Energy-selective confinement of fusion-born alpha particles during internal relaxations in a tokamak plasma

Abstract

Long-pulse operation of a self-sustained fusion reactor using toroidal magnetic containment requires control over the content of alpha particles produced by D-T fusion reactions. On the one hand, MeV-class alpha particles must stay confined to heat the plasma. On the other hand, decelerated helium ash must be expelled before diluting the fusion fuel. Our kinetic-magnetohydrodynamic hybrid simulations of a large tokamak plasma confirm the existence of a parameter window where such energy-selective confinement can be accomplished by exploiting internal relaxation events known as `sawtooth crashes'. The physical picture -- consisting of a synergy between magnetic geometry, optimal crash duration and rapid particle motion -- is completed by clarifying the role played by magnetic drifts. Besides causing asymmetry between co- and counter-going particle populations, magnetic drifts determine the size of the confinement window by dictating where and how much `reconnection' occurs in particle orbit topology.

Main article: 9 pages, 7 figures. Supplementary material: 9 pages, 15 figures. References: 3 pages. 2021 IAEA TCM EPPI Conference

References in corpus (3)

• Nonlinear dynamics of phase space zonal structures and energetic particle physics in fusion plasmas
• Representation and modeling of charged particle distributions in tokamaks
• Bifurcations of the magnetic axis and the alternating-hyperbolic sawtooth

Cited by in corpus (4)

• Kinetic versus Magnetic Chaos in Toroidal Plasmas: A systematic quantitative comparison
• Testing the conservative character of particle simulations: II. Spurious heating of guiding centers and full orbits subject to fluctuations expressed in terms of $\mathbf{E}$ and $\mathbf{B}$
• Approximating the Particle Distribution in Rotating and Tandem Mirror Traps
• Autoresonant Removal of Fusion Products in Mirror Machines