Based on two runs from last night that have finished crunching, Genya
feels the target thickness is only up 10-20% (ed elastic), instead of an
anticipated 60-80% increase. The fill tube for the 12 mm cell has a
smaller diameter, which makes it harder to get the ABS beam into the
cell. He also finds a low tensor asymmetry, although the statistics are
poor. The vector polarization appears to be ok (hPz=0.55). Even at 100
mA, the cell temperature is up to 110-115 K; we had hoped for lower based
on improvements in the thermal contacts. In short, there are no easy ways
to improve the target thickness, and so it is what it is for the weekend.
On the beam side, the empty target lifetime is about 25 minutes with
reasonable rates in the BQMs and the WC scalers. If the slits are out, the
BQMs are much higher than before. The lifetime is only about 10 minutes
with gas in the target, and the BQM rates are 4 times those of the empty
target. The normalized BQM and WC rates are current-dependent, more so
than in 2004. The empty target rates now are somewhat higher than in
October. The maximum injected current with ABS so far has been 100 mA. On
empty target, the max was as much as 140 mA yesterday.
There is a discrepancy between vacuum gauges that confuses the discussion
on what the pressure is that the beam sees. Ligit is reading 7 times
higher than last year on empty target, but Ligit2 is about the same, and
they're close to each other. The suspicion is that Ligit is not reading
properly.
The suspicion is that the cell walls being closer to the beam interferes
with the stored current. Perhaps there are wakefield effects, or something
to do with the (somewhat) thicker target and ions shifting the beam tune.
If the maximum beam current and lifetime can not be improved over the
weekend, we will be changing to the 15 mm cell next week. Therefore, the
work this weekend will be on improving injection efficiency and improving
the beam tune in the ring. The unpolarized gas feed system will be used,
rather than the ABS. The chief operator will close the valve if he/she
wants to try empty target. The detector HV control GUI will be started in
CCR so the chief can reset HV trips if needed.
BLAST experimenters are to call the chief operator (617-253-9249) before
coming in for shift. Likely you will be told not to come in.
Karen
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:32 EST