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
January 17, 2003


We continued work on the Lower Hybrid, ICRF, and DNB systems this
week. Invessel work also continued, while work on the TF tap, TC, and
heater leads was completed.



Physics
-------

Martin Greenwald presented initial results from the analysis of a new
database table. The new table has been loaded with 34 physics
variables for every EFIT time from every C-Mod shot. This table now
contains over 600,000 records and should be a useful tool for analysis
of long term performance trends. Some trends are easily visible - for
example a drop in Wmhd from efit can be seen for ohmic plasmas
beginning in about CY 2000. A drop in electron temperature at
constant density can also be seen, though this has quite a different
time history. Further analysis, particularly including comparisons with
other kinetic data, will be needed to understand these effects.

A dimensional identity experiment was carried out on JET and Alcator
C-Mod on October - November of 2002. The goal of the experiment is to
create plasmas with identical local edge dimensionless parameters
(collisionality, beta, normalized gyroradius) on tokamaks of different
size, and study the characteristics of the plasmas obtained - global
confinement parameters, local H-mode pedestal characteristics and edge
fluctuations. Similar experiments were done on C-Mod and DIII-D in
2001. The results from the JET/C-Mod run indicate (similar to
DIII-D/C-Mod results) that pedestal profiles are similar in
dimensionally identical plasmas, suggesting that plasma transport
plays a dominant role in formation of the H-mode transport
barrier. However, in the JET/C-Mod experiments JET and C-Mod plasmas
have different confinement characteristics and different edge
fluctuation properties at similar pedestal parameters. More
experimental studies are necessary to understand the observed
differences between JET and DIII-D results. The next stage of this
experiment is scheduled on JET for 21 March 2003.


Operations
----------

Invessel installation of the new lower halo Rogowski was completed
this week. Ultrasonic testing of the moly tiles has begun with the
upper vessel tile survey completed. Four out of the approximately 600
upper tiles were found to be delaminating and will be replaced.

We have completed work on the TF tap and TC lead upgrades and are
proceeding with re-assembly of the cryostat.


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

High-power WR187 directional couplers are being installed. This
installation will complete the waveguide assembly for Cart #1.
Re-measuring of the klystron positions in the cart is complete, and
fabrication drawings for the circulator mounting bracket and water
load supports have now been generated.

Work continues on low power microwave control instrumentation and
software.


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

We continue to simulate placement of new current and voltage probes
for the D- and E-Port antennas. We are finding that small changes in
the location of these probes can result in large changes in response.
This effect is under investigation.

Samples of a ferrite material that might be used for our fast ferrite
tuners have been tested. Initial results indicate that the ferrite
can be used in the design of a 40 to 80 MHz high power phase tuner.

Progress was made on the ICRF instrumentation upgrade.


Diagnostic Neutral Beam
-----------------------

A rebuild of the nitrogen cryo frosting valves was completed early
this week. The valves were re-installed, and the DNB was conditioned
and is now operating at very good performance levels.


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

Amanda Hubbard and Miklos Porkolab attended the FESAC meeting at GA in
San Diego this week. Amanda, who is on the FESAC Development Path
Panel, attended the meeting from Jan 13-16. Miklos attended the
subpanel meeting on the 35 year fusion program (Fasttrack) on Jan 13
and 14 and presented the talk : "High Field Approach to Demo". Ron
Parker attended the NRC meeting, also in San Diego this week.

Martha Redi, PPPL, visited MIT from Jan 13 to 15. Discussion centered
on ITB formation and specific assumptions of impurity levels being
used in the gyrokinetic calculations, with MIT experimental
physicists, Catherine Fiore, John Rice, Paul Bonoli, Jim Terry and
Bruce Lipschultz.

Gerd Schilling, PPPL, was at MIT Jan 16 and 17 for discussions on LHCD
launcher progress. He also participated in a design review of the new
boron nitride tiles for the J-Port ICRF antenna, a design review of
the planned modification of the D- and E-Port ICRF antenna
feedthroughs, and discussions on the final design of the boron nitride
tiles for the LHCD launcher. A further meeting of the C-Mod RF group
generated suggestions for presentations at the RF conference in May.