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A non-exhaustive list of the research topics I am interested in!
A non-exhaustive list of the research topics I am interested in!
At the moment I am particularly interested in how the toroidal geometry of tokamaks and stellarators affects turbulence and flows. Beyond intellectual curiosity, understanding turbulence is crucial as mixing by turbulent eddies limits the achievable temperature and therefore the performance of fusion devices.
At the moment I am particularly interested in how the toroidal geometry of tokamaks and stellarators affects turbulence and flows. Beyond intellectual curiosity, understanding turbulence is crucial as mixing by turbulent eddies limits the achievable temperature and therefore the performance of fusion devices.
Turbulence saturation in tokamaks and stellarators
Turbulence saturation in tokamaks and stellarators
This is an incredibly multi-faceted problem, many aspects of which I hope to explore in the future. So far, I have shown using tokamak flux-tube simulations (see picture) that saturated ion-temperature-gradient turbulence satisfies the grand critical balance conjecture [Goldreich & Sridhar 1995, Barnes et al. 2011, Ghim et al. 2013], due to the presence of small-scale zonal flows (see below).
This is an incredibly multi-faceted problem, many aspects of which I hope to explore in the future. So far, I have shown using tokamak flux-tube simulations (see picture) that saturated ion-temperature-gradient turbulence satisfies the grand critical balance conjecture [Goldreich & Sridhar 1995, Barnes et al. 2011, Ghim et al. 2013], due to the presence of small-scale zonal flows (see below).
Relevant publications:
Relevant publications:
Nonlinear zonal flow dynamics in toroidal geometry
Nonlinear zonal flow dynamics in toroidal geometry
Zonal flows are nonlinearly generated by the turbulence and proceed to shear apart the turbulent eddies, providing an effective means of saturation. The toroidal geometry of tokamaks and stellarators is known to be pivotal for the linear zonal flow dynamics (viz. Rosenbluth-Hinton residual and Geodesic Acoustic Modes), so I have been interested in exploring the effects of toroidicity on the nonlinear zonal flow dynamics. This led me to the discovery of toroidal secondary modes, which manifest as small-scale propagating zonal flows in gyrokinetic simulations (see picture).
Zonal flows are nonlinearly generated by the turbulence and proceed to shear apart the turbulent eddies, providing an effective means of saturation. The toroidal geometry of tokamaks and stellarators is known to be pivotal for the linear zonal flow dynamics (viz. Rosenbluth-Hinton residual and Geodesic Acoustic Modes), so I have been interested in exploring the effects of toroidicity on the nonlinear zonal flow dynamics. This led me to the discovery of toroidal secondary modes, which manifest as small-scale propagating zonal flows in gyrokinetic simulations (see picture).
Relevant publications:
Relevant publications:
Stellarator optimisation
Stellarator optimisation
The complex three-dimensional geometry of stellarators needs to be carefully optimised for desirable properties. One potentially desirable property is quasisymmetry, which makes the collisionless particle orbits in stellarators isomorphic to those in tokamaks. To optimise for quasisymmetry, I have worked on deriving (paper #1) and employing (paper #2) adjoint methods, which allow for a fast evaluation of the shape derivative used in gradient-based optimisation. An example stellarator we obtained is shown here, see paper #2 for more!
The complex three-dimensional geometry of stellarators needs to be carefully optimised for desirable properties. One potentially desirable property is quasisymmetry, which makes the collisionless particle orbits in stellarators isomorphic to those in tokamaks. To optimise for quasisymmetry, I have worked on deriving (paper #1) and employing (paper #2) adjoint methods, which allow for a fast evaluation of the shape derivative used in gradient-based optimisation. An example stellarator we obtained is shown here, see paper #2 for more!
Relevant publications:
Relevant publications:
Neoclassical Tearing Mode stabilisation
Neoclassical Tearing Mode stabilisation
Tokamaks are susceptible to magnetohydrodynamic instabilities that open up magnetic islands (see picture) and can eventually cause catastrophic disruptions of the plasma. I have studied how these islands can be stabilised by radiofrequency waves, first by devleoping a code simulating the nonlinear current condensation effect, second by investigating the advantages of stabilising the islands whilst they are locked instead of rotating.
Tokamaks are susceptible to magnetohydrodynamic instabilities that open up magnetic islands (see picture) and can eventually cause catastrophic disruptions of the plasma. I have studied how these islands can be stabilised by radiofrequency waves, first by devleoping a code simulating the nonlinear current condensation effect, second by investigating the advantages of stabilising the islands whilst they are locked instead of rotating.
Relevant publications:
Relevant publications:
Calculating RF current condensation with consistent ray-tracing and island heating
On the stabilisation of locked tearing modes in ITER and other large tokamaks
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