In this work, we present a detailed assessment of fusion-born alpha-particle confinement, their wall loads and stability of Alfvén eigenmodes driven by these energetic particles in the Infinity Two Fusion Pilot Plant baseline plasma design, a four-field-period quasi-isodynamic stellarator to operate in deuterium–tritium fusion conditions. Using the Monte Carlo codes, SIMPLE, ASCOT5 and KORC-T, we study the collisionless and collisional dynamics of guiding-centre and full-orbit alpha-particles in the core plasma. We find that core energy losses to the wall are less than 4 %. Our simulations shows that peak power loads on the wall of this configuration are approximately 2.5 MW m-$^2$ and are spatially localised, toroidally and poloidaly, in the vicinity of x-points of the magnetic island chain $n/m = 4/5$ outside the plasma volume. Also, an exploratory analysis using various simplified walls shows that shaping and distance of the wall from the plasma volume can help reduce peak power loads. Our stability assessment of Alfvén eigenmodes using the STELLGAP and FAR3d codes shows the absence of unstable modes driven by alpha-particles in Infinity Two due to the relatively low alpha-particle beta at the envisioned 800 MW operating scenario.

For small-shear helical-axis stellarators, linear ideal-magnetohydrodynamic (MHD) stability calculations and full-torus, nonlinear, electromagnetic gyrokinetic (GK) simulations (the latter with this unprecedented combination of objectives in stellarator GKs) in their linear phase are shown to yield well agreeing spatio-temporal structures of unstable, globally extended perturbations. Likewise, good agreement is found for their dependence on the plasma pressure and the vacuum-field magnetic well in plasma equilibria with identical gradient lengths of the temperature and density profiles. In the nonlinear phase, these perturbations with MHD signatures entail deformations of the magnetic surfaces, growing magnetic islands which rotate in the electron diamagnetic direction and, eventually, lead to ergodisation of a larger part of the magnetic surfaces.

Curvature-driven instabilities are ubiquitous in magnetised fusion plasmas. By analysing the conservation laws of the gyrokinetic system of equations, we demonstrate that the well-known spatial localisation of these instabilities to regions of ‘bad magnetic curvature’ can be explained using the conservation law for a sign-indefinite quadratic quantity that we call the gyrokinetic field invariant. Its evolution equation allows us to define the local effective magnetic curvature whose sign demarcates the regions of ‘good’ and ‘bad’ curvature, which, under some additional simplifying assumptions, can be shown to correspond to the inboard (high-field) and outboard (low-field) sides of a tokamak plasma, respectively. We find that, given some reasonable assumptions, electrostatic curvature-driven modes are always localised to the regions of bad magnetic curvature, regardless of the specific character of the instability. More importantly, we also deduce that any mode that is unstable in the region of good magnetic curvature must be electromagnetic in nature. As a concrete example, we present the magnetic-drift mode, a novel good-curvature electromagnetic instability, and compare its properties with the well-known electron-temperature-gradient instability. Finally, we discuss the relevance of the magnetic drift mode for high-$\beta$ fusion plasmas, and in particular its relationship with microtearing modes.

Insight into plasma dynamics under usual pulsed laser deposition (PLD) conditions for NiO thin film growth is provided by implementing angle- and time-resolved Langmuir probe (LP) methods. The selective separation generated an acceleration region that separates ions based on nature and ionisation state. A maximum of the kinetic energy for most plasma components was found for 0.5–2 Pa Ar, while the time-resolved analysis revealed a multipeak evolution of the electron temperature, which widened and shifted with increasing pressure. Evidence of two temperature structures for NiO plasma is presented, and the estimation of the accelerating field generated between the two plasma structures reveals selective in acceleration in the first microsecond. The acceleration field has a maximum value for the O2 atmosphere at approximately 2 Pa, which shows the separation between drift-dominated kinetics and reaction-based dynamics. Further investigation in this 2 Pa region revealed the appearance of a perturbation consistent with the formation of a plasma fireball on the probe. The dynamics of these perturbations is affected by the nature of the gas having different incubation times.

This work tackles a significant challenge in dynamo theory: the possibility of long-term amplification and maintenance of an axisymmetric magnetic field. We introduce a novel model that allows for non-trivial axially symmetric steady-state solutions for the magnetic field, particularly when the dynamo operates primarily within a ‘nearly spherical’ toroidal volume inside a fluid shell surrounding a solid core. In this model, Ohm’s law is generalised to include the dissipative force, arising from electron collisions, that tends to align the velocity of the shell with the rotational speed of the inner core and outer mantle. Our findings reveal that, in this context, Cowling’s theorem and the neutral point argument are modified, leading to magnetic energy growth for a suitable choice of toroidal flow. The global equilibrium magnetic field that emerges from our model exhibits a dipolar character. The central insight of the model developed here is that if an additional force is incorporated into Ohm’s law, symmetric dynamos become possible.