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 /24

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

Outline RF pickup for bunch length measurement –Principle of the measurement –Report on activities during 2006 Hardware designed, installed & tested Electronics Software NEW –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 A. Dabrowski, January /24

A. Dabrowski, January 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. 4/24 Solid: σ t = 1 ps Dash: σ t = 2 ps Dash-dot: σ t = 3 ps Power Spectrum [a.u.] Freq [GHz]

A. Dabrowski, January 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 Advantages of the RF-Pickup 5/24

A. Dabrowski, January 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 Goal of new RF-pickup installation in CTF3 C. Martinez et al, CLIC note /24

A. Dabrowski, January New hardware installed CTF3 CT-line, BPR and single WR-28 waveguide to transport the signal to the gallery (~20 m) 7/24 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 Analysis station gallery

Electronics for Acquisition A. Dabrowski, January Acqiris DC282 Compact PCI Digitizer 4 channels 2 GHz bandwidth with 50 Ω standard front end 2-8 GS/s sampling rate 8/24 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

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. A. Dabrowski, January /24 Raw Signal FFT Signal Analysed FFT Signal Labview interface

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

Typical raw and FFT pickup signals A. Dabrowski, January /24 Example, LO 6100 MHz, phase MKS degrees,

Bunch length measurement I, Dec 2006 A. Dabrowski, January /24 Data analysed using a self calibration procedure, by means of Chi square minimization. -Check with Hans about error bars preliminary Maximum of FFT vs phase MKS15

Possible improvement of Setup: RF Window MaterialThicknessEpsilon Al window3.35 ± 0.07 mm9.8 CVD diamond window0.500 ± mm(~6 at 30 GHz CERN by Raquel) A. Dabrowski, January GHz through Al  λ is effectively ~ 1 mm Although obtain Good signal in December commissioning of RF-pickup ; Al window not optimized for good transmission at high frequencies  designed a thin (0.5mm) diamond window with lower ε r. Design prototype for diamond window completed. Brazing Test successful Machining of window in progress  RF properties and test in machine to follow. 0.5mm 14/24

Summary: Bunch Length detector A. Dabrowski, January 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 frequencies is 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

Beam Loss monitoring A. Dabrowski, January Full setup since 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

Reminder Beam Loss Monitoring on Linac A. Dabrowski, November /24 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 –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

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 Linear response between Chamber and Faraday cup Calibration Factor ~ 6 depending on beam loss shower shape A. Dabrowski, January Length of Plateau greater for Ar as expected. He breaks down at > 450 V 18/24 Time (ns) Bias Voltage (V)

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

Testing of Pre-amplifier A. Dabrowski, January /24 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

Test Cherenkov fiber coupled to a Photomultiplier BLM Girder 7: -Cherenkov fiber – PMT- no amplifier BLM Girder 6: -SIC He (2k amp) – 1 st 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 A. Dabrowski, January /24

Conclusions A. Dabrowski, November 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

Acknowledgements A. Dabrowski, November 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, January Backup Slides

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

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