Log entry time 01:42:46 on March 29, 2010

Entry number 314412

This entry is a followup to: 312330

With the new optics tune, it looks like we probably pick up two of the four missing holes from the top and bottom of the expected acceptance. Furthermore, it looks like the left and right arms have different acceptances from either tune from the observed sieve patterns.

For reference, Fig. 1 was from Bob's previous HALOG post regarding this.

http://www.jlab.org/~adaq/halog/html/1003_archive/100320123747.html

We added in an single VDC time offset for each arm, which improved our hole resolution from when we did optics on Monday. Now looking at the data on Monday, there is an asymmetry in the acceptance between the left and right spectrometers, Figs. 2 and 3. It looks like the right arm picks up two additional holes on one side and is missing holes on the other with respect to the left arm.

The right arm also maybe looks a bit different from what Bob had in the aforementioned post. It looks like he has two holes that appear more strongly at phi_tg ~ 0.018, and the two holes at phi ~ -0.012 seem more pronounced in the new data. It almost seems like the acceptance shifted (but maybe we just have better resolution). We re-ran this setting with the previous tune tonight and got pretty much identical results, Fig 4.

To get this shift in the acceptance, something needs to be moved about 1-2mm at the sieve. If it's only from the septum magnet and everything else is centered, this would have to be approximately a 1-2% field difference between the two septa (with the field weaker on the right side). We took a run with the old tune, p0 = 1.063 GeV, but the septum current raised 1.5% (runs 27037, 6383). This still needs to be examined. Furthermore, by all accounts the sieve has been fully in place and the acceptance seems to be reproducible when removing and inserting it, evidenced by tonight.

For the new tune tonight, we seem to get similar patterns as we did before, but with the expected worse resolution. We pick up a couple more holes while the transverse acceptance seems to be about the same, Figs. 5 and 6.

I think the next step would be to do as Bob suggested and use the new tune, play with the quads, and see how the rates change to see if the quads are still limiting the acceptance.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6