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3 GHz high gradient test cavities

This project outlines motivations and objectives of a 3 GHz high gradient test cavity design for reliable operation, optimization, and efficiency. Detailed RF design aspects, advantages of higher gradient for LIGHT, cooling mechanisms, mechanical design, and parameter lists are discussed by expert contributors.

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3 GHz high gradient test cavities

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  1. Rossana Bonomi, Alberto Degiovanni, Marco Garlasché, Silvia Verdú Andrés, Rolf Wegner 3 GHz high gradient test cavities

  2. acknowledgments 2 Thank you • entire CLIC team • in particular Walter, Alexej, Germana, Erk, Igor, Jan, Wilfrid for all advice, discussions and help for our project Thank you • Jiaru  and Walter for scheduling our meeting today

  3. aim of this meeting 3 • to present the 3 GHz test cavity design • to get feedback, suggestions, recommendations=> production will start in ~ 2 weeks • discussion of open issues

  4. outline 4 4 • Motivations and Objectives of the 3 GHz high gradient test – Rolf Wegner • Advantages of higher gradient for LIGHT – Alberto Degiovanni • RF design of the test cavities – Silvia Verdú Andrés • Cooling of the test cavities – Rossana Bonomi • Mechanical design – Marco Garlasché • Tolerances and tuning – Rolf Wegner • Parameter list for high gradient test • Open issues / questions 01/01/2020

  5. Motivations and Objectives of the 3 GHz high gradient test Rolf Wegner

  6. Motivations design values / break down limits @ 3 GHz LIBO (LInac BOoster for protontherapy): design: Es= 1.8 Kilp. = 84 MV/m test: Es> 2.6 Kilp. = 122 MV/m G. Loew, J. Wang: (http://www.slac.stanford.edu/pubs/slacpubs/5250/slac-pub-5320.pdf) Rolf Wegner

  7. motivations of high gradient test design values / break down limits @ 3 GHz LIBO: Es> 2.6 Kilp. = 122 MV/m G. Loew, J. Wang: Es> 300 MV/m = 6.4 Kilp. modified Poynting vector + scaling laws from X and K-band:for BDR= 10-6 1/m, Tpulse= 2.0 µs, Sc= 1.5 MW/mm2=>Es> 300 MV/m = 6.4 Kilp. Can a 3 GHz standing wave cavity be operated reliably with Es= 150 MV/m = 3.2 Kilp. ? => high gradient test Rolf Wegner

  8. objectives of high gradient test operation limit for S-band cavities (BDR) applying found limit to future design ensure reliable operation optimise efficiency by knowing limitations BDR at S-band described by Es (Kilp.) or mod. Poynting vector + scaling law (X, K-band) scaling law BDR ~ Es30 Tpulse5 valid at S-band ? dependency of BDR on temperature, rep. rate assembly procedure TERA: minimising machining cost CLIC: maximising gradient cost optimisation: machining, linac length, operating (power) Rolf Wegner

  9. Advantages of higher gradient for LIGHT Alberto Degiovanni

  10. 30 MeV cyclotron by IBA LIGHT (IDRA-I) 30 MeV R A D I O P H A R M A C Y • Proton accelerator @ 3 GHz • W = 30  230 MeV (β = 0.26  0.59) • 20 acc. modules • 1 unit = 2 modules • 1 module = 2 tanks • 1 tank = 16 ACs • Klystron TH2157: 7.5 MW peak power • ES ≈ 90 MV/m (1.8 Kilp) Linac for Image Guided Hadron Therapy = LIGHT 19 m P R O T O N T H E R A P Y 70 MeV ≤230 MeV Alberto Degiovanni

  11. LIGHT (IDRA-I) • With the current acc. gradient (17 MV/m) each modules consumes about 2.6 MW of peak power, but the klystrons can provide up to 5.4 MW (with 28% reduction for losses) • The accelerating gradient can be increased by 44 % (17 MV/m  24.5 MV/m) • ES increases, up to 130 MV/m • The total length decreases from 19 m to 15 m Alberto Degiovanni

  12. LIGHT (pediatric IDRA) 0.9 cm in water 4.1 5.1 6.1 7.4 8.8 10.4 12.1 14.1 16.2 18.5 cm Alberto Degiovanni

  13. LIGHT (full IDRA) ~ 15 m ~ 19 m Alberto Degiovanni

  14. Advantages of IDRA-II • Reduce the number of modules, and so of modulators and of klystrons (17  13) • Reduce the length for ‘pediatric IDRA’ and ‘full IDRA’ (19 m  15 m) • Make good use of modulators and klystrons • …but Peak Power consumption increases by 33% (52 MW  70 MW) Alberto Degiovanni

  15. Optimizationstrategies • ZTT dependence on the ratio ES/E0 (with nose radius taken as a parameter) gap 2mm gap 11mm With ES=160 MV/m - - -E0= 25 MV/m - - -E0= 35 MV/m Alberto Degiovanni

  16. RF design of the test cavities Silvia Verdú Andrés

  17. Introduction Two structures with different slots* have been designed in order to test the breakdown rate: Breakdowns can occur in the coupler region if the structure has a small slot. The perturbation of the fields is high when the slot is too big. Cell Aperture for adquisition Coupler Waveguide WR284 [*] Slot: Aperture which links the cell with the waveguide Silvia Verdú Andrés

  18. Basic cell geometry optimization Superfish was used to optimize the cell geometry. The Outer Corner Radius RCO and Radius R are different for each test cavity. RCO R L S/2 RCI RNO JC RB RNI Silvia Verdú Andrés

  19. Process of design 19 HFSS 3D Superfish 2D Cavity f0SF=2998.5 GHz, R0 Structure LS / b=1.5 Cavity f1HFSS, R0 Scaling factor* SF-HFSS fSF/fHFSS, QSF/QHFSS • Simulate two cavities with different Slot Length • Exponential law Tuning sensitivity f vs. R [*] fSF/fHFSS= 0.9992 Structure f0SF, f3HFSS, R1 Structure f2HFSS, R0 ∆f = f0SF-f2SF f2SF 01/01/2020 Silvia Verdú Andrés Silvia Verdú Andrés

  20. Mesh 20 • Max. element length for: Cavity + Coupler………3 mm • Max. surface deviation for: Cavity + Coupler.…0.02 mm • Max. delta frequency (convergency): 0.1 % ~65 mm 01/01/2020 Silvia Verdú Andrés Silvia Verdú Andrés

  21. Special Mesh 21 Max. element length for: • All………………….. 5 mm • Beam pipe……… 0.8 mm • Coupler…………. 1.2 mm Max. surface deviation for All: 0.5 mm 01/01/2020 Silvia Verdú Andrés Silvia Verdú Andrés

  22. Special Mesh 22 Max. element length for: • All………………….. 5 mm • Beam pipe……… 0.8 mm • Coupler…………. 1.2 mm Max. surface deviation for All: 0.5 mm 01/01/2020 Silvia Verdú Andrés Silvia Verdú Andrés

  23. Coupling between the cell and the waveguide SW/2 SD SL LSHORT Power Short-cut Silvia Verdú Andrés

  24. Test cavities 24 1st Test Cavity 2nd Test Cavity 01/01/2020 Silvia Verdú Andrés Silvia Verdú Andrés

  25. Test Cavities Silvia Verdú Andrés

  26. Maximum fields 26 Purpose: evaluate maximum fields in cell and coupler. If fields are too big in the coupler region, breakdowns can be originated there. done for the 1st Test Cavity S Conclusions: No breakdowns expected in coupler. E 01/01/2020 Silvia Verdú Andrés Silvia Verdú Andrés

  27. Fields Asymmetries E-field variation 27 Purpose: the slot perturbes the fields. We study the perturbation of the slot in the field pattern Mejorar fig.! done for the 2nd Test Cavity N W E S Conclusion: small perturbations of the fields 01/01/2020 Silvia Verdú Andrés Silvia Verdú Andrés

  28. Cooling of the test cavities Rossana Bonomi

  29. Geometry of OhMEGA1 29 cooling channel flange tuner coupling slot cooling plates inlet-outlet coolant Rossana Bonomi

  30. Sizing channel (MatLab) 1/2 30 • Requirements • Average power to cool (350 W) • Nº of parallel circuit (2) • Turbulent flow (Re>104) • Avoid erosion/corrosion (v < 2 m/s) • Reference temp. for coolant properties (37ºC) • High heat transfer coefficient (~104): minimization of the surface Rossana Bonomi

  31. Sizing channel (MatLab) 2/2 31 • Choices • dT in-out = 1ºC • Deq = 5.5 mm • Re = 13900 • v = 1.77 m/s • h = 10020 W/m2/K Rossana Bonomi

  32. Calculated Data EACH CIRCUIT (2 parallel circuits) • Surface 4320 mm2 • Mass flow 0.042 kg/s (~ 150 l/h = 2.5 l/min) • Expected temp difference wall-axis: ΔTw-a = (P/2)/(h*S) ~ 4.5ºC • dTin-out = 1ºC • Deq = 5.5 mm • Re = 13900 • v = 1.77 m/s • h = 10020 W/m2/K Rossana Bonomi

  33. Geometry, Materials 33 • Symmetry of thestructure • OFE Copper C10100 • 316 Stainless Steel Rossana Bonomi

  34. Steady State Thermal – Boundary C. 1/2 34 • Heat load distribution from Superfish Rossana Bonomi

  35. Steady State Thermal – Boundary C. 2/2 35 • radiation + convection with stagnant ambient air • Forced convection inside channel Rossana Bonomi

  36. Steady State Thermal – Results 36 Coolant Reference Temperature 37ºC Delta max temp: 15≤ ºC Rossana Bonomi

  37. Static Structural – Boundary C. 37 • Ambient and vacuum pressure • Symmetry • Frictionless Support lower face Rossana Bonomi

  38. Static Structural – Results 38 Right nose deformation: -3 micron Max deformation: 70 micron Left nose deformation: 3 micron Rossana Bonomi

  39. Static Structural – Results 39 All stresses less than 10 MPa Rossana Bonomi

  40. Expected Frequency Shift 40 • Deformations lead to frequency shift Rossana Bonomi

  41. Conclusions 41 • Cooling controls temperature (difference between nose and cooling plates less than 15°C) • Cooling keeps stresses far below the maximum yield stress for this material Rossana Bonomi

  42. Mechanical Design Marco Garlasché

  43. Assembly design Model of accelerating system (half cells, tuning rod) Coupling system (waveguide, Lil flanges) Cooling system (two plates, in-out pipes) Connection to acquisition (CF flanges) Marco Garlasché

  44. Model of accelerating system 44 Two asymmetrical half cells: easier brazing, no spikes in slot Cavities: machining precision of 0.02 mm. 01/01/2020 Marco Garlasché

  45. Acquisition angle Acquisition angle: 90˚ CF flange mating surface carved 6mm deep for better acquisition (5.8˚ @ highest point ) Marco Garlasché

  46. First half cell: brazing 78 mm 87 mm OFE Copper Brazing for connection with: 2nd half cell CF flange One tuner on top, diametrical to coupling slot Marco Garlasché

  47. Second half cell OFE Copper Brazing for connection with CF flange Marco Garlasché

  48. Waveguide Brazing with cell 34.036 mm 72.136 mm Brazing with LIL flange 236 mm OFE Copper Any experience on brazings directly on waveguide walls? Marco Garlasché

  49. Cooling plates OFE Copper / 316 LN Two pipes coated and brazed to cooling plate Usual dimension for coating ? Marco Garlasché

  50. Tolerances and Tuning Rolf Wegner

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