From: IRBY@CMOD.PFC.MIT.EDU
Date: Tue, 12 May 1998 8:52:16 -0400
Reply-To: IRBY@PSFC.MIT.EDU
Message-ID: <980512085216.25a00165@CMOD.PFC.MIT.EDU>
Subject: Alcator C-Mod Weekly Highlights
Newsgroups: sci.physics.plasma
Organization: MIT Plasma Fusion Center


Alcator C-Mod Weekly Highlights
May 11, 1998



A review of the TF magnet was held at MIT on Wednesday, May 6th.
Phil Heitzenroeder and Peter Bonanos from PPPL, Phil Edmonds from U.
Texas and ITER, Herb Becker from Sigmilon, and Bruce Montgomery from
MTechnology were on the review committee. A report will be put together by
the review committee chairman, Peter Bonanos. Presentations on the
magnet, cooling system, power system, thermal and electromagnetic analysis,
and proposed fault and repair scenarios were given.
We continue to make procurements, develop procedures, make soldering
tests, build new inductive heating coils, design fixturing, and disassemble
horizontal magnet arms as we proceed with the magnet repair. The latest
inductive heating tests were quite successful in that we both obtained good
data from a thermocouple array arranged on the test fixture, and were also able
to solder four feltmetal pads onto a finger joint. A 100 kW inductive heating
unit is being procured for installation at MIT. Cleanup of the TF core
is also proceeding. Finally, a testing station capable of quantifying
feltmetal under a variety of temperatures, pressures, and current densities,
while sliding is being assembled.
Recent invessel work has been devoted to making accurate
measurements of the relative position of the outer divertor modules using
a gauge that was employed for this same task in 1995. Similar measurements
were made at that time before the outer divertor was strengthened with
solid pins and stronger mother bolts. These measurements will be compared for
any changes in position. A test fit-up of a prototype divertor
'flapper' valve was performed on nine of the ten outer divertor
modules. The unit was found to clear all existing in-vessel hardware
including the fast-thermocouple array at F-port. Limiter locations were also
measured. The FG limiter was found to be slightly tilted left to right (2 mm).
Both the FG and GH limiters have been removed so that new diagnostics can be
added and old ones reworked where needed. The outer divertor module at
F-port was removed from the vacuum vessel. This unit contains the embedded
fast-thermocouple and the outer divertor Langmuir probe arrays. Repairs
of minor damage to the probe sensors and cabling that occurred over the
last two run campaigns will now proceed. William Carmack from INEEL has
continued to collect dust from invessel during this up-to-air. A careful
sweep of the wall was done shortly after we came up-to-air with a 0.5 um
filter. Clusters of small, spherical, molybdenum particles were found along
with some glass fibers associated with insulation from cabling for some of
our diagnostics. A new sweep under the outer divertor modules has just been
completed and the samples have been shipped out to INEEL.
We continued our progress on the DNB. We began development of the
VAX software that will detect the C-Mod State and facilitate limited control
of the beam. This software will be combined with existing timing software to
create a package that will integrate the beam firing and conditioning cycle
with the C-Mod shot cycle. Work continued on these safety interlocks and the
interface of the Master Control Logic (MCL) system to the PLC and to the
arc/filament/snubber supply. The prototype grid drive board for the Mod/Reg
was completed and is being tested. The construction of the Mod/Reg voltage
divider assembly was completed, and its performance is being optimized.
Conditioning of the oil in the tank shared by the arc/filament/snubber
supplies continued with modest improvement in the breakdown voltage. The
arc/filament/snubber cables were terminated at the snubber and an
insulating support for their continuation to the source in the test lab was
fabricated. Calibration and testing of the control system for the arc
notcher was completed. PLC programming for control and monitoring of the
suppressor supply and switch, safety interlocks, magnet supply and Mod/Reg
were begun.
All parts were ordered for the F-port flange which will be the
location of the DNB and various other diagnostics. An assembly and
installation procedure was developed for the periscope, reciprocating
turbulence probe guide tube, and ECE mirrors which are located together in
a very compact grouping near the bottom of the flange. These and other
aspects of the F-Port flange construction, and the DNB diagnostics will be
reviewed on May 20.
We continue to make progress on RF projects. FMIT#4 has
been disassembled. Initial inspection of the output cavity has found no
arc damage; however, a more complete inspection is underway. We
intend to use a spare tube to test whether the tube is bad or the
arc is in some other part of the transmitter. Preparations for installation
of the DC breaks have been completed. The support brackets are in
place and the shielding material is on hand. PPPL has offered to supply a
female-to-female 9" coaxial elbow to keep the plumbing job moving forward.
The backup Inconel shield for the PPPL antenna is out for bids. This bid
is being pursued in case the proposed design changes to the TZM shield fail to
correct the shock failure problem. Assembly of the antenna in the test stand
continues.
Paul Bonoli has been successful in modelling advanced tokamak
single-null scenarios with ACCOME. He has instituted an error minimization
technique which eliminated a convergence problem. Previously, the
code would begin to converge upon a solution after several iterations
but begin to diverge upon subsequent iterations. Resulting
equilibria from the new error minimizations have been cross checked
by Jesus Ramos using the CAXE code. We have also begun to work on a
patch to connect TORIC with TRANSP until TORIC is fully integrated
with TRANSP (PPPL project undertaken by Dan Clark under the supervision
of Cynthia K. Phillips). This patch will simply import a
TORIC deposition profile into TRANSP. We are implementing this patch
because the SPRUCE code in TRANSP has difficulty with off-axis (r/a >
0.5) D(H) minority heating. This patch has the disadvantage that fast
particle effects upon wave damping will not be accounted for
self-consistently. However, given the high densities at which C-Mod normally
operates, this is a minor effect and we will use SPRUCE
calculations to estimate a tail temperature to be utilized in the
TORIC simulations.
Gary Taylor from PPPL visited last week to work on CAMAC and
analysis software for the new ECE grating polychromator (GPC2).