A5077763704- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Laser-Plasma Interactions and Diagnostics
- Fusion materials and technologies
- Superconducting Materials and Applications
- Particle accelerators and beam dynamics
- Fluid Dynamics and Turbulent Flows
- Electromagnetic Launch and Propulsion Technology
- Inorganic Fluorides and Related Compounds
- Geomagnetism and Paleomagnetism Studies
- Geophysics and Gravity Measurements
- High-pressure geophysics and materials
- Dust and Plasma Wave Phenomena
- Inorganic Chemistry and Materials
- Meteorological Phenomena and Simulations
- Renal and Vascular Pathologies
- Inertial Sensor and Navigation
- Advanced Thermodynamics and Statistical Mechanics
- GNSS positioning and interference
- Distributed and Parallel Computing Systems
- Geophysics and Sensor Technology
- Dynamics and Control of Mechanical Systems
- Guidance and Control Systems
- Fluid Dynamics Simulations and Interactions
University of Oxford
2016-2025
Royal Military Academy
2020
Culham Science Centre
2009-2019
Plasma Technology (United States)
2011-2019
Fusion Academy
2011-2019
Fusion (United States)
2011-2019
Culham Centre for Fusion Energy
2009-2019
United Kingdom Atomic Energy Authority
2019
Massachusetts Institute of Technology
2011-2015
The University of Texas at Austin
2014
The 2014–2016 JET results are reviewed in the light of their significance for optimising ITER research plan active and non-active operation. More than 60 h plasma operation with first wall materials successfully took place since its installation 2011. New multi-machine scaling type I-ELM divertor energy flux density to is supported by principle modelling. relevant disruption experiments modelling reported a set three mitigation valves mimicking setup. Insights L–H power threshold Deuterium...
A new analytically and numerically manageable model collision operator is developed specifically for turbulence simulations. The like-particle includes both pitch-angle scattering energy diffusion satisfies the physical constraints required operators: it conserves particles, momentum, energy, obeys Boltzmann’s H-theorem (collisions cannot decrease entropy), vanishes on a Maxwellian, efficiently dissipates small-scale structure in velocity space. process of transforming this into gyroaveraged...
Does overall thermal equilibrium exist between ions and electrons in a weakly collisional, magnetised, turbulent plasma---and, if not, how is energy partitioned electrons? This fundamental question plasma physics, the answer to which also crucial for predicting properties of far-distant astronomical objects such as accretion discs around black holes. In context discs, this was posed nearly two decades ago has since generated sizeable literature. Here we provide case injected into via...
Abstract For the past several years, JET scientific programme (Pamela et al 2007 Fusion Eng. Des . 82 590) has been engaged in a multi-campaign effort, including experiments D, H and T, leading up to 2020 first with 50%/50% D–T mixtures since 1997 ever plasmas ITER mix of plasma-facing component materials. this purpose, concerted physics technology was launched view prepare campaign (DTE2). This paper addresses key elements developed by directly contributing preparation. intense preparation...
A set of key properties for an ideal dissipation scheme in gyrokinetic simulations is proposed, and implementation a model collision operator satisfying these described. This based on the exact linearized test-particle operator, with approximations to field-particle terms that preserve conservation laws H-theorem. It includes energy diffusion, pitch-angle scattering, finite Larmor radius effects corresponding classical (real-space) diffusion. The numerical continuum code GS2 [Kotschenreuther...
This paper reviews transport and confinement in spherical tokamaks (STs) our current physics understanding of this that is partly based on gyrokinetic simulations. Equilibrium flow shear plays an important role, we show how consistently included the framework for flows greatly exceed diamagnetic velocity. The key geometry factors influence effectiveness turbulence suppression by are discussed, toroidal equilibrium can sometimes entirely suppress ion scale today's STs. Advanced nonlinear...
Scaling laws for ion temperature gradient driven turbulence in magnetized toroidal plasmas are derived and compared with direct numerical simulations. Predicted dependences of fluctuation amplitudes, spatial scales, resulting heat fluxes on magnetic field line pitch found to agree results both the driving inertial ranges. Evidence is provided support critical balance conjecture that parallel streaming nonlinear perpendicular decorrelation times comparable at all leading a scaling...
Direct coupling between a transport solver and local, nonlinear gyrokinetic calculations using the multiscale code TRINITY [M. Barnes, “TRINITY: A unified treatment of turbulence, transport, heating in magnetized plasmas,” Ph.D. thesis, University Maryland, 2008 (eprint arXiv:0901.2868)] is described. The microscopic macroscopic physics done within framework theory, which we present assumptions key results. An assumption scale separation space time allows for simulation turbulence small...
This paper presents a complete theoretical framework for studying turbulence and transport in rapidly rotating tokamak plasmas. The fundamental scale separations present plasma are codified as an asymptotic expansion the ratio = ρi/a of gyroradius to equilibrium length. Proceeding order by this expansion, set coupled multiscale equations is developed. They describe instantaneous equilibrium, fluctuations driven gradients quantities, transport-timescale evolution mean profiles these...
Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases This leads a local minimum the heat flux, indicating an optimal $\mathbf{E}\ifmmode\times\else\texttimes\fi{}\mathbf{B}$ shear value for plasma confinement. Local maxima momentum fluxes observed, implying possibility...
We consider a nearly collisionless plasma consisting of species "test particles" in one spatial and velocity dimension, stirred by an externally imposed stochastic electric field-a kinetic analog the Kraichnan model passive advection. The mean effect on particle distribution function is turbulent diffusion space-known as heating. Accompanying this heating generation fine-scale structure function, which we characterize with (Casimir) invariant C_{2}∝∫∫dxdv〈f^{2}〉-a quantity that here plays...
We report the first experimental detection of a zero-frequency fluctuation that is pumped by an Alfvén mode in magnetically confined plasma. Core-localized modes frequency inside toroidicity-induced gap (and its harmonics) exhibit three-wave coupling interactions with fluctuation. The observation consistent theoretical and numerical predictions zonal modes, correlated increase deep core ion temperature, temperature gradient, confinement factor <a:math...
The effect of flow shear on turbulent transport in tokamaks is studied numerically the experimentally relevant limit zero magnetic shear. It found that plasma linearly stable for all nonzero values, but subcritical turbulence can be sustained nonlinearly at a wide range temperature gradients. Flow increases nonlinear gradient threshold also sensitivity heat flux to changes gradient, except over small near where decreased. A bifurcation equilibrium gradients found: given input heat, it...
Two symmetries of the local nonlinear delta-f gyrokinetic system equations in tokamaks high flow regime are presented. The turbulent transport toroidal angular momentum changes sign under an up-down reflection tokamak and a change both rotation shear. Thus, must vanish for symmetric absence This has important implications modeling spontaneous rotation.
The effect of small deviations from a Maxwellian equilibrium on turbulent momentum transport in tokamak plasmas is considered. These non-Maxwellian features, arising diamagnetic effects, introduce strong dependence the radial flux co-current toroidal angular collisionality: As plasma goes nearly collisionless to weakly collisional, reverses direction radially inward outward. This indicates collisionality-dependent transition peaked hollow rotation profiles, consistent with experimental...
Multi-channel transport experiments have been conducted in auxiliary heated (Ion Cyclotron Range of Frequencies) L-mode plasmas at Alcator C-Mod [Marmar and Group, Fusion Sci. Technol. 51(3), 3261 (2007)]. These provide good diagnostic coverage for measurements kinetic profiles, impurity transport, turbulence (electron temperature density fluctuations). In the experiments, a steady sawtoothing plasma with 1.2 MW on-axis RF heating is established scanned by 20%. Measured rotation profiles...
Major developments on the Mega Amp Spherical Tokamak (MAST) have enabled important advances in support of ITER and physics basis a spherical tokamak (ST) based component test facility (CTF), as well providing new insight into underlying physics. For example, L–H transition studies benefit from high spatial temporal resolution measurements pedestal profile evolution (temperature, density radial electric field) stability edge current has been inferred motional Stark effect measurements. The...
Self-consistent equations for intrinsic rotation in tokamaks with small poloidal magnetic field $B_p$ compared to the total $B$ are derived. The model gives momentum redistribution due turbulence, collisional transport and energy injection. Intrinsic is determined by balance between turbulent diffusion convection. Two different turbulence regimes considered: characteristic perpendicular lengths of order ion gyroradius, $\rho_i$, $(B/B_p) \rho_i$. driven gyroradius scale mainly effect...
Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle role plasma fueling shape for onset small ELM regimes. On both devices, regimes with high confinement are achieved if only two conditions fulfilled at same time. Firstly, density separatrix must be large enough (), leading pressure profile flattening separatrix, which stabilizes type-I ELMs. Secondly, magnetic configuration close double null (DN), reduction shear in...
Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat particle loads on wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research ASDEX Upgrade (AUG), MAST TCV. This multi-machine approach within EU-MST, covering wide parameter range, instrumental progress in field, as ITER DEMO core/pedestal SOL parameters are not achievable simultaneously present day devices. A two prong adopted. On one...
The mega amp spherical tokamak (MAST) was a low aspect ratio device (R/a = 0.85/0.65 ~ 1.3) with similar poloidal cross-section to other medium-size tokamaks. physics programme concentrates on addressing key issues for the operation of ITER, design DEMO and future tokamaks by utilising high resolution diagnostic measurements closely coupled theory modelling significantly advance our understanding. An empirical scaling energy confinement time that favours higher power, lower collisionality...
The partition of irreversible heating between ions and electrons in compressively driven (but subsonic) collisionless turbulence is investigated by means nonlinear hybrid gyrokinetic simulations. We derive a prescription for the ion-to-electron ratio $Q_\rmi/Q_\rme$ as function compressive-to-Alfv\'enic driving power $P_\compr/P_\AW$, ion thermal pressure to magnetic $\beta_\rmi$, background temperatures $T_\rmi/T_\rme$. It shown that an increasing $P_\compr/P_\AW$. When compressive...
Collisional transport theory predicts particle depletion in the core of reactor-relevant fusion plasmas confined stellarators. However, this prediction is contradicted by experiments. The conundrum has been solved proving that turbulence provides missing component allows reconciling and experiment.