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Injector Physics / Diagnostics / Gun & L0 Linac RF Design D. H. Dowell, SLAC FAC Review April 29-30, 2004

Detailed examination of injector requirements, configuration, and technical review for gun diagnostics and commissioning. Includes recommendations for optimizing gun performance and utilizing diagnostics effectively.

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Injector Physics / Diagnostics / Gun & L0 Linac RF Design D. H. Dowell, SLAC FAC Review April 29-30, 2004

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  1. Injector Physics / Diagnostics / Gun & L0 Linac RF DesignD. H. Dowell, SLACFAC Review April 29-30, 2004 Injector Requirements Injector Configuration Nov 3, 2003 Injector Technical Review Comments and Response Pulsed Heating of 120 Hz Gun Long Pulse Option Laser Heater Gun Diagnostics and Commissioning Gun Solenoid Field Quality Dual RF Feed on L0-1 Accelerator Section Straight Ahead Diagnostics Cathode Damage

  2. LCLS Injector Performance Requirements:

  3. Slice Emittance Requirements • projected < 1.2 mm.mrad • slice < 1.0 mm.mrad for 80 slices out of 100 • slice(80%) projected emittance for the core 80 slices

  4. LCLS Injector Configuration RF Gun Load Lock L0-1 & L0-2 3-m SLAC Sections Gun Diagnostics Laser Heater Transverse RF Cavity DL1 Bend Straight Ahead Spectrometer

  5. Nov 3, 2003 Injector Review Committee Recommendations and Concerns • Pulsed Heating of Gun Coupling Irises (Study underway, completed L0-1 dual feed) • Eliminate gun tuners (Under consideration, include with field symmetrization) • Two stages of gun commissioning (Not possible given budget + schedule + space; Make extensive use of diagnostics in GTL) • Gun optimization using diagnostics (19-parameter problem => needs detailed commissioning plan) • Spontaneous radiation from laser-heater undulator for e-beam diagnostics • Long bunch experiments at GTF, SDL, etc. (Planning expts. at BNL/DUVFEL) • Prototyping of load lock porcupine concept (Performed during engineering) • Need commissioning plan using diagnostics, need more diagnostics (diagnostics available, still need detailed commissioning plan) • Include streak camera measurement at gun (EO maybe unreliable) (Streak Path to Laser Bay included in design) • S2E using non-optimal injector performance (Not yet done) • More operating time at GTF (GTF is now operating) • Injector layout indicates vault is too small (Too expensive to enlarge vault) • Use chicane to couple laser into laser-heater (Yes!)

  6. Pulsed Heating of Gun Coupling Irises Gun body stress in Pa The maximum steady-state stress of 14 ksi occurs around the RF aperture. Analysis in progress by Zenghai Li and Liling Xiao, SLAC/ACD. (see work on L0-1 Linac Dual Coupler)

  7. Increasing Bunch Length to 17.5 ps Reduces Emittance > Allows Smaller Laser on Cathode< • More compression in Linac now possible with Laser Heater • Experiments possible at BNL/DUVFEL during Dazzler tests Plots from C. Limborg, Injector Requirements, Nov 3, 2003 Injector Review

  8. P0 = 65 MW w0 3 mm sx,y 0.1 mm +73.6 keV -73.6 keV Matlab laser-heater code (thanks to major help from Juhao Wu)

  9. Place undulator inside a chicane to allow laser interaction (thanks to Todd Smith, November 3 Injector Review) 50 cm 10 cm 2 cm q 5.7º 10 cm ~120 cm Horizontal emittance growth is small: De/ex0 ½(sdhx/sx)2< 0.1% sd410-4, hx20 mm ,sx200 mm Slide compliments of P. Emma

  10. R52 (= hx) of chicane smears time coordinates after chicane P0 = 2 MW w0 = 400 mm sx 200 mm sy 200 mm x'21/2hx>>  (20 mrad)(20 mm)>> (800 nm)/2p

  11. Laser-Heater Parameters

  12. WBS 1.2.15 Laser Heater

  13. Gun to Linac Diagnostics Electron Measurements: Thermal Emittance Charge Energy Energy Spread Pulse Shape (streak camera & EO) Longitudinal Emittance by Streaking Spectrometer Screens Gun Spectrometer Resolution: 10 keV with Quads off 3 keV with Quads on

  14. At Low Charge the Gun’s Compression Converts Temporal Modulation into Energy Modulation Plots from C. Limborg, Nov 3, 2003 Injector Review

  15. Gun Solenoid Multipole Fields

  16. L0-1 Dual Feed Coupler Design by Z. Li, SLAC/ACD

  17. w=24.4000 b=35.95032 t=5.84200 R=3.0861 + + 19.09318 tf=0.78740 36.31233 dc=13.000 Racetrack Dual Feed Eliminates Dipole and Quadrupole Field Perturbations in Coupler Cell Design by Z. Li, SLAC/ACD rough dimensions: skin and fillet not corrected for operation temperature

  18. Electron Diagnostics At 135 MeV

  19. Beam Induced Damage to Cu Cathode ~0.5 mm Profilometer Measurements Using a 0.2 Micron Quartz Stylus

  20. Summary and Conclusions • Discussed Nov 3 Review Committee’s Concerns • Gun Diagnostics for Commissioning • 17 Parameter Problem Still Needs Work • Laser Heater Now Part of Injector System • Measured Field Multipoles of Gun Solenoid • Dual RF Coupler Designed for L0-1 • Similar Issues in Dual Feed RF gun • Dual Coupler Design for Gun is Next (Including Pulsed Heating) • Straight Ahead Diagnostics for Commissioning • Cathode Damage Effects

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