Cryosorption pumping for intersecting storage rings

The pumps selected for storage ring vacuum systems must efficiently pump helium and hydrogen at pressures below 10-10 torr. In addition, they have to work in a background of nuclear radiation. The presence of an ample supply of liquid helium in the proposed Intersecting Storage Accelerator (ISABELLE) makes cryosorption pumping very attractive. We have investigated, therefore, the behavior of Linde Type 5A molecular sieve, bonded to a stainless steel panel, at 4.2 and 50K in the pressure range from 10-11 to 10-8 torr. By fitting our experimental data, we obtained the constants K and B in the equation theta = K exp(-- epsilon2B) which can be used to calculate the adsorption isotherms for helium and hydrogen on bonded molecular sieve 5A at various temperatures. Furthermore, we have determined the causes of a steeper slope of the isotherms in the 10-11 torr range. Finally, a pump containing a cryosorption panel was exposed to a flux of 1.7 x 105 protons and pions per second which resulted in no pressure change. A cryosorption pump was designed which can be operated at 4.20K either inside or outside the superconducting magnet dewars. (U.S.)