Turbulent transport in a multi-ion drift fluid model

To meet the future energy demands of the World, fusion energy has been proposed as a possible energy solution as it provides clean, sustainable and reliable means of energy production. However, a working fusion power plant has yet to be realised. Currently, the most promising reactor design is a magnetic confinement device to called a Tokamak.

One of the problems this concept is facing is turbulent transport of particles and energy from the region of closed magnetic field lines to that of open magnetic field lines and onto plasma-facing materials of the reactor. Future reactors inherently contain multiple ion species due to fusing of deuterium and tritium.

Consequently, understanding the influence of the multiple ion species on turbulent transport is of utmost importance. In this work, a drift fluid model is derived that consistently incorporates multiple ion species and collisional interactions between species. The model is derived from the Boltzmann equation and uses the Zhdanov closure to obtain a closed set of equations from which the drift fluid expansion can be performed.

The model equations are solved numerically using the discontinuous Galerkin method and the numerical implementation of the equations is discussed in detail. With the numerical implementation of the equations, two topics are studied, seeded plasma blobs and turbulent transport. For the seeded blobs, the influence of different ion mixes on the propagation of the blobs is examined through scaling of the blob velocity.

The mixes that are studied are deuterium-tritium mixtures as well as deuterium and doubly ionized helium mixes. Finally, fully developed turbulence is investigated. In particular, the impact of multiple ion species on the particle and energy fluxes across the last closed flux surface is examined. For the blobs, it was found that when the mixture is of deuterium and tritium, the velocity of the radial motion decreases as the amount of tritium increases.

From the deuterium helium simulations, it is found that the higher mass of the helium is counteracted by being doubly charged and results in similar blob velocities for deuterium and helium dominated blobs respectively. For the turbulent transport the results indicated that the increased presence of tritium yielded higher flux of particles and energy from the edge to the scrape-off-layer.