nlc intra-pulse fast feedback simon jolly oxford university nlc beam delivery meeting july 2001
TRANSCRIPT
NLC Intra-PulseFast Feedback
Simon Jolly
Oxford University
NLC Beam Delivery Meeting
July 2001
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I have stolen parts of this talk from: Glen White, Steve Smith, PT and then some…..
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Plan of Action
• Requirements of a feedback system.• Current design:
– Physical specs.
– Signal filtering electronics.
– Simulated performance.
• Current status and planned tests.• Track reconstruction.• A brief word on beam jitter.• Short term and long term plans.
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Fast Feedback - Who needs it…?
• Jitter inherent in beams and accelerating structures - leads to relative position offset of beams.
• Position offset leads to
large luminosity loss:
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Y position offset (y)
Percentage Luminosity Loss
0 10 20 30
40
20
40
60
80
100
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Fast Feedback - System Constraints
• Recover significant amount of lost Luminosity.• Correct offset within a single bunch train (266ns -
hence ‘fast’...).• Dominant time factor should be distance to IP,
NOT speed of feedback - too fast for ‘analytical’ electronics.
• Be unaffected by intra-train jitter…..
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A corrective feedback system needs to:
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NLC Fast Feedback SystemQuickTime™ and aPhoto - JPEG decompressor
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System consists of 3 components:
•BPM (+ BPM processor).
•bunch charge gain adjuster. •Kicker (and kicker driver).
Bunch Charge
Use beam-beam interaction to enhance offset measurement
4m
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Design of Feedback System
• Initial system design and “proof of principle” in Simulink simulation by Steve Smith.
• Glen White (Oxford) simulation makes a number of improvements:– Includes “gain” effects.
– Accurate beam-beam interaction model - original flat beyond 12 (GUINEA-PIG).
– Effects of intra-train (bunch-to-bunch) jitter considered.
• System currently only corrects position offset (no angle jitter).
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Simulink Block DiagramQuickTime™ and aPhoto - JPEG decompressor
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Beam parameters (posn. and charge) Beam-beam
interaction
BPM processor
Beam kicker
Delay cable
Effect of kicked beam
Flight of bunches from/to IP
BPM to kicker transport delay
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BPM Processor
Most signal conditioning executed by BPM processor
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Bunch Charge
But what does it do…?
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BPM ElectronicsQuickTime™ and aPhoto - JPEG decompressor
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Band pass filter Mixer Low pass filter
Simulink diagram for BPM processor
Local oscillator for mixer
2nd stripline
1st stripline
Sum and difference
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BPM Signal FilteringQuickTime™ and aPhoto - JPEG decompressor
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Time (ns)5 10 2515 20 30
Signal on BPM
Mixer output
Band pass filter output
Low pass filter output
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BPM Electronics OutputQuickTime™ and aPhoto - JPEG decompressor
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Time (ns)0 100 200 266
BPM processor output
Position of bunch at BPM
Signal from delay cable (Kicker)
Kicker input (BPM + delay signal)
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Beam Correction at IP (Simulink)QuickTime™ and aPhoto - JPEG decompressor
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Time (ns)0 100 200 266
Vertical offset (nm)
0
-8
-6
-4
-2 Uncorrected beam position at IP
Corrected beam position at IP
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Effect of Feedback SystemQuickTime™ and aPhoto - JPEG decompressor
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Effect of the feedback system on the luminosity loss (Glen White).
0 5 10 15 20 25 30 35 400
10
20
30
40
50
60
70
80
90
100
Vertical Beam Offset ( y )
% Luminosity Loss
Feedback Off = 4.0 Gain × 10-6
= 5.0 Gain × 10-6
= 6.4 Gain × 10-6
Y position offset (y)
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What Happens Next?QuickTime™ and aPhoto - JPEG decompressor
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• Bench test BPM electronics.• Beam test of stripline BPM and electronics.• Confirm design of kicker dimensions and power
requirements - dependant upon location, train structure.
• Beam test of complete system (location on a need to know basis….).
• Reconstruction of tracks in beam test use PT’s Collimator Wakefield Matlab routines.
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Collimator Wakefields (PT)
• 4 collimation slots used.• Determination of bunch kick due to
wakefield effects.• To reconstruct kicks:
– Measure positions of bunches (25 per step) along sector 2.
– Subtract ‘reference’ track (100 bunches).
– Use transport matrices to reconstruct bunch position and angle at slot. Collimator slot
dimensions
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Reconstructed wakefield kickQuickTime™ and aPhoto - JPEG decompressor
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Collimator slot height vs. angle deviation
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Reconstructed kicks (slot 1)
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Angular Jitter on Kick ReconstructionQuickTime™ and aPhoto - JPEG decompressor
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Wakefield box slot y posn. (mm)
RMS angular jitter (r)
0-0.5-1 0.5 10
0.5
1.0
1.5
2.0
2.5
Collimator slot height vs. angular jitter for reconstructed wakefield kicks (slot 1)
1.4-1.4
3.5
3.0
4.0
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2D Histogram of beam jitter
A Quick Look at Position JitterQuickTime™ and aPhoto - JPEG decompressor
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Data taken from 160 data samples over 12 days
XY
500 x 500 m
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X and Y jitter on SLC e- beamQuickTime™ and aPhoto - JPEG decompressor
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x distance from mean orbit posn. (m)
Histogram of jitter in x Histogram of jitter in y
y distance from mean orbit posn. (m)
0 50 100-100 -500 50 100-100 -50
x = 17.65 m y = 14.34 m
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Time Dependence of JitterQuickTime™ and aPhoto - JPEG decompressor
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Run number
Beam jitter in y for 3 BPM’s
y (m)
Chart shows beam jitter (rms deviation from mean) for 3 BPM’s during 160 runs. Each point is rms of y position for 100 bunches (1 reference scan).
Includes 12 days worth of data.
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Time Dependence of Jitter (2)QuickTime™ and aPhoto - JPEG decompressor
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Run number
0 40 80 120 160
Beam jitter in y for 7 BPM’s BPM #
114
146
301
411
511
631
801
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And Finally...
• Next step is to bench test BPM electronics.• Start looking at possible solutions for kicker
design.• Longer term: beam tests of BPM systems, kicker
design and complete system.• Very very long term: install system in the NLC….
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