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


Alcator C-Mod Weekly Highlights
February 22, 2000


The Alcator C-Mod up-to-air period ended on Thursday, 2/17, with pumpdown
of the vessel. The ICRF transmitters are coming back online. The
cryostat is being purged with nitrogen gas in preparation for cooldown.


Engineering:

After completing the last installations, final alignments, extensive
documentation, including 35 mm pictures, video, and digital photographs,
and a final wipe down of exposed surfaces, Alcator C-Mod was pumped
down last Thursday. Leaks caused by an improperly installed flange
and window were fixed on Friday and the vessel has now pumped down to
a level at which useful helium leak checking can be done. On Friday we
also verified operation of the cell and power room oxygen alarms, and
then began the GN2 purge of the cryostat, bus tunnel, and magnets. The
humidity detectors in the GN2 line and cryostat indicated rapid removal
of water vapor from the cryo system. We will be able to begin cooldown
of the machine with liquid nitrogen as soon as the moisture level falls
below 10 ppm. The process of bringing the vessel heaters back online
was also begun. A low temperature bake (60 C) of the machine is expected to
begin this week as soon as all these systems have been carefully checked
for proper operation and the vessel has been verified to be leak tight.

The vacuum connection between C-Mod and the DNB was completed. This process
was coordinated with other activities at F-port including installation of
toroidal CXRS optics, installation of an additional lens support for the
MSE/BES optics, installation of waveguide and RF mixer stand for the FRC-ECE
system, and alignment of the FRC turbulence probe.

The J-port antenna electrical characteristics have been measured. The
invessel changes made to the J-port antenna current straps had significantly
changed the electrical characteristics of the antenna. Modifications
to the loop configuration will begin this week.

FMIT#1 and #2 have been tested into a dummy load at up to 2.5 MW without
approaching the tube limits (anode dissipation, anode current, screen
dissipation, screen current, grid dissipation, grid current). We will
begin commissioning and testing FMIT#3 and #4 into a dummy load this
week.

We have completed a modification to the RF demodulator modules used in the
RF data aquisition system. These modules still need power supply upgrades
and re-calibration. A system test of the RF protection circuitry
will begin this week.

Finally, a partial list of invessel work during this up-to-air
period includes:

- addition of a visible TV view of the entire J-port antenna
- new flux probes on two limiters
- new emissive probes on one limiter
- improved TTCI mirror housing
- neutral pressure gauges (5 locations) near the plasma
- refurbished (cleaned) D and E antenna
- designed, fabricated, and installed boron nitride tiles for E antenna
- added 3 additional retroreflectors for inner wall rangefinder measurements
- added MSE shutter (PPPL and Texas)
- refurbished mirror and lens supports for MSE (PPPL and Texas)
- added 2nd set of fibers for tangential edge CXRS (Texas)
- added edge poloidal view for CXRS
- refurbished mirror assembly for McPherson spectrometer
- modified J port antenna to eliminate impurity injections (with PPPL)
- added 2nd Lyman alpha view (inner wall)
- added protective cover over H-port flux loop

In addition, we performed routine maintenance on:

- tiles
- telescopes and periscopes
- limiters and protection tiles
- all flappers
- various gate valves
- many system pumps
- invessel thermocouples

we also

- cleaned and calibrated fibers for core CXRS (Texas)
- calibrated views and refurbished fiber optics for several invessel systems
- completed the neutron calibration
- calibrated the reflectometer
- calibrated Z meter array alignment
- aligned TTCI
- did complete wipe down of vessel walls to remove old boron deposits
and associated compounds


Travel and Visits:

Norton Bretz visited from PPPL to complete work on the MSE diagnostic.
Gary Taylor, PPPL, visited MIT 2/15-17 to remount the GPC2 electronics in a
radiofrequency-shielded enclosure to suppress rf pickup from the J-port
ICRF antenna and to discuss electronics upgrades with Amanda Hubbard.

UT-FRC personnel visiting to complete diagnostic installation work last week
included Keith Carter, Perry Phillips, and David Winslow.