ffag-erit accelerator (nedo project) 17/04/07 kota okabe (fukui univ.) for ffag-dds group
TRANSCRIPT
FFAG-ERIT Accelerator(NEDO project)
17/04/07Kota Okabe (Fukui Univ.)
for FFAG-DDS group
Neutron source for BNCTFFAG-ERIT scheme
Requirements from BNCT(Boron Neutron Capture Therapy): In order to remedy the tumor of 10cm2, 2*1013 neutrons are needed.If we assume that remedy time is 30 minutes => Flux cm2 sec.
Accelerator as a neutron source ; Energy is low, but beam current is very large (I > 40mA [CW])
ERIT : Emittance-Energy Recovering Internal Target
The stored beam is irradiated to the internal target, it generates the neutron in the storage ring. The beam energy lost in the target is recovered by re-acceleration.
Technically hard and expensive
Feature of ERIT schemeBeam current reduced by storage the beam in the ring.
Overview of FFAG-ERIT accelerator system
Requirement performance of FFAG-ERIT
Neutron flax enough for 1 hour treatment ~ 109 n/cm2/s
Injector : Beam energy 11 MeVAveraged beam current 70 ~ 75 A(@ 1000turns storage)Ion species H-
FFAG-ERIT ring :Circurated beam current 70 ~ 75 mAStorage turn num. 500 ~ 1000 turns
Target (Be, 5,10m) :Life time > 1 month
Moderator : fast neutron Nuclear reactor level
Proton linac
AccSys Inc. PULSAR-7
RFQ
DTL(PULSER-7(7MeV proton) is originally developed for PET.)
add a DTL tank for 11MeV
~5.3[m]
Ion speces H—
Injection energy 30keV
Beam current( peak ) ≧ 5mA
(aver.) ≧50μA (〜
100μA )
Extructtion energy 〜 11MeV
RF duty(tube) ~2%
Rep. rate 200Hz
Design issue of FFAG ringBeam dynamics, Magnet, RF Cavity
• Beam dynamics and optics
momentum acceptance dp/p ~ 5 [%] (full)transverse acceptance > 1000 [ mm mrad]strong beam focusing at target y ~ 0.7 [m] (@target)
• Large aperture magnetgap height ~ 15 [cm]
• Ring size (to be the compact which can be installed in the hospital)
mean radius (r0) ~ 2.35 [m]• RF cavity
frequency ~ 20 [MHz] (h = 6)rf voltage > 200 [kV]
Requirement performance Storage turn num. 500 ~ 1000 turns
Beam heating The rate equation of beam emittance passing through a target material is,
LongitudinalLongitudinal
HorizontalHorizontal
VerticalVertical
€
dεy
ds= −
1
β 2E
dE
dsεy +
β y E s2
2β 3mpc2LR E
€
dεx
ds= −
1
β 2E
dE
ds1−
D ′ ρ
ρ 0
⎛
⎝ ⎜
⎞
⎠ ⎟εx +
β x E s2
2β 3mpc2LR E
€
d σ E2
ds= −2
∂(dE /ds)
∂E 0
+dE
ds
1
pcβD
′ ρ
ρ 0
⎛
⎝ ⎜
⎞
⎠ ⎟ σ E
2 +d ΔE 2
rms
ds
Cooling term
Heating term
E
EΔ+
E
EΔ−
0
Wedge Target Acceleration Cavity
When the wedged target is placed at
dispersive point, can be possible.
€
∂(dE /ds)
∂E
Strong beam focus for transverse plane(to suppress transverse heating)
Energy loss
Energy loss rate dE/dx from Bethe-Bloch formula (9Be target)
In the light orange area (5~11MeV) the neutron is stable generated
For example, target thickness ~ 5 m
Energy loss : ΔEt ~ 32.5 keV/turn
11 MeV proton beam
Radial sector & Spiral sector
Spiral sector type :
Radial sector type :
• Small size • Small beam focus for vertical plane• Difficult of operational tunes
• Large size• Large beam focus for vertical plane (suppress overheating of beam)• Change of operational tunes : feasible
We choose Radial Sector (FDF).
Magnetic field calculation (TOSCA)
FDF latticeF-Mag. = 6.4[deg],D-Mag. = 5.1 [deg], F-D gap 3.75[deg], F-Clamp gap = 1.9[deg],Clamp thick = 4[cm]Mean radius = 2.35[m]
11MeV proton beam
x ~ 1.76, y ~ 2.22FD ratio ~3Rev. freq. ~ 3.05[MHz]
Radial sector FFAG ringparameters
Beam energy 11 MeV
Mean radius 2.35 m
Most ext. radius of magnet 3.06 m
F-magnet
field strength 0.825 T
AT 58500 AT
orbit length (@ ave. radius ) 26.25 cm
mass 4.1 ton
D-magnet
field strength 0.727 T
AT 54500 AT
orbit length (@ ave. radius ) 20.92 cm
mass 3.4 ton
Vertical beta function & acceptance
Vertical acceptance ~ 3000π [mm-mrad] Vertical beta function@target ~ 0.83 [m]
Tracking results used TOSCA field.
(Horizontal acceptance > 7000π [mm-mrad])
Ionization cooling simulation
Initial condition Transverse
Hori. emittance = 15 pi [mm mrad], Vert. emittance = 15 pi [mm mrad],
Matched twiss para.Longitudinal
dE = 0, Inial RF phase 10 deg. (moved from synchronous phase.)
ICOOL
• Using TOSCA field map• Fluctuations in the energy : Vavilov distributions• Multiple scattering : Moliere distribution• Particle num. = 1000• Be target is rectangle (no wedge). Target thickness = 5 m
RF amplitude Vrf = 400 kV, (mom. Acceptance ~ 4%)
Surviving turn number
Mean surviving turn num. 810 turns
RMS emittance and energy spread
An analytical solution and the simulation results are corresponding well while beam loss is few.
Vertical beta function - dependent
y = 0.83[m] : y = 2.22, Mean surviving turn num. 810 turny = 0.75[m] : y = 2.32, Mean surviving turn num. 910 turn
ERIT - RF cavity (basic design)
ÅEInner diameter : É”200cmÅC
ÅEaxial length : 40cmÅCcap. electrodeÅFÉ”160cmÅ~t2cmÅC
ÅEgap btw cap. electrode & cavity end plate : 3cmÅC
ÅEtunerÅFÉ”20cmÅ~L50cmÅC
ÅEbeam duct : w38cmÅ~h20cmÅC
ÅEcouplerÅFdiameter : 12cmÅ~L30cmÅCÉ”2cm
Design : RF voltage 200 [kV]RF freq. 18.3 [MHz]harm. Num. 6
Top view of FFAG-ERIT ring
Moderator
RF cavity
Mean radius (2.3m)
Injection point(Details are under consideration.)
Summary
• Physical design is completed. Fabrication is in process.
• Preparation of infrastructure(water, electricity, etc.) at KURRI.