From: IRBY@CMOD.PFC.MIT.EDU
Date: Tue, 18 Feb 1997 21:00:19 -0500 (EST)
Subject: Alcator C-MOD Weekly Highlights
Newsgroups: sci.physics.plasma
Organization: M.I.T.


Alcator C-MOD Weekly Highlights
February 18, 1997



Reassembly continues on Alcator C-Mod. On Wednesday the machine was
moved from the assembly stand back to the lower dome in the center of
the cell. Since that time, the upper wedge plate and all twenty upper
horizontal TF arms have been installed. Work has now begun on the
vertical TF legs. The TF magnet will be complete when the vertical
leg installation is finished. The standard set of hi-pot, continuity, and
resistance checks mentioned here before have been completed successfully
as major components have been installed. With the removal of the
assembly stand, reassembly of the diagnostics stand in the southeast corner
of the cell was begun.
Invessel work resumed as soon as the machine was back in position
on the lower dome. Fitup of a repositioned x-ray detector was
begun. Reorientation of the detector, together with a new collimator, will
allow high spatial resolution measurements to be made at the plasma edge during
H-mode operation. Sean Regan and Mark May from JHU visited last week to
help with the installation of their new invessel spectrometer. New studs
were shot, and the initial fitup was done for this new diagnostic. A gas
capillary was repositioned to allow gas to be fed into the edge bolometer
array box. This change is being made to allow the effects of neutrals and
radiation to be separated in the bolometer data. Work is also moving
forward on the installation of several new brackets that will be used to
support new periscopes and probes.
Work on the DNB included more analysis of the requirements for
the ACCEL supply, mod/regulator, and crowbar units. We are moving
one of the TARA gyrotron power supplies to the power room. One of these
supplies will be able to drive the DNB beamline without the need of a large
capacitor bank and at relatively low voltages compared to a cap bank.
RF work last week included a great deal of progress on the #3
transmitter switchgear. The motorized fused disconnect and circuit
breaker has been wired and tested. The protective relays for the
switchgear have been installed, and the trip circuitry wired and tested.
Work also continues on the new crowbar systems for transmitters #3 and
#4. We are ready to install the ignitrons and high voltage cabling.
The crowbar units will be complete and ready for testing once these
installations are done. High power RF testing of transmitter #1 into the
newly reconditioned dummy load is underway.
Analysis of H-mode regime transition from elm-free to enhanced
D-alpha is proceeding. In some cases the enhancement in D-alpha light was
small, although changes in particle confinement were significant. The fast
edge mode was also observed during the enhanced D-alpha phase with a frequency
near 80 kHz, sometimes both on the reflectometer and on the magnetic pick-up
coils. The escaping neutral flux (CX) was also observed to change
significantly. During the elm-free phase the neutral flux (at energies
above ~2-3 keV) usually increases by large factors (2-10, depending on energy
and conditions), but drops back to near L-mode levels during the enhanced
D-alpha phase. Further analysis is planned regarding a possible connection
with the changes in the edge radial electric field.
Amanda Hubbard was in IPP-Garching meeting with Wolfgang Suttrop,
discussing local H-mode threshold and pedestal measurements on C-Mod and
Asdex Upgrade. She also gave a seminar on our H-modes and met with ITER
JCT personnel regarding a new edge operational space database. Ian Hutchinson
and Earl Marmar were at PPPL last week to discuss the MIT/PPPL collaboration.