Log entry time 00:27:27 on November 07, 2008

Entry number 247192

This entry is a followup to: 246866

We worked with Survey Thursday morning to measure the target positions.
We found:

a) The He3 cell position is basically correct (~1mm or less off the nominal beam axis).

b) The in-beam positions for the rest of the targets (BeO/Optics, Holey Carbon, and reference cell are 4mm high relative to the beam axis when in position. That is, the ladder switch positions that tell the ladder drive to stop are offset high for those targets, but _not_ for the 3He cell. This is why we had to steer the beam to (roughly) +4mm in BPMA/B y to center on the BeO target (and means the associated beam is really 4mm too high on the 3He cell).

c) There's a slight yaw in the entire target ladder -- probably not worth worrying about.

NOTE: The Holey Carbon hole still appears to be high by a few mm relative to the BeO (seen on BPMs and using the laser level: see Entry 246857). I believe I understand the reasons why the other targets positions are 4mm too high, but I don't understand why the C hole is off relative to the BeO.
This discrepancy should be rechecked and fixed when the new target ladder is installed on Monday.

The laser was aligned with a fiducial etched on a vertical post of the target ladder. After working with Survey on the morning of Oct. 6 we found that the laser level (and the etched fiducial) is 4mm higher than the nominal beam axis. I'm guessing that the laser level had originally been aligned to fiducials on the centerline of the RHRS Q1 on the assumption they were on the beam axis. Evidently the RHRS Q1 is high by 4mm...

Official results we be generated by the Survey group in a day or two.

Figure 1: Reference cell vs. laser level. Good alignment to the laser level, but the laser level is 4mm higher than the beam axis. (Photo taken Oct 5).

Figure 2: 3He cell vs. laser level. Laser level is clearly high for this target. (Photo taken Oct. 6).

Figure 1

Figure 2