User name Johna
Log entry time 04:03:27 on July 16,1999
Entry number 14315
Followups:
keyword=Fast Raster size calibrationOK, here's the fast raster story:
MCC nominal: 3 mm x 1.5 mm (nominal from MCC)
Hall C belief: 4 mm x 2 mm (engine analysis)
Harp scan says: 8 mm x 4 mm
In order to figure it out for sure, we decided to put the beam on the 4cm dummy,
and move the ladder down until we find the edge, and then move it again by a known
quantity (10240 channels per mm on the cryotarget position encoder) in order to
set the scale for the raster size.
We go back to 3x3mm nominal (4x4 according to us) raster that we have been using
for (e,e'p). Move to 4cm dummy target. BAD. The central position of the 4cm
dummy is beyond the hardware limit switch. We make an access to reset the switch,
and then go ~1mm above center. We are entirely on the target. We move the target
down 2mm and find the gap between the 4cm dummy and the +/-6 cm optics target.
Move it down 1mm to see how much the gap moves. Then move 2 more to get
a better lever arm. Figure 1 shows the fast raster x vs y with our nominal calibrations
for the four runs. Comparing upper right to lower right, we see that the the gap
appears to move 2.2mm, when in fact we moved the ladder 3 mm. This is easier to
see in detail in figure 2, which is just the y raster distribution for the four runs.
Since the pattern is 4.4mm total using out calibration, the actual size is 6mm,
lower than the harp scan gave, but larger than our calibration or MCCs. However,
it may be that when we ask for 3x3, they think we mean +/-3mm x +/-3mm.
Final conclusions:
1)The sign of the fast raster y is not what I expected. Something may have been
switched, or maybe it's been like this. It might be worth double checking the
way the FR is corrected for in the reconstruction
2)Rolf has been using a big raster (6x6mm), and we have been running offset from
the center of the Iron target. We have 1mm less clearance then we thought.
3)Raster calbration is screwed up. I've modified the gbeam.param.25490 file in the online_replay and replay_example_latest so that it will use the new calibration
(i.e. scaled calibration factor by 2.2/3.0). I did NOT update the numbers in
gbeam.param.23000.
We ask MCC for 2x1mm (which is +/-2 by +/-1) and begin the target boiling tests.
FIGURE 1
FIGURE 2
