Advanced vanced Beam m Instru trumentatio mentation n sup upporting porting AARD RD at t th the A0-Photoinj hotoinjector ector Manfred Wendt Fermilab 1 8/18/2008 A0-Photoinjector Review
Agenda enda • Motivation • Proposed New Activities – Long. diagnostics • Overview on using CTR long. beam diagnostics – Long. bunch profile • OTR Introduction using EOS • Ongoing Activities – HOM signal processing – Streak Camera – Beam tests of a cold ILC – Martin-Puplett cavity BPM prototype – Waveguide pickups Interferometer – OTR Interferometer – EOM-based Time-of-Arrival 8/18/2008 8/18/2008 A0-Phot A0 otoi oinj njector or Review 2
Mot otivation ivation • Need a set of reliable basic beam instruments (upgrades required, see also Ray’s talk): – Intensity, position (orbit), transverse beam size (emittance) • AARD demands advanced beam diagnostics, in particular in the longitudinal domain to study and observe the bunch dynamics in AARD experiments: – Bunch length – Longitudinal bunch profile – Bunch time-of-arrival (wrt. RF phase, or relative between two locations) • No best “I can do everything” instrument available to fully characterize longitudinal bunch parameters – Calibration, measurement range (fs, ps) and time (single/multi shot), (non) invasive, resolution, reproducibility, etc. 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 3
Lo Long ngitudinal itudinal Bea eam m Dia iagnostics nostics Applicable Device Comments bunch lengths • Well understood, expensive commercial device • Single bunch, single pass capability (intensity limited) Streak camera 1 – >100 ps • Dispersion effects dominate at short bunch length Ongoing activity, measurements Bunch profile • Can provide arrival times and jitter • Slow response, scanning using many macropulses Martin-Puplett • Susceptible to upstream CSR and wakefields < few ps Interferometer • Missing phase information makes details of the bunch profile Ongoing, length difficult to obtain • Parametric measurement of the bunch profile, bunch shape CTR angular must be assumed < few ps distribution • Scanning over many macropulses Proposed, length • Susceptible to upstream CSR and wakefields • Single shot capability, fairly expensive, needs a (high power) Electro-optical laser synchronized to the beam 100 fs – 2 ps • Must understand behavior of electro-optical crystal in the sampling frequency regime corresponding to the expected bunch length Proposed, profile • Susceptible to upstream CSR and wakefields Waveguide • Inexpensive and simple, but calibration very difficult. 200 fs – 2 ps pickups • Does not give shape information, just rough bunch length Proposed, length 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 4
(O (Opti ptical) cal) Tra ransition nsition Rad adiati iation on beam beam • Transition radiation 2 2 2 1 d U e I ( , ) 2 2 2 2 ( ) d d h c 0 – Charged particles passes through a media boundary – Monitoring of trans. beam courtesy A. Lumpkin profile (-> emittance), bunch length and energy 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 5
Str treak eak Cam amer era a Pri rinc nciple iple • Dual-sweep streak camera Hamamatsu C5680 (1.5 ps FWHM res.) • Addition of M5676 synchroscan plugin module and the C6878 phase-locked delay box enabled new series of experiments at A0 . Slit (set to 40 µm) 81.25 MHz Sync 81.25 MHz rf IN Phase-locked Delay Box C6878 Sine Wave from Sweep GPIB Based on VG by B.Yang Synchroscan Signal for ANL/S35 review M5676 Ref. In 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 6
Str trea eak k Cam amer era a Sum umma mary ry • Streak camera – Views UV-visible light from a (intercepting or non-intercepting) conversion mechanism, e.g. OTR, OSR to observe the bunch. – Provides a 2-D bunch profile, allowing sliced measurements: • Vertical axis -> time axis • Horizontal axis: preserved (spatial, energy, spectral) • Features – Synchroscan unit (81.25 MHz, phase-locked to master oscillator) • ~1 ps RMS jitter • Synchronous summing of micropulses (statistics, intensity) – Delay unit provides long term stability – Dual-sweep allows simultaneous observation of micropulses • Resolution – 1.5 ps FWHM (monochromatic), larger for broadband light 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 7
Str treak eak Cam amer era a Res esults ults • Bunch length elongation with micropulse charge and slice beam-size effects (50%) at 4 nC observed. 35 10-15-07 R2 FWHM (ps) Rodion Diss. FWHM (ps) ASTRA 30.5 FWHM (ps) 30 Bunch Length (ps) 25 20 ps t 20 15 ~10 mm 10 0 1 2 3 4 5 6 7 8 X Charge (nC) Lumpkin,Ruan: BIW08 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 8
Ste teak ak Cam amer era a Res esults ults (c (con ont. t.) • Bunch compression and transit time changes for different momenta in double doglegs were measured. The line is a fit showing that R 56 is 0.18 m Lumpkin,Ruan: BIW08 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 9
Str treak eak Cam amer era a Res esults ults (c (con ont. t.) • Emittance exchange results in bunch compression. ← 5-cell off ← 5-cell on 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 10 10
Mar artin tin-Puplett Puplett Int nterfe erferometer rometer View from Top courtesy View from Top again Mirrors R. Thurman-Keup Electron Bunch Input Motorized stage Polarizing Polarizer Splitter Transition Mirrors Radiation Polarizing I I Splitter 1 2 S ( ) cos I I 1 2 2 E 0 2 I cos 1 Off-axis 2 2 Paraboloidal 2 E 0 2 I sin Focusing Mirror 2 2 2 Pyro Detector 2 d I ( ) cos S ( ) Pyro Detector 1 d I ( ) Incoherent Coherent • Martin-Puplett interferometer – Needs many beam pulses to 2 I ( ) I ( ) N N ( N 1 ) F ( ) 0 resolve the temporal convolution 1 ˆ 3 i ( x n ) – Difficult to calibrate the detectors F ( ) d x ( x ) e Q 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 11 11
MP MP Int nter erferometer ferometer Res esults ults • Measurement experiment 2008: Emittance Exchange Cavity On – Using improved pyroelectric detector Interferogram (DESY) with suppressed interference 1 – Measured spectrum does not show 0.5 S( ) interferences 0 • -0.5 Bunch length measurement results -25 -20 -15 -10 -5 0 5 10 15 20 25 (ps) Intensity (Arbitrary Units) (deflecting mode cavity on/off), and Spectrum Adjusted 0.8 comparison: Raw 0.6 – Autocorrelation with ratio = 0.69 0.4 0.2 – Reconstructed bunch ratio = 0.43 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency (THz) – Streak camera ratio = 0.66 Intensity (Arbitrary Units) Bunch 0.1 • MP issues 0.05 – Detector response (low freq.) and 0 calibration -6 -4 -2 0 2 4 6 8 t (ps) – Diffraction effects at lower wavelength 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 12 12
MP MP Int nter erferometer ferometer: : Nex ext t Ste teps • Plans – Calibration of the pyroelectric detector frequency response – Experiments with other detector types • Golay cell • Schottky detector – Reproduction and improvements of the MP interferometer hardware (borrowed Martin-Puplett Interferometer from DESY). (borrowed from DESY) 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 13 13
OTR R Int nterfer erferometer ometer (O (OTRI) RI) B: beam =1.8 mrad D: beam =5.0 mrad C: beam =3.3 mrad E: beam =7.0 mrad Intensity, r.u. 1.0 E=16 MeV 2.5 m Mylar E =0.1 MeV 0.5 meas =0.9 mrad • D=0.6 mm OTRI features: – Beam divergence measurement – Beam energy (better accuracy) – Single shot measurement (no scanning) OTRI apparatus at the A0 Photoinjector. Mirror Optical Filter Mirror with Interfering Mirror-like with hole window MCP MCP L 1 hole OTR film screen photocathod e - ~ 2 Transparent film e - L 3 CCD Al Coated L 2 Interfering OTR MCP Transparent film film OTRI principle of operation. OTRI normal incidence setup & optical readout. 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 14 14
OTRI RI Res esults ults 45 0 The interference pattern obtained at incidence setup with Mylar (left) and Mica (right) -based interferometers at the beam energy of 16 MeV. Measured (solid lines) and computed (dots) fringes for the Mylar (left) and Mica (right) - • Results based interferometers at normal incidence, 16 MeV beam with the energy spread of 0.6% and – Measurements taken with the readout resolution of ≈ 0.9 mrad. 2.5 µm Mylar and 6 µm Mica • Next steps double foils – – Mylar foils show very good Experiment with thinner foils agreement with simulation! – Beam divergence measurements – Beam divergence measurement at higher beam energies accuracy ~ 15 % – Measurements in the EEX line?! 8/18/2008 8/18/2008 A0 A0-Phot otoi oinj njector or Review 15 15
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