Plasma turbulence in complex environments

This project addresses a challenging and important area of plasma physics: the interaction of 3D turbulent plasma with neutral gas. This has applications in astrophysical and industrial plasmas, but the focus of this proposal is to broaden and deepen our understanding of plasma-neutral interactions in high power tokamak fusion devices, where the power leaving the core plasma must be handled without exceeding material limits. This is one of the most important issues in fusion research. crucial to the operation of ITER, a 10 billion Euro project currently being built in France, and even more so to the design of a future demonstration power plant DEMO.

Modelling of turbulence in the edge of magnetic confinement devices is a complex problem, but significant progress has been made in this field in recent years. The equations which govern the dynamics of the tokamak plasma edge are well known, but are difficult to solve numerically due to the wide range of time- and spatial scales and strong anisotropy. This project will position the UK at the leading edge of nonlinear plasma edge simulation through development of the BOUT++ code, which has been designed to handle these requirements. A gyro-fluid model will be formulated which can include neutrals whilst conserving momentum and energy, and will be coupled to the state of the art EIRENE Monte Carlo code to follow the neutral particles. By using EIRENE, this project will benefit from almost two decades of work, and enable the model to capture the relevant atomic and molecular physics, and the complicated geometry of real machines including pumps and baffles.

To validate these models, and provide a link to experiment, this project will study plasma edge turbulence in the existing Mega-Amp Spherical Tokamak (MAST) at the Culham Centre for Fusion Energy (CCFE). Through collaboration with researchers at CCFE, the validity of the models and the importance of 3D effects will be tested, in order to understand the level of detail required. Once this is understood, predictions will be made for the novel Super-X magnetic geometry design to be employed on MAST-Upgrade, part of a 30 million pound upgrade due to be completed in 2015. This machine will be very flexible, with a wide range of geometries and plasma parameters possible. By identifying interesting regions of operation which can distinguish between models, this project will guide the experimental campaign and maximise the physics output from this investment.

This project will provide the UK with a unique capability to model coupled 3D turbulence in magnetised plasmas interacting with neutral gas and material surfaces. This will then be used to link tokamak experiments to fundamental physics understanding, and address key issues in the design and operation of future tokamak fusion machines. To maximise the impact of this work, results will be disseminated in journal papers and at conferences; through relevant ITER Physics Advisory groups; national and international collaborators; and through a workshop to be run towards the end of the project.

The world-class simulations which will be carried out under this proposal will have an impact on many levels. On an academic level, this project will further our understanding of plasma turbulence and its interaction with neutral gas; on a national level through the MAST-Upgrade programme and development of UK expertise in plasma edge modelling; and on an international level by addressing an issue of vital importance to the design of tokamak fusion power plants.

This project addresses a fundamental issue in plasma physics; the interaction between plasma turbulence and neutral gas, involving turbulent mixing and ionisation processes. These same processes are also important in many astrophysical and industrial plasmas. By improving our understanding of these environments, this project will have an impact on the wider academic and industrial plasma community beyond fusion.

At a national level, this proposal will provide predictions for the Super-X divertor on MAST-Upgrade, a significant upgrade to the UK's fusion facility. The modelling tools developed will help to maximise the scientific return on this investment by enabling results from this unique machine to be linked to fundamental physics using first principles models. This will then enable results to be extrapolated to larger machines, as well as other fields of plasma research.

This project will position the UK at the forefront of plasma edge modelling, and maintain leadership of the BOUT++ code. By building a larger group of researchers using and improving this code the return on this investment will be maximised. By making the code available to a wide range of national and international collaborators, this proposal will have an impact on research in the UK and internationally.

The design of divertor regions for power handling in future large tokamak devices is challenging and requires a detailed understanding of the interaction of three states of matter: hot plasma; neutral gas; and material surfaces. Due to the complexity of these interactions, there is considerable uncertainty in the scaling of results from existing machines to machines beyond ITER such as DEMO and fusion power-plants. This project will develop a state-of-the-art predictive capability, validated against present-day machines, which will be used to guide the operation and design of these larger machines. This will provide the UK with a capability which could give it an edge in bidding for international funding of the DEMO divertor design, expected in the near future.