Novel Instrumentation for future TeV e+e- colliders Detectors for bunch length measurement and Beam loss monitoring Mayda Velasco, Anne Dabrowski, Alex Carter Northwestern University DOE site visit September 2006 A. Dabrowski, September /33

Overview CTF3 Facility A. Dabrowski, September Drive Beam Injector Drive Beam Accelerator PETS Line 30 GHz source Stretcher Delay Loop TL1 (2006) CR (2006) TL2 (2007) CLEX (2007) 30 GHz tests RF photo- injector test ( ) Electron beam facility 1.5microsecond pulse 150MeV electron LINAC 3.5 Amp current Newly commissioned delay loop Very rich environment for beam instrumentation development 2/33

Overview Northwestern CTF3 Activities A. Dabrowski, September Drive Beam Injector Drive Beam Accelerator PETS Line 30 GHz source Stretcher Delay Loop TL1 (2006) CR (2006) TL2 (2007) CLEX (2007) 30 GHz tests RF photo- injector test ( ) Beam Loss Monitoring Pickup for bunch length measurement 3/33

Outline RF pickup for bunch length measurement –Principle of the measurement –Advantages of this type of bunch length measurement? –Status of the hardware designed, installed and tested in 2005/2006 –Hardware and design improvements still to be installed before the Fall data taking. –Work planned for the Fall: Final setup installed, tested Analysis performed in normal beam operation Beam loss Monitoring –Reminder devices installed and fully instrumented since 2003 –Ongoing work in optimization of setup A. Dabrowski, September /33

A. Dabrowski, September Principle of the measurement I The frequency spectrum of the bunch contains all the information about the bunch shape and length. The field induced in the waveguide has a temporal evolution directly related to that of the electron bunch Hence it is possible to derive the spatial charge distribution from the frequency spectrum of the field excited in the waveguide In this measurement, one takes advantage of the power spectrum in the frequency domain. For a given beam current, the larger the power spectrum amplitude, the shorter the bunch length. The RF-pickup detector measures the spectrum of the electromagnetic field of the bunch collected by a rectangular RF- pickup connected to a waveguide. 5/33

Principle of the measurement II  The smaller the bunch length the larger the signal at a given frequency  The smaller the bunch length the larger measured power  To reach the < ps sensitivity, need to have reach of high frequencies Solid: σ t = 1 ps Dash: σ t = 2 ps Dash-dot: σ t = 3 ps Power Spectrum [a.u.] Consider an electron bunch of N particles with longitudinal charge distribution Λ(z) The frequency spectrum is found by Fourier transformation the fields, e.g. A. Dabrowski, September /33

A. Dabrowski, September 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 If used with the RF deflector and/or a streak camera (method of measuring bunch length at CTF3) –Can provide an excellent cross calibration of device Advantages of the RF-Pickup 7/33

A. Dabrowski, September An RF pickup was installed in CTF2 –Rectangular waveguide coupled to a rectangular hole made on the beam pipe surface –Using the mixing technique it measured bunches as short as 0.7ps. It was limited by a maximum mixing frequency of 90 GHz. This device was dismantled in 2002, and is no longer being used at CTF3. Goal is to re-install the device with an improved design –Increase maximum frequency reach to max mixing at 170 GHz, to reach bunch length measurements of 0.3ps –Design a ceramic/diamond RF window for good vacuum and transmission at high frequency –Spectral analysis by single shot FFT analysis from a large bandwidth waveform digitizer RF-pickup device installed in CTF2 C. Martinez et al, CLIC note /33

A. Dabrowski, September mixing technique in CTF3 Install one WR-28 pickup, with WR-28 waveguide to transport the signal to the gallery Use a series of filters, and waveguide pieces on the same mounting board in the gallery to separate the signal from the beam in the following frequency ranges: WR-28 Waveguide components, and mixer at 26.5 GHz WR-12 Waveguide components and mixer at 56.5 GHz and at 74.5 GHz (27 – 39) GHz ( ) GHz (75 – 90) GHz (60 – 72) GHz WR-6 Waveguide components with mixer at 157 GHz (143 – 157) GHz (157 – 170) GHz Recuperated from CTF2 NEW NWU 9/33

Investment in new hardware A. Dabrowski, September Components purchased by Northwestern –Local oscillator (Down converter) LO 157 GHz RF GHz –D-band waveguide components (waveguide WR mm x 0.83 mm, cutoff 110 GHz) D-band Horn (gain 20dB) D-band fixed attenuator (10 dB) D-band waveguide 5cm Status: Installed and tested - OK 10/33

Investment in new hardware – Filters A. Dabrowski, September Fabrication of Brass filter at 157 GHz –Conical edge at angle of 20 degrees, thickness 3 x diameter of hole Used as a high/low pass filter to study frequency band: – 157 GHz-14 GHz – 157 GHz+14 GHz Other filters to be used from CTF2 setup: 26.5 GHz, 40 GHz, 56.5 GHz, 74.5 GHz Scale (mm) Status: Installed and tested - OK 11/33

Investment in new hardware – Digitizer A. Dabrowski, September Acqiris DC282 High-Speed 10-bit PXI/CompactPCI® Digitizer 4 channel 3 GHz bandwidth with 50 Ω high- frequency front end 2 GHz bandwidth with 50 Ω standard front end 2-8 GS/s sampling rate Auto-install software with application code examples for C/C++, MATLAB, National Instruments LabVIEW etc  Provide a single shot FTT in real time Status: Currently being installed 12/33

Installation of Pickup and waveguides October 2005 Shutdown Pickup with Al window (3.35 mm thickness) installed in the CT line Signal from BPR0523 split, and ½ taken to the gallery along ~ 15m of WR-28 waveguide A. Dabrowski, September 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 /33

Installed analysis station in Gallery A. Dabrowski, September st 26.5 GHz 2 nd 56.5 GHz 3 rd 74.5 GHz Analysis board for (28 – 90) GHz 14/33

A. Dabrowski, September Examples of Signals from May 2006 Mixer: 56.5 GHz LO: 9.6 GHz Peaks: 0.1 GHz  Beam signal 66 GHz Equipment recuperated from CTF2 installed correctly & functions well Mixer: 26.5 GHz LO: 9.6 GHz Peaks: 0.1 GHz  Beam signal 36 GHz 15/33 Plots Alex Carter

A. Dabrowski, September Signal for analysis to the Oscilloscope Input signal from the Local Oscillator for the second stage of mixing Beam signal from WR-28 waveguide Output of 1st mixing stage at 157 GHz 157 GHz brass filter. Analysis of (143 – 170) GHz (setup in transmission or reflection) Installed analysis station in Gallery 16/33

A. Dabrowski, September Analysis of Signals from May 2006 Mixer: 157 GHz LO: 11.4 GHz Peaks: 0.4 GHz  Beam signal 168 GHz ! New 157 GHz mixer works well! Showed proof of principle that power measurements at high frequency can be done at > 150 GHz!  Reach sub-pico second bunch length measurement 17/33

Optimization of Window MaterialThicknessEpsilon Al window3.35 ± 0.07 mm9.8 CVD diamond window0.500 ± mm(~6 at 30 GHz CERN A. Dabrowski, September GHz through Al  λ is effectively ~ 1 mm  Al window not optimized for good transmission  designed a thin (0.5mm) diamond window with lower ε r. (~6 at 30 GHz CERN) Design prototype completed. Machining and brazing test happening now.  plan install window in machine before Fall data taking. 0.5mm 18/33

Work needed before Fall data taking Complete machining and brazing of new diamond Window. Redesign analysis board in gallery: –All 4 mixing stations read out at once with newly installed large bandwidth waveform digitizer. –Careful attention must be paid to alignment Write software: – For new Acquiris data acquisition. –To remotely control the local oscillator Write analysis code to use the new system for data taking during the run. A. Dabrowski, September /33

Calibration of device - Fall data taking A. Dabrowski, September Chicane optics & bunch length measurements Magnetic chicane (4 dipoles) RF Deflector Screen Betatron phase advance (cavity-profile monitor) Beta function at cavity and profile monitor Beam energy RF deflector phase RF deflector wavelength Deflecting Voltage Bunch length  y0 yy Deflecting mode TM 11 RF deflector offRF deflector on Slide from Thibaut Lefevre (CERN) 20/33

Calibration of device - Fall data taking A. Dabrowski, September Bunch Length Measurement with the Streak Camera MTV0550 MTV0361 Two different bunch compression settings in the Frascati Chicane  = 8.9ps  = 4.5ps Maximum Sweep 10ps/mm 21/33

Calibration of device - Fall data taking A. Dabrowski, September MTV0550 MTV0361  = 8.9ps  = 4.5ps Betatron phase advance (cavity-profile monitor) Beta function at cavity and profile monitor Beam energy RF deflector phase RF deflector wavelength Deflecting Voltage Bunch length  y0 yy Deflecting mode TM 11 Calibration Strategy: For various settings on the chicane, take bunch length measurements using both the RF deflector, and the RF-pickup. Calibrate the response function of the pickup.  Once calibrated, the pickup can be installed anywhere else in the machine where a bunch length measurement is needed. The RF-pickup is a much less expensive device than the RF deflector & Streak camera. Should have better resolution than the Streak camera. 22/33

Summary of work on Bunch Length detector A. Dabrowski, September An RF-pickup has been installed in the CT line in CTF3 The setup should provide a bunch length measurement up to 0.3ps The RF-pickup is installed close to the RF deflector for a good cross calibration of bunch length. Proof of principle during May 2006: –Measuring high frequencies with a WR-28 waveguide pickup was possible! –The Mixer at 157 GHz was tested and works well. –The filter machined at 157 GHz works well. Improved RF diamond window for high frequencies is being machined and brazed, and on schedule to be installed in machine before Fall data taking. The new acquiris data digitizing scope is ready for installation, and programming of the DAQ is schedules for the fall. The RF-pickup device is flexible, and can be installed in various locations once calibrated 23/33

BLM s installed along the Linac Beam position monitor Accelerating structure Quadrupoles e-e- Y z x Typical Linac section Design beam optics Goal : To install the BLM at a position where the beam could be lost Install 3 chambers and 1 Faraday Cup per Girder which have an accelerating structure A. Dabrowski, November Chamber installed 24/33

Beam Loss monitoring A. Dabrowski, September Full setup since detectors installed per girder. Cross calibration with Faraday cup Electronics with 2 gain ranges (x10 difference) 25/33

Beam Loss monitoring A. Dabrowski, September Goal is to measure secondary shower, and from there determine if possible where the original source of the shower was: From Geant3.21 simulation [1] Secondary e+/e- flux distribution at 100cm from the point of the beam loss in the X/Y plane transverse to the beam line Secondary e+/e- flux versus the longitudinal position. Each curve corresponds to the output signal amplitude of each of the 4 detectors located at different z positions along a LINAC module. [1] M. Wood, CTF3 note 064, (2004) 26/33

Beam Loss monitoring A. Dabrowski, September Energy distribution of photons and electrons produced by 0.1% loss of 25MeV electrons in the LINAC coming out at an angle of 30mrad Signals in the detector will have dominant contributions from both photons and electrons. Cross sections, at low photon energy 10 MeV pair production.  Signals has contributions from Photoelectric effect, secondary emission and ionisation 27/33

Calibration Plateau Calibration Plateau for chambers 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, September Length of Plateau greater for Ar as expected. He breaks down at > 450 V 28/35

Girder 6 Girder 5 Beam loss with nominal beam optics low x20 gain amplifier Chamber signals for nominal beam optics have good signal and time response with only low x20 gain amplifier (and 50 Ω resistor) Linear response between Chamber and Faraday cup Calibration Factor ~ 6 depending on beam loss shower shape System Provides a Mapping of beam loss in Z along girder ! A. Dabrowski, September /35

Girder 6 High gain (x200) for the electronics Girder 5 Very Low losses Very Low losses on Girder 5 /6 Losses at the limit of the BPM resolution … signals on Girder 6 visible with high gain electronics, but on Girder 5 we are not sensitive to losses  BUT perhaps there were no losses? High gain (x200) for the electronics A. Dabrowski, September /35

Very Low Losses on Girder 6 gain (x200(x20  1K)) for the electronics Data taken with very low loses in the beam … Modified the electronics to increase the sensitivity… 50Ω input impedance to the amplifier replaced by 1kΩ (x20 more) still with the amplifier gain of x20 or x200 Drawback : we loose the time resolution (x20 slower) Since the Calibration Factor between SEM and Faraday cup X5, and input impedance factor is x20, here we are in the less than ‰ region of beam loss A. Dabrowski, November In this condition… SEM sees the beam loss, but the Faraday Cup in the noise. 31/35

Alternative detector for region of low beam loss Signal from PMT Relative calibration with Faraday Cup x200 at 300 V A. Dabrowski, November In the 1 st cavity Girders 11/12 … Energy ~ MeV From Simulation, beam loss is more collimated at higher energy … A PMT as Cherenkov detector was installed in the 1 st Cavity, together with a Faraday Cup. Change PMT voltage, depending of sensitivity required PMT have relatively low dynamic range (10 3 ) within a given voltage gain At 300V bias voltage, the PMT is x200 more sensitive than the Faraday cup Here we estimated the loss to be lower than of the beam current 32/33

Summary … Beam Loss on Linac A. Dabrowski, November  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, Chambers sensitive if one sacrifices resolution, and integrates over large impedance.  Alternate electronics are being considered for the Fall, for a test in Low loss environment.  Amplifier installed inside chamber box (discussions with Jim Crisp at Fermilab Beams division  lot of experience building electronics for beam current monitors). Benefit from reducing the RC (capacitance dominated by cable  increase input impedance and maintain time resolution) 33/33

A. Dabrowski, September Backup Slides

A. Dabrowski, September 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)