• S. Casalbuoni, M. Hagelstein, D. Saez de Jauregui, S. Schleede
  FZK, Eggenstein-Leopoldshafen

Preliminary studies performed with the cold bore superconducting undulator installed in the ANKA storage ring suggest that the beam heat load is mainly due to the electron wall bombardment. Electron bombardment can both heat the cold vacuum chamber and induce an increase in the pressure because of gas desorption. In this contribution we compare the measurements of the pressure in a cold bore performed in the electron storage ring ANKA with the prediction obtained using the equations of gas dynamic balance in a cold vacuum chamber exposed to synchrotron radiation and electron bombardment. The balance results from two competitive effects: the photon and electron desorption of the gas contained in the oxide layer of the chamber wall and of the gas cryosorbed, and the cryopumping of the cold surface. We show that photodesorption alone cannot explain the pressure rise observed and that electron multipacting is needed.