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Looking upward from inside the DIII-D vessel, you see the upper
divertor. Behind the shiny baffle tiles hides a cryogenic pump kept at
4 degrees above absolute zero. The pump is used to remove gaseous
deuterium by condensation. When DIII-D is operating, the plasma
chamber is filled with ionized deuterium (plasma) that is heated to
over 100 million degrees Kelvin. The plasma flows along the magnetic
field lines to the divertor tiles (dark surface at upper left), where
it is neutralized. Then the neutralized deuterium flows though the gap
and is pumped out of the DIII-D vessel. The tiles are made of graphite
in order to handle the extreme heat load from the plasma. The
"windows" in the vessel are ports for various types of
instrumentation. | DIII-D National Fusion Facility |
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Over the past three decades, the General Atomics' fusion program has
been a major contributor to the significant progress in developing
innovative fusion concepts, increasing understanding and
predictability of reactor plasma regimes, extending plasma parameters
to power plant conditions, advancing fusion technology, and refining
magnetic fusion power plant concepts. The DIII-D facility is being
continuously improved to provide the capabilities to address current
research issues. Recent activities include a focus on advanced
tokamak (AT) operating modes, with scientific objectives that include
advancing understanding of plasma turbulence and transport. Within
this broad context, direct interactions with the Center for Multiscale
Plasma Dynamics aimed at extensive experiment and theory iterations to
understand the physics of turbulence, transport and neoclassical
tearing modes naturally complement the DIII-D research program.
Initially, the CMPD is supporting the ongoing research of Peebles,
et al., on DIII-D, utilizing the recently installed microwave
back-scattering diagnostic to investigate the role of ETG fluctuations
and transport. The technique is based on microwave backscattering in
X-mode polarization at approximately 100 GHz to probe
wavenumbers in the range of 40 inverse centimeters. For a typical
DIII-D plasma, this corresponds to looking for fluctuations in the
range where simulations predict strong ETG fluctuations could be
observed. The system will eventually be fully integrated with an
upgraded far-infrared (288 GHz) forward-scattering system at
the same port location, allowing simultaneous probing of large and
intermediate scale turbulence. This will directly support the
Center's effort to study interactions between turbulent fluctuations
at disparate spatial and temporal scales.
Later, as simulations of sawtooth physics and neoclassical tearing
modes become available, the CMPD will support experimental tests of
the simulation predictions.
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