We give a concise review of the empirical properties of liquid and solid 3He-4He mixtures and their phenomenological interpretation. The bulk of the paper is about dilute solutions of 3He in liquid 4He at temperatures well below the tricritical point, where the roton and phonon excitations are comparatively unimportant. We describe the thermodynamic properties in terms of the Landau-Pomeranchuk 3He quasiparticles and the effective interaction between them, introduced by Emery and Bardeen, Baym and Pines. The scattering amplitude, needed to fit the low temperature transport properties, and the effective interaction are related, provided the multiple virtual scattering calculated by Fu and Pethick is included. The multiple scattering should always be included, even for very small concentrations. We present the evidence for the velocity dependence of the effective interaction, and urge that this also be taken into account in the interpretation of experiments. We give a short description of spin-polarized liquid mixtures and of the possibility of pairing superfluidity in solutions of 3He in liquid 4He. The existence of supersaturated solutions may be a way to attain p-wave pairing at accessible temperatures. Beacause of phase separation, the concentration of 4He in dilute mixtures of 4He in liquid 3He becomes very small as the temperature is lowered, making it unlikely that a degenerate Bose gas of 4He quasiparticles can be produced. In addition, the superfluid 4He film on the walls of the vessel makes the achievement of a supersaturated solution very difficult. We briefly review the measurements of the phase separation, the density and specific heat, and show that the spectrum of the 4He quasiparticles and the role of their effective interactions are still in doubt. In solid 3He-4He mixtures the thermodynamic properties and the phase diagram, including the crystallographic transformation, fit the regular solution model very well. On the other hand, dilute solid solutions of either 3He or 4He in the other isotope have NMR relaxation times and spin diffusion which agree with the theory of impuritons (mass fluctuation waves) which tunnel more or less freely through the crystal. The reconciliation of these two theories and an explanation of the accuracy of the regular solution model remain mysteries. A deviation from the regular solution model, the fluctuation specific heat above the phase separation temperature, is discussed in detail. The review includes two tables which list most of the experiments on liquid and solid 3He-4He mixtures published between 1975 and 1990.

Lectures on the properties of liquid and Solid 3He-4He mixtures at low temperatures

A superconducting rectifier fluxpump has been used for the dc power supply of the magnet system of the CMD-2 detector on the VEPP-2M collider at the Budker Institute of Nuclear Physics in Russia since 1989. The fluxpump provides a complete pumping cycle: charging the magnet system, stabilization of the magnetic field, and discharging. The fluxpump consists of an air-core current step-up superconducting transformer and two groups of thermally controlled superconducting switches arranged as a fullwave rectifier. Critical output current during the test was 5.4 kA. The accuracy of the field stabilization provided by the fluxpump is 2.5/spl middot/10/sup -5/. The fluxpump has exhibited reliable and safe operation during its entire history of use.

Superconducting rectifier fluxpump for magnet system of the CMD-2 detector

The Zharkov-Silin Fermi Liquid theory of solutions of4He in normal (non-superfluid) liquid3He is reviewed and slightly extended. The theory is expected to be valid only below ∼0.1 K, and it predicts that there should be a hundred-fold increase in the diffusion coefficient as the temperature is lowered into this region. The limited range of validity explains the apparent disagreement between the recent very low temperature measurements of the phase separation line by Nakamura et al. and extrapolations from higher temperatures. In the low temperature experiments the4He concentration X4 is so small that there is no macroscopic phase separation, only a gradual thickening of the4He-rich film on the walls. We confirm that the phase separation temperature Tps(X4) estimated from the thickening is close to the values which would be observed in an ideal experiment with a macroscopic phase. Fits to Tps(X4) including the new data show that the4He effective mass m
 4
 *
 is close to, and may be equal to, the bare mass m4. The difference in binding at zero pressure between4He in liquid4He and in liquid3He is (E44−EE43)/kB=(0.21+0.03/−0.01)) K. Using the volume measurements of Laheurte to calculate the pressure dependence of E43 indicates that the difference in binding has a minimum of (0.0±0.2) K near ∼11 atm. This implies that the solubility of4He in3He is enhanced in this region of pressure. The behavior of the spinodal line at low temperature, and the possibility of observing Bose condensation in a metastable solution of4He in liquid3He are also discussed.

The Fermi Liquid theory of 4 He in 3 He

A full-wave superconducting rectifier for 100 kA has been developed. Typical design values of this device are: a secondary current of 100 kA, a primary amplitude of 20 A, an operating frequency of 0.5 Hz, and an average power on the order of 100 W. The rectification is achieved by means of thermally controlled superconducting switches with recovery times of 150 to 300 ms. A description of the rectifier system is given. The first experiments, in which the rectifier was tested at up to 25 kA demonstrate reliable and fail-safe operation of the rectifier at lower current levels. It was, for example, successfully used to load and unload a 25-kA coil at a rectifier frequency of 0.4 Hz and an average power of 30 W. During tests without any load, it was found that the secondary circuit of the transformer quenches at about 60 kA. Therefore, it is unlikely that the rectifier in its present configuration will attain 100 kA.

/pdf/development-of-a-thermally-switched-superconducting-44s47w56dk.pdf

Development of a thermally switched superconducting rectifier for 100 kA

The temperature and concentration gradients ∇T and ∇x created by a heat flow in a superfluid 3He–4He mixture with a concentration of 9.8% 3He are measured in the steady state in the temperature range T=70–500 mK. It is found that the ratio ∇x/∇T obtained in the experiment can be described on the basis of a dependence of the osmotic pressure on the temperature and concentration. The data are used to find the thermodiffusion ratio and, hence, the thermodiffusion coefficient of this mixture.

Relation between the temperature gradient and concentration gradient in superfluid 3He–4He mixtures

The feasibility of superconducting rectifier-fluxpumps has to be demonstrated at current levels of 10 - 100 kA, where is asked for in the superconducting devices now being planned. An intensive program has been started at the low temperature division of the University of Twente to construct such high current rectifiers. A thermally switched 9 kA full wave rectifier-fluxpump will be presented. The s.c. rectifier consists of a current step up transformer, two reliable thermally activated switches and a dummy load inductor. Both, load coil and rectifier are fully protected against failure modes. The rectifier is now (March, 1981) under test and has energized yet the load coil to a level of 4.5 kJ at 9 kA within 150 seconds, frequency 0.11 Hz, mean power 30 W, the efficiency of the energy conversion is 99,1%.

/pdf/a-thermally-switched-9-ka-superconducting-rectifier-fluxpump-3gxj6vy34x.pdf

A thermally switched 9 kA superconducting rectifier fluxpump

https://ris.utwente.nl/ws/files/6738613/Klundert77osmotic.pdf

The osmotic pressure of 3He-4He mixtures along the phase separation curve

A 25 kA, 1.5 kW superconducting rectifier system has been developed. This rectifier system working like an a.c.-d.c, converter with a primary current of 35 A at 0.1Hz, will energize a 25 kA coil with an average power of 5.4 MJ/hr and a proposed energy efficiency of at least 96%. Such a highly efficient device might work instead of a 'normal' rectifier and a pair of 25 kA current leads with its energy loss of at least 2 W/kA. The 25 kA current step-up transformer has been tested succesfully concerning its maximum current (26.4 kA) and a.c. losses (2 W at 25 kA and 0.1Hz). A conductor for the 25 kA switches has been manufactured and processed into the switching system. Their construction is described.

/pdf/status-report-of-the-three-phase-25-ka-1-5-kw-thermally-4sn4wx2k4z.pdf

Status report of the three phase 25 kA, 1.5 kW thermally switched superconducting rectifier, transformer and switches

Within the scope of our research program for a 25 kA superconducting rectifier, we have built a 25 kA s.c. coil being a single layer solenoid with a bore of 0.45 meter and a volume of 52 litre. The starting point for the design was to avoid any metallic structural material. This unique coil consists of 26 turns of a Rutherford cable in one layer covered at the outside with 6 millimeter glassfibre reinforced epoxy, in order to lower the azimuthal and axial stresses in the conductor to acceptable values. The coil has been vacuum impregnated with a glassfilling factor of 0.529. The paper describes the strength calculations and the construction details. A theoretical analysis of the mechanical behaviour of the glassfibre-epoxy-conductor lamination is given.

/pdf/a-25-ka-2t-78-kj-52-litre-superconducting-test-coil-strength-185451up4a.pdf

A 25 kA, 2T, 78 kJ, 52 litre superconducting test coil. Strength calculations and construction

The successful test of a 25 kA superconducting rectifier is reported. This rectifier is an important component of a complete cryogenic power system to energise high current superconducting magnets.

https://hal.archives-ouvertes.fr/jpa-00223604/document

H.A. Steffens

Papers

A thermally switched 9 kA superconducting rectifier fluxpump

The osmotic pressure of 3He-4He mixtures along the phase separation curve

Status report of the three phase 25 kA, 1.5 kW thermally switched superconducting rectifier, transformer and switches

A 25 kA, 2T, 78 kJ, 52 litre superconducting test coil. Strength calculations and construction

A 25 kA, 0,5 kW THERMALLY SWITCHED SUPERCONDUCTING RECTIFIER