From:
"Stephen M. Wolfe" <wolfe@psfc.mit.edu>
Reply-To:
wolfe@psfc.mit.edu
Organization: MIT Plasma Science and Fusion
Center
Subject: Alcator C-Mod Weekly Highlights
Newsgroups:
sci.physics.plasma
Alcator
C-Mod Weekly Highlights
May
5, 2003
Plasma operation continued at Alcator C-Mod last week, with
four run days
scheduled and completed. The principal activities were
machine conditioning,
re-comissioning of the ICRF system, and diagnostic
calibration. A total of 80
plasma discharges were produced with startup
reliability of over 90%.
Plasma operations are scheduled to continue
this week.
Operations
----------
All tokamak systems
continued to perform well last week. Overall engineering
reliability was
~90% for the week.
Discharges with upper null and inner-wall limted
equilibria were run in order
to condition all the plasma contact surfaces.
The H/D ratio continues to
decrease as the vessel conditioning proceeds,
and reached the ~10% level in
some discharges on Friday. Brief H-modes
were produced with ICRF heating in
Lower Single Null discharges during
Friday's run, indicating that the proton
fraction is low enough for
minority heating. We are continuing a regimen of
baking at 60C and
electron cyclotron discharge cleaning (ECDC) in deuterium
during
off-operating hours.
Physics
-------
Mode conversion
electron heating was observed during ICRF conditioning
discharges early in
the week, while the H/D ratio was in the ~30-40%
range. Clear
break-in-slope signatures were obtained on the high resolution
FRECE
radiometer signals, which can be analyzed to determine the power
deposition
profile and compare with theoretical predictions.
The Active MHD
Spectroscopy system was operational for all runs last week,
concentrating
on the TAE frequency range around 500kHz. Responses were seen in
both
limited and diverted equilibria. These results are being analyzed.
A
portion of Friday's run was used to cross-calibrate the Thomson
Scattering
density signal to the cut-off of the second harmonic ECE. For
this
calibration, the density is ramped up during the shot and the
toroidal field
is decreased to between 4 and 3.5 tesla. The resulting
cutoff of the ECE
emission is a precise measure of the local density,
which can be used to
determine the absolute calibration of the TS
signal.
Analysis of core toroidal rotation data from the HIREX
system taken during the
locked mode shots observed in run 1030425
indicates that the rotation in these
ohmic L-mode shots slows from ~2e4
m/sec in the counter-current direction to
essentially zero as the locked
mode appears.
ICRF Systems
------------
The D- and E-port
antennas have been conditioned to >1.5MW each at ~20 kV
and the J-port
four-strap antenna was conditioned to ~2.5 MW for short
pulses, into
L-mode plasmas Further conditioning is
required for H-mode
operation which results in higher maximum
voltages.
On Friday a high voltage fault in the screen crowbar unit
prevented operation
of FMIT#4. The
SCR's were replaced and the screen crowbar was successfully
wire
tested. High voltage was then
successfully applied to the transmitter.
Further dummy load tests will be
used to verify operation status.
Diagnostic Neutral Beam
System
-------------------------------
The beam continues to operate
with very good performance. It has been firing
into C-Mod plasmas every
run day with very few faults. Typical parameters are
49 kV, 4A beam
current. BES and MSE diagnostics are
being brought on-line.
Lower Hybrid Project
--------------------
We
continue to bring up the phase and amplitude control system for the
klystrons. A representative from the vendor providing
some of the
control software will be here this week to help develop the
routines
that communicate with our MDS-Plus software. Other programming issues
will also be
addressed.
Mock-ups of the waveguide runs that will connect the
klystrons to the
launcher have been built up in the cell in preparation
for placing
the order for the waveguide.
Travel and
Visitors
----------------------
Paul Bonoli attended the
International Sherwood Fusion
Theory Conference in Corpus Christi, Texas.
He presented a poster
titled "A Comparison of Different Models for
Lower Hybrid Current
Drive". Co-authors on the paper were Miklos
Porkolab and John Wright
from MIT and Bob Harvey from CompX.
Doug
Loesser, Joe Frangipani, and Dave Miller were at MIT this week to
disassemble
the LH launcher for C-Mod vacuum preparation.
Martin Greenwald
visited Dartmouth College to deliver the weekly physics
colloquium and to
confer with Barrett Rogers on edge turbulence and the
density limit.