FFAG-ERIT Accelerator (NEDO project) 17/04/07 Kota Okabe (Fukui Univ.) for FFAG-DDS group

Neutron source for BNCT FFAG-ERIT scheme Requirements from BNCT( Boron Neutron Capture Therapy ): In order to remedy the tumor of 10cm 2, 2*10 13 neutrons are needed. If we assume that remedy time is 30 minutes => Flux    cm 2 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 scheme Beam 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 ~ 10 9 n/cm 2 /s Injector : Beam energy11 MeV Averaged beam current70 ~ 75  1000turns storage) Ion speciesH - FFAG-ERIT ring : Circurated beam current70 ~ 75 mA Storage turn num.500 ~ 1000 turns Target (Be, 5,10  m) : 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 specesH — Injection energy 30keV Beam current （ peak ） ≧ 5mA (aver.) ≧ 50μA （〜 100μA ） Extructtion energy 〜 11MeV RF duty(tube)~2% Rep. rate200Hz

Design issue of FFAG ring Beam 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] Large aperture magnet gap height ~ 15 [cm] Ring size (to be the compact which can be installed in the hospital) mean radius (r 0 )~ 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,LongitudinalHorizontalVertical Cooling term Heating term 0 Wedge TargetAcceleration Cavity When the wedged target is placed at dispersive point, can be possible. Strong beam focus for transverse plane (to suppress transverse heating)

Energy loss Energy loss rate dE/dx from Bethe-Bloch formula ( 9 Be target) In the light orange area (5~11MeV) the neutron is stable generated For example, target thickness ~ 5  m Energy loss :  E t ~ 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 lattice F-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 ~ 2.22 FD ratio ~3 Rev. freq. ~ 3.05[MHz]

Radial sector FFAG ring parameters Beam energy11 MeV Mean radius2.35 m Most ext. radius of magnet3.06 m F-magnet field strength0.825 T AT58500 AT orbit length （＠ ave. radius ） cm mass4.1 ton D-magnet field strength T AT AT orbit length （＠ ave. radius ） cm mass 3.4 ton

Vertical beta function & acceptance Vertical acceptance ~ 3000π [mm-mrad]Vertical beta ~ 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 V rf = 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 turn  y = 0.75[m] : y = 2.32, Mean surviving turn num. 910 turn

ERIT - RF cavity (basic design) Design : RF voltage 200 [kV] RF freq [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.