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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. 1/24. A. Dabrowski, January 16 2007. 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 1/24 A. Dabrowski, January 16 2007

  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 Picked-up using rectangular waveguide connected to the beam pipe, followed by a series of down-converting mixing stages and filters. For a given beam current, the larger the power spectrum amplitude, the shorter the bunch length. Solid: σt = 1 ps Dash: σt = 2 ps Dash-dot: σt = 3 ps Power Spectrum [a.u.] Freq [GHz] 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 reach to 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 • Spectral analysis by single shot FFT analysis from a large bandwidth waveform digitizer • NWU Purchased & commissioned fast Acqiris digitizing card • Design a ceramic/diamond RF window for good vacuum and transmission at high frequency • First design complete, machining in progress  testing to follow C. Martinez et al,CLIC note 2000-020 6/24 A. Dabrowski, January 16 2007

  7. New hardware installed CTF3 Analysis station gallery CT-line, BPR and single WR-28 waveguide to transport the signal to the gallery (~20 m) 4 2 1 • Filters, and waveguide pieces separate the signal from the beam into 4 frequency-band detection stages • Series of 2 down mixing stages at each detection station 3 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. Raw Signal FFT Signal Analysed FFT Signal Labview interface 9/24 A. Dabrowski, January 16 2007

  10. Slide showing how bunch compression is done CTS.MTV 0605 Dump CD.DHL 0101 CD.BPM 0105 CD.VPI 0104 Dump CT.BPM 0515 CT.VVS 0512 CT.QFD 0530 CT.BPR 0532 CT.QDD 0520 CT. PHM 0560 CT. WCM 0525 CT.DHD0505 CT.BHD 0510 CT.BHE 0540 CT.MTV 0550 • Add plot to show where Klystron 15 is, and how bunch compression is done by changing the phase 10/24 A. Dabrowski, January 16 2007

  11. Typical raw and FFT pickup signals Example, LO 6100 MHz, phase MKS15 355 degrees, 06-12-2006 11/24 A. Dabrowski, January 16 2007

  12. Bunch length measurement I, Dec 2006 Data analysed using a self calibration procedure, by means of Chi square minimization. -Check with Hans about error bars Maximum of FFT vs phase MKS15 preliminary 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 Possible improvement of Setup: RF Window @ 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 designed a thin (0.5mm) diamond window with lower εr. 14/24 A. Dabrowski, January 16 2007

  14. 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 well. • 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 140 GHz, can provide additional flexibility in the detection of high frequency mixing stage 15/24 A. Dabrowski, January 16 2007

  15. Beam Loss monitoring • Full setup since 2003 • 3 detectors (SICs) installed per girder, with a cross calibration with Faraday cup • Goal: To provide additional information along the girder that the BPM can’t provide • Electronics with 2 gain ranges (x10 difference) 16/24 A. Dabrowski, January 16 2007

  16. Reminder Beam Loss Monitoring on Linac • Beam Loss Monitoring setup of Small Ionization Chambers and Faraday cups provides additional monitoring information complementary to BPM’s • Used at CTF3 since commissioning in 2003 (see talk 2004 collaboration meeting) • Setup 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 • 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 17/24 A. Dabrowski, November 24 2004

  17. 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 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 18/24 A. Dabrowski, January 16 2007

  18. Increased sensitivity in electronics BLM Girder 6 : - SIC Argon – amplifier 2k - Faraday cup Despite very low/NO losses measured by BPM, chambers provide good signals 19/24 A. Dabrowski, January 16 2007

  19. 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 20/24 A. Dabrowski, January 16 2007

  20. 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 • Cherenkov fiber coupled to a PMT provides flexible and fast response BLM. • Fused silica fiber supposed to be radiation hard up to 1Grad 21/24 A. Dabrowski, January 16 2007

  21. 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. 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 140 GHz implemented in setup 22/24 A. Dabrowski, November 24 2004

  22. Acknowledgements RF-pickup acknowledgements 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 • 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 23/24 A. Dabrowski, November 24 2004

  23. Backup Slides A. Dabrowski, January 16 2007

  24. 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

  25. Bunch length measurement II Two scans, at different LO setting, give consistent results for bunch length measurement as a function of phase preliminary 13/24 A. Dabrowski, January 16 2007

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