[BTeam] summary of 3/17/2020 bteam

[Yves Roblin]

The meeting focused upon discussing the path forward for reducing the blm activity in the east arc due to the Hall C beam.  Several measurements or observations (backphasing, chopper viewer , C beam on/off ) point towards the Hall C bunch formation being the culprit.

It is not clear whether or not its only due to the laser pulse or also has other contributions such as the RF bunching.

We decided that thursday at 9 AM we will swap the Hall B/C seed lasers (or just their fibers, Joe Grames will do this by whichever means he deems adequate). At the same time, we will do a chopper intensity scan before doing that change and after doing that change. We estimated the whole thing will take about 4 hours.

Once Hall C comes back (sometimes friday swing), we will be able to observe (via looking at diagnostic blms on the east side) whether or not the beam loss is gone.

We will report saturday morning via emails on what was observed. At this stage, if we still have beam loss issues, monday morning after the 8AM meeting we will convene and decide what the next steps should be . We discussed adjusting prebuncher amplitude or/and 0L04 gang phase. These last two methods will affect the Hall A setup so the beam parity quality would have to be validated.

The A2 interception drift was also discussed.  It is not conclusive whether or not  the C beam being off is what caused it to become stable . More data is needed . It could be a charging or discharging problem.

The gun lifetime is expected to improve as Joe Grames turned back on the biasing voltage (which is supposed to act as an ion trap). Over the next couple of weeks, Joe will assess whether or not we can make it to the end without reactiving the cathode.


As an aside, it would be very beneficial to start documenting things in technotes. For example, there is a significant number of backphasing measurements that were done over the years. Gathering them all together and analysing them would improve our understanding of the longitudinal optics. There is also the issue of calibration of the 4D00 harp versus the viewer. Using one or the other during backphasing results in a significant difference for the bunch length.

There is also an opportunity to do the same thing for beam stability in the early injector. Joe Grames suggested we go back a few years and get a baseline of what the stability typically is.









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