Effects of undulator interruptions on the performance of high-gain FEL amplifiers

Conference · Sun Dec 31 04:00:00 EST 1995

DOI:https://doi.org/10.1016/0168-9002(95)01209-5· OSTI ID:240868

Kim, K J; Xie, M ^[1]; Pelligrini, C ^[2]

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1. Lawrence Berkeley Lab., CA (United States)
2. Univ. of California, Los Angeles, CA (United States)

The high-gain amplifiers for short wavelength free electron lasers (FELs) such as the LCLS project require a long undulator. The construction of the undulator as well as the FEL operation would become easier if the undulator could be interrupted with drift sections every few gain lengths. We have investigated the influence of such interruption on the FEL performances. Three effects are considered: (i) the diffraction loss, (ii) the phase mismatch and, (iii) the phase smearing due to velocity spread and to dispersion errors. The effect (i) is the loss during the process in which the optical mode in a section of the undulator leaves the undulator, propagates through the free space and then re-enters and re-adjusts in the next section. The effect (ii) is the fact that the phase of the optical beam is displaced with respect to the electrons density modulation for optical FEL interaction due to the slippage of the electron beam in the interruption region. The effect (iii) is the fact that electrons velocity spread, emittance, and dispersion due to misalignment of the quadrupoles used for additional focusing lead to a reduction of the bunching factor. We present an approximate analysis of these effects. When applied to the LCLS parameters, we find that the effect (i) is negligible, the effect (ii) gives a condition on the length of the drift section, and the effects (iii) are small, but could be non-negligible if there are sufficient number of interruptions.

• Research Organization: Brookhaven National Lab., Upton, NY (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 240868
• Report Number(s): BNL--61982-Absts.; CONF-9508156--Absts.; ON: DE96002729
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
43 PARTICLE ACCELERATORS
FREE ELECTRON LASERS
GAIN
LIGHT SOURCES
PERFORMANCE
WIGGLER MAGNETS