Introduction to Advanced Optics Measurements at Tevatron

1
Introduction to Advanced Optics Measurements at
Tevatron
Alexander Valishev

• Motivation
• Differential orbit measurements
• Computer model and Manual fit
• Tuneshifts
• Results

2
Motivation

• First measurements by V. Lebedev revealed large
  discrepancy between the actual and design LowBeta
  optics
• Optics correction performed in May proved to be
  extremely efficient for Tevatron performance
• Further improvements were required to
• Correct beta beating in the arcs
• Correct dispersion
• Achieve better accuracy
• Find and correct locally sources of coupling

3
Differential Orbit Measurements

• The aim is to find gradient errors utilizing the
  fact that quadrupoles act as dipole correctors
  with off-center orbit
• Initially, closed orbit is excited using a single
  dipole corrector
• For the Tevatron (FODO) lattice with pi/3 phase
  advance per cell
• thus, 2 correctors are required
• per plane, total4
• Dispersion measurement
• Use BPM system to measure and record orbit
  differences

4
Computer Model and Fit

• We use OptiM accelerator optics code (V.Lebedev)
• The model contains regular optics elements
  (similar to MAD). Differences are
• Strengths of individual quadrupoles (measured),
  power supply currents are taken from the control
  system
• A1 component in dipoles (correct pattern of
  re-shimmed magnets)
• Unknown quadrupole errors which are found by
  fitting the computed differential orbit to the
  measured
• Disadvantage of such fit some errors are
  linearly dependent (excite same orbit), hard to
  distinguish

5
Direct Beta-function Measurement

• Vary current in quadrupoles which have separate
  power supplies and measure corresponding betatron
  tune shift
• Compare to the calculated tuneshift

6
Results Differential Orbits
X1
Y1
df rf
7
Results Helix and Lattice
Collision helix
Ring-wide betas
8
Results Skew Quadrupole Errors
Closed Orbit Bump at D16 (calculation)
9
Results Measured and Computed TuneshiftsManual
Fit
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Results Measured and Computed TuneshiftsLOCO
Fit
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Results Betas After LOCO Fit