed in the northern hemisphere.

Sano, Yuji; Furukawa, Yukiko; Takahata, Naoto

2010-09-01

317

A quantum computer based on electrons floating on liquid helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electrons on a helium surface form a quasi two-dimensional system which displays the highest mobility reached in condensed matter physics. We propose to use this system as a set of interacting quantum bits. We will briefly describe the system and discuss how the qubits can be addressed and manipulated, including interqubit excitation transfer. The working frequency of the proposed quantum computer is ~1GHz. The relaxation rate can be at least 5 orders of magnitude smaller, f...

Dykman, M. I.; Platzman, P. M.

2001-01-01

318

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

319

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

320

Helium gas bubble trapped in liquid helium in high magnetic field  

International Nuclear Information System (INIS)

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

 
 
 
 
321

Photoionization Energies and Oscillator Strengths of Helium and Helium-Like Ions with Z = 6-8  

International Nuclear Information System (INIS)

In the photoionization process of helium and helium-like ions with Z 6-8(C4+, N5+, O6+), resonance energies of doubly excited autoionizing 1,3P0 states converging on the n = 4 and n = 5 hydrogenic thresholds were calculated by use of the diagonalization method. We also evaluated the oscillator strengths for transitions from 1s2 (1Se) to continuum 1 skp (1P0;) state. The calculations were done with the dipole length and velocity formulas using the six-parameter Hylleraas wavefunction for the ground state. The continuum state was represented by an antisymmetrized product of hydrogenics wavefunctions with completely screened Coulomb functions, and the autoionizing states by wavefunctions constructed in the diagonalization approximation within the framework of the theory of configuration interaction.

322

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

323

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.

324

Helium bubble growth in vanadium  

International Nuclear Information System (INIS)

Helium bubble growth in vanadium has been investigated during postimplantation annealing at 950 degrees C. The gas was introduced into 100-/mu/m-thick specimens at room temperature by sequential ion implantation at 220, 140, 120, and 50 keV. Bubbles produced during annealing were faceted on 100 direction at all times and their growth occurred by migration and coalescence. Bubble mobility is limited by the nucleation of atomic ledges on a bubble facet, and the energy per unit length of ledge is deduced to lie between 3.4 X 10-11 j/m. This parameter is recognized to be particularly sensitive to the composition and cleanliness of the bubble surface

325

Helium two-phase instabilities  

International Nuclear Information System (INIS)

Instabilities encountered in helium two-phase flow during the cool down of superconducting magnets and transmission lines have been experimentally investigated in 1000 mm long vertical tubes of sizes 6.35 and 2.73 mm. Density wave oscillations were measured and recorded in both adiabatic and diabatic flow conditions. Pressure drop oscillations across the test section were observed with the aid of a sensitive differential pressure transducer. The average density at the exit of the experimental test section was a function of the dielectric constant measured by a capacitance probe. The period of the observed density wave sustained oscillations (0.2 to 3 seconds) were found to be of the same order of magnitude of the fluid particles residence time in the heated section. An empirical threshold criteria for the inception of these oscillations has been developed from similarity analysis. (author)

326

Superfluid helium physics and applications  

CERN Document Server

The behaviour of liquid helium is dominated by quantum effects, which give rise to superfluidity at low temperatures. An account will be given of the observed properties of the superfluid phase of liquid 4He, and of the way in which these properties can be described by a two-fluid model, supplemented by the requirement that motion of the superfluid component be irrotational with a hydrodynamic circulation that is quantized in units of h/m4. The existence of superfluidity and the quantization of circulation will be related to the presence of a Bose condensate. The description of excited states of the liquid in terms of weakly interacting thermal excitations (phonons and rotons will be discussed, and the relation between these excitations and the normal-fluid component will be explained. The existence and role of quantized vortex lines in the superfluid component will be discribed. A brief account will be included of topics of current research interest.

Vinen, W F; CERN. Geneva

1999-01-01

327

Anomalously high retention of radiogenic helium in native platinum  

Science.gov (United States)

Relatively quick migration of helium from crystal structures has been known for a long time. However there is a group of minerals - native metals - where stability of radiogenic helium is essentially high [1]. Helium, due to its very low solubility in metals, assembles in atomic clusters - "bubbles" of nanometer size. Migration of helium "bubbles" as a whole from the crystal structures needs relatively high temperature near the melting point of metals. On that ground of special interest are platinoids with melting points (and, consequently, temperatures of "explosion-like" release of radiogenic helium) of more than 1550 oC In this respect we believe that the method based on natural radioactivity of platinum is promising. To verify the idea of anomalously high retention of radiogenic helium in native platinum and to check the efficiency of the proposed 190Pt-4He method of isotope geochronology, we studied independent mineral aggregates of native platinum from chromite-bearing dunites of Galmoenan plutonic complex (10 individual samples) (Koryak-Kamchatka belt, Russia) and Konder massif (5 individual samples) (Khabarovsk district,Russia). Because native platinum always has admixture of Fe, Cu etc. for reliable determination of concentration of platinum in the samples in our study we used electron microscope JSM-6510LA with JED 2200 add-on. Amount of 4He in native platinum was determinate on mass-spectrometer complex MSU-G-01-M. Native platinum consists of 6 isotopes. Among them two isotopes are ?-radioactive and decay according to following schemes: 190Pt ?4He+186Os?4He+182W 192Pt ?4He+188Os Presumably, in native platinum there is always a certain amount of uranium and thorium, absorbed in the process of crystallization. However influence of helium generation from uranium becomes more marked at growing of 238U/Pt ratio and beginning with 238U/Pt ? 10-5 should be taken into consideration. For the same reason helium produced by the decay of 192Pt and 186Os can be neglected [2]. Obtained data was used to build a 4Herad -190Pt isochrone. The age calculated by the tangent of the isochrone slope angle for Galmoenan massif and for neighbor placer is: 72.3 ± 3.4 mln years. The obtained age value is comparable with the results of isotope datings, which were made previously by different methods of isotope geochronology. Rb-Sr, U-Pb, K-Ar, 39Ar-40Ar, Sm-Nd isotope systems shown formation of the complex from 80 to 50 mln.years ago. For the samples from Konder massif was also obtained a good isochrone. The age calculated by the tangent of the isochrone slope angle for Konder "alluvial" placer is 112±7 mln years. That data is also in a good correspondence with other geological data. Thus the data provide the ability of direct 190Pt-4He dating of native platinum. And additionally reaffirm the evidence of anomalously high retention of radiogenic helium in native metals up to the temperatures near their melting points. This study was supported by the RFFI, projects no.07-05-00634 and 11-05-12046-ofi-m-2011, the program of the Department of Earth Sciences of the RAS "Natural Isotope Systems: Methods of Investigations."

Yakubovich, O. V.; Shukolyukov, Yu. A.; Mochalov, A. G.; Kotov, A. B.; Korneev, S. I.

2012-04-01

328

Helium refrigeration system for the KSTAR  

International Nuclear Information System (INIS)

The KSTAR, a tokamak with fully superconducting (SC) magnets, is under construction in the National Fusion Research Center (NFRC). For the proper operation of the KSTAR, the superconducting magnets have to be maintained below the critical temperature of the SC components while charged at their corresponding operation current values. In this paper, a large scale helium refrigeration system (HRS) which has been designed and developed to fulfill such a mission is presented. The cold components of the KSTAR are kept at their operating temperatures thanks to various kinds of cryogenic helium which are produced in the cold box (C/B) of the HRS in combination with the supercritical helium (SHe) cryogenic circulators and a liquid helium (LHe) thermal damper (TD) located in the primary helium distribution box (D/B no. 1). The relative distribution of the cryogenic helium among the cooling channels of each cold component of the KSTAR is performed by the secondary helium distribution system which consists of the secondary distribution box (D/B no. 2) and the cryogenic transfer lines (CTL's)

329

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

330

Evolution of Helium Bubbles in ODS Steel  

International Nuclear Information System (INIS)

Due to the superior thermal creep properties and the high resistance to neutron irradiation, oxide dispersion strengthened (ODS) steels are considered as potential candidate alloys for application in advanced nuclear or fusion reactor. The accumulation of helium after neutron irradiation has a substantial influence on the mechanical properties of materials, e.g. the intergranular embrittlement via helium bubble growth at grain-boundaries at temperatures higher than 0.33Tm (Tm is the melting point of metals), the void swelling, blistering of metal surface, and the rise of the ductilebrittle transition temperature (DBTT) of bcc structure metals. Therefore, the understanding of the helium behavior in ODS steels is important prior to its application in the nuclear energy field. Although a substantial studies have been conducted to investigate the effects and micro-mechanism of helium in ODS steels, the nucleation and growth of Helium in metals is not yet fully understood. In this work, we used low energy helium ions to be implanted into a commercial ODS alloy (MA956TM) sample, and investigated the evolution of the helium bubbles with fluences at room temperature using a TEM (Transmission Electron Microscope)

331

Helium distribution in a mantle shear zone from the Josephine Peridotite  

Science.gov (United States)

A previous study of oceanic mylonites suggested that peridotite helium concentrations are correlated with the degree of high-temperature ductile deformation in the mantle. In order to test this result, this study combines helium measurements with characterization of the deformation state of harzburgite samples in a small (6 m width) ductile mantle shear zone from the Josephine Peridotite, Oregon, USA. All measurements were made by coupled in vacuo crushing and melting, demonstrating that most of the helium (>80%) resides within the solid phases rather than fluid or melt inclusions. The present study confirms the influence of deformation on helium contents, but only at the highest shear strain (?>20) are helium contents significantly higher. The highest helium concentration, by roughly a factor of two, is found in the center-most sample, which also has grain size reduction by a factor of ?4. Dislocations and sub-grain boundaries are present in all samples and do not correlate with helium concentrations. Mineralogy also appears to have a negligible influence in this shear zone, as modal mineralogy is relatively homogeneous, with all samples being harzburgites. These observations suggest that the increase in helium concentration is related to grain size reduction, with grain boundaries proposed as an additional storage site for helium in the mantle. The present data also characterize the isotopic composition of the Josephine Peridotite: 3He/4He=6.7±0.2 Ra (n=33, between 6.3 and 7.1 Ra). The presence of cosmogenic 3He in the matrix is indicated by the helium isotopic composition released by melting: 3He/4He=8.5±0.3 Ra (n=10; from 7.9 to 10.9). This corresponds to an exposure age of 10 Kyr, which is approximately concordant with the end of the last glacial maximum. Very little radiogenic helium is present in the samples, suggesting extremely low uranium and thorium contents ([U]infiltration are also important factors for understanding helium storage in the mantle.

Recanati, A.; Kurz, M. D.; Warren, J. M.; Curtice, J.

2012-12-01

332

Implementation of two-phase tritium models for helium bubbles in HCLL breeding blanket modules  

Science.gov (United States)

Tritium self-sufficiency requirement of future DT fusion reactors involves large helium production rates in the breeding blankets; this might impact on the conceptual design of diverse fusion power reactor units, such as Liquid Metal (LM) blankets. Low solubility, long residence-times and high production rates create the conditions for Helium nucleation, which could mean effective T sinks in LM channels. A model for helium nano-bubble formation and tritium conjugate transport phenomena in liquid Pb17.5Li and EUROFER is proposed. In a first approximation, it has been considered that He bubbles can be represented as a passive scalar. The nucleation model is based on the classical theory and includes a simplified bubble growth model. The model captures the interaction of tritium with bubbles and tritium diffusion through walls. Results show the influence of helium cavitation on tritium inventory and the importance of simulating the system walls instead of imposing fixed boundary conditions.

Fradera, J.; Sedano, L.; Mas de les Valls, E.; Batet, L.

2011-10-01

333

Helium release from aged uranium tritide  

International Nuclear Information System (INIS)

Helium desorption rule from aged uranium tritide was investigated through the pressure measurement and the composition of helium released from uranium tritide stored at room temperature was analysed. After 6 to 7 years aging of uranium tritide, about 38.1%-45.3% He prodeced by disintegration of 3He from uranium tritide was released in the cavum of the uranium bed with the gas pressure of 1.11-1.36 MPa and the purity of 99.9% above, the rest of helium is kept in the solid of uranium tritide with the He/U ratio of 0.177-0.201. (authors)

334

Helium detrapping and release from metal tritides  

International Nuclear Information System (INIS)

Interstitial helium ?-decay products remain trapped in metal tritides until a critical threshold concentration is attained. This concentration appears to be independent of host metal-atom species for a significant number of CaF2-structure ditritides. The role of strains in these materials is discusssed, and a strain model is presented which is consistent with known release behavior as well as x-ray lattice-parameter studies. This model predicts that in many cases the threshold helium concentration is simply related to the critical concentration for (site) percolation of interstitial helium atoms. An experimental test of this model, which I have proposed and which is in preparation, is discussed

335

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

336

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

337

Helium production rates in the LASREF Facility  

International Nuclear Information System (INIS)

The objective of this study is to determine the helium generation rates produced in the Los Alamos Spallation Radiation Effects Facility (LASREF). Foils of Cu, Co, Fe and Ni were irradiated in LASREF. The flux was determined by measurement of the gamma ray intensities induced by transmutation. The induced helium levels were measured by an isotope dilution mass spectrometry method. For copper the helium/dpa ratio was found to be 11.1 appm/dpa, which is ?405 of the rate predicted by an earlier calculation

338

The growth of helium bubbles in stainless steel at high temperatures  

International Nuclear Information System (INIS)

The influence of annealing time (1 to 1000 hours), applied tensile stress (0 to 130 MPa), temperature (973 to 1073 K) and helium content (10 to 300 a.p.p.m.) on the size distribution and density of helium bubbles within the grains of AISI type 316 stainless steel has been studied by TEM of ?-implanted foil specimens. The results are compared with theoretical predictions assuming different growth mechanisms. The experimental data are best described by assuming that (1) the bubble coarsening is due to Ostwald ripening and (2) the helium in the bubbles obeys a highly non-ideal equation of state. From such a comparison an activation energy for helium permeation through the lattice of 3.5 eV can be deduced, which is comparable with theoretical estimates. It was further observed that tensile stresses can lead to bimodal size distributions, which are attributed to the presence of two mobile and supersaturated components (helium and vacancies) during the nucleation stage. The subsequent growth of matrix bubbles seems to be rather insensitive to stress, in contrast to the behaviour of grain boundary bubbles. Finally it could be shown that, within the covered parameter range, the implanted helium is entirely precipitated into bubbles with diameters > approx. 1.5 nm that are detectable by TEM. (author)

339

Theory and modelling of helium enrichment in plasma experiments with pump limiters  

International Nuclear Information System (INIS)

Helium enrichment in the exhaust gas stream flowing from a hydrogen-helium plasma is studied using an analytical theory and Monte Carlo simulations. To provide a sensitive experimental test in a tokamak, an unusual configuration, inverted from traditional designs, is proposed for a pump limiter. The principle can be tested in other plasma devices as well. The theory suggests that for typical plasma edge conditions in a confinement device, namely, n = 1013cm-3 and T/sub i/ = T/sub e/ approx. = 5-30eV, helium enrichment in the neutral gas exhaust stream can be very high, in the range 5 to 7, relative to the helium-hydrogen ratio in the plasma. Such high enrichment factors are achieved by exploiting the difference between the ionization rates of hydrogen and helium and the negligible helium charge exchange rate at these plasma conditions. A limiter arrangement is proposed in which the natural curvature of the toroidal magnetic field is used to isolate, using the plasma itself, the point of plasma neutralization from the location of the gas exhaust. The plasma region then acts to preferentially screen the recycling hydrogen by the processes of ionization and of charge-exchange-induced losses at open boundaries. The theory and analysis suggests that an experiment can provide a sensitive test of modules used to describe the plasma edge and of atomic and surface physics data used in these models

340

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

 
 
 
 
341

Helium magnetic refrigerator. II. Liquefaction process and efficiency  

International Nuclear Information System (INIS)

Magnetic refrigeration techniques are based on the utilization of the magnetocaloric effect. A change in entropy occurring as a result of a change in magnetization leads to heat-transfer processes. The magnetic refrigerator consists of two parts, including the magnetic materials and the heat-exchange system. Advantages of this type of refrigerator compared to the gas refrigerator are related to high efficiency, compactness, and high reliability. The present investigation is concerned with a new Carnot type refrigeration system which liquefies helium with the aid of Gd3Ga5O12 (GGG) as a refrigerant. Attention is given to the heat transfer between GGG and helium gas, the experimental apparatus, and the obtained experimental results. 7 references

342

Effect of Helium Accumulation on the Spent Fuel Microstructure  

International Nuclear Information System (INIS)

In a nuclear spent fuel repository, the aqueous rapid release of radio-activity from exposed spent fuel surfaces will depend on the pellet microstructure at the arrival time of water into the disposal container. Research performed on spent fuel evolution in a closed system has shown that the evolution of microstructure under disposal conditions should be governed by the cumulated ?-decay damage and the subsequent helium behavior. The evolution of fission gas bubble characteristics under repository conditions has to be assessed. In UO2 fuels with a burnup of 47.5 GWd/t, the pressure in fission gas bubbles, including the pressure increase from ?-decay helium atoms, is not expected to reach the critical bubble pressure that will cause failure, thus micro-cracking in UO2 spent fuel grains is not expected. (authors)

343

Genetic changes in Mammalian cells transformed by helium cells  

Energy Technology Data Exchange (ETDEWEB)

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/{mu}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.

Durante, M.; Grossi, G. (Naples Univ. (Italy). Dipt. di Scienze Fisiche); Yang, T.C.; Roots, R. (Lawrence Berkeley Lab., CA (USA))

1990-11-01

344

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

345

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

346

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

347

The Helium Cryogenic System for the ATLAS Experiment  

CERN Document Server

The magnetic configuration of the ATLAS detector is generated by an inner superconducting solenoid and three air-core toroids (the barrel and two end-caps), each of them made of eight superconducting coils. Two separated helium refrigerators will be used to allow cool-down from ambient temperature and steady-state operation at 4.5 K of all the magnets having a total cold mass of about 600 tons. In comparison with the preliminary design, the helium distribution scheme and interface with the magnet sub-systems are simplified, resulting in a considerable improvement of the operational easiness and the overall reliability of the system at some expense of the operational flexibility. The paper presents the cryogenic layout and the basic principles for magnets cool-down, steady state operation and thermal recovery after a fast energy dump.

Delruelle, N; Passardi, Giorgio; ten Kate, H H J

2000-01-01

348

LOCA analysis for Korean helium cooled solid breeder TBM  

International Nuclear Information System (INIS)

One of the major ITER goals is test blanket module (TBM) program which is for the demonstration of the breeding capability that would lead to tritium self-sufficiency in a reactor and the extraction of high-grade heat suitable for electricity generation under the ITER fusion environment. While the engineering design of Korean helium cooled solid breeder (HCSB) TBM and its ancillary systems has been performed, a safety assessment on different possible accident scenarios should be carried out for the purpose of licensing. In this paper, accident analyses for several loss of coolant accident (LOCA) cases were performed in order to assess safety aspects of the TBM design using RELAP5/MOD3.2. Since the TBM forms a loop with helium cooling system (HCS) which is one of ancillary systems required for removing heat deposited in the TBM by neutron wall loading and surface heat flux from plasma, it is necessary to model the complete loop for accident analysis. In this study, the helium passage including the TBM and HCS was nodalized for each accident scenario. The TBM and HCS components were modeled as the associated heat structures provided by RELAP5 to include heat transfer across solid boundaries. Based on computational results it was found that current design of the TBM is robust from the safety point of view.

349

LOCA analysis for Korean helium cooled solid breeder TBM  

Energy Technology Data Exchange (ETDEWEB)

One of the major ITER goals is test blanket module (TBM) program which is for the demonstration of the breeding capability that would lead to tritium self-sufficiency in a reactor and the extraction of high-grade heat suitable for electricity generation under the ITER fusion environment. While the engineering design of Korean helium cooled solid breeder (HCSB) TBM and its ancillary systems has been performed, a safety assessment on different possible accident scenarios should be carried out for the purpose of licensing. In this paper, accident analyses for several loss of coolant accident (LOCA) cases were performed in order to assess safety aspects of the TBM design using RELAP5/MOD3.2. Since the TBM forms a loop with helium cooling system (HCS) which is one of ancillary systems required for removing heat deposited in the TBM by neutron wall loading and surface heat flux from plasma, it is necessary to model the complete loop for accident analysis. In this study, the helium passage including the TBM and HCS was nodalized for each accident scenario. The TBM and HCS components were modeled as the associated heat structures provided by RELAP5 to include heat transfer across solid boundaries. Based on computational results it was found that current design of the TBM is robust from the safety point of view.

Ahn, Mu-Young [National Fusion Research Institute, 52, Eoeun-dong, Yuseong-gu, Daejeon 305-333 (Korea, Republic of)], E-mail: myahn74@nfri.re.kr; Cho, Seungyon; Ku, Duck Young [National Fusion Research Institute, 52, Eoeun-dong, Yuseong-gu, Daejeon 305-333 (Korea, Republic of); Kim, Hyung-Seok; Suh, Jae-Seung [ENESYS, 328, Guam-dong, Yuseong-gu, Daejeon 305-800 (Korea, Republic of)

2009-06-15

350

Helium effects in iron- and nickel-base developmental alloys  

International Nuclear Information System (INIS)

The void swelling of Ni-base gamma-prime precipitation strengthened single crystal alloy (TMS-12) and oxide dispersioned MA 754 and MA 956 was investigated using proton irradiation at temperatures ranging from 723 to 873 K. In TMS-12, the voids preferably formed on the precipitates-matrix interface. The swelling increased with increase of the irradiation temperature and the maximum swelling of 3% was obtained at 873 K, which was lower than that in 10% CW 316 and JPCA. The voids were found to nucleate preferably on the oxide-matrix interface in MA 754. The expected reduction of swelling was not obtained in this alloy. Only few voids were found and excellency in swelling characteristic was found in MA 956. The helium embrittlement of MA 956 was studied using the samples pre-injected with a beam of 26 MeV 3He from the NRIM compact cyclotron to concentration of 40 appm He at 873 K. The tensile test was carried out at 873 K varying the strain rate from 10-3/s to 10-5/s. Superplastic deformation was observable without helium implantation. The reduction of the total elongation due to helium was observed only at the strain rate of 10-5/s. (orig.)

351

Helium transport, fate and management in nanostructured ferritic alloys: In situ helium implanter studies  

International Nuclear Information System (INIS)

High helium levels produced in fusion neutron spectra may lead to severe increases in the brittle fast fracture temperature, enhanced void swelling and degradation of creep rupture properties at lower, intermediate and higher irradiation temperatures, respectively. Thus it is important to develop structural alloys with stable microstructures that can manage helium based on understanding of its transport, fate and consequences. We report on the initial results of a study of helium in a nanostructured ferritic alloy (NFA), MA957, that is dispersion strengthened by an ultra-high density of nm-scale Y-Ti-O nanofeatures (NFs). An in situ helium implanter technique uniformly deposited ?380 appm helium to ?6 ?m in MA957 irradiated in the High Flux Isotope Reactor (HFIR) to ?9 dpa at 500 deg. C. Through focus transmission electron microscopy (TEM) showed that helium is in extremely fine bubbles that often appear to coincide with bright field features taken as a NF.

352

The KfK design of a helium-cooled ceramic blanket for NET  

Energy Technology Data Exchange (ETDEWEB)

A conceptual design of a helium-cooled blanket for the NET double null plasma configuration with a neutron wall load of 1 MW/m/sup 2/ and 600 MW fusion power is presented. The outboard blanket is made up of self-supporting canisters containing the beryllium multiplier in form of plates. The 6 mm wide slits between the plates contain a bed of 0.5 mm Li/sub 4/SiO/sub 4/ pebbles. The helium purge flow at 0.1 MPa carries away the tritium produced in the bed. The first wall of stainless steel and with a graphite tile protection is cooled by toroidally running helium tubes. The inboard blanket is made up of a similar structure, however the helium coolant tubes run in the poloidal direction to allow for more breeding material in the narrow space available. The divertors are composed of TZM elements cooled by helium. The outboard first wall and blanket are cooled by helium at 6 MPa, (inlet temperature=200/sup 0/C outlet temperature=450/sup 0/C), while the divertor and the inboard first wall are cooled in series by helium at 11.5 MPa and the inboard blanket by helium at 8 MPa. The calculated temperatures and stresses in blanket, first wall and divertor, appear to be acceptable. Based on the LISA-2 experiments the tritium blanket inventory is about 400 g. The daily tritium production is 96 g and the three-dimensional real tritium breeding ratio is 1.04 for a /sup 6/Li enrichment of 90%. (orig.).

Dalle Donne, M.; Fischer, U.; Kuechle, M.; Schumacher, G.; Sordon, G.; Bojarsky, E.; Norajitra, P.; Reiser, H. (Kernforschungszentrum Karlsruhe G.m.b.H. (Germany, F.R.)); Baschek, D.; Bogusch, E. (Internationale Atomreaktorbau G.m.b.H. (INTERATOM), Bergisch Gladbach (Germany, F.R.))

1989-04-01

353

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

354

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

International Nuclear Information System (INIS)

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

355

KMC simulation of helium bubble formation in alpha-Fe  

International Nuclear Information System (INIS)

We use Kinetic Monte Carlo (KMC) method to investigate the evolution of Helium-Vacancy clusters under different conditions with emphasizing the influence of system temperature. Our simulation results indicate that when initial helium concentration increases, the size and amount of the Helium-Vacancy cluster will increase dramatically. The Helium-Vacancy cluster will become larger accompanied with a decrease in its amount as the temperature increases. The results also indicate that irradiating He-contained sample produces less helium bubbles compared with other conditions, adding helium during irradiating the sample or adding helium atoms after the sample have been irradiated

356

Ionization of methane clusters in helium nanodroplets.  

Science.gov (United States)

The electron ionization of helium droplets doped with methane clusters is investigated for the first time using high-resolution mass spectrometry. The dominant ion products ejected into the gas phase are the unprotonated (CH(4))(n)(+) cluster ions along with the protonated ions, CH(5)(+)(CH(4))(n-1). The mass spectra show clear evidence for magic numbers, which are broadly consistent with icosahedral shell closings. However, unusual features were observed, including different magic numbers for CH(5)(+)(CH(4))(n-1) (n=55, 148) when compared to (CH(4))(n)(+) (n=54, 147). Possible interpretations for some of these differences are proposed. Products of the type [C(2)H(x)(CH(4))(n)](+), which result from ion-molecule chemistry, are also observed and these too show clear magic number features. Finally, we report the first observation of (CH(4))(n)(2+) dications from methane clusters. The threshold for dication survival occurs at n?70 and is in good agreement with a liquid droplet model for fission of multiply charged ions. Furthermore, we present evidence showing that these dications are formed by an unusual two-step mechanism which is initiated by charge transfer to generate a monocation and is then followed by Penning ionization to generate a dication. PMID:22162091

Leidlmair, Christian; Bartl, Peter; Schöbel, Harald; Denifl, Stephan; Yang, Shengfu; Ellis, Andrew M; Scheier, Paul

2012-02-01

357

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

358

Measurement on helium excitation temperature in the vicinity of substrate during helium plasma irradiation  

Energy Technology Data Exchange (ETDEWEB)

Excitaion temperature of helium atom in the vicinity of substrate in an ECR helium plasma was measured based on multi-thermal equilibrium (MTE). In the case of no substrate in the plasma, clear atomic line spectra of excited helium were not observed. The intensities of line spectra increased with the negative voltage biased at the substrate and the discharge pressure. The intensities were also strong at the position close to the substrate. From the Boltzmann plot, an excitation temperature of approximately 4000 K for helium atom was obtained. This temperature was a little higher in the case of lower pressure and farther from the substrate. (author)

Yakita, Shinichiro; Hirohata, Yuko; Hino, Tomoaki [Hokkaido Univ., Sapporo (Japan). Faculty of Engineering

1999-03-01

359

Measurement on helium excitation temperature in the vicinity of substrate during helium plasma irradiation  

International Nuclear Information System (INIS)

Excitaion temperature of helium atom in the vicinity of substrate in an ECR helium plasma was measured based on multi-thermal equilibrium (MTE). In the case of no substrate in the plasma, clear atomic line spectra of excited helium were not observed. The intensities of line spectra increased with the negative voltage biased at the substrate and the discharge pressure. The intensities were also strong at the position close to the substrate. From the Boltzmann plot, an excitation temperature of approximately 4000 K for helium atom was obtained. This temperature was a little higher in the case of lower pressure and farther from the substrate. (author)

360

Growing metal nanoparticles in superfluid helium.  

Science.gov (United States)

Helium droplets provide a cold and confined environment where atomic and/or molecular dopants can aggregate into clusters and nanoparticles. In particular, the sequential addition of different materials to helium droplets can lead to the formation of a wide range of nanoparticles, including core-shell nanoparticles, which can then be deposited onto a surface. Here we briefly discuss the fundamental properties of helium droplets and then address their implications for the formation of clusters and nanoparticles. Several key experiments on atomic and molecular clusters will be highlighted and new results obtained for nanoparticles formed in this way will be presented. Finally, the versatility, the limitations and new possibilities provided by superfluid helium droplets in nanoscience and nanotechnology will be addressed. PMID:24107922

Yang, Shengfu; Ellis, Andrew M; Spence, Daniel; Feng, Cheng; Boatwright, Adrian; Latimer, Elspeth; Binns, Chris

2013-12-01

 
 
 
 
361

Design curve for liquid helium storage vessels  

Science.gov (United States)

Development of equipment for storage of liquid helium is discussed. Derivation of design curve and working equations for estimating effects of either perfect or imperfect heat transfer in storage device are described. Mathematical models of heat transfer conditions are provided.

Dicarlo, J. A.

1972-01-01

362

Helium Find Thaws the Cold Fusion Trail.  

Science.gov (United States)

Reported is a study of cold fusion in which trace amounts of helium, possible evidence of an actual fusion reaction, were found. Research methodology is detailed. The controversy over the validity of experimental results with cold fusion are reviewed. (CW)

Pennisi, E.

1991-01-01

363

Evolution of thermal perturbation in superfluid helium  

International Nuclear Information System (INIS)

The problem of propagation of thermal pulses in He 2 with a stepwise heat emission is solved on the basis of equations of superfluid turbulence hydrodynamics. The results are compared with experimental data on transient heat transport in helium

364

Helium Dilution Cryocooler for Space Applications  

Science.gov (United States)

NASA's New Millenium Program Space Technology presents the Helium Dilution Cryocooler for Space Applications. The topics include: 1) Capability; 2) Applications; and 3) Advantages. This paper is in viewgraph form.

Roach, Pat; Hogan, Robert (Technical Monitor)

2001-01-01

365

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

366

Gas turbine modeling for NPP with helium cooled reactor  

International Nuclear Information System (INIS)

The performance analyzes of closed helium cycle for NPPs with high-temperature gas-cooled reactors was carried out. Air-turbine units and helium-turbine units were compared. Helium turbine features were particularized in comparison with conventional air turbines. Simulation results of gas turbine setting with helium as a working medium were presented. Problems concerning high economic efficiency advance of helium turbines were discussed

367

Helium swelling and high temperature radiation embrittlement as results of instability of helium-vacancy complexes  

International Nuclear Information System (INIS)

Transmission electron micrscopy combined with cross-section method were used for investigation of defects formation in nickel irradiated at T=350 K with 40 keV He+ ions up to doses of 1020, 1021 and 5x1021 ionxm-2. That was done both immediately after irradiation and after isochronous annealing treatments (1 hours) at temperatures 773, 873 and 973 deg K. Annealing was performed after depositing a fixing coating of electrolitic nickel onto irradiated surface which prevented thermal blistering. On the basis of experimental data here obtained together with those available in literature a correlation of temperatures of the observed sharp rise of the helium swelling of nickel and a start of plasticity decrease were revealed and explained from the single point of view

368

Use of the helium medium for preparation of nano-sized powder materials by the example of industrial cement  

Science.gov (United States)

Based on the phenomenon of the mechanodynamic diffusion of particles of the external medium in solids, a new in principle method has been proposed for the first time for producing nano-sized powder materials using industrial cement milled in a helium medium as an example. The temperature dependences of the extraction rate and the amount of helium in powders upon their heating in a temperature range of 20-1200°C have been obtained using mass spectrometry. It has been shown that milling of the cement powder of the M-400 brand using an MK-1 laboratory mill in helium leads to a considerable shift of its extraction curve towards lower temperatures compared with the air medium. The particle sizes of the powder milled in helium lie in a range of 5-10 nm, which is smaller than the powder size (˜500 nm) after milling in the air medium by a factor of 100. The compression strength of cement samples obtained from the powders milled in helium increased by a factor of 2 compared with the strength of the samples from the initial material. The activation energies of helium extraction from the cement powders milled in helium and in air have been analyzed. The obtained results indicate a high efficiency of the method for producing nano-sized powder materials in the helium medium. The method can be used in the industrial scale based on the existing mill equipment with its minimal modernization.

Klyavin, O. V.; Aruev, N. N.; Boltenkov, B. S.; Pozdnyakov, A. O.; Chernov, Yu. M.; Shpeizman, V. V.

2014-02-01

369

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

370

Helium refrigeration considerations for ADS cryomodule design  

International Nuclear Information System (INIS)

Accelerator-Driven Sub-Critical Systems and its application to utilization of Thorium for energy production are based on superconducting radio frequency (SRF) technology, which in turn depends on the helium refrigeration. The present accelerator technology operations for this application are centered on operating these SRF cavities at 2-K. This requires specialized helium refrigeration systems which are cost intensive to produce and to operate. Some of the cryogenic system design considerations for these challenging applications are discussed. (author)

371

Thin helium film on a glass substrate  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate by Monte Carlo simulations the structure, energetics and superfluid properties of thin helium-four films (up to four layers) on a glass substrate, at low temperature. The first adsorbed layer is found to be solid and "inert", i.e., atoms are localized and do not participate to quantum exchanges. Additional layers are liquid, with no clear layer separation above the second one. It is found that a single helium-three impurity resides on the outmost layer, not si...

Boninsegni, Massimo

2009-01-01

372

Effects of helium impurities on superalloys  

International Nuclear Information System (INIS)

A review of the literature on the effects of helium impurities on superalloys at elevated temperatures was undertaken. The actual effects of these impurities vary depending on the alloy, composition of the gas atmosphere, and temperature. In general, exposure in helium produces significant but not catastrophic changes in the structure and properties of the alloys. The effects of these treatments on the structure, creep, fatigue, and mechanical properties of the various alloys are reviewed and discussed. Suggestions for future work are presented

373

Effects of helium impurities on superalloys  

Energy Technology Data Exchange (ETDEWEB)

A review of the literature on the effects of helium impurities on superalloys at elevated temperatures was undertaken. The actual effects of these impurities vary depending on the alloy, composition of the gas atmosphere, and temperature. In general, exposure in helium produces significant but not catastrophic changes in the structure and properties of the alloys. The effects of these treatments on the structure, creep, fatigue, and mechanical properties of the various alloys are reviewed and discussed. Suggestions for future work are presented.

Selle, J.E.

1977-07-01

374

Nonclassical Rotational Inertia in Single Crystal Helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

It has been proposed that the observed nonclassical rotational inertia (NCRI) in solid helium results from the superflow of thin liquid films along interconnected grain boundaries within the sample. We have carried out new torsional oscillator measurements on large helium crystals grown under constant temperature and pressure. We observe NCRI in all samples, indicating that the phenomenon cannot be explained by a superfluid film flowing along grain boundaries.

Clark, A. C.; West, J. T.; Chan, M. H. W.

2007-01-01

375

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

376

Helium cryostats for cosmic physical investigations  

International Nuclear Information System (INIS)

The desiqn of a cryostat with liquid helium is described. It is designed for use on a space ship board. The specific features of such cryostats are: a phase separator, that prevents the liquid from being thrown out of the helium volume, and a special neck-suspender that decreases the gas convection in it when the cryostat changes its position in space. The results are presented for tests of the designed components in a laboratory and on board the Earth satellite

377

Helium pumping with liquid ring vacuum pump  

International Nuclear Information System (INIS)

At first the main principles for operation and building of liquid ring pumps are remembered and an experiment is described which allowed to assess the performance data of such pumps when used to pump helium gas with oil. Although they have been designed to pump air with water the adaptation for helium is rather simple, the input power is slightly higher in the same flow and pressure conditions, but the limit of the succion pressure is lowered

378

Sonic helium detectors in the Fermilab Tevatron  

Energy Technology Data Exchange (ETDEWEB)

In the Fermilab Tevatron cryogenic system there are many remotely located low-pressure plate relief valves that must vent large volumes of cold helium gas when magnet quenches occur. These valves can occasionally stick open or not reseat completely, resulting in a large helium loss. As such, the need exists for a detector to monitor the relief valve's discharge area for the presence of helium. Due to the quantity needed, cost is an important factor. A unit has been developed and built for this purpose that is quite inexpensive. Its operating principle is based on the speed of sound, where two closely matched tubes operate at their acoustic resonant frequency. When helium is introduced into one of these tubes, the resulting difference in acoustic time of flight is used to trigger an alarm. At present, there are 39 of these units installed and operating in the Tevatron. They have detected many minor and major helium leaks, and have also been found useful in detecting a rise in the helium background in the enclosed refrigerator buildings. This paper covers the construction, usage and operational experience gained with these units over the last several years.

Bossert, R.J.; /Fermilab

2006-01-01

379

Sonic Helium Detectors in the Fermilab Tevatron  

Science.gov (United States)

In the Fermilab Tevatron cryogenic system there are many remotely located low-pressure plate relief valves that must vent large volumes of cold helium gas when magnet quenches occur. These valves can occasionally stick open or not reseat completely, resulting in a large helium loss. As such, the need exists for a detector to monitor the relief valve's discharge area for the presence of helium. Due to the quantity needed, cost is an important factor. A unit has been developed and built for this purpose that is quite inexpensive. Its operating principle is based on the speed of sound, where two closely matched tubes operate at their acoustic resonant frequency. When helium is introduced into one of these tubes, the resulting difference in acoustic time of flight is used to trigger an alarm. At present, there are 39 of these units installed and operating in the Tevatron. They have detected many minor and major helium leaks, and have also been found useful in detecting a rise in the helium background in the enclosed refrigerator buildings. This paper covers the construction, usage and operational experience gained with these units over the last several years.

Bossert, R. J.

2006-04-01

380

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

 
 
 
 
381

Equation of state of metallic helium  

Energy Technology Data Exchange (ETDEWEB)

The effective ion-ion interaction, free energy, pressure, and electric resistance of metallic liquid helium have been calculated in wide density and temperature ranges using perturbation theory in the electron-ion interaction potential. In the case of conduction electrons, the exchange interaction has been taken into account in the random-phase approximation and correlations have been taken into account in the local-field approximation. The solid-sphere model has been used for the nuclear subsystem. The diameter of these spheres is the only parameter of this theory. The diameter and density of the system at which the transition of helium from the singly ionized to doubly ionized state occurs have been estimated by analyzing the pair effective interaction between helium atoms. The case of doubly ionized helium atoms has been considered. Terms up to the third order of perturbation theory have been taken into account in the numerical calculations. The contribution of the third-order term is significant in all cases. The electric resistance and its temperature dependence for metallic helium are characteristic of simple divalent metals in the liquid state. The thermodynamic parameters-temperature and pressure densities-are within the ranges characteristic of the central regions of giant planets. This makes it possible to assume the existence of helium in the metallic state within the solar system.

Shvets, V. T., E-mail: tarval@breezein.net [Odessa State Academy of Refrigeration (Ukraine)

2013-01-15

382

Kaonic Helium Measurements in the Siddharta Experiment  

Science.gov (United States)

The SIDDHARTA experiment (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) had the aim to perform kaonic atoms X-ray transitions measurements, to better understand aspects of the low-energy QCD in the strangeness sector. The experiment combined the excellent low-energy kaon beam generated at DA?NE, allowing to use gaseous targets, with excellent fast X-rays detectors: Silicon Drift Detectors. SIDDHARTA was installed on DA?NE in autumn 2008 and took data till late 2009. Apart of the kaonic hydrogen and kaonic deuterium measurements, we have performed the kaonic helium transitions to the 2p level (L-lines) measurements: for the first time in a gaseous target for helium4 and for the first time ever for kaonic helium3. The interest for such type of measurement was rather high, being it triggered by two reasons: the so-called "kaonic helium puzzle" (even if this was solved by KEK-PS E570 experiment, but a cross-check was useful) and some theoretical predictions of possible high energy shift (at the level of 10 eV). In this paper the preliminary results for the measurements to the 2p level (L-series) for kaonic helium4 and kaonic helium3 are presented.

Sirghi, D. L.; Bazzi, M.; Beer, G.; Bombelli, L.; Bragadireanu, A. M.; Cargnelli, M.; Corradi, G.; Curceanu (Petrascu), C.; D'Uffizi, A.; Fiorini, C.; Frizzi, T.; Ghio, F.; Girolami, B.; Guaraldo, C.; Hayano, R. S.; Iliescu, M.; Ishiwatari, T.; Iwasaki, M.; Kienle, P.; Sandri, P. Levi; Longoni, A.; Lucherini, V.; Marton, J.; Okada, S.; Pietreanu, D.; Ponta, T.; Rizzo, A.; Vidal, A. Romero; Scordo, A.; Shi, H.; Sirghi, F.; Tatsuno, H.; Tudorache, A.; Tudorache, V.; Doce, O. Vazquez; Wiedmann, E.; Zmeskal, J.

383

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)

384

Cryogenic system for the Large Helical Device. The helium refrigerator/liquefier for Large Helical Device  

International Nuclear Information System (INIS)

A large-scale helium refrigerator/liquefier has been developed to provide reliable and safe operation for the Large Helical Device (LHD). The refrigerator is required to satisfy four different types of cooling methods: forced-flow supercritical helium, a pool boiling method, two-phase helium flow and forced-flow low-temperature (40-80 K) helium gas. The forced-flow supercritical helium is widely used in modern large-scale superconducting magnets. This method requires a much more complex refrigeration system than does pool boiling because of the circulation of low-temperature helium within a very long cooling path. The overall refrigeration system is fairly complicated because of these multi-refrigeration requirements. As a matter of fact, it is not likely to find this type of refrigeration plant in the world. The helium refrigerator has a total refrigeration capacity of 5.65 kW at 4.4 K and 20.6 kW at 80 K and 650 l/h liquefaction. The refrigerator was designed to have high processing efficiency since the construction expense is much less than the operating cost. In order to achieve this, the refrigerator has two precooling cycles (300 to 80 K and 80 to 20 K) and has two turboexpanders running in parallel with different temperature levels at the cold end. To achieve a high mass flow rate in a low-temperature regime, eight screw-type compressors are operated at room temperature. There are two compressor groups, group A and group B, to reduce the overall work load. Each group consists of 1st and 2nd stage compression processes. The total mass flow rate becomes 960 g/s at 1.864 MPa. This article reviews the basic characteristics of a 10 kW class helium refrigerator/liquefier and a simple refrigeration cycle. (author)

385

Cryosorption of helium on argon frost TFTR (Tokamak Fusion Test Reactor) neutral beamlines  

Energy Technology Data Exchange (ETDEWEB)

Helium pumping on argon frost has been investigated on TFTR neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are {approximately} 25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, > 20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a two-fold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 torr-l of helium, the beamline base pressure rose to 2{times}10{sup -5} torr from an initial value of 10{sup -8} torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 torr-l of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity. 29 refs., 7 figs.

Kamperschroer, J.H.; Cropper, M.B.; Dylla, H.F.; Garzotto, V.; Dudek, L.E.; Grisham, L.R.; Martin, G.D.; O' Connor, T.E.; Stevenson, T.N.; von Halle, A. (Princeton Univ., NJ (USA). Plasma Physics Lab.)

1989-11-01

386

Cryosorption of helium on argon frost TFTR [Tokamak Fusion Test Reactor] neutral beamlines  

International Nuclear Information System (INIS)

Helium pumping on argon frost has been investigated on TFTR neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are ? 25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, > 20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a two-fold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 torr-l of helium, the beamline base pressure rose to 2x10-5 torr from an initial value of 10-8 torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 torr-l of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity. 29 refs., 7 figs

387

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

388

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

389

Advances in helium ion microscopy  

Energy Technology Data Exchange (ETDEWEB)

With the advent of a reliable high brightness ion source, utilizing helium (He) as the ion species, a new branch of microscopy has emerged. The promise of sub-nm focused probe sizes coupled with the unique He beam/sample interactions has led to a range of both high resolution imaging and high fidelity material modification applications. However, realizing the full potential of the He ion source is not without its challenges. Some of the difficulties are presented, along with a discussion of a systematic effort to overcome these issues. This work has resulted in the ability to routinely take images with an edge resolution of 0.35 nm or better. The nature of the He ion beam interaction with the sample makes possible numerous diverse applications, beyond the high resolution imaging already mentioned. A few of these will be highlighted, including imaging insulating samples, scanning transmission He ion microscopy, and material modification. Finally an extension of the high source brightness technology to utilizing neon (Ne) as the ion species is described. The source properties are given, along with a calculation of the expected probe size from such a Ne ion source and column.

Hill, R.; Faridur Rahman, F.H.M., E-mail: hill@smt.zeiss.com [Carl Zeiss SMT Inc., One Corporation Way, Peabody, MA 01960 (United States)

2011-07-21

390

Advances in helium ion microscopy  

International Nuclear Information System (INIS)

With the advent of a reliable high brightness ion source, utilizing helium (He) as the ion species, a new branch of microscopy has emerged. The promise of sub-nm focused probe sizes coupled with the unique He beam/sample interactions has led to a range of both high resolution imaging and high fidelity material modification applications. However, realizing the full potential of the He ion source is not without its challenges. Some of the difficulties are presented, along with a discussion of a systematic effort to overcome these issues. This work has resulted in the ability to routinely take images with an edge resolution of 0.35 nm or better. The nature of the He ion beam interaction with the sample makes possible numerous diverse applications, beyond the high resolution imaging already mentioned. A few of these will be highlighted, including imaging insulating samples, scanning transmission He ion microscopy, and material modification. Finally an extension of the high source brightness technology to utilizing neon (Ne) as the ion species is described. The source properties are given, along with a calculation of the expected probe size from such a Ne ion source and column.

391

Lung Function Measurement with Multiple-Breath-Helium Washout System  

CERN Document Server

Multiple-breath-washout (MBW) measurements are regarded as a sensitive technique which can reflect the ventilation inhomogeneity of respiratory airways. Typically nitrogen is used as the tracer gas and is washed out by pure oxygen in multi-breath-nitrogen (MBNW) washout tests. In this work, instead of using nitrogen, helium is used as the tracer gas and a multiple-helium-breath-washout (MBHW) system has been developed for the lung function study. A commercial quartz tuning fork with a resonance frequency of 32768 Hz has been used for detecting the change of the respiratory gas density. The resonance frequency of the tuning fork decreases linearly with increasing density of the surrounding gas. Knowing the CO2 concentration from the infrared carbon dioxide detector, the helium concentration can be determined. Results from 12 volunteers (3 mild asthmatics, 2 smokers, 1 with asthma history, 1 with COPD history, 5 normal) have shown that mild asthmatics have higher ventilation inhomogeneity in either conducting o...

Wang, Jau-Yi; Owers-Bradley, John; Mellor, Chris

2011-01-01

392

The prospects of helium injection into large Tokamak  

International Nuclear Information System (INIS)

The prospects of helium injection in comparison with deuterium injection into large tokamaks are reviewed, using an analytical, global description involving as key parameters beam energy, ignition temperature and ?-particle concentration ?sub(i). Special attention has been paid to the accumulation of alpha particles in the plasma, due to the injected beams. In a pure D-T-plasma helium beams penetrate into about the same plasma opacity at 150 keV as deuterium beams but at much higher neutralization efficiency. The effect of the alpha particles accumulating in the plasma, however, degrades the penetration capability, for example 10% of alpha particles in the plasma increases the beam energy by around 50% for the same opacity. The ignition condition is only weakly modified, if the hydrogen ion density in the plasma is kept constant when injecting helium. The plasma beta is slightly increased by the presence of the injected alpha particles, for example 10% of He2+ add about 25% to the beta for given nsub(i)tausub(E) at ignition. Comparing maximum tolerable ?sub(i) and the actually generated ?sub(i) as a function of beam energy and ignition temperature, it is shown that in a full-bore, full-density reactor the penetration requirements for ignition can be fulfilled at energies in excess of 300 keV with an efficiency of <=25% compared to 230 keV for a deuterium beam and an efficiency of 5%

393

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

394

Helium irradiation effects on deuterium retention in tungsten  

International Nuclear Information System (INIS)

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

395

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

396

Measurement of Helium-3/Helium-4 Ratios in Soil Gas at the 618-11 Burial Ground  

Energy Technology Data Exchange (ETDEWEB)

Seventy soil gas-sampling points were installed around the perimeter of the 618-11 Burial Ground, approximately 400 feet downgradient of well 699-13-3A, and in four transects downgradient of the burial ground to a maximum distance of 3,100 feet. Soil gas samples were collected and analyzed for helium-3/helium-4 ratios from these 70 points. Helium-3/helium-4 ratios determined from the soil gas sampling points showed significant enrichments, relative to ambient air helium-3 concentrations. The highest concentrations were located along the northern perimeter of the burial ground. Helium-3/helium-4 ratios (normalized to the abundances in ambient air) ranged from 1.0 to 62 around the burial ground. The helium-3/helium-4 ratios from the 4 transect downgradient of the burial ground ranged from 0.988 to 1.68. The helium-3/helium-4 ratios from around the burial ground suggest there is a vadose zone source of tritium along the north side of the burial ground. This vadose zone source is likely the source of tritium in the groundwater. The helium-3/helium-4 ratios also suggest the groundwater plume is traveling east-northeast from the burial ground and the highest groundwater tritium value may be to the north of well 699-13-3A. Finally, there appears to be no immediately upgradient sources of tritium impacting the burial ground since all the upgradient helium-3/helium-4 ratios are approximately 1.0.

Olsen, Khris B.; Dresel, P Evan; Evans, John C.

2001-10-31

397

Design considerations for very large helium refrigeration system  

International Nuclear Information System (INIS)

Future fusion reactors will require very large cryogenic refrigerators to cool their superconducting magnet systems. The total capacity required is roughly 5 times above the largest cryogenic system presently existing. For redundancy reasons however the capacity will be provided by several parallel plants. The step from today's state of technology to future needs therefore is moderate. The paper presents a draft design of a 150 kW/4.5 K Helium refrigeration system and compares it to today's state of technology. Development needs are identified, which on one hand result from the high capacity and on the other hand are based on weaknesses of today's technology. (author)

398

Helium-Shell Nucleosynthesis and Extinct Radioactivities  

Science.gov (United States)

Although the exact site for the origin of the r-process isotopes remains mysterious, most thinking has centered on matter ejected from the cores of massive stars in core-collapse supernovae [13]. In the 1970's and 1980's, however, difficulties in understanding the yields from such models led workers to consider the possibility of r-process nucleosynthesis farther out in the exploding star, in particular, in the helium burning shell [4,5]. The essential idea was that shock passage through this shell would heat and compress this material to the point that the reactions 13C(alpha; n)16O and, especially, 22Ne(alpha; n)25Mg would generate enough neutrons to capture on preexisting seed nuclei and drive an "n process" [6], which could reproduce the r-process abundances. Subsequent work showed that the required 13C and 22Ne abundances were too large compared to the amounts available in realistic models [7] and recent thinking has returned to supernova core material or matter ejected from neutron star-neutron star collisions as the more likely r-process sites.

Meyer, B. S.; The, L.-S.; Clayton, D. D.; ElEid, M. F.

2004-01-01

399

Anti-helium from dark matter annihilations  

Science.gov (United States)

Galactic Dark Matter (DM) annihilations can produce cosmic-ray anti-nuclei via the nuclear coalescence of the anti-protons and anti-neutrons originated directly from the annihilation process. Since anti-deuterons have been shown to offer a distinctive DM signal, with potentially good prospects for detection in large portions of the DM-particle parameter space, we explore here the production of heavier anti-nuclei, specifically anti-helium. Even more than for anti-deuterons, the DM-produced anti-He flux can be mostly prominent over the astrophysical anti-He background at low kinetic energies, typically below 3-5 GeV/n. However, the larger number of anti-nucleons involved in the formation process makes the anti-He flux extremely small. We therefore explore, for a few DM benchmark cases, whether the yield is sufficient to allow for anti-He detection in current-generation experiments, such as Ams-02. We account for the uncertainties due to the propagation in the Galaxy and to the uncertain details of the coalescence process, and we consider the constraints already imposed by anti-proton searches. We find that only for very optimistic configurations might it be possible to achieve detection with current generation detectors. We estimate that, in more realistic configurations, an increase in experimental sensitivity at low kinetic energies of about a factor of 500-1000 would allow to start probing DM through the rare cosmic anti-He production.

Cirelli, Marco; Fornengo, Nicolao; Taoso, Marco; Vittino, Andrea

2014-08-01

400

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

 
 
 
 
401

Ionization of doped helium nanodroplets: residual helium attached to diatomic cations and their clusters.  

Science.gov (United States)

Electron impact ionization of helium nanodroplets containing a dopant, M, can lead to the detection of both M(+) and helium-solvated cations of the type M(+)·He(n) in the gas phase. The observation of helium-doped ions, He(n)M(+), has the potential to provide information on the aftermath of the charge transfer process that leads to ion production from the helium droplet. Here we report on helium attachment to the ions from four common diatomic dopants, M = N(2), O(2), CO, and NO. For experiments carried out with droplets with an average size of 7500 helium atoms, the monomer cations show little tendency to attach and retain helium atoms on their journey out of the droplet. By way of contrast, the corresponding cluster cations, M(n)(+), where n ? 2, all show a clear affinity for helium and form He(m)M(n)(+) cluster ions. The stark difference between the monomer and cluster ions is attributed to more effective cooling of the latter in the aftermath of the ionization event. PMID:21585216

Shepperson, Benjamin; Liu, Jin; Ellis, Andrew M; Yang, Shengfu

2011-06-30

402

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

403

Quantum statistics and liquid helium 3 - helum 4 mixtures  

International Nuclear Information System (INIS)

The behaviour of liquid helium 3-helium 4 mixtures is considered from the point of view of manifestation of quantum statistics effects in macrophysics. The Boze=Einstein statistics is shown to be of great importance for understanding superfluid helium-4 properties whereas the Fermi-Dirac statistics is of importance for understanding helium-3 properties. Without taking into consideration the interaction between the helium atoms it is impossible to understand the basic properties of liquid helium 33 - helium 4 mixtures at constant pressure. Proposed is a simple model of the liquid helium 3-helium 4 mixture, namely the binary mixture consisting of solid spheres of two types subjecting to the Fermi-Dirac and Bose-Einstein statistics relatively. This model predicts correctly the most surprising peculiarities of phase diagrams of concentration dependence on temperature for helium solutions. In particular, the helium 4 Bose-Einstein statistics is responsible for the phase lamination of helium solutions at low temperatures. It starts in the peculiar critical point. The helium 4 Fermi-Dirac statistics results in incomplete phase lamination close to the absolute zero temperatures, that permits operation of a powerful cooling facility, namely refrigerating machine on helium solution

404

Helium transport in plasma edge regions  

Science.gov (United States)

The transport of neutral helium atoms near diverter or limiter target plates in fusion devices was studied. Two simulation codes, based on Monte Carlo techniques, were developed. The first treats the problem in one-dimensional geometry and the second considers two-dimensional effects. The atomic processes of ionization of helium atoms by electron impact and elastic scattering with plasma ions are included. The total and differential elastic scattering cross-sections were calculated classically using an ab initio calculation of the interatomic potential. The thermal motion and the streaming of the ions along the magnetic field, which can be at an angle to the target plate, are included. Results obtained with the one-dimensional code show significant effects of elastic collisions below about 10 eV, causing a substantial fraction of the helium atoms to be reflected back to the target plate. This effect can be beneficial for the pumping of helium from the discharge chamber. The two-dimensional Monte Carlo code was used to study helium recycling near a flat, vented target plate. A parametric study is performed to examine the dependence of the pumping efficiency on plasma parameters and geometric aspects. Results show that the pumping of neutral helium can be increased by shortening and widening the ports as well as by increasing the angle between the magnetic field and the target plate. Also, keeping the ion temperature below about 10 eV and the plasma density around a few 10(exp 14) cu cm near the targe plate can be beneficial for the pumping of helium gas.

Abou-Gabal, Hanaa Hassan

405

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

406

Application of liquid-helium cryoplants at CERN  

International Nuclear Information System (INIS)

In 1992, the liquid-helium cooling capacity installed at CERN was nearly tripled, passing from 6.8 to 19.7 kW/4.5 K (entropy equivalent). Further tripling is expected in 1993. While the 6.8 kW available in 1991 were produced by 14 plants of moderate size (500 W/4.5 K average), two of the four plants added in 1992 have unit capacities of 6 kW/4.5 K. Four plants of 12 kW/4.5 K, upgradable to 18 kW/4.5 K in a later phase, are presently being installed. Most of the smaller plants are associated with particle physics experiments, cooling superconducting magnets of particle detectors and high-gradient focusing magnets of colliding-beam experiments. Six plants provide liquid helium for development laboratories and test facilities. The recently acquired multi-kW plants will be integral parts of the collider itself. Their present function is to cool superconducting RF cavities designed to increase the beam energy of the Large Electron Positron collider LEP from 50 to above 90 GeV. In the future, the same and additional plants will be available for the cooling of the superconducting magnet ring of the planned Large Hadron Collider LHC. To this end, they will be equipped with complementary 1.8 K final stages

407

Seeing the lungs thanks to helium  

International Nuclear Information System (INIS)

Clear images of lungs were successfully obtained by an American team and by a German team using polarized helium 3 inhalation and NMR imaging. This paper gives a general presentation of the NMR technique applied to medical imaging and the historical development of polarized rare gases in the visualization of lungs. Polarization of helium 3 is obtained using optical laser pumping applied to a rubidium and helium 3 mixture (American technique) or directly to pure helium 3 (European technique). Both techniques provide more brighten images than the classical proton visualization technique and allow the visualization of the hollow parts of organs. Economical implications of this diagnostic technique are not well known yet but the helium 3 NMR imaging technique requires less sophisticated apparatuses and is more easily exportable into developing countries. Improvements of this technique could be obtained using xenon 129 which can rapidly diffuse into the blood and which could be used as a tracer of blood circulation inside the brain or the heart. (J.S.). 9 refs., 2 photos

408

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

409

Transparent Helium in Stripped Envelope Supernovae  

Science.gov (United States)

Using simple arguments based on photometric light curves and velocity evolution, we propose that some stripped envelope supernovae (SNe) show signs that a significant fraction of their helium is effectively transparent. The main pieces of evidence are the relatively low velocities with little velocity evolution, as are expected deep inside an exploding star, along with temperatures that are too low to ionize helium. This means that the helium should not contribute to the shaping of the main SN light curve, and thus the total helium mass may be difficult to measure from simple light curve modeling. Conversely, such modeling may be more useful for constraining the mass of the carbon/oxygen core of the SN progenitor. Other stripped envelope SNe show higher velocities and larger velocity gradients, which require an additional opacity source (perhaps the mixing of heavier elements or radioactive nickel) to prevent the helium from being transparent. We discuss ways in which similar analysis can provide insights into the differences and similarities between SNe Ib and Ic, which will lead to a better understanding of their respective formation mechanisms.

Piro, Anthony L.; Morozova, Viktoriya S.

2014-09-01

410

Development of charcoal sorbents for helium cryopumping  

International Nuclear Information System (INIS)

High vacuum adsorption of helium on activated charcoal at liquid helium temperatures has demonstrated the high specific pumping speeds needed for fusion power systems. However, this method of cryopumping has not been optimized. This paper describes the results of a program to evaluate the effects of different grades of charcoal as well as the effects of various charcoal bonding methods on helium pumping speed and capacity. Coal- and coconut-based charcoals were evaluated using various attachment techniques such as brazing, refractory ceramic adhesives and mechanical retention. Results suggest that both charcoal particle size and grade had a strong effect on pumping speed and capacity. Coconut-based charcoals appear to give superior overall characteristics compared to coal-based charcoals, while smaller particles give higher pumping speeds. Various bonding media and attachment methods have a measurable effect on helium pumping characteristics suggesting that thermal conductivity of the bond and good contact with the charcoal are key parameters. Additional test data show the results of pumping mixtures of helium and deuterium

411

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

412

Development of new technology in helium refrigerator  

International Nuclear Information System (INIS)

For the practical use of nuclear fusion apparatuses, the adoption of superconducting magnets is unavoidable, and as the additional effective heating method of plasma, neutral beam injection is regarded as important. For superconducting magnets and the cryopumps for NB1, helium liquefying refrigerators are required to produce extremely low temperature close to absolute zero. In Hitachi Ltd., the development of the large helium liquefying refrigerator of expansion turbine type has been advanced early, and in 1968, No.1 machine, and in 1979, No.2 machine with improved reliability and operational performance were developed. So far, four machines were delivered for the projects of nuclear fusion, accelerators and others. As the technical development, in addition to the development of expansion turbines, the development of such peripheral equipment as transfer tubes, liquid helium pumps and automatic control has been forwarded in parallel. In this paper, the new technology related to these peripheral equipment is described. The superinsulator, FRP rod type spacers and liquid nitrogen shield for transfer tubes, a centrifugal liquid helium pump with dynamic pressure gas bearings and the automatic control for a helium liquefying refrigerator using a Hitachi DSC-18 digital controller are reported. (Kako, I.)

413

Curious Fluid Flows: From Complex Fluid Breakup to Helium Wetting  

Science.gov (United States)

This work encompasses three projects; pinch-off dynamics in non-Newtonian fluids; helium wetting on alkali metals; and the investigation of quartz tuning forks as cryogenic pressure transducers. Chapter 1 discusses the breakup of a non-Newtonian yield stress fluid bridge. We measured the minimum neck radius, hmin, as a function of time and fit it to a power law with exponent n 1. We then compare n1 to exponent n2, obtained from a rotational rheometer using a Herschel-Bulkley model. We confirm n1=n2 for the widest variety of non-Newtonian fluids to date. When these fluids are diluted with a Newtonian fluid n1 does not equal n2. No current models predict that behavior, identifying a new class of fluid breakup. Chapter 2 presents the first chemical potential-temperature phase diagram of helium on lithium, sodium and gold, using a novel pressure measurement system. The growth and superfluid transition of a helium film on these substrates is measured via an oscillator for isotherms (fixed temperature, varying amount of helium gas), and quenches (fixed amount of helium gas, varying temperature). The chemical potential-temperature plot is similar for gold, lithium and sodium despite the large difference in the substrate binding energies. No signs of a 2-D liquid-vapor transition were seen. Chapter 3 discusses the creation of a 32.768 kHz quartz tuning fork in situ pressure transducer. Tuning forks are used to measure pressure at room temperature, but no work addresses their potential as cryogenic pressure transducers. We mapped out the behavior of a tuning fork as a function of pressure at 298, 7.0, 2.5, 1.6, 1.0 and 0.7 K by measuring the quality factor. The fork is sensitive to pressures above 0.1 mTorr, limiting its use as a pressure gauge at 0.6 K and below. The experimental curves were compared to a theoretical Q(P, T) function that was refined using the 298 K data. At cryogenic temperatures the formula breaks down in the viscous region and becomes inaccurate. The qualitative shape of the theory, but not its quantitative values, matches the data. The discrepancy between the experimental and theoretical Q values appears to be due to unaccounted for dissipation.

Huisman, Fawn Mitsu

414

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

415

Kerr effect in liquid helium at temperatures below the superfluid transition  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electro-optical Kerr effect induced by a slowly-varying applied electric field in liquid helium at temperatures below the $\\lambda$-point is investigated. The Kerr constant of liquid helium is measured to be $(1.43\\pm 0.02^{(stat)} \\pm 0.04^{(sys)})\\times 10^{-20}$ (cm/V)$^2$ at $T=1.5$ K. Within the experimental uncertainty, the Kerr constant is independent of temperature in the range $T=1.5$ K to 2.17 K, which implies that the Kerr constant of the superfluid component ...

Sushkov, A. O.; Williams, E.; Yashchuk, V. V.; Budker, D.; Lamoreaux, S. K.

2004-01-01

416

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

417

Behavior of helium gas in the LHD vacuum chamber  

Energy Technology Data Exchange (ETDEWEB)

In general, helium gas does not remain on vacuum chamber walls because of its small activation energy. However, outgassing of helium gas from the walls has been observed in the LHD plasma vacuum chamber with a very long time constant after helium glow discharge cleaning (GDC), and absorption of helium atoms has been observed in plasma discharge experiments using helium gas. The helium partial pressure before the daily experiments was determined only by the gas species of the last GDC. No dependence has been found between the helium partial pressure and the species of the fueling gas of the last plasma experiment fueling gas. Considering that the outgassing rate of the helium gas is almost the same each morning after He GDC, the retention of helium atoms in the wall after the GDC is almost at the same level. The concentration of helium atoms in the wall before the daily experiments is estimated. The outgassing rate after the GDC is 2x10{sup -4} Pa m{sup 3}/s and the concentration is 4.7x10{sup 16} atoms/cm{sup 2}. These results are of the same order as in another experiments. During helium gas plasma experiments, about a half of the amount of the inlet gas disappears with the missing particles remaining in the wall. The stainless steel wall, which is saturated with He GDC, may still have the capacity to trap high energy helium atoms. However, the energy dependence of trapping helium atoms presently is not clear.

Suzuki, H. E-mail: hsuzuki@lhd.nifs.ac.jp; Ohyabu, N.; Komori, A.; Morisaki, T.; Masuzaki, S.; Miyazawa, J.; Sakamoto, R.; Shoji, M.; Goto, M.; Morita, S.; Kubota, Y.; Motojima, O