Study on forms of activated carbon related to application in CryosorptionCryopump

Abstract

Cryo-sorption Cryo-pumps operating at liquid helium temperature offer large pumping speed and hence find application in pumping magnetically confined fusion grade machine. Enormous amount of exhaust gases such as isotopes of hydrogen from reactor grade machine are pumped by such pumps. Micro-porous activated carbon as sorbents operated close to 4.2 K are used in cryosorption pumps. The development of such pump requires selection of right candidate material as sorbents and their characterization. Most of the sorbents are chosen based on their adsorption behavior and pore size along with cryogenic compatibility and outgassing/degassing behavior. Adsorption isotherms for gases to be pumped help to select the suitable forms of activated carbon. Other parameters include outgassing rate and degassing rates data. For application in cryopump the activated carbon sorbents are bonded to SS panel using an adhesive. To select suitable adhesive-sorbent bonding, experiments were performed to study the adsorption isotherm nature, pore size, outgassing and degassing rates. After characterization of sorbents for their use in cryosorptioncryopump, sorbent coated panel were studied for performance to absorb gases and used as pump in a Single Panel Cryopumping Facility (SPCF). Pumping speed of 2-3 l/s-cm2 was achieved for hydrogen and helium gases.This paper describes the sorbent selection details, study related to their out gassing and degassing ratesand finally pumping speed to select them for using as a potential sorbents to make a pump.