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


Alcator C-Mod Weekly Highlights
July 28, 2003

Alcator C-Mod has completed it's experimental campaigns for fiscal year 2003,
and is currently in a maintenance period. The tokamak is in a standby
mode. Data analysis and modeling of results from the campaign is continuing.

The regular Quarterly Review of the C-Mod Program was held by video-conference
on Monday, July 21, with participation from MIT, PPPL, U. Texas, and DoE
OFES. Presentations are available at
http://www.psfc.mit.edu/cmod/sciprogram/Q_rev_Jul03/

Physics
-------

Analysis of locked mode data with Ip=1 MA, BT=5.4 T indicates that the range
of densities at which the mode appears is reduced from 1.7e20/m^3 with adverse
(i.e. destabilizing) applied 2/1 field to less than 4e19/m^3 with stabilizing
applied field. The factor of >4 in the accessible density indicates that we
are able to compensate the intrinsic error very well in the "best" case. As
previously noted, the C-Mod experiments appear to contradict earlier size
scalings for the threshold error field for mode locking which predicted B_lock
~ R^(-9/5) by a factor>10. The threshold density inferred from 1MA, 5.4T C-Mod
discharges is about a factor of 2 above predictions of dimensionally
constrained scalings based on single-machine fits of DIII-D and JET data.

Diagnostics
------------

The two color interferometer CO2 detector (10 channel) is being refurbished
and its window replaced with coated optics to improve throughput.

ICRF System
------------

FMIT#2 was disassembled and the problem with the driver was identified
as a failed screen by-pass capacitor (a kapton sheet between two
plates). The kapton sheet was replaced and the tube was
successfully hi-potted before reassembly. A control reporting problem
with the driver filament air flow has been investigated and a fix will
be implemented shortly.

Measurements of the D-port resonant loops showed that the high voltage
point was off from the expected location. A new configuration has
been identified and could be tested in the next campaign.

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

Testing has begun on the rear waveguide system . Tests have been completed on
6 out of 48 waveguides. We are able to run up to 500msec pulses at a power
level of 60kW+ and for about 100-200msec at 100kW before transmission line
arcing occurs in the long run from the klystrons to the C-Mod setup area.
There have been no problems in the rear waveguide so far.


Travel and Visitors
-------------------

Stew Zweben(PPPL) was at C-Mod 7/21-7/25 to work on analysis of data from the
summer run. He reviewed GPI data with Jim Terry, discussed TRANSP runs of
MP330 ("Edge Minority Heating for H-mode Control") with Catherine Fiore and
Steve Wukitch, and worked on a code to infer velocity fields from the PSI
camera data. The camera is being returned to PPPL, and will be reinstalled at
C-Mod for the next campaign.

Doug Loesser(PPPL) and Bob Childs (MIT) were at Omley Industries in
Oregon 7/24-25 for discussions on progress in rebrazing the Lower
Hybrid coupler ceramic windows.

Nevell Greenough spent the week at MIT reassembling the Lower Hybrid rear
waveguide for power testing.

Tom Fredian and Joshua Stillerman attended the 4th IAEA Technical Meeting on
Control, Data Acquisition and Remote Participation for Fusion Research, held
at General Atomics in San Diego. Tom Fredian presented a paper: "Migration of
Alcator C-Mod Computer Infrastructure to Linux." Tom Fredian and Joshua
Stillerman also attended the 3rd MDSplus users group meeting, also held at
General Atomics. Fredian chaired the meeting. There were approximately 40
attendees from the US, Europe, Japan and South Korea. A detailed discussion
of "Long Pulse / Continuous extensions to MDSplus" was included in this
meeting.


Bruce Lipschultz co-chaired the ITPA meeting on SOL/divertor physics held in
St. Petersburg Russia the week of July 14, following EPS. A number of studies
on ELM cross-field transport were presented. They indicate that although the
power delivered to the wall in an ELM may not be a concern, that the potential
for sputtering of the wall was significant. A similar concern for the wall
also came up with regard to disruption power deposition. JET either has poor
energy accounting or a substantial fraction of the disruption energy is going
to the wall (primarily during the current quench). The topic of the
wall/blanket tile material was thus a hotly discussed topic. There is a
concern that a Be wall tile will be melted during disruptions with the damaged
surfaces leading to problems during 'normal' operation.



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