Alcator C-Mod Weekly Highlights
                        April 4, 2011

FY2011 weeks of research operations
   Target: 15 weeks
   Completed: 13.9 weeks
   Plasma Shots: 1663

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

Plasma operations continued last week at Alcator C-Mod. One research run day
was scheduled and completed. The nine-hour extended run supported three
Miniproposal in the Transport and Lower Hybrid Physics areas and the
Diagnostic Development task. A total of 33 plasma discharges were produced
with a reliability of 89%.

Plasma operations are planned to continue this week.

Program Planning
----------------

On Monday, a video-conference was held with DoE FES to present and discuss the
C-Mod budget and program plans for FY12-FY13.

Operation Details
-----------------

The first two hours of the run on Tuesday were devoted to MP#622, "q
Dependence of Rotation Reversal Density". The main purpose of this run was to
determine the propagation direction of the turbulent feature observed by the
phase contrast imaging (PCI) diagnostic at high k and frequency which is
evident when the core toroidal rotation is directed co-current. The
experiments determined that this feature propagates in the ion diamagnetic
direction.

The next portion of the run supported MP#640 "ICRF heating of LHCD driven low
density RS plasmas". Mode Conversion ICRF heating (f=50MHz, D(He3)) was
performed, resulting in LH target plasmas with Te0~3.5keV and
0.8<ne0<1.2e20/m^3 at Ip=450kA, Bt=5.4T with P_icrf=1.6 MW from the J-port
antenna. However faulting of both LH and ICRF systems during simultaneous
operation complicated interpretation of the current drive
results. Additionally, interference due to the 50MHz ICRF was observed on
magnetics diagnostics, including those employed in the plasma control system,
possibly contributing to several disruptions.

The last two hours of the day were devoted to MP#647a, "Evaluation of MSE
issues". The purpose of this experiment, which supports the thesis work of an
MIT graduate student, was to evaluate the passband of the MSE filters relative
to the motional Stark effect spectrum. The toroidal field strength was ramped
from 5.4 to 7.2 Tesla at constant q95, and in a separate shot BT was ramped
from 5.4 to 2.5 Tesla, both in low-density ohmic plasmas.  This pair of BT
ramps was repeated as the temperature of the filters was varied from 23 to 60
Celsius, which changes their center wavelength by about 0.6 nm.  Preliminary
analysis indicates that the observed polarization fractions differ
significantly from expectations.


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

Following completion of Tuesday's experiment, the J-port antenna transmitters
and coaxial transmission line network have been tuned to 78 MHz and 2 MW has
been delivered into dummy load from each transmitter, in preparation for this
week's operation.

All four current straps for the new ARRA-funded rotated antenna have been
successfully brazed, and the straps and braze joints are being polished prior
to plating.  The TZM side tiles have been polished and 10 tiles have been
machined to accept thermocouples.  We have received the final two top/bottom
plates from our vendor.  The first back plate has been completed.

The second set of bent Faraday rods have been shipped by the vendor and are
expected in-house this week.  The first Faraday rod set has been sent to be
TiC coated.

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

The LH system was required for experiments on Tuesday of last week.  The J-port
ICRF antenna was found to interfere with LH operation at low plasma currents
(Ip<450 kA) due to the mapping of magnetic field lines from the LH launcher to
the ICRF antenna when the pitch angle is small.  The J-port antenna does not
typically cause difficulties at higher plasma currents.

Progress continues on preparations for the transmitter protection system (TPS)
upgrade, low power microwave controls, and 4th klystron cart.  Voltage
variable attenuator/phase shifter units were tested at a range of temperatures
(80F to 125F) and input powers (-10 dBm to +10 dBm) and performed within spec.
Test results to date were compiled into a written report for future reference.

Diagnostics
-----------

Boron doped polyethylene shielding was installed on the hard x-ray (HXR)
camera to investigate the effects of neutrons on the background HXR
count-rate.  Analysis of the shielded vs. unshielded system is ongoing.

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

Catherine Fiore gave an invited talk at the American Chemical Society meeting
on Monday, April 28th in Anaheim, California in the Francis P. Garvin-John
M. Olin Symposium in Honor of Sherry Yennello.  Her talk, 'Gender Equity
Conversations: A CSWP program,' was given on behalf of the APS Committee on
the Status of Women in Physics.

Wednesday through Friday, Earl Marmar was at PPPL for a meeting of
the FSP Program Advisory Committee, on which he is a member. Martin Greenwald
participated in the meeting as a member of the FSP planning team.

Randy Wilson (PPPL) visited the PSFC to participate in LH experiments on
Tuesday.

The PSFC hosted the 20th meeting of the ITPA Pedestal Topical Group from March
30 through April 1. Thirty ITPA members and guest experts attended the meeting
in person while several more connected remotely, presenting an array of recent
results of experiment and modeling in the pedestal research area. Over 20
institutions from the US, EU, China and Korea and Japan were represented. The
scientific program included reports of progress in the areas of pedestal
structure, ELM mitigation and the L-H transition. Amanda Hubbard, Jerry Hughes
and Yunxing Ma presented recent results and plans on I-mode physics, pedestal
control and L-H transition studies on C-Mod. Several meeting participants took
advantage of their visit to discuss ongoing and proposed collaborations with
C-Mod staff and students.

Tom Osborne (GA), Marc Beurskens (CCFE) and Lorenzo Frassinetti (KTH)
completed their visits to collaborate on analysis of pedestal data in ELMy
H-mode. While on-site, Tom completed an installation of his latest pedestal
profile fitting tools and demonstrated their ability to produce meaningful
profile analysis and kinetic EFITs using C-Mod data. The incorporation of
these tools directly assists our efforts to complete the FES FY11 Joint
Research Target (JRT) in pedestal physics.

A mid-term meeting of the JRT contact persons was held in conjunction with the
ITPA meeting. This meeting was chaired remotely by Rich Groebner (GA), and had
participation from several involved scientists, including the main contact
persons from C-Mod, DIII-D and NSTX, and the GA, LLNL and PPPL theory groups.
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