Pumping speed offered by activated carbon at liquid helium temperatures by sorbents adhered to indigenously developed hydroformed cryopanel

Abstract

Towards the aim of developing a pump with large pumping speed of the order of 1 L/(s-cm2) or above for gases like hydrogen and helium through physical adsorption, development of activated carbon based sorbents like granules, spheres, flocked fibres, knitted and non -knitted cloth was carried out. To investigate the pumping speed offered, a test facility SSCF (Small Scale Cryopump Facility) which can take samples of hydroformed cryopanel (a technology developed in India) of size ∼500 mm x 100 mm was set up as per international standards comprising a dome mounted with gauges, calibrated leak valve, gas analyser, sorbent adhered to cryopanel etc. The cryopanel was shielded by chevron baffles. Pumping speed measurements were carried out for gases like hydrogen, helium and argon at a constant panel temperature in the pressure range of 1x10-7 to 1x10-4 mbar, and pumping speed was found to be in the range of 2000 L/s for a pressure range 1x10-6 to1x10-4 mbar, and 4000 L/s for pressure range 1x10-7mbar and below for a pumping surface area of ∼1000 cm2 thus giving an average pumping speed of about 2 L/(s-cm2). Using the Monte Carlo codes SSCF was modelled and simulation studies performed. Parameters like sticking coefficient, capture coefficients affecting the pumping speed were studied. This paper describes the experimental setup of SSCF, experimental results and its correlation with Monte-Carlo simulation.