Status of PAMELA rf system

1. Status of PAMELA rf system Takeichiro Yokoi(Oxford University) I.Gardner (RAL) Status of PAMELA RF system

2. PAMELA proton ring 1.3m 12.5m Status of PAMELA RF system

3. FFAG Integrated current Step size controls dose time “Digital IM” IMPT:Intensity Modulated Particle Therapy Dose uniformity should be < ~2%  Beam intensity should be modulated depth-wise in spot scanning With pulsed beam of FFAG, to realize intensity modulation ….. (1) Dynamic modulation of injector beam intensity complicated system, but low repetition rate (2) multi-beam painting with small bunch intensity simple system, but high repetition rate In PAMELA, option (2) was taken, due to the injector scheme and uncertainty about precision of intensity modulation of ion source Status of PAMELA RF system

4. Energy gain 15keV/turn* Frequency(h=1) 1.94~4.62MHz Length 1.3m Aperture 23cm Repetition rate 1kHz *8 cavity case Requirements Requirement : 1kHz repetition rate 100kV/turn Available space : 6 drift space  1.2m (Ldrift~1.7m) Target energy gain: 15kV/turn/cavity Requirement : 1kHz repetition**  100kV/turn Available space : 8 drift space  1.2m (Ldrift~1.7m) **With 1kHz repetition rate, 100voxel/sec can be irradiated for a typical tumor (SOBP width:12cm) Challenge : high duty cycle, high rate FM, high field gradient Power dissipation is the most serious problem in high repetition operation P=V2/(4fQL) High Q is favorable Status of PAMELA RF system

5. Options 3 candidates were proposed At the moment, ferrite cavity is taken as the primary option • Relatively high Q (~100) • h=10 Status of PAMELA RF system

6. 2 ferrite core layers Total Length 110cm # of acc. Gap/cvty 2 # of ferrite core/gap 2 Core size 50cm(rout) 25cm(rin) 2cm(w) 1.1m Frequency** 1.94~4.62MHz Max Field/gap 10kV ** h=10 Proposed cavity for PAMELA Status of PAMELA RF system

7. Ferrite characteristics At the moment, two assumptions are introduced in the estimation of cavity performance Q is constant (Q=100) µ’= µ’@fref/f2resonance (fref : 20MHz,unbiased) In a biased system, the data is no longer valid  Measurement of biased ferrite is indispensable to establish feasibility Ferroxcube 4E2 (unbiased) **Q=µ’/µ” Status of PAMELA RF system

8. Ferrite cavity power consumption * Constant Q,100, is assumed Power consumption-wise, lower frequency is favorable. Status of PAMELA RF system

9. Ferrite cavity power consumption Why higher frequency?  To make the cavity length shorter to fit the straight section (available space:1.2m) Still, some room for optimization remains lb_min Status of PAMELA RF system

10. MA cavity power consumption core Brf of present ferrite cavity (Ferroxcube 4D2) Advantage of MA is higher saturation field compared to ferrite  Suitable for higher gradient cavity (Now, Brf of present ferrite rf core of PAMELA is almost reaching the limit of ferrite) Status of PAMELA RF system

11. MA cavity power consumption 3 core(w:25mm,rin:15cm, rout:50cm) Pwr/gap>150kV:DC operation With vertical fast extraction, single bunch acceleration is the only option  Still, the ferrite cavity is a better option from the viewpoint of power dissipation. Status of PAMELA RF system

12. Unknown properties of Ferrite rf system operated with high power, high frequency modulation rate needs to consider ….. ’ (under biased condition) Q (under biased condition) + (3) Dynamic loss effect (FM rate) (4) High loss effect (Brf vs QF) (5) Phase error (6) (sample dependence) Item (1)~(4) are crucial and urgent to know for the establishment of feasibility and test cavity design Status of PAMELA RF system

13. R&D status Development has just started Step 1: Ferrite property measurement Q-value ----- On going (by next year) FM rate dependence (dynamic loss effect) --- Preparing Brf vs QF(high loss effect) --- Planned Step 2: Prototyping (budget request is needed) Power dissipation Phase error Status of PAMELA RF system

14. Upgradeability to Carbon acceleration Final ring requires 4 times higher voltages to keep the repetition rate as same as that of proton ring.  Need another tricks or accept the lower repetition rate for carbon (high RBE of carbon might help) Status of PAMELA RF system

15. 1kHz beam bunch can paint 100 voxel/sec in much bunch painting scheme • In the present rf scheme of PAMELA (h=10), one accelerated beam can contain 5 bunch trains in maximum • Employing Active chopper in injection line can modulate intensity dynamically + = Dynamic intensity modulation of factor of 5  rep. rate-wise, more than factor of 4 enhancement !!! Dynamic intensity modulation of factor of 5  rep. rate-wise, more than factor of 4 enhancement !!! Other tip for upgrade Status of PAMELA RF system

16. Active chopper Existing commercial programable delay generator can actively change a delay timing with a precision of <1ns, (changing speed and frequency are now being asked to the company) • If the beam intensity from injector is sufficiently stable (<2%), larger dynamic range of modulation might be possible • MA cavity comes back as alternative and promising option (1 shot/ 1 voxel) Status of PAMELA RF system

17. Summary • The challenge of PAMELA RF is to realize high repetiton rate, high FM rate, high field gradient at the same time • Ferrite cavity is chosen as the primary scheme • Ferrite property is not unclear at the moment • Measurement has just started • Proposal of prototype machine construction will be follow • Direct intensity modulation using active chopper might enhance the effective repetition rate. Status of PAMELA RF system