Cavity coupler developments at CEA G Devanz

Cavity & coupler developments at CEA G. Devanz CARE/HIPPI meeting CERN, oct 30 th 2008 G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008

b = 0. 47 cavity tested in vertical cryostat • cavity equipped with the helium tank (left open for the tests) • stiffening rods replaced by a compact stiffener to reduce the effect of kext on the static Lorentz detuning coefficient KL • test at 1. 8 K after HPWR only (no new BCP since the first test) • Rs = 6 n. W • Field emission onset 12 MV/m • Quench at 15 MV/m G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 2

Pressure sensitivity highly dependant on external stiffness kext G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 3

b = 0. 47 Lorentz detuning temperature changes during experiment -> pressure changes-> need for a correction of the frequency measurements (black dots) Very good result KL = -3. 8 Hz/MV/m G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 4

b = 0. 47 Lorentz detuning exp. /simulation taking into account the fact that the thickness of the real cavity is not constant: extreme cases : • 4 mm theoretical basis for the design • 3. 3 mm average value measured on the real cavity on the non stiffened part of the cells effect of the external stiffness on KL The real cavity is somewhere in between. . . G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 5

b = 0. 47 mechanical modes Mechanical excitation using a piezo stack x z y signal generator Room temperature measurements using phase demodulation on RF signal piezo amplifier labview PC G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 lock-in amplifier 1300/704 MHz demodulation rack 6

b = 0. 47 mechanical modes G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 7

fast piezo tuner • design based on Soleil, 3 HC, CARE-SRF (aka Saclay-II) family of tuners • symmetric slow tuning +/- 2. 5 MHz • planetary gear box for reliability • single piezo frame with preload independent of cavity tuning • does not increase cavity length • manufacturing process started • expected end of january 2009 G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 8

Magnetic shield • Rs=6 n. W in vertical cryostat, low Eacc, 1. 8 K • Aiming at Rs < 8 n. W in Cry. Ho. Lab • B<0. 6 m. T G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 Cryoperm® material theoretical shielding factor 33 (opera 3 D simulations) 9

Cry. Ho. Lab preparation for HIPPI cavities TTF 9 -cell cavity 700 MHz setup 1. 3 GHz setup G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 10

704 MHz -1 MW power coupler 100 mm diameter 50 W doorknob (air) vacuum gauge electropolished water cooled inner conductor water cooled RF window cryostat flange He cooled outer conductor G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 11

Coupler – window Two complete sets of window + inner conductor received in january 2008 from Toshiba • on time delivery • few fabrication problems (excess EB weld shrinkage on antenna) G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 12

Coupler – outer conductors A lot of problems during manufacturing, including leaks at room temperature -> extra caution was necessary so supplemental tests were done at CEA: • thermal shocks performed on double- walled tube sub-assembly • leak checks performed at ~30 K in a test cryostat (He bath) Copper deposition on the inner surface performed by CERN using magnetron sputtering. • the 2 100 mm conductors are completed • the special 80 -100 mm conductor for INFN cavity ready for Cu sputtering G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 13

Coupler - Doorknobs RF measurement on WR 1150 waveguide delivered in July 08 G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 14

Coupler test stand • working position is horizontal • same doorknob alignment system as on Cry. Ho. Lab COUPLER TEST STAND G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 15

Coupler test stand – coupling box • Connects 2 couplers for TW conditioning • A strong coupling is needed, otherwise the bandwidth is too sharp to be of practical interest • Copper coated for low RF losses • Strong pressure effects if not stiffened, impairs the RF transmission • Extra mechanical adjustment of the frequency by deformation is included in the design Coupler ports HFSS computation of S 11 Pumping port G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 16

Coupler test stand – coupling box • manufacturing completed 2 weeks ago • electrolytic copper deposition done inside the finished waveguide. 3 different sets of electrodes were tried to achieve a uniform layer on flats G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 17

Coupler preparation in clean room G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 18

1 MW RF power source • klystron tested at nominal power (1 MW, 2 ms, 50 Hz) • circulator tested on a matched load at full power (dry N 2) • circulator tested on a variable short at all phases, nominal peak power, reduced repetition rate • breakdowns in the High Voltage Power Supply are being corrected Deliverable : CARE-Report-07 -035 -HIPPI « 1 MW - 704 MHz RF test stand at CEA-Saclay » 1 MW 704 MHz klystron 110 k. V Power Supply G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 HV Pulse Power generator 19

Due to problems encountered in the fabrication of the prototypes (welding of the Helium tank, leaks of the cold part of the couplers, copper coating of the coupling box, breakdown of the HV power supply), the tests are delayed by 9 months. Tests to be done before the end of the HIPPI program: v HIPPI cavity at 2 K in Cry. Ho. Lab critical coupling and low power test (radiation & safety, cryogenics, Qo w/o mag. shielding) v Conditioning of the couplers at RT, in TW and SW (all the phases) G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 20

Fortunately, the proposal about the LLRF+LDF compensation has been accepted by the EC. This 4 -years program (CNI-PP-SLHC) already started last April. In consequence, our activities on SRF systems for High Intensity Pulsed Proton Linacs will continue The program: v preparation of a analog A/phi klystron loop v in-depth characterization of the LFD behavior and first (manual) tests of compensation v study and fabrication of a fully-automated LFD compensation rack v qualification of the LFD system v participation to the study of a LLRF system (and possibly, preparation of a dedicated test) G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 21

Moreover, the proposal about the high beta cavity and surface preparation has been accepted by EC. The work should start at the beginning of 2009. The program: v study of a beta=1 cavity v fabrication of 2 cavity prototypes v development of a EP set-up (vertical) for cavity preparation (needed to reach high gradients) v vertical tests of the prototypes (and eventually, delivery at CERN for assembly in a high beta cryomodule) G. Devanz - CEA/Saclay - HIPPI meeting - CERN oct 30 th 2008 22