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
February 7, 2003
We continue to work
invessel on diagnostics and instrumentation.
Work on ICRF, Lower Hybrid
MIE, and power systems proceeded.
Physics
-------
Matt
Sampsell, UTexas, presented BES measurements of the
quasi-coherent mode at
the weekly C-Mod Physics Meetings.
In
discharges with highly collisional edges and central parameters
with
ne ~ 1.8 10^20 m^-3, Te ~ 2.5 keV, and Btor ~ 5.3 T, the peak
relative
fluctuation amplitude was found to be ~ 26% (ņe/ne). Three
poloidally-spaced
views at Rmid ~ 89 cm were used to obtain a poloidal
wave number for the
mode of ~ 2 cm^-1 and poloidal velocity of ~ 3
km/s. Radially-spaced
channels located the mode in the steep gradient
region, less than 1 cm
inside of the separatrix, with a FWHM ~ 5
mm. Improvements to the BES
spatial resolution were proposed for
future experiments.
David
Mikkelsen, PPPL, spent the week at MIT refining estimates of the
ion
temperature profile in C-Mod plasmas. These estimates are based on
solutions
to an ion power balance equation using measured electron
density and
temperature, and DD neutron emission. Many sources of
uncertainty are
being included in order to derive a range of plausible
values for R/L_Ti
in several C-Mod plasmas, some heated purely
ohmicly, and others also by
ICRF.
Operations
----------
Invessel work this
week included installation of the new f-port probe
cables. These cables were damaged during the last
campaign when an
open shunt connection forced currents generated during
disruptions to
find ground through the cables. The shunt connections are now being
refurbished also.
The
first of the field control coils was completed and tested this
week. The new control coil power supply was used
to drive 3 kA of
current through the coil. Instrumentation for the new supply
including both PLC and
CAMAC hardware and software was operated
successfully. Winding of the second of the eight coils has
also been
completed.
A new LN2 feedline to the ECE diagnostics
lab has been completed and
is now operational. This line will greatly ease maintenance of the
LN2 cooled
ECE detectors during C-Mod operations.
ICRF Systems
------------
We
continue to use the rf simulation code to model the fast ferrite
tuners. We are looking at both waveguide and strip
line structures.
The antenna modifications have made good
progress. The E-port flange has
been
installed on the machine after vacuum testing the individual
feedthroughs. D-port flange has been removed for
inspection and refurbishment
of the feedthroughs. The new center conductors for the D and
E-port
feedthroughs have arrived from the vendor. The bushings for the center
conductors
have also been completed. The J-Port
horizontal flange has been
removed and modifications (additional 1/4-20
taps and copper plating) are
expected to be completed early next
week.
Lower Hybrid MIE Project
------------------------
At
MIT, the HVPS crowbar passed all tests prior to application of high
voltage. We are now working through the fault
detection system with
high voltage applied. Arc detectors are now being tested and
installed on the
carts. Three detectors did not meet
specification,
but more than enough spares were available to populate the
carts. Our
first high power
circulator was shipped by the vendor last week. The
remaining circulators will be delivered by early
summer. Detailed
specifications
are being developed for the waveguide flanges.
A
vendor for the waveguide and flanges will be determined within
the
next few days.
At PPPL, the LHCD launcher is continuing to
progress well. All
components have
now been ordered except thermocouples needed to
monitor temperature
throughout the launcher structure. The
vacuum
shroud and forward waveguide assembly have been welded and
leak
checked. Minor welding
warpage has been corrected for exact fitup of
the port extension to the
waveguide. The radial motion device
has
been reassembled and tested.
The forward waveguide/shroud assembly
will be joined to the port
extension and radial motion device on the
RF Test Facility vacuum test
stand in the coming weeks, and vacuum
integrity and motion will be checked. The instrumentation patch panel
is
being fabricated, and its cabling is >50% completed. The rear
waveguide is expected in house
2/13, the standard loops will be
delivered 2/10, and the remaining
components (high power phase
shifters) are on schedule for delivery in
February as well.
Diagnostic Neutral Beam
-----------------------
An
intermittent inverter protection fault was tracked down and fixed
this
week. This fault has on occasion caused
shortened beam pulses.
A faulty IGBT was the cause of this problem.
Travel
and Visits
-----------------
Bruce Lipschultz traveled to San
Diego to attend the DIII-D Advisory
Committee meeting, February 4-6. The
committee reviewed the DIII-D
group's presentations for their 5-year
plan.