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Impurity-helium solids (Im-He solids) are porous solids created by injecting a beam of mixed helium and impurity gases into superfluid ⁴He. In this work we use electron spin resonance (ESR) techniques to investigate Im-He solids containing atoms and molecules of hydrogen and/or deuterium. We have performed studies of low temperature (T ~ 1.35 K) tunnelling chemical reactions in which deuterium atoms replace the hydrogen atoms bound in H₂ or HD molecules to produce large (up to 7.5×10¹⁷cm⁻³) and relatively stable concentrations of free hydrogen atoms. The time dependence of H and D atom concentrations has been investigated for Im-He samples with different initial ratios of hydrogen and deuterium ranging from 1:20 to 1:1.The satellite ESR lines associated with the dipolar coupling of electron spins of H and D atoms to the nuclear moments of the hydrogen nuclei found in neighboring molecules have been observed in Im-He solids. The forbidden hyperfine transition of atomic hydrogen involving the mutual spin flips of electrons and protons has also been observed.

The Low Temperature Microgravity Physics Facility currently in the design phase is a multiple user and multiple flight facility intended to provide a long duration low temperature environment onboard the International Space Station. The Facility will provide a unique platform for scientific investigations requiring both low temperature and microgravity conditions. It will be attached to the Japanese Experiment Module`s Exposed Facility and can house two science instruments each flight. The Facility consists of a 180-liter superfluid helium dewar, a support enclosure, and control electronics. The facility will be launched full of cryogen, and retrieved after the cryogen is depleted. Industrial partners are responsible for building the reusable facility and standard parts of the instruments. Principal Investigators from universities and other institutions are contracted to develop major parts of the science instrument package. An overview of the detailed technical capabilities of the facility will be presented in this paper.

The thermal conductivity of solid parahydrogen crystal with methane admixtures has been measured in the temperature range 1.5 to 8 K. Solid samples were grown from the gas mixture at 13 K. Concentration of CH4 admixture molecules in the gas varied form 5 to 570 ppm. A very broad maximum of thermal conductivity with absolute value of about 110 W/(m K) is observed at 2.6 K. The data are interpreted by Callaway model considering phonons resonant scattering on quasi-local vibrations of CH4 molecules, phonon-grain boundary and phonon-phonon scattering processes. The increase of grain boundary scattering leads to the decrease of the maximum broadening. The analysis shows that the solid mixture of p-H2 and CH4 is a heterogeneous solution for CH4 concentration higher than 0.1 ppm., 9 pages. to be published in LTP (2003)

The objective of ISLES (inverse-square law experiment in space) is to perform a null test of Newton`s law on the ISS with a resolution of one part in 10⁵ at ranges from 100 mm to 1 mm. ISLES will be sensitive enough to detect axions with the strongest allowed coupling and to test the string-theory prediction with R≥ 5 mm. To accomplish these goals on the rather noisy International Space Station, the experiment is set up to provide immunity from the vibrations and other common-mode accelerations. The measures to be applied for reducing the effects of disturbances will be described in this presentation. As designed, the experiment will be cooled to less than 2 K in NASA`s low temperature facility the LTMPF, allowing superconducting magnetic levitation in microgravity to obtain very soft, low-loss suspension of the test masses. The low-damping magnetic levitation, combined with a low-noise SQUID, leads to extremely low intrinsic noise in the detector. To minimize Newtonian errors, ISLES employs a near-null source of gravity, a circular disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, are suspended on the two sides of the source mass at a distance of 100 mm to 1 mm. The signal is detected by a superconducting differential accelerometer, making a highly sensitive sensor of the gravity force generated by the source mass.

The structure and morphology of low-temperature quench condensed binary alloys of hydrogen with argon and krypton were studied by the powder x-ray diffraction. The nominal hydrogen fraction c in both systems was varied from 0 to 50%; the condensation was performed at 5-6 K; both as-prepared and annealed samples were examined by the x-ray diffraction. Few, often only one reflection can be unambiguously detected for the as-grown alloy samples. In the Kr-H₂ condensates with c < 10%, the x-ray patterns show fine-grain krypton-rich crystallites with rather high actual hydrogen contents as estimated from Vegard`s law. At high nominal hydrogen fractions( %) c ≥ 10 , no the reflections attributable to the krypton lattice were recorded and the incoherent background showed no characteristic swelling around the position of reflection (111) from pure Kr but, instead, the reflections from a hydrogen-rich hcp phase were distinct. As the temperature was steadily raised, first the hydrogen reflections disappeared and then, at a certain temperature, the samples underwent an abrupt transformation, releasing heat and making the krypton component forms larger, x-ray detectable textured crystallites. In the as-grown Ar-H₂ samples, only (111) reflections from the argon-rich phase were recorded. Warmup led to the same consequences, viz., effusion of hydrogen and then recrystallization. In both systems, the recrystallization onset temperature depends substantially on the nominal hydrogen fraction in the gas. The shift of the lattice parameter in the as-grown argon-based phases suggests a strong suppression of the quantum nature of hydrogen in argon lattice environment. The entire set of the experimental findings can be treated as evidence that the quench-condensed hydrogen-containing alloys morphologically resemble helium-impurity solids (gels) whose structure and morphology are currently studied at Cornell University.

Изложены основные тенденции эволюционного развития долгосрочной программы исследований на российском сегменте Международной космической станции (РС МКС), отражающие предполагаемые изменения окончательной конфигурации МКС, существующие предложения о проведении совместных экспериментов, стремление научной общественности к повышению эффективности и реальной практической отдачи программ, а также проанализированы основные направления исследований в области физики и техники низких температур на РС МКС. The main trends in the evolutionary development of a long-term research program for the Russian segment of the International Space Station (RS ISS) are elaborated with allowance for the proposed changes in the final configuration of the ISS, the existing ideas about the conducting of joint experiments, and the desire of the scientific community for more efficient programs with real returns on the practical level. The main fields of study in low-temperature physics and engineering are analyzed.

Рассматривается принцип интеграции низкотемпературных исследований, планируемых к постановке на борту Российского сегмента МКС, с учетом особенностей криогенной экспериментальной аппаратуры, включающей объект исследования и систему криостатирования. Исследуются системные вопросы создания универсальной криогенной лаборатории на орбитальной станции для проведения космических экспериментов с глубоким охлаждением в условиях микрогравитации. Приведены блок-схема лаборатории и классификация оборудования, а также требования к экспериментальной аппаратуре. The principle of integration of the low-temperature research planned for onboard the Russian segment of the International Space Station (ISS) is discussed in relation to the features of the cryogenic experiment packages, including the object of study and the cryostatic system. Systemic questions concerning the creation of a universal cryogenic laboratory on the orbital station for conducting deep-cooling experiments in the microgravity environment of space are examined. A block diagram of the laboratory is given, a classification of the equipment is presented, and the requirements on the experiment packages are discussed.

The phonon spectra and vibrational thermodynamical characteristics of the Pd-H superlattices are investigated. Results of our calculations give a possibility to agree the data of neutronographic and calorimetric experiments and explain for the such systems the atomic mean square amplitudes and correlations between ones.

The results of numerical simulation of Rayleigh-Benard convection in ³He near the thermodynamic critical point are presented. The mathematical model including the full Navier-Stokes equations with two-scale splitting of the pressure and the van der Waals equation of state is applied. The known experimental data on ³He are used in simulations. On the basis of the calibration laws the "real" Rayleigh and Prandtl numbers are estimated. It is shown that one should agree these "real" criteria of similarity in the model and physical media to approach results of simulations to experiments. The Rayleigh number characterising the convection onset is defined from obtained numerical data. This number is shown to be in a good agreement with known experimental and theoretical values.

A negative contribution of the CH₄ impurity to the thermal expansion of the solution has been revealed in the dilatometric studies of solid Kr + 0.76% CH4, Kr + 5.25% CH₄, and Kr + 10.5% CH₄ solutions at 1-23 K. It is shown that the negative contribution results from changes in the occupancy of the ground state of the A-modifications of isolated CH₄ molecules. Assuming that the CH₄ impurity singles and clusters contribute to the thermal expansion independently, we can estimate their contributions. The contribution of the singles to the thermal expansion of the solid solution is negative. The energies of the first excitational rotational states were determined for singles and two-body and three-body clusters of the CH₄ molecules.

Представлены результаты моделирования кипения сверхтекучего гелия в условиях микрогравитации. Анализируется эволюция паровой пленки на поверхности цилиндрического нагревателя, расположенного внутри толстостенного цилиндра с пористыми стенками. Для описания процессов тепло- и массопереноса на межфазной поверхности применяются методы молекулярно-кинетической теории. Решается уравнение движения межфазной поверхности пар-жидкость. Изучено влияние параметров эксперимента на характеристики паровой пленки. Проведено сравнение расчетных данных для микрогравитации и земных условий. The results of a modeling of the boiling of superfluid helium in a microgravity environment are presented. The evolution of the vapor film on the surface of a cylindrical heater placed inside a thick-walled cylinder with porous walls is analyzed. The methods of molecular kinetic theory are used to describe the heat and mass transfer on the interphase surface. The equation of motion of the vapor–liquid interphase surface is solved. The influence of the parameters of the experiment on the characteristics of the vapor film is studied. The results of the calculation for microgravity and terrestrial environments are compared.

EPR spectra of CH₃, CH₂D, CHD₂, and CD₃ radicals have been observed in H₂ matrix in the temperature range 1.6-4.2 K. The radicals were obtained by condensation on a cold substrate of two gas flows: deuterium mixed with 2 mol % methane passed through a discharge and pure hydrogen avoiding the discharge. The CD₃ and CHD₂ spectra were found to be a superposition of two spectra: high-temperature and low-temperature. A transformation of the shape of CD₃ and CHD₂ spectrum with decreasing sample temperature was observed. This is attributed to a change in the populations of the lowest rotational states of the radicals. Compared to known results for deuterated methyl radicals in Ar, the present observations suggest an existence of a hindering barrier for the radical rotation in solid H₂.

The united research plan named "Boiling" is created on the basis of several cryogenic research projects developed by experts in Russia and Ukraine for International Space Station. The "Boiling" plan includes 8 first experiments aimed at investigating the influence of microgravity on boiling processes, heat transfer and hydrodynamics in liquid helium being either under normal or superfluid conditions. The experiments are supposed to be carried out with individual cells collected inside a single cryogenic onboard experimental facility. The international research program experiments are characterized by the following features: utilization of several artificially simulated microgravity levels, owing to rotation of the experimental helium cryostat; visualization of the processes that occur in liquid helium; research of boiling and hydrodynamics both in a large volume of stationary liquid, and in a liquid flow running through a channel. Upon completion of the "Boiling" research plan, the cryogenic onboard facility created for International Space Station would be able to find its application in further scientific and experimental researches with helium.

Acoustic radiation pressure is thought to be very useful for solid ⁴He experiment under the microgravity. We observed that solid-liquid interface of ⁴He was manipulated by the acoustic wave. We applied the sound pulse perpendicularly to the flat interface between two transducers. The interface moved to the sound direction at low temperatures. We also checked how the interface moved when sound was applied parallel to the interface. Dynamics of the interface during and after the sound pulse were recorded by a high speed CCD camera.

С 12 по 18 августа 2002 г. в Научном центре Черноголовка РАН проходил 3-й Международный семинар по физике низких температур в условиях микрогравитации CWS-2002. По традиции семинар CWS-2002 был включен в список сателлитных конференций и семинаров, посвященных одному из быстро развивающихся направлений в физике низких температур, которые сопутствуют проводимой раз в три года Международной конференции по физике низких температур.

The excitations of trapped atoms with a Bose-Einstein condensate in a trap are determined by the conservation of common phonon and roton numbers of atomic motion, and these properties depend on the presence of gravitational field.

Обнаружено, что форма и строение образцов водяного геля, которые образуются при конденсации газообразного ⁴Не с примесью паров воды на поверхности сверхтекучего He II, охлажденного до 1,4 К, существенно зависят не только от условий набора смеси, но и от конструкции экспериментальной ячейки. Приведены результаты наблюдений за эволюцией образцов, приготовленных в широкой ячейке диаметром 29 мм при малой скорости набора смеси. It is found that the shape and structure of watergel samples formed in the condensation of gaseous ⁴Не containing a water vapor impurity on the surface of superfluid He II cooled to 1.4 K depend substantially not only on the conditions of admission of the mixture but also on the construction of the experimental cell. The results of observations of the evolution of samples prepared in a wide cell, 29 mm in diameter, at a low rate of admission of the mixture are presented.

We describe a quantum computer based on electrons supported by a helium film and localized laterally by small electrodes. Each quantum bit (qubit) is made of combinations of the ground and first excited state of an electron trapped in the image potential well at the surface. Mechanisms for preparing the initial state of the qubit, operations with the qubits, and a proposed readout are described. This system is, in principle, capable of 105 operations in a decoherence time.

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

The proximity effect causes the existence of some transition area with the gradual variation of the density of superfluid component instead of the sharp boundary at the level where the hydrostatic pressure realizes the phase transition He II-He I. In the microgravity environment the characteristic length of this effect increases, and more convenient conditions arise for measurements in the transition area. The problem of the expansion of thermodynamical potential in power series in the vicinity of He II-He I interface is considered. The critical values of the size of the superfluid area are determined.