Design and preliminary tests of the liquid helium cooled MFTF cryopumping system

Abstract

The Mirror Fusion Test Facility at Lawrence Livermore Laboratory will contain three distinct cryopumping systems: (1) A large internal cryoarray to pump deuterium at pressures from 10−5 to 10−8 Torr. The array, cooled with liquid helium to 4.35°, has a total surface area of 1100 m2. (2) External regeneration pumps for initial pumpdown of the chamber and for removal of up to 9×105 Torr l of deuterium after warm‐up of the internal array. These pumps are liquid helium cooled and operate between 0.6 and 10−6 Torr. (3) External cryosorption pumps for scavenging helium and hydrogen deuteride at partial pressures as low as 2×10−9 Torr. Utilizing adsorption on argon, these pumps operate at 2.7 K. All these systems are described and test data on the regeneration and cryosorption pumps are presented. Initial tests have demonstrated the ability of the regeneration pumps to perform in the 10−1 Torr range (2×104 l s−1 for N2 at 0.15 Torr) and the cryosorption pumps to absorb helium at very low pressure (6000 l s−1 at 2×10−9 Torr for each pump) where practical data has not yet been published.