# Presentation: 163365

## (Tentative) Re-calibration of the Beam Position Monitors in the Cooling Section

- Recycler departmental meeting
- July 12th, 2006
- L. Prost, S. Shemyakin, (*P. Joireman*)

## Motivation (1) - Observations

- Antiproton trajectories are different now than before the shutdown (at least in the CS)
- Shift and angle...
- But more importantly, the trajectory is not straight
- Electron beam trajectories have larger oscillations in the CS now than before the shutdown
- Drag rate measurements at fixed electron beam current and electron energy jump gave very different results
- (Very) Low *before* the pbar trajectories were tuned correctly
- 50% difference over 4 hours (from 20 to 30 MeV/c per hour, two measurements)
- Trajectories drift ?

## Motivation (2)

- More attention needs to be given to the relative positions of the pbars and electrons
- Might affect cooling
- Definitely important factor for drag rate measurements
- Comparison to models
- Change in electron beam trajectories generally increases the angle due to dipole motion
- True if mechanical motion of the solenoids/BPMs
- True if electronics drift on Autotune BPMs
- False if electronics drift on other BPMs
- For both cases, we want to monitor and control the beams’ position the best we can
*Both cases are a bit of the same...*

## Calibration and calibration procedure

- ‘Calibration’ has several levels... Here, calibration means “adjustments to the table of coefficients used in Paul Joireman’s application program to compute the beam positions”
- Basically, for each BPM:
- Corrections usually applied to the offsets (*d**0*, *c**0* for Y) which are often the largest drifts
- Procedure is pretty simple...
- Pbar trajectories are _assumed to be straight lines_
- Measure pbar orbits for various shifts and angles
- Fit to straight lines
- Difference between measurements and the fits determines corrections to be made to the table of coefficients

## Antiproton trajectories: now and then 

- Pbar trajectories just after last ‘calibration’ (08/04/2005)

- Note that all data sets may not be entirely consistent (things have happened in between !!!)

**Pbar trajectories ****after**** the shutdown**

**Pbar trajectories ****before**** the shutdown**

## BPM noise as a function of the antiprotons’ intensity 

- BPM noise as a function of the antiprotons’ intensity

**“****8 GeV data” during a transfer**

*‘**Bug’ in Excel MACRO used to acquired data *

## Position drifts as a function of the antiprotons’ intensity (1)

**StDev  ****= 3 ********m ****(*****X & Y BPMs together*****)**

**Ref. trajectory for 35e10*****All data taken on the same day***

## Position drifts as a function of the antiprotons’ intensity (2)

**StDev  ****< 3 ********m ****(*****for each BPM, BXC60 excluded*****)**

**Two data sets ****(*****i.e. 2 different ref trajectories*****)**

- BXC60

## Position drifts as a function of the antiprotons’ intensity (3)

**StDev  ****< 6 ********m ****(*****for each BPM)***

**Two data sets ****(*****i.e. 2 different ref trajectories*****)**

## Calibration: Measurement

**35e10**
**8 GeV**
**20 points**

**Displacements are < 2 mm, which should ensure that we remain in the linear regime**

## Calibration: Magnitude of the corrections

***Changes are < 100 ************m for offsets and < 10 ************m for linear coefficients (@ 1 mm)***

## Implementation of the new BPM calibration

- Some improvements but... not to expectations !!!

**Pbar trajectories ****NEW CALIBRATION**

**Pbar trajectories ****OLD CALIBRATION**

- Pbar trajectories just after previous ‘calibration’ (08/04/2005)

- Why do we get a different outcome for almost the same calibration procedure ? (more simplistic in August 2005)

_**Deviation from a straight line (rms)**_**:**
**22 ********m (X BPM) & 28 ********m (Y BPM)**

_**Deviation from a straight line (rms)**_**:**
**59 ********m (X BPM) & 35 ********m (Y BPM)**

## Pbar trajectories drift in time (days, transfers?)...

## ... but the difference in trajectories should be straight lines !

- ... but the difference in trajectories should be straight lines !

- Deviation from a straight line: < 15 m (rms) (X & Y BPMs)

## Conclusions/Comments (1)

- Cooling section BPMs electronics related noise < 4 m (rms) for beam intensities comprised between 20e10 and 102e10
- Except BXC60 which is always worse
- 1400 < BMP intensities < 8000
- This is what really matters
- Depends on bunch structure
- Dec 04: < 1.5 m (rms, reported by Sasha)
- Don’t know why so much better ?!
- Offset changes < 6 m (rms) for beam intensities comprised between 20e10 and 102e10
- Barely above electronics noise
- Dec 04: 50 m (max) for 36e10 < R:BEAM < 200e10
- Maximum change between 50e10 and 100e10 !?
- Low intensity measurements have larger noise and apparent offset drifts

-   Calibration procedure should result in straight trajectories of the pbars to within 10 m (rms).

## Conclusions/Comments (2)

- Tentative calibration of the CS BPMs give results that are outside the expected uncertainties
- Deviation from a straight line ~30 m (rms) !
- Was up to 60 m (rms) before calibration
- August calibration appears to be much better
- Deviation from straight line < 2 m (rms)
-  Trajectories drift in short period of times
- Differences are not simple shifts or angles
- Deviation from a straight line up to 15 m (rms)
- Explains discrepancy of the outcome between August 05 calibration and this calibration (Jul 06)
- Aug 05: Data taken, analyzed and corrections made within a few hours
- Jul 06: Data taken, analyzed and corrections made over a couple of weeks !!
- Trajectories taken a few minutes apart do agree within measurements uncertainties
- Outcome of the calibration made and applied on the same day should work better

**?**

## Conclusions/Comments (3)

- Day-to-day drift of electronics (?) probably limits the accuracy of the cooling section BPMs (and calibration procedure) to ~20 m.
- Less than the typical offset drift over this past year (50 m)
- Recalibration is still an improvement
- Use calibration signal to try to understand better the electronics drift
- In progress...
- Ultimately limits the absolute achievable angle due to dipole motion
- ~25 rad