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
August 10, 2001


Alcator C-Mod is now up-to-air, and invessel inspections, documentation,
and calibrations have begun. Following the run on Friday, August 3rd, the
LN2 cooling system for the machine was shut down and secured. Two
days of helium glow discharge cleaning were run over the weekend to reduce
heavy boron compounds to safe levels. The vessel was brought up-to-air
on Monday, and manned entry began on Wednesday.


Operations
----------

Preparations for the machine inspection began Monday as the process of
removing equipment and diagnostics from around the machine was begun.
Work was concentrated on the top of the machine, so that we can begin
removal of the igloo blocks, and the east side of the cell where LH
site modifications will take place.

Invessel work began with careful documentation of the vessel with both digital
pictures and video tape. The calibrations of several diagnostic systems were
completed by Friday. Following more measurements and documentation next week,
removal of invessel components will begin in preparation for installation
of the new inner divertor.


Physics
-------

Robert Granetz, Bruce Lipschultz, and Bill Rowan presented some of the DNB
CXRS measurements from the recent run campaign at this week's Physics
Meeting. Spectral lines from hydrogen-like species of helium, boron, and
carbon have been observed. Background line emission from recombination and
excitation dominates the emission from beam charge exchange, which makes it
very difficult to extract spatially-resolved ion temperature and velocity
profiles. The strongest CXRS signals came from the B+4 7->6 transition
(494.5 nm), which shows a doubling of intensity when the DNB turns on.
This particular line appears to have significant Zeeman broadening, and
detailed spectral analysis is in progress.

Experiments were performed with a two-coil fast magnetic scanning probe at
A-side to measure the poloidal phase difference of the two coils during the
Quasi-Coherent Mode (QCM) in EDA H-mode. The magnetic probe shows that
QCM ktheta varies from at most 2 cm^-1 to 1.1 cm^-1, typically about 1.4 cm^-1
measured 10 cm above the outboard midplane. Radial decay magnetic
measurements of kr agree reasonably well with direct ktheta measurements from
the double magnetic probe so that kr ~ ktheta. PCI kr measured simultaneously
was typically 5 cm^-1. Much of this discrepancy can be explained by flux
expansion in the divertor and by the angle that PCI makes with respect to
the field lines. Sometimes ktheta varies early in EDA H-mode, sometimes
remains constant. Small ELMs on top of EDA have a broadband spectrum that
interrupts the QCM.


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

Work has begun on installing and configuring the modules needed for the link
to the PLC controlling the Klystron High Voltage Power Supply. Some
components of the PLC software have been completed and downloaded to the
controller.

Work continues on installation of TPS components.

The SFOL transmitter prototype pc board will be sent out to the manufacturer
on Monday. The receiver board will lag by about 2 weeks.


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

Work continues on upgrades to the ICRF control system. PC boards for the
new demodulator scaling and phase detection circuits have arrived and have
been populated with parts. Some testing has started. Verification of the
"as built" drawings of the current control system is underway.


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

Work resumed on stud welding tests this week. The stud-on-stud welding
required at some inner wall locations is working well with full strength
welds being obtained routinely. All fixturing for the Rear Girdle plates
has been completed by our vendor. We hope to have these final girdle
components in house by early September. Work also continues on the new
magnetics and divertor probes that will be installed with the divertor.


DNB
---

Some disassembly of the beam was completed to facilitate the main
C-Mod disassembly. The invessel portion of the BES and CXRS
calibrations, backlighting, and documentation were completed. This work
included absolute intensity calibration of the optical systems at the
principal wavelengths used for measurements and backlighting for
measurement of the plasma volume that was viewed. The beam duct
monitors were calibrated. The remaining calibration work consists of
transfer fiber transmission measurements and spectrometer instrument
function measurements which will be completed next week.


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

Doug Loesser from PPPL visited on Wednesday to discuss the action
items generated by the Lower Hybrid Final Design Review held July 31
at PPPL. All seventeen items were gone over in detail and PPPL and MIT
responsibilities were defined.

Martha Redi visited CMOD at MIT this week, 8/6/01-8/10/01, to work on
gyrokinetic simulations of off-axis RF heated experiments and have
collaborative discussions with MIT scientists Catherine Fiore and
Paul Bonoli.