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

thE REvERSEd FiEld piNch
introduction
during the iteR era, the goal for Reversed Field Pinch (RFP) research as identified by the Fesac
toroidal alternates Panel (taP) is to:
Establish the basis for a burning plasma experiment by developing an attractive self-consistent integrated
scenario: favorable confinement in a sustained high-beta plasma with resistive wall stabilization.
The distinctive feature of the RFP configuration for its fusion application is that electrical current
flowing in the plasma generates most of the confining magnetic field. The externally applied toroidal
magnetic field is relatively small, about two orders of magnitude smaller than that in a tokamak
with similar plasma current. This reduced external magnetic field requirement offers significant
advantages for fusion application. For example, the RFP attains very high engineering
beta (the ratio of the plasma pressure to the maximum magnetic field pressure at the magnets).
smaller magnets are allowed, which could be constructed using normal conductors (nonsuperconducting).
also, the plasma current provides large ohmic heating, reducing or perhaps eliminating
requirements for complicated auxiliary plasma heating systems. While reduced external field underlies
these potential advantages, it also leads to the primary scientific challenges for the RFP.
magnetic fluctuations arise more easily without a large externally imposed stabilizing field, and
this has an impact on both plasma stability and confinement quality. also, the steady-state sustainment
of the RFP’s relatively large plasma current is challenging.
Figure 5. The RFP magnetic configuration. The direction of the magnetic field, B, varies strongly within plasma
as a result of the small externally applied toroidal field.
The small external toroidal magnetic field yields a low value of the magnetic winding parameter,
q, compared with configurations that employ a larger external toroidal field, such as the tokamak,
st, and stellarator. This parameter measures the helical twist of the magnetic field lines in the
plasma. Thus, the RFP also offers unique science opportunities for plasma stability and confinement
that complements the parameter regime of high-q configurations.
Scientific Contributions
achieving the iteR-era goal will contribute significantly to fusion energy sciences and broader
scientific disciplines. examples are: (1) understand transport processes from turbulence that is
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