Alcator C-Mod Weekly Highlights
                        December 27, 2010

FY2011 weeks of research operations
   Target: 15 weeks
   Completed: 7.18 weeks
   Plasma Shots: 868

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

Plasma operations continued last week at Alcator C-Mod. Two
run days were scheduled and completed. A total of 58 plasma
discharges were produced with a reliability of 95%. Experiments supported
research in the Transport Physics and Lower Hybrid Physics topical areas.

This week will be a maintenance week; no plasma operation is planned.

Operations Details
------------------

Tuesday's run was devoted to MP#625, "Effect on X-point location on H-mode
power threshold in SN plasmas". This experiment contributes to an ITPA Joint
Experiment PEP-28, and also comprises part of the thesis research of an MIT
graduate student. Lower single null plasmas were used for this study. On
successive shots the outer strike point was moved from the divertor floor, up
the inclined target plate, and onto the upper surface of the divertor
structure.  A significant reduction in the power threshold was observed when
the strike point was located on the floor tile. The shape parameters,
0.5<delta_l<0.6, kappa~1.6,  were kept roughly constant, but the length of the
outer leg from the X-point to the strike point varied by about a factor of
two, with the lower values of P_th observed with longer leg lengths. A series
of discharges with varying X-point height, keeping the strike point fixed on
the floor tiles, also showed a consistent variation of the threshold with the
length of the outer leg. Analysis of the detailed pedestal profile data
obtained during this experiment are being analyzed.

On Wednesday we carried out MP#623, "The detection of LH waves using
reflectometry". The objective of this experiment is to measure scattered
signals (both frequency up-shifted (64.6GHz) and down-shifted (55.4GHz)) by
the interaction between 60GHz probe waves and 4.6GHz LH waves. This work
supports the thesis research of an MIT graduate student. This run concentrated
on documentation of the detected signal and noise floor during a scan of
target plasma parameters and lower hybrid power. All discharges were upper
single null equilibria at B_T~5.4T. Launched N|| values of 1.9, 2.1, and 2.3
were employed, with net LH power of 200 and 500kW. The L-mode plasma density
was scanned from nebar~7e19/m^3 to 1.5e20/m^3, and the plasma current was
varied from 800kA to 1MA. Scattered signal was observed in the up-shifted
frequency component (f~64.6GHz) for densities above 1.2e20/m^3. Below this
density the noise floor appeared to be greater than the signal
level. Scattered signal was also observed in H-mode discharges, which were
obtained with 2MW of ICRH applied during the LH pulse.

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

The second ARRA funded 4CM2500KG Final Power Amplifier tetrode tube
has been delivered, completing this order. .

FMIT#1 was successfully re-tuned to 80.5 MHz from 78 MHz and produced 2 MW into
dummy load.

The vendor for the Faraday rod bending process, which is required for the
ARRA-funded rotated ICRF antenna, has provided a new quote and delivery
schedule (8-12 weeks).  Discussions regarding this new schedule and its
implications are underway.  Our in-house wire EDM machine went out of service
after cutting 3 bridge sections, and will be serviced after January 3rd.
We will be able to proceed with fabrication of the first strap (strap #1) as
planned.


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

The final two new ARRA-funded klystrons were delivered to the PSFC on Monday.
This completes the order of seven klystrons.  The new klystrons have been
unpacked and preliminary inspection indicates no damage occurred in transit.
All klystrons have been hi-potted to 50 kV without breakdown or vacuum
pressure change.

The LH system was utilized last week for Wednesday's run, and performed
nominally.


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

Dick Majeski (PPPL) visited MIT on Monday, Dec 20, to discuss fueling by
injecting clusters of hydrogenic molecules. The purpose of this fueling method
is to deposit the fuel well past the last closed flux surface, which should
reduce the fueling and buildup of density in the SOL. This technique is being
developed on the LTX device at PPPL and could be of interest to Alcator C-Mod
if it scales favorably to a machine with C-Mod's density and temperature.

Dennis Whyte traveled to Washington DC for the first meeting
of the NRC Committee on Inertial Fusion Energy.
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