The TPC group discussed the issue of injection runs and had two main point son agenda are below.

a) Do the large event affect the reconstruction and DCA’s of data?

The enclosed observations clearly shows much larger effects than even
the gap cleaning during run 18, before and after changing the filling pattern of bunches.

From Gene

“

Following a discussion of "large" events in the injection runs from today's TPC meeting, here's some documentation on SpaceCharge problems visible in injection runs:

https://drupal.star.bnl.gov/STAR/node/46365

It does indeed look similar to the Abort Gap Cleaning distortions from last year, but they're even bigger and spaced a little farther in time (~6.7 seconds?) now.

It may be possible to perform distortion correction on these using DAQ event size data just as we're doing for the Run 18 AuAu27 data, but given that the distortions are even larger now, I'd have concerns about the model of charge within the TPC.”

Comment:

The frequency of ~6 sec is puzzle.  When the injection is done with 110 bunches it takes about 6 minutes which is ~ 3 sec if bunch injection are spaced equally. Is this the case? Is it because it's the files for fast offline?

b) Do the additional high background during injection cause concern for TPC safety?

It seems that background during injection run causes concerns. Over last weekend there were 3 trips during injection run (see Prahshanth’s e-mail), and Wednesday morning where background were not as good as usual there were 4 trips of which at least one was massive. The TPC hardware expert advice from the is to keep #trips down as it affects the lifetime of the TPC; after about 100 trips on a chamber it is quite likely that HV has to be reduced with diminished performance. 

Strong Recommendation:

Do NOT have TPC HV on during injection and therefore an injection run. As only the last part of the ramping has a probability to trip the HV, the procedure to follow could be to ramp the HV with ~2 min during filling and the last minute after filling is complete (physics on)

·       This will greatly reduce the risk to the TPC operation for the future. Little time will be lost if DAQ have issued a zero triggers, and can start run within second of physics

·       The benefit of having injection runs is not obvious, as the analysis of injection runs shows large DCA that would have to be corrected, and the methods for doing this may have to be modified.