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Archived Messages for HALLA_MIN_1996@cebaf.gov: Minutes
Minutes
John LeRose (lerose@CEBAF.GOV)
Thu, 12 Dec 1996 17:03:04 -0500
Minutes of Hall A Group Meeting 10 December 1996
1 Hadron Dipole:
1.1 As reported at the emergency meeting yesterday
(9 December), the hadron dipole has developed
problems - potentially VERY serious. These
notes incorporate both information presented at
the weekly hall meeting (Tuesday) and
additional information from tests Tuesday
afternoon and this Wednesday morning.)
Wednesday of last week the dipole was fully
cold and ready for detailed tests following
repairs to the instrumentation leads
necessitated by incorrect wiring of the dump
resistor. Initial tests were very promising
with the magnet behavior as anticipated. The
magnet was operated successively at 200, 400,
600, 800, 1000, 1200, 1400 Amps, and 1500
Amps(~1500Amps corresponds to 4 GeV). At each
current it was exercised with a slow dump, the
current was restored, and then it was exercised
with a fast dump. Thursday was spent operating
the magnet at 1000 A while the cryo group tried
to sort out unrelated problems in cryogen
delivery ultimately traced to an insulating
vacuum problem in the transfer line. On Friday
we resumed testing, trying to go to 1500 Amps
resulted in a trip of the protection circuits
and an unexpected pressure burst in the helium
return line and a temperature rise was observed
in the lower portion of the cryostat.
Attempts to turn the magnet back on were made
difficult by the quench detection circuit
tripping out at ~600 A. We now know that this
was due to a change in at least one of the two
coils resulting in differing voltage drops
across them during current transients. A
series of tests (with the current limited to
<200 Amperes) have been undertaken to try to
understand exactly what has happened in the
coil and what is the best approach to solving
(or living with) the problems we now have. We
knew yesterday that the apparent coil
inductance (as measured by observing the charge
and discharge rates) has changed significantly
(about a factor of 3), and that the coils were
no longer symmetric. A measurement of the
magnetic field at 200 Amps (corresponding to
about 500 MeV/c) gave a field within 90% of the
expected value but with a very slow ramp up
time. Finally, the insulation resistance of
the magnet/power supply system had dropped from
a few MOhms to about 210 kOhms.
1.2 New information since Monday's meeting:
1.2.1 there are no significant ground fault
currents (ruling out explanations
associated with a time-dependent short to
ground)
1.2.2 measurements of coil voltages as function
of time correlate to changes in field.
1.2.3 measurements of the field vs. current
ramping up to 200 Amps in the electron arm
dipole indicate that its "settling time"
is much faster than that of the hadron arm
at the same current, and confirmed the
expected value of the magnetic field for
200 Amp current (presuming the same number
of turns in both dipole coils!).
1.2.4 measurements of the apparent inductance
using di/dt as provided by one of the
Lakeshore power supplies (which are easier
to use as they regulate well at low
currents and do not incorporate the quench
detection trip circuitry) confirms the
results of decay time constant
measurements that the apparent inductance
of one of the coils is significantly low.
1.2.5 the power supply has good insulation
resistance (about 11 MOhms) and the coil
insulation resistance remains about 210
kOhms.
1.3 Actions:
1.3.1 Verifying status of all taps and bringing
out lead that provides data on the voltage
on the splice between the two coils.
1.3.2 Measuring dc resistance of the power
leads, each coil, and the splice using a
100 Ampere current and sensitive
voltmeter.
1.3.3 Verifying which of the instrumentation
leads is connected to which part of the
coil system.
1.3.4 Repeating resistance measurements at
elevated temperature (where SC wire is no
longer superconducting).
1.4 Possible explanations of the current situation
include a resistive splice (or a resistive
joint between the coil and one of the power
leads), a break in the superconducting wire
(but not in the copper matrix), and turn-to-
turn shorts between the copper matrix holding
the superconducting wire. Much more thoughtful
analysis and tests will be necessary before we
can make a complete diagnosis of the problem.
Until we have resolved the open questions about
the dipole it will be necessary to minimize
operation of the coil to supervised tests at
low currents. We will not run the magnet for
tests of the spectrometer until we have a
diagnosis we believe and can operate the magnet
with confidence that we will not do further
damage. As a result the upcoming run
(nominally planned for the first beam delivery
to the hadron arm) will be shortened and
operations confined to additional single-arm
tests with the electron spectrometer.
2 Field Measuring and Monitoring: (John LeRose)
2.1 NMR probes in Hadron Arm dipole appear to be
working fine.
2.2 Helping with diagnostic measurements on Hadron
Dipole.
3 Commissioning: (Eddy Offermann)
3.1 Struggling with ESPACE.
3.2 Has problems with computer center re
compatibility of different platforms.
3.2.1 Meme has problems too.
3.2.2 Larry asks for detailed list of specific
problems and he’ll see what he can do.
3.3 Run plan for weekend to be discussed at end.
4 Beamline: (Arun Saha)
4.1 Pascal Vernin gives status report on field
measurements in arc dipoles.
4.1.1 Made several checks and improvements on
device used in Test Lab for old
measurements (1992)
4.1.2 Compared new data to old data.
4.1.2.1 Reproducibility improved by a
factor of 2. Now seeing
reproducibility on the order of 1E-04
4.1.2.2 Some possible aging of the magnets
observed.
4.1.3 To get better need to look into the
electronics.
4.1.4 We will have to remap all the magnets to
get what we need.
4.1.5 Draft report on superharp measurements is
available. (See Arun for copies)
4.2 Franco Garibaldi reports on waterfall target.
4.2.1 Movement problems appear to have been
corrected.
4.2.1.1 Communication between computers
improved.
4.2.1.2 Emergency stop switch installed in
counting house. Allows you to stop
movement in the event of a computer
hang-up. Should reduce likelihood of
a limit switch being engaged which
requires a hall access to reset.
5 DAQ: (Bob Michaels)
5.1 Nilange is unifying the Hadron and Electron
codes
5.2 Sarik has written a script for transferring
files to mass storage
5.3 Setting fastbus test stand.
6 Cryotarget: (Jian-Ping Chen)
6.1 Working on cells and cell blocks.
6.1.1 refining etching techniques to better
control thickness
6.1.2 pressure testing. 3 mil thick cell bursts
at 80 psi (marginal). Expect to operate at
25-30 psi.
6.1.3 have starting plating
6.1.4 Dimitri Margoziotis reports on tests of He
cells
6.1.4.1 Still breaking on solder joints.
Have gotten up to 440 psi
6.1.4.2 Cell bursts at 520 psi with o-ring
instead of solder seals. (o-rings
won’t work at cryo temperatures)
6.2 Students and post-docs working on same things
as last week.
7 Hadron Detector Electronics and Waterfall Target:
(Meihua “Meme” Liang)
7.1 Looking at data from 1st Waterfall runs.
Checking stability of target density.
7.2 Optimizing data base for Hadron arm
8 Detectors: (Bogdan Wojtsekhowski)
8.1 Both arms ready to run
8.2 Plane #3 problem still exists but is smaller
8.3 Preparing for Cerenkov counter tests
8.4 George Lolos reports on status of damaged
aerogel
8.4.1 Have cut what was useable. (enough to
instrument several sections)
8.4.2 Aerogel is baking
8.4.3 Both Baking and cutting went smoothly.
Will install into counter tomorrow
(11 December)
8.4.4 Triggered discussion about new “KEK”
aerogel. Franco reports on experiences
(better but expensive)
9 Ops Manual and Møller Polarimeter: (Sirish Nanda)
9.1 Ops manual almost complete.
9.2 Møller Polarimeter:
9.2.1 After meeting with accelerator folks,
schedule now looks firm for 1 phase
installation (29 April - 15 May)
9.2.2 Victor Gorbenko and R. Pomatsalyuk are
leaving next week. Will return in
February.
9.2.3 Victor reports on latest developments with
polarized target.
9.2.3.1 Reviewed schedule/task list
9.2.3.2 Vacuum and cryo testing completed
9.2.3.3 Magnetization testing and
calibration completed
9.2.3.4 Vacuum chamber with Helholtz Coils
and top and bottom flanges ready for
installation.
10 Miscellania:
10.1 Eddy Offermann points out that Will Oren needs
to know how many angle changes will be
required for both oxygen experiments. Arun Saha
and Paul Rutt promise definitive statement
within one hour of close of the meeting.
10.2 Eddy also announces that his studies show that
the addition of an 8 mil Kevlar window at the
entrance of the spectrometer is not a problem.
The exit window still dominates.
11 Weekend Run Plan:
11.1 Electron Arm 845 MeV
11.2 Full solid angle y0 .ne. 0.
11.3 Repeat sieve slit measurements to test
reproducibility.
11.4 All with waterfall target
11.5 Spectrometer as is. (mispointing by 2 cm)
11.6 target thickness measurements
11.7 Shower counter calibrations
11.8 Mohamad Khayat has prepared a document
outlining plan. Eddy has a copy.
12 Quarterly Report: (Larry Cardman)
12.1 Reviewed and discussed content
12.2 Copies available from Larry.
12.3 Will be discussed at the Director’s Council
meeting one week from tomorrow (18 December)
12.4 Content is attached.
-JJL
Hall A: 1/97-3/98
Status:
Electron Spectrometer operational and optical
commissioning essentially complete; performance matches
expectations
Hadron Spectrometer has a serious problem, not yet
fully understood. Worst case downside will be $2M and a
year delay in hall turnon for physics. (The remainder of
this memo assumes we are lucky and can fix it by the end
of January).
Hall Collaboration student & postdoc buildup continues
to progress well.
New Hall Leader (Kees de Jager) arrives 1/2/97.
Basic planning for first year of physics well advanced
- slight delays relative to last quarter due to the
realities of accelerator scheduling.
Ancillary apparatus (cryotarget, polarimetry, beam
energy monitoring, etc.) progressing but still
incomplete.
1/97-3/98 Goals:
Must:
Complete and commission the HRS Spectrometer Pair and
Detector Packages (4/97).
Install and commission the Spectrometer Positioning
System (9/97) and basic beamline Instrumentation
(position and charge measurement; and raster) (5/97).
Complete the 16O(e,e'p) commissioning experiment (1st
half) (7/97).
Install and commission the Møller Spectrometer (by
5/97).
Complete 16O( ,e' ), or, at least 16O(e,e' ) (2nd half
of commissioning experiment w/ polarization at least in
HRSH, i.e. polarimeter working, preferably also)
(7/97).
Complete, install, and commission the Hall A cryotarget
(9/97).
Complete the first complete Hall A experiment (deuteron
form factor) (10/97).
Should:
Complete parity beam tests (Þ ready for 1st PV
experiment) (12/97; must by 3/98).
Install and commission the ARC and (e,p) energy
measurement systems (5/97).
Complete the Second Major Experiment (Virtual Compton
Scattering) (12/97).
Complete the Third Major Experiment (GEp measurement)
(3/98).
Like:
Beam test of polarized 3He target cell (5/97)
Install Compton Polarimeter (9/97-1/98) and begin
commissioning.
Start first post-commissioning experiment.
Improved beamline instrumentation: high precision
(0.1%) current measurement; and on-line beam energy
spectrum measurement implemented (12/97)
Issues:
Hadron Dipole Problem Solution
Will need Accel. Div. technical support for
installation of ancillary equipment.
Must eliminate high radiation associated with tuneup of
beam to Hall A