Privacy and Security Notice

BPM_1

Calibration of the BPM horiz position 11/23/05 

A mistake was found in the previous work below on 11/09/05 for the determination of the beam horizontal position by the HMS.  The HMS survey offset was not converted from mm to cm.  My beamx determined by the HMS now agree with Dave's graph-paper plot here.  By reading off the lab x position at z= 2.3mm from Dave's plot I get:
Run
 Dave's lab_x (mm)
 Ben's lab_x (mm)
 Bens's std dev of the mean (mm)
51388
 -0.9
 -0.92
 0.02
51389
 -1.2
 -1.23
 0.02
51349
 -1.4
 -1.40
 0.03
51017
 -0.85
 -0.86
 0.05
51610
 -1.3
 -1.25
 0.03
51321
 -1.1
 -1.09
 0.09
51570
 -1.25
 -0.95
 0.15

I then attempted to calibrate the BPM lab x position using the HMS again.  Different conditions were tried because there was no linear relationship between the HMS_x and BPM_x at first.
  1. All optics runs  (hcer_npe>2.0)*
  2. All optics runs with no survey offset (hcer_npe>2.0)
  3. Runs at HMS<20 deg including survey offset (hcer_npe>2.0)
  4. All optics runs with average lab_x calculated assuming hsyptar=0 (hcer_npe>2.0)
  5. Runs with raster turned off, including survey offset and assuming hsyptar=0 (hcer_npe>2.0)
  6. All optics runs, nominal HMS acceptance and assuming hsyptar=0  (hcer_npe>2.0.and.nominal_accept.)
  7. Runs with raster turned off, nominal HMS acceptance and assuming hsyptar=0  (hcer_npe>2.0.and.nominal_accept.)
  8. All optics runs, nominal HMS accept. cut for central fast raster position and assuming hsyptar=0 (hcer_npe>2.0.and.nominal_accept..and.abs(gbeam_x)<0.01)
  9. All optics runs, nominal HMS accept. cut for central fast raster position (hcer_npe>2.0.and.nominal_accept..and.abs(gbeam_x)<0.01)
  10. Runs with raster turned off, nominal HMS acceptance (hcer_npe>2.0.and.nominal_accept.)*
The nominal HMS acceptance was abs(hsyptar)<0.04.and.abs(hsxptar)<0.07.and.abs(hsdelta)<8.

There appears to be a problem with calibrating the BPM using runs where the raster was on.  This can be seen by comparing the slopes in plots 9 (slope=0.414) and 10 (slope=1.065).  Plot number 10 would probably be the most reliable calibration, and it shows the most linear relationship between HMS_x and BPM_x.  It is interesting that the cut on the fast raster position has little effect on the position of the data points (compare 6 and 8), but only increases the error bars on those data points where the raster was on.

The calibration for the BPM horizontal position is therefore:

               LAB_x [cm] = (-0.0355 cm) + 1.065 * (BPM_x [cm])

Where median BPM_x [cm] can be extracted from the epics file using the bpm kumac, median kumac and c++ program.  BPM_y[cm] is also output from this kumac.  Only epics events where the current is > 8uA are used.

Note on std dev of the mean used in the plots:  this was determined by fitting a gaussian to the peak and extracting the sigma and height.
std_dev_of_mean = sqrt ( [sigma] * [bin_size] / ( sqrt(2*pi) * [height]) )
However, all of the errors shown in the plots above for HMS_x need to be scaled by 0.14. This error was corrected in the plots for HMS_y.  Plot numbers 1 and 10 (*) were corrected by this factor.

Comment:  This BPM calibration is of little use if the raster changes the calibration.  Is it the BPM calibration that is affected by the raster, or the average reconstructed position by the HMS?  If it is the latter, then it is safe to use this calibration when the raster is turned on.