Alpha heating in D-T Z-pinch fusion simulations using the 5N-moment four-fluid plasma model

Fusion reactions and alpha heating in an axisymmetric, D-T-fueled Z pinch are numerically investigated using the 5N-moment multi-fluid plasma model via the Washington Approximate Riemann Plasma (WARPXM) code [Shumlak et al., Comput. Phys. Commun. 182, 1767, 2011]. WARPXM, developed at the University of Washington, is a high-order-accurate finite element code that uses a discontinuous Galerkin (DG) spatial representation. The Z pinch is modeled as a four-fluid system (deuterons, tritons, alphas, and electrons) with self-consistent electromagnetic fields. The initial conditions are specified using a multi-fluid extension of the Bennett equilibrium. Fusion reactivities are given from empirical expression [Bosch and Hale, Nucl. Fusion, 32, 611, 1992] based on local plasma properties. At sufficiently high plasma currents, fusion alphas can be magnetically confined [Shumlak, Meier, and Levitt, Fusion Sci. Technol., 2023]. The confined alphas collide with the Z-pinch plasma and leads to bulk plasma heating, which is modeled using a slowing-down collision operator for the fast alphas and the Maxwellian Z-pinch plasma while preserving total energy. The primary energy cascade initiates from energetic alphas to electrons, and eventually the electron energy transfers into deuterons and tritons. The fluid diffusive effects due to the viscosity and thermal conductivity will be discussed.