Alcator C-MOD  
			Weekly Highlight Report 
			July 1, 1993

The EFC Chopper supply was exercised during plasma operation for the first
time on Thursday, 6/24.  This initial attempt to use the EFCs to help
stabilize the vertical instability on a relatively high elongation plasma
showed promise, but more tuning of the feedback gain law is required.  Most
of the rest of this week's runs have concentrated on lower elongation,
limiter discharges.

Marfe phenomenology was further investigated. The evolution appears
unaffected either by elongation or by puffing from the outside rather than
the top. As we have always seen, the marfe forms near the inner midplane
and then moves up.

A density scan was carried out for a series of limiter discharges with
plasma current of 300 kA and elongation about 1.2. The line integral
density was scanned from 3.e19/m^2 to 7.e19/m^2 (nominal line averaged
density from 0.6 to 1.5e20). Profile data of electron density (TCI
interferometer), electron temperature (ECE), ion temperature (HIREX),
and radiated power (bolometry) were obtained for confinement analysis. 

Further studies of wall conditioning, both before daily operation and
between shots, have been carried out. We are now routinely performing one
to two hours of ECDC before operation. Standard procedure is to do this 
pre-operational ECDC in H2, but use of He has also been explored. Hydrogen
discharge cleaning between shots loads the wall with H2 but tends to evolve
H2O and leads to higher Zeff on the succeeding discharge. Between shot ECDC
in He has some effect in removing trapped H2 and reducing wall fueling in
the succeeding discharges. Between shot ECDC in Argon was also tried; this
is an alternate way of seeding the plasma with Argon for observation by the
HIREX diagnostic. Subsequent shots showed that the Argon introduced in this
way disappears with a 1 or 2 shot e-folding time. 

Startup studies this week concentrated on reducing the loop voltage during
the early current rise phase, and the voltage required on the EF3 coils,
which are primarily responsible for providing the equilibrium fields. The
loop voltage at breakdown was reduced to between 4 and 5 Volts, while the
maximum voltage during the early current rise was reduced to less than 6
Volts (from around 8V). The corresponding reduction in voltage on the
paralleled EF3 coils was from 1500V to 1050V; this value is well below half
of the available power supply voltage, so that we will be able to proceed
with reconfiguring the EF3 coils from parallel to series operation.