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
May
28, 2001
Plasma operations continued on Alcator C-Mod last week. Two
run days were
scheduled and completed, with the primary focus being
machine clean-up and
conditioning in preparation for physics operation. A
total of 20 plasma shots
were produced, most lasting over 1 second;
startup reliability was nearly 75%,
which is very high for this early in
the campaign.
Operation will continue this week.
Physics
-------
Reflectometry study shows the quasi-coherent (QC) mode associated
with EDA
H-modes is usually localized near the center of the density
pedestal. The
radial width of the mode is estimated to be in the range of
0.1 cm < W < 0.3
cm, where W is the full-width at the half mode
magnitude. W is weakly
dependent on the electron temperature; generally,
the higher the temperature,
the narrower the width. The width inferred
from the reflectometer is similar
to that observed by a Langmuir probe in
several ohmic EDA discharges
(A. Hubbard, et al, Phys. of Plasmas, 8(5),
2033(2001)). Study of the
reflectometry
data also found that the saturated mode level in steady EDA
periods scales
with the parameter (\nu^*q_{95}^2)^0.56. This result suggests
that the
higher \nu^* and higher q_95, the higher transport effect the QC mode
may
have.
Operations
----------
Following the successful
plasma startups obtained during the previous week,
ECDC was continued over
the weekend and during the first three days of last
week. Plasma runs were
scheduled for Thursday and Friday, with the main goals
being to begin the
clean-up and conditioning process. Additional goals
included beam-into-gas
tests, with toroidal field, for the DNB diagnostics,
and diagnostic
checkout. Excellent progress was made in all areas. By Friday,
full length
plasma discharges were being routinely produced with currents up
to 800kA.
In addition to beam-into-gas shots on Thursday, the DNB was
successfully
fired into plasma discharges. Signal to
noise of the MSE system
was good, with signals seen on all channels. The RF group brought the D- and
E-port
antennas up to 1MW reliably delivered into plasma, achieving this
result ahead
of schedule.
The H/D ratio was very high (>2), so there was very
little chance of seeing
any heating from the RF. Most of the fueling was from the wall rather than
the D2
puff. The new Penning gauges are
working and some tests of the
divertor BC gauge with the BC flapper in
operation were made. Preliminary
results
from these tests indicate rather low gas flow through the flapper.
The
rotation measurements were brought back online on Friday. Some oxygen was
seen by the McPherson
UV spectrometer during the rf pulses, but no carbon.
Next week's
runs will be aimed at continued machine clean-up, reducing the H/D
ratio,
and continued conditioning of the ICRF systems, as well as continuing
the
DNB development work and bringing additional diagnostic systems online.
ICRF
System
-----------
ICRF system checkout, calibration and vacuum
conditioning of the ICRF
antennas continued this week. All antennas have been tested and are
at
various stages in conditioning. D and E
have been conditioned to
~40 kV while J-port has been conditioned to ~25
kV (35 kV will be
sufficient to begin plasma operation). The progress on J-port antenna
is
somewhat slower because there were additional diagnostics to
check
out. The tuning calibration was
completed on D and E-port and both
antennas were operated into plasma on
Friday, for the first time in
this campaign. Both antennas are performing
well, with over 1MW total
power coupled, although the high hydrogen
fraction in these targets is
unsuitable for minority heating. At this
stage, the main focus is on
conditioning the antennas at high power, and
reducing the gas influx
coming from the antenna during operation.
Diagnostic
Neutral Beam System
------------------------------
The DNB
continued to operate this week. The
main goal was to acquire data for
beam into a gas filled tokamak. This goal was primarily for MSE
calibration
and for assessment of beam excitation. The beam was fired into plasma for the
first
time during this run period. BES and
MSE data were acquired.
Lower Hybrid MIE Project
------------------------
All
PC Boards for the transmitter control and protection system, except
optical
interface, were ordered. Bids were
solicited from PC board
manufacturers, and a vendor was selected and the
purchase requisition
released. A
comprehensive parts list for electronics parts needed to populate
the
Lower Hybrid transmitter and coupler PC boards was compiled. The parts
list was sent out for
quotation. Purchase requisitions were
prepared and
released based on price, minimum quantities and lead
time. On Thursday, a
joint
internal design workshop was conducted with PPPL.
Inner Divertor
Project
-----------------------
All 1300 tiles have been
received, checked, and are now in-house; 1000 of
these have been baked and
cleaned. All of the tiles screws have been silver
plated, and the plating
quality is excellent. All screws have been baked,
cleaned, and stored in
the clean room.
Machining of ribs on the Upper Section of the Rear
Girdle plates is
proceeding. Ribs on the main body of the two steel plates
and 12 Inconel
plates are complete. Delivery of these plates is now
projected for the end of
June.
Visitors and Travel
-------------------
Many collaborators from PPPL were at MIT this week to work on LH,
RF,
modelling, and diagnostic projects.
Martha Redi (PPPL) came 5/21-22 and
continued her transport
modeling, working with Catherine Fiore, Steve Wolfe
and Paul Bonoli on the
ohmic H-mode and off axis RF heating TRANSP runs and
EFITs needed for the
GS2 analysis. Stewart Zweben worked on
his gas puff
imaging diagnostic 5/21-24 and participated in planning and
discussions for a
new high-speed "movie" camera to capture
motion of edge turbulence structures.
Chris Brunkhorst was at MIT 5/21-22
to help with the ICRF transmitters. Larry
Guttadora came 5/22-23 to
determine layout and cable lengths for the
additional two channels that
form the first part of the C-Mod reflectometer
upgrade; relevant rf
components were returned to PPPL for hookup to the
remaining circuit
elements and for overall system checkout prior to
reinstallation on
C-Mod. Gerrit Kramer came 5/23-25 for
the continuation of
the MSE diagnostic startup and calibration in
conjunction with startup of the
diagnostic neutral beam. Stefano Bernabei, Doug Loesser, Joe
Rushinsky, and
Randy Wilson came for a status discussion of the Lower
Hybrid project on 5/24.
Gerd Schilling helped with all the above at MIT
5/21-24.
While Martin Greenwald was in Fairbanks, AK, attending the
TTF workshop and
the associated meeting on edge transport and turbulence,
he also discussed
plans for future collaborations with (among other
people) Carlos Hidalgo -
density limit studies on JET, Barrett Rogers and
Klaus Halatschek - edge
profile simulations, Xue-Qiao Xu - simulations of
the quasi-coherent mode,
Gary Staebler - simulations of spontaneous
rotation, Bill Dorland -
calculations of edge micro-stability, Bill Nevins
- simulation analysis tools
for the fusion collaboratory.