# Energetic Particle Physics of the International Thermonuclear Experimental Reactor (ITER)

Fusion energy promises baseload electricity generation with zero greenhouse gas emissions, a virtually inexhaustible supply of fuel, and significantly reduced radioactive waste, compared to fission and coal. The International Thermonuclear Experimental Reactor (ITER), which is now under construction, is the final step towards a demonstration power plant. ITER, will explore the uncharted physics of burning plasmas, where the energy liberated from the confined products of reaction exceeds the energy invested in heating the plasma.

To access burning plasmas conditions, ITER will rely critically on external heating methods such as neutral beam injection. These modify the particle distribution function from a thermal Maxwellian (Fig. a).

Schematic particle distribution function with fusion product ($\alpha$) with speed $v_\alpha$, neutral beam injection energy $v_{NBI}$ and thermal speed $v_{th}$

Neutral beam injection can unequally heat directions parallel and perpendicular to the confining magnetic field, resulting in pressure anisotropy, which alters the shape of the internal magnetic fields. As the beam ions slow they can resonate with different Alfvén waves (e.g. Fig. b), the mode amplitude grows (Fig. 1c), and the driving distribution function is flattened. These Alfvén resonances, or “thermonuclear ringtones”, which can also be driven by fusion products, are a function of the magnetic geometry and density profile. The drive of multiple Alfvén resonances can lead to nonlinearly enhanced redistribution and radial transport, and thus threaten particle confinement in ITER.

(b) projection of multiple mode $B_r$ wave field of a TAE, (c) nonlinear evolution of 88 coupled TAE modes for an isotropic, static plasma as a function of wave periods $\omega{t}/2\pi$.

There are several potential projects in this topical area.

• Parameter scans of anisotropy for different ITER scenarios. Part of A/Prof. Hole’s ITER Science Fellowship is quantifying the impact of anisotropy for different ITER scenarios, and assessing the impact of anisotropy on the MHD continuum (gap eigenmodes) and linear stability of kink modes.  This project would involve familiarisation with the mathematical physics of toroidal magnetic force balance, an introduction to ITER physics scenarios, and developing a working knowledge of ANU (co)developed equilibrium and stability codes. The project is suitable for an Honours or Masters project.
• Study of Compressional Alfven eigenmodes. In this project the student will explore the full spectrum of modes permitted within the generalised MHD, MISHKA-3, which comprises the Hall effect. The primary objective is an investigation of Compressional Alfven eigenmodes: these are modes whose frequency extends to the ion cyclotron frequency range and its harmonics, and are driven by velocity gradients of non-Maxwellian energetic beam ions. CAEs, for which the theory is much less developed, are of programmatic importance to fusion, and have been observed in D-T plasmas in the Joint European Torus, and spherical tokamaks. The project is suitable for a Masters or PhD project.