3He 4He Research Articles

Influence of acoustic modes on resonance properties of a quartz tuning fork immersed in superfluid 4He and liquid mixtures 3He–4He

The oscillating quartz tuning fork method has been used to study resonance phenomena in experimental cells of different sizes filled with superfluid 4He and concentrated liquid mixtures of 3He–4He. An analysis of the temperature dependence of the resonance frequencies of the tuning forks showed that in a number of cases, the incompressible fluid model is not sufficient to interpret the experimental results and that acoustic processes in the cell should be taken into account. The frequencies of the resonances of the first sound in cylindrical geometry are estimated and their influence on the resonant frequencies of the tuning fork is shown, which can lead to a distortion of the shape of the resonant line. A comparison is made between experimental results for superfluid 4He and mixtures of 3He-4He with light isotope concentrations of 5% and 15%. It is shown that, in contrast to pure helium, the model of a viscous incompressible fluid cannot be applied to mixtures, even in the absence of first acoustic resonances. This can be explained by the fact that, when studying concentrated solutions, the excitation of the second sound along with the first can have a noticeable effect on the resonance characteristics of the tuning fork.

Utilization of cryogenic phases of helium as “magic” working fluids in laboratory experiments: Pushing the boundaries of fluid dynamics

A surprisingly large part of the valuable scientific contributions of K. R. Sreenivasan—known to his friends and coworkers as Sreeni—to fluid dynamics is directly connected with precisely controlled benchmark experiments with cryogenic phases of helium. These experiments have been performed in a number of leading low temperature laboratories using conventional viscous 4He and 3He gases, normal liquid 4He (He I), as well as liquid 3He–4He mixtures and superfluid phases of 4He (He II) and 3He-B. We review their extraordinary physical properties and describe selected experiments, focusing on various forms of thermal convection, which push the boundaries of classical and quantum fluid dynamics.

Calculation of Reaction Rate and Uncertainty for d(p,γ)3He and 3He(d,p)4He Using Bayesian Statistical Approach in Astrophysics

Calculation of Reaction Rate and Uncertainty for d(p,γ)3He and 3He(d,p)4He Using Bayesian Statistical Approach in Astrophysics

Dilution Refrigeration Technology

As the main means of obtaining extremely low temperatures of 10mK, dilution refrigerators are widely used in quantum computing, condensed matter physics and other fields. The development of the most widely used typical dry dilution refrigerators has been relatively mature internationally, while there is little research on other types of dilution refrigerators, and there is a lack of comprehensive and systematic research on dilution refrigeration technology.<br>This paper focuses on the current status of dilution refrigeration technology research, introduces its basic principles, and points out that the fundamental reason for continuous refrigeration is the limited solubility of 3He in 4He and the enthalpy difference between the concentrated phase and the dilute phase. The implementation forms and research progress of typical dilution refrigerators, 4He cycle dilution refrigerators, cold cycle dilution refrigerators and space dilution refrigerators are summarized, and their respective application occasions and advantages and disadvantages are discussed. The key influencing factors and design calculation methods for realizing dilution refrigerators below 10mK are analyzed from the aspects of Kapitza thermal resistance, osmotic pressure, and resistance, providing a reference for the research of dilution refrigeration technology.

An active molybdenum (polymetallic)-enriching system in foreland basins

Molybdenum (polymetallic)-rich saline brines from the Badain Jaran Desert to the north of the Tibetan Plateau reveal active enrichment of trace metals in the groundwater systems of foreland basins. Molybdenum (polymetallic)-rich brines have salinities of 224–338 g/L and high concentrations of Mo (~3.7 mg/L), Li (~5.8 mg/L), U (~0.65 mg/L), Rb (~2.0 mg/L), Sr (~6.1 mg/L), Mn (~0.62 mg/L), and Ni (~0.52 mg/L). The major ions in the brines are Na+ and Cl−, with small amounts of SO42−. The pH and Eh values are 8.50–8.82 and >200 mV, respectively, with dissolved O contents of >6 mg/L. The δD and δ18O values of these saline brines are −29.2 ‰ to −31.0 ‰ and +0.3 ‰ to +2.8 ‰, respectively, and they exhibit a similar trend to the regional evaporation line, suggesting that the Mo (polymetallic)-rich saline brines originated from evaporation of groundwater in the Badain Jaran Desert. The 3He/4He (R) and R/Ra ratios of the brines are 0.42–2.11 and 0.30–1.51, respectively, and the 38Ar/36Ar and 40Ar/36Ar ratios are 0.194–1.464 and 267.4–360.2, respectively. These results suggest that the Mo-rich saline brines interacted with detrital material in the Badain Jaran Desert and extracted both cosmogenic 3He and radiogenic 4He. We propose that the Mo (polymetallic)-rich saline brines originated from evaporation of groundwater in the Badain Jaran Desert. Regional faults are responsible for the supply of precipitation-derived groundwater to the study area.

Anomalous temperature dependence of energy levels of electrons on helium

We report on magnetoconductivity measurements of electrons on helium exposed to resonant microwave irradiation within the temperature range associated with electron-ripplon scattering. Our findings reveal a non-monotonic temperature dependence of the intersubband frequency, with an abrupt decrease observed at temperatures below 0.3 K. We attribute this unexpected energy levels shift to the adsorption of 3He impurities near the liquid helium surface at low temperatures and such behavior is consistent with recent theoretical calculations of the surface electron energy spectra on 3He–4He mixtures.

Cavitation generated by vibrating quartz tuning fork in concentrated 3He–4He mixture

The state of the problem of cavitation in superfluid helium and the content of previous works on this topic are analyzed. The transition between turbulent flow and cavitation under oscillations of a quartz tuning fork in a normal and superfluid isotopic mixture containing 15% of 3He in the temperature range of 0.5–3 K is studied experimentally. The temperature dependences of the critical velocity for the cavitation onset and the critical transition excitation force are obtained. We compare the results of our measurements with the data obtained by other groups. The results of measurements with tuning forks in restricted and unrestricted geometries suggest that the presence of acoustic emission facilitates the conditions for the onset of cavitation and indirectly confirms the role of vortex lines. A comparison of the temperature dependences of the critical velocity of cavitation onset in pure 4He and a concentrated 3He–4He mixture did not give an unambiguous answer to the reason for the sharp increase of this velocity, at the transition to the superfluid state, and the contributions of both thermal effects and the 3He impurities to the velocity increase.

Acoustic emission in bulk normal and superfluid 3He

We present measurements of the damping experienced by custom-made quartz tuning forks submerged in 3He covering frequencies from 20 to 600 kHz. Measurements were conducted in the bulk of normal liquid 3He at temperatures from 1.5 K down to 12 mK and in superfluid 3He-B well below the critical temperature. The presented results complement earlier work on tuning fork damping in 3He, removing possible ambiguities associated with acoustic emission within partially enclosed volumes and extend the probed range of frequencies, leading to a clearly established frequency dependence of the acoustic losses. Our results validate existing models of damping and point toward the same mechanism of wave emission of first sound in normal 3He and liquid 4He and zero sound in superfluid 3He. We observe a steep frequency dependence of the damping ≈f5.5, which starts to dominate around 100 kHz and restricts the use of tuning forks as efficient sensors in quantum fluids. The acoustic emission model can predict the limiting frequencies for various devices, including micro-electromechanical and nano-electromechanical structures developed for quantum turbulence and single vortex dynamics research.

Study of fundamental symmetries in the few-nucleon systems

In this contribution we present two studies of fundamental symmetries in light nuclei: the investigation of CP violation via the calculation of the electric dipole moments (EDMs) of the deuteron, 3H and 3He, and the possible existence of a new bosonic particle, the so-called X17, in the 3H(p, e + e −)4He and 3He(n, e + e −)4He reactions. The advantage to perform these investigations in few-nucleon systems is related to the possibility to compute accurate ab initio bound- and continuum-states wave functions using well established nuclear interactions. Therefore, if these effects are observed, they can be unambiguously related to underlying beyond Standard Model theories.

Finite Amplitude Oscillatory Convection of Binary Mixture Kept in a Porous Medium

In the present study, the double-diffusive oscillatory convection of binary mixture, 3He–4He, in porous medium heated from below and cooled from above was investigated with stress-free boundary conditions. The Darcy model was employed in the governing system of perturbed equations. An attempt was made, for the first time, to solve these equations by using the nonlinear analysis-based truncated Fourier series. The influence of the Rayleigh number (R), the separation ratio (ψ) due to the Soret effect, the Lewis number (Le), and the porosity number (χ) on the field variables were investigated using the finite amplitudes. From the linear stability analysis, expressions for the parameters, namely, R and wavenumbers, were obtained, corresponding to the bifurcations such as pitchfork bifurcation, Hopf bifurcation, Takens–Bogdnanov bifurcation and co-dimension two bifurcation. The results reveal that the local Nusselt number (NL) increases with R. The total energy is enhanced for all increasing values of R. The deformation in the basic cylindrical rolls and the flow rate are enhanced with R. The trajectory of heat flow was studied using the heatlines concept. The influence of R on the flow topology is depicted graphically. It is observed that the intensity of heat transfer and the local entropy generation are increased as R increases.

Collective mode resonances in superfluid 3He–4He mixtures

The experimentally observed first and second sound resonances caused by vibrations of a closed quartz tuning fork in superfluid helium mixtures are studied. Taking into account the full set of hydrodynamic modes of the system allows us to explain the unusual behavior of second sound resonances observed in experiments due to the redistribution of energy between the dissipative mode and the second sound mode.

Viscosity of concentrated superfluid mixtures 3He−4He when vibrating a quartz tuning fork

The possibility has been investigated for measuring the viscosity of concentrated superfluid mixtures of 3He in 4He in the temperature range 0.4−2.2 K using commercial quartz tuning forks with a resonance frequency of ≈ 32 kHz. It was found that the temperature dependence of the viscosity coefficient in a mixture with a concentration of 5% of 3He in 4He is in good qualitative agreement with the data obtained using other experimental techniques in the entire temperature range of the research. The same dependence of a mixture with 3He concentration of 15% agrees with the previously obtained data only at temperature T > 1.4 K, and at lower temperatures a difference appears that grows with decreasing temperature. The experimental temperature dependences of the viscosity coefficient obtained by different methods are compared with those calculated within the framework of the kinetic theory for the quasiparticles in superfluid 3He−4He solutions, developed by Landau, Khalatnikov, and Zharkov for the temperature range T > 0.6 K and by Baym, Saam, and Ebner for lower temperature.

Dilution Microcryostat–Insert for Microwave Spectroscopy and Magnetic Resonance

An autonomous dilution microrefrigerator manufactured as an insert into a helium cryostat with a superconducting magnet is described. In this refrigerator, the 3He circulation in the circuit filled with a 3He–4He mixture (mixer–heat exchanger–still–condenser–heat exchanger–mixer) is achieved due to the condensation of mixture vapors on the walls of the condenser, which is cooled by the 3He bath pumped out by a sorption pump, as well as entry of the condensate into the mixer under the action of gravity. An 8-mm-range resonator that contains a sample is connected to the mixer via a heat conductor; the sample is located at the center of a superconducting solenoid with a field of up to 80 kOe. Radiation passes from the generator through a waveguide to the resonator, and the signal that passed through the resonator arrives at the detector. The generator and detector are at room temperature. The device is designed for microwave spectroscopy of magnetic materials at temperatures in the range of ~0.09–3 K. The time within which the temperature is maintained at a level of ~0.1 K is 4–6 h. The results of a test experiment on the antiferromagnetic resonance in a MnCO3 single crystal are presented.

Kinetic properties of solid 3He–4He mixtures in the model of freely moving impuritons

Within the framework of the gas-kinetic model of a mixture of weakly interacting gas of quasiparticles—phonons and impurities—the dissipative properties of 3He–4He solid solutions are considered: diffusion, self-diffusion, and thermal conductivity in the range of concentrations and temperatures, where impurities of 3He can be considered as quasiparticles freely moving through the crystal. Explicit expressions are obtained for the dissipative coefficients of spin and mass diffusion and the coefficient of thermal conductivity. The observed in experiments on spin relaxation, heat transfer, and separation of solutions dependencies and parameters of quasiparticles are discussed.

Quantum phase transitions in CePdAl probed by ultrasonic and thermoelectric measurements

CePdAl has been recently recognized as a frustrated antiferromagnetic heavy-fermion compound with a pressure- or field-tuned, extended quantum critical phase at zero temperature. Identifying characteristic signatures of the emerging quantum critical phase, which are expected to be distinct from those near a quantum critical point, remains challenging. In this work, by performing ultrasonic and thermoelectric measurements down to very low temperatures in a 3He–4He dilution refrigerator in the presence of magnetic field, we are able to obtain some crucial thermodynamic and thermal transport features of the quantum critical phase, including a frustration-related elastic softening detected by ultrasound and a Fermi-surface change probed by thermoelectric effect.

Editorial

Editorial

Gamma-ray measurements in D[formula omitted] fusion plasma experiments on JET

Using capabilities of the gamma-ray spectrometry, fusion born alpha-particles were studied in recent D-3He plasma experiments on JET. A substantial population of the alpha-particles was generated in the 3He-rich plasma due to the 3He(D, p)4He reaction. Fast deuterium ions of the neutral beam injection (NBI) heating were accelerated to MeV energies with three-ion scenario D-(DNBI)-3He using radio frequency waves in the ion cyclotron range of frequencies (ICRF). A high reaction rate allowed to measure the alpha-particle production rate and their spatial distribution in the plasma by detecting 16.7-MeV gamma-rays from the 3He(D, γ)5Li reaction, which is a weak branch of 3He(D, p)4He reaction. A branching ratio of gamma-ray transitions to the ground and the first excited states of 5Li was obtained. Due to the beryllium is a main impurity of JET plasmas, intensive gamma-rays from the 9Be(D, nγ)10B, 9Be(D, pγ)10Be and 9Be(α, nγ)12C reactions were observed. Exploitation of the reaction cross-sections and the Doppler shape analysis (DSA) of gamma-lines in the recorded spectra provided the possibility to reconstruct distribution functions of the confined D-ions and the fusion-born alpha-particles.

Second sound resonances in superfluid 3He–4He mixtures

The resonances occurring during oscillations of quartz tuning forks in superfluid helium and its mixtures are studied. Quartz tuning forks are used to study various properties of helium, and also as a precision temperature sensor. Experimental observations of resonance phenomena were carried out in a wide range of temperatures and pressures, but the results of observations have not yet been exhaustively described theoretically. In this work we consider the pressure, entropy, and velocities oscillations in order to determine the conditions under which oscillations of a solid wall excite the first and second sound in superfluid helium and sound in supercritical helium, and to calculate the contributions of these processes to the formation of resonances during oscillations of closed tuning forks. In particular, the experimentally observed excitation of standing waves of pressure and entropy oscillations by an oscillating closed tuning fork, the appearance and properties of resonances depending on the temperature and pressure of helium are considered.

Helmholtz Free Energy Equation of State for 3He–4He Mixtures at Temperatures Above 2.17 K

The work presents the first wide-range equation of state (EOS) for 3He–4He mixtures based on the reduced Helmholtz free energy multi-fluid approximation model. It covers the temperature range from 2.17 to 300 K and the pressure from the vapor pressure up to 3 MPa for any given mixture 3He mole fraction. In this model, the 4He and 3He reduced Helmholtz free energy equations and departure functions from the literature are employed and only five unknown mixture parameters are needed for each given departure function. The parameters and the best model for the concerned binary mixture were determined by the Levenberg–Marquardt optimization method. With the best developed model, the liquid, gaseous, and saturated thermophysical properties of the mixture can be mostly described with an accuracy better than 5%. Furthermore, a database for the thermophysical properties of 3He–4He mixtures is generated and provided for interpolation in temperature, pressure, and 3He mole fraction. The current EOS and database can be applied to the design and optimization of ultra-low temperature refrigerators.

The turbulent drag force in superfluid 3He−4He mixtures under oscillations of a quartz tuning fork

We have studied the resonance curves of a quartz tuning fork of the fundamental frequency 32 kHz immersed in superfluid 4He and mixtures 3He–4He with 3He concentration of 5 and 15% in the temperature range of 0.35–2.5 K at saturated vapor pressure. Two types of experiments have been carried out, with a tuning fork both not covered by a bulb and coated by a bulb, i.e., in the restricted geometry. In both cases, the velocity-force dependences for the tuning fork showed a linear damping force at low peak velocities and extra drag due to the appearance of vortex lines accompanying the transition to turbulence under increasing peak velocity. These dependencies are mainly determined by the density of the normal helium component. There is a pronounced difference between superfluid 4He and mixtures of 3He in 4He, where 3He impurity particles provide a constant temperature-independent contribution to the normal component of the mixture. The extra contribution to the damping force, so-called “turbulent drag force”, decreases with concentration increase at the same peak velocity of the tuning fork that can be explained by the extension of the range of laminar flow with an increase in the concentration of 3He. We found that the drag coefficient in superfluid 4He and mixtures 3He–4He reaches a plateau at different peak velocities and different exciting forces and explained this fact by different conditions for vortex formation, depending on the different thickness of the near-wall viscous layer. The comparison between the data obtained in restricted and unrestricted geometries shows that there is an excessive dissipation of the tuning fork motion associated with the emission of the first sound wave in unrestricted geometry.