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User name A. Puckett
Log entry time 23:51:06 on January21,2009
Entry number 257199
keyword=Swing shift summary
At start of swing shift, beam had just been restored to the full production current and we are taking data. Previous shift had asked for a 0.25 uA/s ramp rate for the beam current because many BB WC trips had occurred after beam trips during day shift. However, at .25 uA/s ramp rate, it takes 56 seconds to ramp up the beam. If there are 15 trips/hour, then we lose ~25% of the beam time to ramping. I asked MCC to increase the ramp rate to 1 uA/s, or 4x the old ramp rate, so that it only takes 14 seconds to ramp up. 14 seconds x 15 trips/hr = 210 s or 3.5 minutes lost/hr.
For about 80 minutes after increasing the ramp rate, there were no trips. The first HV trip occurred at about 19:07 and a second trip occurred a little before 20:00. Then the frequency of the trips started increasing. Eventually it became clear that the MWDC HV trips were associated with beam trips immediately preceded by large beam position excursions. So data taking was very stop and go for most of the evening, although things eventually quieted down during the last hour (fingers crossed...)