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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!