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 2009And possible future experiment.

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

Validation of Quad stabilization principle (1/2)

Stabilized Quad

Standard Quad

Standard Quad

Standard Quad

Standard Quad

Standard Quad

Standard Quad

Calibrated mechanical exciter

High sensitivity

BPM

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

Diode detectors on PU-Q8W

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.

Amplitude Calibration

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

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0F req u e n cy [H z]

-1 1 0

-9 0

-7 0

-5 0

-3 0

Mag

nitu

de [

dBFS

]

2 G eV e le c tro n sE x c ita tio n a t 2 0 , 4 0 , 8 0 , 1 6 0 , 3 2 0 , 6 4 0 H z , 1 7 .2 m A rm s

m eas . 2 0 _ 4 0 _ 8 0 _ 1 6 0 _ 3 2 0 _ 6 4 0 _ fin a l

Simultaneous excitation with 6 different tones @ 17.2 mA rms each

4 um reference tone @ 20 Hz

1 nm line

40 pm

FFTs averaged

sigma

1 18,07 pm

22 3,67 pm

Noise evaluation

Ratio: 4,92 <-> sqrt 22 = 4,69

18 pm in 47 s measurement time = 0.12 nm/sqrt(Hz)

Compare to Libera Brillance with 0.25 um @ 2KHz = 5nm/sqrt(Hz)

Is all we measure beam motion?

There is more signal with the synchrotron off

What is this pedestal?

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.

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.

1 nm line

Perspectives for the future

Feedback Off

Feedback ON

Priority 1: Understand this

shoulder

Priority 2:

Prepare a detailed experiment of a

stabilized PM magnet in CESR-TA

NLC prototype magnet

PM magnet

180 Tesla/m measured at 5mm

Adjustable to 144 Tesla/m

12 mm aperture

About 15 cm long

2 pieces available at FNAL (J.Volk)

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.We need to find a cure for the problem.

• 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 will possibly except to have a CLIC quad installed (for all machines): not the real CLIC quad: higher aperture, lower strength… the NLC prototype would be OK.

• 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!