From:
IRBY@PSFC.MIT.EDU
Reply-To: IRBY@PSFC.MIT.EDU
Subject: Alcator C-Mod
Weekly Highlights
Newsgroups: sci.physics.plasma
Organization:
MIT
Alcator C-Mod Weekly Highlights
Jan
2, 2001
Alcator C-Mod
was warmed up last week in preparation for in-vessel
work scheduled to
begin this week. Work on ICRF and Lower
Hybrid equipment,
the glow discharge system, and new tiles and septum for
the J-port
antenna also continued.
Physics
--------
Data obtained from the fast
scanning magnetic and Langmuir probes during
EDA discharges have been
carefully analyzed over the past few weeks.
A strong (~ 5 G at LCFS)
magnetic component of the Quasi-Coherent (QC) mode
in the 100 - 150 kHz
frequency range was found in EDA H-mode together with
local density
fluctuations of (delta n)/n ~ 30% that were sufficiently in
phase with the
electric field fluctuations to drive substantial particle
transport. Thus,
the QC mode appears to be responsible for the increased
edge particle
transport found in EDA H-mode. A letter
is being prepared for
submission to Plasma Physics and Controlled Fusion
entitled "Quasi-Coherent
Signature of Enhanced D alpha H-modes in
Alcator C-Mod", by J. Snipes,
B. LaBombard, M. Greenwald, I.H.
Hutchinson, J. Irby, Y. Lin, A. Mazurenko,
and M. Porkolab.
General Engineering
-------------------
Alcator
C-Mod has been warming up since 12/22 and is now warm enough to
shut down
the GN2 vaporizer and vessel heaters, both necessary operations
required
before in-vessel work can begin. Glow
discharge cleaning
in helium will be run overnight to break down any
remaining heavy boron
hydrides and will, along with multiple backfills
with moist room air, make
the vessel safe for entry.
Work
continued on a new board layout and upgraded design for our ratiomatic
vacuum
gauge controllers. A prototype
controller was tested successfully
during the last week of the run
campaign. These controllers provide an
analog
output proportional to the log of the pressure over the several
decade
pressure range needed during C-Mod operation.
A
modification to the glow discharge system has been made to allow
arc
detection trip points to float with a programmed offset relative
to the
electrode voltages. As adjustments to
electrode current are made,
or electrode voltages change during
conditioning, the trip points now
automatically adjust to these changing
conditions.
ICRF
System
-----------
Preparations for the invessel work on the
J-port antenna continues. The new
boron
nitride tiles, septum, and RF probes are in various stages of
detailed
design or fabrication. An internal
review of proposed changes to
the antenna was held on 12/22/00, and a
decision was made to proceed with the
up-to-air to implement them.
Work
continued on the new demodulator design.
The design incorporates
modern, more easily obtainable limiter and
mixer components, that
will provide more operational reliability and
range. Prototype testing
of the
design is progressing. The new
demodulator is part of an ongoing
upgrade of the ICRF control
system.
Repairs have been made to the phase shifter that limited the
J-port antenna
power level during 70 MHz operation.
Lower Hybrid System
-------------------
The
first Lower Hybrid control chassis from National Instruments
arrived last
week. We have begun to set up the
hardware and bring up
networking capability so that testing can
begin. This system will be used
for
fast control of the lower hybrid RF phase and amplitude. It will control
the power reaching the
launcher from the twelve klystron sources.
Work is
also progressing on new analog fiber optic link
circuitry. Breadboarding of
some
Lower Hybrid protection circuits was also started last week.
DNB
System
----------
A small change to the DNB beamline vacuum
system is being made so that
DNB testing can continue during the
up-to-air.
Visitors and
Travel
-------------------
Tom Fredian visited NIFS in Toki,
Japan to install MDSplus on the CHS
experiment. Tom together with Jeff
Schachter from General Atomics
installed MDSplus and MDSplus related utilities
such as ReviewPlus and
provided training on the use of the software.
Several
people from PPPL visited MIT over the last couple of weeks as part of our
collaboration. Joel Hosea visited on 12/18-19 to join in
the ICRF group
discussions on modifications to the PPPL J-port
antenna. Stewart
Zweben came
12/19-21 to participate in the experiments and obtain
additional edge
turbulence images under different plasma
conditions. The weekly diagnostic neutral beam
meeting was held on
12/18, with
Norton Bretz and Gerrit Kramer attending via videoconference
and Gerd
Schilling attending in person.
Yuri Rokhman and David Terry attended
Labview software programming courses
from 12/18/00 to 12/22/00 at National
Instruments in Woburn, MA.