From: IRBY@PSFC.MIT.EDU
Date: Tue, 26 Aug 1997 07:53:25 EST5EDT4,M4.1.0,M10.5.0
Message-ID: <009B957D.98797920.23@woods.uml.edu>
Subject: Alcator C-MOD Weekly Highlights
Newsgroups: sci.physics.plasma
Organization: MIT



Alcator C-MOD Weekly Highlights
August 25, 1997


The Alcator C-Mod maintenance period continued last week with
work on the alternator, DNB, Power, and RF systems. Analysis of data from
the last run period continues.
Rapid progress is being made on the alternator repair. All
field coil copper has been removed from the rotor, and much of it has
been cleaned. Clean up of the rotor forging has begun, and ultrasonic
testing is expected to begin in the next few days.
Assembly of the DNB beamline vacuum system was completed and control
cables installed. During tests of the backing pump, the beamline was partially
evacuated. Control cables and connection points in the DNB vacuum system
controller were identified for use by the PLC interface. Testing of the
CAMAC modules for the thermocouple/secondary emission data acquisition
system began at UT-FRC and will be shipped to MIT as soon as the testing is
done. Several options for the isolation amplifier system were identified, and
these are being compared. Control wiring for the variac cabinet was
completed. Work has started on the control wiring for the magnet supply.
We have begun work on the TF power supply aimed at determining
the cause of junction overtemp trips during the last run campaign. The
overtemp circuits are being fed simulated TF waveforms in an attempt to
reproduce the trip conditions.
Maintenance on FMIT#1 and #2 is continuing. Both transmitters are
undergoing testing into an detuned dummy load, and the arc detection system in
the power room is being tested. New tuned arc detectors have been designed.
The tuned arc detectors will be installed on D and E ports to isolate
the signal from each antenna. This upgrade will allow the arc
detector to better discriminate against power radiated from one antenna to
the other, which has often caused erroneous trips of the arc detection circuits.
The demodulator calibration is nearing completion and the H-probe has
been repaired and awaits pressure testing. The PLC wiring for FMIT#3
and FMIT#4 is continuing and the 120 V power to the new racks in the control
room has been upgraded.
J. Snipes, in collaboration with King-Lap Wong and Guoyong Fu of PPPL
is making comparisons between experimental data and rough calculations of the
Toroidal Alfven Eigenmode physics. Short bursts of fluctuations have been
observed on poloidal field pick-up coil signals during strong ICRF heating
applied early in the current rise. The oscillation frequency varies from
about 200 to 400 kHz in approximately 15 ms with a very sharp
frequency spectrum (FWHM of less than 10 kHz, 1 ms window). The comparisons
with TAE theory suggest that a fast ion tail driven by the central resonant
H minority ICRH could be responsible for driving TAE modes under these
conditions. Measurements with a charge exchange analyzer indicate that there
was indeed a strong H ion tail present out to energies of at least 100 keV
during the relatively low density (1 x 10^20 m^-3) ramp-up phase of the
discharge with strong ICRF heating. TRANSP calculations with FPPRF also
indicate tail energies of about 100 keV.
Craig Petty of DIII-D spent two days at the PSFC discussing analysis
of dimensionless scaling experiments. Approximately half the time was
spent going over analysis of DIII-D/C-Mod non-dimensional identity L-mode
experiments which were conducted last year, and half on future plans. These
included dimensionless scaling experiments of L and H-mode confinement,
particle (impurity) transport, L/H threshold, MHD, and turbulence. Dr. Petty
also presented a seminar on results of non-dimensional scaling experiments
and implications for future devices.