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 15, 2002

Plasma operations continued at Alcator C-Mod last week. Four run-days were
scheduled, but only two were accomplished, due to computer problems. A total
of 19 plasma discharges were obtained, with a startup reliability of over
90%. Work continued on the ICRF, DNB, and Lower Hybrid Systems. Plasma
operations are scheduled to continue this week.

Operations
----------

Abbreviated plasma runs were carried out on Wednesday and Thursday last week,
with several hours in the morning of each day being reserved for repair of
some ICRF components and commissioning of the new contol system. The main goal
of the plasma operation was continued clean-up of the tokamak in preparation
for the first boronization of the campaign, now slated to take place early
this week. By Friday, the H/(H+D) ratio was below 10%. A plot of the history
of this ratio over the course of the conditioning can be found at
http://www.psfc.mit.edu/people/irby/htod0712.pdf
A few shots were taken at a reduced toroidal field of 4.5T in order to obtain
a calibration of the ECE temperature diagnostic at this field; most of the
clean-up operation has been conducted at our usual operating field of 5.3T.

A failure in our highly redundant disk storage system (based on RAID
technology) used for data acquisition prevented operation of the machine
through Wednesday. The problem was caused by the failure of two (redundant)
power supplies in the system which in turn corrupted some of the configuration
settings in the RAID controllers. This then caused the data stored on the
system to become corrupted. The supplies were replaced and the files required
for operation of C-Mod were restored from tape backups to enable operation to
resume on Thursday. The remainder of the files (archived C-Mod pulse data,
approximately .5 terabytes) are being restored from tape backups.

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

J-port plasma conditioning was limited by an instrumentation problem that
prevented obtaining a proper antenna match. D-port vacuum conditioning
reached 33 kV; conditioning into plasma will begin once a value of 35kV has
been achieved in vacuum. Vacuum conditioning of the E-port antenna was
limited by a series of problems in the low-power section of the amplifier
chain. A spare 500W amplifier has been installed, and conditioning will resume
this week.


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

Work was done on running water to RF dummy loads on cart #2. New current
probes were installed on Cart #3, and the BNC interface on the cart was
modified to accept the four additional cables. Interface boxes to allow both
body current sensors to travel back to the TPS on one cable were designed and
built.

Our engineers reviewed the HVPS crowbar system designs, and recommended
changes which are being adopted by the supplier. These will protect against
loss of the +5V power supply used for the crowbar trigger and will allow the
crowbar to fire after a supply loss as required.



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

DNB repairs are in progress. The accelerator was returned to operation after
repairing additional arcing damage. The plasma source power supply was found
to have sustained some damage during the original event. The symptoms were
forwarded to the engineers at Budker institute and diagnostic recommendations
were promptly received from them. Matt Sampsell, UT-FRC, was at MIT to finish
calibrating the BES system. The BES spectrometer was absolutely calibrated
and the fiber transmissions measured, enabling a quantitative determination of
the throughput of the in-vessel optics for numerous sightlines. Also, the new
bandpass-filter rotators were calibrated with a spectrometer. This will allow
much more precise positioning of the passband observed by BES.


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

Ian Hutchinson, Earl Marmar, Miklos Porkolab, Joe Snipes, John Rice, and Ron
Parker attended the Fusion Energy Summer Study in Snowmass, CO.

Bill Rowan and Jerry Hughes participated in the 14th Topical Conference on
High Temperature Plasma Diagnostics in Madison, WI.







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