SPS studies:
Latest news
Since 1998/99, beam induced multipacting is observed in
the SPS, when operated with the LHC batch. The first
evidence was a charge up of the feedback pick ups during
the passage of the LHC bunch train. This effect could be
reduced by a weak solenoidal field. Further observations
include a pressure increase by more than an order of magnitude
in most parts of the SPS ring, even for a
duty cycle of only a few percent, and a fast instability at
injection, or after excitation, which affects the later
parts of the bunch train, and can result in beam loss and
emittance growth.
EPA irradiation tests:
Latest news
Using synchrotron light from the EPA machine
(running at 308 MeV, with a critical photon
energy of 45 eV, similar to that of LHC at top energy),
we have measured the reflectivity for several surface roughnesses
and photoelectron yield with a magnetic field up to 0.4 T,
obtained by a conventional magnet with field orientation either parallel or
perpendicular to the surface of a photocathode placed at the end of a special
4 m long vacuum chamber.
Multipacting tests in a superconducting magnet:
Latest news
With a wide-band power amplifier (1-1000 MHz, 100 W) we
have excited TEM modes
in a 1 m long coaxial structure accomodated in the cold bore of
an 8.4 T magnet. The secondary electron yield and its possible
reduction by a strong B-field could be
inferred from the multipacting level reached under suitable resonance conditions
(either for pulsed or CW excitation). Measurements of photoelectron yield
are also possible, using UV light from a Xe flash lamp mounted near or inside
the coaxial tube.
10/07/2001
Frank.Zimmermann@cern.ch