From: irby@PSFC.MIT.EDU
Reply-To: IRBY@PSFC.MIT.EDU
Subject: Alcator C-Mod Weekly Highlights
Newsgroups: sci.physics.plasma
Organization: MIT

Alcator C-Mod Weekly Highlights
October 12, 2001


Disassembly of C-Mod continued this week. Analysis of inspection data
is ongoing. Work is moving forward on ICRF control systems and the
Lower Hybrid MIE Project.


Inspection
----------

The "big lift", during which the machine, consisting of the vacuum
vessel, PF coil packages, OH stack, lower wedge plate, and TF core
and lower arms, is moved from the center to the southeast corner of the cell,
occurred on Friday, 10/12/01. This move is required to gain access to the
lower TF arms and OH2 lower coax. Disassembly will be completed within the
next 10 days with the removal of the lower horizontal TF arms, the lower
wedge plate, and the lower coax.

The OH coax bolts and mating helicoils removed from the upper connections
showed indications of high stress along the threads. We are considering
changes to the coax connections to alleviate this effect. A mockup of the
coax assembly is being put together so that both stress and cycle tests can
be run to simulate what has been seen.


Lower Hybrid MIE Project
------------------------

We worked with the contractor this week installing electrical service and
lighting to the new HVPS. In addition, all of the switching modules
have been put into place. However, experiences in the commissioning of a
similar HVPS at Wendelstein W7-X have forced a parts change in the modules for
our supply. The W7-X power supply has experienced a number of module failures
that were traced to a defective transformer. New transformers are being
made and will take several days to install here at MIT.

A demonstration of a new real-time control software package, which is being
considered as a replacement for the software we are currently using, is being
planned. The objective is to do a direct comparison of software capabilities.
Orders were placed this week for booster amplifiers, I-Q Detectors, and
hardware to be used in our test of the new software package.

Fiber optic cable has been pulled from the power room to the temporary test
control room for power supply tests. Conduit and cable tray runs from
power room to power supply should be completed next week. The power supply
power distribution panel has arrived and work will start shortly to
install it, together with the lighting and convenience outlets, in the power
supply containers.

Installation of the klystron water cooling system continued. Components have
begun to arrive at MIT for the cell mezzanine that will support the klystron
carts.


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

Work continued on the simulations of the D, E, and J-Port antennas. We are
now close to a decision about the design changes required to eliminate
rf breakdown at the bridge location of the J-Port antenna strap. Work on
developing models for the transmission systems also continues.

Work continued on the new control system and improved phase detectors. We
have decided to implement a down-convertor scheme to improve the linearity
of the phase measurements.


Inner Divertor
--------------

All fixturing and stud welding equipment has been tested and is ready
for operation. Invessel work was temporarily suspended during the big lift,
and will resume as soon as disassembly is complete.

All twelve Rear Girdle Plates and one C-Plate have been silver plated.


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

Bench tests of the MSE/BES in-vessel optics performed at PPPL were
reported last week. We have now begun ray-tracing analysis.
The goals are to first understand the transmission and then to improve
the optical design without changing the existing optical components.
The ray tracing analysis is beginning to reproduce the bench tests.
A single CXRS spectrometer will be used to analyze the light from
several distinct plasma chords. A model of the CXRS spectrometer was
developed to allow design of the fiber optic input array to make up
for spectrometer aberrations and to prevent the spectra from the
distinct chords from interfering with each other.

The FRCECE is undergoing some modifications to take advantage of new
opportunities that have become available with the reallocation of
space on F-port. Redesign of the mirror mount for the FRCECE system
on F port flange is in progress. The mirror will be moved to the
centerline of the flange to simplify prediction of the optical
performance. The external waveguide will be rerouted to accommodate
modifications in the DNB duct. Boards and components for the new
FRCECE amplifiers were ordered this week.

Work is continuing at PPPL developing ideas for upgrading the
reflectometer to allow core turbulence measurements to be obtained.


Control Room Upgrade
--------------------

MIT has agreed to finance an upgrade to the C-Mod control room. This
upgrade will expand the control room to support more C-Mod physicists, and
provide an area for the Lower Hybrid control and data acquisition equipment
and personnel. A meeting was held last week with representatives from MIT,
C-Mod, and the prime contractor, to begin planning for the upgrade.
Renovation of the control room carpeting, ceiling, air conditioning ducts,
and all painted surfaces will also be undertaken.


Trips, Visits, and Collaborations
---------------------------------

Klaus Hallatschek from the Max Planck Institute for Plasma Physics
spent the week working with C-Mod staff members including Stewart Zweben (PPPL).
On Wednesday, October 10th, this group was also joined by Barrett Rogers of
Dartmouth University. Klaus and Barrett model plasma turbulence with a first
principles 3D fluid code. We are comparing the results of their code with
experimental measurements and images of turbulence in the edge of C-Mod.
Klaus also presented a seminar on "Oscillating Zonal Flows in 3D Edge
Turbulence Simulations."

While at MIT, Stew Zweben presented a dry-run of his invited
talk on the Gas Puff Imaging results for the upcoming APS meeting.

Bill Beck and Steve Wukitch participated in the JET-EP ICRF Antenna High
Power Prototype Conceptual Design Review. The participants included JET,
PPPL, ORNL, MIT and DoE engineers, physicists, and managers.