Alcator C-Mod Weekly Highlights
                        August 24, 2009

FY2009 weeks of research operations
   Target: 9 weeks
   Completed: 4.4 weeks
   Discharges: 627

Operations
-----------

Plasma operations continued on Alcator C-Mod last week.  A total of 60 plasma
discharges were produced over 2-plus run days, with a reliability of
80%. The runs supported experiments from the Boundary, Transport, and ITER
H-mode Scenarios research programs.

On Wednesday, Following testing of the temporary repairs to the TF
instrumentation which was involved in the ground fault incident on August 14,
we began a short experimental shift in support of MP#563 "Toroidal asymmetry
of impurity seeding in support of ITER divertor gas injection", with the
intent of completing the ohmic L-mode density scan that began on August
14. The target discharge was successfully established, but a series of vacuum
and power system difficulties prevented completion of this phase of the
experiment.

Thursday's run was devoted to part one of MP#560, "High density fueling and
density limits". The goal was to document the evolution of the edge
temperature profiles and turbulence as the density limit is approached. Data
were successfully obtained in a series of deuterium discharges employing the
inboard midplane "NINJA" capillary for fueling. This fueling mode was most
successful for equilibria which were limited on the "nose" of the lower inner
divertor. Initial data were also obtained in helium discharges. In these cases
the normal outboard piezo valves were used for fueling so that the NINJA could
be used to puff gas for the Gas Puff Imaging turbulence diagnostic.

On Friday we carried out an extended (ten hour) experiment dedicated to MP#559
to investigate the H-mode threshold in helium plasmas in support of planning
for the pre-nuclear phase of ITER. Joseph Snipes (IO) served as Session Leader
for this experiment, participating remotely from Cadarache. Density scans were
carried out first in helium and then in identical deuterium plasmas, at the
nominal ITER field of 5.3T. The observed thresholds were higher in helium by
factors of 1.4 to 2, depending on the density. These results are in contrast
to recent experiments on ASDEX-Upgrade, which found the thresholds were
essentially the same in helium and deuterium, while being more consistent with
JET results. These results are therefore less optimistic than those from
ASDEX-U for the prospects for obtaining H-mode in ITER during the pre-nuclear
phase. However, given the differences among the different facilities, a better
physics understanding is required to reliably extrapolate to the ITER
conditions.

A fresh boronization was carried out following the run on Friday.
Plasma operations are planned to continue at Alcator C-Mod this week.


ICRF Systems
------------

A fault in the FMIT#4 (J-port) crowbar trigger module occurred during the
experiment on Friday, preventing use of the J-port antenna. The problem was
diagnosed and repaired following the run.

Lower Hybrid System
-------------------

Three of the sixteen 4-way splitters are awaiting e-beam welding.  Following
successful completion of this operation, fabrication of all sixteen 4-way
splitters will be complete.  A test of the induction braze of stainless steel
inserts to the transformers has been completed and is undergoing a leakcheck.
These inserts are needed to couple the transformers to the 4-way splitters.



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