Recent%20drag%20rate%20measurements

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Recent drag rate measurements

• Recycler Departmental Meeting
• November 8th, 2006
• L. Prost, S. Shemyakin

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Data taken

• Drag rate measurements with the electron beam on
  axis, 2 kV jumps
• 100 mA 400 mA
• Nominal file (806)
• Magnetic field realigned recently
• Modified file 806
• SPB01I changed from 13.5 A to 14.5 A
• From focusing optimization based on equilibrium
  changes of a cooled beam at 200 mA (1 mm offset)
• Equilibrium to equilibrium
• Check old SA calibration
• Got unexpected data due to slow energy
  oscillations
• Additional output
• Energy vs y-position at R01
• Jumps calibration

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Drag rates ranged from 25 to 50 MeV/C per hour
All but 6/15/06 data were taken with R38 lt4gt
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Comparison to current density profile Better
agreement ?
Unexplained discrepancy (?!?!) Otherwise, good
agreement between the two detectors
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Data may not be straightforward to interpret
because of a wobbling energy
Pbars drift before the jump
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Slow (6 minute period) energy oscillations are
observed

• Comparison of the Pelletron voltage variation dU
  recorded with GVM and the electron energy
  variations dE calculated from BYR01S
• Both signals are averaged over 30 sec
• Calibration from a jump (last week presentation)
• 0.31 mm/kV

• Source of these oscillations is unknown
• Voltage regulation loop ?
• Temperature ?

This is a new observation
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Taking advantage of the oscillations as an
independent measurement of the drag rate for
small deviations

• The blue curve shows the evolution of the pbar
  momentum Pi predicted from BYR01 positions Yi as

where P0 - initial momentum offset ? 33 hr-1 -
drag rate coefficient D - coefficient
translating the dispersion in BYR01S into the
units of MeV/c per mm Y0 - beam position in
BYR01S corresponding to an equilibrium energy
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Energy jumps calibration/uncertainties
380 V
100 mA, on axis
Intended jump (3.67 MeV/c)
Error on jump (1s) 0.23 MeV/c
GVMVLT gives 0.11 MeV/c for 1s
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Summary/Conclusions/Questions

• Fastest drag rates ever recorded
• Max 50 MeV/c per hour for Ib 300 mA
• Better magnetic field alignment
• Better alignment with pbars
• Smaller emittances ?
• Better focusing ?
• In particular for 300 mA case
• Should not matter on axis
• May be slightly better agreement with estimation
  of the dependence of the drag force with the
  current density on axis
• But still abnormally low drag rate for high
  electron beam current (e.g. 400 mA)
• Standard data analysis (shown here) may be too
  simple for this set because of the energy
  wobbling continuously (see following points)

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Summary/Conclusions/Questions (cont)

• Slow and relatively large energy oscillations
  were observed (with pbars and R01 position) for
  the whole duration of the measurements
• New phenomenon/observation
• Better (higher) drag force ?
• Temperature variations ?
• Relatively good agreement between the two
  measurements using a linear model for the drag
  force
• Small oscillations
• Possibility to use an applied sinusoid for
  automated measurement of the drag force
• Continue to use R01 position as a spectrometer
• Estimated errors for the jump 0.23 MeV/c (1s)
• Based on GVMVLT data, the estimated error is
  half the one calculated with position data
• But it is less sensitive

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Not a real plan but

• We want to continue (and accentuate) the
  investigation of the friction force and cooling
  rates
• More measurements will be requested
• Visitors from BNL will come to Fermilab in
  December for that purpose
• Very important for their project which goes into
  review in the Spring
• Goals
• Improve cooling (FNAL)
• Rates, lifetime,
• Understand cooling (FNAL, BNL,) !!
• Physics contribution of the Electron cooling
  project