1. magnetic confinement - ENEA - Fusione
1. magnetic confinement - ENEA - Fusione
1. magnetic confinement - ENEA - Fusione
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120<br />
4. MISCELLANEOUS<br />
4.8 Cryogenics<br />
The prototype consists of three refrigerating stages; the first can be cooled down to<br />
about <strong>1.</strong>5 K, by pumping on a liquid 4 He bath, which allows liquefaction of the 3He<br />
and the 3 He/ 4 He mixture stored in the second and third stages, respectively.<br />
Pumping on liquid 3 He in the second stage makes it possible to achieve<br />
temperatures below 300 mK, thus ensuring a good phase separation of the gas<br />
mixture in the mixing chamber. The final cool-down is realised by pumping on the<br />
3 He rich phase.<br />
Preliminary experiments gave encouraging results, with a minimum recorded<br />
temperature at the mixing chamber of about 127 mK. The temperatures of the second<br />
and third stages, during a typical dilution test, are as follows. The mixing chamber<br />
temperature reaches a first plateau at 175 mK, lasting about 3 h, then it achieves its<br />
minimum (135 mK in this run). The existence of the first plateau in not yet well<br />
understood. The overall duration of the dilution process (T
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