Abstracts Brochure - CERN

THPCH — Poster Session 29-Jun-06 16:00 - 18:00
filter design which treats each of maximum 220 bunches as an independent oscillator which has to be damped. More
sophisticated mode filter algorithms may be required to get better noise performance. The FPGA-board output signal
modulates a 104 MHz sine-wave. The resulting logitudinal correction kick signal is provided by the kicker-cavity.
Beside the technical details we present first operational experience and the actual system performance.
The Longitudinal Coupled Bunch Feedback for HERA-p
A longitudinal broadband damper system to
control coupled bunch instabilities has recently
been constructed and installed in the
920∼GeV proton accelereator HERA-p at the
M.G. Hoffmann, S. Choroba, F.E. Eints, P.M. Morozov, J. Randhahn,
S. Ruzin, S. Simrock, U.H. Uwe, E. Vogel (DESY)
Deutsches Elektronen-Synchrotron DESY. This represents one of the attempts to increase the specific luminosity at
HERA by reducing the bunch length. The final bunch length is defined by the initial emittance after injection and
by the acceleration process where multiply occuring coupled bunch instabilities provoke bunch length blow up at
discrete energies during the ramp. The actual feedback design consists of a fast, high precision bunch centroid phase
detector, a 1∼kW feedback cavity with 104∼MHz centre frequency and 8∼MHz bandwidth (FWHM), a I/Q-vector
modulator, the low level digital FPGA-board with 14 Bit ADCs and DACs and a cavity transient diagnostics. The
system measures the phases of all bunches and calculates corrections in real time (bunch spacing: 96∼ns) which are
then applied to the beam via a longitudinal kicker. The filter deals with a slowly changing synchrotron frequency
(20-80 Hz).
Layout and First Experience with a Local IP Orbit Feedback at HERA-e
At the electron-proton collider HERA it is
often observed that the proton emittance J. Keil, E. Negodin, R. Neumann (DESY)
growth rate of colliding bunches is larger
compared to non-colliding proton bunches. In addition the proton background rates are increasing when the two
beams are brought into collision. There are indications that a contribution comes from closed orbit oscillations of the
electron beam at the two IPs. In the arcs of HERA-e oscillation amplitudes of 100-200 micrometer with frequencies
of 2-15 Hz and harmonics of 50 Hz are observed. In order to stabilize the orbit at the IPs in both planes a local
digital orbit feedback system with a bandwidth of more than 20 Hz has been developed. The beam position at the
IPs is measured with BPMs using dedicated electronics. The four local orbit bumps are produced by air-coil steerer
magnets. The data are transmitted using SEDAC field bus lines to a central PC, which is used for the computation of
the correction.
Design and Operation of a Ferrite Loaded Kicker Cavity for the Longitudinal Coupled
Bunch Feedback for HERA-p
A longitudinal broadband damper system to
control coupled bunch instabilities has recently
been constructed and installed in the
920 GeV proton accelereator HERA-p at the
J. Randhahn, S. Choroba, M. Ebert, F.E. Eints, M.G. Hoffmann, S.
Simrock (DESY)
Deutsches Elektronen-Synchrotron DESY. The goal of this system is to reduce the bunch length and thus increase
specific luminosity at HERA-p. Within the control system a kicker cavity is used as an actuator. The original aspect of
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