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
May
11, 2001
The 120C bake of the vessel has been completed
and ECDC wall conditioning
has begun.
Work continues on rf, DNB, divertor, and Lower Hybrid systems.
Engineering
and diagnostic systems are being checked out and readied for
machine
operation early next week.
Physics
-------
At
the physics meeting Bruce Lipschultz updated the C-Mod group on the
ongoing collaborative work between C-Mod and DIII-D
on SOL transport.
Similar
measurements have been made on both experiments for a range of
densities.
It is found, at least for the L-mode discharges studied,
that the scrapeoff
layers of both experiments exhibit two e-folding
lengths - a short one in
the 'near' SOL (near to the separatrix) and a
longer e-folding length in
the region farther from the separatrix (far SOL).
These measurements
have allowed the same analysis technique to be applied
to the SOL data
from each machine. The results of this analysis show
similarities in
ionization profiles and an inferred cross-field particle
diffusion
coefficient, D_eff. D_eff is low near the separatrix, rising by a
factor
of 10 or more in the far SOL. The main differences between the two
experiments
in this analysis were in the magnitude of D_eff.
The discharges on
the two experiments are similar in a
dimensionless sense. Using the
dimensionless scaling of density
(1/a^2) the SOL profiles of density from
both experiments can be
overlayed, again showing the near and far SOL
e-folding length
similarities. The profiles overlayed well with the far SOL
e-folding length
becoming longer (flatter) at higher density . The
primary difference was
in the near SOL where the DIII-D density
e-folding length was longer (in
r/a) than that for C-Mod.
Operations
----------
The
120C bake was ended with very good results on Monday, 5/7. A helium
leakcheck found no leaks. ECDC wall conditioning in deuterium was
started
in the afternoon and will continue almost continuously until
operation begins.
A problem with a new data acquisition computer was fixed
on Thursday and shot
cycle tests were begun. Proper operation of the engineering CAMAC data
acquisition
equipment was confirmed and new hi-yard and alternator signals
were
checked. The gas fueling system was
used to puff gas into the vessel
and confirm operation and measure
response times of the diagnostic pressure
gauges, including the new J-Port
gauge. The rf and magnetics data
acquisition
modules were tested, among many others. The Hybrid computer, which is
used for
real-time plasma control, is operational.
ICRF Systems
------------
We
continue to methodically work through and check all fault and
interrupt
signals for all transmitters and antennas.
Protection electronics
trip levels are being checked. Calibration of the phase detectors
continues.
Lower Hybrid MIE Project
------------------------
Assembly
instructions and wiring information for the transmitter
equipment rack HV
control panel were released this week.
The layout for
the current transformers has also been
completed. The layout of the PC
boards
for both the transmitter equipment rack and the coupler
protection system
is proceeding. We continued discussions
with our HV
power supply vendor to finalize the key-interlock system. We have begun
planning the waveguide
runs from the klystron carts to the launcher.
A list of design
requirements is being developed to guide this process.
Cable, water, and
air runs will be integrated into this design.
DNB
---
The
DNB duct pressure monitors were completed this week. The ion gauge
was repaired and reinstalled with a gate valve
so that any future
failures will not require venting of the beam for
repair. Two
H-alpha monitors were
installed and software developed to compare their
signals. The baratron gauge was tested and integrated
into the data
acquisition system. Continuation of the beam conditioning,
which was delayed
last week by the failure of a pressure gauge, was
further delayed this week by
a system-wide CAMAC problem. Conditioning of the beam was resumed on
Friday.
Inner Divertor
--------------
Vendors
continued fabrication of the C and backing plates. In house work
focused on the new probe array to be installed
in the divertor, and
completion of the inner divertor mockup. All tiles are now inhouse.
The tiles
and tile support plates are being baked.
Power Systems
-------------
The
alternator was brought up to 500 RPM on Friday and all major support
systems
were checked for proper operation. A
full speed test will be
carried out next Monday.
Travel
and Visits
-----------------
Miklos Porkolab, Steve Wukitch,
Paul Bonoli, and Eric Nelson-Melby attended
the 14th Topical RF Conference
in Oxnard, Ca this week. Steve Wukitch
gave
an invited talk on "Results from ICRF Experiments on Alcator
C-Mod." Eric
Nelson-Melby
also gave an invited talk on "Phase Contrast Imaging of Ion
Bernstein
and Fast Waves in Alcator C-Mod."
Paul Bonoli presented a poster on
the "Analysis of ICRF-heated
Transport Barrier Experiments in Alcator C-Mod."
Yongkyoon In
visited KSTAR (Korea Superconducting Tokamak Advanced Research)
project in
late April. He was told that the
project is on schedule for
completion in 2004.