part iv applications. prototype of cancer therapy machine with proton 150 mev ffag as a prototype...
TRANSCRIPT
Prototype of Cancer therapy machine with proton
• 150 MeV FFAG as a prototype• Commissioning to accelerate up to ~15 MeV is done.• Tune survey
Requirements
• Accurate positioning
– Irradiate a well defined 3-dimensional volume (and not outside.)
• Accurate dose
– Dose at each point should be controlled with accuracy of 1%.
Broad beam method (Conventional)
Final collimator
Bolus
Ridge filter
•Inevitable irradiation outside of the treatment field.
•Each patient needs his own shaped bolus.
Spot scanning method
•A small beam spot makes it possible to irradiate a well defined area.
•Non-uniform irradiation in the area is possible.
•Simultaneous dose measurement using supersonic waves.
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Supersonic wave detector Reconstruction of
irradiated volume in 3D space.
Treatment volume
Pulsed beam produces pulsed supersonic wave from irradiated position
Experiment (green)
Calculation (red)P
ressure of sound
Detection of supersonic waves induced proton beam pulse
Disadvantage of spot scanning
•Sensitive to respiratory motion•Organ motion during scanning should be suppressed.•Beam irradiation time should be shortened much less than respiratory motion.
•Intensity of each pulsed beam should be accurately controlled.
Dream machine
• Small spot beam with variable extraction energy (pulse by pulse).– A beam is delivered to localized volume (no other places.)
• Beam intensity is well controlled (pulse by pulse).– Accurate dose distribution.
• High intensity (per pulse) pulsed beam.– Short irradiation time compared to respiratory motion.
• Pulsed beam with very high repetition frequency– Simultaneous dose measurement using supersonic waves.
• Small size, low cost, and easy operation.
FFAG as a medical accelerator
• Spot scanning with 1kHz or more repetition rate.
• Variable energy extraction, pulse by pulse.
• 1% level of does control in a pulse using beam chopper after ion source.
• High peak as well as high average current is available due to very rapid cycling and alternating gradient (strong) focusing.
• Small size, low cost, and easy operation.
Injector (Cyclotron)
RF system
Extraction beam line
The system for
Spot scanning
5m
150MeV FFAG - Overview
Commissioning at East-Experimental hall of KEK-PS
Schematic view of 150MeV FFAG
Parameters
Design of the magnet pole
Magnetic field in the center of the sector BL
•Gap is not exactly rk in low momentum region.•Rogowski like patch is attached on focusing magnet.•BL is adjusted instead of local B().
with patch
w/o patch
Correction of magnet• The design of the edge of the F-sector pole
• The final design of the poles
with extension
w/o extension
BL-F/D ratio vs. radius
75.75400
21 ⎟⎠
⎞⎜⎝
⎛=r
halfgap
32.95400
20 ⎟⎠
⎞⎜⎝
⎛=r
halfgap
57.94900
9.39555.11
+⎟⎠
⎞⎜⎝
⎛=r
halfgap
Focusing sector
Defocusing sector
)49004500( Å`=r
)54004900( Å`=r
Unit : mm
A comparison of F-sector magnetic field
on the medium plane
excursion
Betatron tunes
• Betatron tunes by a beam simulation with final design of the magnet.
Betatron tunes
vs. mean radius
integer resonance
half integer resonance
third resonance
Tune diagram
Return Yoke Free Magnet
• “Return Yoke Free Magnet ” The return yoke of Focusing sector is removed.
F Sector
D Sector
Shunt
ΦF: Magnetic field in F Sector
ΦD: Magnetic field in D Sector
ΦS: Magnetic field in Shunt Yoke
F coil D coil
•Space for the extraction
Measurements of magnetic field.
-3.0-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.53.0
-120 -100 -80 -60 -40 -20 0 20X (cm)
É¢B/BÅ@(Åì)
Discrepancy (ΔB/B)
Measurements of magnetic field with hole probe.
The discrepancy between any two magnets is 0.3% at most. The alignment error of hole probe explained that discrepancy.
Y=-35~+45cm
5cm step
-15000
-10000
-5000
0
5000
10000
15000
20000
-120 -100 -80 -60 -40 -20 0 20
X (cm)
Bz (G
auss
)
Magnetic Field (Bz)
X
Y
D F D
Defocus
sector
Focus
sector
Defocus
sector
Focus sector
Magnet center
Goal of study
Prototype machine (150MeV) is under commissioning.
• MA based RF cavity
• Yoke-free magnet
• Demonstration of 3D spot scanning
PRISM phase rotator
• To study muon rare decay, mono chromatic muons are necessary.• Secondary particles produced by intense protons have large momentum
spread.– Phase rotation to convert large dp/p and small dt to small dp/p and large dt.– 5 turns in FFAG makes 1/4 synchrotron oscillation.
• PRISM specifications– Number of sector 8 (or 10)– Radius 5 m– Triplet sector– Acceptance 10,000 pi mm-mrad
FFAG for ADS
• Feasibility study of ADSR
– Five year program from 2002 to 2006
• Subjects
– Accelerator technology
• Variable energy FFAG
– Reactor technology
• Basic experiments for energy dependence of the reactor physics
• Hosted by Kyoto University Research Reactor Institute (KURRI)
What is ADSR?
• Accelerator driven Sub-critical Reactor
• Chain reaction is controlled by beam.
acceleratorSub-critical reactor
Target for generatingneutrons
Accelerator driven sub-critical reactor (ADSR)
• Basic study of accelerator driven system.• 3 stage FFAG
– 2.5 MeV spiral (ion beta) FFAG with induction cores– 25 MeV radial (booster) FFAG with RF and flat gap– 150 MeV radial (main) FFAG with RF and tapered gap
• Variable output energy become possible by– Variable k value at booster FFAG
• Orbit excursion should be the same to locate the same injection and extraction radius.
• Momentum ratio at main FFAG is constant. Magnetic strength is variable.
• Upgrade to 1 GeV system is considered.
Layout of ADSR FFAG
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Neutrino factory
• Accelerate muons to 20 - 50 GeV/c• Initial momentum is 0.3 - 1 GeV/c• 3 or 4 FFAG cascade
– 0.3 - 1 GeV/c (0.3 - 1 GeV/c with nuon cooling)– 1 - 3 GeV/c or 1 - 4.5 GeV/c– 3 - 10 GeV/c 4.5 - 20 GeV/c– 10 - 20 GeV/c
• JPARC 50 GeV Main Ring is a proton driver.
Acceleration of muons
• No time to modulate RF frequency.• 1 MV/m (ave.) RF voltage gives large longitudinal acceptance.• From 10 to 20 GeV/c within 12 turns.
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