Late Friday evening, Once again the polarized source 300 kev
acceleration column experienced arcing inside the SF6 pressurized tank.
Recall that we first noticed that last week and traced it to what
appeared to be an old SF6 gas tank (4 years old) and the problem
eventually went away after a newer SF6 gas tank was installed and the
tank was filled.
Last night the problem occurred after about a week of running beam. It
could point to either a) some residual contamination from previous tank
still remains or b) the gas goes bad for some unknown reason after a
period. The first arcing at 300 KV with beam on took some injector
power supplies and IOC down. During a HV processing following this arc
and before the gas change it was arcing at 350 KV after only about 5
minutes. After the gas change, the column was able to hold 350 KV for at
least 75 minutes before we lowered the HV for running at 300 KV.
For the time being, we will run beam as the problem is gone after the
gas load was changed. However, once a week during the snake fill we will
change SF6 gas by emptying the tank, pumping/purging and pressurizing
with new gas load. Hope this will eventually eliminate the problem
completely.
Manouchehr
Electronic Log Book wrote:
>
> Operators: clasie seely ----
>
> no beam until 2pm. ran tensor polarized deuterium.
>
> runs:
> 1553 tensor -, waveplate out, 250 kevents (crunching)
> 1554 tensor -, waveplate out, 250 kevents (crunching)
> 1555 tensor +, waveplate out, 250 kevents (crunching)
>
> problem from previous shift was being solved for most of the day. there was arcing in the polarized source. ccr changed the SF6 again and were able to start running.
>
> 6pole top and 6pole bottom alarms were disabled since they were continually high. this was per ET from previous shift. both were stable all day.
> 6pole top = 1.6e-6 (setpoint = 1.20e-6)
> 6pole bot = 3.9e-6 (setpoint = 3.08e-6)
> stopped taking runs around 3:30pm so HK could do ABS scans.
>
> JS BC
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