Suppressed ion-scale turbulence in a hot high-β plasma

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.

Genetics of brain age suggest an overlap with common brain disorders

“…Magnetic resonance imaging (MRI) is a powerful tool to unveil abnormal brain development 12,13 and age-related degeneration 14,15 . Machine learning techniques enable robust estimation of the biological age of the brain using MRI-derived features 16 , and initial evidence suggests that a deviation between brain and chronological age – termed the brain age gap - is present in several brain disorders 17 .…”

Combination Doppler backscattering/cross-polarization scattering diagnostic for the C-2W field-reversed configuration

“…The lower limit is given by the detectable Doppler shift, and the upper limit is due to the scattering geometry and the expected CPS sensitivity limit, based on previous DBS results for toroidally propagating density fluctuations. 5,6 Simultaneous cross-correlation measurements of density and magnetic field fluctuations in corresponding wavenumber intervals are therefore possible for the first time in FRC geometry. Due to the intrinsic toroidal plasma curvature, the wavenumber response of both DBS and CPS is broadened, as described in Ref.…”

“…In the C-2U FRC device at TAE Technologies, 1,2 Doppler Backscattering (DBS) measurements 3,4 with a diagnostic described earlier 5 clearly show that fluctuations at low toroidal wavenumber are absent/stable in the FRC core. 6 Gyrokinetic stability analysis has attributed core stability to the combined effect of large ion Larmor radius, short field-line connection length restricting the parallel wavenumber spectrum, and favorable magnetic field gradient. 7,8 Only low-level electron-scale fluctuations are observed in the FRC core.…”

Control of ion gyroscale fluctuations via electrostatic biasing and sheared E×B flow in the C-2 field reversed configuration

“…Initial results have been reported [17] and a more detailed description will be provided in a separate publication [30]. In the SOL, the dependence on normalized toroidal wavenumber is best described by an exponential spectrum with a decay constant of α k~0 .16 (the corresponding exponent for the decay of the fluctuation energy density [~(ñ/n) 2 ] is ~0.33]).…”