#### A V Dudkovskaia J W Connor D Dickinson P Hill K Imada S Leigh H R Wilson

A nonlinear 4-dimensional drift island theory derived in (Imada et al 2019 Nucl. Fusion 59 046016 and references therein) provides qualitative predictions of the plasma response to a stationary neoclassical tearing mode (NTM) magnetic island in a low beta, large aspect ratio tokamak plasma. (Dudkovskaia et al 2021 Plasma Phys. Control. Fusion 63 05…

Published#### D. Kennedy M. Giacomin B. S. Patel W. A. Hornsby D. Dickinson C. M. Roach

We present herein the results of a linear gyrokinetic analysis of electromagnetic microinstabilites in the conceptual high−β, reactor-scale, tight-aspect-ratio tokamak STEP (Spherical Tokamak for Energy Production, https://step.ukaea.uk). We examine a range of flux surfaces between the deep core and the pedestal top for the two candidate flat…

Preprint Published#### M. Giacomin D. Kennedy C. J. Ajay D. Dickinson B. S. Patel C. M. Roach

In this work, we present the results of first-of-their-kind nonlinear local gyrokinetic simulations of electromagnetic turbulence at mid-radius in the burning plasma phase of the conceptual high-β, reactor-scale, tight-aspect-ratio tokamak STEP (Spherical Tokamak for Energy Production). A prior linear analysis in D.Kennedy et al. submitted to Nucl…

Preprint#### M. Giacomin D. Dickinson D. Kennedy B. Patel C. M. Roach

Linear and nonlinear gyrokinetic simulations are performed in experimentally relevant scenarios built from a MAST case where a microtearing mode instability dominates at ion Larmor radius scale. This collisional microtearing mode instability appears only when a vel…

Preprint Published#### Daniel Kennedy Bhavin S Patel Colin M Roach

Microinstabilities often result in turbulence that influences energy confinement in tokamak discharges. One such microinstability, of particular importance to the design of next-generation spherical tokamaks (STs) such as STEP [1], is the microtearing mode (MTM), a tearing-parity mode centred on high-order rational surfaces. MTMs are short-wavel…

Preprint#### H. G. Dudding F. J. Casson D. Dickinson B. Patel C. M. Roach E. A. Belli G. M. Staebler

A new quasilinear saturation model SAT3 has been developed for the purpose of calculating radial turbulent fluxes in the core of tokamak plasmas. The new model is shown to be able to better recreate the isotope mass dependence of nonlinear gyrokinetic fluxes compared to contemporary quasilinear models, including SAT2 [1], whilst performing at least…

Preprint Published#### B.S. Patel D. Dickinson C.M. Roach H.R. Wilson

Spherical tokamaks (STs) have been shown to possess properties desirable for a fusion power plant such as achieving high plasma β and having increased vertical stability. To understand their confinement properties in a reactor relevant regime a 1GW fusion power spherical tokamak plasma equilibrium was analysed using linear gyrokinetics to deter…

Preprint Published#### M. R. Hardman F. I. Parra C. Chong T. Adkins M. S. Anastopoulos-Tzanis M. Barnes D. Dickinson J. F. Parisi H. Wilson

Ion-gyroradius-scale microinstabilities typically have a frequency comparable to the ion transit frequency. Hence, it is conventionally assumed that passing electrons respond adiabatically in ion-gyroradius-scale modes, due to the small electron-to-ion mass ratio and the large electron transit frequency. However, in gyrokinetic simulations of io…

Preprint#### C J Ham A Bokshi D Brunetti G Bustos Ramirez B Chapman J W Connor D Dickinson A R Field J P Graves T Kiviniemi S Leerink B McMillan S Newton S Pamela C M Roach S Saarelma J Simpson S F Smith P Strand A Virtanen the JET Contributors*

The pedestal plays an important role in determining the confinement in tokamak H-mode plasmas. However, the steep pressure gradients in this transport barrier also lead to edge localized modes (ELMs) [1]. There is good understanding of the pedestal in type I ELM regimes [2], however, type I ELMs are known to damage plasma facing components and f…

Preprint Published#### J. T. Parker P. A. Hill D. Dickinson B. D. Dudson

Tridiagonal matrix inversion is an important operation with many applications. It arises frequently in solving discretized one-dimensional elliptic partial differential equations, and forms the basis for many algorithms for block tridiagonal matrix inversion for discretized PDEs in higher-dimensions. In such systems, this operation is often the …

Preprint Published