A prototype experiment on cryocooler based cryopump

To characterize ITER Diagnostic Neutral Beam (DNB) in Indian test facility (INTF), ∼ 106 l/s installed pumping speed is required to ensure low re-ionization losses and stripping losses of extracted negative hydrogen ions from the ion source in presence of ∼ 14.6 Pa.m3/s hydrogen gas throughputs. Such large pumping speed will be provided using 12 cryopumps based on Cryo-sorption mode of operation and are dispersed symmetrically along the 9 m length of the test vessel. Each pump has a speed of ∼ 1 × 105 l/s.The engineering configurations of the pumps are charcoal based Cryosorption type with cryopanel at 15K temperature, cooled by a cryocooler. The pumping surface is surrounded by Chevron shaped liquid nitrogen cooled radiation shield at 85K temperature. An experimental validation of the temperature distribution on the Helium surface has been carried out on a prototype using a 20 W @ 15 K cryocooler (Sumitomo make). The experiment establishes temperature uniformity within 0. 5 K at the extremities of the Helium panel for heat loads that is a factor of 1.5 higher than the estimates, and closely corroborates the simulation data, thereby ensuring a reliable pumping performance. The results of the prototype experiment leads to a technical decision of incorporating 12 cryocooler based cooling for the Helium section, thereby obviating the need for a dedicated 15 K Gaseous Helium Supply System. The paper shall present a brief configuration of the Cryopump, the details of the prototype, the experimental results and the conclusions arrived at.