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LCLSIIsc CDR: Laser Heater Specs

LCLSIIsc CDR: Laser Heater Specs. M. Venturini , Z. Huang (contributions from Alan, Paul, Tor) 23 Oct 2013. Basic requirements/assumptions. Nominal beam energy @LH: E=98 MeV A llow for max E=100MeV beam energy Minimum undulator gap :

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LCLSIIsc CDR: Laser Heater Specs

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  1. LCLSIIsc CDR: Laser Heater Specs M. Venturini, Z. Huang (contributions from Alan, Paul, Tor) 23 Oct 2013

  2. Basic requirements/assumptions • Nominal beam energy @LH: E=98 MeV • Allow for max E=100MeV beam energy • Minimum undulator gap: • Min gap correlates to max beam energy, i.e. E=100MeV • Laser wavelength: (Yb:glass fiber laser) • consistent with availability of high-power high rep-rate sources • Beam dynamics considerations favor shorter wavelength (e.g. the ‘trickle’ effect). Have to make sure this is acceptable • Laser pulse length: (FWHM) • Long enough for i) heating uniformily along beam (for FWHM bunch length, heating variation is ), ii) accommodating longer bunches if needed • Max. heating capacity: (rms) • A bit generous? With , a(rms) at the FEL (rms) • Leave room for other modes of operation using less magnetic compression (and needing more heating) • No. of undulator periods: • Not too largein order to have enough bandwidth • Model for peak magnetic field in PM undulator[P. Elleaume, et al. NIMA 455 503 (2000)]. • Consistent (within a few %’s) with field measurements of LCLS LH undulator [Huang, et al., PRST-AB 13 020703 (2012), Eq. (2)] (b=2.076 T, a=3.24) (1)

  3. LH Chicane: 10-OCT-13 Lattice 0.124m 0.124m 0.124m 0.124m S S B B B B U 0.603m 0.603m *From undulator to exit of chicane

  4. Determine the undulator period • Set max energy (E=100MeV). Use undulator resonance condition, B-field model (1), and to parametrize u-gap and u-period as functions of u-parameter K • Min. undulator gap determines period • Calculate laser pulse peak-power (and energy) required for desired heating (20keV) • Laser pulse transverse size same as the electron beam’s. • Diffraction effects not included gap vs. K Laser-pulse peak power vs. K vs. K Laser-pulse energy vs. K

  5. Set beam energy to nominal (98MeV) Check laser-pulse energy requirements (and other parms) over a range of beam energy LH Parameters (baseline beam) • Requirement for laser pulse is • Or 7.5W average power @1MHz Gap vs. beam energy Kvs. beam energy vs. beam energy Laser-pulse vs. beam energy Solid line: including power loss due to diffraction

  6. Beam dynamics issues: the ‘Trickle’ effect , etc. • Tricke effect: a form of echo, where a laser-induced bunching (at laser wavelength) may show up downstream of the chicane • LSC induces energy modulation adding to heating from the laser • Analysis done using Zhirong’s analytical model () • Analytical model predict small but noticeable effect In the presence of the trickle effect In the absence of the trickle effect • Separate issue: emittance growth (heating in dispersive region) is expected to be less than 1%

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