Update 5/19/11. Kirk Davis, Mike Drury, Leigh Harwood, Mark Wiseman, etc. Andrew Hutton

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1 R100 Microphonics i Update 5/19/11 Andrew Hutton Reporting on work by Kirk Davis, Mike Drury, Leigh Harwood, John Hogan, Curt Hovater, Thomas Plawski, Mark Wiseman, etc.

2 The Problem Vibrations of the superconducting cavities (microphonics) change the frequency of the cavity Because the resonant frequency of the cavity is very narrow, the cavity can go off resonance This increases the fraction of RF power that is reflected back from the cavity More RF power is needed to provide the required gradient RF control module can lose lock Loses ability to control lthe cavity

3 R100, C100 cavities are nominally identical No stiffening rings Welded into helium vessel R100 cavities were made at JLab C100 00cavities were eemade by RI Anecdotal evidence that RI cavities arestifferthan than JLab cavities Work hardening? Hardware Description

4 Numbers Admiral cryomodule in the FEL 1 Hz Admiral is now installed in CEBAF at SL21 Renaissance in CMTF 0.5 Hz HTB with 2 C100 cavities in CMTF 2 Hz R100 in CMTF 7 20 Hz Spec for C100 in CEBAF ~ 5 Hz CMTF Cryo Module Test Facility in the Test Lab

5 Mechanical Description Tuning force Tune cavity in tension SST, Al and Ti construction Fulcrum bar (2) Warm drive components (not shown) Pivot-arm(2) Untuned Position Tuned Position Tension shaft Compression shaft Jack arms (4) Fulcrum bars Fulcrum bars Tuner Assy w/cavity Pivot-arms(4) How the Tuner Works Jack arms (4) Cryomodule Design Review 21 May, 2007

6 Design Changes Interface with helium vessel has been redesigned to fit available space Reduced hardware count/type No design change in tuner mechanism No design change in warm drive components SL21/FEL03 Pivot-Arm C100 Pivot-Arm Al casting Al Plate SST tab welded to helium vessel Cryomodule Design Review 21 May, 2007

7 Update: Tuner Stand We have a tuner test stand that will be used to measure vibration modes Cavity has been remeasured for field flatness Tests are about to start

8 Example of Data 13 Hz vibration prominent Variable during the day Likely noise in CMTF* 2 Resonances ~20 Hz 2 Resonances ~45 Hz Both likely to be cavity resonances * Breaking news: 13 Hz associated with heavy return gas load to Kinney pump Update identification still unclear Kirk Davis, Mike Drury

9 Two possible causes 1. Higher vibrations in the Test cave Priority 1 Why Historically ~twice as bad as the CEBAF tunnel Is it worse now due to TEDF or cryogenics changes? 2. Cryomodule more susceptible to vibrations Cavities floppier? Tuners, etc. not as well supported? First priority is to determine the leading cause

10 Background R100 in CMTF Most noise sources <60Hz except line harmonics Must avoid120hz

11 Background R100 in CMTF If we drive all lines below 1 Hz better, but not in spec Leigh Harwood Intermittent 13Hz is a problem but line is not a resonance

12 Frequency Shift 13 Hz noise masks effect of other driving terms 25 Hz

13 Comparison of Noise Terms Excitation Terms?

14 CEBAF Tunnel at SL21 Baseplate Vibration Measurement

15 CMTF at R100 Baseplate Vibration Measurement low frequency noise (<30 Hz) significantly worse at CMTF

16 Primary Cryogenic Return Measurement CEBAF tunnel at SL21 Noise level ~3 times stronger than baseplate

17 Primary Cryogenic Return Measurement CMTF at R Hz Noise level ~3 times stronger than baseplate Noise level ~3 times stronger than CEBAF Tunnel

18 R100 is currently in the CMTF Cryomodule vs Environment Installation planned in CEBAF Zone SL23 Admiral is currently in CEBAF zone SL21 Use a vibrator near both cryomodules to measure response to external vibrationsof of knownfrequency and amplitude If response is similar, problem is CMTF environment R100 should ldbe OK in CEBAF If response is different, the frequency can be correlated to knownmechanicaldifferences between the cryomodules Tells us where to look to fix R100 (and therefore C100) First tests in CMTF yesterday swing, more this evening When procedure is wrung out, will repeat in CEBAF

19 Hammer response at Baseplate R100 is ~100 times more responsive than the Admiral

20 Hammer response at Primary Cryo Return R100 is ~10 more responsive than the Admiral Admiral Response at Primary Cryo Return ~10 times Admiral response at Baseplate

21 Piezo Transfer Function

22 Piezo Transfer Function - Admiral

23 Piezo Transfer Function R100 Low Frequency plateau is ~8db higher Resonant Response

24 Priority 2 Develop Mechanical Solutions Some possible mechanical solutions can be tested now Increase lateral stabilization of tuner stack Add vibration damping pads under the cryomodule feet Both should be tested with the vibrator Develop ideas for mechanical fixes SNS cavities had spider support Can we retrofit? Canweuse wires under tension? Update Prototype spider support being built (takes two weeks) Mark Wiseman, Kirk Davis, Mike Drury

25 Priority 2 Develop Electronic Solutions Can new Digital RF Controller stabilize cavities Successful up to ~8 MV/m takes 2.8kW Can stabilize cavity at 15 MV/m but only for ~1 second Breaking news without 13 Hz can lock up to 19 MV/m Measure the response of the individual cavities to the piezo electric transducers (PZTs) installed on the tuners Also affects neighboring cavities (only ~5 db isolation) Use the PZTs to try and damp the microphonics Try and use Lorentz detuning (expansion of cavity as RF power increases) to feedback on microphonics Curt Hovater, Thomas Plawski

26 Priority 3 Gather Data A lot of data is being gathered to be evaluated later Every cavity has been characterized more than once Use PZTs as listening devices Are cavity oscillations in sync? Measure CMTF ground motion at regular intervals in a day Try and identify source Kinney? Mechanical vibration? Cryogen oscillations? Update: Will use Test Lab power outage to try and identify if source (Paul Powers)

27 12 GeV Project Status C100 1 and C100 2 assembly is proceeding On track for installation into CEBAF as planned String assembly of C100 3 is ready to begin On hold waiting for more information from R100 Welding of helium vessels onto cavities is on hold Pending decision on whether mechanicalsupport is required Pending decision on whether mechanical support is required ( spider )

28 Outlook (Andrew s opinion) Problem is serious, but not intractable Solution will most likely be a combination of several different fixes My preference is for passive fixes first, feedback second I do not see a reason to advance R100 installation I expect modified R100 to be installed in CEBAF as planned Commissioning i i order may change???? We will be judged by how well we address this problem not by the problem itself

29 As presented last week by John Hogan Install R100 in SL21 slot Measure microphonics Remove R100 Install C100 1 in SL21 slot Measure microphonics i Remove C100 1 Take to CMTF for standard commissioning Current Plan Install C100 1 as foreseen in original 6MSD planning