ILC Tech Meeting, March 29 th 2007

1. Cold quadrupole vibration measurements on Module 6 during the 10th/11th thermal cycles at CMTB Ramila Amirikas, Alessandro Bertolini,Wilhelm Bialowons, Markus Kubczigk DESY ILC Tech Meeting, March 29th2007

2. Some views of the CMTB at Bldg.70 Feedbox Feedbox to feedcap connection Cryomodule (quad side) to endcap connections ILC Tech Meeting, March 29th2007

3. The experiment Two new seismic sensors (one vertical+one horizontal geophone) were installed aboard the Module 6 quadrupole for the 10/11th thermal cycles, from February 19st to March 8th. ILC Tech Meeting, March 29th2007

4. The experiment - Goals • Test geophone behaviour at 4 K inside a fully operating cryomodule • on-board seismic sensor with adequate noise level down to below 1 Hz potentially available for quad and cavities. • behaviour unknown, never been tested by the manufacturer in these extreme conditions, the company recommends use of the device down to -40°C, only one cryogenic application cited in literature. • the very robust and mature (~30 years) design was encouraging and the test has been successful. • Quadrupole vibration measurements at 4 K • chance to give a first quantitative (from 1 Hz) evaluation of the impact of cryogenic plant and high gradient RF on the quadrupole vibration level, not possible so far because of the lack of sensitivity of cooled piezo accelerometers below ~10 Hz ILC Tech Meeting, March 28th2007

5. Test amplifier Laptop Data logging Spectral analysis (FFT, PSD, Coherence, RMS,Transfer function,etc.) Cold/warm Geophone 24 bit Güralp digitizer 20 m cable 200 S/s preamp Inverse filter Inverse filtering provides equalization of the geophone response down to 0.35 Hz The experiment – Setup Ground vertical sensor (horizontal transverse companion not visible) Some definitions Vessel top vertical sensor (horizontal transverse companion not visible) ILC Tech Meeting, March 29th2007

6. Quadrupole vibrations – Cryomodule warm I General features of the spectra Typical DESY site spectrum at low frequencies. Technical noise dominating > 20 Hz; strongest peak from the insulation vacuum pump at 48 Hz. Module vertical resonance at 27 Hz; quad vs top transfer function almost flat below 40 Hz. Values @ 1 Hz: Ground 76 nm Top 90 nm Quad 103 nm ILC Tech Meeting, March 29th2007 *2 hrs data measured at the end of the 10th thermal cycle

7. Quadrupole vibrations – Cryomodule warm II Coupling between axes Coupling with the 18 Hz horizontal longitudinal mode at both quad and top positions. Coupling with the 11 Hz horizontal transverse rocking mode on quad (due to the off-axis location). ILC Tech Meeting, March 29th2007

8. Quadrupole vibrations – Cryomodule warm III RMS analysis In the low frequency band the quadrupole motion tracks the ground vibration level. Slight amplitude differences are related mainly to the mechanical transfer function of the module on its support system. Non perfect equalization of the sensor response can also affect the accuracy. Low frequency quad RMS overestimated (~10%) because of the low resonant frequency (4.14 Hz) of this geophone at room temperature. ILC Tech Meeting, March 29th2007

9. Quadrupole vibrations – Reaching the cold steady state – no RF - I RMS analysis Ground motion tracking confirmed at low frequencies, with ~10% quad/gnd and top/gnd rms ratios. No difference with warm operation. The refrigeration system doesn’t affect the quadrupole vertical stability at low frequency (f<30 Hz). Large vibrations due to the build up of a strong peak above 30Hz. The peak shows slow frequency changes from 30.1Hz up to 32Hz. The amplitude can vary from 200 nm up to > 1 µm. Not a mechanical resonance of the cryomodule; not visible at all in the quad vs top transfer function. Steady state ILC Tech Meeting, March 29th2007

10. Quadrupole vibrations – Reaching the cold steady state – no RF - II 08 March in steady state Quad LHe inlet flow: 8.2 g/sec Quad LHe inlet valve: 20% Cavity 2K Inlet valve: 56% Cavity 2K He flow: 5 g/sec Cavity 2K He reservoir level:43% Comments Peak frequency ~ 32Hz in this case. The integrated RMS @1 Hz values are 78 nm (ground), 206 nm (vessel top), 260 nm (quad). The peak is also visible in the ground spectrum. ILC Tech Meeting, March 29th2007

11. Quadrupole vibrations – Cold operation with LLRF and RF High gradient 20 February High gradient steady state Quad LHe inlet flow: 5.5 g/sec Quad LHe inlet valve: 100% Cavity 2K Inlet valve: 50% Cavity 2K He flow: 4.5 g/sec Cavity 2K He reservoir level:43% 23 February Low gradient steady state Quad LHe inlet flow: 5.5 g/sec Quad LHe inlet valve: 100% Cavity 2K Inlet valve: 35% Cavity 2K He flow: 3.8 g/sec Cavity 2K He reservoir level:43% Note: EMI from the klystron modulator at 10 Hz and harmonics; reduced by a factor ~10 with better digitizer and battery operation. ILC Tech Meeting, March 29th2007

12. Quadrupole vibrations – RF high gradient – 2K/1.8K/1.6K RMS analysis Ground motion tracking confirmed at low frequencies. Usual large vibration amplitude at high frequency. The high gradient RF operation doesn’t affect the quadrupole stability. High frequency vibrations stopped during the refilling of the cavity reservoir at 9:12AM. The quad-LHe inlet valve is closed in that case. Suspects on the 4.5K circuit are confirmed. ILC Tech Meeting, March 29th2007

13. Quadrupole vibrations – RF high gradient – 2K/1.8K/1.6K Correlations? The high frequency RMS level seem correlated to changes in the LHe level in the Feedbox Heat exchanger. ILC Tech Meeting, March 29th2007

14. Summary of the results • Geophone test at 4.5K • classic 4.5 Hz industrial geophone can operate at 4K without any loss of sensitivity • in-situ high accuracy calibration procedure demonstrated • Quadrupole vibration measurements at 4.5K • low frequency(1-100 Hz)quadrupole vertical stability is not affected by high gradient RF operation • quadrupole vertical stability is not affected by the refrigeration system at frequencies up to 30 Hz; results not conclusive at higher frequency because of the presently not completely understood mechanical behaviour of the CMTB 4.5K circuit. • need to continue investigation on Module 7 at CMTB (for better understanding) and on Module 6 in different conditions (in operation in the FLASH linac for example). • Module 8 will operate at 2K… ILC Tech Meeting, March 29h2007

15. Next Module 7 at CMTB: Two cold geophones+the existing two piezo accelerometers already installed aboard the quadrupole. Complementary geophones on top of the vessel and on the ground. Continuous data acquisition for the whole test (only one thermal cycle). Two or more DOOCS acquisition channels should be available for the beginning of the run. Cool down starting end next week. Geophone pair mounted in front of the Module 7 quadrupole; new stiffer holder will be installed this afternoon Module 6 in FLASH linac: Geophones will stay on Module 6 and Module 7 permanently. MKS asked for more sensors to also equip ACC4 and ACC5. Data acquisition with sufficient number of channels must be produced. Cool down of the FLASH linac is scheduled for the end of July. Thanks to: Rolf Lange, Kay Jensch, Wolfgang Maschmann, Peter Smirnov, Oliver Paschold, Helmut Remde ILC Tech Meeting, March 29h2007