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.