Cryogenic Subsystem to Provide for Nominal Operation and Fast Regeneration of the ITER Primary Cryo-sorption Vacuum Pumps

The ITER cryogenic system includes provision for cooling the eight cryo-sorption pumps that maintain vacuum conditions within the tokamak plasma vacuum vessel. The eight pumps are operated such that at any given instant four pumps pump the plasma vessel and four pumps are undergoing four sequential stages of regeneration, each having a duration of 150 s. The regeneration includes a cold helium exhaust stage, warm-up from 4.5 K to 80-100 K, desorption and pump-out of released gases and cool-down from 80-100 K to 4.5 K. Thus after every 150 s of operation one of the four pumps is taken off-line for regeneration and another just-regenerated pump is restored to the set of four pumps that provide the nominal pumping.This paper presents the current design status of the cryogenic subsystems for cooling and heating the cryopumps during pumping and fast regeneration and details of the fluid-dynamic numerical analysis of the cryopumps (Vincenta code) used to study the transient behaviour of helium flow in the cryo-sorption panels during regeneration