In our search for surfaces exhibiting the lowest photon stimulated desorption, we have exposed a 3-m-long beam tube to photons from the vacuum ultraviolet ring of the National Synchrotron Light Source having critical energy of ∼500 eV. Desorption of H2, CH4, CO, and CO2, which are the main gas species, was studied as a function of the beam dose for the following surface treatments: standard chemical cleaning, Ar 10% O2 glow discharge, N2 glow discharge, and radio frequency glow discharge using O2 disassociation. In addition, we measured the desorption as a function of vertical collimator position. N2 glow discharge treatment yielded the lowest desorption.

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