Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

The blanket and the divertor have an additional radiation shield behind them to prevent any remaining
radiation from damaging the vacuum vessel and superconducting magnets. The vacuum
vessel is a large structure that contains the fusion plasma, allows for good vacuum conditions to
be created, and serves as a safety confinement barrier for radioactive materials. The shield captures
only a small amount of the total energy, which is typically removed with a low temperature
coolant and discarded as waste heat.
all of these systems are connected to systems that deliver new coolant, accept the returning heated
coolant, and couple that stream to some thermodynamic power cycle. coolant circulation and
power conversion systems must be both highly safe and reliable, as they communicate between
the plasma and the balance of the plant, transporting energy, and possibly tritium and radioactive
impurities that must be strictly controlled.
all these power extraction components are inside the vacuum vessel and in immediate proximity
to the plasma. This has strong implications on design, materials, maintenance and reliability requirements
for such components. Power extraction components:
• cannot have any leaks without spoiling the vacuum.
• must tolerate significant heat flux and plasma erosion of surfaces, including off-normal
events like plasma disruptions that produce severe surface energy pulses.
• must be replaceable in reasonably short times.
• are damaged by fusion neutrons and plasma particles, and so have evolving material
properties and a limited lifetime.
• have complicated geometries to conform to the shape (toroidal in a tokamak) of the plasma
and accommodate many penetrations for plasma fueling, heating, and instrumentation
equipment.
• are electromagnetically coupled to the plasma in complicated ways and so must be
designed for compatibility with plasma operations, including off-normal events like
plasma disruptions that induce severe electromagnetic forces.
These significant constraints and interrelationships make fusion power extraction a challenge.
Compelling Scientific issues
The goal of fusion power extraction research is to establish the scientific underpinnings and technological
development needed to efficiently, safely, and reliably capture and transport fusion energy
while remaining compatible with tritium breeding and plasma operation. The scientific issues
encountered are related mainly to understanding the:
• Thermal and fluid dynamics behavior of liquid metal and gas coolants.
• Thermal and mechanical behavior of the materials and structures.
• Generation and transport of tritium, corrosion and undesirable radioactive impurities.
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