novel beam instrumentation for future linear e + /e - colliders

Novel Beam Instrumentation for Future Linear e+/e- Colliders

Anne Dabrowski

Northwestern University

Mayda Velasco (NU), Hans Braun (CERN) Thibaut Lefevre (CERN)

Bag Lunch SeminarNorthwestern University

February 21st 2007

A. Dabrowski, February 21 20071/25

Motivation: TeV lepton collider


Slide R Corsini

S. Redaelli

• High luminosity 3TeV Collider based on the ‘Two Beam Scheme’• High accelerating field of 100MV/m

CLICSlide, T Lefevre

RF power source – ‘Drive Beam’

‘Colliding Beams’

Efficient way of producing RF power with a Drive Beam:• Fully beam loading acceleration in the drive beam linac• Flexible and precise bunch frequency multiplication using RF deflector injection techniques in a delay loop and combiner rings• Efficient deceleration sections with a high Beam to RF conversion efficiency.

CLIC

CLIC parameters

CLIC ILC

Center of mass energy (GeV) 3000 500

Main Linac RF Frequency (GHz) 12 1.3

Luminosity (1034 cm-2 s-1) 6.5 2.5

Accelerating Gradient (MV/m) 100 28

Proposed sight length (km) 47 33


CLIC ILC

Bunch Length in the Linac (fs) 120 900

Typical Beam size in the Linac (μm) 1 5

Beam size at Interaction Point: σx/σy

(nm)60/0.7 550/5

Most Critical Beam Parameters for diagnostics

Machine is in design phase, parameters constantly being optimized for performance & cost. Above parameters are typical examples.

Drive Beam Parameters


Diagnostics on the beam is important in order to prevent damage of machine.

Slide, reference T. LefevreCERN Academic Training LectureJune 16 2006

Overview 3rd CLIC Test Facility

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

(2006-2007)

Electron beam facility• 1.5microsecond pulse• 150MeV electron LINAC• 3.5 Amp current • Newly commissioned delay loop• Very rich environment for beam instrumentation

development

7/25 A. Dabrowski, February 21 2007

Northwestern CTF3 Activities

A. Dabrowski, February 21 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

8/25

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– Future improvements to setup



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.

10/25

22

)( e

Solid: σt = 1 ps

Dash: σt = 2 ps

Dash-dot: σt = 3 ps

Pow

er

Sp

ectr

um

[a

.u.]

Freq [GHz]

Pow

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Sp

ectr

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[a

.u.]

Freq [GHz]

Theory

Theory


• 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

11/25

A. Dabrowski, September 05 2006

• 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 was no longer being used at CTF3.

• Goal is to re-install the device with an improved design– Increase maximum frequency reach max mixing of 170 GHz, to

reach bunch length measurements of 0.3ps. Invested + commissioned D-band waveguide components & mixer @ 157 GHz

– 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 2000-020

12/25

Investment in new hardware

– Local oscillator (Down converter) • LO 157 GHz • RF 142-177 GHz

– D-band waveguide components (waveguide WR-6 1.65 mm x 0.83

mm, cutoff 110 GHz)• D-band Horn (gain 20dB)• D-band fixed attenuator (10 dB)• D-band waveguide 5cm

– Brass high pass filter, size of holes determine cutoff



New Detector Setup

CT-line, BPR and single WR-28 waveguide to transport the signal to the gallery (~20 m).

14/25

•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.

Analysis station gallery

1

2

3

4

From the

beam

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

15/25

Signals from Acqiris scope visible in control room for real time monitoring & DAQ

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

Screen for analysis

FFT Signal

Bunch length manipulation in the INFN chicane Bunch length manipulation in the INFN chicane


KlystronV(t)

t

Accelerating structures@Girder 15

4 Bends Frascati Chicane

RF pick-up

Delay Loop

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

• 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

Nominal energyHigher energy

Lower energy

Slide T. Lefevre

Calibration of device – RF Deflector

Chicane optics & bunch length measurements - 2004

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 deflectorwavelength

Deflecting Voltage

Bunch length

y0

y

Deflecting mode TM11

RF deflector off RF deflector on

Slide T. Lefevre


Calibration of device – RF Deflector

OTR@ MTV0550SR@ MTV0361

= 8.9ps = 4.5ps

y0

y

Deflecting mode TM11

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.

RF-pickup better resolution than the Streak camera ( < 2ps).


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

Fourier Transformed signals

FFT

33 GHz

81 GHz

63 GHz, 51 GHz

162 GHz

10 measurements, at each local oscillator & phase setting. FFT done on each measurement result averaged, std dev of mean < %.


Reminder of the Theory

•Measure the power spectrum at each frequency band:

The maximum height of each FFT peak.Fit to the best bunch length, σt

21/25

Pow

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ectr

um

[a

.u.]

Freq [GHz]

Theory

(30 – 39) ; (45-69) ; (78-90) & (157-171) GHz

Bunch length measurement result


• 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

• Sub-pico second sensitivity reached.

• Self calibration method used & reliable (many measurements taken & consistent)

next step to improve & optimize setup

16 3

2)()2((2 )(22

j iij

fi yeA ji

preliminary

Improvement: Increase transmission @ high frequencies New RF Window in design

Material Thickness Relative 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 (> 100 GHz) designed a thin (0.5mm) diamond window with lower εr.

First design complete, brazing test successful, machining in progress testing to follow

Will test new window in 2007

rf

c

23/25


Improvement in setup foreseen

24/25

Analysis station gallery

1

2

3

4

From the

beam

Note:

At high frequency mixing stage:

High Pass filter @ 157 GHz;

(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 simultaneously analysed sample more frequencies

Modify filters to have spherical shape, to focus signal, capture more power higher signal.

Summary: Bunch Length detector


• RF-pickup detector has been successfully installed in the CT line in CTF3– Bunch length measurement made as a function of phase on MKS15!– The Mixer & filter at 157 GHz was tested and works.– Using Single waveguide to Pickup signal works.– The new acquires data digitizing scope installed, 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 ~143 GHz, can provide additional flexibility in the detection of high frequency mixing stage.

• Spherical surfaces on the filters to better focus the signal on the analysis board, through the detector stages.

25/25


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 (T. Lefevre, CERN)(T. Lefevre, CERN)

novel beam instrumentation for future linear e + /e - colliders

Documents

high beam

given beam

drive beam parametersa

critical beam parameters

novel beam instrumentation

beam currentat ctf3

beam pipe surfaceusing

beam loss monitoringpickup