.
These were proposed in conjunction with Ray Fonck's group at the DIII-D
Brainstorming Session on January 14 - 16, 1997.
.
A list of especially relevant experiments follow. In addition, other potentially
relevant experiments have already been performed in which BES data was taken
by the UWM group. We propose to assist in analysis of that data.
Experiment: Theory-Based Models of Tokamak Transport, TA# T1.1 No. of Days: 2 Tentative Dates: After 9/8/97 (first day postponed twice) Leader: Schissel (Bravenec is a co-experimenter) Experiment: High-Beta H-mode Scaling to Ignition, TA# T5.2 No. of Days: 1 Tentative Date: 9/15/97 Leader: Petty Experiment: Rotation Effects in Dimensionless Scaling, TA# T5.3 No. of Days: 1 Tentative Date: 10/14/97 Leader: Petty
DIII-D mini proposals co-authored for the current campaign:
Testing Theory Based Transport Models Using Perturbative Techniques, D3DMP
No. 435.
[This experiment not only attempts to test simulation-based transport models
such as the IFS/PPPL model, but also attempts to reproduce the "cold-pulse"
results on TEXT (a phase inversion of the temperature pulse from edge to
center)].
Other topics of interest to us will be investigated during other MP's, e.g.:
Summary of contributions to the DIII-D five year plan
We have attempted to limit the number of topics that we address and proposed
them for both machines. The same topics as listed for C-Mod are also included
in the DIII-D five-year plan (GA Draft Report. GA-C22631, June 1997, Secs.
3.1.3 - 3.1.5).
The University of Texas took charge of the 32 channel ECE heterodyne radiometer
diagnostic on the DIII-D tokamak in January with one on-site scientist responsible
for its maintenance and operation. During the machine vent that was in progress
at the time the antenna pattern of the horn antenna was measured. The beam
pattern was found to have a 3 dB width of 10 cm at a distance corresponding
to the center of the vacuum vessel. During the months prior to the start
of experimental operations in April the heterodyne system was thoroughly
checked out. Some modifications to the transmission line were necessary
to accommodate new diagnostics near the ECE port on the vacuum vessel. A
notch filter to block 110 GHz power from the ECH gyrotrons was inserted
into the transmission line and adjustments were made to the various channels
to balance the radiometer response.
During the first operations period in May the ECE radiometer was calibrated
against absolute measurements of plasma electron temperature by the Michelson
interferometer and Thomson scattering diagnostics. The calibration was shown
to be stable over time. In the 3 months of operations the ECE radiometer
was a key diagnostic in several experiments, three most notably: 1) Dependence
of Stability on Plasma Shape Exp. where the fast ECE data was used to identify
tearing modes, 2) Electron Transport Barrier Exp. where the ECE was monitored
to observe the steep gradients in Te and 3) ECH Exp. where the radiometer
data provided the power deposition profile.
The University of Texas also assisted in the maintenance of the other major
ECE system on DIII-D, the Michelson interferometer. This system is important
for measuring the central electron temperature on DIII-D, and is presently
the only absolutely calibrated diagnostic able to do so. FRC staff performed
the calibration procedure in April and was solely responsible for operating
the Michelson during May, June, and July. A major failure in the control
electronics of the diagnostic during the first operations period was addressed
and resolved. Also, the UT collaborator helped in the development of a new
type of notch filter that functions as part of the corrugated waveguide
transmission line for the Michelson. The instrument provided electron temperature
profile data for all experiments except for those during the week when the
control electronics were being repaired.
Besides the operation of ECE diagnostics, the UT on-site staff member was
involved in other research activities. A paper was presented at the 10th
Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance
Heating in Ameland, the Netherlands, titled Determination of Wall Reflectivity
for ECE Frequencies in DIII-D. An abstract was submitted for the APS
Division of Plasma Physics meeting, titled Using ECE to Improve EFIT
Results in NCS Discharges in DIII-D. Work was started on studying the
evolution of electron temperature during non-sawtoothing discharges where
spontaneous improvements in electron energy confinement are seen. As part
of this study, the effects of the ECE diagnostic spatial resolution on the
temperature measurements is being investigated. UT staff participated in
and contributed to the DIII-D Advisory Committee meeting in February and
the DIII-D/C-Mod Tokamak Workshop in July.
In the next couple of months an upgrade to the ECE heterodyne radiometer
will be made which consists of adding more channels and improving the existing
video amplifiers. Eight more channels will be added at higher frequencies
to cover the full width of the usable second harmonic ECE spectrum for DIII-D
discharges at full field (2.2T). This will provide fast measurements of
central electron temperature in the core in many experiments. Also, the
gain of the video amplifiers will be increased to assure that the detectors
are operating in the linear regime and to utilize the full resolution of
the digitizers. Both of these improvements are crucial for transport barrier
and ECH power deposition experiments.
In the long term, plans are being made to improve the ECE antenna and to
add another ECE radiometer to DIII-D. As was mentioned, the current antenna
for the heterodyne system has a spot size of about 10 cm. In terms of measuring
turbulent fluctuations, this spot size limits the maximum measurable 
to approximately
. For a spot size of 2 cm a as large as 
would be measurable.
A spot size of this diameter is achievable with a strongly focusing antenna
system. The smaller spot size would also benefit the study of MHD and other
small scale phenomena. For these studies also, an additional heterodyne
radiometer with its sightline displaced toroidally from the existing system
would aid in mode identification. In addition, a system capable of measuring
third harmonic frequencies would permit Te measurements at high density
where the second harmonic frequencies are cut off. Recent advances in millimeter
wave hardware would allow acquisition of these radiometers at lower cost
than was possible in the past.
There are two components to our involvement in the BES diagnostic on DIII-D:
We plan to participate in two categories of scheduled experiments:
Improvements in the BES data acquisition system
Most of our part of the development is being done in Austin where we have
similar hardware. Some software work can be done from Austin via the Internet.
Approximately two on-site weeks would be adequate for installation/implementation.
We must keep in mind that implementation might be limited by lack of money
so we must be prepared to commit these two weeks to another area. The two
things that we planned are