Minutes of Hall A Group Meeting April 6, 2010
1)	Run Report: Mark Dalton
a)	For details see 
http://www.jlab.org/~dalton/presentations/prex_RC
.pdf
b)	Target incident this morning. More later from 
Dave Meekins
c)	Gives status of various commissioning activities 
(Møller, Compton, Detectors, Spectrometer, Beam 
position and alignment, Transverse asymmetry
2)	Dave Meekins
a)	There is a leak in the scattering chamber. As of 
now we don’t know where.
b)	It’s too hot to get near the chamber to hunt for 
the leak.
c)	Meeting with RADCON to discuss options for what 
we can and can’t do and when.
d)	Leak appears to be correlated with motion.
e)	At the earliest we could start to cool down 
sometime tomorrow (4/7)
f)	Best guess is won’t get to really investigate 
until tomorrow and then work from there
3)	Kees de Jager
a)	There is a rumor that the leak started when we 
were running 50 micro-Amps on the thin lead 
target. This is NOT true. We never ran 50 micro-
Amps on the thin lead target.
b)	Between 1 and 2 AM this morning, while we were 
running with the optics target, the radiation 
monitors in the Hall gradually increased to four 
times the level normally associated with 
50 micro-Amps on the thick lead target. This 
looks like something to do with the beam
c)	The target chamber vacuum problem has nothing to 
do with a target operator error in Hall A.
d)	Encourages PREX spokespeople to make the detector 
move now while we’re down anyway. Of course, in 
the end that’s up to the spokespeople to decide.
4)	Bert Manzlak
a)	The lab got good marks during last week’s peer 
review of industrial hygiene
5)	Sirish Nanda
a)	Compton commissioning is going pretty well
b)	Still don’t know the status of the fiber 
amplifier sent back for repairs
6)	Abdurahim Rakhman gives more details about the 
Compton commissioning
a)	For details see: 
http://www.jlab.org/~rahim/Rakhman_HallAMeeting_0
6Apr-2010.pdf
b)	Reviews goals, upgrades, and general status
c)	Shows beam quality
d)	Shows optical setup
e)	Cavity is locking “beautifully”
f)	Problems:
i)	Motorized ¼ wave plate gets stuck sometimes
ii)	EPICS problems communicating with the fiber 
amplifier. Experts working on this.
7)	Megan Friend presents a summary of recent Compton 
data
a)	Summed spectrum for Friday with very low 
background
b)	Compares to high background data
c)	Good Asymmetry, 89% from Friday, very preliminary 
(only 8 laser cycles)
8)	Sasha Glamazdin
a)	Møller Commissioning
b)	Complains about a cable being disconnected in the 
counting house sometime in the March 30-31 
timeframe.
c)	Did alignment/magnet tests
i)	Sent request to alignment group for realignment
d)	Have data from 4 target foils
e)	Magnet and controls running well
f)	Did spin dance measurements yesterday (4/5)
g)	Fast DAQ running and taking data.
9)	Al Gavalya
a)	Working on DVCS now
b)	Waiting for information on g2p
c)	Robin is working on Hall C stuff until further 
notice
d)	Whit is working on SRC and taking software 
classes
10)	Alexandre Camsonne
a)	GEM’s: 
i)	put chambers back with better grounding
ii)	replaced some electronics
b)	Compton: started trying to use the electron 
detector, background was too high
c)	DVCS: setting up DAQ in the testlab
11)	Bob Michaels hopes to get PREX into production 
mode
12)	Jixie Zhang
a)	Reports on He level fall off in the Møller 
solenoid after two hours of running
b)	Suggests having remote control fill capability
c)	Tried new software for analyzing FADC data. Still 
learning.
d)	Re He level: 
i)	Mark Dalton adds that we had 4 left Q1 trips 
over the last week and that magnet shares cryo 
with the Møller.
ii)	Kees adds we should be careful before 
allowing cryo to change anything in the Hall
iii)	Javier gives a long explanation of the cryo 
system for the Møller target (level drops 
7%/hour when running
13)	J-P Chen
a)	Submitted summary of Hall A target cryo needs for 
the rest of 6 GeV running and foreseen 12 GeV 
running
b)	Will give a presentation to the review committee 
next week. They want more details about the 6 GeV 
running.
c)	Polarized 3He: target is setup and can be 
polarized
d)	G2p: Don Crabb says the magnet is at Oxford and 
has been reconditioned. It is ready for cold 
tests. Don will be there for the cold tests. So 
far, no real problems.
14)	Bogdan Wojtsekhowski
a)	Preparing for APEX test run
i)	Parts for new VDC electronics are ready
ii)	S0 counters are tested
iii)	Work is ongoing for re-installation of lead-
glass
iv)	Made a small magnet to compensate for the 
septum field on the beam line
v)	Need to design and build an adapter to install 
the target on the waterfall target lifter
vi)	SLAC is proceeding with ordering parts for 
the target (They will build the target)
b)	VDC repairs:
i)	Making good progress on chamber #4
ii)	Expresses need for a clean tent. We had one, 
but Hall D is using it. Clean tent is useful 
for many detectors. Kees suggests Bogdan talk 
to Eugene re funding to build another tent.
c)	Proceeding with GEn paper
d)	Hears that Mainz is interested in pursuing an A’ 
search too.
15)	Ole Hansen 
a)	Working on replay software:
i)	PREX GEM
ii)	SBS simulations
iii)	High rate VDC analysis for APEX
b)	Wants to install a video card on a workstation in 
the counting house. Bob says OK.
c)	Have some small improvements to the analyzer. 
Will update in the counting house machines.
16)	John LeRose working with PREX on spectrometer 
optics
17)	Arun Saha
a)	Going over Joaquin’s draft thesis. Once that is 
finished will start papers on that.
b)	Working on archival paper
-JJL