Simulating fusion alpha heating in a stellarator reactor

Abstract

Gyrocenter following simulations of fusion born alpha particles in a stellarator reactor are preformed using the BEAMS3D code. The Wendelstein 7-X high mirror configuration is scaled in geometry and magnetic field to reactor relevant parameters. A 2 × 10 20 m−3 density plasma with 20 keV core temperatures is assumed and fusion birth rates calculated for various fusion products assuming a 50/50 deuterium-tritium mixture. It is found that energetic He4 ions comprise the vast majority of the energetic particle inventory. Slowing down simulations of the He4 population suggest plasma heating consistent with scaled energy confinement times for a stellarator reactor. Losses for this configuration appear large suggesting optimization beyond the scope of the W7-X device is key to a future fusion reactor. These first simulations are designed to demonstrate the capability of the BEAMS3D code to provide fusion alpha birth and heating profiles for stellarator reactor designs.

Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry

“…To further study the mechanisms for the deviations in J , we perform GC integration in several vacuum equilibria that are optimized for quasiaxisymmetry on the boundary [58] in addition to having a value of ι = 0.52 on the boundary and aspect ratio 6. For the base equilibrium, the optimization is terminated when the quasisymmetry on the boundary is f QS = 1.8 × 10 −2 , see (9). We compare with two other equilibria, for which the optimization is terminated at f QS = 1.8 × 10 −3 and f QS = 1.3 × 10 −4 .…”

“…The confinement of fusion-born alpha particles is largely determined by collisionless physics. Comparisons of collisionless with collisional alpha particle losses have found that pitchangle scattering effects are insignificant for losses before the slowing-down time of ≈0.05 seconds in a W7-X reactor configuration [9]. Generally, the difference between collisionless and collisional calculations is configuration dependent [10].…”

Energetic particle optimization of quasi-axisymmetric stellarator equilibria

“…BEAMS3D's deposition model has been validated [30] and a preliminary validation and benchmarking of the slowing down model has been done [29]. The simulations for this work were done using a new feature created for BEAMS3D that models fusion births and uses the birth rates to initialize particles for simulation [19].…”

“…The weighting of each particle is then determined by the fusion birth rate at its initial location divided by the volume of its cell and the number of particles within. In this way, particles from the edge region, in which the birth rate is several orders of magnitude lower, can still be sampled [19].…”

“…Next, in order to determine the success of optimization, all resulting equilibria were scaled up to match the volume V = 444 m 3 and volume-averaged magnetic field strength ⟨B⟩ = 5.86 T of ARIES-CS [17], and Monte-Carlo simulations of fusion alpha particles in these devices were performed using the code BEAMS3D [18,19] in order to assess losses. Simulations were performed both with and without collisions.…”