Progress in Barrier Stacking
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Transcript of Progress in Barrier Stacking
MAP Meeting, IUCF March 12-13, 2007 1
Progress in Barrier Stacking
W. Chou, J.Griffin, K.Y. Ng, D. WildmanFermilab
Presented to MAP MeetingIUCF, Indiana
March 12-13, 2007
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Content of Talk
• Motivation• Method• Simulation• Experiment
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Fermilab Accelerator Complex
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Booster – the Bottleneck
• The Booster is a 30 years old machine has never been upgraded.
• The 400-MeV Linac can deliver 25 x 1012 particles perBooster cycle.
• The 120-GeV Main Injector can accept 25 x 1012 particlesper Booster cycle.
• However, the 8-GeV Booster can only deliver 5 x 1012
particles per cycle.
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Solution — Stacking
• A solution is to stack two Booster bunches into one Main Injector RF bucket.
• This is possible because the much larger momentum acceptance of the Main Injector.
(bucket width = 18.9 ns) Booster MI
Mom. Acceptance
0.13 eV-s (±11 MeV)
0.70 eV-s (±58 MeV)
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Stacking Goal
• Goal for Run II – To increase protons per second (pps)on the pbar target by 50%– Baseline: 5 x 1012 every 1.467 sec– Goal: 2 x 5 x 1012 every 2 sec
• Goal for NuMi – To increase pps on NuMi target by 60%– Baseline: 3 x 1013 every 1.867 sec– Goal: 2 x 3 x 1013 every 2.333 sec
• Slip stacking can raise proton intensity from 5.0 x 1012 per batch to 7.0 x 1012. (K. Seiya, et al., PAC’05)
• We are going to study barrier stacking here.
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Barrier Stacking by J. Griffin
Booster batch injected off-energy so that top of batch slips 42 bkts per booster cycle.
Barrier moves to left at 42 bkts per booster cycle.
After 1 booster cycle, first batch passes front of barrier.
2nd batch is injected 42 bkts from 1st batch.
Strength of barrier is determined by δf1 = δf2
.This is the only parameter in the model.No solution if energy spread is too large.
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• For the injection of Booster batch into MI, allowablemaximum energy spread is ΔE = ±4.90 MeV.Corr. integrated barrier strength VT1 = 3.142 kV-µs.
• Booster bunch area: ~0.10 eV-s, bucket width: 18.9 ns.
• If completely debunched, ΔE = ±2.64 MeV.• For the bunch filling whole bucket,. ΔE = ±4.15 MeV• If a harmonic cavity is installed, booster bunch can be
lengthened with ΔE reduced.
• E.g., bunch at Vrf = 5.0 kV and a 3rd harmonic cavity reduces ΔE to ±5.18 MeV.
• E.g., bunch at Vrf = 4.8 kV and a 2nd harmonic cavity reduces ΔE to ±4.56 MeV.
• If ΔE can’t be reduced, method still works if barrier is allowed to move faster. However, this will reduce the number of batches to be injected.
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Simulation of Stacked Injection
1st batch injection 2nd batch injection
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3rd batch injection 4th batch injection
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6th batch injection5th batch injection
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8th batch injection7th batch injection
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10th batch injection
9th batch injection
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12th batch injection
11th batch injection
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After 12th Booster cycle After 13th Booster cycle
Best time to re-capture
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Hardwares
• Task: To build two ±8 kV wideband RF cavities. (i.e., the barrier RF)
• There is no low-level RF. The on-and-off of the RF voltage is handled by a high voltage solid-state fast switches made by Behlke Co. (German).
• These fast switches have been applied to the design of an RF chopper built at Chiba by a KEK-Fermilab team.
W. Chou, et al., Design and Measurements of a Pulsed Beam Transformer as a Chopper, KEK Report 98-10 (Sep. 1998).
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Finemet Cavity as a Chopper(installed on the linac of HIMAC in Chiba)
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Finemet Core(a nanocrystal magnetic alloy patented by Hitachi)
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High-Voltage Fast Switch(MOSFET Switches made by Behlke Co.)
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The Broad-Band Barrier RF Cavity
W.Chou, et al., Barrier RF System and Application in MI, PAC’05
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Building of the Barrier RF System
Switch
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Building the Barrier RF Cavity
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Testing a RF Cavity
One barrier Two barriers per MI period
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Barrier Stacking Experiment
Normal Inj. from Booster to MI at frf = 52,811,400 Hz.Injection is on-energy. No drift at all. Barrier is off.2nd batch injected 84 bkts from first batch.Mountain-view is 256 MI turns per trace.
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Off-Energy Injection with Barrier Off
Inject at frf = 52,812,014 Hz (614 Hz > nominal).
Booster above transition, so beam energy <
nominal. 2nd batch injected 42 bkts from the first.
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Computation of ΔE offset
• (Δfrf/frf)B = 1.163x10-5
• Booster slip factor ηB= 0.022436
• Mom offset Δp/p = -ηB-1(Δfrf/frf)B= 5.136x10-4
• Energy offset ΔE = -4.54 MeV
• However, once inside MI, which is at ηMI= -0.008888,
beam revolves at a lower frequency than nominal:
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clock
beam
11.56 MeV
4.54 MeV
Because there is no low-level RF, the barrier and the mountain-view will be at the locked RF frequency.
The movement of the barrier can be accomplished by adding a delay.
frf = 52,812,014 Hz
frf = 52,811,400 Hz normal
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Turning on Barrier on the Right Side
The beam is seen reflected from barrier on the right.
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Stationary barrier One barrier moving
Barrier trigger = Mountain view = 52,812,014 Hz
Adjusting Barrier Position and Speed
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Moving Barrier, 4 Pulses, No Bunch Rotation
Mountain view = 52,812,014 Hz, frf = 52,812,014 Hz
Consecutive batch spacing 42 buckets
Final beam width of 4 pulses only ~3.5 μs, half of that w/o barrier
3.5
μs (unstacked 4 batches: 6.36 μs)
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Moving Barrier, 6 Pulses, No Bunch Rotation
Mountain view = 52,812,014 Hz, frf = 52,812,014 Hz
Consecutive batch spacing 42 buckets
Final beam width of 6 pulses only ~5.5 μs, half of that w/o barrier
(unstacked 6 batches: 9.54 μs)
5.5 μm
Some reflected beam catches up with moving barrier.
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Mountain view = 52,812,014 Hz, frf = 52,812,014 Hz
Consecutive batch spacing 42 buckets
Final beam width of 6 pulses only ~5.5 μs, half of that w/o barrier
Moving Barrier, 6 Pulses, with Bunch Rotation
(unstacked 6 batches: 9.54 μs)
5.5 μs
Some reflected beam catches up with moving barrier.
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Moving Barrier, 8 Pulses, No Bunch Rotation
Mountain view = 52,812,014 Hz, frf = 52,812,014 Hz
Consecutive batch spacing 42 buckets
(The 8 injections were lousy but no time to improve it)
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Recapture (no bunch rotation)
Mountain view = 52,812,016 Hz,
frf = 52,812,016 Hz
2nd batch 42 bkts from 1st injection
Capture Vrf = 850 kV in ~45 ms
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First Few Turns of the First Batch
Mountain view = 52,812,016 Hz, frf = 52,812,016 Hz
No bunch rotation
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First Few Turns of the First Batch
Mountain view = 52,812,016 Hz, frf = 52,812,016 Hz
With bunch rotation, B:BRLVL = +8.7
Not as dramatic as expected.
Capture result almost the same.
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beam
11.59 MeV
4.55 MeV
Barrier width is fixed at T1 = 0.3 μs, height is reduced gradually from V = 12 kV until beam leaks out.
is confined,
from which beam’s energy spread ΔE can be inferred.
frf = 52,812,014 Hz clock
frf = 52,811,400 Hz normal
beam
Beam’s Energy Spread
ΔE
ΔEtotal
barr
ier V
T1
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With BR, 9.5 kV —> ΔE = 6.42 MeV With BR, 9.0 kV —> ΔE = 5.77 MeV
Thus half energy spread is 5.77 MeV < ΔE ≤ 6.42 MeV But with BR off, need 11 kV to avoid leakage, ΔE ≤ 8.14 MeV. Thus bunch rotation works, although not dramatically.
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It is hard to imagine ΔE > 13.15 MeV for 6-turn beam.
We are told that it should be from 8 to 12 MeV.
With BR, 2-turns injection11 kV —> ΔE > 8.14 MeV
With BR, 6-turns16 kV —> ΔE > 13.15 MeV
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Re-capture Results
First 3 turns After capture
Vrf 786 kV 926 kV
Full Bunch Length 5.10 ns 14.0 ns
Half Bunch Height 0.025 V 0.0111 V
Bunch Area (xconstant)
0.099 eV-s 0.807 eV-s
Height x Width 0.128 V-ns 0.156 V-ns
Bunch area increases 8.15-fold.
Amount of charge captured proportional to Height x Width, or 0.156/0.128/2 = 61%.
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Recapture
Vrf= 850 kV, frf= 52,811,400 Hz
bunch rotation (yes or no?), 6 Booster turns
Large beam loss. Maybe ΔE is much larger and cannotpenetrate the moving barrier. Beam passes through reflecting barrier on the right; strength of that barrier is not large enough.
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Moving barrier: 6 kV, 0.3 µs, integrated strength 1.8 kV-µs. Barrier is not strong enough to accel. top of beam to +ve energy. Final energy spread is large —> beam loss in recapture. At this moving rate, barrier V can increase up to V = 8.69 kV.
frf = 52,811,400 Hz nominal
frf = 52,812,014 Hz clock
4.6 MeV
11.6 MeV
6.4 MeV
17.5 MeV
17.5 MeV
beam
0.15 MeV
Then final half spread is ΔE = 15.0 MeV. This can be further reduced by increasing V and let barrier move faster.
beam
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• We have been successful in– injecting into MI off-energy,– setting a barrier moving at a prescribed rate,– stacking so far up to 8 booster batches into a width of
~ 4 batches,– re-capturing the stacked beam, although with large
increase in bunch area and large beam loss.
• Future improvement:– Better understanding of the beam and RF maneuvering.– Improvement in bunch rotation in Booster so as to reduce
ΔE, which is the source of beam loss in recapturing.– To built a low-level RF, if possible, so that barrier and
mountain view can be referenced to MI nominal frequency.– Study with more intense beam and more batches.
Summary