booster cogging robert zwaska fermilab (university of texas at austin) accelerator physics &...
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![Page 1: Booster Cogging Robert Zwaska Fermilab (University of Texas at Austin) Accelerator Physics & Technology Seminar Dec. 8, 2005](https://reader036.vdocuments.us/reader036/viewer/2022062515/56649cc25503460f9498ae7e/html5/thumbnails/1.jpg)
Booster Cogging
Robert ZwaskaFermilab
(University of Texas at Austin)
Accelerator Physics & Technology SeminarDec. 8, 2005
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Cogging
• Defined: adjusting the revolution frequency of bunched beam in a synchrotron to correspond to some external frequency
• Examples:Centering collisions in an IR
• e.g. Tevatron, RHIC
RF synchronous transfer between rings • Phaselock
Synchronization with external beam• Booster Cogging
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“Phaselock refers to experiments
on the interconnectedness of the
universe, where changes in one
part, create instantaneous changes
in the rest of the universe.”
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Example: Booster Phaselock• Match fB = fMI, B = MI • Control beam’s radial position
L. C. Teng, FERMILAB-TM-0281
)(
)()(
rC
rhvrfB
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Need for a Notch• Extraction kicker has risetime of ~ 40 ns
Only ~ 10 ns between bunches
• Beam lost at 8 GeV during extraction
• Instead, beam is removed at 400 MeV Reduces energy lost 20x
• Notch implemented for start of Run II and
MiniBooNE Reduces extraction loss 10x
• With a single batch, Booster determines
beam position in the MI
84 RF bucketsaround circumference
Notch
Booster
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Multi-Batch Operation
Batch 1 (PBar)
Batch 2
Batch 3
Batch 4
Batch 5
Batch 6
Booster
Main Injector
½ Batch(empty) ½ Batch
(empty)
• Two beams must be accelerated together in the Main Injector Extracted to PBar & NuMI
• Requires “multi-batch” operation 6 or more batches from the Booster
NuMI
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BoosterCogging
84 RF buckets
Notch
Booster
Main Injector
Circulating Beam
• Extraction on notch
Notch must be coincident with kicker pulse
Booster must be aligned with MI beam
• However:
Accelerators are not synchronized
• Cogging aligns the azimuthal position of
the notch with beam in the MI
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Do it like phaselock?• Revolution frequency is 1/84th of
RF frequency
84x the distance to be moved
Needs longer time or larger bump
• Booster has no flattop
• Bump can only be slightly larger
Need to cog during acceleration
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Cogging
Notch
MI RF
Concept – Not Reality
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Cogging turns corrected error signal
84 buckets(one turn)
Pellico & Webber
Cogging Proof of Principle
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Too Much Feedback
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The Cogging System• Controls:
Booster Radial Position Notching Extraction
• MI LLRF constraints Frequency maintained Marker maintained Takes resets from the Booster
• GMPS feedforward
• Beam Information MDAT & Booster Beam Gate
• Triggering BDOT signal TCLK timing
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Cogging Electronics• Use the “Generic” Booster Board
Also for GMPS, BLMs, etc.
• Digital and analog inputs/outputs
• Altera FPGA for fast counting
• DSP for calculations
DSPAltera
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Measurements• Monitor Notch position throughout
the cycle• Use Main Injector RF as a standard
clock• Booster RF frequency varies with
energy 38 53 MHz
• Start counting on Main Injector revolution marker (every 11 s)
• Stop Counting on Booster revolution marker (every 1.6-2.2 s)
• Makes a table of positions (tripplan)
588 buckets @ 52.8114 MHz
Mai
n In
ject
or
Rev
olut
ion
Mar
ker
84 buckets @38 – 53 MHz
Boo
ster
Rev
olut
ion
Mar
ker
(Not
ch) B
oost
er R
F
38 – 53 MHz
in 1in 2in
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Raw position
Following the Notch• RF buckets slip at a rate fMI – fB ≤15 MHz
Notch wraps around the Booster many times
• Extraction with one batch
Count RF buckets to make a marker
Extract on marker
Reset Main Injector
• With several batches
Clean extraction is possible if total slippage
is exactly the same cycle-to-cycle
Requires 1 in 1,000,000 consistency…
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Raw position Relative to baseline
~ 3 turns
Relative Slippage
• In software, we calculate the relative slippage cycle-to cycle Use a previous cycle as a baseline
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Sources of Slippage• Any perturbation to RF will cause slippage
• Over 33 ms f = 30 Hz gives 1 bucket slippage• f = 37 – 53 MHZ → part per million problem
MaximumMagnet Current
Magnet Frequency
Timing
MinimumMagnet Current
Time (ms)
S(t
) (
norm
aliz
ed)
• Several possible errors shown below: Timing: 1 s 15 bucket slip Magnet Frequency: 1 mHz 6 bucket slip Minimum Magnet current (pi): 1/10,000
10 bucket slip Maximum Magnet current (pe): 1/10,000
7 bucket slip
t
RFtdtt f
0
'' )()(Slippage
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Timing Errors• TCLK trigger is predicted from the Bdot of the
previous cycles Needs to occur few ms before the minimum
• Small variation in 15 Hz frequency can lead to s errors
Cycle trigger2.2 ms before
Bdot
64.5 ms
(Booster Momentum)
15 Hz
Fix: trigger data-taking on magnet minimum instead of clock
588 buckets @ 52.8114 MHz
Main Injector Revolution Marker
Current Minimum Cogging Start
Internal Marker
• MI markers come at arbitrary times w.r.t.
trigger
• Leads to a timing error of as much as 11 s
• Solution Generate an internal marker
synchronized to the cogging start
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GMPS Regulation• Pulsed devices drag line current
down Particularly, RF & bias supplies
• Lower line current reduces power input to GMPS
• Apply feedforward correction to GMPS inputs
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Error Corrections
~ 3 turns
w/o correction and w/ correction
~ 1 turn
• Also need MI to maintain reference RF frequency
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Predictive Notching• Delay creation of the notch 5 ms
Use information of that period Make notch anticipating further slippage.
~ 20 buckets
w/o correction and w/ correction
~ 90 buckets
Sample
Notch
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Radially Induced Slippage
• Induced slippage scales with radial offset Rates of ~ 1 kHz/mm
Calculation
r
C
r
r
p
p
2T
1
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Proportional Feedback• Notch using prediction• Radial Feedback late in the cycle• r = k ∙ S
Exponential damping k 0.2 mm / bucket e-folding time 10 ms
Notch RadialFeedback
Notch
RadialFeedback
Transition
Radial Offset
ProportionalFeedback
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Higher Gain• Causes beam loss
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Sustained (Flat) Feedback• Flat & proportional feedbacks
Small error goes to proportional feedback• Gigher Gain
Larger errors go to a large constant value of feedback
• Stay there until error is small
Notch
RadialFeedback
0 ms 33 ms15 ms 35 ms
Transition Large ConstantPost-Transition Bumps
Radial Offset
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Final Cogging Algoritm• Several timing improvements reduced beam slippage
in the Booster
• Timing improvements reduce slippage: 200 → 70
buckets
• Ultimate synchronization goal: 1 RF bucket
• Notch delayed, and placed in anticipation of slippage Pre-transition bump
• Uses a prediction algorithm• Reduces post-trans. cogging necessary
Flat feedback is the same as above Proportional feedback is doubled
Large ConstantPost-Transition Bumps
ProportionalFeedback
Transition
Feed-Forward Pre-Transition Bump
Radial Offset
Notch
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Figure of Merit: Extraction Losses• Cogging reduces extraction losses substantially
80-90%, depending on conditions
• Occasional misses caused by phaselock or small timing errors Override reduces phaselock losses by pushing error into MI
• Overall – running such that cogging losses rarely limit Booster throughput
NuMI Booster Cycles
Cogged LossesUncogged Loss
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Cogging in Balance• Hardware running stably
Very few glitches
Extraction losses reduced 80-90%
• Only method for multibatch Adequate for today’s running
• In the future: Only a few tweaks in cogging algorithms
are possible• Maybe inputs to other ramped systems
Higher intensity beam might require smaller range of movement
Phaselock can be redesigned
Faster kickers?
…
• Cogging effects: Later notch results in more loss
Radial motion• Before trans: ± 1(2) mm
• After trans: ± 2(4) mm
GMPS must be controlled
BDOT signal is vital
Phaselock interferes
MI is more constrained
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Summary: Beam Delivered• Booster cogging on multibatch cycles for slip-stacking and NuMI
Sources of variation were identified, and eliminated where possible
System to enforce synch by feedback (feedforward) System made operational ~ 1 yr ago
• Over 30,000,000 cogged cycles
• Peak proton power to NuMI has approached 300 kW, achieving 1020 protons
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Booster Cogging
Robert ZwaskaFermilab
(University of Texas at Austin)
Accelerator Physics & Technology SeminarDec. 8, 2005