July 31, 2003Tevatron Alignment Review JCT (Re-)Shimming of Tevatron Dipoles  Recent ‘cold lift’ measurements indicate ‘creep’ or shrinkage of the coil/cryostat support structure (lowering the coil roughly ~3mils) which translates into ~ 1unit of a 1 ; this can corrected by re-shimming  Re-shimming is a well-established procedure that was done hundreds of times in production on magnets at liquid helium temperature  Magnetic effect of re-shimming has been calculated several times and measured many, many times  Re-shimming studies are being carried out in the Magnet Test Facility to verify procedures: a 1 behaves as expected/calculated – not an issue Field angle changes ~.1-.2 mrad – well within alignment ‘budget’ but being studied A brief review of present status

July 31, 2003Tevatron Alignment Review JCT (Re-)Shimming of Tevatron Dipoles “Smart” Bolt “Dumb” Bolt Tevatron Dipole Cross Section

July 31, 2003Tevatron Alignment Review JCT Measured Change in Cold Lift (from D. Harding)  No change in (Q1-Q2)/2  left-right OK  0.15 mm change in (Q1+Q2)/2  0.1 mm lowering

July 31, 2003Tevatron Alignment Review JCT Shimming of Tevatron Dipoles  a 1 due to up-down asymmetry – position or upper-lower coil differences  original corrections made on MTF test stands: measure & shim to <1 unit and ship…  Mean  0.16,   0.53 unit: shimming well understood!

July 31, 2003Tevatron Alignment Review JCT a 1  strong coupling, possibly caused by creep in the coil/cryostat support structure relative to yoke that occurred during first years of Tevatron operation Magnet  (cold lift) (mils)  (a1) (units) TB / * TC / * TB / +11+3* TC / * * '82 and '02/'03 measurements were performed with measurement probes of different lengths at different measurement positions in the magnet body. Therefore the data – although of the right sign and magnitude - are only qualitative: conclusions cannot be drawn yet since there is significant variation of a 1 along the magnet length Magnetic Measurements: a 1 Issue (from P. Bauer)

July 31, 2003Tevatron Alignment Review JCT Re-shimming of smart bolts with 3 mils  expected change of 1 unit of a 1 tc1077: 4mil shims at stations 2-8; then, add 4mil shims at stations 1 & 9. Summary of Re-shimming Results (from G. Velev)

July 31, 2003Tevatron Alignment Review JCT Field Angle Measurements (from J. DiMarco)  Measure field angle with ‘Stretched Wire’ system before and after re-shimming  Measure ‘Kaiser coil’ angle before and after re-shimming  Measure roll angle (‘Level’) at both ends, before and after re-shimming using antique fixture Four magnets re-shimmed to date – NOTE: units are mrad

July 31, 2003Tevatron Alignment Review JCT Kaiser Coil Measurements (from J. DiMarco)  the Kaiser coil is a loop of wire fixed in the yoke, nominally in the vertical plane, used to detect change in coil/cryostat alignment with respect to the iron  Magnet is excited with a AC current and the Kaiser coil is read out after each shim change

July 31, 2003Tevatron Alignment Review JCT Kaiser Coil Calibration (from J. DiMarco)

July 31, 2003Tevatron Alignment Review JCT Possible causes: Variations of coil position with respect to yoke Coil shape variations, especially between lower and upper pole Dipole tc0525 Probe position number Longitudinal Variation of a 1 (from P. Bauer)

July 31, 2003Tevatron Alignment Review JCT (Re-)Shimming of Tevatron Dipoles Summary  Shimming is a well-established procedure  Magnetic effect of shimming is understood  Re-shimming studies carried out in the Magnet Test Facility verify : a 1 behaves as expected/calculated – not an issue Field angle changes (after tilt removed) ~ mrad are well within alignment ‘budget’ Additional magnet to be studied  Internal (TD) Readiness review for re-shimming in the tunnel to be held 8/8/03