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
February
16, 2001
We
continued work on modifications to the J-Port antenna, maintenance
of
other rf systems, and fabrication and testing of Lower Hybrid
components. A review of the DNB and related diagnostics
was held on
Thursday, 2/15.
Physics
-------
John
Rice has returned to MIT following 6 weeks of work at LHD. Recent LHD
achievements
include 1 MJ of stored energy, 4% beta, and a 2 minute steady
state
discharge. While there John worked on
analysis of 'naturally'
breathing plasmas, and a comparison with those
induced by running the plasma
against the stainless steel wall of the LHD
vacuum chamber. There is a strong
dependence of the breathing frequency on
the plasma density. There is
also a perturbation on the electron density
and radiated power emissivity
which modulates at the breathing frequency,
located near r/a = 0.5.
John also analyzed some CHS titanium x-ray data
from an imaging camera
system. In the plasma periphery, the emission is
dominated by inner
shell satellites from B- and C-like titanium, and it
can be concluded
that the impurity diffusion is very slow in the plasma
center, and
highly anomalous near the edge. He also attended the large
tokamak
workshop and review of JT60-SC in Tokai, Feb. 7 and 8, where he
presented
recent C-Mod results.
ICRF Systems
------------
After
final checks of the solid model and fitups of the prototypes the
first of
the stripline component data files was e-mailed to the electric
discharge
machining (EDM) vendor. The EDM
machines will be programmed
and final aluminum prototypes will be made and
checked here at MIT. The
inconel 625
needed for the actual components is now in house. We also
made good progress on several small scale
modifications to the back plate
and Faraday screen this week. A new antenna support bracket has been fit
up
invessel. Small modifications will be required to the bracket to allow
for
interference with magnetics diagnostics on the vessel wall.
Oak
Ridge under the direction of Dave Rasmussen has begun to develop
a model
of the PPPL J-Port antenna. Phil Ryan
and Rick Goulding will
work to get the RANT3D and ANTMOD codes up and
running on the rather
complex antenna geometry. Steve Wukitch has provided them with the
data required to
implement the codes and also extensive information
on the damage we
discovered to the antenna components.
We continue to inspect, clean,
and refurbish rf transmitter cavities
in preparation for our next
operation period. We successfully
tested remote
dummy load operation for transmitter #1 and #2. Good progress has been made
on the
acoustic arc detector. The transducers
have shown more than adequate
sensitivity to detect 2 kV/4 joule arcs in
the transmission line.
We have seen phase delays from the mechanical
impulse that should allow
localization of the arc source.
Work
on adding new phase balance fault detection for J antenna continues.
The
fault indicator board construction is complete. The phase balance board
construction is still in progress
with completion expected next week.
DNB
---
A
review of the DNB and related diagnostics was held at MIT on Thursday,
2/15. The panel members were Fred Levinton
(PPPL), Ray Fonck (UWM), Larry
Grisham
(PPPL), and Al Von Halle (PPPL). Chuck
Finfgeld organized the review
and represented DoE. Many from MIT attended including Bob
Granetz,
Earl Marmar, David Terry, Howard Yuh, Jim Irby, Bruce Lipschultz,
Jim Terry,
and John Rice. Gerd
Schilling and Garrit Kramer attended from PPPL.
Rostom Dagazien (DoE)
participated in the review via video conference.
The charges to the panel were:
Please
comment on the progress in installation and initial operation
on Alcator
C-MOD of the University of Texas Diagnostic Neutral Beam (DNB),
giving due
consideration to the financial, material and human resources that
have
been available.
Please comment regarding the difficulties that have
been encountered
in initial DNB operation, and give every suggestion you
can for improving
DNB performance.
Please provide your best
assessment of the potential ultimate
performance of the DNB and the
resulting prospects for the desired plasma
diagnostic measurements,
including current density profile (MSE), ion
temperature and rotation
profiles (CXRS) and internal fluctuations (BES).
A complete report
will be provided by the committee soon.
Earl Marmar has assigned
responsibility for coordinating DNB and
related diagnostic activity to Bob
Granetz, implementing a suggestion made
by the C-Mod Program Advisory
Committee that a senior staff member take
on this challenge.
Lower
Hybrid Project
--------------------
The drawing package
provided by Symmes, Maini & McKee Associates
(SMMA) regarding the
Lower-Hybrid space change is being reviewed.
Several problems have been
noted mainly with water pipe routing.
We are preparing a response.
Information
of cell layout, launcher/coupler drawings from PPPL, and
mezzanine layout
from SMMA have been used to create a Lower-Hybrid cell
layout
drawing. This drawing is to be given to
SMMA to assist in water
plenum routing to avoid mechanical
conflicts.
The circulator source selection has been completed and
the procurement
process has begun.
Modifications to and wiring
of klystron carts continue.
The vector modulator that will be used
to control the amplitude and
phase of the output power from the klystrons
is now in house. A test
setup is
being assembled to characterize this new component. Work has
begun on the LH timing system interface design.
Work continued on software
tests and development for active controllers.
Progress was also made on SFOL
fiber optic links. The fiber transmitter will be operational
next week.
Inner Divertor
--------------
Tiles
and other components continue to arrive and go through Q/A. Silver
plating of fastener hardware is
proceeding. The fabrication of
the
rear girdle and C-plates is on schedule.
Power
Systems
-------------
The rework of the OH commutation
capacitor banks is nearly complete.
These
changes will reduce the strain on the capacitor terminals
during
commutation.