Beam acceleration of 150 MeV FFAG at Kyushu University ~ Proton and Heavy ions ~

1. Beam acceleration of150 MeV FFAG at Kyushu University~ Proton and Heavy ions ~ Contents ・Purpose of this study ・Longitudinal simulation ・Development of RF cavity ・Summary ・Something new Tandem – FFAG AMS Department of Applied Quantum Physics and Nuclear Engineering, Graduate School of Engineering Kyushu University M1 Hidenobu TAKASE

2. Purpose of this study・Achievement of high efficiency acceleration at 100Hz.・Optimization of accelerating pattern for FFAG of Kyushu University. Designed parameters of 150 MeV FFAG Over view of 150 MeV FFAG

3. Number of particles at extraction energy Survival rate (%) = Number of injected particles Longitudinal simulation ・Proton acceleration to 125 MeV with repetition of 100 Hz is simulated. ・The acceleration method to realize higher survival rate is investigated.

4. 50 turns 0 turn Beam acceleration (not optimized) Injection beam from Cyclotron ΔP/P = ±0.2% Acceleration condition ・No capture ・Accelerating voltage is 8 kV. ・Synchronous phase is 30°. Extraction Beam outside accelerating bucket is lost. Survival rate : 53.3% In this condition, only about a half of the particles can be accelerated.

5. Effective acceleration To accelerate the beam more effectively, two methods are applied successively. ① Adiabatic capture (φs= 0°) ② Phase shift method (φs= 0°→ 30°)

6. 1600 turn ① Adiabatic capture 1600 turns (1 msec) 1000 turns 0 turn Accelerating bucket when gap voltage is 6 kV. The rate becomes nearly constant, after 1600 turns (1 msec). 1 msec is enough to capture. Rate of particles in accelerating bucket (%)

7. ② Phase shift method ・After adiabatic capture, Phase shift method is applied. Phase shift method Synchronous phase is gradually changed from 0°to 30°at a constant rate. If stable area moves adiabatically, beam loss will decrease. φs = 10° φs = 30° φs = 0°

8. Capture → Phase shift method(φs=0°→ 30°) ・Survival rate becomes higher with decreasing phase variation. ・Time for acceleration becomes longer with decreasing phase variation. This figure shows a data when gap voltage is 6 kV. This figure shows a data when gap voltage is 6 kV. In order to optimize phase variation, It is needed to consider the balance between survival rate and time for acceleration.

9. 0.3 deg/turn H - factor If survival rate becomes larger or time for acceleration becomes smaller, H factor has larger value. H factor has a maximum value at 0.3 deg/turn.

10. Voltage required for 100Hz operation Capture time : 1 msec Phase variation / turn : 0.3 deg/turn In these conditions, to realize working frequency of 100Hz, available time for acceleration is 9 msec. 8.4 kV More than 8.4 kV of gap voltage is required to accelerate protons up to 125 MeV within 9 msec with phase shift method.

11. Result of simulation Phase shift 0.3 deg/turn (φs: 0°→ 30°) Acceleration 8.4 kV (φs = 30°) Adiabatic capture (1 msec) Injection beam Adiabatic capture 8.4 ・Survival rate amounts to 99.4% by applying these methods. gap Vol. (kV) 2.5 0.1 t (msec) Phase shift ・It has been shown that 8.4 kV of gap voltage is required for 100Hz operation. 30° φs 0 10 1 t (msec) 1.06

12. P : power dissipation V : gap voltage R : shunt impedance Acceleration with two RF cavities ・8.4 kV of gap voltage is required for 100Hz operation. ・In this condition, the power dissipation of the cavity is serious problems. ・The power dissipation reaches about 90 kW. ・The temperature of surface of the core reaches over 200 degrees. Temperature should be under about 100 degrees in order to realize stable operation. ・ To resolve this problem, we decided to employ two cavities. ・A new cavity with high-efficiency cooling system has been developed. ・Required voltage for each cavity is 4.2 kV / cavity ・The power dissipation of the core becomes a quarter.

13. Development of new RF cavity with high efficiency cooling system The MA core Cooling plate Thermal conductive spacer MA core Since heat flux is inversely proportional to the thickness of conductive spacer, thickness of thermal conductive spacer has been changed from 3 mm to 1 mm. The cooling plate The contact area between cooling water and the core is designed to be 7 times larger than the former cavity. The cooling efficiency is expected to be 21 times larger than the former cavity.

14. Development of New RF cavity 4.2 kV The gap voltage of 4.2 kV has been achieved.

15. Summary (proton acceleration) ・When adiabatic capture and phase shift method are used , survival rate amounts to 99.4%. This method is very effective for high-efficiency acceleration. ・Accelerating voltage required for 100Hz operation is 8.4 kV. ・In order to decrease power dissipation per cavity, the second cavity with new cooling system has been developed. ・Required voltage for each cavity is 4.2 kV / cavity ・Power test of the second cavity has been successfully performed.

16. Feasibility study of Tandem – FFAG AMS Plan 5 MV-class small Tandem accelerator as heavy ion injector of FFAG One of the proposals using Tandem accelerator and FFAG Tandem – FFAG Accelerator Mass Spectrometry (AMS) Advantages of Tandem – FFAG AMS Prof. N. Ikeda Nov. 10. 2008 in this workshop Example : Simulated results for 36Cl AMS

17. Ex. Feasibility of 36Cl AMS with FFAG Assumption ・36Cl and 35Cl are injected to FFAG alternately. ・Operation parameters of FFAG are fixed. ・Injected isotopes have same P/q as 10 MeV proton. ・q of Cl is 12+. ・Hypothetical particle 35.5Cl is set as synchronous particle. For deduction of reliable 36Cl/35Cl value P : momentum q : charge state Simulation : how many particles (36Cl ＆ 35Cl) survived.

18. Simulation Acceleration conditions ・No capture. ・Synchronous phase is 30°. 1000 turns 35Cl12+ 35.5Cl12+ 36Cl12+ Gap voltage is 8 kV

19. Result ・Survival rates of both particles are about 40% and almost same When gap voltage is around 8 kV. ・The beam with ΔM/M = ±1.4% can be accelerated with FFAG. Optimization of acceleration method is under way, in order that survival rates of both particles may become higher and exactly equal.

20. Summary (Tandem – FFAG AMS) ・It is shown that 36Cl and 35Cl can be accelerated alternately by FFAG with fixed operation. ・Survival rates of both particles are about 40% and almost same when gap voltage is around 8 kV. ・The beam with ΔM/M = ±1.4% can be accelerated. ・Acceleration method will be optimized so that survival rates of both particles become higher and exactly equal.