J. P. Hobson1, K. Welch2
1National Vacuum Technologies Inc., Box 4160, Postal Station E, Ottawa, Ontario K1S 5B2, Canada
2RHIC Project, Brookhaven National Laboratory, Associated Universities Inc., Upton, New York 11973
Tóm tắt
Many particle accelerators and colliders throughout the world make use of superconducting magnets to focus highly relativistic beams. These magnets are cooled to ∼4.2 K. For practical reasons, the beam pipes, encircled by the magnets, also operate at these cryogenic temperatures. This article presents a theoretical model for determining pressure profiles, in space and time, stemming from either helium or hydrogen gas leaks into the cold-bore tube with appendage pumps located at periodic intervals. It is shown that a wavelike pressure gradient propagates from the leak source at a rate which is dependent on the leak magnitude, gas species, speed and location of the appendage pumps, and the geometry and effective roughness of the cold-bore tube. Steady-state, linear pressure gradients eventually equilibrate between the appendage pumps in a magnitude commensurate with the mass flow in the beam pipe, while the approach to equilibrium is controlled primarily by the adsorption isotherm of the species. Results are given for a variety of conditions relevant to the relativistic heavy ion collider being constructed at Brookhaven, and a general procedure, with expressions, is provided for the making of similar calculations in other installations.
