1. Status of developments at CEA-Saclay
WP10: SRF
Task 10.2: SC Cavities for proton Linacs
Status of developments at CEA-Saclay

2. The team High beta Cavity Design/Study:
G. Devanz, J. Plouin & S. Chel /
S. Cazaux, Ph. Hardy, A. Mohamed
Vertical EP station Study/Installation:
F. Eozénou, Y. Gasser & S. Chel /
J.-P. Poupeau, T. Vappereau

3. High b cavity: Sub task breakdown
design of b=1 cavities (HE Cav) This presentation
purchase of Nb material
fabrication of 1 or 2 HE cavity prototype(s)
surface preparation of cavity prototype(s)
new vertical EP station Fabien’s presentation
new HPR station
low power RF test of cavity prototype(s)
set-up for tuning of field flatness
vertical insert of cryostat

4. Reference Parameters (see CDR SPL II)
High b cavity: RF design
Reference Parameters (see CDR SPL II)
RF frequency
704.4 MHz
Gradient
25 MV/m
Number of cells/cavity 5
Average pulse current
40 mA
Synchronous phase
-15°
Optimisation of cavity design in 3 steps:
Step 1) Find the best cavity shape with respect to r/Q, Ep/Eacc, Bp/Eacc
Step 2) Do what is necessary to reach the optimal coupling Qex
Step 3) Add stiffeners to keep the LFD under control

5. RF design: cavity shape
SPL
Tesla
HIPPI
Number of cells 5 9
Frequency [MHz]
704.4
1300
Beta 1
0.47
Bpk/Eacc [mT/(MV/m)]
4.20
4.26
5.59
Epk/Eacc
1.99 2
3.36
G [W]
270
161
Cell to cell coupling [%]
1.92
1.87
1.35
r/Q [W]
566
1036
173
Lacc = Ngap.b.l/2 [m]
1.065
1.038
0.5
Operating Temp. [K)
2 K
Theor. O.T. [nW]
3.2 11
Q0 O.T. for RBCS
8.4
2.5
RF parameters for the TM010
after iterations between step1 & step2
and optimisation
outer ½ cell pick-up side
Inner ½ cells
outer ½ cell FPC side
Equator REQ
Iris RI 65
64.6 70
Length AL
103.07
106.47
E_ellipse A1
74.45
77.5
E_ellipse B1
83.27
76.89
I_ellipse A2
18.5
22.1
I_ellipse B2
24.9
35.1

6. safe for b=1 and b=0.65 cavities
RF design: coupler location
With our set of cavity and beam parameters:
Qex,opt=1.2 e6 ; Pbeam=Pin,max=1029 kW
50W – Ø100mm coaxial coupler is free of multipactor levels
either around 1MW or 500 kW
safe for b=1 and b=0.65 cavities 35
Ø 100
Ø 43.5
144 60 R5 R7
Optimisation of coupler location
ØOC = 100mm
ØIC = 43.5 mm

7. Qualification of 700MHz - 1MW coupler
Two couplers successfully processed last year on a dedicated RF test stand up to 1.2 MW DC in TW for 300hrs
Assembly of one coupler on HIPPI cavity (700 MHz, b=0.5) in ISO4 CR, and installation in test cryostat CryHoLab
Only short time of RF processing in full reflection was necessary to reach high power levels
Cavity and coupler operation at 1MW full DC for several hours
Efficient counter-flow GHe cooling of the coupler leading to limited heat transfer to the LHe bath
Qualification of 704 MHz power coupler on sc cavity at 2K operated at Ppeak=1.2 MW with tpulse=2 ms and frep=50Hz

8. Due to the pulsed mode operation, LFD is of major concern
RF design: LFD
Due to the pulsed mode operation, LFD is of major concern
To limit this effect and partially compensate for it, mechanical stiffeners and piezo actuators are used (correction algorithm is optimised in SLHC-PP )
Wall thickness
3mm
Eq. weld thickn.
2mm
Optimal position of stiffeners: Rring= 91 mm
35 kN/mm
Measured tuner stiffness: 35 kN/mm
Saclay IV tuner on HIPPI cavity
For the cavity+tuner : |KL|  1 Hz/(MV/m)2

9. RF design Dimensions for cavity fabrication
assymetric cavity
3 shapes of ½ cells
stiffening rings between adjacent cells
large beam tube ø140 mm with a ø100 mm port for power coupler
small beam tube ø130 mm with a ø10 mm port for pick-up probe
inner diameter of the cavity flanges fixed to 80 mm
tapers connect the beam tubes to the cavity flanges
each beam tube is equipped with one ø40 mm HOM port
outer ½ cell pick-up side
inner ½ cells
outer ½ cell FPC side
External radius (REQ)
190.86
Iris radius (RI)
64.89
64.49
69.90
Length (AL)
103.22
106.62
Equator ellipse a (A1)
74.36
77.41
Equator ellipse b (B1)
83.19
76.80
Iris ellipse a (A2)
18.73
22.33
Iris ellipse b (B2)
25.14
35.35
Stiffening Ring (RR) -
91.0
Dimensions for cavity fabrication
before any chemical polishing and at room temp.

10. Frequency sensitivity
SPL
Nominal wall thickness [mm] 3
Cavity stiffness Kcav [kN/mm]
3.84
Tuning sensitivity Df/Dz [kHz/mm]
164
Stress per mm of tuning [MPa/mm] 25
KL with fixed ends [Hz/(MV/m)2]
-0.55
KL with free ends [Hz/(MV/m)2] -5
KL with realistic bound. cond. [Hz/(MV/m)2] -1
Sensitivity to He pressure [Hz/mbar] (fixed ends)
1.2
15 MPa
25 MPa
1 mm
A frequency shift of ~ 500 kHz is induced by a cavity shrinkage of ~ 3 mm
(standard value for the Saclay IV tuner)
Maximum cavity stress ~ 75 MPa remains far below the yield strength of Nb at 2K

11. Mechanical design
At this step, fabrication of cavity prototype could start and it would fit on our frames for surface preparation and vertical test.
To perform qualification tests in horizontal cryostat or cryomodule, studies of a fully equipped cavity (with tuner, coupler, tank, …) are necessary:
power coupler port cooled by LHe
one beam tube inside the He tank with FPC and HOM port
opposite beam tube under vacuum with PU and HOM port
lateral frequency tuner (Saclay IV type)
located on the beam tube under vacuum
symetric load with one piezo actuator
each beam tube is equipped with one ø40 mm HOM port
fabrication of cavity and He tank without brazing
Helium tank made of Ti
Flanges made of NbTi

12. Tuner: status Design principle:
The tuner load is applied on the Ti flange while keeping He tank at the same position
If Ti flange and He tank are stiff enough, the tuner load is almost entirely applied on the cavity
Pre-design of cavity+tuner is necessary to:
- Optimise the relative stiffness of the components
- Reserve enough room to HOM and flanges
- Determine the assembly sequence
Special ass’y tool used in CR for cavity leak check
Tool removed out of CR after assembly of the tuner on the cavity

13. Tuner: He tank
Efficiency of the tuner strongly depends on the tank stiffness
Thickn. = 3 mm
Thickn. = 4 mm
Goal: stiffness = 70 kN/mm
(2x tuner stiffness)
Stiffness = 25.7 kN/mm
Optimisation still going on:
shape of lateral rounded disk
Ti flange (radius, thickness)
wings (location, shape, number)
thickness
Thickn. = 4 mm
Thickn. = 4 mm
Stiffness = 43.4 kN/mm

14. To be fixed before fabrication
Before cavity fabrication:
relative angles between couplers (main and HOM) should be fixed
HOM
Power coupler
Before tank fabrication:
Fix position/angle of Helium ports
Add smooth holes in some pieces welded to He Tank
Optimisation of the tank stiffness (> 70 kN/mm)
Optimisation of the Ti flange and ass’y tool
Can be done in parallel with cavity fabrication

15. Achievements
Cavity design complies with the requirements of the SPL b = 1 cavities (peak fields, r/Q, Qex)
The beam tube cooled by LHeII insures thermal stability with safety margin
After mechanical optimization and considering the results of tests done in the frame of SLHC-PP, LFD should not be an issue
A lateral tuner (Saclay IV type) should provide the required tuning range with limited mechanical stress
Most of the flanges and interfaces are now fixed
With this design, existing and qualified coupler and tuner fit the b=1 cavity
After measurement of fundamental parameters (Eacc, Qo) in a vertical cryostat, this cavity could be tested in an horizontal cryostat (CryHoLab) or be operated in a complete cryomodule

16. Plans for the next 12 months
Detailed drawings of b=1 cavities (HE Cav)
Purchase of Nb material
Call for offers for cavity fabrication
Fabrication of diabolos for 1 or 2 HE cavity prototype(s)
Delivery of cavity w/o LHe tank
Tuning and field flatness (modification of the tuning set-up)
Surface preparation of cavity prototype(s)
Electropolishing (vertical EP station)
HPR (new rinsing station)
Low power RF test of cavity prototype(s)
modification of vertical insert of cryostat (not assessed yet)

17. Schedule

18. Task 10.2: CEA expenses
2009 Total Cost :
227k€ (tbc)

19. The End