12/08/2003 H. Schlarb, DESY, Hamburg

Transcription

1 K. Bane, F.-J. Decker, P. Emma, K. Hacker, L. Hendrickson,, C. L. O Connell, P. Krejcik,, H. Schlarb*, H. Smith, F. Stulle*, M. Stanek, SLAC, Stanford, CA 94025, USA *

2 σ z NDR 6 mm 1.2 mm 3-stage compression 50 µm 12 µm X-Rays E = 1 RTL 1.2 GeV e - /bunch γε x =40 µm γε y = 4 µm New 2 Chicane 9 GeV 28.5 GeV I pk =30 ka 3 FFTB PEP II SLC Repetition rate 10 Hz/1 Hz

3 ! Wake loss scan had to adapted to FFTB operation Opportunity to measure the energy profile more accurate Problem: for ultra-short bunches bunch length diagnostics more difficult (even not available) Electro-Optic Sampling experiment in preparation Use THz detector to optimize bunch length

4 " # Special setup to give 100 mm bunch length with more charge at the head of the bunch head Measured at the end of FFTB Cherenkov radiator in air gap (airogel)

5 $ % " Shortest bunch in FFTB with slight over-compression in linac foil wake losses LINAC CTR radiation wavelength comparable to bunch length Pyro-detector pyro FFTB GADC

6 !& '$!% OTR Screen mirror beam Also used to adjust timing of EOS experiment Photodiode for EOS mirror Pyro-detector

7 % # ' Five step changes in linac phase t= 30, DR13 Ph 63= -2.7 t= 70, DR13 Ph 63= -2.2 t=100, DR13 Ph 63= t=140, DR13 Ph 63= -1.2 t=180, DR13 Ph 63= -0.8 Next, try dither feedback control

8 $ ( Bunch length monitor response # ' Feedback correction signal ping optimum Dither time steps of 10 seconds Linac phase L. Hendrickson

9 ) Complex dielectric function: Fit used for extrapolation Absorption in the sapphire vacuum window: d=5mm n α Ref: Grischkowsky et.al. J. Opt. Soc. Am. B/Vol.7, No 10, Oct 1990 ~ 0.1 THz nearly no transmission of the CTR above 2.5 THz

10 ) Water absorption after 80 cm FIR transport

11 ) Pyroelectric-sensor: FIR heats LiTaO 3 crystal Dielectric polarization current is measured Model of detector predict: + material properties of LiTaO 3 crystal with two lattice oscillator model fitted mm 3 refraction electrodes electrodes absorption Schall el.al, 1999 Uni Freiburg

12 ) Response function of the pyro-electric detector (P1-45 Molectron) Constructive interference in crystal Only n(ω) determines acceptance Destructive interference in crystal

13 ) Spectral density of a bunch with σ z =35µm measured with pyro-electric detector (d=100 µm) C. Settakorn SLAC-R-576 Pyro-detector acceptance Including form factor

14 ) % $ Expected frequency response function for the SPPS-FFTB setup: lower cutoff at 0.1 GHz sapphire window water absorption pyroelectric detector

15 # rms I peak! Q = 3.5 nc Compr. Ampl. = 42 MV/m 2-6 linac phase = -20 FWHM/2.4 gauss Very demanding phase tolerances

16 # Total radiated energy! Power spectrum

17 # Total radiated energy & detected signal! Power spectrum 20 pyro-detector predicts within 0.5 deg the phase with maximum I peak low freq. cut -> narrows high freq. cut -> widen Power spectrum response fct.

18 #! Simulation and measured pyroelectric signal Signal does not vanish if beam is over-compr. Larger width than expected

19 ** Transmission Transmission of Quarz (Type crystalline SiO2) Ordinary rays 4.5 THz Wavelength (µm) Extraordinary rays Transmission through crystalline quartz try air or nitrogen atmosphere z-cut quartz window (2 mm thickness) band pass filters i.e. grids, windows Centers are shifted

20 " # Pockels effect: E r of e - -bunch rotates laser polarization M1 M2 EO crystal Beam axis EO vacuum chamber Probe laser

21 " # Pockels effect: E r of e - -bunch rotates laser polarization M1 M2 EO crystal Beam axis EO vacuum chamber Probe laser Laser beam incidence with an angle spatial-time correlation small fraction of laser is modulated readout with line camera expected resolution < 100 fs (limited by laser pulse duration)

22 " E r electrons P EO Xtal E r Original planed to use Kerr effect (in glass 100 µm) ========== later GaAs Elevation view End view Principal of temporal-spatial correlation Line image camera E r Plan view

23 " BW limited pulse Short chirp Long chirp Spectral profiles T res = T T 0 C Temporal profile

24 Laser beam σz = 750 µm Position of crystal (not included in simul.) ' " * beam mirrors σz = 100 µm between mirrors Does not work => mirror 45 rotated

25 " ( collimator toroid quadrupole EO-crystal laser Force lines Radial electric field at r = 10 mm beam FWHM ~ +6%

26 " ( σ z = 100 µm σ z = 50 µm σ z = 25 µm FWHM ~ +6% FWHM ~ +15% FWHM ~ +36%

27 Å Photons/s,0.1%BW ε/ε ε 1 [kev] Former APS wiggler

28 ,

29 Calculated Measured Pulse length 80 fs << 1 ps FWHM Peak Brightness 2x Photons/s/mm 2 /mrad 2 /0.1%BW Photons/pulse x10 7 Source size 160 x µm FWHM Divergence 15 x 16 - µrad FWHM (undulator fundamental) Beam size in hutch (95 m) 1.5 x 1.6 ~ 2 x 2 mm FWHM Repetition rate Hz Average flux x10 8 Photons/s

30 No major difficulties during commissioning LLBC and FFTB beam line SPPS operation is compatible with PEP II operation X-ray beam line has been commissioned successfully, experiment have started already Deflecting cavity operation has been improved and extended toward measurements in the 50 um range Energy loss due to wake fields in good agreement to theory for design setting, but disagree for other machine operation (not yet understood) Method to optimize bunch length in Linac and the FFTB have been established