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 19, 2001


All lower TF arms have been removed from the machine and are being
carefully inspected. Work continued on the Lower Hybrid Project, with
a large amount of activity focused on the HVPS installation. We also
continue to work on the ICRF systems and prepare for the new DNB.


Physics
-------

The addition of a taper to the waveguide transition pieces has improved the
Gaussian beam pattern significantly in the ECE radiometer at
F-port. This change allowed for the shift of the Gaussian beam waist from
R=0.9 m (near separatrix) to R=0.75 m (r/a=0.3) with smaller poloidal
width (~8 mm). With these improvements, the cross power correlation studies
of electron temperature fluctuations have made progress. At r/a=0.7, a pair
of channels showed coherent thermal fluctuations in the frequency range of
550 - 680 kHz, which started to appear within 2 % error and became
conspicuous at 1.5 % error (increased number of shots in the average).
The data were numerically simulated (Te fluctuation = 1 % of the standard
deviation of random background noise) successfully. However, the cross phase
information in the coherent region obtained from the experiments may not be
reliable yet in that there were non-random cross phases even in non-coherent
frequency ranges.

A great deal of work is now going into preparations for the APS meeting.
Dry runs of the oral talks and poster sessions which began on Thursday of
this week will continue until mid next week.


Inspection
----------

All lower TF horizontal arms have been removed from the machine and access
has been gained to the OH2 lower coax. A detailed inspection of the TF
arm and core fingers will begin next week. We expect to remove the OH2 lower
coax next week at which point the disassembly of Alcator C-Mod will
be complete.


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

We continue to install lights, receptacles, switchgear, panels, and blowers
in the HVPS. Outside conduit runs for 208 volt AC service to the HVPS are
complete and wiring is pulled and terminated. Fiber optic cables between the
HVPS and power room are pulled and ready for termination on Monday. Control
cables between the HVPS and power room are pulled and terminated at the power
supply and junction box ends. The ground to the HV Junction Box in the power
room is being run. Work has started on mounting the snubber and electronics
in HV Distribution box in the power room.

Wiring of the transmitter control and protection cabinets is
progressing with the first cabinet complete, and the second one started.
Wiring of the transmitter test setup was completed this week. A systems
test of the control, protection, and supply control circuits will begin
soon. Drawings for the water system instrumentation interfaces are complete
as are the design and PCB layout of the pump controller optical interface
boards.

Brackets and panels for the LH Low Power Microwave Rack booster amplifiers
have been fabricated.

The date for circulator design review to be held at the vendor's location
in Backnang, Germany has been set for December 3 and 4.

Contractors continue work on the klystron water cooling system and the cell
mezzanine.


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

Work continued on the phase demodulator system. Selection of the proper
local oscillator to use is underway. Drawings are being developed for the
new layout of the rf racks in the cell and power room. Development of a
transmission line model using simulation results from the antenna code
continues. Design of new boron nitride tiles for the J-Port antenna is
well underway. The changes to the tiles will reduce plasma interaction with
the plasma facing surfaces.


DNB
---

Dexter Beals (UT-FRC) is now permanently on-site at the PSFC as DNB Engineer.
The requirements for the Padova beam are being compared to the present DNB
resources to determine the extent of required changes, and the equipment that
can be recycled into a new system. Thus far, it is evident that we can
recycle vacuum equipment, PLCs, and some beam diagnostics. New support
systems will be required to provide liquid helium for the cryopumps
and SF6 handling and recovery for the step-up transformer.


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

Joe Snipes presented a proposal for a new magnetic probe array at the weekly
Physics Meeting. It would consist of a closely spaced (4 mm) array of five
poloidal magnetic field pick-up coils to be mounted on the inner wall at the
midplane to measure the quasi-coherent mode (QCM). The array would measure
the mode amplitude and k_theta at the inner wall for comparison with
similar outboard measurements to determine if the QCM has a strong ballooning
character or not, and to verify the expected strong dependence of k_theta on
poloidal position.


Visitors
--------

Richardo Maqueda, our LANL collaborator, was on-site all this week
to help with data analysis of divertor surface temperatures from the long
pulse discharges, and to ship the IR camera back to LANL.