Design of FFAG-ERIT 05/12/07 Kota Okabe (KEK) for FFAG-DDS group

Contants 1. Back ground of this project 2. Ionization cooling 3. Design of FFAG-ERIT 4. Summary

BNCT (Boron Neutron Capture Therapy) About BNCT Boron neutron capture therapy (BNCT) is a targeted radiation therapy. BNCT is a binary approach: A boron-10 ( 10 B) compound is administered that delivers high concentrations of 10 B to the target tumor relative to surrounding normal tissues. This is followed by irradiation with thermal neutrons or epithermal neutrons that become thermalized at depth in tissues. Because range of the Alpha ray and the 7 Li particles (~10 mm) is short, it is possible to treatment only the tumor cell without damaging the normal cell. About differences usual radiation therapy and BNCT 1.BNCT make tumor selective killing without damage for adjacent normal tissue. 2.Treatment ends by one day irradiation, because the therapeutic gain is high.

Neutron source for BNCT Requirements from BNCT: 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. As a neutron source : Nuclear reactor Accelerator It have established as powerful thermal neutron source. But, it is difficult to adjoin the remedy facility and the reactor. Generating the neutron with 7 Li (p,n) and the 9 Be (p,n) reaction. But average beam current >20mA is necessary, also thermal load of the target becomes problem. For example, it is difficult technically to achieve average beam current 20mA with linacs.

What is ERIT ? ERIT : 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. Feature of ERIT system Average beam current of injector is suppressed. The proton beam be sure to do track the circumference in inside the storage ring. Therefore, there are no times when the charged particle exists together in the neutron beam. The storage ring require to large acceptance(dp/p~10%) FFAG Suppression of beam heating Ionization cooling method Proton beam power is mostly consumed by ionization in the target, not by neutron production. ( Efficiency ~ <1/1000)

10 Be(p,n)B reaction cross section and the energy dependency In order to obatin φ>10E9 n/cm2/s Neutron production reactions 9 Be(p,n)B, 7 Li(p,n)Be Proton beam energy ~10MeV current >20mA(cw)

Emittance growth Using an internal target in the ring, the beam emittance can be increased in 3-D directions by Ratherford multiple scattering and stragling In ERIT scheme, however, the beam emittance growth can be cured by Ionization Cooling effect

Ionization cooling (1) 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.

Ionization cooling (2) Energy loss rate dE/dx from Bethe-Bloch formula ( 9 Be target) In the light orange area the neutron is stable generated For example, target thickness ~ 5  m Energy loss :  E t ~ 35 keV 10 MeV proton beam ~ -2.82e-3 Energy loss :  E t ~ 60 keV 5 MeV proton beam ~ -9.37e-3 Beam energy 10MeV is profitable

Ionization cooling (3) x - z coupling  ’ : variation of thickness

Overview of FFAG-ERIT accelerator system Injector(RFQ + DTL or IHDTL ) FFAG ring ERIT system RF cavity Full energy injection H - kinetic energy 10 [MeV] Average beam current ~ 40 [  A] Repetition 1 [kHz] H - injection proton kinetic energy 10 [MeV] Average beam current ~ 40 [mA] Turn number > 1000 turn Internal target thickness ~ 5 [  m] Neutron beam intensity > 10 9 [n/cm 2 /sec] RF voltage > 200 [kV] Harmonic num. ~ 5

Requirement for FFAG Radial sector type or Spiral sector type ? Large acceptance momentum acceptance dp/p ~ 10 [%] transverse acceptance 1000 [  mm mrad] It is necessary to adjust the phase advance to less than 90 degrees to secure a large acceptance. (from recent study, M.Aiba et al ) Separation of neutron and beam The numbers of sectors are few, easy to take about separation. Length of straight section (to install large RF cavity) The numbers of sectors are few, length of the straight section are easy to guarantee. To be the compact which can be installed in the hospital mean radius (r 0 ) < 2 [m]

Spiral sector type (4 sector) Tune Diagram Lattice parameters Cell num. = 4 Open sec. angle = 90 deg Open F angle = 36 deg Packing fac. = 0.4 Average radius = 1.8 m B field of F (ref.) = 0.58 [T]

Spiral sector type (sector num. 8) Tune Diagram Lattice parameters Cell num. = 8 Open sec. angle = 45 deg Open F angle = 13.5 deg Packing fac. = 0.3 Average radius = 1.8 m B field of F (ref.) = 0.82 [T]

Spiral sector type (8 sector) Lattice parameters Cell num. = 8 Open sec. angle = 45 deg Open F angle = 13.5 deg Packing fac. = 0.3 K value = 2 Spiral angle = 26 deg Average radius = 1.8 m B field of F (ref.) = [T] x = 1.89 y = 1.34 maximum energy : r (Rmax) 12 [MeV] : 1.87 [m] minimum energy : r (Rmin) 8 [MeV] : 1.72 [m] Drift length ~ 0.8 [m] Rev. freq. (10 [MeV]) ~ 3.87 [MHz] Used hard-edge tracking code

Spiral sector type (8 sector) Twiss parameters From  xmax =1.48,  ymax =2.03, Beam size Hori. ~ 3.8[cm], Vert. ~ 4.5 [cm] (1000 [mm mrad])

Radial sector type (8 sector) Lattice parametars Lattice parameters Cell num. = 8 Open sec. angle = 45 deg Open F angle = 7 deg Open D/2 angle = 2 deg Packing fac. = 0.4 Average radius = 2.0 m K value = 2 FD ratio = 7.2 B field of F (ref.) = 0.83 [T] B field of D (ref.) = 0.40 [T] Rev. freq. (10 [MeV]) ~ 3.45 [MHz] Drift length (r = 1.8 [m]) ~ 0.83 [m]

Radial sector type (sector num. 8) Twiss parametars Orbit shift (8MeV~12MeV) ~ 13 [cm] Half gap Hori. ~ 3.7 [cm], Vert. ~ 3.9 [cm] (1000 [mm mrad])

Radial sector type (sector num. 8) Summary It is difficult to adjust the phase advance per sector 90 degrees when number of sector less than 8. The size of the accelerator becomes small a spiral sector type compared with the radial sector type. In regard to the circumstances of the tune diagram, radial sector type is the same as spiral sector type. By selecting FD ratio, we can change the vertical tune radial sector. It is thought that 8 sector lattice is suitable. And to develop compact machine, we chose spiral sector type.

2d calculation of magnetic field Half gap : r = 1.63 ~ 1.98[m], [cm] r = 1.63 ~ 1.98[m], 14*(r/1.8) [cm]

2d calculation of magnetic field medium plane MMF ~ [Ampare turns] Current density ( Effective coil area 65% ) 7.4 [A/mm 2 ] r 0 = 1.8 [m] : ~8240 [G]

2d calculation of magnetic field local k value < r < [cm] : error of k value < 1%

FFAG Magnet Summary We estimated form of pole and the coil roughly with the magnetic field calculation which uses POISSON. Presently, three dimensional magnetic field calculation which uses TOSCA is doing.

One of typical RF cavity for ERIT beam duct panel : [cm] RF freq.19.8 [MHz]Shunt impe.Rs188 [kΩ] Q value13842 Driving Pow. ( for 100kV ) 26.6 [kw] Calculated from MAFIA

Top view of FFAG-ERIT storage ring

Wedge target Proton beam Ｗ Ｒ ｔ ｔ ｘ Thickness of target ＝（１ + （ x/w ）） ｔ Proton beam Ｒ curve that thickness of target becomes (1+ (x/200))t The target that changes the thickness by R is necessary for the beam cooling. The film thickness of the part over which the beam passes is adjusted by bending the target of a constant thickness.

H - injection & neutron orbit 19 deg The electron strapping foil is shared with the target for the neutron source.

Summary Design of FFAG-ERIT system is doing. Basic parameter We should simulate ERIT scheme using GEANT