Highgradient proton accelerating structure developments at CERN Alexej

High-gradient proton accelerating structure developments at CERN Alexej Grudiev 6/02/2014 CLIC 14 Workshop

Acknowledgements • This work is done in close collaboration between CERN (M. Garlasche, A. Grudiev, I. Syratchev, M. Timmins, W. Wuensch) and TERA foundation (U. Amaldi , S. Benedetti, A. Degiovanni, P. Magagnin, G. Porcellana) in the frame work of the CERN Knowledge Transfer (KT) Fund project: “High-gradient Accelerating Structure for Proton Therapy Linacs” 2

Outline • Introduction – RF cavities constraints for hadrontherapy • Backward travelling wave cell design and optimization for high gradient operations – Nose cone study – Tapering – Couplers • Comparison of different structure designs – SW SCL design – backward TW • Engenearing design • Conclusions 3

TULIP 2. 0 at 3 GHz with E 0 ≅ 50 MV/m ≤ 230 Me. V ruct t s W w. T b z H G 5 -6 m new 3 11 m ure 60 Me. V 3 GHz SCDTL ENEA 5 Me. V 750 MHz RFQ CERN TULIP - UA - 6. 3. 14 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. T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 • 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 5 . . .

COMPARISON BETWEEN TW AND SW STRUCTURES 6

Comparison between TW structure and SCL Tapered structures: the coupling holes are smaller along the structure Geometry of LIBO structure 7

Comparison of E-field in TW and SW 2/3 π phase advance π/2 phase advance 8

PROs and CONs of b. TW compared to standard SCL design + simpler mechanically - small wall thickness + less material and brazing needed (lower number of cells) + tuning is easier for TW + shorter filling time + no bridge couplers - 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) waveguide accelerating cavities coupling cavities 9

NOVEL DESIGN FOR HIGH GRADIENT OPERATION 10

Proposal for b. TW design for hadrontherapy DESIGN GOAL and CONSTRAINTS Ea: = E 0 T ≥ 50 MV/m Sc/Ea 2 < 7 10 -4 A/V with: Sc < 4 MW/mm 2 t. TERA = 2500 ns t. CLIC = 200 ns BDRTERA = BDRCLIC = 10 -6 bpp/m Proposed by A. Grudiev P_wall P_load L P_0 vg_in ~ 0. 4% c vg_out ~ 0. 2% c filling time ~ 0. 3 µs z 11

half gap Nose geometry optimization nose radii • Scan on: – – – Nose cone angle nose angle Gap Nose cone radius(*) Phase advance (120°-150°) coupling hole radius (vg = 4 ‰ and 2 ‰ ) septum bore radius • Optima: – Minimum of the quantity: * based also on results of the SCL optimization 12

Optimization plots - fields

Optimization plots R’/Q [Ω/m] vg [10 -3 c] Sc/Ea 2 [10 -3 Ω-1]

150° - 16 holes – nose 1 -2 mm – gap and angle scan g 7. 0 mm A 55 deg

150° - 16 holes – nose 1 -2 mm – gap and angle scan g 7. 0 mm A 55 deg

Tank optimization 1. Minimization of the SW pattern by adjusting the out -coupler 35500 35000 70. 120 mm Ez [V/m] 34500 70. 121 mm 34000 70. 122 mm 70. 123 mm 33500 -35 69, 353 69, 358 69, 363 69, 368 69, 373 69, 378 0 -45 d. B[S 11] 70. 125 mm 32500 -40 50 100 150 Distance along the z-axis [mm] 200 wg_apert=25 mm wg_apert=25. 05 mm -50 wg_apert=25. 06 mm wg_apert=25. 07 mm -55 wg_apert=25. 1 mm -60 -65 70. 124 mm 33000 ac. D [mm] 2. Final optimization of the incoupler to get the final design of the tank 17

RF design of the full structure is done The Sc/Ea^2 < 7 e-4 A/V constraint is respected 18

ENGENERING DESIGN 19

Backward travelling wave accelerating structure Cooling plates Accelerating elements 20

Accelerating structure 150° of phase advance 4 holes for dimpler tuners 21

Joining procedures Hydrogen Bonding: THB=1050 °C Gold Brazing: TGB=950 °C Silver Brazing: TSB=820 °C OFE Copper melting point 1083 °C CREEP? 22

Evaluation of different cells structural performance 150° of phase advance 120° of phase advance g Load: gravitational force g 23

Creep tests 20 discs, to be tested at the 3 temperatures, in order to simulate vertical and horizontal bonding/brazing. S = 2 mm 24

Thermal Test at Bodycote 5

0, 050 -0, 050 1 2 3 4 H 0, 009 6 7 V 0, 013 0, 011 9 10 11 12 H 13 V 0, 009 0, 013 15 16 17 18 H 19 0, 011 -0, 020 0, 007 0, 250 -0, 011 0, 005 0, 006 0, 005 0, 012 14 0, 010 0, 004 -0, 013 0, 004 0, 006 0, 004 0, 012 8 0, 008 0, 150 0, 114 0, 180 0, 275 0, 300 0, 005 -0, 003 0, 005 5 0, 005 0, 014 0, 029 0, 007 0, 013 0, 000 0, 009 0, 058 0, 200 0, 005 0, 027 0, 009 Creep [mm] Creep Results in general - Summary Axial Radial 0, 100 20 V Average Axial: 13 μm ; Average Radial: 6 μm (without cells 2 and 8) 10

Summary • Optimization of TW structures for high gradient operations has been performed for 120° and 150° phase advance. • 150° phase advance has been chosen • The RF design of the input and output coupler is finished. • Creep tests have been performed to validate H-bonding at 1050 ° C • The Engenering design including thermo-mechnical simulation is progressing well • The design and test of the novel b. TW structures is boosting the TULIP project! 27

High-Gradient RF Test Stand plans at IFIC-IFIMED, Valencia CLIC Workshop 2014 3 -7 February 2013 A. Faus-Golfe on behalf of IFIC, GAP (Group of Accelerator Physics) http: //gap. ific. uv. es Valencia, Spain

Framework ►The IFIMED: Research on Imaging and Accelerators applied to Medicine. As an R&D Institute on Medical Physics it is configured through two Research Groups: • Image Science: New Imaging devices as Compton combined with Positron Emission (PET) in the context of the ENVISION project, as well as the development and design of the reconstruction algorithms • Accelerators: Linacs for medical applications as cyclinacs (S and C-bands) in the context of PARTNER project in collaboration with TERA and Beam Instrumentation for hadrontherapy

Objectives ►In the framework of the KT project: “High Gradient Accelerating Structures for proton therapy linacs”, whose scope is the design, construction and high power test of two high-power prototype 3 GHz accelerating structures at 76 Me. V (low energy) and 213 Me. V (high energy) which corresponds to the lowest and highest energy of the proton linac. • The idea is to complement these studies with the design and test of two intermediate (2 nd and 3 rd) proton linac structures. This complementary study will give us the possibility to simulate the most realistic conditions and running operation conditions of this kind of linacs. • Test stand with two klystrons (3 GHz have 7. 5 MW power each, 5 ms RF pulse duration and 400 Hz), the RF system becomes much more flexible allowing arbitrary phase and amplitude pulse shapes even when using a pulse compressor.

Location IFIMED R&D labs integrated in the Scientific Park of the UV RF and Instrumentation labs

BACK-UP slides

SUMMARY 120 deg 150 deg SCL base SCL – HG wall thickness (mm) 1. 5 3. 0 gap (mm) 5. 5 7. 0 5. 1 9. 5 nose cone angle (deg) 65 55 25 55 length (mm) 189. 9 ncell 15 12 10 10 Ea_avg (MV/m) 25 25 Sc_nose (MW/mm 2) 0. 149 0. 185 0. 486 0. 188 t_pulse (ns) flat 2500 expected BDR (at given Ea and t_pulse) (bpp/m) based on Sc limit 1. 1 E-22 2. 9 E-21 5. 7 E-15 3. 7 E-21 max Ea (for BDR of 10 -6 bpp/m) (MV/m) 85. 2 76. 3 47. 1 75. 7 Pin (MW) (w/o recirculation) 2. 70 5. 19 2. 49 5. 10 1. 75 2. 26 Pout (MW) (w/o recirculation) - 2. 90 - 3. 02 - - Q 0 (first/last) 6482/6721 7088/7545 8291 8250 vg (first/last) [%c] 0. 421/0. 226 0. 404/0. 236 - - R’/Q (first/last) [Ohm/m] 7872/7847 7835/7794 8406 6355 440 1050 time constant (ns) 320 field 30/05/2013 rise time (time to reach 99% field) (ns) (w/o recirculation) 750 340 A. Degiovanni 204 800 204 33