From: IRBY@CMOD.PFC.MIT.EDU
Date: Tue, 23 Jun 1998 7:26:27 -0400
Reply-To: IRBY@PSFC.MIT.EDU
Message-ID: <980623072627.25a0ebe2@CMOD.PFC.MIT.EDU>
Subject: Alcator C-Mod Weekly Highlights
Organization: MIT
Newsgroups: sci.physics.plasma


Alcator C-Mod Weekly Highlights
June 22, 1998



Engineering:


TF magnet refurbishment activities last week included the last
cleanup details on the lower TF arms and upper TF core. Final inspection
of this work will be followed by the silver plating activity scheduled
to begin early next week. The cracked TF core finger has been machined
down to clean copper in preparation for the electroforming activity
scheduled to begin early next month. Test samples of both the silver
plating and electroformed copper will be analyzed this week. We also
continue to improve the inductive heating process. Temperature gradients
along the feltmetal pad have been reduced another factor of two. We expect
to begin full-scale soldering tests this week. The new Rogowski coils to
be used during the full-scale joint tests have been tested and calibrated,
along with the integrators and CAMAC equipment required for data acquisition.
Work continued on the DNB. The arc detection sensors in the beamline
were fully characterized. Plans were laid for testing of the power supply
variacs, the arc/filament/snubber supplies, and their PLC controls. The
interface for communications between the CAMAC and the PLC was successfully
tested. The arc/filament/snubber interface chassis which links the supplies
with the master control logic and the PLC was completed and is ready for tests.
Final preparations for conditioning of the plasma source began. In this
work, a plasma will be generated for conditioning of the magnetic bucket
source, and new setpoints will be defined for optimum operation with the
new gas control system. However, no beam will be extracted until the
accel supply and modulator are ready for operation.

Physics:

Comparisons have been made of edge pedestals in H-mode measured by
various diagnostics. Te profiles measured by Langmuir probes, ECE, and Thomson
scattering are generally consistent and show a 'foot' near the separatrix
and a variable width. In L-mode, ECE tends to give lower separatrix
temperatures, perhaps due to lower optical depth. When the probe reaches the
separatrix, a steep density profile is seen which can reach more than
1.5e20 m-3, or half the average core density. X-ray pedestals are consistently
8-12 mm inside the separatrix and narrower than Te pedestals. XUV photon
emissivity profiles also steepen inside the separatrix during H-mode.

Travel and Visits:

Gary Hallock from the University of Texas, Austin arrived last
week and is collaborating on the Phase Contrast Interferometry (PCI)
diagnostic. The data obtained during the last run period is being discussed
as are upgrades to PCI for the next campaign. Hidetoshi Yoshida from JAERI
also visited last week and discussed Thomson scattering, interferometry,
reflectometry, and machine engineering with several PSFC scientists.
Miklos Porkolab attended the "Next Step Option" meeting at UCSD,
San Diego, last week and participated in discussions and worked on the
"ITER-Reduced Scale" draft document, as well as Advanced Tokamak
features of the Next Step.