Helium cryopumping for fusion applications

Abstract

Large quantities of helium and hydrogen isotopes will be exhausted continuously from fusion power reactors. This paper summarizes two development programs undertaken to address vacuum pumping for this application: (i) A continuous duty cryopump for pumping helium and/or hydrogen species using charcoal sorbent and (ii) a cryopump configuration with an alternative shielding arrangement using charcoal sorbent or argon spray. A test program evaluated automatic pumping of helium, helium pumping by charcoal cryosorption and with argon spray, and cryosorption of helium/hydrogen mixtures. The continuous duty cryopump pumped helium continuously and conveniently. Helium pumping speed was 7.7 l/s/cm2 of charcoal, compared to 5.8 l/s/cm2 for the alternative pump. Helium speed using argon spray was 18% of that obtained by charcoal cryosorption in the same (W-panel) pump. During continuous duty cryopump mixture tests with helium and hydrogen copumped on charcoal, gas was released sporadically. Testing was insufficient to explain this unacceptable event.

Axisymmetric Magnetic Mirror Fusion-Fission Hybrid

“…Studies of ITER cryopump regeneration have found three regeneration temperature regimes: 90 K releases all hydrogen isotopes and helium, 300 K releases all other gases except water, and 475 K releases water [Hauer 2007]. Helium pumping with cryopanels requires special techniques have been developed [Sedgley 1988]. The regeneration system for a steady state facility is more challenging than for a low-duty factor facility like ITER, but should be addressed by neutron sources before a hybrid is built.…”

“…Pump the gas in the end tank. All are readily pumped by cryosurfaces, with one exception: Helium is harder to cryopump, but can be pumped with surfaces below 4.6 K, or by spraying Argon gas onto a cryosurface to weakly bond to helium, or by coating the cryosurface with activated carbon [Sedgley 1988, Dremel 2009]. …”