# Presentation: 142398

## (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**

## (Re-)Shimming of Tevatron Dipoles

- “Smart” Bolt

- “Dumb” Bolt

**Tevatron Dipole Cross Section**

## 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**

## 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!**

## Magnetic Measurements: a1 Issue(from P. Bauer)

| Magnet |  (cold lift)  82-02 (mils) |  (a1) 82-02 (units) |
| --- | --- | --- |
| TB0269 | +8.5 / +7.0 | +1* |
| TC1220 | +4.1 / +6.0 | +1* |
| TB0834 | +11.3 / +11 | +3* |
| TC0483 | +4.2 / +6.2 | +0.4* |

**** '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)***

## Summary of Re-shimming Results(from G. Velev)

_***Summary of Re-shimming Results***_***(from G. Velev)***

## 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***

## 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**

## Kaiser Coil Calibration(from J. DiMarco)

## Longitudinal Variation of a1(from P. Bauer)

**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***_***)***_

## (Re-)Shimming of Tevatron DipolesSummary

**Shimming is a well-established procedure **
**Magnetic effect of ****s****himming 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) ~.06-.16 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**