From: "Stephen M. Wolfe" <wolfe@psfc.mit.edu>
Reply-To: wolfe@psfc.mit.edu
Organization: MIT Plasma Science and Fusion Center
Subject: Alcator C-Mod Weekly Highlights
Newsgroups: sci.physics.plasma


Alcator C-Mod Weekly Highlights
Nov 24, 2003

Plasma operations continued at Alcator C-Mod last week. Four run days were
scheduled, but only two and a half were completed, due to a computer
problem. A total of 59 plasma discharges were produced with a startup
reliability of over 85%. Experiments were conducted in support of
Divertor/Edge, Transport, and RF Group research priorities. Work also
continued on Lower Hybrid System Development.

Plasma operations are scheduled to continue this week.

Operations
-----------

Tueday's run was devoted to a continuation of MP#335 on "Edge plasma flows in
upper vs lower X-point discharges" begun the previous week. Tne SNU/SNL
density scan called for in the MP was completed, leaving the DN scan to be
completed. These experiments provide input to Level 1 Milestone SC6-1b,
"Compare energy confinement, H-mode threshold and divertor particle dynamics
in SN, DN and inner-wall limited discharges in Alcator C-Mod". The run was
interrupted for about 4 hours due to a problem with the main data acquisition
server. The problem was apparently resolved in time to allow an hour of
operation at the end of the day, but the same computer crashed again on
Wednesday morning and had to be taken out of service. The experiment planned
for Wednesday has been rescheduled for this week. A replacement computer was
installed and plasma operations resumed on Thursday. The cause of the computer
failure is under investigation.

Thursday's run was devoted to MP#350, "ICRF Loading Studies". The primary
purpose of this run was to simultanously obtain ICRF coupling measurements and
radial density profiles in the core, edge and scrape-off layer using Thomson
scattering and the A-port Scanning Probe (ASP). This run was quite
successful. Radial profiles were obtained simultanously with coupling
measurements for D and E, and we had good data from the probes even with 1 MW
of ICRF power. Initial comparison between the measured loading for D- and
E-port antennas and the prediction from the 1D model is encouraging. The
measured profiles and coupling measurements will also be suitable for more
advanced simulations using the TOPICA code. This experiment provides data in
support of Level 1 Milestone SC6-1e, "Design advanced, high-power, load
tolerant ICRF antenna for C-Mod."

Friday's run was devoted to MP#368 "A-coil effect on ohmic EDA operation" and
MP#334A "QC mode in ohmic EDA's - radial extent, k-poloidal and high frequency
companions". The first portion of the run was spent optimizing and documenting
the use of the C-Mod non-axisymmetric control coils (A-coil) to eliminate
disruptions which had prevented access to the desired EDA regime (Bt<3T,
Ip~800kA, q95<3) when MP#334A had been attempted last July. Non-disruptive
operation was obtained for intermediate values of A-coil currents between 1000
and 1400A, corresponding to calculated total B_21 fields based on our model of
the intrinsic error-fields of <2 Gauss. The latter part of the run (MP#334A) was
dedicated to observations of the Quasi-coherent mode in these EDA plasmas with
an array of fluctuation diagnostics, including scanning probes, PCI,
reflectometry, BES, and gas puff imaging. Good measurements of the k-spectrum
and radial extent of the mode were obtained. The high frequency (1-2MHz)
companion predicted by one theory of the QC phenomenon was not observed.

With the exception of the computer problem, all tokamak subs-systems performed
well last week, and the startup reliability has markedly improved from a week
ago.

Run Planning
--------------

The C-Mod Experimental Program Committee met on Monday, Nov 17, to review
MiniProposals for upcoming experiments. The meeting was video-conferenced with
participants from MIT, PPPL, and U. Texas. Nine new MP's were approved. One of
these, MP#363, is in direct support of the H-mode threshold aspect of Level 1
Milestone SC6-1b. All C-Mod MiniProposals are viewable on the Web at
http://www.psfc.mit.edu/cmod/operations/mini_proposals.htm .

Lower Hybrid System
--------------------

Work continued on the Lower Hybrid launcher. The forward wave guide shroud
assembly is in the final stages of machining. The coupler end has been
completed, and the rear wave guide end has also been completed and will be
inspected 11/24 prior to delivery to PPPL for testing.

Diagnostics
-----------

Fourteen new channels were added to the CXRS diagnostic. Those put in service
were used for poloidal views during this week. Perry Phillips and Alan Lynn
(UT-FRC) made Improvements in the FRCECE data programs to handle missing data
and to improve calibration.

Travel and Visitors
--------------------

Rick Goulding (ORNL) and Phil Ryan (ORNL) visited in part to participate in an
ICRF antenna design discussion. This discussion was videoconferenced with
R. Wilson (PPPL), R. Pinsker (GA), and TV George (DoE). The discussion was
centered on developing an antenna concept to replace the D and E-port
antennas. The new 4-strap would incorporate the improvements made to J-port
and desirable mechanical features of D and E-port antennas. This effort is
related to the Level 1 Milestone SC6-1e.

David Mikkelsen (PPPL) visited Bill Dorland 11/19-20 at the University of Maryland
to discuss changes to the gyrokinetic turbulence simulation code GS2
and simulations of Alcator C-Mod plasmas. The new GS2 will be tested soon at
PPPL and should make simulations with many modes faster and more
reliably re-startable.

Steve Scott (PPPL) and Howard Yuh (MIT) were at General Atomics 11/20-23 to
participate in an internal calibration of the DIIID Motional Stark Effect
diagnostic. The techniques used, and the experience gained, will be
valuable for the planned calibration of the C-Mod diagnostic this winter.

Manfred Bitter and Ken Hill were at MIT for the week, continuing to work on
the NSTX X-ray Crystal Spectrometer diagnostic. The main problem is still
an excessive count rate, leading to detector saturation when ICRF auxiliary
heating is applied.

Earl Marmar, Miklos Porkolab, and Martin Greenwald attended the FESAC meeting
in Washington on Monday-Tuesday. Porkolab and Marmar also attended the Fusion
Power Associates annual meeting and Forum on the Future of Fusion on
Wednesday-Thursday; Marmar presented a talk entitled "Status of Tokamak
Research: Alcator C-Mod and the Path to ITER and Beyond."

Amanda Hubbard visited Columbia University on Friday. She gave a Plasma
Physics Colloquium entitled "Advanced Tokamak Research on Alcator C-Mod:
Towards Profile Control and Long Pulses". Future collaborations on wall
stabilization issues were discussed with Columbia researchers.





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