Alcator C-MOD Weekly Highlights
				June 30, 1994

Operation of Alcator C-MOD this week included experiments on impurity
screening in divertor plasmas and investigation of the closed loop dynamic
response of elongated plasmas. 

The objectives of Thursday's run (MP#044) were 
 (1)  To puff He, Ne, and Ar into the private flux zone in the divertor and to
  measure how much gets into the  confined plasma, thereby being able to
  estimate screening factors for impurities which can be compared to  theory.
 (2)  To measure the amount of molybdenum sputtered by injected impurities as a
  function of the target electron temperature and hence to get some information
  on the sheath potential. 
These experiments were motivated, in part, by  ITER Physics R&D needs. These
experiments were quite successful, with data being obtained for all three
species. A preliminary assessment indicates screening of >99% in each case.
There is evidence for sputtering of Mo by Argon above a threshold temperature
of about 20eV, consistent with theoretical expectations.

On Friday, closed loop response of the plasma to a series of steps in the Z
position programming was carried out for several values of proportional and
derivative feedback gain. The object was to test our dynamical models as well
as to provide a basis for further optimization of our control algorithms. 

During the run on Friday, the OH2_L coax bus suffered arc damage. The damage
occurred during precharge, following a long series of successful, uneventful
shots. Repair of this bus will require a partial disassembly of the machine.
We have therefore begun our summer hiatus one week earlier than originally
planned, and have started the repair process. 

The machine disassembly is proceeding rapidly. The igloo cover and top two
tiers of igloo blocks have been removed, and a vent has begun. The upper port
cross assemblies have been removed, as have two of the horizontal flange
covers (at C and G-ports).The ventilation system has been attached and manned
access activities are underway. The in-vessel survey and inspection indicates
that the tiles, divertor assemblies, and other internals are in excellent
condition. The transmission lines from the ICRF tuning stubs to the antenna
ports have been removed. Diagnostic connections to the machine are being
removed, but most diagnostic systems will remain in place during the repair.

Ian Hutchinson, Steve Golovato, and Joe Snipes are presenting papers at the
European Physical Society Meeting in Montpelier, France, this week.
Thirty-five contributed abstracts from C-MOD are being submitted to the APS
DPP meeting.