[en] Cryogenic applications extend over the whole range of power types: from small power types with infra-red detection. Satellite communication, cryopumping and the medical applications of superconductors to the large power types with cryogenic alternators and superconductor magnets for fusion. The question actually arises wether magnetic refrigeration cycles can have higher reliability and higher efficiency than classical gas refrigerating machines. Before discussing the state of the art, we will point out some general thermodynamic conditions that have to be respected for magnetic cycles as for gas cycles. Magnetic Carnot cycle refrigerators are now capable of pumping heat efficiently when all the cycle is executed in liquid helium temperature range

[en] It is pointed out that magnetic refrigeration can provide additional cooling for infrared detectors on space missions, taking into account the Shuttle Infrared Telescope Facility (SIRTF) and the Large Deployable Reflector (LDR). From a temperature of 2 K provided by the primary cryogens, magnetic refrigerators could cool bolometers or pumped photoconductors to 0.1 K or below. Such a reduction in operating temperature would increase the sensitivity for bolometers, while the response at longer wavelengths for pumped photoconductors would be improved. Two types of magnetic refrigeration cycles have been proposed. One type uses a complete demagnetization. The present investigation is concerned with the second type, which uses a feedback-controlled isothermal demagnetization, taking into account the temperature stability limits. Attention is given to control system resolution, thermometer noise, reaction time, and thermal time constants

[en] The Energy Saver Refrigeration System is based on the concept of a central helium liquefier (5000 l/hr) providing liquid to 24 satellite refrigerators (966 W at 4.6/degree/K), which operate as amplifiers with a gain of 12. This concept was tested, cooling two 125 m long strings of superconducting magnets. The test was run using one satellite refrigerator operating as the ''central liquefier'', shipping liquid helium through a 250 m long transfer line to a second satellite refrigerator, which in turn cooled the magnets. In addition to testing the satellite concept, the heat loads of the magnets and transfer line were also measured. 3 refs

[en] Studies related to the development of magnetic refrigeration and heat pump systems in temperature ranges from 4 K to ambient temperature and above have been conducted, taking into account the testing of the properties of packed-particle beds and regenerators at cryogenic temperatures as low as 4 K as an essential part of these studies. The present paper provides a description of the developed experimental apparatus and presents the results of recent measurements on packed-particle beds in the liquid helium and liquid nitrogen temperature ranges. Attention is given to a schematic of the apparatus and the data acquisition system, the various modes of gas flow, a schematic of a typical test bed with thermocouple positions, the calculation of transient heat transfer rates at different positions in the bed, the governing equations, and the procedures used for solving these equations. 8 references

[en] Methods of adiabatic demagnetization were limited until very recently to one-shot operations or to power levels below 1 mW. This paper describes the results of a reciprocating magnetic refrigerator operating between 1.8 K and 4.2 K, with a useful power greater than 1 watt. In this type of machine there are various problems associated with heat transfer between magnetic substance and heat sources and inside the substance itself. The refrigerator described here overcomes some of these problems and achieves good efficiency

[en] This thesis includes three parts. (1) Construction of a study alternating refrigerator. This is essentially a double acting machine, with ancillary refrigeration by helium expansion. This refrigerator operates in a liquid helium bath at 4.2 K and the cold source is a superfluid bath whose temperature can be brought down to 1.6 K. The magnetic components, actuated by a periodic translation movement, are magnetized cyclically in the 4.2 K bath, then demagnetized in the central bath forming the cold source. The bar slides in guide bearings, isolating the central chamber of the 4.2 K bath. This can be cooled through the copper wall by the refrigeration bath. A relief valve and a level gauge enable the operation of the ancillary refrigerator to be adjusted. A temperature of under 1.8 K was obtained in a superfluid bath at atmospheric pressure. (2) Study of possible thermal exchange improvements in supercritical helium by artificially creating turbulency between two walls. This study could concern rotary machines described in an addendum. (3) Some physical properties of paramagnetic rare earth salts are also studied

[en] An experimental prototype magnetic refrigerator based on the well known adiabatic demagnetization principle is described. A continuous process is employed in which gadolinium garnet follows successive magnetization-demagnetization cycles between a hot liquid helium source at 4.2K and a cold superfluid helium source at T<= 2.16K. The performance achieved with the first version is as follows: - limiting temperature at zero utilizable power: 1.32K; - utilizable power of 1.2W at 1.8K with an efficiency of 45%. In a second version, it was possible to increase the efficiency to 64% for a utilizable power of 0.9W at 2.1K. Same general remarks are made on the possibility of extrapolating to a 300W refrigerator operating at 1.8K, on a continuous rotating magnetic refrigerator of a different design, and on efficiency comparisons between gas and magnetic refrigerators

[en] The Cryogenic System of the Satellite Refrigerator for the Energy Saver Accelerator Ring comprises 12 interrelated closed loops and several open loops. A quasi-optimal algorithm to control the Cryogenic System, under different modes operation, is described. The constraints imposed to define these algorithms and the process followed to characterize the functional parameters are described. A report on the results obtained with the algorithms in a test facility will be presented. 6 refs

[en] As it known the resolution and sensitivity of Electron Spin Resonance (ESR) experiment increases with microwave frequency. Thus the working frequency of modern magnetic resonance spectrometers shifts to more and more high values as the technology progresses with time. Today it reaches area corresponds to millimeter and submillimeter wavelength band. The main component part of ESR spectrometer is the resonator architecture, concentrating electromagnetic energy on the sample under study. The electro-dynamical structure amplifies a weak high-frequency informative ESR-signal from the specimen. The open resonator is one of the most perspective structure for spectroscopy due to its high quality factor as well as due to other intrinsic features. This paper is devoted to the solution of a problem of design and investigation of the non-cooled open resonator experimental cell for ESR experiment with the cooled sample. The sample under study is cooled with external source (continuous flow cryostat) and placed between reflectors of open resonator. The result of this investigation of key electro-dynamical properties of open resonator designed for study of specimens cooled down to cryogenic temperatures are presented. Results of test ESR-measurements demonstrating virtues of the resonator structure are given

[en] The simple evaluation model utilizing the selective parameters for the preliminary analysis for magnetic refrigerator (MR) development is proposed in this paper. The magnetocaloric effect and the related magnetic field applied for MR are also discussed. The model and system analysis following the algorithm expressions and the material characteristics required for MR are arranged and derived in related evaluation terms. The simulation results verify the feasibility and applicability for this simple evaluation model