EP Collaboration Meeting

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E-P Collaboration Meeting

• S. Henderson
• Accelerator Physics Group Leader

August 31-Sept 1, 2004
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Agenda

• Tuesday August 31
• 900-1200 Proton Beam Observations, R. Macek
• 1200-100 Lunch
• 100 500 E-p Feedback Experiment Discussion
• Feedback System Overview, Henderson
• Properties of available striplines, Macek
• Signal Processing Options
• Estimate of power requirements
• Power Amplifier Options
• Wednesday September 1
• 900-1030 SNS Site Tour
• 1030-1230 ORBIT/e-p simulation results update
  and discussion, Y. Sato, A. Shishlo
• 1230-130 Lunch
• 130-330 Wrap-up
• Plan for writing proposal for beam time
• Plan for next steps with hardware
• Plan for additional collaborators

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Elements of a Feedback System

• Four Basic components
• Pickup
• Signal Processing
• RF Power Amplifier
• Kicker
• Pickup Sufficient bandwidth to adequately
  deliver coherent motion
• Signal Processing produce corrective (low-level)
  signal based on error signal
• RF Amplifier amplifies low-level correction
  signal to produce corrective voltage pulse
• Kicker Sufficient bandwidth to cover coherent
  spectrum

Signal Processing
RF amp
Kicker
Pickup
Beam
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Basic Formulae for a Feedback System

• Apply kick proportional to displacement
• Gives damping rate turns-1
• where ?1 is the phase advance between pickup
  and kicker

• For a stripline kicker with plates driven at /-
  Vk
• For a pair of striplines driven by a single RF
  power source via a 180 deg hybrid, the Kicker
  Sensitivity is
• With

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Basic Formulae, continued

• The Transverse Shunt Impedance is
• For optimal BPM/kicker phase advance,

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Transverse Shunt Impedance (wd, ?0.85, 50?,
d15cm)
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Transverse Shunt Impedance (wd, ?0.85, 50?,
d15cm)
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Parameters for an e-p feedback system at PSR

• Bandwidth
• Treat longitudinal slices of the beam as
  independent bunches
• Ensure sufficient bandwidth to cover coherent
  spectrum
• Need 50-200 MHz
• Damping time
• To completely damp instability, we need 200
  turns
• To influence instability, and realize some
  increase in threshold, perhaps 400 turns is
  sufficient
• Input parameters
• ?y 7 meters
• Xmax 1mm
• Stripline length 0.5 m, separation d 0.10,
  w/d 1.0
• 800 MeV

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Damping Time vs. Power at 150 MHz
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Damping Time vs. Frequency at Fixed Power
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Feedback Hardware Topics of Discussion

• High-bandwidth Pickup (installedgood to 200
  MHz?)
• Signal processing
• Digital or Analog?
• Options
• Build system from scratch (as prototype for SNS?)
• Borrow similar system (SLAC/LBL/INFN system has
  250 MHz BW)
• Do we need to correct intensity dependence of
  signals?
• RF Power Amplifier
• Need to nail-down parameters to know final power
  requirements
• Options
• Borrow appropriate amplifier from Byrd/Corlett
• Rent one
• Buy a used one (several on the market)
• Buy a new one
• Stripline Kicker
• Bob has measured some striplines
• Are they right for the job?