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LCLS bunch length monitor utilizing coherent radiation

LCLS bunch length monitor utilizing coherent radiation. Purpose of this study Current status What to improve. Juhao Wu, Apr. 03, 2006. LCLS BLM utilizing coherent radiation. LCLS feedback system schematic. BPM. BLM. Observables (6):

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LCLS bunch length monitor utilizing coherent radiation

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  1. LCLS bunch length monitor utilizing coherent radiation • Purpose of this study • Current status • What to improve Juhao Wu, Apr. 03, 2006 Juhao Wu jhwu@SLAC.Stanford.EDU

  2. LCLS BLM utilizing coherent radiation • LCLS feedback system schematic BPM BLM • Observables (6): • Energy: E0 (at DL1), E1 (at BC1), E2 (at BC2), E3 (at DL2) • Coherent Radiation energy bunch length: z,1 (at BC1), z,2 (at BC2) • Controllables (6): • Voltage: V0 (in L0), V1 (in L1), V2 (effectively, in L2) • Phase: 1 (in L1), 2 (in L2 ), 3 (in L3) Juhao Wu jhwu@SLAC.Stanford.EDU

  3. LCLS BLM utilizing coherent radiation • Coherent Radiation (CR) as nondestructive diagnostic tool • Synchrotron (magnet), Edge, and Diffraction Radiation • For a group of Ne electrons • CR spectrum • Form factor  bunch length information Single e- Juhao Wu jhwu@SLAC.Stanford.EDU “thin” beam approximation

  4. LCLS BLM utilizing coherent radiation • Let us start with “ideal” calculation • ISR power spectrum from a bending magnet • Far field, infinite long bending magnet • For an azimuthal milliradian of the electron orbit () and integrated over all the vertical angles Juhao Wu jhwu@SLAC.Stanford.EDU

  5. LCLS BLM utilizing coherent radiation • Parameters at BC1 and BC2 • CSR pulse energy can be as much as J Juhao Wu jhwu@SLAC.Stanford.EDU

  6. LCLS BLM utilizing coherent radiation • Phase jitter affects CSR spectrum after BC1 • Density distribution — parabolic Black: Nominal Blue: 1= 2.1o Red: 1= - 2.1o Juhao Wu jhwu@SLAC.Stanford.EDU

  7. LCLS BLM utilizing coherent radiation • Wake-induced double-horn structure after BC2 With Laser-Heater ( ) Juhao Wu jhwu@SLAC.Stanford.EDU

  8. LCLS BLM utilizing coherent radiation • Sharp-edge induces high freq. component after BC2. • However, low freq. region independent of shape Black: double-horn Blue: Gaussian with same Red: Step with same Non-Gaussian? Fine  low freq. region Juhao Wu jhwu@SLAC.Stanford.EDU

  9. LCLS BLM utilizing coherent radiation • Stay in the low frequency regime • Pyroelectric detector, diode detector? • Detector with fixed , the integrated power • Gaussian — density distribution • Detected power Juhao Wu jhwu@SLAC.Stanford.EDU

  10. LCLS BLM utilizing coherent radiation • Low charge case (0.2 nC) at BC1 Diode: WD — 03 Pyro: PI — 45 X=0.3 X=0.9 X=1 X=3 exp(- x2) X  2 p sz / l X  (0.3,1.4) X Juhao Wu jhwu@SLAC.Stanford.EDU

  11. LCLS BLM utilizing coherent radiation • So much for the “ideal” calculation • Let us now study the real experimental setup • Near-field, far-field • Finite magnet length • Edge radiation • Diffraction radiation • Finite aperture Juhao Wu jhwu@SLAC.Stanford.EDU

  12. LCLS BLM utilizing coherent radiation • UCLA design Juhao Wu jhwu@SLAC.Stanford.EDU

  13. LCLS BLM utilizing coherent radiation • UCLA design Juhao Wu jhwu@SLAC.Stanford.EDU

  14. LCLS BLM utilizing coherent radiation • SLAC modification • No turret • Diamond  quartz • Mylar splitter  two detectors (pyro & diode?) • Add camera Mylar splitter quartz Juhao Wu jhwu@SLAC.Stanford.EDU

  15. BX14 LCLS BLM utilizing coherent radiation • Schematic plan view • Aperture allows CSR to couple out • Mirror with hole collects arc of 1.7° to5° detector 4.0 in. ~20 in QM12 1.5 in. e- 0.6 in. 3.0 in. 5° 3.3 in. 6.3 in. 10.0 in. 12.7 in. Juhao Wu jhwu@SLAC.Stanford.EDU

  16. LCLS BLM utilizing coherent radiation • Schematic optics setup To detector CDR CSR Bending Magnet CER CER e-bunch CSR Reflecting / focusing mirror with hole Juhao Wu jhwu@SLAC.Stanford.EDU

  17. LCLS BLM utilizing coherent radiation • Edge Radiation (ER) • “Zero-edge length” model • For  >>1, radially polarized • Photon flux per unit solid angle ( in photons / s-relative bandwidth /-steradian) R.A. Bosch, Il Nuovo Cimento, 20, 483(1998) Juhao Wu jhwu@SLAC.Stanford.EDU

  18. LCLS BLM utilizing coherent radiation Far field & near field Juhao Wu jhwu@SLAC.Stanford.EDU

  19. LCLS BLM utilizing coherent radiation Far field & near field • In Near field regime • R = 25 cm • Reflecting part aperture 0.8 cm =>  = 1.7o • Reflecting part is 3.8 cm off-axis =>  = 8.5o • Will capture the peakof ER • SR interferes with ER R R sin()  D Juhao Wu jhwu@SLAC.Stanford.EDU

  20. LCLS BLM utilizing coherent radiation • Possible situation 3rd bend 4th bend CER Mirror CSR CER from 4 edges, and CSR from 2 arcs Juhao Wu jhwu@SLAC.Stanford.EDU

  21. LCLS BLM utilizing coherent radiation • Evolution of RMS Bunch Length Through BC1 • CSR from B4 • CER from B4 and B3 (with proper bunch length) B4 B1 B2 B3 constant 200-mm rms bunch length through final bend Juhao Wu jhwu@SLAC.Stanford.EDU

  22. LCLS BLM utilizing coherent radiation • Response function • Signal detection • Diode detector • Pyrodetector 0.1 1 10 100 (mm) Juhao Wu jhwu@SLAC.Stanford.EDU

  23. LCLS BLM utilizing coherent radiation • CER: Calculate E-field at four edges, sum up with proper phase difference then power • Do not calculate interference between CSR and CER • Diode: WD — 06 detector CSR (green) CER (red) Juhao Wu jhwu@SLAC.Stanford.EDU The black solid curve is simply the sum

  24. LCLS BLM utilizing coherent radiation Diffraction radiation concentrates for a R Juhao Wu jhwu@SLAC.Stanford.EDU

  25. LCLS BLM utilizing coherent radiation • Transition Radiation • Infinite Plate • Finite Plate S. Reiche et al., PAC2001, p. 1282 Juhao Wu jhwu@SLAC.Stanford.EDU

  26. LCLS BLM utilizing coherent radiation Diffraction Radiation — Finite Plate with Hole Y. Shibata et al., Phys. Rev. E 52, p. 6787 (1995) Juhao Wu jhwu@SLAC.Stanford.EDU

  27. LCLS BLM utilizing coherent radiation • Coherent Diffraction Radiation • Diode: WD-06 detector CDR  Juhao Wu jhwu@SLAC.Stanford.EDU   (0.01;0.02;0.05;0.2;0.5 )

  28. LCLS BLM utilizing coherent radiation • Signal strength (at birth) • Ceramic gap (optical diffraction model) >100 • CR Juhao Wu jhwu@SLAC.Stanford.EDU

  29. LCLS BLM utilizing coherent radiation • Current mechanical design would collect CER, CDR along with CSR • Further improvement • CSR near-field, far-field calculation • O. Chubar and P. Elleaume Synchrotron Radiation Workshop • Power loss on the mirror • Reflectivity — p-polarization, and s-polarization • Transmission of the system in general Juhao Wu jhwu@SLAC.Stanford.EDU

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