# Particle Orbits in a Force-Balanced, Wave-Driven, Rotating Torus

## TL;DR

This paper explores the physics of particle orbits in a novel wave-driven rotating torus fusion device, emphasizing force balance, magnetic and electric field effects, and potential impacts on plasma transport.

## Contribution

It introduces a detailed analysis of particle orbits and force balance in the wave-driven rotating torus, highlighting the role of plasma current and magnetic fields for stability.

## Key findings

- Force balance requires a small plasma current and vertical magnetic field.
- Particle orbits show velocity-space anisotropies due to electric and magnetic field interactions.
- Potential neoclassical effects on conductivity and transport are identified.

## Abstract

The wave-driven rotating torus (WDRT) is a recently proposed fusion concept where the rotational transform is provided by the E x B drift resulting from a minor radial electric field. This field can be produced, for instance, by the RF-wave-mediated extraction of fusion-born alpha particles. In this paper, we discuss how macroscopic force balance, i.e. balance of the thermal hoop force, can be achieved in such a device. We show that this requires the inclusion of a small plasma current and vertical magnetic field, and identify the desirable reactor regime through free energy considerations. We then analyze particle orbits in this desirable regime, identifying velocity-space anisotropies in trapped (banana) orbits, resulting from the cancellation of rotational transforms due to the radial electric and poloidal magnetic fields. The potential neoclassical effects of these orbits on the perpendicular conductivity, current drive, and transport are discussed.