Pressure stability under a pump failure

Ions produced by a beam on the residual gas induce desorption from the beam pipe wall and may lead to a runaway pressure build up. The main mechanism of ion production is usually inelastic collisions of the beam particles. It may not be true for PEP-II where the combination of high energy and high beam current leads to MWs of the total power in synchrotron radiation. The photoeffect on the residual gas may produce more ions than produced in the inelastic collisions due to a much larger cross-section of the photoeffect at low photon energies where the number of photons is maximum