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 meetingJanuary 2007

A. Dabrowski, January 16 20071/24

Overview Northwestern CTF3 Activities

A. Dabrowski, January 16 2007

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

(2006-2007)

‘Gallery’

Timing & 100MHz ADC’s

0-2kVPower supply

Cables Patch Panel

Beam position monitor

Acceleratingstructure

Quadrupoles

e-

‘Tunnel’

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

– Results of data taking in the Fall NEW NEW– Future improvements to setup

• Beam loss Monitoring

– Reminder: devices installed and fully instrumented since 2003

– Ongoing work in optimization of setup



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.

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22

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Solid: σt = 1 ps

Dash: σt = 2 ps

Dash-dot: σt = 3 ps

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Freq [GHz]

Freq [GHz]


• 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


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 2000-020

6/24


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

1

2

3

4

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

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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.


Raw Signal

FFT Signal

Analysed FFT Signal

Labview interface

Slide showing how bunch compression is doneSlide showing how bunch compression is done

• Add plot to show where Klystron 15 is, and how bunch compression is done by changing the phase


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10/24

Typical raw and FFT pickup signals


Example, LO 6100 MHz, phase MKS15 355 degrees, 06-12-2006

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

preliminary

Maximum of FFT vs phase MKS15

Possible improvement of Setup: RF Window

Material Thickness Epsilon

Al203 window 3.35 ± 0.07 mm 9.8

CVD diamond window 0.500 ± 0.005 mm (~6 at 30 GHz measured @ CERN by Raquel)


@ 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.

•Design prototype for diamond window completed.

•Brazing Test successful

•Machining of window in progress RF properties and test in machine to follow.0.5mm

rf

c

14/24

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 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


‘Gallery’

Timing & 100MHz ADC’s

0-2kVPower supply

Cables Patch Panel

Beam position monitor

Acceleratingstructure

Quadrupoles

e-

‘Tunnel’

•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

Reminder Beam Loss Monitoring on Linac

A. Dabrowski, November 24 200417/24

• 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 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

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


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


BLM Girder 6 :- SIC Argon – amplifier 2k- Faraday cup

6000 7000 8000-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

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SIC Ar (2k amplifier)- Position Quad Fadaday cup - Position QuadA

mpl

itude

(a.

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Time (ns)

Despite very low/NO losses measured by BPM, chambers provide good signals

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

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


Conclusions

A. Dabrowski, November 24 2004

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 resolutionA pre-amplifier connected directly to the chamber tested and provides additional sensitivityA 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 24 2004

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


Backup Slides


Why is this measurement needed?

• Optical radiation• Streak camera -------------------- xxxxxxx xxxxxxx > 200fs• Non linear mixing ----------------- xxxxxxx xxxxxxx Laser to RF jitter : 500fs• Shot noise frequency spectrum -- xxxxxxx xxxxxxx Single bunch detector

• Coherent radiation• Interferometry ------------------- xxxxxxx xxxxxxx• Polychromator --------------------- xxxxxxx xxxxxxx

• RF Pick-Up -------------------------------- xxxxxxx xxxxxxx xxxxxxx > 500fs

• RF Deflector ----------------------------- xxxxxxx xxxxxxx xxxxxxx

• RF accelerating phase scan -------------- xxxxxxx xxxxxxx xxxxxxx High 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

1 n! Limitations

Performances of Bunch Length detectors Performances of Bunch Length detectors (table thanks to Thibaut Lefevre, CERN)(table thanks to Thibaut Lefevre, CERN)

Bunch length measurement II


Two scans, at different LO setting, give consistent results for bunch length measurement as a function of phase

preliminary

detectors for bunch length measurement and beam loss monitoring

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