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
April 13, 2001


Work continued this week on the J-Port antenna modifications, LH
MIE Project, and several diagnostic systems. Installation of the
J-Port antenna will begin early next week.


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

All stripline components for the J-Port antenna upgrade are back in-house
following copper plating. Final machining operations have been completed
and the components have been fitup on the antenna test stand. A picture
of the fitup can be seen at

http://www.psfc.mit.edu/cmod/operations/EngImages/RF/ICRF/P0001488.JPG

Note that the surfaces conducting rf currents have been copper plated while
the rest of the surfaces have been left bare inconel. This design
detail reduces disruption forces by a factor of two.

The components are now undergoing a vacuum bake after which installation
invessel will begin early next week.

The windows, pressure monitoring tube, electric break, bellows, and gauge
have all been successfully leakchecked on the J-Port flange. The fibers
have been installed in the windows, back illuminated, and aligned to view
the striplines. Components for supporting the gauge, magnetic shielding,
and pressure tube have been machined and are undergoing fitup. The
PMT amplifiers needed for the fiber views have been modified for the faster
response time needed for fault detection and are ready to be re-installed
in the cell.

The rf vacuum feedthroughs are being installed and leakchecked.

Sixteen of approximately twenty phase demodulator modules have been upgraded,
checked for proper operation, and re-installed. The primary focus for work
on the rf instrumentation has now shifted to maintenance of interconnecting
wiring and cabling.


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

The CXRS F-Top periscope has been reinstalled. Transmission measurements
were completed and show that the transmission increases from more
than 70% at 2500 A to more than 80% at 7500 A. Measurements
following removal at the beginning of the current vacuum break
indicated no transmission at the lower wavelenghts due to
plasma-induced coating. The coating was removed by polishing.

The machining of the core and edge shutters for the invessel CXRS optics
is complete. Both systems have been re-installed invessel and tested
for proper operation. The only remaining task is spot welding the control
cable runs into position. Adding shutters to these systems was a strong
recommendation of the DNB review committee. The high-resolution edge CXRS
system has also been re-installed. A new window and grounding grid have been
added to this systems to protect its mirror from glow discharge cleaning
and boronization.

The modified waveguides for the heterodyne ECE system were brazed, cleaned
and baked, and the optics were re-installed at F-port. The modifications to
the in-vessel quasioptical focussing system are now complete. The transition
waveguides were modified to improve the imaging of the ECE system and
increase the maximum k that can be observed by the system.

Work continued on the design of the driver electronics for the MHD
antenna.


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

At PPPL, two three-window prototype couplers have been successfully
brazed and passed leakchecks. A process for repairing leaking
window seals was also developed and tested successfully.
Windows with larger corner radii, which would have reduced stress levels
compared to the current windows, are also being prepared. These tests
are very encouraging, and indicate we can expect good results as we go
to the 24 waveguide coupler modules needed for the lower hybrid launcher.

MIT and PPPL are discussing plans for high power component testing to
be done when the high voltage power supply and klystron installations
are complete in approximately seven to eight months. The list includes
3db couplers, water loads, DC breaks, phaseshifters, and tapers.

Limiter shape and field ripple data have been given by MIT to PPPL to be
used in designing the coupler plasma facing surface.

The prototype digital serial fiber optic link is now running at its
design speed of 50 Ksamples/s. The prototype will be linked to the
I/Q vector modulator as a primary test of the link. Work on the LH
phase and amplitude control system continues. Digital i/o definitions
and descriptions have been completed.

The walk-through for prospective contractors for the LH site modifications
was held this week.

Work proceeds on the klystron cart modifications and wiring. A new
safety interlock key/lock was test fitted. This lock is manufactured by
the same company used by our high voltage power supply vendor, and will
use their key interlock system. This system will provide seamless
compatability with the safety key interlock system in the power supply
container used to provide access to high-voltage areas associated with the
Lower Hybrid transmitter.

The electrical design of the transmitter control electronics is nearly
complete. Work this week concentrated on the interconnection wiring;
specifically, the EMI/RFI interface.


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

Components continue to arrive and be checked. The vendors for the
backing- and C-plates continue to make progress. Pictures of
tile fitups on one of the plates can be found at

http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/Apr12_09.jpg

The fish scale design of the tiles can be seen as well as the ribs
machined into the plate to restrain tile motion.


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

All work on the commutation capacitor banks has been completed,
including calibration of the Rogowski coils.


Travel and Visits
-----------------

Les Gereg and Joe Frangipani from PPPL visited this week to help with
the fitup of antenna components and the installation of the rf
feedthroughs.

Pat Diamond visited Thursday and Friday and gave two informal talks and
the PSFC seminar. He talked with several C-Mod physicists.

Martin Greenwald travelled to Lausanne Switzerland to participate
in the international database meeting held April 2-5. He took
the opportunity to meet with Jo Lister, Basil Duval, Richard Pitts
and Yves Martin to discuss plans for joint experiments with the TCV
group.

Last Friday, 4/6, Amanda Hubbard gave the Plasma Physics Colloquium at
Columbia University, NYC, entitled "Edge transport barrier and
fluctuations in Alcator C-Mod".

John Rice was at the Univ. of Wisconsin on Monday, Apr. 9, and gave
a seminar on the latest C-Mod results.

Rejean Boivin was at GA this week and gave a talk on neutrals.

Paul Bonoli participated in the NTCC PAC meeting.