Photon stimulated desorption of unbaked stainless-steel vacuum chambers

Two stainless-steel vacuum chambers, after putting them through a usual lab oratory ultrahigh vacuum processing, have been exposed to a white synchrotr on radiation photon beam, 3.75 keV critical energy at DCI. However, no "in- situ" bake out was performed on the vessels before the irradiation. The fir st test chamber was a simple 130 mm diameter circular tube 3.6 m in length. Beam scrubbing for a photon dose of 2.3 x 10(23) photons m(-1) was found t o decrease the molecular yields to below 10(-5) molecule per photon for the main relevant gas species CO and CO2. Wall pumping speeds developed by irr adiation for these gas species have been measured. The second test chamber, a prototype vacuum vessel for the quadrupole section of the future synchro tron radiation source SOLEIL, was irradiated in a similar situation. The re sults of this test, which are close to the real conditions of a ring vacuum chamber, are compared to those obtained on the first test chamber. (C) 200 1 Elsevier Science Ltd. All rights reserved.