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
August
31, 2001
Disassembly of Alcator C-Mod continues. Work also continues on the new
inner
divertor, and the ICRF and LH systems.
Operations
----------
All
LN2 cooling lines, horizontal port extensions, and most of the magnet
bus
components have been removed from the machine. The lower cryostat panels
have
been removed. Both the upper and lower
cryostat panels are now available
for modifications that will allow better
access to the horizontal ports, and
will add new instrumentation
ports. The stand required to support
the
equipment needed to remove the lower drawbars has been installed below
the
machine. The upper drawbars,
drawbar pins, and wedge plate taper pins are all
ready for removal. Measurements of TF and OH joint resistances
have been
made and found to be within specs.
Physics
-------
At
the weekly physics meeting Bob Granetz discussed the automated
between-shot
xray tomography analysis, which was initiated during the most
recent run
campaign with the help of former intern Nitya
Kallivayalil. The inversion
algorithm
involves the use of orthogonal expansion harmonics to reconstruct
the
emissivity; specifically Fourier harmonics in angle and Bessel harmonics
in
radius. Due to CPU and disk space limitations, the automatic inversions
are
done only every 100 ms throughout the discharge and written back into
the XTOMO
tree, but the analysis can be re-run offline for any number of
time slices
for shots of particular interest. As an example, a movie of xray
emissivity was shown at the
meeting consisting of 4000 frames showing a
large m=1 instability (data
were digitized at 50 kHz) rotating around the
q=1 surface. Other interesting topics currently being
studied include xray
peaking and sawtooth heat pulse propagation during
ITB discharges.
Gerrit Kramer from PPPL has completed the modeling
of reflectometer wave
propagation in the peaked C-Mod internal transport
barrier
discharges. An appropriate
new set of frequencies, allowing the
measurement of turbulent fluctuations
inside the transport barrier,
has been chosen, and the relevant hardware
has been specified.
A reflectometer upgrade proposal will be presented to
the rest of the C-Mod
team in the near future.
Daren Stotler of
PPPL has begun neutral transport simulations of the Gas Puff
Imaging
experiments that are being carried out on C-Mod in collaboration with
PPPL. Stotler is using the DEGAS 2 Monte Carlo
neutral transport code to
verify that the simulated average location and
size of the emission cloud
arising from the gas puff are similar to those
observed with the fast visible
camera.
An initial simulation indicates qualitative agreement, confirming
that
the descriptions of the plasma and gas puff being input to the code
are
valid.
Lower Hybrid MIE Project
------------------------
Work
continues on the PLC control and PC interface programs that will be
used
to control the LH HVPS. The dummy load
needed to test the
LH HVPS is under construction in our shop. Work continues on wiring of
protection
circuitry, and the layout has begun on the low power microwave
rack.
The
contractor continues to install the klystron water cooling system.
Much of
the 8" and 6" diameter piping in the basement has been
installed.
The brick wall into the power room has been cored for access
for the piping.
Some magnet bus components in the power room have been
relocated to make room
for the pipe runs.
ICRF
Systems
------------
The 9" transmission lines for the D
and E-Port antennas on the east cell
wall have been removed in preparation
for the cell modifications.
A new commercially available
electromagnetic simulation package is being used
to model the D, E, and
J-Port antennas, and the J-port antenna mockup.
A comparison of the J-port
mockup antenna measurements and simulation has
shown excellent
agreement. This package can now be used
to model any
proposed antenna modification.
Inner
Divertor
--------------
We expect to have all major inner
divertor components in-house by the
end of next week. A fitup of the entire inner divertor will be
done
invessel as soon as relocation work on diagnostics that run under
the
divertor is complete. The old
inner divertor has been completely removed
from the machine, and
measurements of stud and diagnostic positions on the
inner wall are being
made.
A picture of the first fitup of inner divertor backing and
c-plates
together with some tiles can be found at
http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/Aug31_08.jpg
A
view of the back of the divertor assembly can be found at
http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/Aug31_10.jpg