AVS 46th International Symposium
    Vacuum Technology Division Friday Sessions
       Session VT-FrM

Paper VT-FrM1
Electron-Cloud-Induced Effects in the APS Storage Ring*

Friday, October 29, 1999, 8:20 am, Room 610

Session: Vacuum Systems, Design, and Engineering
Presenter: R.A. Rosenberg, Argonne National Laboratory
Authors: R.A. Rosenberg, Argonne National Laboratory
K.C. Harkay, Argonne National Laboratory
Correspondent: Click to Email
Synchrotron radiation interacting with the vacuum chamber walls in a storage ring produces photoelectrons that can be accelerated by the beam and scatter from the walls, producing secondary electrons. If the secondary-electron yield (SEY) coefficient of the wall material is greater than one, the electron intensity can be amplified (termed "multipactoring") and a runaway condition can develop. This "electron cloud" can degrade the stored beam through direct interaction or by electron-stimulated desorption of gases from the chamber walls. The energy and intensity of the electron cloud is strongly dependent on both the amount of charge in each bunch of the stored beam and their temporal distribution. In order to obtain direct evidence of the properties of the electron cloud, a special aluminum (SEY > 1) vacuum chamber was built and inserted into the Advanced Photon Source (APS) storage ring. The chamber contains ten rudimentary electron-energy analyzers. Measurements to date have shown that the intensity and electron energy distribution are highly dependent on the temporal spacing between adjacent positron bunches and the amount of current contained in each bunch. Dramatic increases in pressure are observed when the temporal distribution and intensity of the bunches are configured to maximize multipactoring. Results of measurements of the electron energy distribution and concurrent pressure will be presented and discussed in terms of models of the electron cloud. *The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory ("Argonne") under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.