Pumping speed of Hydrogen and Helium gases using activated carbons as sorbent material at liquid helium temperature for cryopump applications

Abstract

Cryopump is a widely studied subject and with an inherent scope for improvement. The newlinechallenge lies in pumping the voluminous amount of exhaust gases of the order of 2000 to newline4000 mbar-l/s (especially helium) in a continuous mode. Pumping a colossal mass of gases is newlinea topic of intense demand in the field of vacuum science. The areas demanding massive newlinepumping speed include environmental test facility in space research, fusion plasma devices, newlineaccelerators, laser interferometer gravitational-wave observatory like LIGO, etc. The required newlinepumping speed is of the order of 100 to 500 thousand-l/s, and the market of vacuum pumps newlinefalls scanty of the kind of the pumps needed to fulfil such requirements. Also, when it comes newlineto the pumping of the large volume of light gases like helium and hydrogen, there is a newlinelimitation with commercially available solutions. newlineThe principal objective of the work presented is an experimental investigation of using a newlinespecific kind of charcoal with large surface area, an adhesive which adheres charcoal to metal newlinecryopanels and sorbent coated cryopanels sustaining high temperature which helps in newlineremoving adsorbed gases from pores of the sorbent making it fresh surface. The study of newlineadsorption isotherm of charcoal was carried out to know its pore surface area, pore-volume, newlinepore size, etc. The sorbent used is coconut shell charcoal, it is microporous with pore size in newlinethe range of lt 2 nm and pore surface area of 1285 (± 5%) m2/g. The glue/adhesive was newlinecharacterized for its vacuum compatibility, thermal conductivity, and thermal cycling. To the newlinemetal surface, the charcoal coating is done using a glue. The glue is thermally conducting. It newlineis stable during thermal cycling from 4 K to 200°C and is vacuum compatible with a low newlineoutgassing rate. Indigenously developed charcoal coated sample panels were tested for newlinethermal cycling from 4 K to 2000C. Charcoal and glue was then, used to coat cryopanels with newlinesurface area of 0.1 m2. newlineThe cryopanels are a special kind of heat exchanger plate formed by j