Alcator C-Mod Weekly Highlights
			December 20, 1999


	We continued work on the RF antennas, the transmitters, invessel
activities, DNB, power systems, and general maintenance of the machine
last week.


Engineering:

A wooden mockup of the edge turbulence imaging telescope was taken 
into the vacuum vessel for preliminary alignment and fitup.  These
measurements will guide the final fabrication and installation of
this new diagnostic.  Other work involving invessel activities included
repair of the diborane feedlines and planning for the new cold cathode
pressure gauges.

The OH1, OH2U, OH2L commutation switchgear maintenance work has been completed
and the work on EF1 is in progress.  All but one of the 15 volt instrumentation
power supplies have been installed in the TMX supplies.  These supplies
replace older ones that had proved unreliable.  Work continues on  the TMX
contactor maintenance, and checking the torque of the interior bus connections.
Maintenance work still continues on the 13.8 Vacuum bottle breakers with one
being completed and a second one underway.

Repair of the PPPL 4-strap ICRF antenna at J-port made good progress last week.
The SS cups protecting the resistive elements terminating the ends of
the Faraday screen rods are installed on half on the Faraday rod
assemblies.  The remainder will be completed this week.  These cups
are designed to provide shielding from the high rf fields of the
adjacent antenna current straps, and provide a metallic ground in
case of arcs to the strap.  Arcing  had damaged several of the 
elements during the last run campaign.  The arc and melt damage to the
protection tiles, large and small leads, and the septum components of J-port
has been cleaned up after documenting.  Digital photographs were
particularly useful in allowing off-site PPPL collaborators to participate in
the discussions and analysis of the problems.  In addition, we reduced the
height of the large and small lead elements by 1/4" to increase the distance
between the lead and the vessel wall.  This change should reduce
arcing while changing the inductance of the element by only 1-2%.
Along with three antenna straps from D and E-port, the large and
small leads have been sent out to be replated.  The first test piece
showed delamination of the plating on one side of the strap.  This problem 
was attributed to the growth of an oxide layer.  Before the next plating
attempt, the surface is going to be reconditioned using a fine glass bead
blast.  Finally, a metal strap is being fabricated to short circuit the gaps
between adjacent front surface tiles to eliminate rf arcing at this location.

Work on D and E-port antennas included the repair of the broken loop probe
used in the phase balance protection circuit.  This loop probe was associated
with the D-port antenna strap that was damaged.  A fit-up
of the new BN protection tile was performed on the D-port antenna and
a review of the tile and fastener will be done this week.

Work continued on the transmitter FPA cooling systems.  Changes to all four
tanks and installation of the new heat exchangers are now complete.
Work on the associated electrical systems has begun.
 
We continued to check and clean filters for the LN2 cooling system.  This
work is now complete.  We continue to make upgrades to some of the LN2
manifold feedthroughs to improve their seals.

DNB work continued on schedule with work on the MCL and Mod/Reg systems
making good progress.


Physics:

In-vessel measurements have been made of the R and Z coordinates of the A-port
and F-port scanning probes. The A-port probe (ASP) was placed at its
rest position and a test shot recorded. It was found that the PLUNGE data
signal returns the value of 0.7 mm when the probe was at its rest position.
The major radius of the rest position was measured with respect to the inner
wall and found to be consistent with the coordinates in the data tree
(within 0.1 mm). Therefore, evaluation of the probe position from the 
tree values would indicate that the ASP probe is 0.7 mm further inserted
(i.e., has smaller major radius) than actual.

The R,Z coordinates of the F-port probe (FSP) rest position was
measured by a different method than in the past. The probe was
inserted as far as possible, raising the head  up to the Z level where
the inner divertor nose tiles and the inner wall tiles meet. In this way,
the major radius of the gas nozzle (center of the probe pyramid) was
measured from the inner wall tiles. Also, the Z location was measured by
projecting a level straight edge along R from the nose/wall tile interface
point and measuring the vertical distance to the top of the probe head.
This procedure yielded R=28.7679" (0.7307) and Z=-15.3316 (-0.3894).
Therefore, evaluation of the probe position from the tree values would
indicate that  the FSP probe is 1.2 mm under-inserted in R (i.e., has larger
major radius) and 1.0 mm under-inserted in Z (i.e., has a more negative Z)
than actual.

In summary, the ASP and FSP probe position position data in the tree are
very close to recently measured values. Mapped to the midplane, the corrections
correspond to changes in major radius of ~ 0.7 mm. These corrections are well
short of the apparent ~ 5 mm discrepancy between FSP and ASP profile data
using the EFIT midplane mapping.

Invessel calibration of the visible continuum array has also been completed.
Using illuminated fibers positioned in the vessel to a precision of +/-0.5 mm
with respect to the surface of the inner wall limiter tiles, tangency radii
for three locations on the detector array were located. This yields an absolute
major radius position for the array data collected during the 1999 run campaign.
The absolute position was shifted out by 2.6 mm from that assumed when the
camera was installed, based on dead reckoning. Combined with shifts resulting
from calibration of the edge Thomson scattering viewing optics, these two
measurements are now generally in very good agreement in the measurement
of the foot location of the H-mode density pedestals.


Travel and Visits:

Several of our PPPL collaborators were at MIT last week.
Joel Hosea came to C-Mod on 12/14 with suggestions for modifications 
to the current feed straps in order to reduce induced rf currents in 
the vacuum vessel and suppress arcing in the antenna return current 
structure.  Raffi Nazikian came on 12/14-15 for discussions on the 
reflectometer upgrade, and Norton Bretz came 12/15-16 to replace the 
first lens in the MSE optics and install its shutter.