Dust in magnetized plasmas

Lead Research Organisation: Imperial College London
Department Name: Physics

Abstract

Dusty plasmas are ubiquitous: they occur naturally, in fusion, in industry, and as the subject of special laboratory experiments. Magnetic fields can be present in all these areas, but in spite of this, our understanding of the basic dust-plasma physics in the presence of a magnetic field is far from complete.
An improved understanding of magnetized dusty plasmas is particularly important for fusion. In the last few years dust has been recognised as a critical issue for ITER. Solid particles can enter the plasma from the walls or divertor. It is vital to be able to predict the fate of such particles. If they enter the core plasma they rapidly evaporate, thus depositing impurities which can compromise the fusion performance. On the other hand, those which leave the plasma can give rise to serious operational and health and safety problems.
We propose a collaborative and unified programme of theoretical, computational and experimental work on dust in magnetized plasmas, involving Imperial College and the Universities of Liverpool, York. Although the main emphasis is on fusion applications, the work would benefit other areas, for instance the industrial plasma community.
The proposed research covers three overlapping areas: (1) the effect of magnetic fields on the basic dust-plasma interaction, (2) the interaction of dust with magnetically driven filaments, particularly in the tokamak edge, and, (3) improved tokamak dust transport simulations. As part of the project a new high magnetic field dusty plasma experimental facility will be set up at Liverpool.

Planned Impact

This project concerns magnetized plasmas which contain dust. Such plasmas occur in space, fusion, industry, special laboratory experiments. The main application of the work which we will study in detail is fusion. However, improved understanding of the basic physics of such plasmas is potentially important for other applications, and we will initiate dialogues with those in other communities to publicize our work and try to assess its possible significance.

From the perspective of the EPSRC strategic themes, this project falls under the headings of: Energy, and Future Manufacture.

The international fusion programme is entering a crucial phase with the construction of the next-step global fusion experiment, ITER. This tokamak reactor, in which the first plasma will be created in 2019, should achieve net energy gain. It aims to investigate many of the science and engineering issues vital to a working fusion power station. The deleterious effect of dust is one of these issues. Looking beyond the university plasma physics community, we therefore plan to get more closely involved in the ITER programme, using our existing contacts and by presenting our work at international fusion conferences. Securing ITER recognition is an essential part of the present project.

Plasma based devices are finding increasing uses in industry, notably for applications involving materials processing and surface engineering. Plasma technology is both enabling, allowing new processes to be exploited, and more environmentally friendly than older technologies. Discharges involving magnetic fields, for instance magnetrons, are routinely used, and our work will be directly relevant to the basic physics of such devices. In order to assess the potential importance of this work we plan to promote it within the technological plasma community, e.g., by attending specialist conferences in this area. The University of Liverpool also has close ties with this community which we plan to exploit.

With regard to public outreach, we will ensure that all the post-doc's on this grant attend appropriate courses on public engagement, and we will work with the Media and Communications offices at the participating Universities to promote public awareness of the project.

Publications

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Holgate J (2016) Charging of nonspherical macroparticles in a plasma in Physical Review E

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Holgate J (2018) Electron emission from electrically isolated spheres in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena

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Holgate J (2019) Simulated dynamics of a plasma-sheath-liquid interface* in New Journal of Physics

 
Description Magnetic fields are present in many dusty plasmas, notably in fusion tokamaks, where the dust is generated by erosion of the plasma facing surfaces. We have studied the effect of magnetic fields on the basic dust-plasma interaction, and modeled the dynamics of dust immersed in various magnetized plasmas. The most basic manifestation of the dust-plasma interaction is the charging of plasma-immersed dust by collection of ions and electrons from the plasma. The effect of magnetic fields on dust charging has been studied using our tree-code. We find that as the magnetic field is increased the magnitude of the dust floating potential falls as the electrons become magnetized, but at higher fields, when the ions also become magnetized, it increases above its B=0 value. We have also upgraded our tokamak dust transport code, DTOKS, making various improvements to the basic physical model (notably in the treatment of evaporation and the ion drag force). The upgraded code has been used to model the dust-injection experiments carried out by our collaborators from Liverpool University at the MAGNUM-PSI facility. For these simulations we use plasma backgrounds from BOUT++ simulations, provided by our collaborators at York University.
Exploitation Route Our work will enable more accurate simulations to be made of dust behaviour in magnetized plasmas. For instance there are several tokamak dust transport codes in existence, including Imperial College's DTOKS code. We are currently implementing our results on magnetic field effects on dust charging in this code. In the short term we anticipate two further projects which build on this work. Firstly, we plan another collaboration with the University of Liverpool on agglomerates in magnetized dusty plasmas. Secondly, we plan to collaborate with JET/CCFE to develop a tool for identifying dust events in existing camera data on the JET and MAST tokamaks, and integrate these data with other diagnostics.
Sectors Energy

Manufacturing

including Industrial Biotechology

 
Description During the project two postdocs were trained in high-performance computing and plasma modelling, resulting in publications on modelling of linear plasma devices to study the effect of plasma-neutral interactions and geometry on the turbulence within these devices. Two computational tools ("Hermes" and "DiMPl") developed during the project have formed the basis of three PhD student projects to date. Hermes has been applied to modelling of the UK's MAST-Upgrade tokamak, and to studies informing the design of the STEP fusion reactor, and continues to be developed and applied to both linear devices (e.g. LAPD in the US) and tokamak basic and applied science. DiMPl has been used to study the effect of magnetic fields on basic dust plasma interactions, including plasma flows, and has been instrumental in upgrading the DTOKS tokamak dust transport. Links to DIFFER and the Magnum-PSI facility have been developed through collaborative projects which have grown out of this work. These international links are strategically important, and provide access to experimental facilities not found in the UK.
Sector Energy
Impact Types Policy & public services