electron beams in order to sense nm-size mechanical vibrations?

1. electron beams in order to sense nm-size mechanical vibrations? CERN: Marek Gasior: BBQ electronics(Andrea Boccardi: VME electronics)Juergen Pfingstner: Beam measurementsMagnus Sylte: Vibration measurementsHermann Schmickler: not much useful CESR: Mark Palmer, Mike Billing, operations crewand the valuable support at “lightning speed” of John Barley Report on machine experiments at CESR in June 2009

2. Outline • Motivation • Experimental Set-up • First results- amplitude calibration- residual beam motion- noise of detection system • Conclusions and Perspective

3. Necessary complementary verification ? • The demonstration of the stabilization of the magnet (=Magnetic field?) is based on “zero” signals of electromechanical sensors on the outer shell of the magnet. • The physical size of the sensors do not allow to mount them close to the pole tips or inside the magnet. • Pole tip vibrations, coil vibrations might exist without the outer monitors measuring them. • The limited number of monitors might not catch all vibrations. Question:can another physical process be used to verify the stability of the magnetic field?  try a high energetic low emittance particle beam

4. Standard Quad Standard Quad Standard Quad Standard Quad Standard Quad Standard Quad Stabilized Quad High sensitivity BPM Calibrated mechanical exciter Validation of Quad stabilization principle (1/2)

5. Validation of Quad stabilization principle (2/2) • insert a CLIC quadrupole (fully integrated into a CLIC module with a mechanical simulation of the environmental noise) into an electron synchrotron • in frequency bands in which the intrinsic motion of the particle beam is smaller than 1nm, observe the effect of quad stabilization on/off • in frequency bands, where the particle beam moves more than 1nm, the beam validation is limited to exciting mechanical vibrations of the quad at larger amplitudes and measuring the gain of the feedback. The performance of the feedback system at lower amplitudes would in this case to be estimated from the signal to noise ratio of the actuators and sensors. objective of the test experiment at CESR-TA:- what is the rms of the residual eigen-motion of the CESR beam as a function of frequency- what are the limits in noise performance of the BPM electronics?

6. experimental set-up • Excitation of beam with a vertical orbit corrector dipole,direct connection to dipole coil (Q10W) • Observation of beam oscillations on vertical pickups with modified BBQ electronics (Q8W) heavy downsampling in special acquisition cards, up to 17 minutes measurement time. • Calibration of the system using a 300 um peak-peak oscillation measured in parallel with BBQ system and local orbit system. • Various beam conditions, partial shutdown of injector complex etc… • 4 measurement shifts • Very friendly and effective support by CESR team

7. Diode detectors on PU-Q8W

8. Getting BPM resolutions below the nm • Aperture of BPM approx. 50 mm or more • Wide band electronics thermal noise limit: 10^-5 of aperture • Narrow band front-end gains factor 10…100 • State of the art commercial BPM system (“Libera Brilliance”)reaches 5nm/sqrt(Hz), i.e. with 1000 s measurement time 150 pm rms noise. • Different approach:BBQ electronics: “Zoom in” getting high sensitivity for beam oscillations, but loosing absolute information of DC = closed orbit information.

9. Amplitude Calibration Measured in parallel with turn by turn orbit system: measured amplitude: 300 um pp ~ 100 um rms

10. Simultaneous excitation with 6 different tones @ 17.2 mA rms each

11. 4 um reference tone @ 20 Hz 1 nm line

12. 18 pm in 47 s measurement time = 0.12 nm/sqrt(Hz) Noise evaluation 40 pm Ratio: 4,92 <-> sqrt 22 = 4,69 Compare to Libera Brillance with 0.25 um @ 2KHz = 5nm/sqrt(Hz)

13. Is all we measure beam motion? There is more signal with the synchrotron off What is this pedestal?

14. PM to AM demodulation of Rf-noise • With the BBQ detection principle the system is sensitive to hase jitter of the RF, i.e. jitter of the revolution time.

15. Additional possible explanation • Dispersion at the pickup:Rf phase jitter (= jitter in revolution time = jitter in beam energy) Translates into position variation:dx = D * Dp/pLet us say D= 10cm a Dp/p of 10-6 already expalins 100 nm fake motion.

16. Vibration Sensors, Setup 1 Quadrupole Q8W Geophones Sensitivity: 2000 V/(m/s) Frequency range: 1/30 – 80 Hz Accelerometers Sensitivity: 1 V/(m/s^2) Frequency range: 0,1 – 200 Hz 18/06/2009 Mechanical Measurement Lab Magnus Sylte EDMS 1004462

17. Average Spectra on ground and on top of quadrupole compared to beam motion Average FFT Geophones Average FFT BPM Ground Vibration Quadrupole Vibration 18/06/2009 Mechanical Measurement Lab Magnus Sylte EDMS 1004462

18. Quad (black) Beam Does not really fit, but there are more than 100 quads on different supports…

19. Vibration Sensors, Setup 2 Accelerometer 2 Accelerometer 1 08/07/2009 Mechanical Measurement Lab Magnus Sylte EDMS 1004462

20. Accelerometer 1 Accelerometer 1 Geophone on the floor Average FFT 08/07/2009 Mechanical Measurement Lab Magnus Sylte EDMS 1004462

21. Accelerometer 2 Accelerometer 2 Geophone on the floor Average FFT 08/07/2009 Mechanical Measurement Lab Magnus Sylte EDMS 1004462

22. Comparison BPM vibration and beam spectrum

23. Perspectives for the future 1 nm line Feedback Off Feedback ON

24. Conclusions and Perspectives • An electron beam (tens of um beam size) can be used to sense disturbances (vibrations) down to the sub-nm level- using an optimized BBQ electronics- using about 10^9 samples in 17 minutes measurement time • In the observed spectra at CESR-TA we need to understand the frequency range below 80 Hz. We need to clarify what fraction of this is PM-AM demodulation of RF-phase jitter and what comes from residual dispersion. • PSI will receive us 25-28 October for the same measurementwith the following changes:- a more stable machine- parallel measurement of Rf-phase noise- only vertical pickup- prepared dispersion bumps • CESR-TA would hopefully except to have a CLIC quad installed (for all machines): not the real CLIC quad: higher aperture, lower strength… still a lot of information to be gained by these experiments • Presently we study the CESR optics in order to calculate the amplitude factor between quad motion and visible amplitude in the BPM.This factor can be much bigger than 1!

25. Conclusions and Perspectives (2/2) • Other European light-sources have been contacted(Diamond, Soleil, PSI, ESRF, PetraIII) for similar experiment. so far no “enthusiasm” to install a new quadrupole into their machine PSI will receive us in late autumn for the same measurementand proposes to stabilize an existing SLS quadrupole • CESR-TA would hopefully except to have a CLIC quad installed limited experimental program at low frequencies (for all machines): not the real CLIC quad: higher aperture, lower strength… still a lot of information to be gained by these experiments • Presently we study the CESR optics in order to calculate the amplitude factor between quad motion and visible amplitude in the BPM.This factor can be much bigger than 1! • Such an experience is only possible at all due to a major improvement in BPM sensitivity for beam oscillations from 5 nm/sqrt(Hz) (Libera Brillance) to 0,12 nm/sqrt(Hz) (BBQ) • Several details of BBQ noise performance, frequency dependence, beam current dependence and dependence of beam emittance to be measured