Alcator C-Mod Weekly Highlights
			December 3, 2007

FY2008 weeks of research operations:
     Target: TBD
     Completed: 0 weeks

Operations
----------

Plasma startup and conditioning operations commenced at Alcator C-Mod last
week.  Runs were carried out Tuesday through Thursday, following completion of
low-temperature (60C) baking and electron cyclotron discharge cleaning (ECDC)
over the weekend. Successful current rise (to >400kA) was obtained on eight
shots, including one full length (2 sec), 800kA plasma discharge.

Proper operation of the three new (replacement) flux loops which were
installed during the up-to-air period was confirmed, and new plasma control
shape estimators utilizing these sensors were successfully
implemented. Initial comparison of EFIT reconstructions using the new loops
with an equilibrium calculated using only the diagnostic set available last
summer indicates variations in the inferred outer surface location on the
order of 5mm.

Experiments were carried out to determine the effectiveness of an applied
vertical B-field to localize the plasma density profile around the upper
hybrid resonance during ECDC in helium. With the electron cyclotron resonance
held fixed at R=0.6m, the langmuir probe on the Surface Science Station was
scanned radially from 0.59<R<0.95m with different values of applied vertical
field. These experiments are related to optimization of the boronization
process.

A new technique for calibration of the edge CXRS system was implemented,
employing ECDC in neon. Previously, wavelength and instrumental calibrations
for this diagnostic were performed using a neon pen lamp, which
is capable of illuminating only 6 out of 108 channels at a time.  This
calibration process is time consuming, and requires channel-to-channel
cross-calibration to be performed on a shot to shot basis, which introduces
additional errors.  The ECDC technique illuminates all of the CXRS
channels at once, allowing the calibration data to be taken simultaneously
and eliminating the need for cross-calibration.  Moreover, this
calibration procedure can be performed easily on a routine basis. Initial
test of the technique carried out last week demonstrated the feasibility of
this calibration approach.

Based on the results of three days of plasma operation, additional baking to
120C, in conjunction with ECDC, was begun on Friday and continued through the
weekend.

Plasma operations are planned to continue this week.

ICRF System
------------

All four ICRF transmitters are ready for operation.  Issues associated
with controlling the transmitter power using the newly installed demodulators
have been resolved.

The fast ferrite tuner (FFT) system for real-time tuning of the E-port dipole
antenna matching system will be ready for operation, pending completion of
some cabling and updates to the control code.

Conditioning of the J-port (four strap) antenna into vacuum has begun.

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

First tests of the new LH_B and LH_D NINJA capillaries were conducted on
Thursday.  These capillaries were installed for the purpose of locally
increasing electron density in front of the LH grill without perturbing the
line averaged plasma density.  Experiments from the previous run campaign show
that under-dense plasma in front of the LH antenna was a cause of increased
reflected power under some operation conditions.  Test shots with gate valves
closed were used to determine the flow rate for a plenum pressure of roughly
2psi. Preliminary analysis shows flow rates ~.5 torr*l/s, at 94 torr D2 in the
plenum. This is in the range of the design flow rate of ~.1-.5 torr*l/s.

The lower hybrid transmitters were operated at >1.6 MW into dummy loads last
week, in preparation for plasma operation. Calibrations of the drive and
monitor legs were completed, although additional work is required to confirm
the calibration values for drive leg #3. The lower hybrid system is expected
to be ready for operation with plasma this week.

Long Pulse Diagnostic Neutral Beam System
------------------------------------------

In order to enhance the radial spatial resolution of the MSE measurements, the
main component of an aperturing system for the diagnostic neutral beam was
installed last week.  This component can narrow the beam in the horizontal
direction by a variable amount using two remotely-controlled moveable
water-cooled copper shutters.  The hardware was built at the Budker Institute
of Nuclear Physics in Novosibirsk, Siberia by the group that built the DNB
itself.  The beam is now pumping down, in preparation for operation into
plasma this week.

Travel and Visitors
--------------------

Bruce Lipschultz attended the 6th meeting of the IEA Large Tokamak Workshop
(W66) on Implementation of the ITPA Coordinated Research Recommendations, held
at JET in Culham UK November 28-29, 2007 hosted by the EFDA staff there. He
represented C-Mod in the discussions of C-Mod commitment to running
collaborative experiments. He also represented the ITPA SOL/Divertor group in
the discussions of the SOL/Divertor group proposals for collaborative
work. Before the meeting he gave a JET seminar entitled "Characteristics of D
retention in a high-Z tokamak: A new retention process?". This was attended by
members of the JET and MAST groups as well as ASDEX-Upgrade and TCV scientists
through video-conference.
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