Alcator C-Mod Weekly Progress Report
                                May 27, 1997

Startup plasma operations continued on Alcator C-Mod last week. Plasma current
was raised to 800kA, and full length shots (into ramp-down) were obtained. A
total of 35 plasmas were produced in three and a half days of running.
On Friday, the toroidal field was run under hybrid control, which allowed
us to initiate the discharge at 5.3T and ramp the field down to the 4 Tesla
level required for some of the planned 40MHz RF experiments.

Most plasmas that had successful current rises ran to full current and
lasted past end-of-flattop. However, the startup success rate was not good,
with a high fraction of fizzles and duds. This situation seemed to be improving
on Friday, which approached a 50% startup success rate.

Thursday's run was abandoned and Friday's started late because of a
problem with the EF3 power supply and breaker. Following a power supply fault,
the breaker failed to operate and was taken out of service. A spare breaker
was installed, but the spare was found to be inoperable as well, so the
original breaker had to be repaired and reinstalled; this was completed around
noon on Friday.

During the afternoon run on Friday, May 23, scattered laser light from
the plasma was observed on the X-point Thomson scattering system on several
C-MOD discharges.  The peak in the scattering amplitude appear to occur near
the X-point. The scattered signal was observed during a horizontal scan of
the laser beam with respect to the viewing optics and occured at a position
which was to one side of the nominal center. This and other data indicate that
the next issue that must be resolved, before the X-point Thomson scattering
system becomes a routine diagnostic, is that of maintaining alignment both
during the plasma shot and long term during over a run day. This alignment system
has already been partially implemented. The X-point Thomson scattering
system is a collaborative effort between PPPL, MIT and Princeton Scientific
Instruments.

Work on the 40MHz RF system continues. The Uptegraff high voltage supply
on unit #4 failed, with the result that transmitter 4 is out of service for
the time being. Transmitter #3 has been tested up to 800kW into the dummy
load, for .65 sec. Low power levels (in the kW range) have been pulsed into
the machine between shots for instrumentation checkout. The gas system for
pressurizing the coax is operational; the 9" and 6" lines are pressurized with
N2. Testing into plasma will begin this week.

Preparation of the DNB test lab continued with installation of power.
Bill Rowan, UT-FRC traveled to Texas to retrieve more hardware for the DNB.
During this visit, he acquired the original master control logic and documented
the high voltage transmission line to allow duplication at MIT.

Roger Bengtson, UT-FRC, was on-site to begin implementation of the PLC
for the Texas fast-scanning probe and to arrange for installation in the
cell.