APEX HF Schottky Calibration

1
APEXHF Schottky Calibration

• Peter Cameron and Al Dellapenna

2
Outline

• BBQ parasitic to resonance compensation
• Mission Accomplished, but
• 3D sensitivity to beam loss
• Emittance calibration of HF Schottky
• Preparation parasitic behind a store
• The experiment
• Conclusion high resolution, significant
  potential value
• Chromaticity Calibration
• A caution to Operations
• Artus in chrom application did not give
  meaningful and reliable chrom measurements during
  this study.
• Is this also sometimes the case during normal
  operations?
• HFS chrom measurements are presently useless.
  This requires further study, algorithm refinement
  

3
BBQ

• Steve Peggs declare Victory
• Peter Cameron Mission Accomplished
• One messy little detail
• BBQ sensitivity to electrons/beam loss (thank you
  Mike Brennan)
• We are working on it

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BBQ during tune scan (x const)
Vert I and Q
.01 units of tune
Horiz I and Q
Tunes and beam decay
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BBQ effect of beam loss
Vert I and Q
Horiz I and Q
loss of lock
Tunes and beam decay
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BBQ

• Steve Peggs declare Victory
• Peter Cameron Mission Accomplished
• Steve Peggs tell them what youre going to
  tell them, then tell them, then tell them what
  you told them
• Peter Cameron Mission Accomplished
• Just one messy little detail
• Sensitivity to beam loss/electrons
• And one more puzzle
• Anomalous sensitivity to tune separation (at
  small and large tune separations, but not at
  intermediate ie lt700Hz) when fully decoupled

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Outline

• BBQ parasitic to resonance compensation
• Emittance calibration
• Preparation parasitic behind a store
• The experiment
• Chromaticity Calibration

8
e calibration - the principle

• Simple
• Schottky pickup is moveable controllable
  beam offset
• Schottky signal is macro-particle of charge
  sqrt(N), where N is number of beam particles
• This macro-particle deposits power in the
  spectrum at both revolution and betatron
  frequencies
• Beam offset at which power in rev line equals
  power in betatron line is the rms beam sigma (see
  next slide)
• For preliminary exploration we just did this by
  eye

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Spectra at 3 pickup positions
Counts 75
Counts 1275
Counts 675
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mirrored down for least squares fit
Departure from straight line indicates
non-Gaussian profile, can be fit to determine
profile
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Comparison with IPM

• Blue IPM and Schottky are both at the Q4 end of
  sector 2, a few meters apart
• Schottky says s 0.8mm
• IPM says s 1.68mm sqrt(20/29) 1.4mm
• With b difference gives factor of 2? Where?

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More comparison with IPM
flattop

• Resolution gt x10 better
• No beam kick
• May be useful on ramp
• Schottky point every 4 sec

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Yet more comparison with IPM
Schottky
IPM
These differences are meaningful related to
shape of transverse profile
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The experiment

• Preliminary data was taken at store
• This experiment at injection
• Large distorted revolution line problem for cal
  only
• Distorted betatron lines - from turning Landau
  off?
• Abandoned this part of the experiment (can be
  done parasitically to stores) to concentrate on
  chromaticity

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Schottky emittance measurement

• Has excellent resolution
• Beam decay monitor more useful than Current
  monitor for tuning
• Might an emittance decay monitor ( emittance
  gain/hr) be more useful than an emittance
  monitor?
• Schottky has sufficient resolution to permit this
• Data is always there, for free does not perturb
  the beam
• Can be given absolute calibration via moveable
  pickup
• Profile can be extracted from position scan
• For the most part agrees well with IPM. When it
  does not, there is useful information (shape of
  transverse profile)
• Relatively small effort to make this available at
  store
• Slightly larger effort to make it available at
  injection and on the ramp (LO frequencies need to
  be tied to frev)

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Outline

• BBQ parasitic to resonance compensation
• Emittance calibration
• Preparation parasitic behind a store
• The experiment
• Chromaticity Calibration

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x calibration - the principle

• Simple
• Measure linear and non-linear chrom via standard
  radial shift method, using Artus and BBQ
• Compare with Schottky
• Change the chromaticity
• Repeat

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Blue at the start
Artus drawn to other eigenmode?
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Blue tunes
x 1 both planes
x 2 both planes
x 2 both planes
x 1 both planes
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Blue chromaticity
x 1 both planes
x 2 both planes
x 2 both planes
x 1 both planes
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Blue summary

• Data pretty confusing, the only one I trust is
  BBQ in this data set
• A caution for operations?
• Schottky algorithm needs refinement
• Present calculation is ad hoc, complex, many
  fudge factors
• Need to incorporate calculation of non-linear
  chromaticity

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Yellow overall
Opposite shift - Artus is wrong sign for chrom
at integer minus tune
xh 1 xv 1
xh 2
restore
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Yellow Summary

• Data dumped to elog was for Blue!
• Are chrom measurements archived?
• if not, they should be
• If we can find chrom data, will go back and
  analyze yellow
• Overall summary
• Schottky CAN give good chrom data, requires
  attention