Magnetic design of a superconducting magnet for the FFAG accelerator T.Obana, T.Ogitsu A,T.Nakamoto A,K.Sasaki A A.Yamamoto A, M.Yoshimoto A, Y.Mori A,T.Origasa B The Graduate University for Advanced Studies High Energy Accelerator Research Organization A Toshiba Corporation B

Contents 1.Background & Purpose 2.How to generate FFAG field 3.2D &3D Calculation Results 4.Conclusion

Background Downsizing the FFAG accelerator is essential so that the FFAG can be widely used. High energy physics Electric power High magnetic field is required. FFAG field is constant. Superconducting magnet is proposed for FFAG accelerator. Cancer therapy

Purpose The purpose of this study is to develop the superconducting magnet of the FFAG accelerator. 150MeV FFAG Conventional magnet of 150MeV FFAG accelerator at KEK

Magnetic Field for FFAG 0 Beam tube Beam area Center of the magnet Center of the accelerator r : Distance from the accelerator center [m] R 0 : Distance between the accelerator center and the magnet center [m] B o : Magnetic field at the magnet center [T] K : K value ( Geometrical field index)

How to generate the FFAG Field! Di-pole Quadru-pole Sextu-pole Realize FFAG magnetic field with mutipole combination ！

Current distribution ++ – – X Y – – – X + – Y X Y It ’ s too difficult to make a multi layer coil ! n=3 n=2 n=1 Up to n=8 I=I 0 cos(nθ) Multi layer coil

Current distribution – ＋ X Y Simplify! – ＋ X Y Left-Right asymmetry & Ellipse ++ – – X Y – – – X + – Y X Y Downsize! With single layer Left-Right asymmetry Up to n=8 n=1 n=2 n=3

Major axis0.8 m Minor axis0.6 m K value10 Ro5.0 m Excursion0.4 m Turn number Bo T Excursion Coil Coil parameters of FFAG for cancer therapy – ＋ X Y Current distribution FFAG FFAG for cancer therapy Energy ～ 200Mev Current ～ Several 100μA FFAG for cancer therapy High Energy Beam Low Energy Beam Cross-Section + -

K value & Field distribution on 2D K value Field distribution Excursion Local K is used to evaluate K value. K value Positions of the conductor can be optimized in 2D!

Single coil In single winding, one coil makes one layer. Y X Z X Z Y Z Y Z-Y plane Z Y Straight section Superconducting wire

Single coil Coil end is large. Demerit Merit Straight length is same in each turn with 2 layers. 2 layers with 2 coils Z Y Z Y Z-Y plane Y X Z X Z Y

Twin coil In twin winding, two coils make one layer. X X Z Z Y Y Z X X Z Y Z Y Z-Y plane Straight section Superconducting wire

Twin coil Straight length is different in each turn. Coil end is small. Merit Demerit 1 layer with 2 coils Z Y Z Y Z-Y plane X X Z Z Y Y

Field distribution on ３ D Field distribution on ３ D Single Winding Twin Winding Coil end X Z Z X Z-X plane Trajectory X=0 m 5.8° 10.0° 0°0° Coil Center of FFAG Top view θ

K ３ D-Result θ= 0° Single Winding Coil end 0°0° θ X=0 m 5.8° Coil Center of FFAG Top view X X Z Z Z-X plane Twin Winding K value X[m]

K ３ D-Result θ= 2° 0°0° θ X=0 m 5.8° Coil Center of FFAG Top view 2°2° Z Z X X Z-X plane Single winding Twin winding Coil end K value

K ３ D-Result θ= 4° Single winding Twin winding Coil end Z-X plane XX Z Z 0°0° θ X=0 m 5.8° Coil Center of FFAG Top view 4°4° K value

K+1 value by ３ D-Result K+1 value by ３ D-Result X=0.0 m 5.8° 10.0° 0°0° Coil Center of FFAG BL= K+1 value

Conclusion 2D & 3D FFAG magnetic fields are calculated. The optimizing program of the conductor position in 2D is developed. Two types of 3D coil configuration are compared in terms of K value & BL. Future plan Tracking will be done with 3D magnetic filed. Prototype of single winding coil will be made from this October.

What ’ s FFAG accelerator ? Can be High repetition & High Intensity ! Strong focusing in horizontal and vertical Synchrotron Constant magnetic field strength in time Cyclotron FFAG 〔 Fixed Field Alternating Gradient 〕 accelerator Properties...

Various Accelerators FieldFixRampFix Closed Orbit Large MoveFixSmall Move FocusingWeakStrong Duty Factor LargeSmallLarge

Why ’ s SC magnet required? Normal Conducting Magnets –Low Current Density< 10 A/mm2 Field by Iron Pole –Iron Saturation 2 Tesla Superconducting Magnets –High Current Density< 500 A/mm2 Field by Current –Tevatron4.5 Tesla –LHC8.4 Tesla High magnetic field can be generated by SC magnet. Accelerator size can be downsized !

Accelerator Driven System (ADS) FFAG Proton Reactor Core neutron Target (Uranium )

Winding Technique Direct Winding Superconducting wire can adhere directly to the base. Reference

Superconducting wire Nb-Ti Cu 1.0 mm

How to evaluate K value Total field Local field

Straight length with 2 layers Single winding Z Y Z Y First Second First Second Z-Y plane Z Y Y Z Straight length with 2layers Twin winding

0° 90° 180° -90° -180° (-90°) (90°) θ Expansion plane θ X Y 0° 90° -90° Twin winding Single winding

How to evaluate K+1 value BL= X=0.0 m θ = 0° Coil Center of accelerator θ r

K value & K+1 value by BL Z B Z X X-Z plane Local evaluation of the field Beam traveling direction K value K+1 value by BL Total evaluation of the field

How to optimize the positions of the conductor Current angle 180° SS S S S S 1.Evaluate the current distribution 2.Divide the area so as to be same

How to adjust the target! How to adjust the target! X[m] K+1 value X[m] K+1 value Adjust the 2D target so that K+1 can reach 3D target Difference Target Adjust target! Calculation