Incoherent Tune Measurement

1
Incoherent Tune Measurement
BNL SNS Diagnostics Design Review

• Peter Cameron

March 26-27, 2003
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Outline

• Action Items
• AP Requirements
• Incoherent Tune Measurement Options
• Schottky/BTF Measurement
• Quadrupole Measurement
• Layout and Lattice
• ICD, Process Variables, Acceptance Criteria
• Summary and Conclusions

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Action Items from the July Design Review

• Refine day one requirements - in progress,
  related to handoff issues
• Use turn-by-turn mode available in BPM system -
  Will be done at App level, in addition to stand
  alone system
• Dedicated tune/Schottky detectors are a good idea
  - will be present
• Short on implementation details - this and
  following presentation
• Incoherent tune from injection oscillations are
  problematic - agree, capability will be
  available, but this is neither of the baseline
  systems
• Zero in on areas requiring early decisions - done

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AP Requirements for Tune Measurement

• Coherent tune
• accuracy .001
• Resolution .0005
• Incoherent tune
• accuracy .005
• Resolution .0025
• Both measurements will require averaging

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Tune Footprints - blue dot is coherent tune
halo
halo
core
core
Footprints for 3 intensities (0.1, 1, and
2x1014) at cycle end
Footprints after 263, 526, and 1060 turns, 1014
beam
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Incoherent Tune Measurement Options

• Incoherent Tune - RF portion of Dual AFE, measure
  tune of 400 MHz microbunches before decoherence -
  requires Injection and Orbit Apps
• Incoherent Tune - Schottky - resonant pickup
  DAQ
• Incoherent Tune - Beam Transfer Function
• Use resonant kicker to reduce power requirements
• Use resonant transverse pickup to improve
  sensitivity, reduce common-mode dynamic range
  problem
• Resonate above coherent spectrum (40MHz) to
  reduce common-mode dynamic range problem
• Incoherent Tune - Quadrupole Oscillations,
  common-mode dynamic range problem
• Use resonant kicker to reduce power requirements
• Use resonant pickup to improve sensitivity,
  reduce common-mode dynamic range problem
• Resonate above coherent spectrum (40MHz) to
  reduce common-mode dynamic range problem
• Resonance crossing - at App level by AP guys

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Incoherent Tune Measurement

• Two methods are being implemented, Schottky/BTF
  and Quadrupole
• Schottky/BTF is the more conventional - were it
  not for strong input from AP group, this would be
  the only system chosen by Diagnostics
• Quadrupole gives a separate method to measure
  incoherent tune, and in addition provides a
  diagnostic for other things that interest the AP
  group (parametric resonances, emittance, )
• SY Lee, Quadrupole Mode Measurements and their
  Applications, presented at the ORNL ICFA
  Diagnostics Workshop http//www.sns.gov/icfa/prese
  ntations/

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• Schottky/BTF System

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Schottky Signal Relative to RHIC Au
Power spectral density Nx2q2fk2g/nhdp/p
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Linewidths, Chromaticity, Space Charge,

• Tune spreads at the lower sideband due
  to chromaticity (f0xdp/p) and revolution harmonic
  (f0nhdp/p) cancel at about 40MHz for nominal SNS
  conditions, leaving only the space charge
  contribution. This would be a good frequency for
  the resonant kicker and resonant pickup

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Resonant BPM

• M. Kesselman et al - PAC 2001
• Stub-tuned 1/4 wave resonator
• Simulated in Spice
• frequency 240MHz (8.5xRF)
• Qloaded 100 optimal coupling
• In-tunnel hybrid for S and D
• Resonate difference mode - not sum mode signal
  at revolution line
• Moveable - minimize difference mode signal at
  revolution line
• Resonate above coherent spectrum

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BTF Block Diagram
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RHIC BTF Measurement
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UAL Simulation Preliminary result

• Beam response (without space charge) to
  narrowband kick continuous thru accumulation
  cycle. Each peak corresponds to one cycle. Result
  is reasonable picture of tune spread due to
  chromaticity

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Filter, filter, filter,

• FFT of RHIC PLL output, 30dB S/N on a few
  109 debunched deuterons with 100 micron 1.2Hz
  radial modulation

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Kicker Power

• Need to know BTF to specify kicker power!
• Scale from experience
• RHIC coherent kicker - 4m long, 3KV
• RHIC BTF kicker - 0.25m long, 1mW, Q100
• relative kick strengths - coherent/BTF .000003
• SNS strength
• SNS BIG kicker - 4.5m long, 14KV, 15 kicks to
  collimator
• 0.01 x BIG requires 10W, gives factor x3000
  relative to RHIC
• spec 50W

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Hardware Status - Schottky/BTF

• Resonant Pickup - frequency 40MHz with Q 100
• prototype in the lab, not yet resonated
• Resonant Kicker - same f and Q
• strength 0.01 x BIG requires 10W, spec 50W for
  some margin
• Prototype in the lab
• Rad hard preamp - attenuation is 2dB/100m at
  40MHz for 3/8 heliax
• no in-tunnel preamp or filter
• Analog Filter - specified, design has begun
• Digitizer - BPM IFE w/ 100MS/s A/D
• Timing - in the gate array
• NCO - in the gate array
• Power Amplifier - Amplifier Research 50W1000B, to
  be located in HV room (avoid bleedthru)

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Software Status - Schottky/BTF

• Existing DSP code from RHIC PLL/LF Schottky/BTF
  system was written by the same person (Joe Mead)
  who programs the SNS BPM gate array
• Existing LabVIEW code from RHIC PLL/LF
  Schottky/BTF system was written by the same
  person (Chris Degen) who writes the LabVIEW code
  for this system
• Wims LabVIEW template

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• Quadrupole System

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QMM Block Diagram
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Basic Method - Quadrupole Oscillations

• Incoherent tune shift in x plane is related to
  measured quadrupole frequency by
• Q2 2Q0 - (1.5-0.5ax/(axay))dQinc
• Where
• Q2 measured quadrupole frequency
• Q0 coherent tune
• dQinc incoherent tune shift
• ax horizontal beam dimension
• ay vertical beam dimension
• Delivers a number - rms incoherent tune spread.
• In addition, Quadrupole BTF possible with this
  system.

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Dynamic Range Problem

• Dynamic range problem - need to see the
  Quadrupole mode signal in the presence of sum and
  difference mode signals. The approach is
• Excite the beam in quadrupole mode only, above
  the coherent spectrum to minimize sum and
  difference mode signals
• Use a resonant kicker to minimize amplifier power
  requirement
• Use a resonant pickup to enhance sensitivity to
  quadrupole mode
• Use phase cancellation to minimize response to
  dipole
• Filter, filter, filter
• Ring beam is large compared aperture - this is a
  big help

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Kicker Power/Pickup Sensitivity

• Problem is same as Schottky/BTF - need to know
  BTF, so again we resort to scaling
• Non-Intercepting Emittance Monitor, Clendenin
  et al, PAC 87
• Relative strengths
• monopole 1
• dipole 2 x/a
• quadrupole 2(xwidth2 - ywidth2)/a2 (x2 -
  y2)/a2

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Kicker and Pickup locations
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Lattice

• Beta fcns at kicker - not so good

Beta fcns at pickup - very nice
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Status

• Hardware is essentially the same as for BTF
  system, substituting quadrupole kicker and pickup
  for dipole
• Software essentially the same as for BTF system,
  with the addition of accelerator physics input at
  the application level
• Pickup has been resonated in quadrupole mode
• Pickup has been installed in RHIC, will attempt
  to take data this run
• BIG/Tune kicker can also be fired in quadrupole
  mode, opening possibility of using IPM for the
  same measurement - at the moment not included in
  baseline, but we do intend to pursue this

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Resonant Quadrupole Plumbing
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Quadrupole mode resonance

• Stub-tuned 1/8 wave resonator
• Simulated in Spice
• frequency 117MHz ( .5 x dipole)
• Q 65
• Suppression of dipole mode via phase cancellation

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QMM BTF - CERN(LEAR)
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• Schottky/BTF and Quadrupole Systems

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ICD/Process Variables

• Inputs from control system
• Plane to kick - Selects plane in BTF mode
• Amplifier Power
• Gain
• Filter BW
• Center Tune
• Tune Window
• Timing - cycle start? (resonant system)
• Outputs to control system
• Schottky spectrum - updated cycle-by-cycle
• Tune slice - thru the accumulation, updated
  cycle-by-cycle
• BTF - Calculated result from LabVIEW

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Acceptance

• Traveller for each pickup and kicker
• Leakcheck
• Impedance check
• S21 of resonant response
• Electronics
• Vertical integration at BNL (on resonator)
• Vertical Integration at ORNL (on resonator)
• System with beam
• red items not in present scope

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Summary and Conclusions

• Move to BPM IFE simplifies life both at BNL and
  ORNL
• LabVIEW template simplifies life both at BNL and
  ORNL
• Existing RHIC PLL software and hardware has
  considerable similarity to the SNS systems
• Acceptance criterion is major concern - handoff
  has the potential to be a serious problem, must
  be addressed soon at the project level