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Detectors for bunch length measurement and Beam loss monitoring

Detectors for bunch length measurement and Beam loss monitoring. Anne Dabrowski (on behalf of all involved) Northwestern University CTF3 Collaboration meeting January 2007. A. Dabrowski, January 16 2007. 1/24. Overview Northwestern CTF3 Activities. Drive Beam Injector. PETS Line

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Detectors for bunch length measurement and Beam loss monitoring

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  1. Detectors forbunch length measurementand Beam loss monitoring Anne Dabrowski (on behalf of all involved) Northwestern University CTF3 Collaboration meeting January 2007 A. Dabrowski, January 16 2007 1/24

  2. Overview Northwestern CTF3 Activities Drive Beam Injector PETS Line 30 GHz source Delay Loop TL1 (2006) Drive Beam Accelerator Stretcher CR (2007) RF photo-injector test (2006-2007) 30 GHz tests CLEX (2008) TL2 (2007) Pickup for Bunch Length Measurement Beam Loss Monitoring 2/24 A. Dabrowski, January 16 2007

  3. Outline • RF pickup for bunch length measurement • Principle of the measurement • Report on activities during 2006 • Hardware designed, installed & tested • Electronics • Software • Results of data taking in the Fall  NEW • Future improvements to setup • Beam loss Monitoring • Reminder: devices installed and fully instrumented since 2003 • Ongoing work in optimization of setup 3/24 A. Dabrowski, January 16 2007

  4. Principle of the measurement The RF-pickup detector measures the power spectrum of the electromagnetic field of the bunch For a given beam current; the larger the power spectrum amplitude, the shorter the bunch length. Picked-up using rectangular waveguide connected to the beam pipe, followed by a series of down-converting mixing stages and filters. Solid: σt = 1 ps Dash: σt = 2 ps Dash-dot: σt = 3 ps Power Spectrum [a.u.] Theory Freq [GHz] Theory Power Spectrum [a.u.] Freq [GHz] 4/24 A. Dabrowski, January 16 2007

  5. Advantages of the RF-Pickup • Advantages • Non-intercepting / Non destructive • Easy to implement in the beam line • Relatively low cost (compared to streak camera and RF deflector) • Relatively good time resolution (ns)  follow bunch length within the pulse duration • Measure a single bunch or a train of bunches • Relative calibration within measurements • Short comings in the calibration • Beam position sensitive • Sensitive to changes in beam current • At CTF3: the RF deflector and/or a streak camera can provide an excellent cross calibration of device 5/24 A. Dabrowski, January 16 2007

  6. Goal of new RF-pickup installation in CTF3 Goal: Improve on the RF-Pickup installed in CTF2 • Increase maximum mixing frequency to measure max beam frequency signal at 170 GHz sensitivity to bunch length measurements of 0.3ps • (CTF2 the maximum frequency was 90 GHz) • NWU purchased + commissioned D-band waveguide components & mixer @ 157 GHz • Spectral analysis by single shot Fast Fourier Transform (FFT) analysis from a large bandwidth waveform digitizer • NWU Purchased & commissioned fast Acqiris digitizing card • Design a thin diamond RF window for improved transmission at high frequency • First design complete, brazing test successful, machining in progress  testing to follow C. Martinez et al,CLIC note 2000-020 6/24 A. Dabrowski, January 16 2007

  7. 4 2 1 3 New hardware installed CTF3 CT-line, BPR and single WR-28 waveguide to transport the signal to the gallery (~20 m). Analysis station gallery • Filters, and waveguide pieces separate the signal from the beam into 4 frequency-band detection stages: • (30 – 39) ; (45-69) ; (78-90) & (157-171) GHz • Series of 2 down mixing stages at each detection station. From the beam 7/24 A. Dabrowski, January 16 2007

  8. Electronics for Acquisition Acqiris DC282 Compact PCI Digitizer 4 channels 2 GHz bandwidth with 50 Ω standard front end 2-8 GS/s sampling rate Mounted in the same VME crate as the 30 GHz conditioning team’s cards Signals from Acqiris scope visible in control room using OASIS Viewer software 8/24 A. Dabrowski, January 16 2007

  9. DAQ and Analysis code Software: Data acquisition controlled by a Labview program, with built in matlab FFT analysis routine. Code to extract the bunch length in real time written. System used from control room in regular running operation Labview interface Raw Signal FFT Signal Screen for analysis 9/24 A. Dabrowski, January 16 2007

  10. Bunch length manipulation in the INFN chicane Accelerating structures @Girder 15 4 Bends Frascati Chicane Delay Loop RF pick-up Lower energy Nominal energy Higher energy Changing the phase of Klystron 15 to insert a time to energy correlation within the bunch Convert energy correlation into path length modification and time correlation Measure the Bunch frequency spectrum Klystron V(t) • On-crest Acceleration – the bunch length is conserved through the chicane • Positive Off-crest Acceleration – the bunch gets shorter • Negative Off-crest Acceleration – the bunch gets longer t 10/24 A. Dabrowski, January 16 2007

  11. Typical raw and FFT pickup signals Example: Synthesizer (second down-mixing stage) set at 5300 MHz phase MKS15 355 degrees, 06-12-2006 Raw signals from the beam in time domain Transformed signals 63 GHz, 51 GHz 33 GHz FFT 81 GHz 162 GHz 10 measurements, at each local oscillator & phase setting. FFT done on each measurement  result averaged, std dev of mean < %. 11/24 A. Dabrowski, January 16 2007

  12. Bunch length measurement result Maximum of FFT vs phase MKS15 (degrees) preliminary • Data analysed using a self calibration procedure, by means of Chi square minimization. • 16 measurements (corresponding to the 16 phases on MKS15) • Fit done with lowest 3 mixing stages. • 19 free parameters fit  3 response amplitudes and 16 bunch lengths 12/24 A. Dabrowski, January 16 2007

  13. Design prototype for diamond window completed. • Brazing Test successful • Machining of window in progress  RF properties and test in machine to follow. 0.5mm Improvement: Increase transmission @ high frequencies  New RF Window in design @ 90 GHz through Al203λ is effectively ~ 1 mm Although obtain Good signal in December commissioning of RF-pickup ; Al203 window not optimized for good transmission at high frequencies (> 100 GHz)  designed a thin (0.5mm) diamond window with lower εr. 13/24 A. Dabrowski, January 16 2007

  14. 4 2 1 3 Improvement in setup foreseen Analysis station gallery • Filters, and waveguide pieces separate the signal from the beam into 4 frequency-band detection stages: • (30 – 39) ; (45-69) ; (78-90) & (157-171) GHz • Series of 2 down mixing stages at each detection station Note: At high frequencies, filter at 157 GHz, separates the transmitted signal > 157 GHz,from the reflected signal.  only (157 + 14) GHz signal is analysed in 4th mixing stage. Modifying the high pass filter to 143 GHz would allow (157 ± 14) GHz to be analysed  sample more frequencies From the beam 14/24 A. Dabrowski, January 16 2007

  15. Summary: Bunch Length detector • RF-pickup has been successfully installed in the CT line in CTF3 • First bunch length measurement made as a function of phase on MKS15! • The Mixer & filter at 157 GHz was tested and works. • The new acquires data digitizing scope successfully installed and online analysis and DAQ code tested and working. • Self calibration procedure stable. Possible improvements to the setup: • Improved RF diamond window for high frequenciesis being machined and brazed and will be installed for future tests. • An additional filter at ~143 GHz, can provide additional flexibility in the detection of high frequency mixing stage. 15/24 A. Dabrowski, January 16 2007

  16. Outline: Beam Loss Monitoring on Linac • Goal: • Beam Loss Monitoring should provide additional monitoring information to the BPMs, in the regime where the BPM’s are insensitive (<< % loss of beam current) • Detectors should time resolve the losses within the pulse. • Status of the system • Small Ionization Chambers (SICs) and Faraday cups have been installed. • Setup is sensitive to ‰ of the beam loss along the girder (sensitivity increases with a loss of timing resolution) • Revisited system over the Fall 2006. • Modify electronics - Increased input impedance to gain additional sensitivity with the SICs • Tested a Pre-Amplifier directly mounted onto the chamber was tested (supplied by Jim Crisp at Fermilab Beams division  lot of experience building electronics for beam current monitors). • Assembled and tested Cherenkov fiber coupled to a Photomultiplier • Summary of Beam Loss Monitoring devices Tested at CTF3 16/24 A. Dabrowski, January 16 2007

  17. Expected Beam Loss flux Geant3.21 simulation [1], estimated flux of particles produced, give ‰ loss of the beam current. Max flux estimated: 1011-1012 particles/cm2/s  High Rate, fast radiation hard detector was suggested as good application. A candidate detector was ceramic SEM chamber shown to with stand rates > 1012particles/cm2/μs [2] • SEM chambers were installed and tested, but clear: • Fluxes estimated lacked additional normalisation  time of the pulse. • Flux: ~105-106 particles/cm2/μs • From 2005  SEM chambers were replaced with more sensitive small ionisation chambers (SICs). Gas sealed and filled with He/Ar (8/94). SIC chambers saturate ~ 1011 particles/cm2/μs [1] M. Wood, CTF3 note 064, (2004) [2] M. Velasco CTF3 Collaboration meting (2003) 17/24 A. Dabrowski, September 05 2006

  18. Beam Loss monitoring Gas sealed small ionisation chambers (SICs) • Full setup since 2004 • 3 detectors (SICs) installed per girder, with a cross calibration with Faraday cup • Electronics with 2 gain ranges (26/46dB 300MHz from CERN ) 18/24 A. Dabrowski, January 16 2007

  19. Typical signals: Calibration Plateau Calibration Plateau for chambers (SIC) filled with He or Ar gas taken in the CTF3 machine, normalized to the Faraday cup Plateau taken in the CTF3 machine, Ar and He chambers see slightly different showers profiles Operation voltage chosen to be 200V as nominal operating voltage Time (ns) Linear response between Chamber and Faraday cup Calibration Factor ~ 6 depending on beam loss shower shape Bias Voltage (V) Length of Plateau greater for Ar as expected. He breaks down at > 450 V Ionization signal efficiency 8/94 for He/Argon gas …and independent of energy. Chambers designed for high rate environment and saturate (with Argon) at ~ 1011cm2/μs pulse 19/24 A. Dabrowski, January 16 2007

  20. Increased sensitivity in electronics BLM Girder 6 : - SIC Argon – amplifier 2k - Faraday cup Despite very low/NO losses measured by BPM, beam loss system provides good signals Low gain (x20 CERN amplifier card) High gain (x200 CERN amplifier card) Not shown 20/24 A. Dabrowski, January 16 2007

  21. Testing of Pre-amplifier BLM Girder 5 : - SIC Argon – Fermilab pre-amplifier - Faraday cup Shielded Pre-amplifier mounted directly to chamber improves sensitivity: additional modification to be made in the future to decrease decay time of the amplifier. Principle is encouraging 21/24 A. Dabrowski, January 16 2007

  22. Test Cherenkov fiber coupled to a Photomultiplier • BLM Girder 7: • Cherenkov fiber – PMT- no amplifier • BLM Girder 6: • SIC He (2k amp) – 1st Cavity • SIC Ar (2k amp) – QUAD • Faraday Cup (2k amp) - Quad Low gain (x20 CERN amplifier card) • Cherenkov fiber coupled to a PMT provides flexible and fast response BLM. • Fused silica fiber supposed to be radiation hard up to 1Grad 22/24 A. Dabrowski, January 16 2007

  23. Summary - BLM devices Tested at CTF3 23/24 A. Dabrowski, January 16 2007

  24. Conclusions Beam Loss Monitoring: • Chambers are sensitive to beam loss along the girder …. Additional monitoring complementary to BPM has been used since 2003 • In regions of very low loss, additional sensitivity can be obtained with loss of time resolution • A pre-amplifier connected directly to the chamber tested and provides additional sensitivity • A Cherenkov fiber when coupled to a PMT, can also be used as a beam loss detector. • Many beamloss devices tested in CTF3 linac  Experience to make a good choice for what to install in TBL. Bunch Length Measurement: • Successful commissioning of the full detector in December 2006 Possible minor improvements to setup in future: • Modifications to RF-window • Additional filter at 143 GHz implemented in setup 24/24 A. Dabrowski, January 16 2007

  25. Acknowledgements RF-pickup acknowledgements and thank you’s must be made to: • Hans Braun and Thibaut Lefevre for advising and collaboration in the design of the system • Alberto Rodriguez for assistance and advice in the Labview Acquisition and DAQ for pickup • Roberto Corsini, Peter Urschuetz, Frank Tecker and Steffen Doebert assistance in general, and in particular for the machine setup of the bunch compression scan to do the first measurement. • Stephane Degeye for Aquiris card installation • Jonathan Sladen and Alexandra Andersson general consultation • Erminio Rugo and Frank Perret for mechanics • Romain Ruffieux and Christian Dutriat for electronics (BLMs & pickup) 24/24 A. Dabrowski, January 16 2007

  26. Backup Slides A. Dabrowski, January 16 2007

  27. s 1 n! Why is this measurement needed? Performances of Bunch Length detectors (table thanks to Thibaut Lefevre, CERN) Limitations • Optical radiation • Streak camera -------------------- xxxxxxx xxxxxxx > 200fs • Non linear mixing ----------------- xxxxxxx xxxxxxx Laser to RF jitter : 500fs • Shot noise frequency spectrum -- xxxxxxxxxxxxxx Single bunch detector • Coherent radiation • Interferometry ------------------- xxxxxxxxxxxxxx • Polychromator --------------------- xxxxxxxxxxxxxx • RF Pick-Up -------------------------------- xxxxxxxxxxxxxxxxxxxxx> 500fs • RF Deflector ----------------------------- xxxxxxxxxxxxxxxxxxxxx • RF accelerating phase scan -------------- xxxxxxx xxxxxxxxxxxxxx High charge beam • Electro Optic Method • Short laser pulse ------------------ xxxxxxxxxxxxxxxxxxxxx Laser to RF jitter : 500fs • Chirped pulse ----------------------xxxxxxxxxxxxxxxxxxxxx > 70fs • Laser Wire Scanner ---------------------- xxxxxxxxxxxxxxxxxxxxx Laser to RF jitter : 500fs A. Dabrowski, January 16 2007

  28. Bunch length measurement II Two scans, at different LO setting, give consistent results for bunch length measurement as a function of phase preliminary A. Dabrowski, January 16 2007

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