CESR-TA experiment

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

Outline

• Motivation

• Experimental Set-up• First results

- amplitude calibration- residual beam motion- noise of detection system

• Conclusions and Perspective

CLIC stabilization requirements• Mechanical stabilization requirements:

Quadrupole magnetic axis vibration tolerances:

• Main beam quadrupoles to be mechanically stabilized:– A total of about 4000 main beam quadrupoles – 4 types – Magnetic length from 350 mm to 1850 mm

Final Focus quadrupoles

Main beam quadrupoles

Vertical 0.1 nm > 4 Hz 1 nm > 1 Hz

Horizontal 5 nm > 4 Hz 5 nm > 1 Hz

Present design approach(CLIC stabilization WG, C.Hauviller et al.)

• Mechanical active stabilization in a feedback loop using electromechanical sensors and (piezo) actuators

• Optimized mechanical design for- girders, magnets and electromechanical alignment system- best choice for number and position of actuators and sensors- low Q mechanical resonances in order to avoid vibration amplification- mechanical resonances at the highest possible frequencies

• Mimimization of environmental noise through isolation from vacuum chamber vibration, coolent flows, cable vibration and microphonic coupling

• Experimental verification of the result of stabilization:- construction of real hardware based on a quadrupole prototype, an active stabilization system Present work program: A type 4 quad ready for lab tests mid 2010.

Main Beam Mock-up

Work launched within the collaboration

• Functionalities – Demonstrate stabilization in operation:

• Magnet powered, Cooling operating• Configurations

– 1- Stand-alone – 2- Integrated in Module– 3- Interconnected

• Accelerator environment

• Parts / Measuring devices– Floor (damping material)– Support– Pre-alignment– Stabilization– Magnet– Vacuum chamber and BPM– Independent measurement

Slide taken from C.Hauviller, ACE 2009

Main beam quadrupole

• Under final design.• Plain material (incompatible with corrector magnet)• Assembly methods to be tested (accuracy of some microns!)

Slide taken from C.Hauviller, ACE 2009

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

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?

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

Data processingNIM crate

DAC sine wave generation

ADC sown samplingfactor 4

6 ch.

6 ch.

VME crate with DABs

down samplingfactor 1 to 256

FFT

Laptop (Windows XP)

• Data transfer and• Control of DABs and DAQs

LabView program

Storage Display

• DAC and ADC • sampling rate: 44kS/sec• resolution 24 Bit

•FFT:• Length: 64kS• no windowing• 22 FFTs are averaged (measurement time >1000sec)

USB

DAQ

Ground motion meas.

In CTF3 this measurement would take about 100 days

Digitizers

VME-crate with DAB cards

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.

M.Gasior, BE-BI

Direct Diode Detection (3D) – the principle

Peak detection of position pick-up electrode signals (“collecting just the cream”) fr content converted to the DC and removed by series capacitors

beam modulation moved to a low frequency range (as after the diodes modulation is on much longer pulses) A GHz range before the diodes, after the diodes processing in the kHz range Works with any position pick-up Large sensitivity Impossible to saturate (large fr suppression already at the detectors + large dynamic range)

Low frequency operation after the diodes• High resolution ADCs available• Signal conditioning / processing is easy (powerful components for low frequencies)

M.Gasior, BE-BI

Direct Diode Detection – The principle

 = 0,  = 0.01

q = 0.1, Cf = Cpu

  = T

  = 100 T

4 bunches  = 100 T

Detector signal differenceSignals of both peak detectors

M.Gasior, BE-BI

Architecture of the Base Band Q (BBQ) Measurement System

Analog front-end box (2 channels)Detector box (for one PU electrode)

For CESRTA the system bandwidth is 10 Hz – 5 kHz

Amplitude calibration

• The BBQ electronics does not have a good absolute calibration for the measurement of absolute beam oscillation amplitudes.

• On the contrary the BBQ electronics is linear over many decades and frequency independent within the bandwidth given by the electronic filters.

• Disconnect orbit steerer from control system and get two wires for own excitation…

• 1st attempt of calibration: DC mode: inject 1 A ( lab current source)of DC current into steerer magnet, measure (calculate) orbit displacement at BBQ-pickup and use this relation for future low current AC excitations.Done, but problem is unknown bandwidth of magnet and vacuum chamber

• 2nd attempt: AC-mode: inject AC modulation (0.5 A rms) at various frequencies and measure resulting orbit oscillation with BPM system.(For 0.5 A we had to borrow a HiFi amplifier and we just managed to be above the sensitivity of the turn by turn CESR orbit system:0.5 A at 20 Hz gave a 300 +-30 um peak-peak orbit oscillation.

CalibrationDC

AC

0.5 A@20 Hz 300 +-30 um

0.5 A@40 Hz 150+-30 um

0.5 A@80Hz 80+-30 um

Preliminary “fit by eye”; data of this calibration (CESR BPM rawdata) on a file on a website, which is presently not accessible to us

- 1 mm at Q8W

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 en cy [H z]

-1 1 0

-9 0

-7 0

-5 0

-3 0

Mag

nitu

de [

dBF

S]

2 G e V e lec 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 e a s . 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

Calibration

• In the end we decided to leave a continuous 20 Hz excitation of 20 mA as reference excitation through all measurements.

• This corresponds to a beam oscillation of about 4 um rms at 20 Hz.

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)

GeophonesSensitivity: 2000 V/(m/s)Frequency range: 1/30 – 80 Hz

AccelerometersSensitivity: 1 V/(m/s^2)Frequency range: 0,1 – 200 Hz

Vibration Sensors, Setup 1

Mechanical Measurement LabMagnus Sylte

EDMS 100446218/06/2009

Quadrupole Q8W

Acquisition System and Analysis Parameters

Max sampling frequency: 384 KHzA/D converter: 24 bit Dynamic range: 10mV-50V

Version:MKII

Mechanical Measurement LabMagnus Sylte

EDMS 100446218/06/2009

Analysis Parameters:Measurement length: 1024s and 1440sWindow: HanningSampling rate: 1024HzBlock length: 64sAverage: LinearOverlap: 66,7%

Average Spectra on ground and on top of quadrupole compared to beam motion

Ground Vibration

Quadrupole Vibration

Average FFT Geophones Average FFT BPM

Mechanical Measurement LabMagnus Sylte

EDMS 100446218/06/2009

Beam

Quad (black)

Does not really fit, but there are more than 100 quads on different supports…

Transfer function Coherence

Phase

First vertical bending modes

Mechanical Measurement LabMagnus Sylte

EDMS 100446218/06/2009

First lateral bending modeTransfer function Coherence

Phase

Mechanical Measurement LabMagnus Sylte

EDMS 100446218/06/2009

Vibration Sensors, Setup 2

Mechanical Measurement LabMagnus Sylte

EDMS 1004462

Accelerometer 2

Accelerometer 1

08/07/2009

Accelerometer 1

Mechanical Measurement LabMagnus Sylte

EDMS 1004462

0 10 20 30 40 50 60 70 80 90 100Hz

100f

1p

10p

100p

1n

10n

100nm

Accelerometer 1

Geophone on the floor

08/07/2009

Average FFT

Accelerometer 2

Mechanical Measurement LabMagnus Sylte

EDMS 1004462

0 10 20 30 40 50 60 70 80 90 100Hz

100f

1p

10p

100p

1n

10n

100nm

Accelerometer 2

Geophone on the floor

08/07/2009

Average FFT

Comparison BPM vibration and beam spectrum

Side product:modified BBQ electronic with higher bandwidth:

perfect tune-monitor with 60 db signal/noise ratio

1 nm line

Perspectives for the future

Feedback Off

Feedback ON

Conclusions and Perspectives (1/2)• 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

• At CESR-TA the accelerator itself has disturbances that add up to - smaller values than 1 nm rms above 80 Hz- to much larger values below 80 Hz

• Hence in the interesting region 10 Hz – 100 Hz no full demonstration of the stability of a CLIC quadrupole proto-type can be made,but:- in this frequency range the gain of a stabilization loop can be measured at 10-100nm levels- a special optics can be designed in order to get higher sensitivity using the amplification of the lattice.

• Due to its availability CESR-TA stays interesting as CLIC test-bed

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 is ready to receive us in late autumn for the same measurementand proposes to stabilize an existing SLS quadrupole

• CESR-TA would potentially 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

• 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