Abstracts Brochure - CERN

MOPCH — Poster Session 26-Jun-06 16:00 - 18:00
Study of the Electron Beam Dynamics in the FERMI @ ELETTRA Linac
A study of the electron beam dynamics in
the linac is made within the framework of
the design of a free electron laser (FEL) at the
Syncrotrone Trieste*. A scope of the work includes
analysis of two operational scenarios,
M. Cornacchia, P. Craievich, S. Di Mitri (ELETTRA) I.V. Pogorelov,
J. Qiang, M. Venturini, A. Zholents (LBNL) D. Wang (MIT) R.L.
Warnock (SLAC)
one with relatively long electron bunches of the order of 1.5 ps and a moderate peak current of 500 A and one with
shorter bunches of the order of 0.7 ps and higher peak current of the order of 800 A. In both cases, care has been
taken to preserve the slice and projected emittances formed in the photocathode gun injector and to minimize the
slice energy spread. The latter goal is accomplished by balancing the onset of the microbunching instability driven
by the longitudinal space charge forces and the emission of coherent synchrotron radiation using Landau damping
produced by a so-called laser heater. Various analytical techniques and tracking codes have been employed to obtain
the reported results.
*C. Bocchetta, et al., this conference.
Linac Coherent Light Source Electron Beam Collimation
This paper describes the design and preliminary
simulations of the electron beam colli- J. Wu, P. Emma (SLAC)
mation system in the Linac Coherent Light
Source (LCLS) linac. Dark current is expected from the gun and some of the accelerating cavities. Particle tracking
of the expected dark current through the entire LCLS linac, from L0-linac exit to FEL undulator entrance, is used to
estimate final particle extent in the undulator as well as expected beam loss at each collimator or aperture restriction.
A table of collimators and aperture restrictions is listed along with halo particle loss results, which includes an
estimate of average continuous beam power lost on each individual collimator. In addition, the transverse wakefield
alignment tolerances are calculated for each collimator.
Trajectory Stability Modeling and Tolerances in the Linac Coherent Light Source
To maintain stable performance of the Linac
Coherent Light Source X-ray Free-electron J. Wu, P. Emma (SLAC)
laser, one has to control undulator trajectory
stability to a small fraction of the rms beam size. BPM based feedback loops running at 120 Hz will be effective
in controlling jitter at low frequencies less than a few Hz. On the other hand, linac and injector stability tolerances
must control jitter at higher frequencies. In this paper, we study the possible sources of such high frequency jitter,
including: 1) steering coil current regulation; 2) quadrupole (and solenoid) transverse vibrations; 3) quadrupole (and
solenoid) current regulation in presence of typical 200-micron misalignments; 4) charge jitter coupling to RF cavity
transverse wakefield due to alignment errors; and 5) bunch length jitter coupling to Coherent Synchrotron Radiation
in Chicane. Based on this study, we then set tolerances on each item.
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