RF structure design

1. RF structure design KT high-gradient medical project kick-off 30.05.2013 Alberto Degiovanni TERA Foundation - EPFL

2. Outline • Introduction • RF cavities constraints for hadrontherapy • Backward travelling wave cell design and optimization for high gradient operations • Nose cone study • Tapering • Comparison of different structure designs • SW SCL design • backward TW • Preliminary studies for linac design • Conclusions A. Degiovanni

4. Linac layout and BDR requirements • Quasi-periodic PMQ FODO lattice sets a limit to the length of each structure and determines the group velocity range. • The cells in each structure (tank) have the same length, while from one tank to the next, the cell length increases: β tapering in the range 0.22-0.60 • Trade-off between transverse acceptance and RF efficiency: bore aperture = 5 mm • Max BDR: 1 BD per treatment session (~ 5 min) on the whole linac length (~ 10 m).  BDR ~ 10-6 bpp/m ... A. Degiovanni

5. Novel design for high gradient operation A. Degiovanni

6. Proposal for bTW design for hadrontherapy P_wall DESIGN GOAL and CONSTRAINTS Ea:= E0T ≥ 50 MV/m Sc/Ea2 < 7 10-4 A/V L P_0 P_load z with: Sc< 4 MW/mm2 tTERA = 2500 ns • tCLIC = 200 ns • BDRTERA = BDRCLIC = 10-6 bpp/m Proposed by A. Grudiev vg_in ~ 0.4% c vg_out ~ 0.2% c fillingtime ~ 0.3 µs A. Degiovanni

7. 8 holes (22.5 deg sweep) – radius scan vg [10-3 c] ~ (r[mm])3.65 ROI group velocity ROI nose_Sc/Ea^2 normalizedSc in the couplinghole [10-4Ω-1] doubling the number of holes will double vg while keeping Sc_hole almost constant

8. Nose geometry optimization half gap • Scan on: • Nose cone angle • Gap • Nose cone radius(*) • Phase advance (120°-150°) • coupling hole radius (vg = 4 ‰ and 2 ‰ ) • Optima: • Minimum of the quantity: noseradii nose angle septum bore radius * based also on results of the SCL optimization A. Degiovanni

9. angle scan – 120 deg g5 a25 g5 a75 g5 a55 A. Degiovanni

10. Optimization plots

11. Optimization plots R’/Q [Ω/m] R’ (or ZTT) [MΩ/m]

12. Optimization plots - fields

13. Optimization plots vg [10-3 c] R’/Q [Ω/m] Sc/Ea2 [10-3Ω-1]

14. Optimization plot – 120 deg – gap = 5.5 mm min {Max {Xnose,Xslot}}

15. Optimization plot – 120 deg – gap = 5.5 mm

16. gap and angle scan – 120 deg g4 a55 g4 a75 g4 a25 g5 a25 g5 a75 g5 a55 g6 a25 g6 a75 g6 a55

17. 120° - 16 holes – nose 1 -2 mm – gap and angle scan g 5.5 mm A 65 deg g 5.5 mm A 65 deg

18. 120° - 16 holes – nose 1 -2 mm – gap and angle scan g 5.5 mm A 65 deg g 5.5 mm A 65 deg

19. 150° - 16 holes – nose 1 -2 mm – gap and angle scan g 7.0 mm A 55 deg g 7.0 mm A 55 deg

20. 150° - 16 holes – nose 1 -2 mm – gap and angle scan g 7.0 mm A 55 deg g 7.0 mm A 55 deg

21. COMPARISON between TW and SW structures A. Degiovanni

22. Comparison between TW structure and SCL Tapered structures: the coupling holes are smaller along the structure PUT NEW PLOT Geometry of LIBO structure A. Degiovanni

23. Comparison of E-field in TW and SW π/2 phase advance 2/3 π phase advance A. Degiovanni

24. waveguide accelerating cavities coupling cavities PROs and CONs of bTW compared to standard SCL design I. Syratchev A. Degiovanni

25. Preliminary design for high gradient bTW linac ~15-16 MW klystron 2 x 7.5 MW klystrons 1 3 3 load load load load 2 2 T1 T1 T2 T2 MKs MKs Independent rotary joints -3 dB recirculation Small RF load compared to TW A. Degiovanni

26. Global optimization of bTWlinac Gain ~ 1.8 • Energy range: 60-230 MeV • 16 structures (tanks) – Total length: 5.9 m • 16x7.5 MW klystrons – 8 modulators • Total peak power needed: 206 MW • Peak power with recirculators: 114 MW • Effective filling time increases to 2.1-3 μs • Total average power from MKs: 150 kW • Energy range: 65-230 MeV • 16 structures (tanks) – Total length: 5.5 m • 16x7.5 MW klystrons – 8 modulators • Total peak power needed: 260 MW • Peak power with recirculators: 120 MW • Effective filling time increases to 1.8-2.5 μs • Total average power from MKs: 150 kW Gain ~ 2.2 A. Degiovanni

27. Fast active energy and intensity modulation:RF pulses and beam pulses 5.0 μs Klystron RF pulse P 8 ms Active energy modulation 2.5 μs P RF power into the tanks I Proton pulses from source Active intensity modulation time A. Degiovanni

28. Summary • Optimization of TW structures for high gradient operations has been performed for 120° and 150° phase advance. • The RF design of the input and output coupler is now ongoing. • The optimization of the whole linac layout has started recently and needs some iterations, but looks promising • The design and test of the novel bTW structures is boosting the TULIP project! A. Degiovanni

29. BACK-UP slides

30. TULIP-CLIC-bTW – beta=0.3798 (W=76 MeV) Circular coupling holes Racetrack slot position DIAM/2 angle R_coupling Rc Rectangular slot csl_h GAP/2 Rcorner position angle LENGTH R_coupling A. Degiovanni

31. A. Degiovanni