Alcator C-Mod Weekly Highlights
			Sept 15, 1997


The maintenance period continued at Alcator C-Mod last week.
The alternator repair, DNB, and RF upgrades are progressing.  Analysis
of physics data from the last run period continues.  We have begun
electron cyclotron discharge cleaning experiments which may have an
impact on ITER operations.

Six out of twenty field coils have now been installed on the alternator
rotor.  Each coil has passed an extensive set of tests including DC
resistance checks, turn-to-turn AC resistance checks, and a DC Hi-Pot to
6000 volts (more than ten times the normal operating voltage).

The assembly of the diagnostic neutral beam in the test lab is continuing.
Voltage dividers and current shunts for the measurement of beamline
parameters have been installed. Work has begun on the fuel handling system,
and assembly of the vacuum PLC control interface has continued.  The design
of the low capacitance transmission line was completed, and assembly
and lab modifications can begin.  Preliminary layouts for installation of the
DNB in the cell have been completed. Ron Bravenec, UT-FRC, completed a noise
model of the BES detector/amplifier system and began benchmarking his BES
spectral analysis codes against the codes used for BES at DIII-D.

Maintenance on FMIT#1 and #2 continues.  The arc detection system
based on reflected power fraction has been calibrated and tested.
The threshold is ~50 kW and the trip setting (P_refl/P_forw) is ~25%.
The remaining interlocks, phase balance and voltage limit, are being
tested.  Testing has also begun on the position feedback control.
Work on FMIT#3 and #4 PLC wiring is also progressing.

High voltage DC power supplies, formerly used for the LH system on
Alcator-C, are being examined to determine whether they can be used
for the proposed LH system on Alcator C-Mod.  The options being explored
include refurbishing these supplies or buying new ones.  Uptegraff has been
asked to provide an estimate on both refurbished and new supplies.

Alcator C-Mod has been cooled down sufficiently to allow ECDC to be made
operational again.  As part of an ITER relevant project we are gathering
density and ion temperature profile data during ECDC using the Omegatron
probe.  Preliminary results indicate appreciable density only outboard of
the electron cyclotron resonance, consistent with particle drifts in a
purely toroidal field.   Ion temperatures of approximately 5 eV have been
found.  A scannable probe has also been installed so that the surface erosion
rate of carbon films can be determined.

Preliminary analysis has been made of local impurity dispersal from
trace-impurity injection experiments performed during the June run campaign.
During these experiments, controlled injections (10 msec duration) of 10^17
to 10^19 molecules of impurity gas (He, N2) were delivered by a modified fast-
scanning probe onto targeted flux surfaces in the scrape-off layer. Images of
the resultant impurity line-emission 'plumes' (NII, NIII, HeI,  HeII) at the 
injection point have been analyzed. Plumes of ionized impurities 
extended along field lines, closely matching the local field line
trajectory as deduced from magnetic reconstructions (EFIT). A small asymmetry
is evident in NIII and HeII plumes, consistent with a reversed parallel flow
(Mach number ~0.1) near the separatrix. These data  appear to corroborate 
the reversed flows seen by the Langmuir-Mach probe near the separatrix. The 
spatial extent of the plume along field lines is consistent with DIVIMP
simulation results (collaboration with U. Toronto group). However, saturation
of pixels viewing closest to the injection point does not allow a
comparison with the complete image to be made. DIVIMP modelling shows that
images of NIV emission would be more sensitive to parallel flows in these
high density (10^20 m^-3) and high temperature (>50 eV) scrape-off layer
plasmas. The possibility of looking at a CIV line arising from an
acetylene (C2D2) injection is begin considered. A number of other
improvements to the diagnostic have been identified.

Bob Cutler and Gary Taylor of PPPL brought up the hardware for a new 19-channel 
grating polychromator this week.  This instrument, formerly used on TFTR,
will  be brought on-line during the next run campaign and will double the
number of radial positions for fast Te measurements.

Steve Lisgo from U. Toronto is visiting C-Mod for a two week period.  He is
here to help calibrate and maintain the H_alpha arrays for C-Mod. This data
will be used in the DIVIMP modeling he is doing, and will allow him to
reduce large uncertainties in the flow driven ionization source rate.

Paul Bonoli visited PPPL last week and worked with Cynthia Phillips,
Doug McCune, Randy Wilson, Dan Clark, and John Wright as part of the
C-Mod/PPPL RF collaboration.  Discussions concerning global issues related
to the TRANSP/FPPRF code interface, and the question of passing equilibrium
information efficiently between TRANPS and TORIC were held.  The IDL
postprocessor on the PPPL HYDRA was updated to the latest version developed
at MIT. This change will allow 2D electric field contours as well
as rf driven current profiles to be displayed.  The use of the new finer
resolution ECE diagnostic to clarify crucial issued in rf power deposition
profiles was also discussed.