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


Alcator C-Mod Highlights
Mar 22, 1999

The scheduled maintenance period on Alcator C-Mod continued last week. No
plasma operation was scheduled. A short, clean vent with He backfill was
carried out on Friday, in order to install a detector array designed to
measure deuterium Lyman alpha emission with high spatial resolution. A visual
inspection of in-vessel components including limiters and ICRF antennas was
carried out using a borescope; all inspected components were found to be in
nominal condition. The vent was completed before noon, and the machine pumped
down again. Electron cyclotron discharge cleaining was run over the
weekend. The maintenance period will continue this week.

The omegatron probe, which combines a gridded energy analyzer and an
ion mass spectrometer, was sucessfully aligned with the toroidal
magnetic field. A fixture was added to permit a few degrees of
rotational freedom from a linear motion bellows. The alignment was
checked by inserting the omegatron into an ECR plasma and measuring
the electron current to the ion collection plates.

The Experimental Program Committee met on Monday to review miniproposals for
the next operational period. Nine new or revised MP's were approved.

ICRF Systems:
-------------

The J-port 78 MHz coax configuration was installed, and the system is now
ready for testing. A fixed decoupling stub, which will replace the
presently-installed tunable stub, is being manufactured along with components
for the 60 MHz configuration. FMIT#3 was tuned to 78 MHz and produced 2+ MW
for short pulses before the transmitter failed. The problem was associated
with a mechanical malfunction that resulted in an arc the FPA output cavity.
One of the drives for the tuning element was slipping. Over time, this
resulted in a misalignment of the tuning element. The tuning element was
replaced by a spare and the drive mechanism was adjusted to avoid this problem
in the future. Chris Brunkhorst (PPPL) has also investigated the placement
and length of an additional stub to lower the plate impedance, which would
lower the necessary voltage to produce 2 MW. The critical path item is
FMIT#3. Once the present problems have been fixed, system testing can begin.

The D-port stub tuner was repaired and installed last week. Initial tests (10
kV high pot and verified range of motion) indicated that the repair was
successful. The more demanding power tests will be done once the system is
evacuated and back-filled with N2.

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

Testing of High Voltage Crowbar was completed. The high voltage system is now
ready for installation and testing of the modulator/regulator circuits. As
was reported last week, we are somewhat behind schedule because of a delay in
the design of the tube reg/monitor PC board, due to a software problem. This
task has now been completed. All other progress continues to be satisfactory.

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

Drs. Noriyuki Inoue and Hisamichi Funaba from LHD/NIFS visited C-Mod on Mar 15
and 16, to review our surface analysis of Mo tiles and dust from the vacuum
chamber, and to look over the laser blow-off system. The LHD and C-Mod glow
discharge and ECR vessel cleaning techniques were also discussed.


Romik Chatterjee of UT-FRC began a 1 month visit to C-Mod to work on
hardware and data analysis for the FRC/AU ECE heterodyne radiometer.
Ashley Shugart, a UT-FRC graduate student and his thesis advisor, Gary
Hallock, arrived to kick off Ashley's first extended visit to C-Mod. While
here, Gary worked with Ashley and Alex Mazurenko (PSFC) to remove
oscillation problems in the PCI amplifiers supplied by UT-FRC for interim
use while new amps are being designed and constructed at UT-FRC. Bill
Rowan, UT-FRC, returned to UT during the week to package and ship fibers
and fiber optic hardware for the CXRS tests.

Raffi Nazikian (PPPL) visited last week to work on the reflectometry
diagnostic on C-Mod with Yijun Lin and Jim Irby. During his visit, he helped
identify the source of a phase error which had been previously noted in
reflectometer profile data. The problem appears to have been magnetic field
effects in a ferritic component; local shielding to remedy this problem is
being implemented. Raffi plans to continue to help with hardware upgrades to
the C-Mod system, bench marking of the PPPL and MIT 2D codes, and data
analysis.