From: IRBY@CMOD.PFC.MIT.EDU
Date: Tue, 19 Aug 1997 8:19:46 -0400 (EDT)
Subject: Alcator C-MOD Weekly Highlights
Newsgroups: sci.physics.plasma
Organization: MIT

Alcator C-MOD Weekly Highlights
August 18, 1997


The Alcator C-Mod maintenance period continued last week with
work on the alternator, DNB, and RF systems. Analysis of data from the
last run period continues.
All wedges have been taken off the alternator rotor, and the
field copper is being removed. The coil cleanup crew is onsite and
will begin cleaning the field copper as soon as they can complete the setup
of their equipment.
Assembly of the DNB beamline in the test lab is complete. The
beamline has been supported in a configuration appropriate for installation
on C-Mod. Quotes on components for the low capacitance transmission line
that will connect the beamline to its power supplies were received,
including those for ductwork, insulators and standard transition boxes.
Location for the transmission line was determined, and design of the
supporting trestles has begun. Development of the PLC interface for the
vacuum system continued, and PARAGON screens on vacuum system status are
now available. Modifications to the waveform generators used with the arc
and mod/reg supplies were completed and tested. We began development of an
improved diagnostic system for collection of the thermocouple and secondary
emission data required to measure beam footprint, neutralization efficiency,
and progress on beam conditioning. System requirements were determined, the
data acquisition system design was completed, and appropriate CAMAC modules
have been located.
A detuned dummy load connected to FMIT#1 has been used to simulate
operation when the antenna match to the plasma load is imperfect due to
changing plasma conditions. As was expected, the final stage gain is phase
dependent. When operating at maximum source power (2 MW), an increase in
gain can result in a screen overload fault, and the transmitter trips
off temporarily. The transmitter arc detectors (there is another pair
of arc detectors located near the antenna) will be tested using the detuned
load as well.
Further analysis and testing of FMIT#4's Uptegraff power supply has
found a failed capacitor in one phase of the supply. Previously the problem
was thought to be blown diodes in one of three secondary legs, but modelling
the power supply with failed diodes could not reproduce the measurements.
When the failed capacitor was included in the model, the model and experimental
measurements were in agreement.
Analysis of the 40 MHz RF Testing and Conditioning experiments
has shown central direct electron heating consistent with excitation of mode
converted Ion Berstein waves. The peaked profile has a full-width half-maximum
of < 0.2 r/a. The analysis was done with by break-in-slope analysis
of the 9 channel grating polychromator ECE diagnostic. The fraction of
total power deposited into electrons as determined by this method is <0.25.
TORIC simulations indicate that approximately 50% of the power is absorbed
directly by ions.
On Thursday of last week the vessel was backfilled with
hydrogen to complete the Core Thomson Scattering calibration.