barrier rf stacking
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Barrier RF Stacking
Weiren Chou and Dave WildmanFermilab, U.S.A.
October 20, 2004
Presentation at the Proton Driver SessionICFA-HB2004, Bensheim, Germany, Oct 18-22, 2004
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Barrier RF Study Group
Fermilab-KEK-Caltech collaboration:
• Fermilab - D. Wildman, J. Griffin, K.Y. Ng, J. MacLachlan, C. Bhat, W. Chou• KEK - A. Takagi, Y. Mori• Caltech - H. Zhang, D. Michael
Acknowledgement: Helpful discussions with Takayama’s group
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Outline
Motivation Goals and methods Simulations Barrier rf system Beam experiments Summary
http://www-bd.fnal.gov/pdriver/barrier/
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Collider Experiment Run2
Pbar target
CDF
D0
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Neutrino Experiment NuMI
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Booster – the Bottleneck
The new Main Injector can accept 25e12 protons per Booster cycle.
However, the old Booster can only deliver 5e12 particles per cycle.
Beam Energy Lost During Acceleration10/9/2000 Data (Notch off & excluding extraction)
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5 6
Protons/Pulse (E12) at 8GeV
Kil
ojo
ule
s/P
uls
e L
os
t in
Rin
g
Beam Loss vs Intensity
0
0.05
0.1
0.15
0.2
0.25
0 1 2 3 4 5
Intensity (e12 protons/pulse)
Ener
gy L
ost
(KJo
ules
/pul
se)
Webber’s data in October 2000
Prebys/Lackey’s data in January 2004
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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 Main Injector longitudinal acceptance (0.72 eV-s) is larger than the Booster beam emittance (0.13 eV-s)
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Goals
Run2 – To increase protons per second (pps) on the pbar target by 100%
• Present: 5e12 every 2 sec
• Goal: 2 x 5e12 every 2 sec
NuMI – To increase pps on the NuMI target by 70%
• Baseline: 3e13 every 2 sec
• Goal: 2 x 3e13 every 2.333 sec
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Two Methods
Adiabatic stacking: Beam injected on-axis
Adiabatically compress the beam by moving rf barrier
Fast stacking: Beam injected off-axis
Using two barriers, one stationary, another moving
Continuous injection and stacking
First proposed by J. Griffin
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Two Types of Barrier
Stationary barrier
Moving barrier
+V
-V
+V
-V
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Adiabatic Stacking
Simulation (K-Y. Ng)
Measurement
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Fast Stacking Simulation: 2-Batch
(courtesy K.Y. Ng)
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2-Batch Stacking (cont…)
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Fast Stacking Simulation: 12-Batch
(courtesy K.Y. Ng)
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12-Batch Stacking (cont…)
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12-Batch Stacking (cont…)
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12-Batch Stacking (cont…)
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12-Batch Stacking (cont…)
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12-Batch Stacking (cont…)
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12-Batch Stacking (cont…)
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Barrier RF System
Design goal: 6 kV wideband RF system
Two main components: Cavity: made of Finemet cores (Hitachi, Japan)
Modulator: made of high voltage fast switches (Behlke, Germany)
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Specifications
Fast Switch (Behlke)
HTS 161-06-GSM Peak voltage 2
16kV Peak current 60 A Pulse width 300 ns Pulse spacing 0.4-11s Repetition rate 100
kHz Burst length 400 ms Burst rep rate 0.5 Hz
Finemet Core (Hitachi)
FT3M OD 500 mm ID 139.8 mm thickness 25 mm Inductance 56 H (per
core) Resistance 190 (per
core)
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Barrier RF System (cont…)
Finemet core High voltage fast switch
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Finemet vs. Ferrite (4M2)
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Barrier RF System (cont…)
Modulator Cavity
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Full-Bridge Push-Pull Bipolar Circuit
in the tunnel
upstairs
9:1 1:9
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Bench Test
triggercurrent
primary voltage
gap voltage
Before tuning After tuning
6 kV
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Beam Experiment in the Main Injector
capture
debunchsqueez
e
rebunch
acceleration
Beam intensity
RF voltage
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Beam Experiment (cont…)
Squeezing Squeezed
Moving barrier
Beam squeezing
6 kV
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Mountain View
Stacking off Stacking on
t
1.6 s
3.2 s
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More Mountain Views
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8.3e12
@120 GeV
squeezing
High Beam Intensity after Stacking
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53 MHz RF voltage
Beam intensity (10e12)
Try Even Higher Beam Intensity
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Emittance Simulation ESME (2 x 5e12, final bunch after recapture, courtesy J.
MacLachlan)
Bucket size = 0.30 eV-s
Bucket size = 0.35 eV-s
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Stationary bucket, beam intensity = 5.23e12, emittance = 0.13 eV-s
Emittance Measurement – Injected Bunch
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Low intensity
Emittance Measurement – Stacked Bunch
High intensity
Medium intensity
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Bunch width = 10 ns moving area factor = 0.45
Stationary bucket area = 1.6 eV-s bunch emittance = 0.72 eV-s
Emittance Measurement – Accelerated Bunch
Width of Constant H Contours
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 10 20 30 40 50 60
Synchronous phase (degrees)
Co
nto
ur
wid
th (x
pi)
phi(N=1)
phi(N=0.9)
phi(N=0.8)
phi(N=0.7)
phi(N=0.6)
Area Factor of Contant H Contours
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60
Synchronous phase (degrees)
Are
a fa
ctor
alpha(N=1)
alpha(N=0.9)
apha(N=0.8)
alpha(N=0.7)
alpha(N=0.6)
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Summary
A barrier RF system has been built and installed in the Main Injector
It has successfully stacked two Booster batches into one and reached 8.3e12 at 120 GeV, ~ 60% increase in beam intensity
There is large emittance dilution during stacking Causing losses at the beginning of acceleration
Making bunch too long for pbar production
But not a problem for NuMI
A second system is under construction and will be used for fast stacking experiment
Questions?
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