Beijing ILC Workshop Global Design Effort 1 High-Gradient Module Test Lutz Lilje

Beijing ILC Workshop Global Design Effort 2 Thanks! To D. Kostin, Rolf Lange, R. Paparella, K. Przygoda for the viewgraphs Many other people involved e.g. DESY technical groups etc. Dislaimer: –Some testing still on-going –Final evaluation after 10th cryo-cycle

Beijing ILC Workshop Global Design Effort 3 Module Test at DESY A high gradient module has been assembled Test in dedicated test stand underway e.g. –Thermal cycles –Heat loads –Cavity performance –Coupler conditioning –Fast tuner performance

Beijing ILC Workshop Global Design Effort 4 Overall Module Performance Thermal cycling –10 cycles total planned 7 done so far –No leaks –Wire position o.k. Heat loads –Statical heat loads as other modules tested in TTF/FLASH

Beijing ILC Workshop Global Design Effort 5 Wire Positions Preliminary Plot illustrates that positions are repeatably achieved Final evaluation to follow Also on-going vibration measurements

Beijing ILC Workshop Global Design Effort 6 Cavity Performance (courtesy D. Kostin – DESY) Average gradient: 28 MV/m planned

Beijing ILC Workshop Global Design Effort 7 Q(Eacc)

Beijing ILC Workshop Global Design Effort 8 HPP on Cavity 5 +6 For short pulses up to 300 us gradient is high >30 MV/m Radiation levels are relatively low This hints to a thermal quench

Beijing ILC Workshop Global Design Effort 9 Cavity results 6 cavities perform very similar to previous tests –Even up to 35 MV/m pulsed operation 2 don‘t… –Even after HPP, limitation likely thermal quench –The reason is NOT understood (yet)! –Suspicious: Cavities behave like twins in all tests –Speculations (!!!!!!!): Assembly procedures –After the cavity on position 4 an intermediate leak check is made, and the necessary additional flange assembly and disassembly could lead to contamination Coupler 5 had leak in the warm part (see below), exchange needed –Should not have impact on cavity vacuum. Both cavities have not seen 120°C bakeout for schedule reasons –But CHECHIA test was o.k.

Beijing ILC Workshop Global Design Effort 10 Coupler Processing (courtesy D. Kostin – DESY) Done in to steps –1st set of 4 couplers Very tight vacuum interlock thresholts –2nd set of 4 couplers Used ‘relaxed’ vacuum interlock thresholts Very fast processing –Due to improved handling after pre-processing at LAL Orsay –Comparable to individual cavity high power test results

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Beijing ILC Workshop Global Design Effort 13 Coupler 5: Leak in Warm Part

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Beijing ILC Workshop Global Design Effort 15 Reconditioning after Repair

Beijing ILC Workshop Global Design Effort 16 Second Set of Coupler

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Beijing ILC Workshop Global Design Effort 19 Fast Tuner Tests (R.Paparella –INFN, K. Przygoda – Uni. Lodz, L. Lilje DESY) Cavities have two piezos installed –sensor-actuator, redundancy Technical remark –All measurements with RF feedforward (no feedback) –All detunings refer to the ‘Flat-Top’-region (beam acceleration) of the RF pulse Detuning rather similar for all cavities All cavities (but one) compensated at maximum gradient with simple pulse –E.g. Cavity 3 at 35 MV/m –Cavity 5 Piezo no mechanical contact at 1,3 GHz Known problem: Piezo fixture stiffness for large pre-detuning of cavity –Currently cavities are compressed, thus exerting an extension of the piezo brackets –This will be changed for future cavities, cavities will pull on fixture »N.B.: All ILC tuner designs use cavity that pull. ‘Natural’ frequency of Cavity 5 after cooldown is 317 kHz above 1.3 GHz, larger compression of cavity needed At 10 kHz above, operational Further investigation ongoing e.g. effects due to thermal cycling –Piezo Voltages within margin Could also use bipolar operation, but not needed –Delay of piezo can be used to set cavity pre-detuning

Beijing ILC Workshop Global Design Effort 20 Lorentz Force Detunings in Module 6 cavities

Beijing ILC Workshop Global Design Effort 21 Example: Cavity 3

Beijing ILC Workshop Global Design Effort 22 Cavity 3: Gradient 35 MV/m

Beijing ILC Workshop Global Design Effort 23 Cavity 3: Phase

Beijing ILC Workshop Global Design Effort 24 Cavity 3: Detuning

Beijing ILC Workshop Global Design Effort 25 Maximum Compensation per Cavity

Beijing ILC Workshop Global Design Effort 26 Voltage Needed for Compensation

Beijing ILC Workshop Global Design Effort 27 Compensated Detuning vs. Delay to MV/m

Beijing ILC Workshop Global Design Effort 28 Pre-Detuning Change Due to Piezo Pulse Delay Can change the cavity pre-detuning of the cavity by changing the delay of the ‘second‘ pulse in the order of 200Hz Changes in pre- detuning could be compensated by changing piezo delay instead of using stepper motor –Less motor usage, increase lifetime –Correponds to He drifts of a few mbar

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Beijing ILC Workshop Global Design Effort 30 Summary –No leaks, Static heat loads are o.k. –Cavities Six cavities show expected performance Two cavites perform significantly below their individual high power test results –Not understood (yet) –Other components work well Coupler processed quickly –Improved handling paid off Fast tuners perform up to 35 MV/m –One exception: Problem of the fixture understood –Module test stand is a big asset Independent tests of FLASH E.g. Rapid thermal Cycles

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