Alcator C-MOD  
			   Weekly Highlight Report  
				October 7, 1993

Plasma operation continues as scheduled on Alcator C-MOD. This is the fourth
run week of the current operating period. 

High elongation studies were extended, along with investigations of the
dynamics of vertical disruptions. Single null 650ka discharges with
elongations up to about 1.7 have been run successfully; growth rates and
disruption behavior were studied by turning off the feedback control. A test
of between shot discharge cleaning (ECDC), using either He or D2, to
improve recovery after a disruptive shot was carried out; this technique was
not demonstrated to reduce the frequency of bad shots following disruptions.

This week, we have begun operating with reversed field and current, i.e. with
the ion-grad-B drift in the direction of the x-point for lower single null
divertors.  This field direction is believed to be favorable for producing
H-mode; the opposite direction of toroidal field, which we have used up to
now, is believed to lead to more balanced heat loads on the divertor. The
direction of the plasma current was reversed as well, in order to keep the
helicity constant, so that the field angle remainsconsistent with the slant of
the ICRF antenna Faraday shield elements and the orientation of the the sloped
tiles on the divertor modules adjacent to ports. Low field experiments were
also continued with the reverse-field configuration.

ICRF experiments have continued. Over 450kW has been coupled through the
movable monopole antenna into D plasmas with H minority. Disruptive behavior
that was observed at a 100kW power level during the last couple of weeks (with
the limiter and antenna farther in) was not encountered in these experiments,
which employed a larger outer gap.At higher power levels there were definite
signs of  increased impurity (C, Mo) and deuterium influx, but the radiated
power increase was of the order of 1/4 of the injected rf power increase, 
even at the highest power level. 

Following overnight discharge cleaning in He, Thursday's experiments are
concerned with recycling behavior and particle confinement. Low-density
plasmas (nebar < 1.e19 m^-3) have been produced with walls conditioned in this
manner. A density scan is being carried out.