Alcator C-Mod Weekly Highlights
			Mar 29, 1999

The scheduled maintenance period on Alcator C-Mod continued last week. No
plasma runs were scheduled. 

Physics/Analysis:
-----------------

At the weekly staff meeting, first results from the newly rebuilt A-port
horizontal scanning probe were presented.  The new probe is virtually
identical in size and geometry to the F-port vertical scanning probe. Both
probes are Langmuir-Mach probes, having four eletrical elements arranged
around a pyramid structure. These probes can be used to monitor parallel flows
as well as density and temperature profiles up to the separatrix.

Initial analysis has focussed on comparing the denstiy and temperature
profiles bwtween the F-port and A-port probes. Only ohmic, L-mode discharges
has been considered so far. The density and temperature profiles were found to
match very well. However, there appears to be a flux surface mapping and/or
probe position error: The density and temperature profiles overlay when the
F-port data is shifted outwards in flux surface mapping, corresponding to 6 mm
in major radius at the midplane.  Possible reasons for this discrepancy are
being investigated.

A new CCD array detector has been installed on the tokamak to measure visible
continuum emissivity profiles with sub-mm spatial resolution. In the spectral
region covered by the transmission filters, the emission is dominated by
free-free bremsstrahlung. The camera views the plasma tangentially, in the
midplane, with major radius coverage 0.60m<R<0.93m. The camera has a 2048x1
pixel detector, and laboratory calibrations of the optical system show that
chordal resolution of 1 mm or better should be achieved along the entire length
of chords passing tangentially near to the location of the steep density
gradient seen in H-Mode.  Depending on signal strength, the camera is capable
of time resolution between 0.25 and 3.3 ms. The system is ready to take data
when tokamak operation resumes.

ICRF Systems:
------------

The RF group in collaboration with PPPL continued to work on the j-port
antenna transmission line and new transmitters.  The transmission line is
installed from the transmitters in the power room to the antenna.  We are
currently leakchecking the line.  Once it is leak tight, we will pump it down
and outgas it for approximately 24 hours, at which point it will be ready to
be pressurized and brought into operation.  One of the phaseshifters is
undergoing a repair after it was discovered that it did not respond to tuning
commands.  This repair should be a one to two day operation.  Both j-port
transmitters have been modified with new current limiting resistors on the
screen supply and have been tested at over 2 MW into a dummy load for 1
second.  We have also continued to upgrade both the #1 and #2 transmitters
that feed the D and E-port antennas.  A new feedback board has been
successfully tested in the #1 transmitter and installation in #2 is
proceeding.  We expect this new board to improve the response of the RF system
to changes in plasma loading.  Current limiting resistors are also being
installed in the #1 and #2 screen supply.  The new resistors should provide
higher immunity against screen trips during operation.

Diagnostic Neutral Beam:
------------------------

Progress on DNB systems remains satisfactory, with present status
approximately one week behind baseline (2/11) schedule. All high voltage
systems up to the modulator/regulator tube cage have been operated to full
performance. The supressor grid supply has been operated and the
modulator/regulator for the supressor grid is being tested at the present
time.


Visits and Travel:
------------------

Joe Snipes, Paul Bonoli, Antonio Bruno, Xavier Bonnin, Miklos Porkolab, Eric
Nelson-Melby, and Sergei Krasheninnikov attended the APS Centennial Meeting
and the associated Sherwood Theory Meeting, in Atlanta last week. 

Ron Bravenec, UT-FRC, began a one-week visit to install the BES fiber
optics and to calibrate the BES system in preparation for test of his BES
system using ambient plasma light and for benchmarking of his estimates of
the background plasma light.