Large diameter horizontal helium cryostats

The designs of two, large, horizontal helium cryostats with vapour cooled radiation shields (a gravitational wave detector cryostat and an accelerator cryostat) are described. The problems of cooling heavy inserts and large vertical indium seals with stainless steel fianges are discussed.     

Analysis of the cooling of continuous flow helium cryostats

A mathematical model of the cooling of a continuous-flow cryostat which takes into account real values of the specific and latent heat of the cryogenic fluid and of the specific heat of the cryostat material is presented. The amount of liquid in the cooling fluid and four parasitic heat flows, caused by radiation and heat conduction in the construction materials and in the rest gas in the vacuum insulation, are also taken into account. The influence of different model parameters on performance, particularly in the non-stationary regime, is demonstrated by means of numerical solutions of the modelling equations. A quantitative criterion which assesses the properties of the planned cryostat, is formulated. The theoretical conclusions are compared with measurements performed on a continuous flow helium cryostat.     

Calculation of the helium thermodynamic state in rotating cryostats

The present paper contains basic essential data for the design of rotating cryostats. The effect of the filling factor, angular velocity of rotation, reduced temperature at the axis of rotation and the method of helium supply to a rotating cryostat on temperature, pressure and density distribution is discussed. The maximum sub-cooling and distance from the axis of rotation at which the critical pressure is reached is studied theoretically. For vapour phase quasi-saturation there is a good agreement between the calculated data on temperature distribution and the experimental results available.     

Optimal sizes of suspension tubes in nitrogen-free helium cryostats

An analytical method is proposed for the computation of the optimal size of suspension tubes of nitrogen-free helium cryostats.     

Porous heat exchangers for continuous flow helium cryostats

An investigation was made into the effective application of porous heat exchangers of cylindrical shape through which fluid passes axially. On the basis of a theoretical analysis the conclusion derived was that the best thermal efficiency can be reached by the use of porous material with a large heat-exchanger surface, a high radial and low axial thermal conductivity (ie with a marked anisotropy of thermal conductivity), and a small radius of the heat exchanger operating at lower flows of cooling agent. The results of experiments carried out at helium and nitrogen temperatures are presented. These results have confirmed the high effectiveness of porous heat exchangers, even in comparison with chamber-type heat exchangers. For the temperature range from 1.5 to 300 K the heat exchangers composed of highly conductive metal nets (mesh gauge of the order of magnitude of 10^?1 mm) stacked perpendicularly to the direction of flow of the cooling fluid, appear to be the most promising ones.     

Interfacing small closed-cycle refrigerators to liquid helium cryostats

Several different means of connecting small closed cycle refrigerators to liquid helium cryostats for the purpose of reliquefying the boiloff or reducing the boiloff rate are described. Interface principles which enhance the reliability and serviceability are presented. Most of the interfaces which are described permit the refrigerator to be serviced while maintaining liquid helium in the cryostat.     

High voltage heavy current leads for liquid helium cryostats

Properties of insulation for high voltage cryoelectric equipment are considered. The results of investigation into surface dieletric 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 ere tested at 80 and 100 kV with 5.5 kA current and the results are presented.     

Study of heat transfer in the gas-cooled necks of helium vessels and cryostats

A method of calculating heat flow along helium-cooled necks is refined on the basis of an experimental study.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 5, pp. 749–753, November, 1984.     

Numerical investigation of radiative heat exchange in the throats of helium cryostats

A mathematical model of radiative heat exchange in the throats of wide-necked helium cryostats is analyzed. A comparison of the numerical results with known calculated and experimental data shows their good agreement.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 4, pp. 627–634, October, 1985.     

Computation of the rate of helium evaporation in nitrogen-free cryostats with high-vacuum insulation

An approximate method is proposed for computing the rate of liquid helium evaporation and the temperature of the radiation shields in cryostats in which the shields are cooled by vapors of evaporating helium.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 19, No. 1, pp. 53–61, July, 1970.     

Rotating cryostats for heat transfer and fluid flow studies on the helium cooling of superconducting generator rotors

This paper describes the design and construction of two 1 m diameter rotating cryostats for the study of the heat transfer and fluid flow behaviour of helium at 3000 r.p.m. towards the design of refrigeration systems for superconducting a.c. generators. The first LO rotating cryostat has been in continual operation since 1976 and a great deal of basic data has been produced on the high convective heat transfer performance of helium, on the self-pumping capability of helium gas loops and their associated intrinsic instability, on the behaviour of superfluid helium and the He I/He II interface, and on the forward and reverse flows in thermo-siphon loops, together with a wide range of practical experience with rotating helium and instrumentation at 3000 r.p.m., 5000 g or 150 ms⁻¹ tip speed. A second LX rotating cryostat with increased working volume is also described.     

Calculation of the emergency regimes of cryostats

Analytical expressions are obtained that allow one to evaluate the dependence between the time of pressure growth in cryostats containing cryogenic fluids and the thermal energy entering the cryostat. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 3, pp. 413–419, May–June, 1997.     

Performance comparisons of space borne cryostats

We discuss the performance of liquid helium cryostats that have flown in space or are planned for space flight. Usual figures of merit are total cryostat mass or depletion rate of the cryogen. These often fail to accurately represent other important characteristics which affect cryostat performance such as the method used to survive launch lock-up or the temperature of the cryostat vacuum shell obtained by radiative cooling. To address these issues, we define the ratio, H/R in W day/l as metric to judge cryostat performance. The parameter H=σ_BA_tank(T⁴_shell−T⁴_tank) is the Stefan Boltzmann law for energy transfer to the helium tank, where σ_B is the Stefan Boltzmann constant, A_tank is the surface area of the cryogen tank and T_shell and T_tank are the vacuum shell and cryogen temperatures. The average cryogen depletion rate R=V_f/t is computed using the total cryogen volume, V_f, at the last fill before launch, including the volume of ‘booster tank' cryogen if used and the cryogen lifetime, t, to depletion on-orbit. Cryostats launched on the Space Shuttle have the same H/R≈60 W day/l whether the cryogen was liquid helium or solid neon, and for a broad range of vacuum shell temperatures 113<T_shell<300 K, cryogen volumes 2200>V_f>85 l, and mission times, 9 days to >2 years. Cryostats launched on unmanned rockets have a higher H/R≈300 W day/l. Only one, the X-Ray Spectrometer (XRS), out of the four solid neon and two solid hydrogen cryostats showed a clear advantage of using a cryogen other than liquid helium.     

Thermal links for reducing the heat leakage to cryostats

An experimental study was made concerning the effect of thermal links on the rate of helium evaporation in a nitrogen-free cryostat with a few suspension tubes. As a result, the optimum number and location of links on such suspension tubes has been established.     

Application of magnetofluid seals for high-speed rotating cryostats

A practical application of the magnetofluid seals in a rotating cryostat is described. These seals ensure both the sealing of the cold shaft going through several series-connected chambers operating under various pressures (up to 10^?3 Pa), and the coolant evacuation out of the test section. The peculiarities of their operation at high rotational velocities (ω = 10–40 ms^?1) low temperatures and high vacuum are shown.