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 30/05/2013A. Degiovanni2

4. T1T2T3T4T5 T6 T7 T8 T9 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... 30/05/2013A. Degiovanni4

5. NOVEL DESIGN FOR HIGH GRADIENT OPERATION 30/05/2013A. Degiovanni5

6. Proposal for bTW design for hadrontherapy with: S c < 4 MW/mm 2 t TERA = 2500 ns t CLIC = 200 ns BDR TERA = BDR CLIC = 10 -6 bpp/m DESIGN GOAL and CONSTRAINTS E a := E 0 T ≥ 50 MV/m S c /E a 2 < 7 10 -4 A/V Proposed by A. Grudiev P_0 P_load P_wall z L vg_in ~ 0.4% c vg_out ~ 0.2% c filling time ~ 0.3 µs 30/05/2013A. Degiovanni6

7. 8 holes (22.5 deg sweep) – radius scan doubling the number of holes will double vg while keeping Sc_hole almost constant normalized Sc in the coupling hole [10 -4 Ω -1 ] cone AgapRccs_hac_DiamvgR'/QSc/Ea^2_slot degmm ‰Ohm/m10-4 V/A 255.222872.3310.4581112.00 255.22.52872.1721.0481272.46 255.232871.9272.0481473.01 255.23.52871.5643.5481773.57 255.242871.0935.6382154.40 ROI nose_Sc/Ea^2 ROI group velocity vg [10 -3 c] ~ (r[mm]) 3.65

8. Nose geometry optimization 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: * based also on results of the SCL optimization nose radii bore radius half gap septum nose angle 30/05/2013A. Degiovanni8

9. angle scan – 120 deg g5 a25 g5 a55 g5 a75 30/05/2013A. Degiovanni9

10. Optimization plots

11. R’/Q [Ω/m] R’ (or ZTT) [MΩ/m]

12. Optimization plots - fields

13. Optimization plots v g [10 -3 c] S c /E a 2 [10 -3 Ω -1 ] R’/Q [Ω/m]

14. Optimization plot – 120 deg – gap = 5.5 mm min {Max {X nose,X slot }}

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

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

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 30/05/2013A. Degiovanni21

22. Geometry of LIBO structure Comparison between TW structure and SCL PUT NEW PLOT Tapered structures: the coupling holes are smaller along the structure 30/05/2013A. Degiovanni22

23. Comparison of E-field in TW and SW π/2 phase advance 2/3 π phase advance 30/05/2013A. Degiovanni23

24. + simpler mechanically + less material and brazing needed (lower number of cells) + tuning is easier for TW + shorter filling time + no bridge couplers - small wall thickness - material properties change during brazing - Dissipated power is higher (half power goes to the load)  Recirculation loop (power for TW 10-20% higher than SW) PROs and CONs of bTW compared to standard SCL design waveguide accelerating cavities coupling cavities I. Syratchev 30/05/2013A. Degiovanni24

25. Preliminary design for high gradient bTW linac 1.Independent rotary joints 2.-3 dB recirculation 3.Small RF load compared to TW T2T1 load MKs ~15-16 MW klystron 2 3 T2T1 load MKs 1 2 3 2 x 7.5 MW klystrons 30/05/2013A. Degiovanni25

26. Global optimization of bTW linac 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 Gain ~ 1.8 30/05/2013A. Degiovanni26

27. Fast active energy and intensity modulation: RF pulses and beam pulses Klystron RF pulse RF power into the tanks Proton pulses from source 5.0 μs 2.5 μs 8 ms time I P P 30/05/2013A. Degiovanni27

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! THANKYOU 30/05/2013A. Degiovanni28

29. BACK-UP slides

30. TULIP-CLIC-bTW – beta=0.3798 (W=76 MeV) Rc csl_h DIAM/2 GAP/2 LENGTH position R_coupling angle R_coupling position Rcorner Racetrack slot Rectangular slot Circular coupling holes 30/05/2013A. Degiovanni30

31. SUMMARY 120 deg150 degSCL baseSCL – HG wall thickness (mm) 1.5 3.0 gap (mm) 5.57.05.19.5 nose cone angle (deg) 65552555 length (mm) 189.9 ncell 151210 Ea_avg (MV/m) 25 Sc_nose (MW/mm2) 0.1490.1850.4860.188 t_pulse (ns) flat 2500 expected BDR (at given Ea and t_pulse) (bpp/m) based on Sc limit 1.1 E-222.9 E-215.7 E-153.7 E-21 max Ea (for BDR of 10 -6 bpp/m) (MV/m) 85.276.347.175.7 Pin (MW) (w/o recirculation) 2.705.192.495.101.752.26 Pout (MW) (w/o recirculation) -2.90-3.02-- Q0 (first/last) 6482/67217088/754582918250 vg (first/last) [%c] 0.421/0.2260.404/0.236-- R’/Q (first/last) [Ohm/m] 7872/78477835/779484066355 time constant (ns) 320340440 field rise time (time to reach 99% field) (ns) (w/o recirculation) 7502048002041050 30/05/2013A. Degiovanni31