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
