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

• study FRc stability at small ion gyroradius in a new or upgraded facility with energetic ion
sources. success will enable integrated tests of stability, confinement, and sustainment.
• develop improved current sustainment methods for the spheromak. small experiments
will feed transformational ideas to a larger facility to test integrated confinement and
sustainment.
• extend confinement scaling and demonstrate current sustainment at high temperature in
a new large-current RFP. a staged, upgradeable facility would eventually demonstrate nearburning
plasma conditions with integrated plasma-boundary and magnetohydrodynamic
(mhd) stability control.
• Quantify the benefits of low external field and ct geometry in system studies with
updated physics and engineering information. evaluate pulsed vs. steady-state reactor
operation.
Scientific and technical Research
minimizing the external magnetization required to confine fusion plasma would be a major advance
toward making fusion power an economical reality. This goal guides research efforts for
the RFP, spheromak, and FRc magnetic configurations and motivates research that answers important
scientific questions. magnetic fluctuations arise more easily without a large externally
imposed stabilizing field, and this affects both plasma stability and confinement quality. Understanding
the scaling of fluctuations is crucial to predict reactor-grade performance. efficient
plasma current drive is vital, and many of the techniques are distinct from methods used for tokamaks.
control of the plasma boundary is essential for any fusion system, and optimized solutions
will depend to some degree on magnetic geometry. While the integration of stability, confinement,
and boundary control and other scientific challenges are particular for any magnetic
configuration, the underlying physics has a large degree of commonality.
The similarities of the scientific issues for low external-field configurations help define a unified
thrust; nevertheless, the configurations described in this Thrust are distinct and offer unique approaches
to achieving a fusion power source. each of them requires separate experimental work
but contributes to a common physics understanding. The magnetic profile of the RFP is characteristically
paramagnetic with the magnetic field orientation changing from toroidal in the core to
purely poloidal near the edge. The profile therefore has large negative shear, which enhances mhd
stability to interchange distortion at moderately high plasma-b (the ratio of plasma pressure to
magnetic energy density). also, many robustly damped helical modes resonate within the plasma,
enhancing nonlinear stability. The toroidal geometry facilitates external control of the magnetic
field at the surface of the plasma. This control has been used to achieve high confinement, and it
underlies the RFP scheme for ac current drive.
engineering requirements are further simplified for the two ct configurations. The plasma-containment
volumes are basically cylindrical with no components placed along the geometric axis.
access to all plasma facing components is therefore relatively simple. The absence of external toroidal
field coils allows more flexibility for designing the divertor systems that strongly influence
edge plasma conditions while channeling hot plasma exhaust. however, qualitative differences
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