Alcator C-MOD Weekly Highlights
		      January 14, 1997



	Alignment of the central column is complete, and installation
of the lower coil package is ready to begin.  Alignment of the central
column involved centering the TF core and OH stack relative to the
vacuum chamber to within +-.005" and then milling the  plates on the central
column to accept the inconel pins attached to the OH mounting plates.
New sensor coils mounted on both the OH stack and mounting plates will allow
accurate measurements of stack movement relative to the vessel to be
made.
	Progress on the RF systems included completion of the
deionized water system for the new transmitters, continued installation
of the new RF crowbar systems, winding of pulse transformers required for
the crowbar triggers, specification of 9" coax components that will be
provided by PPPL, and debugging and repair of breaker control problems in
the high yard step-start house.  The 480 volt distribution panel for the
DNB is now wired in, and we are isolating all supplies so that a common ground
can be maintained.  The contactors for our TMX power supplies have been
refurbished and are ready to be installed.  Work continues on the self-powered
crowbar circuits.
	Work also continued on diagnostic systems.  Components for the
tangential two-color interferometer (TTCI) box which will enclose and protect
the entire optical system have been fabricated.  Cleaning, baking, and assembly
of invessel fiber systems have been moving forward.  Fabrication of components
for new shutter systems for the A-Port wide angle camera and the TTCI
mirror at C-Port are nearly complete.  These shutter systems will be
assembled and cycle tested before installation invessel.  The prototype
divertor cryopump is being installed on the vacuum test stand inside a mockup
of the outer divertor so that more pumping tests can be made.  Components
have been specified and ordered for an upgrade to our gas system that will
allow very accurate measurements to be made of fueling and impurity gas
flow rates.
	A new "Fast Edge Mode" that sometimes occurs during the Enhanced
D-alpha H-modes in Alcator C-Mod is being analyzed. It is an
n=1 MHD instability with little or no ballooning character, predominantly
m=4 and hence resonant near the separatrix. It rotates in the counter-Ip
direction, equivalent to a very large negative radial electric field
drift, larger than appears explicable by diamagnetic drifts. If
diamagnetic drifts are indeed insufficient, the mode is either a
diagnostic of extremely large edge electric fields or a new unidentified
type of instability.
	In response to queries from ITER about the width of the pedestals in
H-mode,	we have analysed in more detail our edge Te(R).  For a few enhanced
D-alpha H-modes	with fairly steady conditions, field ramps of a few percent
were used to sweep the position of channels on the ECE diagnostic, giving many
more radial points than usual.  The profiles were fit using a tanh function,
giving widths of typically 12 mm.  After deconvolving the instrumental
resolution of 9 mm FWHM, the best estimate for the actual pedestal width is
8 mm.  However, since the ECE resolution is comparable to the pedestal width,
uncertainties are fairly large.  We hope to improve on this measurement using
a heterodyne radiometer to be installed this year in collaboration with
U-Texas and Auburn University.
	The first annual "C-Mod Ideas Forum" was held at M.I.T. on
January 9-10, as part of the planning process for the Spring 1997 C-Mod
Operating Campaign. A total of 80 short talks (5 minutes, plus 2-3 minute
discussions), covering a wide variety of proposed experiments in the areas of
Divertor Physics, Transport, MHD, RF Physics, Advanced Tokamak Physics, as
well as non-fusion aspects of plasma science, were presented. All the
sessions were well-attended, and the discussions, within the time constraints,
were lively and constructive. About one-quarter of the presentations came
from collaborators representing seven institutions outside M.I.T. In addition
to providing a framework for planning the experimental program for the
upcoming campaign, the forum proved to be a useful mechanism for acquainting
the many new collaborators in attendance with the C-Mod program and
capabilities.