1. Status of CIEMAT work on PETS
P. Abramian, F. Aragon, J. Calero, D. Carrillo, J.L. Gutierrez, A. Lara, L. Sánchez, E. Rodríguez, F. Toral, CIEMAT
S. Doebert, S. Mathot, G. Riddone, A. Samoshkin, I. Syratchev, CERN
X-BAND Workshop, 1/12/2010

2. Outline TBL PETS prototype TBL PETS series production
Double length CLIC PETS

3. RF design of TBL PETS Previous design 30 GHz PETS
(4 waveguide extractor)
Electric field produced when
electrons are “decelerated”
RF optimization
Power extracted
Final version:
12 GHz PETS
(2 waveguide extractor)
Electron
beam

4. General layout of TBL PETS
Fiducials
Cooling pipes
WR90 waveguide
Copper rods
Power extractor
Vacuum port
Supports

5. Copper rods production (I)
Each PETS was made of eight OFE copper rods (800 mm long).
These were the most difficult parts to fabricate: profile tolerance is +/ mm and roughness Ra should be better than 0.4 micron.
The coupling cell is smaller: two different milling tools were necessary.
Two intermediate thermal treatments for stress relaxation: 180ºC, 1 hour.
Copper rod

6. Copper rods production (II)
The rods were measured unscrewed, mechanically free. Therefore, there was a significant sag which was corrected during the assembly with an intermediate octagonal ring.
The rod elongation per degree of temperature increase is 13 microns. The workshop had not controlled temperature.

7. Single rod RF test bench
A special test bench has been designed to do RF measurements on each rod.
It consists of two side blocks put together with a single PETS bar in order to create inside a mode with same properties as the decelerating mode.
Results agree with 3-D mechanical measurements.
Phase S31 vs position
HFSS model
E field and probe
Mode TE10

8. Cooling pipes production

9. Waveguides

10. Power extractor
Courtesy Serge Mathot, CERN

11. Brazing parameters PETS part Type of joint Filler alloy (%wt)
Filler melting range (ºC)
Brazing temperature (ºC)
Superficial treatment
Power extractor
Cu/Cu
68.5 Ag/26.5 Cu/5Pd
823 No
Cooling circuit/connector
Cu/SS
72 Ag/ 28 Cu
780
800
Ni plating on SS
Waveguide/flanges
82 Au/18 Ni
950
980

12. Copper structure assembly

13. Mechanical measurements
Before shims
After shims
Nominal distance between the back sides of opposite rods is mm

14. Power extractor RF measurements (I)
Port1
Port2
Port4
Absorbe r
Absorbe r
Choke
Coax to WR90
Coax to WR90
Input
Coupler
Power Extractor
Input
Coupler
Absorbe r
Port3

15. Power extractor RF measurements (II)
Experimental results
S11
HFSS Simulation
No visible change in S11 when removing wire or absorber from port 4.
Both S21 and S31 are aprox. -3dB at 12 GHz

16. PETS RF measurement bench
A special test bench was designed to measure the copper assembly.
A coaxial antenna was used to measure the field through the slots between the rods.

17. PETS dispersion curve
In the worst case, a 10% loss of extracted power is expected
11944 MHz
50 MHz detuning

18. PETS tank assembly (I)

19. PETS tank assembly (II)

20. TBL PETS commissioning (I)
RF pulse phase
RF power produced
Beam current along the line
a 10 A beam through PETS
20 MW max produced at a pulse length of 280 ns
Power production consistent assuming a form factor of 0.9
Courtesy Steffen Doebert, CERN

21. TBL PETS commissioning (II)
RF power produced
Last news: up to 17 A beam through PETS
50 MW max produced at a pulse length of 160 ns
Power production consistent assuming a form factor of 0.9
Courtesy Steffen Doebert, CERN

22. PETS tank at CLEX (spring 2009)
Quadrupole
Mover
Courtesy Steffen Doebert, CERN
BPM

23. Repair of leak (April 2010) Two cooling circuits leaked.
The origin of the problem was the aluminum Helicoflex gasket.
When the tank was opened, a very strong corrosion was observed.
The aluminium gaskets are replaced by copper ones (custom machined), after cleaning the sealing surface.
The tank was opened and closed in only two days!

24. Outline TBL PETS prototype TBL PETS series production
Double length CLIC PETS

25. Series production of TBL PETS
Eight TBL PETS are under production.
Three will be assembled at CIEMAT, and five at CERN.
CIEMAT takes care of three vacuum tanks, the waveguides and cooling circuits for the whole series. CERN will provide the rest of components.
Production of waveguides is finished and cooling pipes is still ongoing.
The vacuum tanks are already at home, leak tested and measured.
The assembly of the first series tank has been started at CERN.

26. Design modifications for series
CERN has reviewed the prototype design made at CIEMAT, and several modifications have been implemented:
Copper assembly supports,
Cooling pipes connectors and flexibility,
Dowel pins for positioning of copper rods,
A unique steel flange for waveguides, and
RF absorber plates.

27. Courtesy R. Zennaro, CERN and T. Pieloni, PSI
RF absorbers
The RF absorbers are necessary to damp the high order modes.
The required properties are: dielectric constant in the range of 20 to 30, loss tangent at least of 0.3.
An exhaustive market survey has been done to identify the potential materials: AlN, SiC and ferrites have been studied.
The most promising materials have been characterized at CERN: Ekasic-F has been chosen because of its performance, cost and availability.
The ceramic tiles will be fired in a vacuum furnace at 1000ºC prior to installation in the tank. 27
Courtesy R. Zennaro, CERN and T. Pieloni, PSI 27

28. Outline TBL PETS prototype TBL PETS series production
Double length CLIC PETS 28

29. Double length CLIC PETS
In the frame of EUCARD, a double length CLIC PETS is under engineering design at CIEMAT.
It is based on a compact coupler design developed at CERN for a 11.4 GHz device to be tested at SLAC, combined with a mini-tank configuration.
The copper rods have 80 regular cells, yielding 523 mm long. The shape tolerance is very tight: +/- 15 microns, roughness 0.4 microns.
It will be installed in the Test Module at CLEX. 29 29

30. Engineering design (I)
The eight rods will lay on their lateral sides as an octagon. Afterwards, they will be electron beam welded.
There will be EkaSiC-F plates attached on both sides of the rods for HOM’s damping.
There are two vacuum ports for ionic pumps.
The length of the vacuum tank will be machined to guarantee the electrical contact of the rods and the couplers. 30 30

31. Engineering design (II)
Compact couplers will have a cooling circuit for 100 W heat deposition (both RF and beam losses).
There will be two brazing steps.
There is an ancillary stainless steel ring brazed to the extractor to allow the production of the wall tank also in stainless steel. Besides, final welding to close the tank will be done with TIG. 31 31

32. Fabrication
Fabrication of the first copper rod has been started at DMP. They use high speed milling, and aim to demonstrate that can reach the tolerances necessary for the CLIC accelerating structures (quadrants). 32 32

33. Conclusions
CIEMAT has been collaborating with CERN on the PETS development since 2008.
First step was the engineering design, fabrication and tests of a PETS tank for the TBL experiment. The fabrication of the long copper rods (800 mm) with tight tolerances was specially challenging. The vacuum tank was made from steel, independently of the copper assembly.
After successful installation and beam tests up to 50 MW power extraction of the prototype at TBL, a series production of eight units has been launched.
Finally, the engineering design of a double length CLIC PETS is ongoing, which will be part of the Test Module to demonstrate the two beam acceleration concept as proposed for CLIC. In this case, a new compact coupler design is implemented, with a mini-tank for vacuum tightness.

34. Acknowledgements
Utillajes Huerta and DMP for the copper parts machining,
CIEMAT workshop and Utillajes Jucar for steel and aluminium parts,
AIMEN for the cooling pipes and waveguides brazing, and
Trinos Vacuum Projects for the vacuum tanks.. 34 34