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
6, 2001
Installation
of the J-Port antenna began this week.
Work continued on the
RF control system, DNB, inner divertor, and
Lower Hybrid MIE project.
Physics
-------
Analysis
of neutral particle transport in the main-chamber scrape-off layer
(SOL)
at the outer midplane has been performed for a small set of discharges
using
a newly developed neutral transport code, KN1D. This new
code is a 1-D
space, 2-D velocity kinetic code that treats atomic and
molecular
transport including molecular dissociation, charge exchange, and
elastic
collisions between neutral and plasma species. The code takes as input
the
measured plasma density and temperature profiles in the main-chamber
scrape-off
layer and the measured molecular neutral pressure near the wall at
the
midplane. A unity recycling condition on main-chamber limiter and wall
surfaces
is imposed, consistent with that expected in experiment.
In most cases,
neutrals contribute to an inward-going heat flux 'pinch' across
the
separatrix. A comparison with the magnitude of cross-field plasma heat
convection
in the near and far SOL shows that neutrals play only a minor
role in the
total heat transported across the scrape-off layer.
A meeting was
held at MIT on April 3 to investigate the possibility of
using Li as a
divertor material in Alcator C-Mod. Mike Ulrickson
(SNLA), Dennis Whyte
(UCSD), Dick Majeski (PPPL) and Jeff Brooks
(ANL) all came to participate
in this meeting. Participants from
C-Mod included Bruce Lipschultz, Brian
LaBombard, Jim Terry, Spencer
Pitcher, Jim Irby, Earl Marmar and Bob
Granetz.
Dennis Whyte spent an additional day at C-Mod
discussing
wall-recycling data taken at DIII-D as part of a joint
mini-proposal
in which Bruce Lipschultz participated. Progress was made
on
issues of how to present data from C-Mod and DIII-D jointly and in
what
format. Discussions with Brian LaBombard included observations
and
computations of particle and energy fluxes in the SOL of C-Mod
and
a comparison of fluctuations phenomena observed in the SOL of DIII-D
and C-Mod.
ICRF Systems
------------
Machining
and polishing of all stripline components were completed this
week, and
copper plating of these components will be completed early
next week. Following a vacuum bake, they will then be
ready for installation
invessel. A
picture of one of the long striplines ready for plating
can be found
at
http://www.psfc.mit.edu/cmod/operations/EngImages/RF/ICRF/P0001428.JPG
A
fitup invessel of the new antenna support plates has been completed
and
studs have been installed to support the plates. The new J-Port windows
and pressure port have been installed
on the flange and are ready to be
leakchecked. The flange support plate has been taken invessel and
punched
for drilling at the new diagnostic port locations. The Faraday screen has
been aligned on
the test stand and will be ready for installation following
laser welding
of the new gap cover plates. The vessel
wall in and around
J-Port has been ground and polished to a near mirror
finish in preparation for
the antenna installation.
Testing and
calibration was begun this week of the six phase demodulator
modules to be
used for phase fault detection on the D, E, and J-Port
antennas. The new prototype demodulator board is back
in house from the
vendor and will soon undergo testing.
DNB
---
The
beam was operated in automatic mode for two days this week as we
continue
the conditioning process.
The optical sections of the edge and core
CXRS in-vessel optics were
cleaned, calibrated, and reassembled. In-vessel backlighting tests
demonstrated
that the alignment is adequate for the experiments. The
shutter assemblies for the two systems are under
construction and
delivery is expected on Monday. Installation of the shutter
actuation
cables has begun.
Lower Hybrid MIE Project
------------------------
Work
continued on the serial fiber optic link.
The prototype is working
and undergoing tests. Digital I/O definitions are being finalized
for the
LH phase and amplitude control system. Some hardware/software issues that
have caused program
crashes are being worked out with the
vendor.
A 3 kW, 2.45 GHz
source is being setup in the LH lab and will be used to
test arc detection
concepts and electronics.
Further progress is being made at PPPL on
the design of details of
the Lower Hybrid launcher. Advantages are becoming apparent in
replacing
the original geared chain-driven launcher drive with a
hydraulic
version.
Over the last two weeks, Ron Parker and Montgomery Grimes
visited Tore-Supra,
JET, and our LH high voltage power supply vendor. At Tore Supra, they
discussed recent
lower hybrid current drive results and plans for the next
campaign
including the design of the new launching antenna.
At JET, recent
progress in the JET lower hybrid experiments was discussed.
These
experiments had been plagued by coupling problems, especially during
high-power
auxiliary heating. Recently the coupling has been substantially
improved
due to a number of factors including better congruence between the
coupler
and plasma shapes, puffing of CD4 near
the launcher to increase
the plasma density near the multijunction grill,
and four days of dedicated
run time during which optimization of the
coupling could occur. A
"trophy
shot" with 3 MW of lower hybrid power and ~ 20 MW of NBI and ICRF
power
that maintained a reversed shear discharge for ~ 8 s was obtained.
Both
electron and ion ITB's were formed and the non-inductive current drive
has
been calculated to be > 80%. The
possibility of expanding the
collaborative relationship between C-MOD and
JET was also discussed.
The Lower Hybrid high voltage power supply
is progressing on schedule.
Preparations for installation and the required
acceptance tests were
discussed.
Inner
Divertor
--------------
Tiles continue to arrive and machining
continues to be done on the
new inner divertor. A picture of one of the C-Plates being machined
can be found
at
http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/Mar30_05.jpg
Note
the keyways for holding the tiles in place.
Power
Systems
-------------
Work on the EF1U-L Capacitor bank
modifications was completed this
week.
We have started installation of new Hi-Yard instrumentation
to better
monitor power delivered to the LH, ICRF, and Alternator systems
this week.
Travel and Visits
-----------------
Steve
Wukitch attended the US-Japan RF physics workshop in Japan March 22-24.
Miklos
Porkolab attended the Annual Sherwood Fusion Theory Conference in Santa
Fe,
NM, on April 2-4. Paul Bonoli also attended the conference.
Bob
Childs was in Brooklyn, NY supervising copper plating of the stripline
components.
Martin
Greenwald was in Lausanne for an International Database meeting.
David
Mikkelsen (PPPL) presented a talk on "Turbulent Transport
Simulations
of C-Mod" at the Confinement Database and Modelling Workshop
at CRPP
in Lausanne - 2-6 April, 2001.