Plasma turbulence in complex environments

Lead Research Organisation: University of York
Department Name: Physics


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.

Planned Impact

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.


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Dudson B (2017) Hermes: global plasma edge fluid turbulence simulations in Plasma Physics and Controlled Fusion

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Dudson B (2014) BOUT++: Recent and current developments in Journal of Plasma Physics

Description We have developed models which for the first time combine state-of-the-art plasma turbulence simulations with models for neutral gas. The aim is to improve our understanding of how hot plasma at the edge of tokamak fusion devices mixes with cold neutral gas surrounding the plasma, in order to improve designs for future fusion power plants. We have carried out simulations which show a significant effect on plasma dynamics due to neutral gas, primarily through momentum exchange, and quantified the impact this could have on predictions from plasma simulation codes. Results have been presented at conferences in the UK and Japan, and a paper is currently in preparation.
Exploitation Route The code developed will be made open source, as part of the BOUT++ public repository (see software outputs). This will allow researchers to verify and then build on what we have done. Several other groups are interested in developing these capabilities, including CCFE and Riso DTU, and our results will help guide their efforts. We have made use of presentations and workshops, including a BOUT++ workshop organised as part of this grant, to increase impact.
Sectors Energy

Description In this project we developed improved simulation models for the edge region of tokamaks and other magnetised plasmas such as linear devices, and used national supercomputers (e.g. HECToR and ARCHER) to carry out plasma turbulence simulations. The ultimate goal of this work is to develop a predictive model which can be used to design future fusion power plants. In these devices the interaction between the hot plasma and the neutral gas which surrounds it is crucial to reducing the heat loads to surfaces. This interaction is complex, and remains an active area of research: This project provided the foundation for follow-up work which has led to state-of-the-art models (e.g Hermes, which have been used to study turbulence and neutral gas dynamics in a number of experiments (Magnum-PSI, ISTTOK, DIII-D, MAST). These models continue to be used and developed, and are currently being appled to simulations of TCV (in Switzerland), and the new UK flagship tokamak MAST-Upgrade, which is due to start operating in 2020. As part of this ongoing work, the outputs of this project have been used to train undergraduate students through final-year projects, PhD students, and post-doctoral researchers. Many of these people have stayed in the field, while the others have gone on to apply the high performance computing techniques they learned to other areas of the high-tech economy.
First Year Of Impact 2014
Sector Energy
Description Dust in magnetized plasmas
Amount £291,602 (GBP)
Funding ID EP/M001423/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2014 
End 03/2018
Title BOUT++ neutral gas models 
Description Neutral gas plays a crucial role in understanding the behaviour of the edge region of magnetically confined plasmas, such as plasmas. Interactions between hot plasma and neutral gas modify heat and particle fluxes to the walls of the machine, a critical issue for future fusion power plants, and can affect plasma dynamics by modifying sources and sinks of particles and energy. Until now there has been little work done on incorporating neutral gas physics into plasma turbulence codes. We have implemented two different models for neutral gas into BOUT++: A kinetic (particle-following) model by coupling to the EIRENE monte-carlo code, and a fluid model for neutrals which is less accurate, but also less computationally demanding. 
Type Of Technology Software 
Year Produced 2014 
Open Source License? Yes  
Impact This development is now producing some of the first studies of the effect of neutral gas on turbulence in the edge of tokamak devices. 
Description BOUT++ workshop 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact 13 PhD students, PDRAs and staff attended this 2-day workshop from York, CCFE, DTU (Denmark), Dublin City University (Ireland), and CEA Cadarache (France). Talks and posters were given on recent developments and future plans. Discussions on collaborations followed.

Stronger collaboration with DTU Denmark has resulted, and is continuing. A PhD student has visited York from DTU, and we are currently collaborating on a paper to be submitted shortly.
Year(s) Of Engagement Activity 2014