From: IRBY@PSFC.MIT.EDU
Reply-To: IRBY@PSFC.MIT.EDU
Subject: Alcator C-Mod Weekly Highlights
Newsgroups: sci.physics.plasma
Organization: sci.physics.plasma

Alcator C-Mod Weekly Highlights
August 7, 2000



After a several day long GN2 purge of the cryostat and magnets to remove air
and water vapor, a cooldown of the C-Mod retaining cylinder and domes was
started on Tuesday of last week. Cooldown of the magnets to approximately
-25 C was completed on Wednesday, and the vacuum bake of the vessel was then
brought up to 120 C. Work also continued last week on RF and
Power systems, and the divertor upgrade.


Engineering
-----------


The two klystrons that had exhibited high voltage breakdowns have now
been successfully tested with new insulators installed. Testing of the
klystrons just returned from PPPL has already begun. We now have ten
klystrons qualified for service. Twelve will be needed for the first
lower hybrid experiments.

The gas fill and pressure indicator system for the ICRF transmission lines
is being modified to accept 1/4'' npt fittings. The D-port phase
shifter has been repaired and installed. The 9'' coax reassembly is
progressing for D, E, and J-port. We have recalibrated the voltage
probes and directional couplers (EDC2, EDC3 and EDC4, and DDC3 and
DDC4).

A water leak in the FMIT#4 anode cooling lines was apparently caused by low
resistivity water has been diagnosed and repaired. The water system was
recently modified to be closed loop to increase the water flow while reducing
the head pressure from the main C-Mod loop. A clogged filter in this new
system eventually resulted in an erroneous resistivity measurement and in a
large current flow through the cooling lines when the transmitter was in
operation. Small pumps are being added to all the cooling systems to
continuously replace the cooling water with high resistivity main loop
water every 20 hours.

We continue to add new diagnostic signals to the power systems in preparation
for long pulse operation. Cabling and conduit are being run, and the
CAMAC equipment required to record the new data installed. Simulations
of the solid state power system components are complete and indicate
all components will operate in a safe range during 10 second long
pulses. Simulations of the main fuses in the system are now underway.

Aluminum prototypes of the new divertor upgrade tiles have been made to
verify the design and drawings. We are now ready to go out for final bids
for the approximately 1000 tiles needed. We are also in the process of
producing a test piece for the tile support structure (girdle). Heat
conductivity tests used to model the heat transfer from the girdle to
the vessel wall indicated a 30% improvement in conductivity when silver
plating was added to the girdle components. We have also successfully tested
a mockup of the tile keeper components. Completion of these inner
wall/divertor modifications is scheduled for the winter maintenance period,
and these changes will allow for full plasma current operation (> 2 ma)
in the 2001 campaign.

Work continued last week on the upgrade to the glow discharge and diborane
systems. The Diborane/Glow discharge rack equipment wiring cleanup was
completed. A new glow discharge HV chassis was installed in the rack and
bench testing has been started. High power resistor rack wiring was
completed. Interconnect cables from the new glow discharge rack to the
Diborane/Glow discharge PLC rack were completed. Multipin connector panels
for the Diborane/Glow discharge PLC rack were wired. The glow discharge switch
control chassis is built and wiring is underway. All design work is complete.
Spare glow paddles are being installed in our vacuum test stand so that the
new system can be checked offline before installation on C-Mod.


Travel and Visits
-----------------

Gary Taylor spent the week at C-Mod working on the GPC2 electron
cyclotron emission diagnostic.