TeV Orbit Calculations: Beam Smoothing Tools - PowerPoint PPT Presentation

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TeV Orbit Calculations: Beam Smoothing Tools

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Slide the fits so that a single cusp does not spoil the identification of mavericks ... Cusp fitter implemented but as yet not at tested/tuned ... – PowerPoint PPT presentation

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Title: TeV Orbit Calculations: Beam Smoothing Tools


1
TeV Orbit CalculationsBeam Smoothing Tools
  • Cusper
  • Smoother

2
Cusper
  • Fitter to detect distortions in the magnetic
    field based on deviations from the expected form
    of the beam position measurements
  • Includes heuristics for rejecting BPM
    measurements as suspected bad readings
  • Identifies positions and strengths of apparent
    distortions

3
Smoother
  • Tool to suggest optimum DFG settings to correct
    for distortions
  • Optimization includes criteria which existing
    tools do not
  • Recognition of DFG current range restrictions
  • Penalty for larger DFG currents
  • Penalty for large inter-step slew

4
Identifying Maverick Readings
  • Technique
  • Local sine-curve fits to BPM data (corrected for
    b function)
  • Fit with and without a key point (or pair of
    points) to be evaluated
  • Bayesian approach Assume some a priori
    likelihood of a given measurement being bad
  • Which is more likely?
  • the (worse c2) probability of the fit including
    the key point
  • the (better) probability of the fit excluding the
    key point, times the assumed likelihood of a bad
    measurement
  • Slide the fits so that a single cusp does not
    spoil the identification of mavericks

5
Subtleties in Identifying Mavericks
  • There are various ways for the data to fool a
    heuristic for identifying mavericks
  • The presence of a maverick, coupled with unlucky
    normal fluctuations, to cause
  • incorrect rejection of a good reading
  • incorrect acceptance of a bad reading
  • Unit-testing the code exposed a number of such
    headaches

6
Subtleties in Identifying Mavericks
  • The presence of a true maverick here distorts the
    fit such that an acceptable measurement is
    rejected
  • Modifications to the heuristic to correctly
    handle most of these subtleties have been made.
  • Some situations still fool the filter, but these
    now involve very rare combinations of
    circumstances

7
Identifying Cusps
  • Fit with varying window sizes and positions
  • Find three best fit curves
  • across the interval in question
  • just to the right of the interval
  • just to the left of the interval
  • Again a Bayesian approach is used
  • Some a priori likelihood for distortion in any
    given interval
  • Which is more likely?
  • the (worse c2) probability of the fit without a
    distortion
  • the (better) probability of the fit excluding the
    key point, times the assumed likelihood of a
    distortion
  • Last-pass overall optimization of cusp positions
    and magnitudes

8
Cusper Status
  • Can read BPM and Twiss parameter info from a
    couple of formats and use it to try to do the fit
  • Display capability via Root
  • Rejection filter implemented and unit-tested and
    tuned
  • 99 of the effort, as usual, went into the
    boundary and pathological cases
  • Cusp fitter implemented but as yet not at
    tested/tuned
  • Major issue once the linux-based cusper exists
  • How (and whether) to integrate this with the
    control-room accessible tools
  • Effort has been on back burner for a while

9
Smoother
  • Given the BPM readings and the desired target
    orbit readings, find the best DFG settings to
    correct the orbit.
  • Global optimization across time steps in the
    ramp and squeeze, to minimize large slews
  • Avoidance of suggested currents which are too
    large for the DFG to handle
  • Consideration to avoiding large total currents
  • Two DFGs should not fight each other at large
    currents
  • The overall optimization can be computationally
    intense
  • This has been on the back burner for quite a
    while
  • When the tool exists, integration with
    accelerator controls will also be an issue

10
Beta Tool
  • Once
  • cusper is implemented
  • new BPMs are in place
  • it becomes possible to evaluate, for a given
    frame, the corrections to the b function which
    would explain BPM fluctuations not explained by
    identified cusps.
  • A single such measurement is not very meaningful.
  • An ensemble of these corrections, over time,
    might be helpful in determining the b function to
    better accuracy.
  • Is this something people would be interested in?
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