Newsgroups: sci.physics.plasma
From: FAIRFAX@CMOD2.PFC.MIT.EDU (Steve Fairfax)
Organization: MIT Plasma Fusion Center
Subject: Alcator C-MOD

ALCATOR C-MOD

Alcator C-MOD is the third in a series of compact,
high-field, high-performance tokamaks designed and built at the
Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts,
USA. The design combines flexible shaping and dominant auxiliary
heating with plasma performance that will rival today's largest
machines.
Alcator derived from the Italian words "Alto Campo Tori," or high
field torus. The hallmark of the Alcator program has been compact, high
field devices that produce plasmas with low Zeff, high plasma density,
high current density, and good confinement. Alcator A, with a toroidal
field of up to 10 Tesla, major radius R=64 cm, and minor radius a=10 cm,
demonstrated the validity of this approach. Alcator B was designed but
rejected as not aggressive enough. Alcator C, with a toroidal field of
12 Tesla, R=64 cm and a=16 cm, extended the results of Alcator A and
achieved record confinement with a Lawson parameter of 6x10^19 sec - m^-3
in 1983.
Alcator C-MOD is a modification of the Alcator C facilty. The
Alcator C tokamak was transferred to Lawrence Livermore National Laboratory
and renamed the Microwave Tokamak Experiment (MTX). MTX studied the use of
free electron lasers to provided electron cyclotron heating in high-field
fusion plasmas. The MTX project has been suspended due to budgetary
limitations.
Alcator C-MOD uses some of the facilities of Alcator C (primarily
the energy supply) but the tokamak core is of entirely new design.
Authorized for design and construction in 1987, it incorporates plasma
shaping, diverters, and dominant auxillary heating.

Parameters:
Design Achieved
Major Radius 0.67 m 0.67
Minor Radius 0.22 m 0.22
Toroidal Field 9 Tesla 5.3 Tesla
Flat-top 1 sec @ 9 Tesla
7 sec @ 5 Tesla
Plasma Current 3 MA 1.1 MA
Aux. Heating 4 MW 2 MW ICRH @ 80 MHz; Upgrade to 8 MW
planned.
Elongation 1.8 1.7
Triangularity 0.4
Volt-seconds 7.5 Wb
Magnet Energy 500 MJ

The choice of parameters is intended to provide maximum performance
and relevance to future experiments consistent with today's limited budgets.
Ohmic performance is expected to provide values of n_tau up to
10^20 sec m^-3 at temperatures up to 3 keV. The addition of the
present 4 MW ICRF heating will raise electron and ion temperatures to
about 6 keV and provide important information for next generation experiments.
The device incorporates a metallic (Mo) first wall and two
diverters. The upper diverter is a flat-plate design while the
lower diverter is closed. The plasma can be run single-null,
limited, or double-null. The plasma shape and position control
system can make these changes between shots or during a shot.
The experiment became fully operational in May of 1993.
Early experiments included discharge development and diagnostic
calibration, but rapid progress was made and within 5 months 1 MA,
fully diverted discharges with up to 1 MW ICRH power were achieved.
Early confinement results included L-mode scaling and the achievement
of Ohmic H-modes. After a shutdown to upgrade the energy storage and
install two dipole ICRH antennae in the vacuum chamber,
operations resumed in April 1994.

Alcator C-MOD Weekly Highlights
July 21, 1994

The maintenance/repair period is continuing. The partial disassembly is now
complete. This procedure took a total of 26 calendar days, slightly less than
the initial projection. The OH2L coax buss has now been removed, and the
central column, comprising the three OH coils and the TF centerpost, has been
extracted and re-positioned on the lower dome.

As anticipated, the problem with the OH2L buss was in the vicinity of the
bolt-up connection between the buss and the terminal block on the coil,
specifically, with the center conductor of the coax. Detailed examinations
of the OH2L and OH2U coaxes, as well as tests on a dummy (prototype) coax, are
being conducted to identify the cause of the problem and qualify the solution.

Some minor damage is present on the mating surface of the OH2L terminal block.
This will be repaired by resurfacing in situ. The integrity of the coil does
not appear to have been compromised, based on electrical measurements, and
initial xray inspection. The effects of the coax problem are localized to the
immediate vicinity of the bolted connection, and no other coils were affected.

Dr. Roger Richards of ORNL is onsite to install his CO2 laser scattering
experiment. The main shipment of equipment from Oak Ridge arrived on Tuesday,
and the apparatus is being set up in one of the three experimental bays
adjacent to the C-MOD cell. This experiment will measure ion tails produced
during ICRF heating on C-MOD. The diagnostic is prototypical of an alpha
particle diagnostic proposed for ITER.

Dr. Yuichi Takase has begun a three-week visit to JT-60U in Japan. He will be
participating in their ICRF experiments. Dr. Earl Marmar attended the first
meeting of the ITER International Experts Group on Diagnostics at the San
Diego Co-center this week. From there he is proceeding to Austin, where he
will be working on the APS DPP program committee. Dr. Bruce Lipschultz is
attending the TPX PAC meeting in Tennessee.

[Moderator: As stated in the opening statement of purpose for the
sci.physics.plasma newsgroup, FUSION PLASMA POSTINGS ARE WELCOME although
we want to maintain a balance with other plasma science and technology
entries. For reference purposes to supplement the above Alcator description,
Steve Fairfax suggests the standard plasma physics journals as well as
APS and EPS conference proceedings.]