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As the second most-abundant chemical element in the universe, helium makes up a large fraction of giant gaseous planets, including Jupiter, Saturn, and most extrasolar planets discovered to date. Using first-principles molecular dynamics simulations, we find that fluid helium undergoes temperature-induced metallization at high pressures. The electronic energy gap (band gap) closes at 20,000 K at a density half that of zero-temperature metallization, resulting in electrical conductivities greater than the minimum metallic value. Gap closure is achieved by a broadening of the valence band via increased s-p hydridization with increasing temperature, and this influences the equation of state: The Gruneisen parameter, which determines the adiabatic temperature-depth gradient inside a planet, changes only modestly, decreasing with compression up to the high-temperature metallization and then increasing upon further compression. The change in electronic structure of He at elevated pressures and temperatures has important implications for the miscibility of helium in hydrogen and for understanding the thermal histories of giant planets. high pressure | metallization | giant planets | gap closure | hybridization

Performance tests are carried out on the subcooling system for the Large Helical Device (LHD) helical coils. The studies have shown that the coil temperature is around 3.6 K under a steady heat load of 100 W from outside of the coil case in the system, which has maintained the above performance.

The concept of the closed-loop cooling by a cryocooler for a 21 T Fourier transform ion cyclotron resonance (FT-ICT) magnet system is described. The helium liquefaction system using a cryocooler is designed and the helium liquefaction system will be integrated into the proto-type 21 T magnet system.

A pair of power leads is required for the fast cycling accelerator magnet system and the design study has shown that a conventional leads made of copper rods is suitable for the application. The helium consumption is in the range of 6 g/s for each lead and the heat leak into the helium bath will be reduced since the HTS tapes are chosen to be used as the transmission line conductors.

The measurement of the stability of many superconducting Rutherford cables exposed to short point-like heat pulses on strands has shown that the edge of a cable is less stable than the central part of the cable. The analysis with neutron tomography of the cable cross-section has shown that the interstrand contact surface, void fraction and the contact surface between strand and helium have varied strongly.

A zero-dimensional (0-D) thermal model is built to analyze the stability of the LHC SC magnets by considering all relevant He phases. Stability measurements for steady state energy deposition are performed on few LHC magnets.

The updated design for the MICE coupling magnet is described. The cold mass support system and helium cooling system for the coupling magnet, which is capable of carrying a longitudinal force up to 500 kN are discussed.

A large bore superconducting magnet is described, prepared and evaluated for developing the uninterruptible power supply (UPS)- superconducting magnetic energy storage (SMES) applications. This superconducting magnet is manufactured in the transparent winding structures and the compact cryostat has shown very good cryogenic performance that is operated in the absolute zero evaporation condition.

The cryogenic stability of the Large Helical Device (LHD) helical coils is improved by installing an additional cooler like subcooled helium at 3.0 K. The temperature rise by excitation is analyzed as it is required for maintaining low temperatures for better heat transfer.

The process of the power test quality assurance and performance evaluation, which is applied during the LHC magnet series tests, is analyzed. The main test results of magnets tested in both supercritical and superfluid helium, which has included the quench training, the conductor performance and the magnet protection integrity are discussed in terms of the design parameters and the requirements of the LHC machine.

Rovibrational spectra for the HCCN.HCN and HCN.HCCCN binary complexes in helium droplets at low temperature are measured. No Q-branch is observed in the infrared spectrum of the linear HCN.HCCCN dimer but a prominent Q-branch is found in the corresponding infrared spectrum of the HCCCN.HCN complex.

Density functional calculations were used to study the structure and energetics of [super 3]He and [super 4]He nanodroplets doped with alkaline earth atoms. It was predicted that alkaline earth atoms form Mg to Ba go to the center of [super 3]He droplets, while Ca, Sr, Ba reside in a deep dimple at the surface of [super 4]He drops and Mg is at their center and for Ca and Sr the structure of dimples is shown to be very sensitive.

The transfer of heat from the coil of the Large Hadron Collider (LHC) dipole magnet to helium II is evaluated. Findings reveal the transfer of nearly 1.4 to 1.7 times more power to helium II.

The study evaluates the effects of the superfluid helium on the superconducting properties of the Bi-2223 tapes, which are used for high temperature superconducting (HTS) inserts. The cooling of the tape with helium is found to lead to higher field contribution and more stability.

Techniques like emission spectroscopy are used to determine and study the proton, helium and hydrogen temperatures in an extremely large-scale microwave plasma source with a very high microwave power. The study of various temperatures, including the Doppler and rotational temperatures clearly shows that the kinetic temperature of the hydrogen atoms is much higher than the background gas temperature.

The performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne, He+ [H.sub.2] and Ne+ [H.sub.2] was studied at temperatures in the range of 3-293 K. This paper reports on previously published measurements and additional studies on the effects of the purity of the gases in which the GEM performance is evaluated. In He, at temperatures between 77 and 293 K, triple-GEM structures operate at rather high gains, exceeding 1000. There is an indication that this high gain is achieved through the Penning effect as a result of impurities in the gas. At lower temperatures the gain-voltage characteristics are significantly modified probably due to the freeze-out of these impurities. Double-GEM and single-GEM structures can operate down to 3 K at gains reaching only several tens at a gas density of about 0.5 g/l; at higher densities the maximum gain drops further. In Ne, the maximum gain also drops at cryogenic temperatures. The gain drop in Ne at low temperatures can be re-established in Penning mixtures of Ne+-[H.sub.2]: very high gains, exceeding 104, have been obtained in these mixtures at 30-77 K, at a density of 9.2 g/l which corresponds to saturated Ne vapor density at 27 K. The addition of small amounts of [H.sub.2] in He also re-establishes large GEM gains above 30 K but no gain was observed in He+[H.sub.2] at 4 K and a density of 1.7 g/l (corresponding to roughly one-tenth of the saturated vapor density). These studies are, in part, being pursued in the development of two-phase He and Ne detectors for solar neutrino detection. Index Terms--Cryogenic noble gases, electron bubble, gas electron multiplier, helium, neon, Penning mixtures.

The thermal and diffusion properties of hot gas around a dc arc discharge under a gravity-free condition are examined by using a jet plane in order to improve the arc production of carbon clusters. The results have shown that carbon clusters including single-walled carbon nanotubes are synthesized around the arc plasma where the He temperature is higher than 1000 K and the large bundles of fatter single-walled carbon nanotubes are produced under the gravity-free condition.

(Super 3)He is inserted into the cavity of an open-cage fullerene derivative close to room temperature, reaching an incorporation fraction of 0.1 percent. The rate of escape of (super 3)He from this fullerene was monitored by (super 3)He NMR to yield the activation barrier and to compare the size of the orifice to those of other open-cage fullerenes.

The guest-host dynamics of NO2 embedded in He(sub n) droplets were examined by recording depletion spectra of mass spectrometer signals at m/z values if 8 (He(sub 2)(super +)), 30 (NO(super +)), and 46 (NO(super +)) throughout the wavelength range 340-402 nm. Results indicate that small polyatomics embedded in He(sub n) droplets that have values of ~10(super 4) or larger would not undergo net unimolecular reaction if the gas-phase pathway was barrierless, with two possible exceptions, if one or both of the products has a positive chemical potential and if the scattering cross section of the products with helium is small.

The first experimental observation of (HF)(Sub n) (n = 4,5,6) clusters, grown in helium nanodroplets is reported. Four of the five H-F stretching vibrational bands of a new isomer of (HF)(Sub 5) are observed corresponding to a tetramer ring to which a fifth HF is hydrogen bonded.

An excitonic pentamer model is proposed for the core Qy states of the photosystem II reaction center. This model is the result of theoretical simulations of several types of spectra obtained at liquid helium temperatures in the Qy region and Pheo Qx region of the absorption spectrum.

Measurements of the mobility of excess electrons in a high density helium gas are reported. Extended ranges of temperature [(26 [less than or equal to] T [less than or equal to] 77) K] and density [(0.05 [less than or equal to] N [less than or equal to] 12.0) atoms.[nm.sup.-3]] are investigated to ascertain the effect of temperature on the formation and dynamics of localized electron states. The main result of the experiment is that the formation of localized states essentially depends on the disorder of the medium and, hence, on the gas density. Moreover, it appears that the transition from delocalized to localized states shifts to larger densities as the temperature is increased. This behavior can be understood in terms of a simple model of electron self-trapping in a spherically symmetric square well.

Research describing the formation, evolution and extended defects of bubbles in helium implantation in silicon is presented. In particular the microstructural features of the defects were characterized by means of transmission electron microscopy.

The hydrostaticity of a helium-pressure medium is evaluated with powder x-ray diffraction techniques up to 77 GPa at room temperature. The powder x-ray diffraction method is compared with the ruby fluorescence method in order to get a better understanding of nonhydrostatic stress conditions.

The suppression of thermally induced generation of hole traps in SiO2 layers of Si/SiO2 and poly-Si/SiO2/Si structures by He ambient is analyzed as a function of the gas pressure p. The result suggests that a short-range interaction between the noble gas atoms and the Si/SiO2 network atoms is at the basis of the degradation blockage effect.

A solution to the nonlinear conduction equation appropriate to the problem of a saturated bath He II heat exchanger is proposed. An extended surface heat transfer formulation serves as the basis for the problem. Results indicate that the nonlinear differential equation may be integrated for the special case of constant characteristics that provide a simple solution appropriate to the design and analysis of practical heat exchangers.

The Peng-Robinson equation of state (EOS) is employed to quantify the effects of entrained helium when helium head pressure carbon dioxide (HHPC[O.sub.2]) is used in supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC). Naphthalene serves as a model analyte, and the unlike interaction energy parameters of the EOS are obtained from the respective second cross-virial coefficients. The Peng-Robinson EOS provides a reasonable description of the vapor-liquid equilibrium in HHPC[O.sub.2] storage tanks at room temperature. Variations in the content of helium in HHPC[O.sub.2] within the relevant range (between 0 and 5 mol %) are predicted to produce significant changes in the density and solubility parameter of HHPC[O.sub.2], in the solubility of naphthalene in HHPC[O.sub.2], and in the chromatographic retention of naphthalene if HHPC[O.sub.2] serves as the mobile-phase fluid. These results provide a computational indication that the use of HHPC[O.sub.2] in SFE and SFC should be avoided.

The steady-state heat transfer coefficient of supercritical helium in a cable-in-conduit conductor (CICC) was measured at different temperatures, pressures and mass flow rates to investigate its impact on the thermal stability of CICCs. The stability of CICC joints between coils, where a temperature increase in supercritical helium occurs due to joule heat generation, was also evaluated with respect to Stekly's condition for the cryostability of bath-cooled conductors.

With the goal of intensifying turbulent free convection from heated vertical plates to cold gases, five binary gas mixtures are examined in this technical note. Helium (He) is chosen as the principal gas while xenon (Xe), nitrogen ([N.sub.2]), oxygen ([O.sub.2]), carbon dioxide (C[O.sub.2]), and methane (C[H.sub.4]) are the companion gases. From thermal physics, the thermophysical properties affecting turbulent free convection of binary gas mixtures are the viscosity [[mu].sub.mix], the thermal conductivity [[lambda].sub.mix], the density [[rho].sub.mix], and the heat capacity at constant pressure [C.sub.p,mix]. Invoking the similarity variable transformation, the system of two nonlinear differential equations is solved numerically by the shooting method and a fourth-order Runge-Kutta-Fehlberg algorithm. From the numerical temperature fields, the allied mean convection coefficients [[bar.h].sub.mix]/B changing with the molar gas composition w in the w domain [0, 1] are plotted in congruous diagrams for the five binary gas mixtures under study. Keywords: vertical plate, turbulent free convection, binary gas mixtures, maximum mean convection coefficient

Micro-Raman spectroscopy measurements are used for analyzing the temperature distribution of current-carrying, suspended carbon nanotubes in different gas environments near atmospheric pressure. The results have shown that the heat dissipated in the suspended nanotube is removed by its surrounding gas molecules and that the thermal boundary conductance is higher in carbon dioxide than in nitrogen, argon and helium, despite the lower thermal conductivity of carbon dioxide.

A novel spectroscopic method is described that has used superfluid helium nanodroplets to record IR spectra of cold molecular ions. The spectra are recorded with a high sensitivity, have displayed only a small matrix shift and the widths of the individual transitions have depended on the excited vibrational level.

Asymmetric double probe theory is developed for collisional plasmas and it is used to microwave-sustained helium plasma jets in order to estimate the plasma parameters at atmospheric pressure avoiding the overestimation of electron temperature.

The fabrication and the performance of the room-temperature reciprocating active magnetic refrigerator prototype are discussed. These prototypes are shown to exhibit extremely high cooling power with a wide temperature span.

The thermoacoustic field is studied quantitatively by the Taconis oscillations with finite amplitude in a helium-filled, quarter-wavelength tube. The significant variation observed in the density, temperature, and entropy diverted the mean values from the respective values in quiescent state.

The studies of large H atom line broadening observed throughout the volume of surface wave generated He-[H.sub.2] and [H.sub.2] microwave plasmas at low pressures are reported. The measurements obtained for the Doppler temperatures corresponding to the H[beta], H[gamma], H[delta] H[epsi] , and H[zeta] line profiles are found to be higher than the rotational temperature of the hydrogen molecular Fulcher-[alpha] band and the Doppler temperature of the 667.1 nm singlet He line.

A theoretical model is presented for equation of state (EOS) of aluminum with helium bubbles and the impact of helium bubbles on shock loading is examined. The bubble mass and concentration has affected the Hugoniot curve and the EOS model has minor significance, indicating that the model is not sensitive to the details of the helium EOS.

Several experimental studies are conducted to explain the spatial densities and the intensity distribution of the enhanced hydrogen emission from low-pressure He plasmas. A new mechanism describing the contribution of helium metastable excited state to the experimental phenomenon is also discussed.

X-ray diffraction measurements as well as electron, optical, and atomic force microscopies are used for analyzing the thermally induced stress relief mechanisms in coimplanted [H.sup.+] and [He.sup.+] ions into (001) Si substrates at moderate energies. Localized exfoliation is described with the help of distinct coarsening processes linking the initially formed gas filled nanosized platelets to crack structures and the delamination behavior is described in terms of unstable crack propagation process triggered at a single nucleation site.

A self-consistent model of charged and neutral particle dynamics which could be applied to atmospheric small-space (200 [mu]m) discharges in helium is detailed. The gas heating, neutral depletion initiation, and electric field reversal observed for microplasmas provide insight into the close interaction between neutral gas and charged species that govern the evolution of the microplasma.