Alcator C-MOD Weekly Highlights
		      December 10, 1996


	The OH2U and OH1 coaxes have now been modified. Similar
tests to those performed on the OH2L are still required. Work continues on
the lower TF arm cover plates.  Inspections of the upper TF arms revealed
nothing of concern, and we are cleaning them and getting them ready for
re-installation.  We are also in the process of upgrading the engineering
diagnostics for the OH stack.  Several new position sensing coils and a set
of partial flux loops are being added.  Better analysis of the stresses on
the coil during disruptions will be possible with this new information.
	We continue to make progress on other engineering systems.
Work on the new RF transmitters has been concentrated on the crowbar
trigger and control circuits.  The control wiring is now ready for
testing.  Preparations are being made for setting up the DNB
beamline so that vacuum tests can be carried out.  We have also begun
the layout of the beamline support stand in the power room.  Power
supply maintenance and upgrades continue.  We have completed work on
the TF master control board.  The OH1 junction overtemp control board
has been calibrated.  Development of an improved self-powered crowbar
circuit to be used in several of our supplies continues.
	Invessel work last week involved removal of some inner wall modules
in preparation for tests and calibrations of the inner wall strain gauges,
and also the possible installation of new b-dot probes.  Plans are also
being made for the installation of new tangentially viewing XUV detector
arrays, one viewing the plasma edge with high spatial resolution, and the
other viewing from the edge to just inside the plasma major radius.
	In collaboration with Rudi Neu of ASDEX-U and Kevin Fournier of LLNL,
we have begun to identify and model tungsten x-ray emission in the 5-15 A
range obtained from a rotating crystal spectrometer system on ASDEX-U. Lines
have been identified from charge states between W38+ to W47+.  This work
may be of great importance to ITER since estimates of impurity radiation
from material from the 1st wall cannot be calculated without good models of
the atomic physics.  Data from C-Mod, for example, has modified
considerably the emission levels expected for molybdenum.  We intend to extend
the work on tungsten with experiments on C-Mod.
	Analysis continues on quantifying the types of ELMs observed on C-Mod
together with some mode analysis of their magnetic precursors.  Type III ELMs
are the most typical with a frequency that decreases with increasing input
power (range from 1 to 6 kHz).  Type III ELMs often have oscillating
magnetic precursors with frequencies in the range of 100 - 160 kHz and
high m and n numbers, both typically around 9 or 10.  After
boronization, Type III ELMs became more rare and another kind of H-mode,
an Enhanced D alpha H-mode was found. In this mode, the overall D alpha
emission increases again after the initial drop into H-mode. The emission
can reach L-mode levels even though the plasma remains in H-mode.  The
enhanced D alpha emission shows no magnetic ELM activity over the range of
frequencies observed (up to 500 kHz).  In some cases, during Enhanced D alpha
H-modes, there are events on the D alpha and edge ECE signals that may be
compared to Type II ELMs, since they are rather chaotic in time with small
amplitude, reminiscent of "Grassy" ELMs.
	Dave Johnson, Boris Grek, and Joe Bartolick are visiting this week
from PPPL to work on the edge Thomson scattering system.  Bob Granetz was at
PPPL last week for a FESAC subpanel meeting on disruption issues in ITER.