Abstracts Brochure - CERN

THPCH — Poster Session 29-Jun-06 16:00 - 18:00
the design of the linac upgrade. In this paper we give a detailed description of the applied procedures and present
the obtained results.
*C. Bocchetta et al. "FERMI@ELETTRA - Conceptual Design for a Seeded Harmonic Cascade FEL for EUV and Soft
X-rays", this conference.
Beam Break-up in the FERMI@ELETTRA Linac
The beam break-up instability is studied for
the 1.2 GeV linac of FERMI@ELETTRA FEL*. S. Di Mitri, P. Craievich (ELETTRA)
This instability is driven by transverse wake
fields acting on an electron beam travelling off-axis in the accelerating structures due to the launching errors in
positions, angles, energy and misalignment of various lattice elements. Two operational scenarios are considered:
one with a relatively long electron bunch of 1.5 ps and a moderate peak current of 500 A and one with a shorter bunch
of 0.7 ps and a higher peak current of 800 A. Attention is given to the correction of the "banana" shape of the electron
bunch caused by the instability. The simulation results are compared with the analytical predictions.
*C. Bocchetta et al. “FERMI@Elettra – Conceptual Design for a Seeded Harmonic Cascade FEL for EUV and Soft
X-rays”, this conference.
Transverse Head-tail Modes Elimination with Negative Chromaticity and the Transverse
Multi-bunch Feedback System at ELETTRA
The rigid dipole head-tail mode threshold at
ELETTRA is by now quite low and increasing E. Karantzoulis, M. Lonza (ELETTRA)
positively the chromaticity does not bring a
much overall advantage in the machine performance. Using the bunch-by-bunch transverse feedback (TMFB), a
threshold increase has been observed until the onset of the higher modes, which being bunch shape modes cannot
be detected and therefore eliminated by the feedback system. To overcome this problem the machine has been set to
a small but negative chromaticity. In this case the m=0 mode is unstable with a very low (