Identifying the Key Factors Currently Preventing Ignition in Inertial Confinement Fusion Experiments.

Lead Research Organisation: Imperial College London
Department Name: Dept of Physics

Abstract

Thermonuclear fusion is the mechanism by which energy is generated in the Sun. For decades scientists have been attempting to harness fusion for electrical power production because of the huge advantages it offers as a safe, clean and almost inexhaustible supply of energy. In laboratory experiments, fusion is normally studied by heating the heavy isotopes of hydrogen to very high temperatures forming a plasma, in which the rapid motion of the positively charged ions is sufficient to overcome their electrostatic repulsion and allow them to undergo nuclear reactions. One of the main approaches to extracting energy from these reactions is Inertial Confinement Fusion. This involves assembly of the thermonuclear fuel to ultra-high density (over 1000 times the density of water) inside a mm-scale capsule through a spherical implosion driven by high-power lasers. Central to this method is the process of ignition in which the energetic alpha particles emerging from the reactions are themselves used to further heat the fuel, resulting in a self-sustaining burn wave which releases copious amounts of energy. This is a very exciting time for fusion research because with the completion of the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL), the first laboratory facility with the capacity to demonstrate ignition is now operational.
Early results from the NIF however have highlighted differences between the predictions of computer models and the behaviour observed. Most importantly the number of nuclear reactions has remained too low to initiate ignition. The PI and Co-I on this grant have worked extensively with scientists at LLNL to understand the origins of these discrepancies and participated in the Science of Ignition workshop which identified priority research directions to address these issues.
For this proposal we wish to capitalise upon our experience with plasmas of extremely high density and temperature to address key uncertainties in the design of inertial confinement fusion experiments and the physics of ignition and work to provide an explanation of why the current design does not achieve ignition and burn. Key areas of research will include understanding the way in which the radiation used to drive the implosion is absorbed in the surface of the capsule, the susceptibility of the imploding capsule to hydrodynamic instabilities which cause the fuel to disintegrate before it is fully compressed and the tendency of the high temperature and low temperature regions of the fuel to stir and mix together which quenches the burn. We will also investigate the physics of the ignition process itself, evaluating whether the energetic alpha particles are able to escape the fuel before depositing their energy and the role of spontaneously generated magnetic fields which provide a form of thermal insulation and serve to keep the heat within the fuel.
Part of the work will involve developing a number of advanced computer modelling capabilities. In addition to their use in fusion research, these capabilities can also be used to exploit large scale laser facilities for fundamental research in plasma physics, nuclear physics and laboratory astrophysics. Using these computer models to simulate a fusion capsule in which we deliberately introduce an imperfection, we can calculate what characteristic signatures of this defect are embedded within the flux of energetic neutrons and X-rays emanating from the reacting fuel. Comparing synthetic diagnostic data with that obtained in experiment then allows us to isolate which physical processes are responsible for limiting fusion performance. The same computer models can then be used to design improvements which mitigate these effects and allow us to make progress towards achieving ignition. The work described in this proposal therefore represents an opportunity for UK science to make a significant contribution to what would be a major scientific achievement.

Planned Impact

For decades the prospect of a clean, almost inexhaustible supply of energy from thermonuclear fusion has fascinated research scientists and the public alike. Within recent years, the HiPER design project did much to raise public awareness of inertial fusion energy. The key scientific challenge of ignition is being addressed right now at the National Ignition Facility. This proposal represents an opportunity for UK science to be directly involved in what would be a major scientific achievement. If ignition is achieved then the short term impact would be significant in terms of the public engagement in fusion science, the stimulation of academic and industrial research and policy decisions over investment in fusion energy. The longer term societal and environmental impact, should inertial fusion energy be realised would be substantial.

The computational models developed as part of this work will enhance our capability to design other experiments in high energy density physics and laboratory astrophysics. We will make use of the Centre for Inertial Fusion Studies at Imperial College to facilitate collaborations with other academic groups and to maximise the impact of these tools on fundamental research. If ignition can be achieved and a thermonuclear burning plasma created in the laboratory this would provide access to regimes of extreme physical conditions with significant impact for the high energy density physics community providing a new platform for experiments in plasma physics, nuclear physics and laboratory astrophysics. Another principle beneficiary of the research will be the UK defence industry and particularly AWE Aldermaston, who will benefit not only from the exchange of results, but also from collaboration on model development and from staff training on the post-graduate plasma physics plasma course at Imperial College.

The research staff involved in the project will be trained in wide range of plasma, atomic, nuclear and computational physics techniques. They will also benefit from the considerable experience in these areas within the project partners. Such skills are much sought after within the academic community and national laboratories with many of the techniques involved being transferable to other areas of the economy.

Public dissemination of the work will take place through publication in high impact factor peer reviewed journals, through presentations at international conferences and specialist meetings organised by the Centre for Inertial Fusion Studies and through the schools outreach programme at Imperial College.

Publications

10 25 50
 
Description During the four years of this grant we concentrated upon the development of opacity, radiation transport and radiation hydrodynamics models and applied them to understanding the sensitivity of inertial confinement fusion capsules to asymmetry in the radiation drive and capsule defects. We also developed a more comprehensive understanding of the effects of asymmetry on the behaviour of the hotspot at the centre of these implosions and the interpretation of neutron spectra and other diagnostics as signatures of the phenomena which can limit fusion performance. We used these models to make predictions for the effects of the principle sources of asymmetry on fusion performance in indirect drive drive experiments on the National Ignition Facility and have calculated the anticipated diagnostic signatures of such asymmetries. This work has helped to identify the principle causes of performance limitation in the previous and present capsule designs and has contributed to an improved understanding that has allowed higher performing capsules to be realised.
Exploitation Route Taking this work forward we are now using these models to examine alternative approaches to design optimisation as well as more fundamental studies of the physical processes governing ignition and the release of higher yields in ICF targets. We continue to use the models developed in this work to predict the potential performance benefits of alternative designs. Our results continue to contribute to an evolving consensus of the research priorities within the field of inertial confinement fusion.
Sectors Aerospace, Defence and Marine,Energy

 
Description These results have had a considerable impact upon the consensus of research priorities for the field of inertial confinement fusion. They have also contributed to the scientific objective of achieving an ignited burning plasma in the laboratory and to assessing the long-term viability inertial confinement fusion as a potential energy source.
First Year Of Impact 2014
Sector Aerospace, Defence and Marine,Energy
Impact Types Societal,Economic

 
Description Centre for Inertial Fusion Studies
Amount £499,254 (GBP)
Organisation Atomic Weapons Establishment 
Sector Private
Country United Kingdom
Start 10/2013 
End 09/2016
 
Description Centre for Inertial Fusion Studies 2016-2019
Amount £270,516 (GBP)
Organisation Atomic Weapons Establishment 
Sector Private
Country United Kingdom
Start 10/2016 
End 09/2019
 
Description EPSRC Doctoral Prize Fellowship (via Imperial College) - Dr Arthur Turrell
Amount £45,558 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2013 
End 09/2014
 
Description Inertial Confinement Fusion - exploring the options for ignition.
Amount £434,848 (GBP)
Funding ID EP/P010288/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 08/2017 
End 07/2020
 
Description Lawrence Livermore Laboratory Academic Partnership
Amount $444,000 (USD)
Organisation Lawrence Livermore National Laboratory 
Sector Public
Country United States
Start 10/2016 
End 09/2020
 
Description Upgrade of dedicated ICF/HEDP computing facilities at Imperial College
Amount £139,920 (GBP)
Organisation Imperial College London 
Sector Academic/University
Country United Kingdom
Start 11/2014 
End 10/2018
 
Description ICF collaborations with Lawrence Livermore Laboratory 
Organisation Lawrence Livermore National Laboratory
Country United States 
Sector Public 
PI Contribution We participate in a number of areas of collaboration with LLNL in relation to the design and interpretation of results from inertial confinement fusion experiments. These include understanding the effects of asymmetric radiative drive and capsule defects on the stability of the implosion and the shape of the hotspot. Our main contribution is in assessing the unique contributions of 3D asymmetries to degrading fusion performance and how this can be diagnosed from neutron spectra measurements.
Collaborator Contribution Exchange of information on experimental and simulations configurations and data. Incorporation of ideas developed through the collaboration into experimental proposals as well as the interpretation of experimental results and the factors limiting fusion performance.
Impact Influence on the consensus opinion of the research field about research priorities in inertial confinement.
Start Year 2011
 
Description Neutron spectroscopy collaboration with LLE and MIT 
Organisation Massachusetts Institute of Technology
Country United States 
Sector Academic/University 
PI Contribution Simulation of and interpretation of results from inertial confinement fusion experiments on the National Ignition Facility with a particular emphasis on the inference of residual bulk motion of the plasma at stagnation from the apparent Doppler shift and spread of energies in neutron spectra.
Collaborator Contribution Access to neutron time of flight and magnetic recoil spectrometer data. Collaborative discussions on the behaviour of the plasma that can be inferred from the data and the significance of this for the success of fusion ignition.
Impact Influence on the consensus opinion of the research field about research priorities in inertial confinement.
Start Year 2012
 
Description Neutron spectroscopy collaboration with LLE and MIT 
Organisation University of Rochester
Department Laboratory for Laser Energetics
Country United States 
Sector Academic/University 
PI Contribution Simulation of and interpretation of results from inertial confinement fusion experiments on the National Ignition Facility with a particular emphasis on the inference of residual bulk motion of the plasma at stagnation from the apparent Doppler shift and spread of energies in neutron spectra.
Collaborator Contribution Access to neutron time of flight and magnetic recoil spectrometer data. Collaborative discussions on the behaviour of the plasma that can be inferred from the data and the significance of this for the success of fusion ignition.
Impact Influence on the consensus opinion of the research field about research priorities in inertial confinement.
Start Year 2012
 
Title Chimera 3D radiation hydrodynamics model - 2016 version 
Description Chimera is a new capability for modelling high energy density physics experiments using soft X-ray indirect drive. The model is based on an efficient parallel 3D magneto-hydrodynamics algorithm and has been modified to include multi-group radiation diffusion models based on non-LTE DCA opacity data. The code can run in Cartesian, cylindrical or spherical geometry. 
Type Of Technology Software 
Year Produced 2016 
Impact This new model has enabled us to investigate the effects of the growth of 3D asymmetries on the performance of inertial confinement fusion capsules on the National Ignition Facility, including the effects of asymmetry in the driving radiation source and defects in capsule manufacture. 
 
Title non-LTE radiation and atomic physics program 'Spooky' 
Description The 'Spooky' code allows detailed atomic population, radiation spectra and opacity calculations. The model utilises a non-LTE collisional radiative equilibrium model solution of the Saha equation with detailed configuration accounting and n-l splitting. The effects of Doppler, Stark and lifetime broadening are included in the line shapes. 
Type Of Technology Software 
Year Produced 2013 
Impact This software has enabled accurate calculations of radiation cooling rates in large scale radiation hydrodynamics and MHD simulations of high energy density plasmas. It also enables the generation of synthetic experimental X-ray spectra to be generated in post-processing calculations as well as the generation of detailed opacity tables for use in radiation transport models. 
 
Description Cambridge University Physics Society, public lecture 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact Generated enthusiasm for the research field amongst undergraduate and postgraduate student members to the Cambridge University Physics Society.

Further contacts were made with the society to initiate laboratory tours and further stimulate interest in the subject as well as encouragement to undertake a PhD in this area.
Year(s) Of Engagement Activity 2014
URL http://physics.soc.srcf.net/wiki/index.php?title=Cambridge_University_Physics_Society
 
Description Institute of Physics Plasma Annual Lecture - Dr Arthur Turrell 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Very positive feedback from exit poll.

Requests for further information from members of the public and events organisers
Year(s) Of Engagement Activity 2014
URL http://plasma14.iopconfs.org/260215
 
Description Research Frontiers presentation - Imperial College 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact Informed audience of recent interesting developments in the field and generated enthusiasm in undergraduates for direct participation in the research field.

Further interest in participation in research through summer internships and requests for PhD positions.
Year(s) Of Engagement Activity 2014
URL http://www3.imperial.ac.uk/Physics/events/resfrontiers
 
Description Royal Society Summer Exhibition 2017 - How to Make a Supernova 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Royal Society Summer Exhibition - How to Make a Supernova - Centre for Inertial Fusion Studies participated in an exhibit. Visited by several thousands members of general public over one week.
Year(s) Of Engagement Activity 2017
URL https://royalsociety.org/science-events-and-lectures/2017/summer-science-exhibition/exhibits/how-to-...
 
Description Royal Society Summer Science Exhibition 2014 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Preparation and manning of a stand at the Royal Society one week long Summer Science exhibition, showcasing the best of British science. Them "Set the controls for the heart of the sun". Presentations, talks and demonstrations for several thousand visitors ranging from groups of school children through to journalists and Fellows of the Royal Society




Improved public understanding of the case for Fusion Energy.
Year(s) Of Engagement Activity 2014
URL http://sse.royalsociety.org/2014/heart-of-the-sun/
 
Description Science in Parliament Vol 71 No 4 Autumn 2014 - Dr Arthur Turrell 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? Yes
Geographic Reach Local
Primary Audience Policymakers/politicians
Results and Impact An article written in Science in Parliament magazine, to inform decision makers of the strategic importance of Inertial Confinement Fusion research within the UK.

It is too soon to gauge whether this had the desired impact.
Year(s) Of Engagement Activity 2014