Relativistic Six-Fluid Rotating-Plasma Force-Balance Equilibria for p-11B Fusion Conditions in Spherical Tori

Abstract

We formulate an axisymmetric spherical torus (ST) six-component magnetofluid equilibrium model for p_11B plasmas composed of thermal and suprathermal proton, boron, and electron fluids. The model is designed for p_11B parameter regimes where ion energies, strong current drive, energetic electron populations, and ion-electron temperature separation can render a single_fluid static_equilibrium description inadequate. It generalizes rotating_plasma equilibrium theory by incorporating relativistic thermal enthalpy corrections to the electron fluids via h(T/m_ec^2) and by constructing modified flux functions Y_α associated with canonical angular momentum for each component α. The equilibrium is determined by a Grad-Shafranov-like Ampere law for the poloidal magnetic flux Psi, algebraic density relations constrained by quasineutrality, and prescribed profile functions F_α(Y_α), T_α(Y_α) and K_α(Y_α). The manuscript includes the relativistic magnetofluid equations, the axisymmetric equilibrium formulation, the six_fluid computational method, and four numerical equilibria: two reactor_relevant ST p_11B parameter sets and two EHL-2 ST cases. The examples span toroidal beta b_T = 0.058_0.253, plasma currents I_p = 2.697_12.59 MA, and suprathermal electron temperatures T_eh = 287 keV_2.37 MeV, with h up to 19.1. Over these parameter ranges, Ampere's law accuracy, electrostatic potential accuracy, and component_resolved radial force balance can have errors ranging from 3% to below 0.1%. These results indicate that high-temperature p_11B ST equilibria can differ qualitatively from the single_fluid tokamak equilibria and require analysis of equilibrium component_resolved force balance, relativistic electron enthalpy, and explicit reproducibility diagnostics.