Advanced Accelerator Design/Development

Report
Advanced Accelerator
Design/Development
Proton Accelerator Research and Development at RAL
Shinji Machida
ASTeC/STFC/RAL
24 March 2011
Advanced Accelerator of protons
what is it?
• = Fixed Field Alternating Gradient (FFAG) accelerator
in today’s talk.
• Not “advanced” in terms of fundamental principle.
• But “advanced” from practical view point
– easy construction and operation
– Potential to get high beam power
– possibly cheaper
FFAG accelerators
what is it? (1 slide)
• Alternating Gradient focusing accelerator without
ramping magnet.
• Momentum independent bending and focusing is
provided in space not in time.
FFAG accelerators
“advanced”
• DC magnets
– Free from eddy current issue.
– No expensive AC resonant power supply.
– No tracking between dipole and quadrupole.
• Repetition is only determined by available rf power.
– no tracking between magnet and rf.
– Higher the voltage, higher the repetition and higher the
beam power.
FFAG accelerators
no difference from others
• DC magnets
– Like the one for storage ring (PSR, SNS).
– Field can be highly nonlinear, but not complex.
• rf cavity
– Ferrite (Magnetic Alloy) loaded cavity.
– Fixed frequency cavity without material.
• Injection and extraction
– Same problems of kicker and septum.
Applications
• Accelerator for particle therapy [- high repetition -]
– Proton as well as carbon.
• Proton drivers for [- high average current -]
– Neutron (muon) source.
– ADSR (Accelerator Driven Subcritical Reactor).
• Accelerator for secondary particles [- fast acceleration -]
– Muon
– Unstable nuclei
• Accelerator for industry and security
[- easy operation -]
H. Tanaka, et al, cyclotron2004
Projects at RAL (or in UK)
• EMMA
– Demonstration of rapid acceleration.
– Proof of principle of nonscaling FFAG for many
applications.
• PAMELA
– An accelerator complex for proton and carbon therapy.
• Others
– Design study of (proton and muon) accelerator for
neutrino factory.
– Design study of accelerator for neutron source and ADSR.
– Beam transport with FFAG optics.
EMMA (1)
• EMMA is an electron model, but its principle
(nonscaling FFAG) should be used for proton and
muon acceleration rather than electron.
• In UK, only project of FFAG beyond paper study.
EMMA (2)
goals
• Rapid acceleration with large tune variation due to
natural chromaticity.
• Serpentine acceleration or acceleration outside rf
bucket.
• Large acceptance for huge muon beam emittance.
9
EMMA (3)
in pictures
Cavity
Ion
Pump
FQUAD
DQUAD
Ion
Pump
Ion
Pump
Girder
10
EMMA (4)
complete ring
• A beam circulates first for three turns and then for
thousands turns a few day later.
– on 16 August 2010
First Turn
Second Turn
11
EMMA (5)
fixed momentum mode
• Beam position around the
ring with fixed
momentum.
– Orbit shift in horizontal.
– COD distortion is rather
large.
– Peak at cell 25 is not real.
12
EMMA (6)
acceleration mode
• With rf voltage of 2 MV, orbit seems to start moving
outward.
• Detailed study is underway.
13
PAMELA (1)
• Prototype of proton and carbon therapy.
• Prototype of proton driver for neutron source and
ADSR.
PAMELA (2)
our involvement 1
• Novel FFAG optics
– Nonscaling but has scaling features such as zero
chromaticity.
– Operate at the second
stable area of Hill’s
qy=0.0
equation, which makes
(0.25, 0.25)
orbit shift ~5 times less.
qx=0.50
(0.75, 0.25)
qy=0.50
15
PAMELA (3)
our involvement 2
• FFAG beam transport
– Momentum acceptance of +/- a few 10%
– Between acc and gantry.
– To beam dump when trip occurs.
Normal cell
Dispersion suppressor
Neutron source and ADSR (1)
potential to high beam power
• Beam power is a product of
– Particle per pulse: N [ppp]
– Repetition rate: F [Hz]
– Particle energy: E [GeV]
• N is similar to synchrotron.
• F can be 100 times higher.
• E is between cyclotron and synchrotron.
Neutron source and ADSR (2)
potential to high beam power
• N = 2 x 1013, F = 1 kHz, E = 2.5 GeV gives 8 MW.
• However, space charge limit at injection is one of big
issues.
– e.g. at J-Parc, tune shift of -0.25 at 400 MeV with N=8.33 x
1013.
– Need space charge study in FFAG.
– A lot of expertise is here at RAL.
Neutron source and ADSR (3)
• FFAG proton driver (no update since 2009.)
250 MeV booster FFAG
31 MeV injector cyclotron
1.5 GeV main FFAG
Summary
• FFAG accelerator is not a fancy new comer.
• Hardware is similar or same with the one for
synchrotrons.
• It operates differently to maximize repetition and
beam power.
• One criticism: no operational machine exists.
– Hardware R&D for synchrotron directly applies.
– Operation experience of EMMA and others helps.
Backup slides
EMMA (2)
Muon FFAG and EMMA
Muon FFAG
EMMA
Ratio
Momentum
12.6 – 25 GeV/c
10 – 20 MeV/c
1 : 0.001
rf voltage
1214 MV
2.28 MV
1 : 0.002
Number of cell
64
42
1 : 0.66
Circumference
667 m
16.6 m
1 : 0.025
QD/QF length
2.251/1.087 m
0.0777/0.0588 m
1 : 0.035/0.054
Straight section
5m
0.2 m
1 : 0.04
Aperture
~ 300 mm
~ 30 mm
1 : 0.1
• Requirement of rf is much lower, a factor of 1000.
• Space is more packed in longitudinal than in transverse.
– Relatively large aperture magnets.
– Injection/extraction might be harder than Muon FFAG.
22
EMMA (4)
ALICE and EMMA at Daresbury
• Accelerators and Lasers in Combined Experiments
Parameter
Value
Nominal Gun Energy
350 keV
Injector Energy
8.35 MeV
Max. Energy
35 MeV
Linac RF Frequency
1.3 GHz
Max Bunch Charge
80 pC
Emittance
5-15 mm-mrad
EMMA
23
EMMA (5)
betatron oscillation measurement
• Beam position at
consecutive 7 cells tells
– Betatron oscillation
frequency (cell tune)
– Dispersion function from
the average of these.
– Both consistent to model.
Horizontal
Vertical
24
EMMA (6)
time of flight measurement
• BPM signal is measure w.r.t. 1.3 GHz rf wave form.
– Use different magnetic strength as easier than changing
ALICE injector momentum.
Variable ALICE energy fixed
EMMA fields
Fixed ALICE Energy
Variable EMMA fields
25

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