Running fermi with one-stage compressor: advantages, layout,performance

Cornacchia, M. ; Craievich, P. ; Di Mitri, S. ; Penco, G. ; Venturini, M. ; Zholents, A.

COLLABORATION -ELETTRA

关键词: Compression;    Peaks;    Lasers;    Mitigation;    Fel, Microbunching Instability, Jjitter;   

DOI  :  10.2172/929314
RP-ID  :  LBNL--62765
RP-ID  :  DE-AC02-05CH11231
RP-ID  :  929314

美国|英语

来源: UNT Digital Library

【 摘 要 】

CBP-Tech Note-345 (July 2005), devoted to a study of microbunching instability in FERMI@ELETTRA linac quotes '...the above analysis shows that the most of the gain in microbunching instability occurs after BC2, i.e. after transformation of the energy modulation to the spatial modulation that takes place in BC2. It is possible to avoid that if we use only BC1 for all our needs for bunch compression. There are also additional advantages for a mitigation of the microbunching instability related to that. First, we would need to increase R56 in BC1 (for given energy chirp in the electron beam). Second, a relative energy spread is significantly larger at BC1 than at BC2. Both these factors would contribute to instability suppression due to increased Landau damping effect.' One additional argument was however missed in that report. Instability smearing due to finite emittance is stronger in BC1 simply because the geometrical emittance is larger than in BC2. In spite of the considerations in favor of a lattice with one-stage compressor, it was thought at the time that the two bunch compressors configuration was still preferable as it appeared difficult to obtain a flat-flat distribution at the end of the linac with only one bunch compressor. A flat-flat distribution has constant medium energy and a constant peak current along the electron bunch. Now, two years later and more studies behind, this problem is solvable. It has been demonstrated1 that shaping the intensity of the electron bunch at the injector using intensity modulation of the photocathode laser allows to use the linac structural wake fields to advantage to obtain a flat-flat distribution at the end of the linac in a two-stage compressor. This report shows that, using the back-tracking technique, it is possible to obtain a flat-flat distribution also in a single-stage compressor. Preliminary results of a study of the microbunching instability applied to the FERMI lattice with one-stage compressor are shown in this report . There is concern that the effect of jitter in accelerator parameters is more pronounced with one bunch compressor: the results of jitter studies are given and are compared with the case of a two-stage compressor.