Inertial Confinement Fusion - exploring the options for ignition.

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

Abstract

The vast quantity of energy emitted by the Sun is produced by thermonuclear fusion. Harnessing fusion power on earth has long been a goal for scientists as it would provide an almost limitless supply of safe, clean electrical power. In the laboratory, experiments to study fusion involve heating isotopes of hydrogen to very high temperatures such that a plasma is formed. If the plasma is sufficiently hot then the rapid motion of the positively charged ions can overcome the electrostatic repulsive force resulting in a nuclear fusion reaction. One of the main approaches to producing these conditions is Inertial Confinement Fusion (ICF). The thermonuclear fuel is initially contained in a spherical capsule with a 1 mm radius. This capsule is compressed using high-power lasers such that within a few billionths of a second it becomes more than 1000 times denser than water and hotter than the core of the Sun. The key process in ICF is ignition in which the energetic alpha particles emitted by nuclear reactions cause further heating of the fuel. This results in a self-sustaining burn wave of reactions which releases copious amounts of energy. This is a very exciting time for fusion research because the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) is currently operational, producing thermonuclear plasmas at temperatures and densities never before observed in the laboratory.
Recent results from the National Ignition Facility have demonstrated a landmark achievement in generating an energy release from fusion reactions that is greater than thermal energy of the fusion fuel. Nevertheless, the number of fusion reactions remains too low to initiate the ignition process and as a consequence, the energy released is still far lower than the total energy used by each experiment. Previous work by the PIs was amongst the first to highlight the detrimental effects that three-dimensional asymmetries can have on the fusion performance. Such asymmetries are now widely believed to be the principal obstacle to achieving higher energy yields. Over the last three years, the PIs and PDRAs have worked extensively with scientists at LLNL to understand the key physical processes at work and to identify diagnostic methods which can be employed to isolate the principal causes of reduced yields.
For this proposal we wish to capitalise upon the experience we have gained from studying experiments on the NIF to explore a range of future options for progressing towards ignition in Inertial Confinement Fusion. Our work will make use of a combination of advanced theoretical models of dense plasmas, large scale parallel computing using our multi-dimensional radiation hydrodynamics codes and detailed analyses of experimental data. We will extend our computer models to calculate the anticipated response from a broad range of new diagnostics currently being introduced on NIF. This will help us contribute to the optimisation of diagnostic design and the methods used to isolate the principal causes of reduced performance. We will use this data to establish how theoretical models describing how the fusion plasma is confined need to be modified to take into account asymmetry and how learning to live with asymmetry leads to different approaches to the optimisation of yield. We will use these approaches to assess the likely impact of a number of proposed changes to the design of current experiments on NIF. We also propose a different approach to the design of experiments, which avoids some of risks associated with the pursuit of high energy yields, where the objective is instead to provide a reliable means of studying the physics of the ignition process itself. Finally, by exploiting the common physical processes which govern the final stages all inertial fusion experiments, we will use insights gained from experiments on NIF to evaluate the longer term viability of alternative approaches to achieving ignition and high energy yields.

Planned Impact

The potential for thermonuclear fusion to provide a clean, almost inexhaustible supply of energy has fascinated both research scientists and the public for decades. For inertial confinement fusion, it is the process of ignition which is the critical step to achieving significant energy yields. The first series of laboratory experiments designed to investigate the ignition process, are taking place at this time on 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. The experience gained with ICF calculations through this grant will help to guide our development of radiation transport models for the HEDP community radiation hydrodynamics code 'Odin' which we are currently developing together with the Universities of Warwick and York (EPSRC grant EP/M01102X/1).We will make use of the Centre for Inertial Fusion Studies at Imperial College and the Oxford Centre for High Energy Density Science 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 principal 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 through the Centre for Postgraduate Training in Plasma Physics and High Energy Density Science jointly run by Imperial, Oxford and Warwick.

The research staff involved in the project will be trained in a 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. Recent examples of this are the secondment of one of our PDRAs to work in the defence industry and the movement of another PDRA to a research position within the Bank of England.
 
Description We have identified a number of physical processes occurring during the hotspot formation and the nuclear burn phases of the ICF implosion that require the development of novel theoretical and computational models.
These include a possibly transformative approach to inertial fusion capsule design, where the addition of intense magnetic fields can be used to reduce heat losses due to thermal conduction and could potentially trigger ignition of a burning plasma with large energy releases.
In addition we have identified important "kinetic" in magnetised burning plasmas which are driven by particles which are not behaving in a hydrodynamic manner. These processes include kinetic effects in the energy spectra of neutrons produced in the nuclear reactions, which may affect the experimental measurement of plasma temperatures, and kinetic effects in the coupling of energy and momentum from fast alpha particles to the electrons in plasma, which may affect the onset of ignition and burn propagation in ICF. Work is currently underway to develop models for these processes that are compatible with the radiation-hydrodynamics models, which accurately simulate the bulk implosion. These models will allow the kinetic effects to be studied in an integrated manner with the hydrodynamic processes such that their significance can be accurately assessed.
Exploitation Route It is envisaged that a novel set of computational models will be developed and utilised in order to understand the importance of magnetised ignition and kinetic effects. Other researchers in the field will be interested in how these effects can be accurately modeled.
Sectors Aerospace, Defence and Marine,Energy

 
Description These results are now beginning to have an impact of future 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 2018
Sector Aerospace, Defence and Marine,Energy
Impact Types Societal,Economic

 
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 Magnetised burning plasma with Sandia National Laboratory 
Organisation Sandia Laboratories
Country United States 
Sector Private 
PI Contribution Development of novel computational models for calculation of transport coefficient in magnetised burning plasmas. Adaptation of unique approaches to calculating neutron spectra to magnetised plasmas and secondary DT reactions.
Collaborator Contribution Hosted and financed visit to Sandia National Laboratories from November to December 2017. Provided data and information on ongoing magnetised inertial fusion experiments at Sandia.
Impact Paper in preparation.
Start Year 2017
 
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
 
Description Science Museum Lates - 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 Exhibit on the work of Centre for Inertial Fusion Studies in Laboratory Astrophysics.
Year(s) Of Engagement Activity 2017
URL https://www.sciencemuseum.org.uk/see-and-do/lates