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
March 30, 2001


Work continued on modifications to the J-Port antenna and ICRF control
system. The DNB, inner divertor, and Lower Hybrid MIE projects all moved
forward this week.


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

All ebeam welding of the striplines has been completed. Final machining
operations are now being done on the components. An 0.0005" layer of
copper will be plated on the striplines early next week followed by a
vacuum bake. A picture of one of the long stripline can be seen at

http://www.psfc.mit.edu/cmod/operations/EngImages/RF/ICRF/P0001408.JPG

The last of five diagnostic access holes in the J-Port flange has been
completed. Invessel cleanup inside the port can now begin in preparation
for installation of the antenna. We expect reassembly of the antenna to
begin within the next 10 days as scheduled.

All six of the B-dot probes for the J-Port antenna have been fabricated.
An absolute calibration of the probes will be done over the next few days.
Invessel cabling and cable clamps are being installed for the probes.

Small adjustments to the auto-tuning PLC program were completed this week.
This system is now operational. Changes to the ICRF tuning
components can be made from the VAX workstations with a direct link
from the tuning program.

The prototype phase demodulator board has been sent out for fabrication.
However, improvements are also being made to the PPPL demodulator modules to
improve their phase response during fault conditions over the next run period.

We continue maintenance and upgrades to the #1 and #2 transmitters.


DNB
---

The automatic mode for the DNB was brought into operation this week and the
time between pulses decreased from 150 to 120 s. Data for the arc current
overshoot was taken. An anticipated strong dependence on the time between
the prepulse and the main pulse did not materialize. The overshoot does
change with the time between pulses, but is not eliminated. We will continue
investigation of the overshoot by making correlations with spectral
measurements of the arc plasma and by monitoring it as a function of
conditioning time.


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

More testing of the active controller was done this week. A loop
test summing amplifier was built so that we could add an error voltage to
the closed loop to test the PID program calculations. We did some tests
with both square wave and sine wave perturbations and were able to show
that the program is working correctly.

The high yard protection systems are being reviewed and work is underway to
verify that the existing cabling and breakers are acceptable for supporting
the new LH systems, and that we will be able to set the protective relays for
proper coordination.

A meeting was held with MIT this week to finalize the schedule for the
MIT funded LH site modifications. Details of the Hi-Yard changes and
work to be performed in the cell were discussed.

Work continues on the klystron carts.


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

Tiles continue to arrive and proceed through QA. We now have all the upper
and lower transition tiles. The vendor is on schedule fabricating the rear
girdle plates. They have stress relieved all plates to prevent movement after
machining. Another vendor has nearly completed machining of the ribs
on all the C plates. This process is the most difficult of the machining
operations and provides the keys to limit motion of the tiles. High
strength bolts and nuts continue to arrive and undergo testing.


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

Modifications to the EF1U-L commutation bank have begun. The other banks
are now complete except for installation of a few recently repaired capacitors.


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

A laser will be loaned to MIT from UT-FRC for cold pulse experiments during
the continuation of the current run campaign. This laser was used
on TEXT for the same type of experiments. It was taken out of
storage and tested recently at UT-FRC. The laser is now packed for
shipping and should arrive for installation and commissioning prior
to the resumption of experimental work.

The first of the CXRS shutter parts was delivered by the MIT Central
Machine Shop. Other parts are being fabricated in the Alcator and UTex
shops as we press to get the shutters installed invessel.


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

Stewart Zweben visited this week from PPPL to discuss upgrades to his
fast imaging fluctuation diagnostic.

Jim Irby visited PPPL last week for discussions with Douglas Loesser,
Randy Wilson, Stefano Bernabei, and Gerd Schilling on the Lower Hybrid
Launcher. He also met with Raffi Nazikian and attended a PPPL/MIT proposal
review of the reflectometry collaboration.