Design of FFAG-ERIT

05/12/07Kota 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 (10B) compound is administered that delivers high concentrations of 10B 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 7Li 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 10cm2, 2*1013 neutrons are needed.If we assume that remedy time is 30 minutes => Flux cm2 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 7Li (p,n) and the 9Be (p,n) reaction. But average beam current >20mA is necessary, also thermal load of thetarget becomes problem.For example, it is difficult technically to achieve average beam current 20mA with linacs.

What is ERIT ?

ERIT : Energy Recovering Internal TargetThe 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 stora

ge 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%) FFAGSuppression of beam heating Ionization cooling method

Proton beam power is mostly consumed by ionization in the target, not by neutron production. (Efficiency ~ <1/1000)

10Be(p,n)B reaction cross section and the energy dependency

In order to obatin φ>10E9 n/cm2/s

• Neutron production reactions 9Be(p,n)B, 7Li(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,

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

Ionization cooling (2)

Energy loss rate dE/dx from Bethe-Bloch formula (9Be target)

In the light orange area the neutron is stable generated

For example, target thickness ~ 5 m

Energy loss : ΔEt ~ 35 keV

10 MeV proton beam

~ -2.82e-3

€

∂(ΔE)

∂E

Energy loss : ΔEt ~ 60 keV

5 MeV proton beam

~ -9.37e-3

€

∂(ΔE)

∂E

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 injectionH- kinetic energy 10 [MeV]Average beam current ~ 40 [A]Repetition 1 [kHz]

H- injectionproton kinetic energy 10 [MeV]Average beam current ~ 40 [mA]

Turn number > 1000 turnInternal target thickness ~ 5 [m]Neutron beam intensity > 109 [n/cm2/sec]

RF voltage > 200 [kV]Harmonic num. ~ 5

Requirement for FFAG

Radial sector type or Spiral sector type ?

Large acceptancemomentum 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 beamThe 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 areeasy to guarantee.

To be the compact which can be installed in the hospitalmean radius (r0) < 2 [m]

Spiral sector type (4 sector) Tune Diagram

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5Horizontal Tune

Vertival Tune

k=0.1

k=0.70.1step

Ƀ=20Åã

Ƀ=5Åã

5Åãstep

É¢ ÅÅ120ÅãÅFTune 1.33

ÅÅ90ÅãÅFTune 1.0

Lattice parameters

Cell num. = 4Open sec. angle = 90 degOpen F angle = 36 degPacking fac. = 0.4Average radius = 1.8 m

B field of F (ref.) = 0.58 [T]

Spiral sector type (sector num. 8) Tune Diagram

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5Horizontal Tune

Vertival Tune

k=2.5

Ƀ=40Åã

5Åãstep

0.1step

k=1.0

Ƀ=5Åã

É¢ ÅÅ120ÅãÅFTune 2.67

ÅÅ90ÅãÅFTune 2.0Lattice parameters

Cell num. = 8Open sec. angle = 45 degOpen F angle = 13.5 degPacking fac. = 0.3Average radius = 1.8 m

B field of F (ref.) = 0.82 [T]

Spiral sector type (8 sector) Lattice parameters

Cell num. = 8Open sec. angle = 45 degOpen F angle = 13.5 degPacking fac. = 0.3K value = 2Spiral angle = 26 degAverage radius = 1.8 mB field of F (ref.) = 0.828 [T]

x = 1.89y = 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

Fromxmax=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. = 8Open sec. angle = 45 degOpen F angle = 7 degOpen D/2 angle = 2 degPacking fac. = 0.4Average radius = 2.0 mK value = 2FD ratio = 7.2

B field of F (ref.) = 0.83 [T]B field of D (ref.) = 0.40 [T]

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

horizontal tune

vertical tune

structure

3rd

2nd

1st

k=ÇQÅDÇOÅAFDÅÅÇVÅDÇQ

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])

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

s [mm]

sqrt_beta [m^1/2]

0.63

0.64

0.65

0.66

0.67

0.68

0.69

0.7

0.71

eta

sqrt_beta_H sqrt_beta_V F_mag Drift D_mag eta

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], 8.651 [cm] r = 1.63 ~ 1.98[m], 14*(r/1.8)-2.01[cm]

2d calculation of magnetic field medium plane

MMF~ 47500 [Ampare turns]

Current density(Effective coil area 65%) 7.4 [A/mm2]

r0 = 1.8 [m] : ~8240 [G]

2d calculation of magnetic field local k value

166.5 < r < 195.0 [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

3 2.5

86

12

40

20

75

2

88

beam duct

panel

40

42

: [cm]

RF freq. 19.8 [MHz] Shunt impe.Rs 188 [kΩ]

Q value 13842 Driving Pow. (for 100kV) 26.6 [kw]

Calculated from MAFIA

Top view of FFAG-ERIT storage ring

Wedge target

0

50

100

150

200

250

0 50 100 150 200 250

X(mm)

Y(mm)

Proton beam

Ｗ

Ｒ

ｔｔ

ｘ

Thickness of target ＝（１ + （ x/w ））ｔ

Proton beamＲ

curve that thickness of target becomes (1+ (x/200))t

dxa

x

a

xy ⋅⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛=∫ 2

2

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