Measurement of the primary phodesorption yield at 4.2 K, 77 K and room temperature in a quasi-closed geometry

In the context of the Large Hadron Collider project, the normal incidence photodesorption yield of neutral gases from a stainless steel surface has been measured at 4.2 K, 77 K and room temperature. The yields were measured using a synchrotron radiation photon beam with a critical energy of 45.3 eV, which is very near that to be expected in the LHC. It has been shown that the primary photodesorption yield decrease with decreasing temperature. The gases desorbed were H2, CH4, CO and CO2. At 4.2 K and 77 K the H2O primary photodesorption yield was practically zero. At room temperature the primary photodesorption yields were 5 10-4, 1.6 10-5, 2.5 10-4 and 2.2 10-4 molecules photon-1 respectively for H2, CH4, CO and CO2. At 77 K the primary photodesorption yields of H2, CH4, CO and CO2 were reduced by factors of 2, 4, 17 and 32 respectively with respect to room temperature. At 4.2 K, these corresponding reduction factors were 14, 20, 42 and 31.