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Counteracting Trapped Ion Effects in the HESR

By Frank Hinterberger


Methods to counteract trapped ion effects in the High-Energy Storage Ring HESR are studied in the present report. The circulating antiproton beam ionizes the residual gas molecules of the UHV vacuum. The produced ions are trapped in the negative potentential well of the antiproton beam. Trapped ions can be extracted using either single isolated clearing electrodes or continuous clearing electrodes. In addition resonant transverse shaking of trapped ions and damping of coherent ion-beam oscillations can be used in order to reduce the adverse effects of trapped ions. In the region of dipole magnets the problem of trapped ions can be mitigated by upgrading the UHV vacuum, i.e. by sputtering thin-film NEG coatings onto the surfaces of the vacuum chamber and by using heat jackets along the beam tubes. The highest clearing efficiencies in dipole magnets can be achieved by extracting the trapped ions in the vertical direction along the magnetic field lines. A distinctive feature of the HESR ring is the internal PANDA target which deteriorates the vacuum by a huge local pressure bump. Near the PANDA target continuous clearing electrodes are necessary in order to counteract the high production rate of trapped ions. In the region of the electron cooler (EC) the optimum neutralization is reached if η = 1/γ2 e . Then, the azimuthal cross-field drift velocity of the electrons is zero and the space-charge potential is reduced. A stable neutralization with η = 1/γ2 e can be achieved using the Ion-Cyclotron-Resonance (ICR) heating. The ICR heating can be realized using the electrodes of the beam position monitors. The RF can be tuned to be in resonance with the characteristic cyclotron frequencies of the ion species in the magnetic field of the EC solenoid

Topics: info:eu-repo/classification/ddc/500
Publisher: Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Year: 2012
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