Rossana Bonomi, Alberto Degiovanni, Marco Garlasché, Silvia Verdú Andrés,

Rolf Wegner

3 GHz high gradient test cavities

acknowledgmentsacknowledgments

Thank you• entire CLIC team• in particular Walter, Alexej, Germana, Erk, Igor,

Jan, Wilfridfor all advice, discussions and help for our project

Thank you• Jiaru  and Walter

for scheduling our meeting today

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19/04/23

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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

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outline

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

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Motivations and Objectives of the

3 GHz high gradient test

Rolf Wegner

19/04/23

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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)

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Rolf Wegner

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 19/04/23

7

Rolf Wegner

objectives of high gradient test

1. operation limit for S-band cavities (BDR)2. applying found limit to future design

ensure reliable operation optimise efficiency by knowing limitations

3. BDR at S-band described by Es (Kilp.) or mod. Poynting vector + scaling law (X, K-band)

4. scaling law BDR ~ Es30 Tpulse

5 valid at S-band ?5. dependency of BDR on temperature, rep. rate6. assembly procedure

TERA: minimising machining cost CLIC: maximising gradient cost optimisation: machining, linac length, operating (power)

19/04/23

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Rolf Wegner

Advantages of higher gradient for LIGHT

Alberto Degiovanni

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LIGHT (IDRA-I)

Proton accelerator @ 3 GHzW = 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 powerES ≈ 90 MV/m (1.8 Kilp)

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

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Alberto Degiovanni

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/mThe total length decreases from 19 m to 15 m

44.1MW 6.2

MW 4.5''

0

0 P

P

E

E L

ZT

TEnP

2

20

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Alberto Degiovanni

LIGHT (pediatric IDRA)

4.1 5.1 6.1 7.4 8.8 10.4 12.1 14.1 16.2 18.5 cm0.9 cm in water

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Alberto Degiovanni

LIGHT (full IDRA)

~ 19 m

~ 15 m

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Alberto Degiovanni

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)

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Alberto Degiovanni

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

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Alberto Degiovanni

RF design of the test cavities

Silvia Verdú Andrés

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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.

[*] Slot: Aperture which links the cell with the waveguide

Waveguide WR284

Coupler

Aperture for adquisition

Cell

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Silvia Verdú Andrés

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.

Cell parameter Symbol Value

Length [mm] L 18.9

Gap length [mm] g 4.7

Inner Corner Radius [mm]

RCI1.9

Inner Nose Radius [mm]

RNI1

Outer Nose Radius [mm]

RNO1

Cone Angle [°] C25

Septum Thickness [mm]

S 3

Bore Radius [mm] RB3.5

RCO

RCI

R

L

S/2

RB RNI

RNO

C

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Silvia Verdú Andrés

Tuning sensitivity

f vs. R

HFSS 3DSuperfis

h2D

Scaling factor* SF-HFSS

fSF/fHFSS, QSF/QHFSS

Process of design

Cavityf0SF=2998.5 GHz,

R0

Cavityf1HFSS, R0

StructureLS /

=1.5

Structuref2HFSS, R0

• Simulate two cavities with different Slot Length

• Exponential law

f2SF

∆f = f0SF-f2SF

Structuref0SF, f3HFSS,

R1

[*] fSF/fHFSS= 0.9992

n

b

a

b

a

x

x

x

x

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Silvia Verdú Andrés 19/04/23

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Silvia Verdú Andrés

Mesh

Max. element length for: Cavity + Coupler………3

mm

Max. surface deviation for: Cavity + Coupler.…0.02

mm

Max. delta frequency (convergency): 0.1 %

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Silvia Verdú Andrés

~65 mm

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Silvia Verdú Andrés

Max. element length for:• All………………….. 5 mm• Beam pipe……… 0.8 mm• Coupler…………. 1.2 mm

Max. surface deviation for All: 0.5 mm

Special Mesh

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Silvia Verdú Andrés 19/04/23

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Silvia Verdú Andrés

Max. element length for:• All………………….. 5 mm• Beam pipe……… 0.8 mm• Coupler…………. 1.2 mm

Max. surface deviation for All: 0.5 mm

Special Mesh

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Silvia Verdú Andrés 19/04/23

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Silvia Verdú Andrés

Coupling between the cell and the waveguide

Power

Short-cut

LSHORT

SW/2

SL

SD

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Silvia Verdú Andrés

Test cavities

Cavity

Radius [mm] 32.61

Outer Corner Radius [mm]

3.4

Coupler

Length SL 28.8

Width SW 3

Depth SD 5

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Silvia Verdú Andrés

Coupler

Length SL 25.5

Width SW 6

Depth SD 5

Cavity

Radius [mm] 32.38

Outer Corner Radius [mm]

2.0

Waveguide WR284

Height 72.14

Width 34.036

1st Test Cavity 2nd Test Cavity

19/04/23Silvia Verdú Andrés

Test Cavities

Frequency [GHz] 2.9985

fHFSS [MHz] 0…+3

Q0HFSS 8880

ZTT [MOhm/m] 67

df/dR -70 MHz/mm

Coupling coefficient

1.5 ±0.05

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Silvia Verdú Andrés

Maximum fields

S

E

Field Cell Coupler

Emax [MV/m] 150 63

E0 [MV/m] 23 ----

SCmax [MW2/mm2] 0.46 0.15

P[kW] 140 3

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Silvia Verdú Andrés

Purpose: evaluate maximum fields in cell and coupler. If fields are too big in the coupler region, breakdowns can be originated there.

Conclusions: No breakdowns expected in coupler.

done for the 1st Test Cavity

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Silvia Verdú Andrés

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Fields AsymmetriesE-field variation

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Silvia Verdú Andrés

Mejorar fig.!

Conclusion: small perturbations of the fields

-0,04

-0,02

0

0,02

0,04

0 0,5 1 1,5 2 2,5

East Line [mm]

(E-N

)/N

-0,04

-0,02

0

0,02

0,04

0 0,5 1 1,5 2 2,5

West Line [mm]

(W-N

)/N

-0,04

-0,02

0

0,02

0,04

0 0,5 1 1,5 2 2,5

South Line [mm]

(S-N

)/NPurpose: the slot perturbes the fields.

We study the perturbation of the slot in the field pattern

done for the 2nd Test Cavity

W

S

N

E

19/04/23Silvia Verdú Andrés

Cooling of the test cavities

Rossana Bonomi

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Geometry of OhMEGA129

cooling channel

coupling slot

tuner

flange

cooling plates

inlet-outlet coolant

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Rossana Bonomi

Sizing channel (MatLab) 1/2

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

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Rossana Bonomi

2 4 6 8 10

x 10-3

0

1

2

3

4x 10

4

X: 0.0055Y: 1.39e+004

REYNOLD no circuits 2 ref temp 37

Deq [m]

Re

[]

dTio 1

dTio 2dTio 3

Sizing channel (MatLab) 2/231

Choices dT in-out = 1ºC Deq = 5.5 mm Re = 13900 v = 1.77 m/s h = 10020 W/m2/K

2 4 6 8 10

x 10-3

0

2

4

6

8x 10

4

X: 0.0055Y: 1.002e+004

CONV COEFF no circuits 2 ref temp 37

Deq [m]

h [

W/m

2/K

]

dTio 1

dTio 2dTio 3

2 4 6 8 10

x 10-3

0

5

10

15

X: 0.0055Y: 1.771

SPEED no circuits 2 ref temp 37

Deq [m]

v [

m/s

]

dTio 1

dTio 2dTio 3

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Rossana Bonomi

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

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19/04/23Rossana Bonomi

dT in-out = 1ºC Deq = 5.5 mm Re = 13900 v = 1.77 m/s h = 10020

W/m2/K

Geometry, Materials33

Symmetry of thestructure

OFE Copper C10100

316 Stainless Steel

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Rossana Bonomi

Steady State Thermal – Boundary C. 1/2

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Heat load distribution from Superfish

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Rossana Bonomi

Steady State Thermal – Boundary C. 2/2

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radiation + convection with

stagnant ambient air

Forced convection

inside channel19/04/23

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Rossana Bonomi

Steady State Thermal – Results36

Coolant Reference Temperature 37ºC

Delta max temp: 15≤ ºC

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Rossana Bonomi

Static Structural – Boundary C.37

Frictionless Support lower

face

Symmetry

Ambient and

vacuum pressure

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Rossana Bonomi

Static Structural – Results38

Max deformation:

70 micron Left nose deformation:

3 micron

Right nose deformation:

-3 micron

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Rossana Bonomi

Static Structural – Results39

All stresses less than 10

MPa

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Rossana Bonomi

Expected Frequency Shift40

Deformations lead to frequency shift

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Rossana Bonomi

Conclusions41

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

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Rossana Bonomi

Mechanical Design

Marco Garlasché

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Assembly design

Model of accelerating system(half cells, tuning rod)

Coupling system(waveguide, Lil flanges)

Connection to acquisition(CF flanges)

Cooling system(two plates, in-out pipes)

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Marco Garlasché

Model of accelerating system44

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Two asymmetrical half cells: easier brazing, no spikes in slotCavities: machining precision of 0.02 mm.

# 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

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Marco Garlasché

Acquisition angle

Acquisition angle: 90˚

CF flange mating surface carved 6mm deep for better acquisition (5.8˚ @ highest point )

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Marco Garlasché

First half cell: brazing

OFE Copper

Brazing for connection with: 2nd half cell CF flange

One tuner on top, diametrical to coupling slot

78 mm

87 mm

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Marco Garlasché

Second half cell

OFE Copper

Brazing for connection with CF flange

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Marco Garlasché

Waveguide

Brazing with cell

Brazing with LIL flange

OFE Copper

Any experience on brazings directly on waveguide walls?

236 mm

34.036 mm

72.136 mm

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Marco Garlasché

Cooling plates

OFE Copper / 316 LN

Two pipes coated and brazed to cooling plate

Usual dimension for coating ?

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Marco Garlasché

Tolerances and Tuning

Rolf Wegner

19/04/23

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tolerances

part dz dr df

µm µm kHz

1. top straight ± 20 ± 10 ± 1022

2. OUTER_CORNer_radius ± 20 ± 10 ± 1008

3. web ± 20 ± 10 ± 1065

4. INNER_CORNer_radius ± 20 ± 10 ± 182

5. nose angle ± 20 ± 10 ± 504

6. OUTER_NOSE_radius ± 20 ± 10 ± 3654

7. flat_top ± 20 ± 10 ± 240

8. INNER_NOSE_radius ± 20 ± 10 ± 2001

9. beampipe ± 20 ± 10 ± 32

total ± 9707

12

3

456

78

9

z

rfull cell dL=2dz= ± 40 µm

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Rolf Wegner

tuner

tuning range: -1 .. +19 MHz

reduction in Q: 0 .. -5%

Ø tuner: 8.4 mm

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Rolf Wegner

tuning

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 19/04/23

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Rolf Wegner 19/04/23

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Parameter list for high gradient test

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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 Pin= 380 kW

Tpulse * frep 3 μs * 300 Hz 0.9 ‰

Pin,avg= 340 W Pin,avg= 340 W

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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 !

Es [MV/m]

Sc [MW/mm2]

lg(BDR) !

X+K !

140 1.5 150 0.46 -18.2 150 0.46 -18.2

240 1.5 200 0.82 -14.5 200 0.82 -14.5

380 1.5 250 1.28 -11.6 250 1.28 -11.6

550 1.5 300 1.84 -9.2 300 1.84 -9.2

740 1.5 350 2.51 -7.2 350 2.51 -7.2

970 1.5 400 3.27 -5.4 400 3.27 -5.4

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Open issues / questions

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Open issues, Questions

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?)

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Thank you very much for your attention

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EXTRA-SLIDES

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Accelerating cells geometry

Symbol Cell Parameter

L cell Length

D cell Diameter

g Gap length

RcoOuter Corner Radius

RciInner Corner Radius

RnoOuter Nose Radius

RniInner Nose Radius

CA Cone Angle

S Septum thickness or Web

RbBore Radius

Rco

Rci

Rno

Rni

CA

S/2

L

D/2

Rb

g

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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

'

'

0

0

n

n

E

E

L

ZT

TEnP

2

20

19/04/23

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35MeV/u

41 48 55 63 71 80 89 99 109 119 130 142 153 166 178 230MeV/u

~ 19 m

204 217191

18 19 201 2 3 4 5 7 8 9 10 11 12 13 14 15 16 176

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2D cavity optimization

with Superfish

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.

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)

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Parameters 1st TC

Frequency [GHz] 2.9985

= 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 1.537

Scaling Exponent n 6.779

Change in freq [MHz] 15.85

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Parameters 2nd TC

Frequency [GHz] 2.9985

= 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 1.522

Scaling Exponent n 6.583

Change in freq [MHz] 18.25

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Open issues

?

?

?

Characteristics of the experimental bench:

- disposition of cooling, vacuum- disposition of acquisition (solely linked to

prototype?)- where to attach prototype

Thickness of nickel-copper coating (7 μm÷15 μm)

Retrieval of components:- waveguide- flanges (CF, Lil)- pipes and seals

Advice on general mechanical design

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Open issues: flanges

- Dimensions obtained from straight guide flange (‘CTFARFNE0003’)

- Where to obtain flange seal?

- Do we need to completely machine flange?

- Dimensions of coupling flanges (distance of holes, diameter, possible threading) (SCEM 18.60.18.005.3)

bolted UHV flange (18.60.18.005.3)

remachining

forged blank (18.60.19.070.0)

-Thickness of intermediate see-through seal

Dimensions of intermediate metal seal (18.60.55.850.6)

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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)

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