Log entry time 00:00:31 on April 01, 2012

Entry number 368795

Followups:

• 368803 04/01/12 00:24 roblin horizontal orbit is the cause for scraping

We have been seeing very weird behavior with the trigger rate on third
arm since we came back from Moller run on Friday. Firstly, immediately
after Moller run the rate went up by six times. The reason for this
increased rate was due to an offset of -3mm on X (1H01 BPM) when we came
back after Moller run. 

MCC fixed this offset Sat. afternoon and rates dropped on thirdarm, but
the not to the level they should be (dropped from 18KHz to 5 kHz, while
the expected rate was only 2-3 Khz). Also, we saw periodic fluctuation(
almost like a sine function) of rate going from 5 KHz to 8 KHz and back.
Moreover, deadtime shot to >50% even with  5Khz rate (thirdarm DAQ can
handle high rates). By changing slow raster sizes we found that at 1.8cm
size, the rate becomes stable and DT goes to normal. My hypothesis is
that with 2cm size the beam is definitely scrapping something with this tune.

We are currently running with 1.8cm raster size and will continue until
we fix the tune. Thirdarm not only works a P_b*P_t monitor, but also as a
beam diagnostics!!