[Bteam] report on 11/10 B-team meeting

[Jay Benesch]

I forgot to write down attendees.  Pete Francis, Tony Delacruz, Brad 
Sawatzky, Rob Mahurin and Mark Dalton were among the unusual ones.

Radiation survey done at 0810 11/10 was put up and Qweak folks asked if 
the 10 mR/hr in front of the target, at the 3H09 girder, was expected. 
No one present knew enough of the GEANT model work to reply.  Tungsten 
plug was thought to be the source, but ....  This is an ALARA issue for 
the BPM work.  Qweak tried to keep current low overnight to cut 
radiation at 3H09.  The 11/11 survey is not in the log book. A and B but 
not C.

Problem with the hall C 3H08 and 3H09B BPMs were summarized by me.  Pete 
reported that the 3H09B can was definitely bad.  He had been able to 
borrow a portable network analyzer yesterday morning to check the system 
and found it well out of spec.  3H08 is an M20 instead of an M15.  Both 
BPMs are being replaced today.

Arne asked in the agenda whether this could have been solved in a more 
timely manner, e.g. during the summer down.  For 3H09B the answer is 
yes.  I first elogged the problem July 10 but didn't file an Ops-PR and 
didn't really flag the issue until the current dependence of the Y 
position readback was seen in the last few weeks.  3H08 replacement is 
an opportunistic response to a hall "should", not a must.

We then moved on to a discussion of the 60 Hz phenomenon.  I put up 
hclogs showing the problem as a function of FFB/FF status.  I sent 
others to this bteam list earlier today so I won't do it again.

Scott Higgins summarized what the various modes of FFB/FF on/off do.  He 
wrote this down in
https://hallcweb.jlab.org/hclog/1011_archive/101111102954.html
Hall C has been running with FF DAC switch off.

The reduced efficacy of the FFB system was assigned to anomalous 
response of the vertical FFB correctors.  Unfortunately I pulled up the 
wrong Optim file during the meeting.  Hall C quads are on design.  There 
should be sufficient phase advance between 3H02V and either 3H04V or 
3H07V for FFB to work properly. There isn't.  I asked for CASA 
assistance.  Plan arrived at:

a. take harp traces down the line.
http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1552078

b. download design optics.  Moot since machine is at Optim design optics

c. calibrate FFB system.  Ops couldn't calibrate the system, or at least 
couldn't see any change in the BPMs during the second-long calibration 
and didn't see any calibration graph changes at the mm level.  Scott 
Higgins has turned off/on the crate to force records to zero.  The FFB 
systems in A and C will require full initiation this evening when beam 
is restored.

d. MultiHarp data taken.  See
http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1552098
http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1552099
for elegant analysis results.

AFAIK the FFB corrector response is still anomalous WRT design optics 
expected phase advance.  We'll see what the corrector graphs look like 
when beam is restored and new calibrations are forced by what Scott did.

Due to my Optim file error the group broke up at 1600 hopeful that 
restoring the design optics would improve FFB function.  Since design 
optics was in the machine, quandary remains.

Scott Higgins feels, based on plots in hall C log book overnight, that 
FFB and FF are working as designed.  The problem may "simply" be that 
the vertical 60 Hz is five times the amplitude of the horizontal 60 Hz 
and the FFB/FF can't null the vertical as well as the horizontal.


Todd indicated that he will be ready to start running the meeting 
December 1.  This assumes that there are possible attendees other than 
him who aren't burning up use or lose.