NEW TYPES OF DILUTION REFRIGERATOR AND SPACE APPLICATIONS

Dilution refrigerators are now commercially available with a lowest te mperature of the order of 5 mK. However, for special applications, spe cial purpose refrigerators are needed. After a presentation of the dif ferent possible ways to cool down by dilution of He-3 in He-4, we disc uss two designs that give more flexibility than the classical dilution refrigerators: (i) dilution refrigerators without 1 K pot; (ii) doubl e still systems to allow a precooling by circulation of the mixture. I n the second part, we compare the different possibilities to obtain lo w temperatures in space (T less-than-or-equal-to 100 mK). Finally, we describe the dilution in open cycles which is presently the only dilut ion refrigerator insensitive to gravity.