LCLS X-Ray FEL Output Performance in the Presence of Highly Time-Dependent Undulator Wakefields

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Energy loss due to wakefields within a long undulator, if not compensated by an appropriate tapering of the magnetic field strength, can degrade the FEL process by detuning the resonant FEL frequency. The wakefields arise from the vacuum chamber wall resistivity, its surface roughness, and abrupt changes in its aperture. For LCLS parameters, the resistive-wall component is the most critical and depends upon the chamber material (e.g., Cu) and its radius. Of recent interest[1] is the so-called ''AC'' component of the resistive-wall wake which can lead to strong variations on very short timescales (e.g., {approx} 20 fs). To study the ... continued below

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4 pages

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Fawley, W.M.; /LBL, Berkeley; Bane, K.L.F.; Emma, P.; Huang, Z.; Nuhn, H.-D. et al. September 30, 2005.

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Energy loss due to wakefields within a long undulator, if not compensated by an appropriate tapering of the magnetic field strength, can degrade the FEL process by detuning the resonant FEL frequency. The wakefields arise from the vacuum chamber wall resistivity, its surface roughness, and abrupt changes in its aperture. For LCLS parameters, the resistive-wall component is the most critical and depends upon the chamber material (e.g., Cu) and its radius. Of recent interest[1] is the so-called ''AC'' component of the resistive-wall wake which can lead to strong variations on very short timescales (e.g., {approx} 20 fs). To study the expected performance of the LCLS in the presence of these wakefields, we have made an extensive series of start-to-end SASE simulations with tracking codes PARMELA and ELEGANT, and time-dependent FEL simulation codes GENESIS1.3 and GINGER. We discuss the impact of the wakefield losses upon output energy, spectral bandwidth, and temporal envelope of the output FEL pulse, as well as the benefits of a partial compensation of the time-dependent wake losses obtained with a slight z-dependent taper in the undulator field. We compare the taper results to those predicted analytically[2].

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4 pages

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  • Contributed to 27th International Free Electron Laser Conference (FEL 2005), Stanford, California, 21-26 Aug 2005

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  • Report No.: SLAC-PUB-11504
  • Grant Number: AC02-76SF00515
  • Office of Scientific & Technical Information Report Number: 878360
  • Archival Resource Key: ark:/67531/metadc881134

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  • September 30, 2005

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  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 7, 2016, 4:30 p.m.

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Fawley, W.M.; /LBL, Berkeley; Bane, K.L.F.; Emma, P.; Huang, Z.; Nuhn, H.-D. et al. LCLS X-Ray FEL Output Performance in the Presence of Highly Time-Dependent Undulator Wakefields, article, September 30, 2005; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc881134/: accessed November 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.