The DIII-D National Fusion Facility has completed a series of
important enhancements, providing researchers with several
first-of-a-kind tools for controlling and understanding the
function of fusion plasmas.
These upgrades will further strengthen DIII-D’s
standing as one of the most flexible and capable magnetic fusion
research facilities in the world and help close key physics gaps
between current experiments, the first fusion pilot plants (FPPs),
and future fusion reactors.
“The upgrades made to DIII-D over the last eight
months provide us with exciting new capabilities and key
enhancements to existing systems for studying fusion energy,”
DIII-D Director Richard Buttery said. “Our
scientists will be able to use our upgraded systems and diagnostics
to answer key questions on commercial industry–relevant technology,
materials, and operations, as well as continue our support of ITER
and advancement of foundational scientific understanding.”
DIII-D is a U.S. Department of Energy (DOE)
Office of Science user facility and a world-class fusion laboratory
where over 700 researchers from more than 100 domestic and
international institutions – including U.S. national laboratories,
academic institutions, and industry – explore a wide range of
topics from fundamental plasma science to fusion power plant
operations.
At the heart of the facility is the DIII-D
tokamak, a toroidal (doughnut-shaped) vacuum chamber surrounded by
powerful electromagnets that confine plasmas – a state of matter
with large quantities of ionized particles – at temperatures
exceeding 10 times those of the Sun. At these high temperatures,
hydrogen isotopes fuse together and release energy.
The facility has been offline since July 2023 as
a multi-institutional team of engineers and technicians worked to
install new capabilities. These include systems for enhanced
control of fusion plasmas; a range of new diagnostic instruments;
enhanced capabilities for heating plasmas and driving the current
that supports the fusion reaction; and enhancements to the divertor
system that removes exhaust heat and impurities from the
tokamak.
Together, the new technologies installed during
the eight-month upgrade will play a key role in developing the
scientific basis for fusion as a reliable and nearly limitless
energy source. When experiments restart in May, researchers will
use these tools to optimize the performance of fusion plasmas and
help bring practical fusion energy closer to reality.
Enhanced Plasma Control
DIII-D’s plasma control system (PCS) is a
key tool for researchers in shaping and controlling fusion plasmas
during experiments. Upgrades to its computational and diagnostic
capabilities will allow for more rapid development and deployment
of new and increasingly complex real-time control and analysis
techniques in support of research on DIII-D. The upgrades include
32 new processing cores that were added to the PCS real-time
computing systems, additional signals from diagnostic instruments
for additional data inputs, and improvements to real-time signal
filtering.
New Diagnostics
The diagnostic upgrades include a mix of new
instruments and new support systems to enhance the performance of
existing instruments. These instruments will provide more accurate
measurement of important characteristics of DIII-D plasmas.
One method for handling the intense power
exhausted by the plasma is to maintain neutral gas in the wall
region where the exhaust is directed. To better understand how the
plasma exhaust interacts with this background gas it is necessary
to measure the distinct gas pressures of each present species;
however, traditional pressure gauges are ineffective in the
presence of strong magnetic fields. As a solution, DIII-D
scientists devised an innovative method using light emissions to
gauge pressure. This instrument, called a Wisconsin Penning gauge,
measures the pressures of different gases that accumulate near the
wall.
Due to the extremely harsh plasma environment,
the main wall of a future fusion reactor will be made of robust
metals such as tungsten. However, tungsten impurities (and other
elements high on the periodic chart) can cause significant cooling
of the plasma. To better study the transport behavior of tungsten
and similar elements, as well as the associated effects, existing
systems were given a larger UV-transparent window and diagnostic
platform to enable a much wider view and more flexibility in the
viewing region. Another instrument, the Radial Interferometer
Polarimeter (RIP), provides measurements of the equilibrium and
behavior of the magnetic fields. The RIP system was upgraded to
improve its sensitivity and range of measurement while also
expanding its sensitivity to the 3D-characteristics of these
fields.
The radiated power from plasmas can be measured
by an instrument known as a bolometer. However, thermal stability
and electromagnetic interference are common issues with
conventional bolometers. DIII-D scientists developed a new
instrument that avoids interference with a measurement approach
that does not use electronics. The Fiber-Optic Bolometer is an
optical device that measures radiated power using an interferometer
to convert radiation into temperature variations, which are
measured from the shift in the reflection spectrum.
A system known as Charge Exchange Recombination
(CER) Spectroscopy is used to measure temperature, density, and
behavior of the plasma. A subset of the components in this system
known as MiCER is used to measure emissions from the hydrogen fuel.
A new MiCER system that allows measurement of higher energy
particles near the divertor has been installed. This new system
will be used to improve understanding of boundary plasma
physics.
Enhanced Heating and Current
Drive
FPPs and future power plants will require much
more powerful systems to create and drive the fusion reaction. The
new, more efficient systems added to DIII-D will allow researchers
to access plasma regimes that scale well to advanced FPP scenarios.
These scenarios have an elevated “plasma beta,” which is a metric
for energy produced from the plasma compared to the amount of
energy needed to confine it.
The new Lower Hybrid Current Drive system was
installed during the upgrade period and now enters the
commissioning phase to establish operation of all associated
subsystems in preparation for future experiments. This system
incorporates first-of-its-kind additively manufactured (AM)
components, called waveguides, that carry microwave heating energy.
The use of AM allows for design features that cannot otherwise be
manufactured.
The system also adds eight new microwave
generating units, called klystrons, that deliver heating and
current to the DIII-D plasma via the new AM waveguides. This is a
high-field launch system, meaning microwaves are transmitted to the
plasma from the center post rather than the outside edges. Modeling
predicts this location will lead to higher efficiency since it
enables the microwaves to be absorbed on their first pass through
the plasma, which also limits the potential for escape and damage
to the tokamak interior. The Lower Hybrid Current Drive system will
provide the first-ever demonstration of this high-field launching
approach.
Divertor Upgrades
During operation, a tokamak must be able to
remove excess heat, impurities in the plasma, and fusion
by-products on an ongoing basis. A system known as the divertor
serves this role, but additional research is necessary to determine
optimal divertor design and configuration for fusion power plants.
This challenge has been identified by the fusion community as one
of the key questions for extrapolating current tokamak plasmas to
FPP scenarios.
A new configuration called Shape and Volume Rise
(SVR) divertor is the first of a series of modular divertor
configurations that DIII-D will test in its near-term research
plan, with the goal of developing a high-performance scenario at
more FPP-relevant conditions. In particular, the new design will
enable access to plasma shapes that are expected to produce high
fusion power performance but were not possible with the previous
divertor geometry. SVR is designed for efficient removal of plasma
impurities to allow better control of the plasma density. This will
enable researchers to close key physics gaps between current
experiments and future fusion reactors.
About the DIII-D National Fusion
Facility. DIII-D is the largest magnetic fusion research
facility in the U.S. and has been the site of numerous pioneering
contributions to the development of fusion energy science. DIII-D
continues the drive toward practical fusion energy with critical
research conducted in collaboration with more than 800 team members
and over 700 actively contributing scientists representing 100
institutions worldwide. As a U.S. Department of Energy, Office of
Science User Facility, participation in DIII-D research is open to
all interested parties. For more information,
visit d3dfusion.org.
- DIII-D 2024 SVR Upgrade
- DIII-D 2024 Interior
Evan Polisar
DIII-D National Fusion Facility
619-538-2700
Evan.Polisar@ga.com