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
Jul 22, 2002

Plasma operations continued at Alcator C-Mod last week. Four run days were
scheduled, but only three were completed. The run on Thursday was deferred in
order to provide time for trouble-shooting and repairs of the ICRF control
system. The main goals of this week's operation were evaluation of the first
boronization of the campaign and continued conditioning of the ICRF
antennas. Discharge development for planned experiments later in the campaign
was also accomplished. A total of 38 plasma discharges were produced, with a
startup reliability of 70%. Work continued on the Lower Hybrid and Diagnostic
Neutral Beam Systems. Seven C-Mod physicists were off-site, participating in
the Snowmass Fusion Summer Study. Thirty-eight abstracts related to C-Mod
results, including 13 contributed oral presentations and two invited talks,
were submitted to the APS to be presented at the November meeting of the
Division of Plasma Physics in Orlando, FL.

Plasma operations are scheduled to continue this week.

Operations
----------

The first boronization of the present campaign was successfully carried out on
Monday evening. Approximately 2050 A of boron was deposited; this coating is
about the same thickness used during the previous campaign. The run on Tuesday
was largely devoted to evaluation of and recovery from the boronization. As is
typical, the startup reliability on the first operating day after boronization
was degraded at first, but improved during the day; reliability later in the
week was at the 80% level. The H/D ratio was observed on Tuesday to be in the
3% range, a factor of two or more reduction from the pre-boronization levels
and suitable for hydrogen minority heating experiments. Radiated power, as
measured by the 2pi diode bolometer, was also down by over a factor of two
from pre-boronization levels.

The remainder of the week's runs were devoted primarily to RF antenna
conditioning. ICRF instrumentation problems noted in the earlier runs were
identified and repaired on Thursday. While these repairs were taking place, a
series of no plasma shots were carried out in order to calibrate the gas puff
valves. RF conditioning into plasmas resumed on Friday, reaching MW power
levels. This activity will continue this week. Also on Friday, equilibrium
development in support of future experiments was carried out, including shape
development for a JET similarity experiment and low-triangularity equilibria
for investigations of the shape dependence of the EDA regime.

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

Antenna operation into plasma was begun after boronization. Boronization had
a significant negative impact on antenna conditioning, requiring additional
vacuum conditioning shots. Operation was further hindered by false phase
balance and voltage faults that were identified and fixed for the run on
Friday. Antenna operation on Friday was significantly improved over
Wednesday. Before the run, the D and E-port were vacuum conditioned to 35 kV
(0.5 sec) and the voltage and phase balance fault electronics were modified to
eliminate oscillation in an instrumentation amplifier. Operating into plasma,
D-port and E-port reached 20 kV and 25 kV respectively. They also operated to
~1.4 MW together. J-port had less vacuum conditioning and its operation into
plasma reflected this fact. J-port required a fast rise time (~1 msec to 100
kW) at low power to avoid what appears to be discharge formation. D and
E-port still require more vacuum and plasma conditioning. J-port requires
significantly more vacuum conditioning and work on the phase feedback
instrumentation.

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

During the week, the suppressor supply was repaired. Several capacitors in
the accelerator bank were replaced and several open bleed resistors were
found. Repairs on the DNB power supplies have progressed to the point that
the beam has again started firing at nearly full parameters (50 kV, 3 A, 40
ms). Issues concerning the regulation of the arc current are still being
investigated. The Budker group in Novosibirsk has been extremely helpful in
aiding our engineers on this repair. The next operation of the beam will be
early this week and will be intended to check the regulation of the arc
supply.


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

Fast current sensors to measure body current were installed on transmitter
#3. Coax cables were run from current sensors to the cart external interface.
The external interface was modified on cart #3 to accept four new cables. An
interface box consisting of resistor and diode was constructed to allow new
and old current sensors to share same cable to the TPS. Back panels for EMI
racks for transmitters #1 & 2 were modified to accept interface board #1, and
Rivnut installation was begun for these modified back panels.

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

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

Martha Redi visited MIT July 15-17th, working with Catherine Fiore, Steve
Wukitch and Darin Ernst on nonlinear gyrokinetic simulations of the C-Mod
ohmic H-mode and off-axis RF internal transport barrier experiments. Gerd
Schilling was at MIT July 15-19, continuing to help to bring up the ICRF
system.





-----------------------------------------------------------------------

The contents of this message have been scanned for viruses by
the Clearswift ES Policy Server, and no viruses were found.