From:
irby@PSFC.MIT.EDU
Reply-To: IRBY@PSFC.MIT.EDU
Subject: C-Mod Weekly
Highlights
Newsgroups: sci.physics.plasma
Organization: MIT
Alcator C-Mod Weekly Highlights
February 14, 2003
Work
continued on ICRF components, the Lower Hybrid MIE Project,
and
fabrication of the new control coils.
Results from gas conductance
and flow experiments from the last run
campaign are discussed.
Physics
-------
Analysis
of gas conductance and flow data obtained from a series of
dedicated
experiments performed during the 1020725 run day (MP#313,
"Instrumented
Divertor Leakage Experiments") has been performed. In
these
experiments, a known deuterium gas flow rate was injected
through
capillary tubes located at a variety of points in the vacuum
vessel where
neutral pressures and/or gas flow (inferred via D-alpha
emission) are also
recorded (open ports, closed ports, under the
C-divertor flap, and over
the C and D-divertor flap). The idea
was to
run a reference discharge with no capillary puffs and record
the
pressures, and then repeat discharges with known capillary gas
throughput
at a variety of locations and measure the neutral pressures
again
(focusing on their change). From this data, the effective gas
conductance
was quantified (i.e., relationship between gas throughput
and pressure
difference). By puffing gas and
recording pressure
changes without plasma, the vacuum conductance was
also
measured. Conductances measured with and without plasma were used
to
constrain numerical modeling of neutral transport and to provide
guidance
for optimizing a cryopump located in the upper chamber.
Analysis
indicates a strong plasma plugging effect at locations where
the divertor
structure is opened for diagnostics access (the so-called
"open-port"
locations), as evidenced by a factor of ~4 reduction in
the local gas
conductance with plasma present. The effect is most
dramatic for locations
in the upper chamber region where there is no
neutral baffle structure; a
factor of ~5 reduction in the local gas
conductance is found there. Gas
conductance through an open divertor
flap is measured to be a factor of ~3
lower than that which has been
commonly assumed using the area of the open
flap. The conductance
through the flap is found to be similar with or
without plasma
present, indicating that there is no "plasma
plugging" effect
occurring at this location. The gas flow rate
through a flap that is
adjacent to an "open-port" location is
found to be a factor of 2 lower
than at a location distant from open
ports. The latter result suggests
that significant toroidal variations in
the pressures exist under the
lower divertor modules. A preliminary draft report can be found
at:
www.psfc.mit.edu/people/labombard/gas_cond_n_flow_meas.pdf
Operations
----------
We
continued with fabrication and installation of the new control
coils. Four of the eight coils are now complete,
and one has been
installed on the igloo.
Layout of the patch panel needed to connect
the coils to the power
supply has been completed and procurement of
parts begun.
ICRF
Systems
------------
Work continued on the fabrication, copper
plating, and installation of
upgrade components for the antennas needed to
improve voltage handling
capability.
Detailing of the BN tile modification drawings has been
completed
and machining on the new tiles will begin next week. Work
on the control system upgrades continued.
Diagnostic
Neutral Beam
-----------------------
Modifications to the java
code that operates the beam are being made.
The current software requires
a manual START input from the operator
at the control console before each
C-Mod shot. This function will be
automated
before the next run campaign.
Lower Hybrid MIE Project
------------------------
At
MIT, the HVPS crowbar system is now operational with high voltage
applied. The dummy load for the HVPS is being brought
back into
operation in preparation for tests of the HVPS and crowbar next
week.
We have received the first high power circulator from the
vendor. A
mounting frame is being
fabricated to secure the circulator to the
cart. Work continues on PLC control software, and the fast phase
and
amplitude control systems.
Fiber optic terminations from the network
lines to the transmitter
data acquisition chassis have been completed.
The fiber optic network
lines have been successfully tested.
At PPPL, removal of excess
braze material from the air side of the
ceramic windows for the LH coupler
has been completed. Careful but
tedious
manual scraping and very fine sandblasting were successful in
cleaning the
ceramic surface. A far smaller amount
of material
remains to be removed from the vacuum side, and, following a
vacuum
leak check, the metal surfaces will then be copper plated. The
remaining assembly work is also
progressing well. A check on the
delivery
of outstanding procurements together with the in-house
progress indicate
completion by the end of March.
Travel and Visits
-----------------
Amanda
Hubbard was at PPPL for a meeting of the FESAC Fusion
Development Path
Panel this week.
Martha Redi, PPPL, visited MIT this week to work
with Catherine Fiore
and Paul Bonoli on analysis of the off-axis RF ITB
for gyrokinetic
drift mode instabilities.
New results discussed were comparative
simulations with the GYRO
code and GS2, use of the GKV viewer for
nonlinear simulations, and
eigenfunction plots of instabilities in the
ITG, TEM and ETG range of
frequencies. Work is progressing on
preparations for the spring meetings
and journal publications.