Test and Energy measurement with the LEP Spectrometer

1
Test and Energy measurement with the LEP
Spectrometer

• E.Barbero - SL/BI/SD
• 1. Laboratory test of BPM Electronic
• (Frequency , Current)
• 2. Tunnel Test of BPM Electronic
• (Temperature, Stability)
• 3. Environmental magnetic field in the drift
  space.
• (Corrections)
• 4.Conclusions

2
Spectrometer Principle
Concept Measurement bending angle of particle
passing a magnetic dipole field.

• Measure ? Bdl and to give the Ebeam the
  accuracy required
• ? Bdl from local NMRs and field map
• Max.error from the BPMs 1?m?
• Max.error on integral magnetic field
  (almost zero)

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Spectrometer Setup

• Spectrometer is located between arc and straight
  section. (425 m from IP3)
• Laminated steel dipole magnet ( 4NMR Probes).
• 6 BPMs monitoring the incoming and outgoing beam.
• BPMs mounted on individual limestone block to
  provide independence and shielded against
  synchrotron radiation.
• Triple wire position system (WPS) to provide a
  reference against the ground and thermal-driven
  motion of BPM bodies.

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Laboratory Test of BPM Electronics
1. Setup of the electronic

• A Simulator card provide an input signal similar
  to the beam signal .
• Four coaxial cables connected in parallel to the
  card (ensure the button inputs on the BPM
  electronic card receive the same signal).
• Laboratory test of the electronic
• BPM card temperatures variations 8 C
• Signal frequency changes on BPM cards
• Beam current changes
• Stability of the beam position measurement

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Laboratory Test of BPM Electronics
2. Effect of signal frequency Changes

• Frequency changes until 5kHz have been set.

• Results

• The AGC signal and BPM readings show some
  dependence
• ?f ? 5kHz ? ?BPM ? 8?m
• The frequency changes in LEP order of
• ?f ? 100 Hz ? ?BPM ? 0.16?m

No significant effects due to frequency changes.
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Laboratory Test of BPM Electronics
3. The effects of the beam current

• Switchable attenuator unit.
• Same attenuation to each input signal

• Results

Expected change in the AGC output
Change BPM position readings
Dependence of the position on beam current
larger than expected.
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Laboratory Test of BPM Electronics
3.1. The effects of the beam current LEP running

• We have been placed in the region
• with a offset ? 400 ?m
• and a of 0.8.
• With LEP running conditions
• a of 0.025

10 ?m
0.31 ?m
No significant effects due to beam current
changes.
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Tunnel Test of BPM Electronics
1. The effects of the temperature changes

• Variation on the BPM temperatures by blowing
  air.
• Results
• Different changes for different BPM cards.
• ?T? 8?C ? ?BPMi ? 4?m
• ?BPMii ? 7?m
• ?BPMiii ? 200?m

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Tunnel Test of BPM Electronics

• Equal sum changes for all BPM s cards. (6 mV)
• Results

?Temperature
Change reference of sum signal
Change sum signal
Change BPM position readings
BPM Electronic housed in temp-controlled rack
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Tunnel Test of BPM Electronics
1.1. Effects of the temperature changes LEP
running

• The rack ?Temperature
• Mean 0.005 ºC
• Sigma 0.03 ºC
• With laboratory experience make a prediction in
  
• ? BPMreadings? 0.7 ?m

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Tunnel Test of BPM Electronics
2. Stability of the beam position measurement

• Signal of one BPM card over 7h.
• Results
• In the absence temp. changes (?Tlt0.02 C) ? ?
  100 nm

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Beam test of BPM Electronic
1. Cross-Calibration/Gains analysis

• Relative gains calibrations with beam movements
  and rotation around 4 and 2.
• Test of the reproducibility of the method used
  for calibration.
• 2 relative gains ( horizontal and vertical
  plane) for each BPM.

• Gain Calibration in different conditions
• e High current
• e- High current
• e Low current
• e- Low current

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Beam test of BPM Electronics
1.1. Different mean per different particles types

• Different mean value one side of 4.
• Variation smaller 2.

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Beam test of BPM Electronics
1.2. No energy dependence
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Beam test of BPM Electronics
1.3 Conclusions

• Identical conditions ? Identical gains
• Mean gains difference e-, e.
• No Energy Dependence.
• Time dependence predictable.

CONSISTENCE IN THE RESULTS
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Environmental magnetic field
1. Environmental Field (Earth fieldcablesvacuum
pumps)

• Environmental field along spectro., 10E-4
  changes expected.
• Field was assume constant along the
  spectrometer.
• Changes of 2-3.10E-4 were observed.

• Results

• Installation of additional flux gates.
• Maping the field in the drift space at
• diff. Energies.
• Calculation of the corrections for the
• BPM readings.

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Environmental fields
2. Stability of the fluxgates measurements

• Three days of measurements without field.

• Results

• Measurements stable order of 10 mG.
• Effect of the TGV observed.
• Good correlation between fluxgates.

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Environmental fields
3. Environmental Field Map/ Correction
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Conclusions

• Current and temperature dependence on the BPM
  readings .
• First solved by choosing appropiates LEP
  running parameters.
• Second housing the BPM card in a temp-controlled
  rack.
• Bunch frequency variation not large enough during
  LEP running to cause perturbations.
• Relative calibration of BPMs have been
  sufficiently well determinate to prevent
  systematic errors.

Both beam-based and electronic measurements
indicate BPM cards are stable with time for the
Spectrometer application.

• Correction needed for the environmental ambient
  fields in the drift space.

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Acknowledgements
All the work done in the Laboratory/Tunnel BPM
Electronic Test has been mainly developed by John
Matherson. I would like to express my sincere
thanks to my supervisor Bernd Dehning. I have to
express my gratitude to Massimo Placini and to
the members of the LEP Energy Calibration Group
for their support and collaboration.