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

acknowledgments Thank you entire CLIC team 2 Thank you entire CLIC team in particular Walter, Alexej, Germana, Erk, Igor, Jan, Wilfrid for all advice, discussions and help for our project Jiaru  and Walter for scheduling our meeting today 21/04/2017

aim of this meeting to present the 3 GHz test cavity design to get feedback, suggestions, recommendations => production will start in ~ 2 weeks discussion of open issues 21/04/2017

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 21/04/2017 21/04/2017

Motivations and Objectives of the 3 GHz high gradient test Rolf Wegner 21/04/2017

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 21/04/2017

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 21/04/2017

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 21/04/2017

Advantages of higher gradient for LIGHT Alberto Degiovanni 21/04/2017

LIGHT (IDRA-I) Proton accelerator @ 3 GHz 30 MeV cyclotron by IBA R A D I O P H A R M A C Y P R O T O N T H E R A P Y ≤230 MeV 30 MeV 70 MeV Linac for Image Guided Hadron Therapy = LIGHT 19 m 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) Alberto Degiovanni 21/04/2017

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 21/04/2017

LIGHT (pediatric IDRA) 4.1 5.1 6.1 7.4 8.8 10.4 12.1 14.1 16.2 18.5 cm 0.9 cm in water Alberto Degiovanni 21/04/2017

LIGHT (full IDRA) ~ 19 m ~ 15 m Alberto Degiovanni 21/04/2017

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 21/04/2017

Optimization strategies 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 21/04/2017

RF design of the test cavities Silvia Verdú Andrés 21/04/2017

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 21/04/2017

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 Cell parameter Symbol Value Length [mm] L 18.9 Gap length [mm] g 4.7 Inner Corner Radius [mm] RCI 1.9 Inner Nose Radius [mm] RNI 1 Outer Nose Radius [mm] RNO Cone Angle [°] JC 25 Septum Thickness [mm] S 3 Bore Radius [mm] RB 3.5 L S/2 RCI RNO JC RB RNI Silvia Verdú Andrés 21/04/2017

Simulate two cavities with different Slot Length 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 Silvia Verdú Andrés Silvia Verdú Andrés 21/04/2017 21/04/2017 19

Mesh Max. element length for: Cavity + Coupler………3 mm 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 Silvia Verdú Andrés Silvia Verdú Andrés 21/04/2017 21/04/2017 20

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 Silvia Verdú Andrés Silvia Verdú Andrés 21/04/2017 21/04/2017 21

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 Silvia Verdú Andrés Silvia Verdú Andrés 21/04/2017 21/04/2017 22

Coupling between the cell and the waveguide SW/2 SD SL LSHORT Power Short-cut Silvia Verdú Andrés 21/04/2017

Test cavities 1st Test Cavity 2nd Test Cavity 24 Cavity Cavity Coupler Radius [mm] 32.61 Outer Corner Radius [mm] 3.4 Cavity Radius [mm] 32.38 Outer Corner Radius [mm] 2.0 Coupler Length SL 28.8 Width SW 3 Depth SD 5 Coupler Length SL 25.5 Width SW 6 Depth SD 5 Waveguide WR284 Height 72.14 Width 34.036 Silvia Verdú Andrés Silvia Verdú Andrés 21/04/2017 21/04/2017 24

Test Cavities 2.9985 0…+3 8880 67 -70 MHz/mm 1.5 ±0.05 Frequency [GHz] DfHFSS [MHz] 0…+3 Q0HFSS 8880 ZTT [MOhm/m] 67 df/dR -70 MHz/mm Coupling coefficient b 1.5 ±0.05 Silvia Verdú Andrés 21/04/2017

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 Field Cell Coupler Emax [MV/m] 150 63 E0 [MV/m] 23 ---- SCmax [MW2/mm2] 0.46 0.15 P[kW] 140 3 Co S Conclusions: No breakdowns expected in coupler. E Silvia Verdú Andrés Silvia Verdú Andrés 21/04/2017 21/04/2017

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 Silvia Verdú Andrés Silvia Verdú Andrés 21/04/2017 21/04/2017

Cooling of the test cavities Rossana Bonomi 21/04/2017

Geometry of OhMEGA1 cooling channel flange tuner coupling slot 29 cooling channel flange tuner coupling slot cooling plates inlet-outlet coolant Rossana Bonomi 21/04/2017

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 21/04/2017

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 21/04/2017

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 dT in-out = 1ºC Deq = 5.5 mm Re = 13900 v = 1.77 m/s h = 10020 W/m2/K Rossana Bonomi 21/04/2017

Geometry, Materials Symmetry of thestructure 33 OFE Copper C10100 316 Stainless Steel Rossana Bonomi 21/04/2017

Steady State Thermal – Boundary C. 1/2 34 Heat load distribution from Superfish Rossana Bonomi 21/04/2017

Steady State Thermal – Boundary C. 2/2 35 radiation + convection with stagnant ambient air Forced convection inside channel Rossana Bonomi 21/04/2017

Steady State Thermal – Results 36 Coolant Reference Temperature 37ºC Delta max temp: 15≤ ºC Rossana Bonomi 21/04/2017

Static Structural – Boundary C. 37 Ambient and vacuum pressure Symmetry Frictionless Support lower face Rossana Bonomi 21/04/2017

Static Structural – Results 38 Right nose deformation: -3 micron Max deformation: 70 micron Left nose deformation: 3 micron Rossana Bonomi 21/04/2017

Static Structural – Results 39 All stresses less than 10 MPa Rossana Bonomi 21/04/2017

Expected Frequency Shift 40 Deformations lead to frequency shift Rossana Bonomi 21/04/2017

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 21/04/2017

Mechanical Design Marco Garlasché 21/04/2017

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 21/04/2017

Model of accelerating system 44 # 1 # 2 Cavity radius [mm] 32.61 32.38 Inner corner radius [mm] 3.4 2.0 Coupling slot [mm] 28.8 x 3 25.5 x 6 Two asymmetrical half cells: easier brazing, no spikes in slot Cavities: machining precision of 0.02 mm. Marco Garlasché 21/04/2017 21/04/2017

Acquisition angle Acquisition angle: 90˚ CF flange mating surface carved 6mm deep for better acquisition (5.8˚ @ highest point ) Marco Garlasché 21/04/2017

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 21/04/2017

Brazing for connection with CF flange Second half cell OFE Copper Brazing for connection with CF flange Marco Garlasché 21/04/2017

Waveguide OFE Copper Brazing with cell Brazing with LIL flange 34.036 mm 72.136 mm Brazing with LIL flange 236 mm OFE Copper Any experience on brazings directly on waveguide walls? Marco Garlasché 21/04/2017

Cooling plates OFE Copper / 316 LN Usual dimension for coating ? Two pipes coated and brazed to cooling plate Usual dimension for coating ? Marco Garlasché 21/04/2017

Tolerances and Tuning Rolf Wegner 21/04/2017

tolerances r z full cell dL=2dz= ± 40 µm 1 2 3 4 6 5 9 7 8 part dz dr df µm kHz 1. top straight ± 20 ± 10 ± 1022 2. OUTER_CORNer_radius ± 1008 3. web ± 1065 4. INNER_CORNer_radius ± 182 5. nose angle ± 504 6. OUTER_NOSE_radius ± 3654 7. flat_top ± 240 8. INNER_NOSE_radius ± 2001 9. beampipe ± 32 total ± 9707 Rolf Wegner 21/04/2017

tuner Ø tuner: 8.4 mm tuning range: -1 .. +19 MHz reduction in Q: 0 .. -5% Rolf Wegner 21/04/2017

tuning df [MHz] compensation dR [mm] sensitivity dR= + 1.0 mm - 70 53 df [MHz] compensation dR [mm] sensitivity dR= + 1.0 mm - 70 sensitivity tuner dL= +1.0 mm + 3.0 machining tolerances ± 10 compensated by tuner tuner (dL= 0 mm) - 9.0 + 0.129 thermal expansion (dT= 15 K) - 2.0 - 0.024 air => vacuum (T0=20°C) + 0.97 Tuning: f0(air, T0=20°C)= 2999.530 MHz => f0(vacuum, To=35°C)= 2998.500 MHz Rolf Wegner 21/04/2017 21/04/2017

Parameter list for high gradient test 21/04/2017

parameter list for high gradient test 1st cavity (slot width= 3.0 mm) 2nd cavity (slot width= 6.0 mm) Q0, 2D 9110 8988 Q0, 3D 8884 8876 Qloaded,expected (tuner: 3%, T=35°C: 3%, surf. roughness, assembly => total - 9%) 4042 4039 Es= 250 MV/m Pin= 380 kW Tpulse * frep 3 μs * 300 Hz 0.9 ‰ Pin,avg= 340 W 21/04/2017

parameter list for high gradient test 1st cavity (slot width= 3.0 mm) 2nd cavity (slot width= 6.0 mm) Pin [kW] Tpulse [μs ] Es [MV/m] Sc [MW/mm2] lg(BDR) ! X+K ! Sc [MW/mm2] lg(BDR) ! X+K ! 140 1.5 150 0.46 -18.2 240 200 0.82 -14.5 380 250 1.28 -11.6 550 300 1.84 -9.2 740 350 2.51 -7.2 970 400 3.27 -5.4 21/04/2017

Open issues / questions 21/04/2017

Open issues, Questions RF pickup for cavity ? 3rd test cavity ? 58 RF pickup for cavity ? 3rd test cavity ? purchase of S-band components: waveguide CF and LIL flanges, spacers, seals cooling pipes high power test test stand connections to RF, cooling, vacuum system instrumentation (dimensions, weight, solely linked to test cavity?) 21/04/2017 21/04/2017

Thank you very much for your attention 21/04/2017

EXTRA-SLIDES 21/04/2017

Accelerating cells geometry Rco Rci Rno Rni CA S/2 L D/2 Rb g Symbol Cell Parameter L cell Length D cell Diameter g Gap length Rco Outer Corner Radius Rci Inner Corner Radius Rno Outer Nose Radius Rni Inner Nose Radius CA Cone Angle S Septum thickness or Web Rb Bore Radius 21/04/2017

CABOTO-S New design will probably be with a different number of cells per tank, in order to increase as much as possible the gradient having in all the structure the maximum allowed ES 1 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 6 241 MeV/u 252 263 274 286 297 309 320 332 344 355 367 379 391 403 415 428 ~ 24 m 21/04/2017

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 35 MeV/u 41 48 55 63 71 80 89 99 109 119 130 142 153 166 178 191 204 217 230 MeV/u ~ 19 m 21/04/2017

Superfish gives a good approach to resonant frequencies Why? Superfish gives a good approach to resonant frequencies Fastest and simplest way to find which geometry provides the maximum ZTT We get: Appropriate dimensions of the cavity Tuning sensitivity (frequency – diameter) 2D cavity optimization with Superfish 64 Study of HFSS performance Why? To check if HFSS simulations are reliable. Study of accuracy for determinate mesh size and distribution. We get: Appropriate mesh. 3D structure design with HFSS / GdfidL Why? The whole structure can be simulated by these programs. They provide good calculations for Q-values. 21/04/2017 21/04/2017

Parameters 1st TC 21/04/2017 Frequency [GHz] 2.9985 b = v/c 0.3781 Transit-time Factor 0.8934 Q-value 8690 R/Q [Ohm] 70.311 ZTT [Mohm/m] 67.767 Emax [MV/m] 155.64 Emax [Kilp] 3.32 Emax/E0 6.49 Hmax [A/m] 63709 Hmax [kW/cm2] 2.91 Coupling Coefficient b 1.537 Scaling Exponent n 6.779 Change in freq [MHz] 15.85 21/04/2017

Parameters 2nd TC 21/04/2017 Frequency [GHz] 2.9985 b = v/c 0.3 Transit-time Factor 0.8934 Q-value 8690 R/Q [Ohm] 70.363 ZTT [Mohm/m] 66.904 Emax [MV/m] 155.63 Emax [Kilp] 3.32 Emax/E0 6.45 Hmax [A/m] 63761 Hmax [kW/cm2] 2.91 Coupling Coefficient b 1.522 Scaling Exponent n 6.583 Change in freq [MHz] 18.25 21/04/2017

Open issues ? ? ? Advice on general mechanical design Thickness of nickel-copper coating (7 μm÷15 μm) ? Characteristics of the experimental bench: - disposition of cooling, vacuum - disposition of acquisition (solely linked to prototype?) - where to attach prototype ? Retrieval of components: waveguide flanges (CF, Lil) pipes and seals 21/04/2017

Open issues: flanges - Dimensions obtained from straight guide flange (‘CTFARFNE0003’) Where to obtain flange seal? Do we need to completely machine flange? Thickness of intermediate see-through seal - Dimensions of coupling flanges (distance of holes, diameter, possible threading) (SCEM 18.60.18.005.3) bolted UHV flange (18.60.18.005.3) Dimensions of intermediate metal seal (18.60.55.850.6) remachining forged blank (18.60.19.070.0) 21/04/2017

Open issues: cooling dimensions of coupling’s pipes how are pipes normally connected (raccords, threading) eventually made out of 316L - coating of tubes 316L (39.36.05) 21/04/2017