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


Alcator Weekly Highlights
August 4, 2003


Alcator C-Mod continues a period of maintenance. Work proceeded last
week on preparations for the alternator inspection, high power testing
of lower hybrid components, and work on ICRF systems.


Physics
-------

Stewart Zweben, PPPL, was at MIT this week to continue analyzing data
from the "Edge Minority Heating" experiment in June. First results
from TRANSP runs done by Catherine Fiore suggest a significant
fraction of minority ion tail loss for the inner edge resonance
location. First analysis of the fast GPI diode data show an apparent
reduction in edge light fluctuations during edge RF; however, this
effect may be due to profile changes rather than electric field
changes, since the frequency spectrum does not change significantly
with RF.


Operations
----------

Alcator C-Mod is now at room temperature and the vessel heaters have
been turned off. Maintenance work on the cryostat and LN2 cooling
system will begin this week.

Preparations for the alternator inspection which will begin early this
week have continued. The 2 MW drive motor has been removed from the
drive train. Instrumentation and electrical connections have also
been removed. Vendor equipment needed for the inspection has arrived
on-site.


Lower Hybrid Project
--------------------

At MIT, the first high power tests of the lower hybrid rear waveguide
assembly (RWG) were conducted successfully last week. From 35 to 60 kW
of power for up to 250 ms was delivered to several of the coupler
channels. The tests were limited by arcs in the waveguide delivering
power to the RWG from the cell. We are investigating the cause of
these arcs. This waveguide run is temporary and was set up for these
tests only; it will not be used when the system is installed onto
C-Mod. Nevell Greenough, PPPL, spent last week at MIT working with
Monty Grimes to complete the RWG testing.

A decision has been made by PPPL and MIT to remove the ceramic window
bricks from the titanium couplers based on the results received from a
series of prototype coupler braze tests performed by our vendor over
the past month. A new set of test brazes will be performed on
prototype couplers that will have the ceramic windows removed using a
braze removal process being developed by another of our vendors. In
parallel, a purchase order will be awarded to have 150 new ceramic
bricks fabricated and metalized to facilitate re-brazing with new
ceramic bricks if the old bricks are not usable. This new scope will
reduce the risk of failed braze attempts on the four couplers and also
remove and replace several ceramic windows that cracked during the
initial brazing process.

MIT and PPPL worked together to analyze the mechanical stresses in the
titanium couplers and ceramic windows induced during the braze
process. There is some concern that the ceramic windows will crack
when they are removed from the couplers. This issue also relates to
the cracks seen in some of the ceramic windows. MIT will continue this
analysis work and try to identify the source of the cracking.

Low power testing of the forward stacked waveguide assembly (FWG) was
completed at PPPL this week with very good results from 91 of the 96
waveguides (losses less than 0.4 db). Five channels have losses
greater than 0.5 db and will be reworked to reduce these losses to an
acceptable level. To investigate the value of hand polishing
discolored blotches on the copper plating, PPPL will disassemble one
FWG stack and hand polish five adjacent plates at one end of the
stack. After polishing, the plates will be reassembled into the stack
and re-tested at low power to determine the effect of polishing on
losses. The polishing fixture was delivered from the local machine
shop this week to support this effort. A decision will be made next
week on whether to polish all the plates or to start final assembly of
the FWG.


ICRF Systems
------------

A driver grid capacitor and some associated interlock instrumentation
have been repaired on the FMIT #2 transmitter. Testing and tuning of
the driver is planned for this week

ICRF related hi-yard equipment has been inspected as part of routine
maintenance of these systems.


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

Miklos Porkolab and Martin Greenwald traveled to Gaithersburg, Md to
attend a meeting of the Fusion Energy Sciences Advisory Committee on
Thursday and Friday of last week.


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