The influence of magnetic geometry on the plasma edge region of future fusion reactors

Lead Research Organisation: University of York
Department Name: Physics

Abstract

Je-S summary: Developing a portfolio of energy producing solutions is imperative to advance the economy, keep society functioning and to fight the advance of climate change. Commercial fusion will play an important role as part of that portfolio when technical challenges are overcome, having the ability to provide a low-carbon, essentially limitless, steady source of energy on a large scale, with a small land footprint.
Arguably the biggest challenge to the magnetic fusion energy concept is how to safely channel the reactor heat exhaust to the surrounding material surfaces. The fusion reactions occur between ions in the hot fusion core that are at a temperature ~ 100 million oC. This provides enough energy for the positively charged nuclei to overcome their electrical repulsion and come close enough for the attractive nuclear force to take over. The two ions then bind to form a new nucleus with less mass than the original two ions, releasing energy. The hot plasma is contained within a magnetic 'bottle', called a tokamak, which has the shape of a torus. Exhaust energy and particles, which leak out of the magnetic bottle in steady state, are diverted away along magnetic field lines to remote material surfaces (termed 'divertor targets') designed to handle the resulting high power densities. The excellent confinement of energy within the magnetic bottle necessary for fusion energy production results in a narrow channel of exhaust power flowing to the divertor targets which, for a tokamak of radius ~ 5m, has a channel thickness of order 1 mm. The resulting heat flux flowing along the magnetic field to the divertor target likely approaching 25GigaWatts/m2. This is about 500x times the heat flux of an arc welder and 2500x what the engineering limits of steady state heat transfer to a solid material allows (10MegaWatts/m2).
We employ several methods to reduce this heat flow to surfaces to below engineering limits: a) The simplest is to arrange the angle of the target to the heat flux to be small, spreading the divertor heat over a larger area, reducing the peak heat flux by x20; & b) More significantly, we encourage light (power) to be emitted from the plasma. We also utilise other atomic processes to remove energy, momentum and even particles from the plasma in a process we call 'detachment'. Detachment has been the main process to reduce the heat flux to the target, but more reduction is needed for a viable reactor-scale device.
The goal of this research project is to evaluate how modifications of the magnetic fields and geometry in the divertor target ('alternative divertor configurations') region can further enhance the power removal properties of the plasma & reduce the heat fluxes reaching divertor surfaces below the engineering limit. In the research proposed we will: a) test our model predictions that alternative divertor configurations remove more heat from the plasma & better control the detachment processes using data from existing and new diagnostics we develop; and b) study both the dynamics of how the plasma is cooled through the processes mentioned and the sensitivity of the detachment process to external controls.
This project will promote the UK into a world-leading role in the area of fusion reactor divertor physics research through development of key knowledge and research capabilities within the UK. Indeed, we will contribute unique results to the upcoming EU decision of what the appropriate divertor solution is for commercial reactors, reducing the time to a demonstration fusion power plant. The proposed work will also accelerate fusion research at the £50M upgrade to the MAST tokamak at Culham, where the first (worldwide) embodiment of the so-called 'super-x' alternative divertor topology will occur. By the UK playing a key role in achieving fusion the country will benefit economically from commercial applications as well as having an essentially limitless, steady source of clean energy into the future.

Planned Impact

Je-S Impact Summary: Developing a portfolio of energy producing solutions is imperative to advance the economy, keep society functioning and to fight the advance of climate change. Commercial fusion will play an important role as part of that portfolio when technical challenges are overcome, having the ability to provide a steady source of energy on a large scale, with a small land footprint. Fusion energy also provides a low-carbon, sustainable, essentially limitless, energy source.
The research in this proposal will accelerate the progress towards commercial fusion energy production, benefitting the UK, and the world. Our proposed work, based on our model predictions, will compare several potential enhancements, or alternative solutions to the tokamak fusion reactor device power exhaust capability, called a 'divertor'. Those enhancements will both increase reactor power exhaust capability, allowing smaller and more cost-effective reactors, and better control of heat exhaust physical processes, imperative for ITER (the penultimate step to a reactor being built by the EU and worldwide partners in France) and DEMO (the proposed demonstration fusion nuclear reactor expected to be operational in the second half of this century). The EU roadmap to fusion energy* states that because heat loads predicted for the DEMO divertor are so high 'an aggressive programme on alternative solutions for the divertor is necessary'.
This project will promote the UK to a central, if not leading role in the key area of fusion reactor divertor physics research through: (1) development of key knowledge and research capabilities within the UK, and (2) providing an accelerated, or earlier assessment of the various alternative divertor solutions, thus providing critical knowledge to the upcoming EU, and worldwide decision of what the appropriate DEMO divertor solution is. In addition we will have more confidence in a fusion reactor concept as well as be ready earlier to build DEMO. The proposed work will also accelerate fusion research at the £50M upgrade to the MAST tokamak at Culham, of which a central focus is the first (worldwide) true embodiment of probably the most-promising divertor topology alternative, the super-x divertor. By the UK playing a key role in achieving fusion the country will benefit economically from commercial applications as well as a steady source of energy into the future..
The plasma and atomic physics associated with power exhaust has much in common with low-temperature plasmas which have a range of applications. As well as displays and lighting, there are other applications of these plasmas, such as the erosion, functional modification and coating of surfaces. Applications span a wide range, from human tissue to mirror surfaces, as well as ways to create new surface materials that are advantageous in terms enhancing hydrogen production (for fuel and storage) and catalysis of gases. Beyond surfaces the physics of heat exhaust has similar physics to that associated with spacecraft plasma thrusters that utilise embedded magnetic fields.
There will be three post-doctoral Research Associates involved in this research. PDRA1 & PDRA2 will have an experimental emphasis, whilst PDRA3 will be focussed on modelling. This work will provide a deep education in divertor and plasma physics in the effort to understand the differences amongst the three divertor configurations studied. They will have a unique training applicable to fusion research and, more generally, in the use of plasmas for commercial applications mentioned above. Three PhD students will be involved in the programme (funded through the EPSRC CDT in Fusion Science & Technology led by York). Similar to the PDRAs they will also be provided with unique training that will make them well-equiped for careers across fusion and commercial plasma applications.
* https://www.euro-fusion.org/wpcms/wpcontent/uploads/2013/01/JG12.356-web.pdf

Publications

10 25 50

 
Description Initial experimental results with experiments at the TCV tokamak contradicted the prediction of our simple model (Nucl. Fusion 56 (2016) 056007 doi:10.1088/0029-5515/56/5/056007) in that the detachment threshold did not drop as the major radius of the divertor target, 'Rt' was increased. We have successfully modelled the experimental results: Apparently, physics processes associated with neutrals compensated for the 'Rt effect'. We have also shown how the Rt and neutral effect can be made to synergistically work together as opposed to against each other with modifications of the divertor geometry in a paper (Plasma Phys. Control. Fusion 62 (2020) 035008 https://doi.org/10.1088/1361-6587/ab69bb) and presentation. We have applied the same analysis to the SOLPS predictions of the MAST-U tokamak and have submitted a paper showing that the effect of the baffling in MAST-U is more uniform over Rt and thus the effect of total flux expansion is more clear (doi.org/10.1088/1741-4326/ac81d8
).
A study of the detachment threshold as measured by the decrease in the ion current reaching the target has been published (doi.org/10.1088/1361-6587/ab1321). The development of a new camera diagnostic system for use on the MAST-U tokamak has been delayed but was installed and operated in 2021 during the delayed experimental campaign with excellent results allowing us to track the front edge of the detached region - comparison to the 2016 model have started with initial agreement. The development of the Integrated Data Analysis (IDA) has been successful in the proof of principle demonstration (doi.org/10.1088/1361-6587/ab759b) and poster at the 23rd International Conference on Plasma Surface Interactions May 18-22, 2018. Since then, the IDA development has focussed on making the analysis more robust against errors/uncertainties in the experimental data.
Pre-grant, we published a prediction of how the detachment location in the divertor can be predicted with a combination of control parameters and details of the divertor magnetic and physical geometry - the analytic 'DLS'model. During the grant we compare the DLS model predictions to the SOLPS numerical model which includes essentially all known divertor physics. The resulting paper (10.1088/1741-4326/ac7a4c) reports that the DLS model is a very good tool for improving divertor magnetic topology and control of the detachment location, although conservative. And recently, the DLS model has been compared to MAST-U data with a paper in the next year or so.
Exploitation Route At the moment our results are primarily of interest to specialists in the fusion energy research field. The ways that they can utilise our results fall into several categories - The development of the Integrated Data Analysis (by our PDRA) is a quantum step forward in diagnosing and understanding divertor plasmas. The modelling of our existing results (by our PDRA) has shown that there is a path forward to better optimising the design of the divertor region of tokamaks. We are making steady progress on comparing our model of detachment location sensitivity to external controls with very good agreement through the modelling of the MAST-U divertor and with comparison of experimental measurements to the JET tokamak divertor. All of the above results have been shared with the International community through workshops and conferences (and publications).
Sectors Education

Energy

 
Description CCFE - Edge modelling 
Organisation EURATOM/CCFE Fusion Association
Country United Kingdom 
Sector Academic/University 
PI Contribution Close collaboration on modelling of tokamak edge and divertor plasmas, mainly with the SOLPS code. Weekly meetings to discuss progress, joint supervision of PhD students, and York PDRAs based at CCFE.
Collaborator Contribution Weekly meetings to discuss progress, joint supervision of PhD students and day-to-day management of PDRAs.
Impact Joint publications and presentations.
Start Year 2015
 
Title SD1D 
Description Calculates the time evolution of plasma in the edge of fusion devices, including the flow of heat along magnetic field lines to the walls of the device. 
Type Of Technology Software 
Year Produced 2018 
Open Source License? Yes  
Impact Paper publication https://arxiv.org/abs/1812.09402 
URL https://github.com/boutproject/SD1D
 
Description A Poster Presentation at the Joint ICTP-IAEA Workshop on Atomic Processes in Plasmas: Data-driven Research; 13-17 December 2021 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Daniel Greenhouse, whose research is in developing the IDA technique, gave a poster presentation entitled 'Study of the Required Balmer-Lines for Integrated Data Analysis Systems in Tokamak Divertors'. Designed to prompt discussion between audience members in order to find avenues in which to progress the research.
Year(s) Of Engagement Activity 2021
URL http://indico.ictp.it/event/9657/
 
Description A. Fil presentation at the 46th European Physical Society Conference on Plasma Physics, EPS 2019; University of Milano - BicoccaPiazza dell'Ateneo Nuovo, 1Milan; Italy; 8 July 2019 through 12 July 2019 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Gave a paper presentation entitled 'Towards understanding the relative role of divertor geometry and magnetic topology on detachment(Conference Paper)'
Year(s) Of Engagement Activity 2019
URL https://www.scopus.com/record/display.uri?eid=2-s2.0-85084021266&origin=inward&txGid=2bb7d35dda2121a...
 
Description CCFE Edge Theory meeting, 26 Oct 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Presented work on "The role of particle, energy and momentum losses in 1D simulations of detachment", prior to submitting the paper. The aim of this was to invite comments and suggestions for improvement, and to advertise the work to a broader audience.
Year(s) Of Engagement Activity 2018
URL https://arxiv.org/abs/1812.09402
 
Description Contributed paper/poster at international conference (Plasma Surface Interactions, Princeton, NJ) - Simon Orchard 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Simon Orchard presented a poster on 'Improved understanding of detachment on JET through improved camera tomography'. The purpose was for him to open up discussions with other researchers about his techniques and results. He gained very good experience at the conference.
Year(s) Of Engagement Activity 2018
URL https://psi2018.princeton.edu/
 
Description Contributed paper/poster at international conference - Chris Bowman 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Chris Bowman (PDRA on this grant) presented a poster presentation entitled 'A Bayesian multi-diagnostic inference system for divertor physics studies in MAST-U'. This presentation was the accomplishment of the near term goal of hs work - a proof of principle demonstration that the Integrated data analysis of multiple divertor measurements can allow for determination of the plasma solution. Chris and Bruce Lipschultz interacted with a number of attendees at the conference and it led to feedback on his work as well as new directions. The preliminary work presented has matured in the 9 months from the meeting and is currently being drafted into a publication.
Year(s) Of Engagement Activity 2018
URL https://psi2018.princeton.edu/
 
Description Invited presentation by C. Cowley at Mar 2023 Institute of Physics Plasma meeting in Cambridge UK entitled 'Detachment Control Considerations for Divertor Design' 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact PhD student presented an invited talk entitled 'Detachment Control Considerations for Divertor Design' to a general plasma audience. The talk covers his research using analytical and code models to extract the primary design attributes of a divertor and, in a relative sense, how important the various design attributes are to detachment threshold and control.
Year(s) Of Engagement Activity 2023
URL https://www.iop.org/events/49th-iop-annual-plasma-physics-conference#gref
 
Description Invited talk given at KSTAR 2018 fusion conference Muju, S Korea 21-23 Feb 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk given at KSTAR 2018 fusion conference Muju, S Korea 21-23 Feb 2018
Year(s) Of Engagement Activity 2018
 
Description Oral presentation by C. Cowley at Nov 2022 IAEA Technical meeting on divertor concepts 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact CYd Cowley (PhD student) gave a presentation entitled 'Detachment Control Considerations for Divertor Design' which was well received as it makes a case for guiding physics principles extracted from modelling that can be used in tokamak divertor design for fusion reactors.
Year(s) Of Engagement Activity 2022
URL https://conferences.iaea.org/event/286/
 
Description Pecha Kutcha (short) presentation of PhD research at the 2021 EU FuseNet conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact Cyd attended the 2021 Fusenet conference, attended by hundreds of Fusion student in Europe from the 22nd to 23rd of November 2021. The event consisted of keynote speakers, virtual poster sessions, and pecha kutcha (short) talks. Cyd gave a talk about his research which is the study of sensitivity of the detachment extent from divertor target to the x-point ('detachment location') to control variables and to the characteristics of the divertor magnetic topology.
Year(s) Of Engagement Activity 2021
URL https://fusenet.eu/news/8-bit-fusenet-phd-event
 
Description Poster presentation at the 2017 Plasma Edge Theory conference on his work modelling TCV plasmas 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Alexander Fil (Post-doc on this grant) presented a poster and submitted (accepted) paper entitled 'Identification of the primary processes that lead to the drop in divertor target ion current at detachment in TCV' at the 2017 PET conference in Marseilles, France, 27-29, September, 2017. This paper describes Alex's work in modelling the divertor plasma at the TCV tokamak experimental device, a central goal of the grant and his work.
Year(s) Of Engagement Activity 2017
URL https://pet16.sciencesconf.org/
 
Description Presentation at International Plasma Surface Interactions 2018 conference by Dr. Alex Fil: 'On the effect of total flux expansion on TCV detachment modeling with SOLPS-ITER' 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Alexandre Fil (PDRA on grant) presented a poster entitled - 'On the effect of total flux expansion on TCV detachment modeling with SOLPS-ITER' detailing his work comparing experiment and modelling and resolving the various bits of physics affecting the divertor plasma condition. As described elsewhere, he has been able to show that while the physics predicted by our model is extant in that data, there are other bits of physics which ae playing a strong role. This is actually useful as it points to a way to synergistically bring different effects together to improve the design of the divertor region in tokamaks.
Year(s) Of Engagement Activity 2018
URL https://psi2018.princeton.edu/
 
Description Presentations made at workshop on grant work 
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 Bruce Lipschultz presented two talks on the grant work - a) the current results form both modelling as well as experimental findings on the sensitivity of the detachment location to external controls; and b) our development of a better understanding of the development (steps) of detachment and its relationship to power and momentum loss. Both talks stirred up considerable interest. The attendees were official experts from 7 different 'partners (e.g. the EU, China, Korea, US...) and, given the workshop atmosphere, there was a very good discussion which is helpful to the grant and helpful for communicating the new knowledge.
Year(s) Of Engagement Activity 2018
URL https://uwmadison.eventsair.com/plasmawkshp/
 
Description SD1D paper clearance, MST1 Task Force Meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact A talk given on the topic and key results of a paper, prior to clearance through the EUROfusion pinboard. The audience were experts, professional researchers from across Europe.
Year(s) Of Engagement Activity 2018
URL https://arxiv.org/abs/1812.09402
 
Description • Cyd Cowley's talk 'Optimizing Detachment Control Using the Magnetic Configuration of Divertors', ITPA scrape off layer and divertor topical group meeting 18 Jan 2022. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Cyd Cowley (PhD student) remotely attended the 18 Jan 2022 ITPA divertor and SOL working group meeting, to give a talk on his research and take part in talks and discussions on key physics challenges and breakthroughs for the ITER divertor. These twice-yearly working groups are attended by leading experts in the field, and detailed discussions occur after every session.
Year(s) Of Engagement Activity 2022
URL https://www.qst.go.jp/site/jt60-english/31st-itpa-divsol.html