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
January 29, 2001


We continued last week with design work on upgrades to the J-port
antenna striplines. Work also continued on the Lower Hybrid and DNB
systems.


Physics
-------

Joe Snipes spent the week of 22 - 26 January 2001 at JET to take part in
experiments attempting to obtain Enhanced D alpha H-mode on JET. The
experiment took place on 24 January. While long ELM-free H-modes were
obtained, there was insufficient time to complete the experiment due to
maintenance problems. In the final shot of the experiment, gas puffing into
an ELM-free H-mode did produce a mode that was visible on the 92 GHz edge
reflectometer channel at about 40 kHz during the ELM-free phase. The mode
numbers have not yet been determined. However, since the density and radiated
power continued to rise in the ELM-free phase, it was clear that the mode did
not significantly reduce edge particle confinement. Contingency time was
approved for the experiment, and an additional six shots will be performed
on 2 February in an attempt to complete the experiment.


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

Work continued on the redesign of the striplines feeding the PPPL
ICRF antenna. A first review of the proposed modification was held
via videoconference on 1/26, with Randy Wilson, Bob Ellis and Gerd Schilling
representing PPPL. We have decided to proceed with the detailed design
following agreement on the conceptual design during the meeting. The
striplines will be rotated approximately 90 degrees relative to their current
orientation to take advantage of magnetic insulation. The separation between
the stripline and the ground plane will be increased by 50% to reduce the
electric fields. The conceptual design solid model can be viewed at

http://www.psfc.mit.edu/people/irby/jport_antenna_stripline3a.jpg

Digital panel meters and associated modified circuit boards were
installed for the tuning indicator upgrade to FMIT3 and 4. Problems
were found with the limit switches during tests. These are now being
debugged.

The dummy load remote switch upgrade for FMIT1 and 2 is waiting for
documentation to be completed before the PLC connections can be made.

Design is proceeding on an upgrade to the phase shifter and stub tuner control
system which will allow for more automated control. This change will require
some hardware installation in the CAMAC system and a small amount of wiring
to the PLC in addition to new PLC programming.


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

The Lower Hybrid group is preparing for a design review to be held at
MIT on 2/7 and 2/8.

The circulator source selection committee met at MIT Bates Accelerator Lab
last week. In attendance were Monty Grimes (C-Mod), Abbi Zolfaghari (Bates),
and Bill North (a consultant). It was determined that more information from
the suppliers will be needed before a selection can be made.

Two more of the three lower hybrid carts, have been stripped, cleaned, and
repainted. Each cart will support four klystrons. The first of the carts is
now well along with installation of the klystron support hardware.

Work continues on the fast hardware and software needed to
control the klystron power levels and relative phases. Tests were done
to verify hardware timing operation for synchronization of multiple
controller chassis. Using the asynchronous internal 20MHz
clocks on two chassis running identical programs we determined that time to
start sampling after the common start pulses varied only a few tens of
nanoseconds from chassis to chassis with many repeated tests. This is more
than adequate for the application.

Progress was also made in program development for the active controller.
A test program was written to allow characterization of the vector modulator
and i-q detector operation. The i-q detector arrived last Friday and we
are now making plans to characterize its operation. Also, a test
program for communicating between the host computer and two embedded
processors was started and some testing was done.

The Serial fiber optic line (SFOL) receiver prototype board was built
and is ready to be tested with the SFOL transmitter prototype board built
last week.


DNB and Related Diagnostics
---------------------------

Work continued on remounting one of the mirrors in the MSE/BES
in-vessel optics enclosure on to its backing plate. Tests of several
epoxies having advertised low outgassing rates were carried out
using a spare mirror and a sheet of stainless steel. So far, the
epoxied mirrors are resistant to shearing shocks. A final decision
on the best means of securing the mirror will await some additional
tests with epoxies and may include a supplementary means of securing
the mirror to the plate.

The planned repairs to the process gas system for the DNB were completed
last week and the beam was operated for two days. High voltage operation
at 48 kV was easily achieved. The full energy component is significantly
increased over December operation, but still remains below 30%. We will
continue our attempts to improve it this week. Water was still present
in the beam, but at a reduced level which appears to be decreasing with
operation, although more data is needed to confirm this observation.


Power Systems
-------------

Our power engineers met with representatives from NWL to discuss the failure
of two capacitors used in our commutation bank. The capacitors will be
sent back to the company for analysis and possible repair. These capacitors
have already been replaced with spare ones, and the commutation banks are
ready for operation.


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

Dr. Parvez Guzdar, from the University of Maryland, visited last Thursday.
He presented his recent theory of LH transitions and we had useful
discussions regarding possible comparisons with C-Mod threshold data.

Jean Jacquinot, director of the Tore-Supra program at the CEA in Cadarache,
France, visited the PSFC last week. During his one-day visit, in addition to
presenting an IAP lecture on the Highlights and Plans of the European Fusion
Program, he also toured C-Mod and held discussions with various Alcator
scientists. Among the topics covered were possible collaborations with the
Tore-Supra group on ICRF, lower hybrid and diagnostics. He was also consulted
with regard to our proposed J-Port ICRF antenna modifications.

Eric Melby traveled to Los Alamos National Laboratory last week (Jan 23-25) and
gave a talk entitled "Phase Contrast Imaging Observations of Ion Bernstein
Waves in the Alcator C-Mod Tokamak."