From:
WOLFE@PSFC.MIT.EDU
Reply-To: WOLFE@PSFC.MIT.EDU
Subject: Alcator
C-Mod Weekly Highlights
Newsgroups: sci.physics.plasma
Organization:
MIT
Alcator
C-Mod Weekly Highlights
March 13, 2000
Alcator C-Mod
is now undergoing ECDC conditioning of the vessel wall.
ECDC will be in
operation more or less 24 hours a day over the next two
weeks as we
prepare for plasma startup. Work
continues on the RF
and DNB systems, and diagnostic installation.
Engineering:
-----------
ECDC
was begun last Tuesday. Cleanup of the
vessel surfaces has been
going well, with our primary interest being the
the reduction of water
and hydrogen in the machine. The light from the ECDC has also been
useful
for testing and aligning new TV views of the antennas.
The
alternator came back online this week.
It was brought up to half
speed on Wednesday, vibration levels were
checked, and all systems
were checked for proper operation. New signals monitoring the exciter
supply
have been added to the CAMAC system.
The diborane system has been
moved from under the diagnostic stand to
the cell entry vestibule. This change gives much better access to
the
diborane cabinet while also freeing up valuable real estate near
the
machine. Re-routing of control
cables, gas lines, and vents was
required.
DNB
---
All filament and arc supply gate and voltage
regulator boards were
tested and adjusted as required for proper
regulation in dummy loads. Gate
block
circuits were added to all filament supplies to block gates if
the
setpoint is below a couple of volts;
all were tested successfully.
Smoothing capacitors were tested on
filament 2 supply with marked
improvement in ripple. We will be adding these capacitors to each
of the
four filament supplies.
The filament cables and
connectors were inspected, and problems identified by
testing with 100A at
10V. The filaments were characterized and
documented. Parallel cables were
added for the longest straight run of
filament cabling, to reduce the
voltage drop, and the tests were repeated. The
data are being analyzed to
evaluate the improvement.
ICRF:
-----
We completed
modifying the resonant loops on D and E-port to move the feed
point to a
high voltage point. This required
shortening the 36" probe section
to 17.3" and 12.5" for D
and E-port, respectively. Impedance
measurements
indicate that loop lengths correspond to 80.1 MHz and 80.3
MHz for D and
E-port, respectively.
During the disassembly process, E-port feedthru #3
(numbered from
top of the port down) was found to have a loose center
conductor
connection. It had arc damage and
required a rebuild. We made
measurements
so that a single piece could be made to eliminate this assembly
problem.
Transmitter
tuning and testing is being repeated due to identification of a
calibration
error in the diagnostics used in tuning the transmitters. We have
requested RF engineering
support from PPPL and expect C. Brunkhorst to visit
this week.
Physics:
--------
The
TCI interferometer is back in operation.
Changes have been made to the
plasma arm to allow measurements to
be made somewhat farther out in major
radius. The radial coverage has also been reduced to increase the
radial
resolution on the outer channels. These
changes also allowed nearly
3 meters of optical pathlength together with
several large mirrors and mounts
to be removed from the plasma and
reference arms which should
improve alignment stability.
The
new visible TV view of the E-port antenna is operational.
Gerd
Schilling continued work on the C-Mod collaboration Field Work
Proposal,
and prepared the C-Mod contribution to the US - Japan RF
Workshop to be
held at PPPL March 14-16.
Visitors and Travel
--------------------
Bruce
Lipschultz traveled to JET to participate in US-JET collaboration
discussions
held March 7-9. He was part of a group representing the
different US
laboratories as well as particular physics areas. Bruce
collected from US
labs proposals for work on edge physics for JET for
2001-2002. The meeting
was very helpful for understanding the JET program
and their plans. The
JET task force leades expressed strong interest in a
number of US
proposals including those from MIT.
Bruce
also spent part of 3/9 and 3/10 discussing a number of physics issues
with
the JET edge/divertor group. These discussions centered around
similarities
between C-Mod and JET in the area of wall-recycling. He brought
back some
typical JET data for comparison with C-Mod results. He also gave 2
presentations
- SOL transport and wall recycling, and Mo impurity sources and
their
effect on the core plasma.