Gas desorption and surface conditioning of a synchrotron radiation source

Synchrotron radiation induced neutral gas desorption from baked Al alloy vacuum chambers cleaned using alkaline detergents has been measured in a test beam line at the DCI storage ring at LURE, Orsay, France.The gases desorbed were H2, CH4, CO and CO2 and with time the H2 and CO desorption decreased as D−1/2 where D is the radiation beam dose in mA hours. Similar results for electron induced neutral gas desorption from small samples showed a similar behavior and led to the proposal of a model of gas diffusion from near surface layers and from the bulk to the surface which determined the desorption characteristics. For H2 the model described well the behavior of the H2 desorption.Measurements of the photoelectron currents produced at 11 mrad glancing angle of incidence and also at normal incidence, when compared with calculation, showed differences which could be explained if the photons with energies up to between 1.2 and 1.5 keV were reflected at 11 mrad with reflectivities approaching 1. Using published...