novel beam instrumentation for future linear e + /e - colliders
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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
A. Dabrowski, February 21 20072/25
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
A. Dabrowski, February 21 20075/25
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
A. Dabrowski, February 21 20076/25
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
A. Dabrowski, February 21 20079/25
A. Dabrowski, February 21 2007
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
er
Sp
ectr
um
[a
.u.]
Freq [GHz]
Theory
Theory
A. Dabrowski, February 21 2007
• 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
13/25 A. Dabrowski, February 21 2007
A. Dabrowski, February 21 2007
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
A. Dabrowski, February 21 2007
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
A. Dabrowski, February 21 200716/25
Labview interface
Raw Signal
Screen for analysis
FFT Signal
Bunch length manipulation in the INFN chicane Bunch length manipulation in the INFN chicane
A. Dabrowski, February 21 200717/25
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
18/25 A. Dabrowski, February 21 2007
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).
19/25 A. Dabrowski, February 21 2007
Typical Raw and FFT pickup signals
A. Dabrowski, February 21 200720/25
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 < %.
A. Dabrowski, February 21 2007
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
er
Sp
ectr
um
[a
.u.]
Freq [GHz]
Theory
(30 – 39) ; (45-69) ; (78-90) & (157-171) GHz
Bunch length measurement result
A. Dabrowski, February 21 200722/25
• 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)
A. Dabrowski, February 21 2007
@ 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
A. Dabrowski, February 21 2007
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
A. Dabrowski, February 21 2007
• 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
A. Dabrowski, February 21 2007
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)
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