Simulations of the pressure profiles of the PETRAIII frontends

Abstract

PETRA III will be a high brilliance third generation synchrotron radiation source [1]. The undulators will provide photon beams with small beam size and therefore the components in the frontend are as compact as feasible. The resulting narrow cross sections of the vacuum system will yield a small conductance in the whole beamline. The design of the frontends has reached an advanced state so that the initial design of the vacuum system can be finalized now. The vacuum specification of the beamline components [2] demands for a hydrocarbon and dust free vacuum systems. To provide this, the beamline will be initially pumped down with dry pumping stations [9] to a pressure of at least 10 -6 mbar. At this pressure a set of ion pumps will be switched on to pump the beamline continuously. For lifetime reasons of the ion pumps it is necessary that during operation the pressure in the pumps is below 10 -6 mbar. During the start up of the beamline system a high amount of gas will be photo desorbed especially at the high power slit systems. To cope with this, the pumping concept of the beamline has been revised. Monte Carlo simulations of the pressure profiles in the beamline show that additional pumping near the slit systems is mandatory for a long lifetime of the ionpumps. The paper reports the layout process of the pumping system.