Abstract
An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements.
Highlights
An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field
The field-reversed configuration[2,3] (FRC) is characterized by a much higher ratio b of the plasma kinetic pressure to the external magnetic field energy density, with volume-averaged br0.9 and peak bmax 1⁄4 1. This magnetic configuration is of great interest as a fusion reactor concept due to its compact, axisymmetric geometry and the potential for aneutronic fusion based on advanced fuels, such as the proton-boron fusion reaction[4] (p-B11)
We present evidence that the nature of the saturated fluctuation spectrum is entirely different in the Field-reversed configuration (FRC) core and SOL, and that FRC core fluctuations are fundamentally different from tokamak core plasma turbulence
Summary
An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. The field-reversed configuration[2,3] (FRC) is characterized by a much higher ratio b of the plasma kinetic pressure to the external magnetic field energy density, with volume-averaged br0.9 and peak bmax 1⁄4 1. This magnetic configuration is of great interest as a fusion reactor concept due to its compact, axisymmetric geometry and the potential for aneutronic fusion based on advanced fuels, such as the proton-boron fusion reaction[4] (p-B11). FRC turbulence properties can be substantially different[8,9,10,11,12] from tokamak plasmas, where r*B10 À 3 À 10 À 2, and where ion-temperature-gradient-driven instabilities are often dominant, with perpendicular wavelengths substantially larger than the ion Larmor radius (k>rio[1], where k>is the turbulence wavenumber perpendicular to the magnetic field)
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