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


Alcator C-Mod Weekly Highlights
March 14, 2003


We continue invessel work in preparation for pumpdown early next week.
Work on lower hybrid, ICRF, and MSE diagnostic components also
continued.


Physics
-------

John Rice presented data at the weekly Physics meeting indicating that
ohmic L-mode discharges which develop into an upper null configuration
tend to have substantial (~30 km/s) counter toroidal rotation over
most of the core. The amount of power required to produce the equally
substantial co-current rotation observed in normal H-mode discharges
is large, and may be related to the increased H-mode threshold seen
for upper null plasmas.

Alan Lynn, U. Texas FRC, also reported at the Physics meeting that the
FRC ECE radiometer has observed a high-frequency (~80 kHz) mode during
RF centrally heated ITB plasmas at 5.5 T. This mode is localized at or
near the on-axis RF resonance location (~70.4 cm) with a FWHM ~2 cm.
When sawteeth are present, the mode is suppressed at each sawtooth
crash limiting the amplitude to d(Te)/Te < 0.9% . In a few discharges
where sawteeth were not present, this mode was able to grow to large
amplitudes ( d(Te)/Te ~ 4.8% ). Work is ongoing to further
characterize and identify this mode.


Operations
----------

We continue to bring up engineering systems in preparation for
operation. The TORVAC pumping station and RGA are back on-line.
Thermocouple and vessel heater systems are being reconnected and
tested. Most invessel work will be completed this weekend, with
pumpdown expected early next week.

The upgrade of the Active MHD antennas to stand off rf voltages
induced by the ICRF antennas has been completed, and the antennas have
been installed in vessel. The antennas together with their new
triaxial feeds have been designed to handle over 10 kW of rf power
coupled from the ICRF antennas and have been successfully hi-potted to
over 5 kV.


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

Preparations are being made to test operation of the FMIT#3 and #4
transmitters at 53 MHz so that He3 mode conversion heating can be done
at a toroidal field of 5.4 T. We continue work on the new transmitter
control and protection system.


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

At MIT, we continue to test and bring on-line the rf control and
protection circuits for the klystrons. Work also continues on the low
power microwave assemblies and data and timing systems.

At PPPL, attachment and calibration of standard waveguide components
onto the launcher rear waveguide assembly have continued. All vacuum
components have been leak checked successfully separately, and the
fully assembled launcher will soon be leak checked on the vacuum test
stand. Aluminum mock ups of the BN protection tiles have been
fabricated, checked, and found acceptable. The BN tiles are now being
fabricated.

MSE Diagnostic
--------------

We completed fabrication, installation, alignment, and calibration of
the disruption-hardened Motional Stark Effect diagnostic on schedule
this week at MIT. Two large glass mirrors are now cradled along most
of their periphery by a stainless steel "rib" to reduce flexing during
disruptions. The backplates are now comprised of Inconel, rather than
stainless steel, to increase stiffness and reduce eddy-current forces.

Work is resuming on a multi-channel visible Bremsstrahlung background
diagnostic that will provide real-time measurements of the VB noise
level for subtraction from the MSE signals. This system will improve
the capability of MSE to provide q-profile measurements even when the
plasma conditions change during the 50-ms neutral beam pulse,
e.g. across H-mode and ITB transitions.


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

Benjamin Carreras, ORNL, is visiting MIT. He is working with Amanda
Hubbard on L-H dynamics, and Brian LaBombard and Martin Greenwald on
edge turbulence.