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



Alcator C-Mod Weekly Highlights
July 26, 1999

Plasma operations continued at Alcator C-Mod last week. Three runs were
scheduled and completed. All the runs were devoted to commissioning of the
ICRF system and conditioning of the antennas.

The shot duty cycle continued to be limited by cooling of the alternator, due
to the relatively high temperature (73F) of the river water at the inlet of
the heat exchanger. Maintenance on the heat exchanger was performed this
weekend, and it is expected that this unit will operate more efficiently in
the next series of runs. Startup reliability was unexpectedly low during the
Wednesday and Thursday runs; it was subsequently discovered that the
pre-ionization source was not operating. This was remedied on Friday and
startup became significantly more dependable.

Physics and Analysis
--------------------

First data from RFPCI (RF phase contrast interferometry) was obtained. The
RFPCI measures the density fluctuation associated with the launched RF wave.
This diagnostic will allow measurement of core RF waves. Probes will continue
to provide information about the edge. Initial analysis suggests that the
amplitude scaled with injected RF power. Further testing and experiments is
required to verify operational and measurement reliability.

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

Good progress was made in conditioning D and E-port antennas. Both FMIT#1 and
#2 worked up to their operational limits. FMIT#1 is limited to between 600 -
800 kW because of its 1 MW plate dissipation limitation. FMIT#2 is limited to
about 1.4 MW by the high voltage supply, which is currently being operated at
the lowest transformer tap position. The anode voltage will be raised on all
the transmitters as the intial commissioning is completed. We were able to
inject up to 1.4 MW into the plasma; however, on some discharges the
transmitter overloaded at the L->H transition. More reliable operation was
achieved at 1.2 MW. Until the anode voltage can be raised, the reliable power
will be limited to this power level.

The first significant power from J-port was obtained as well. Power ramps up
to 600 kW were obtained from FMIT#3 and up to 150 kW from FMIT#4. More
conditioning effort is required to increase the output power and run them
simultaneously.

The repair of the FMIT#3 phase shifter was completed. The FMIT #4 phase
shifter has a G11 push/pull rod like the one in PS#3, and this will probably
need to be replaced in the near future. We plan to continue to run FMIT#4 at
moderate power levels since a great deal of information about J-port antenna
operation can be obtained. The phase shifter will be upgraded as soon as a
several day long window can be scheduled. Components for the upgrade are
being fabricated.

A long-standing problem associated with FMIT#1 breaker was solved. There were
intermittant breaker closings as a result of the relay coil being
marginally driven. Removing a stepdown transformer between the 240V supply
and the relay allowed the breaker to function properly.

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

Finite Element Analysis calculations are being performed on the neutral beam
superstructure from the wall to the tokamak. Results will determine the size
and cross section of the beams to be used to carry the load.

Data Acquisition
----------------

Compaq Corporation and Jorway Systems have been investigating an intermittent
problem we have been experiencing with our CAMAC serial highway equipment. The
problem causes SCSI bus time-outs which often results in the loss of data from
one or more CAMAC modules. During the course of a normal run day we might
experience two or three of these time-outs. Last week Compaq provided us with
a patched SCSI software driver for OpenVMS. Since the new driver was installed
we have not experienced any more of these time-outs.



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

Many C-Mod physicists participated in the 1999 Fusion Summer Study,
"Opportunities and Directions in Fusion Energy Science for the Next Decade"
held at Snowmass, CO, over the last two weeks.

Josh Stillerman attended the 2nd IAEA Technical Committee Meeting on Control,
Data Acquisition and Remote Participation on Fusion Research which was held in
Lisbon, Portugal. Josh gave an oral presentation titled "WWW interfaces for
runtime relational database applications".