Operation of 3He4He dilution refrigerator with newly developed turbomolecular pump

✍ Scribed by K. Uhlig; W. Hehn

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 214 KB
• Volume: 29
• Category: Article
• ISSN: 0011-2275
• DOI: 10.1016/0011-2275(89)90300-7

✦ Synopsis

torque on the tight contacts improved the contact resistances from values between 5 and I0 /~ to values between 1 and 2/zQ. 6 Tests with variable forces on the contacts were also carried out. The effect of the force was not reversible and the results for a particular force depended on whether the level of force was increasing or decreasing (see Figure 2). In all cases the effect of force on the contact resistance was not very great. With a decreasing force good contact is maintained with only a very small force applied on the contact. Friction in the sliding O-ring seal probably explains this effect. 7 With total helium gas flow of 0.022 gs-1 at I= 0, extraction of the two leads reduced total helium consumption to 0.007 gs-1, which is the evaporation rate of the cryostat alone.

Conclusions

Research and technical notes

At liquid helium temperature with 375 N force, the values of electrical contact resistances are reproducible and fall in the range 5-10 /all. With 100 A these values are compatible with a thermal dissipation of 0.1--0.2 W. A small torque on a tight contact improves the contact resistance by a factor of five (thermal dissipation 20-40 mW). The liquid helium consumption due to the Joule dissipation of the gold contacts is small compared to the saving when the leads are extracted. Using the average values obtained, it is estimated that with a magnet operating time of 6 h per day (at 100 A), disconnectable current leads can increase the efficiency by a factor of two over that for permanent current leads.