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

2. acknowledgments Thank you entire CLIC team2
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

3. 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

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
21/04/2017
21/04/2017

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

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: (
Rolf Wegner
21/04/2017

7. motivations of high gradient test
design values / break down 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= /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

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
21/04/2017

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

10. 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 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

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
21/04/2017

12. 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

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

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
21/04/2017

15. 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

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

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
21/04/2017

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
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

19. Simulate two cavities with different Slot Length
Process of design 19
HFSS 3D
Superfish 2D
Cavity
f0SF= 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=
Structure
f0SF, f3HFSS, R1
Structure
f2HFSS, R0
∆f = f0SF-f2SF
f2SF
Silvia Verdú Andrés
Silvia Verdú Andrés
21/04/2017
21/04/2017 19

20. Mesh Max. element length for: Cavity + Coupler………3 mm20
Max. element length for:
Cavity + Coupler………3 mm
Max. surface deviation for:
Cavity + Coupler.…0.02 mm
Max. delta frequency
(convergency): %
~65 mm
Silvia Verdú Andrés
Silvia Verdú Andrés
21/04/2017
21/04/2017 20

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

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

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

24. 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

25. 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

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
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

27. Fields Asymmetries E-field variation27
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

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

29. Geometry of OhMEGA1 cooling channel flange tuner coupling slot29
cooling channel
flange
tuner
coupling slot
cooling plates
inlet-outlet coolant
Rossana Bonomi
21/04/2017

30. Sizing channel (MatLab) 1/230
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

31. Sizing channel (MatLab) 2/231
Choices
dT in-out = 1ºC
Deq = 5.5 mm
Re =
v = m/s
h = W/m2/K
Rossana Bonomi
21/04/2017

32. Calculated Data EACH CIRCUIT (2 parallel circuits) Surface 4320 mm2
Mass flow 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 =
v = m/s
h = W/m2/K
Rossana Bonomi
21/04/2017

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

34. Steady State Thermal – Boundary C. 1/234
Heat load distribution from Superfish
Rossana Bonomi
21/04/2017

35. Steady State Thermal – Boundary C. 2/235
radiation + convection with stagnant ambient air
Forced convection inside channel
Rossana Bonomi
21/04/2017

36. Steady State Thermal – Results36
Coolant Reference Temperature 37ºC
Delta max temp: 15≤ ºC
Rossana Bonomi
21/04/2017

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

38. Static Structural – Results38
Right nose deformation:
-3 micron
Max deformation: 70 micron
Left nose deformation:
3 micron
Rossana Bonomi
21/04/2017

39. Static Structural – Results39
All stresses less than 10 MPa
Rossana Bonomi
21/04/2017

40. Expected Frequency Shift40
Deformations lead to frequency shift
Rossana Bonomi
21/04/2017

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
21/04/2017

42. Mechanical Design
Marco Garlasché
21/04/2017

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
21/04/2017

44. Model of accelerating system44
# 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

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

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
21/04/2017

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

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

49. 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

50. Tolerances and Tuning
Rolf Wegner
21/04/2017

51. tolerances r z full cell dL=2dz= ± 40 µm 1 2 3 4 6 5 9 7 8 part dz drdf 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

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

53. tuning df [MHz] compensation dR [mm] sensitivity dR= + 1.0 mm - 7053
df [MHz]
compensation dR [mm]
sensitivity dR= mm
- 70
sensitivity tuner dL= +1.0 mm
+ 3.0
machining tolerances
± 10
compensated by tuner
tuner (dL= 0 mm)
- 9.0
thermal expansion (dT= 15 K)
- 2.0
air => vacuum (T0=20°C)
+ 0.97
Tuning: f0(air, T0=20°C)= MHz => f0(vacuum, To=35°C)= MHz
Rolf Wegner
21/04/2017
21/04/2017

54. Parameter list for high gradient test
21/04/2017

55. 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

56. 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

57. Open issues / questions
21/04/2017

58. 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

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

60. EXTRA-SLIDES
21/04/2017

61. 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

62. 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

63. 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

64. 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

65. 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

66. 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

67. 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

68. 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 )
bolted UHV flange ( )
Dimensions of intermediate metal seal ( )
remachining
forged blank ( )
21/04/2017

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