Writing The Code for Clean Energy
28 Mar 2018
- Helen Towrie

A new project led by the CLF is exploring the viability of the recently proposed 'Shock Ignition' approach to laser fusion.




As the fuel source is found in sea water, this offers an essentially limitless source of clean energy for mankind, if it can be realised. A new project led by the CLF is exploring the viability of the recently proposed 'Shock Ignition' approach to laser fusion.

Laser fusion, also called laser inertial confinement fusion (ICF), is initiated by 'ablating' the surface of a small spherical capsule containing fusion fuel (a mixture of Deuterium and Tritium) until it is heated enough to turn into plasma. This then accelerates outwards from the capsule surface, creating an equal and opposite inward force, accelerating the remaining capsule inwards, creating a spherical implosion. If the implosion could be made sufficiently spherical, this would compress the fuel within the capsule to 4,000 times solid density (1,000g/cc), and heat the centre to 60 million degrees Kelvin – the same conditions found within a stellar interior, igniting the tiny star's core*. This triggers a chain reaction; a thermo-nuclear burn-wave then spreads into the rest of the fuel. Only once this occurs, would we see energy gain (when more energy is liberated than that input by the lasers).

As it stands, efforts to achieve energy gain via laser fusion are yet to be successful, but a recently proposed method called 'Shock Ignition' is looking very promising. In principle, this method is more efficient than conventional ICF schemes (e.g. those explored on NIF), so energy gain should be possible with a significantly smaller (therefore cheaper!) laser system than current multi-billion dollar laser fusion systems.

The coupled, non-linear nature of the physics of laser fusion, means simulation models are critical for designing and interpreting the experiments. Unfortunately, current simulation models are not sufficiently accurate to predict the observed experimental behaviour. A leading hypothesis for the causes of these inaccuracies are kinetic laser plasma interaction instabilities (LPIs). These alter the experiments in ways that are both hard to measure experimentally, and hard to model. The issue we face, is that current simulation codes used to design the laser fusion experiments do not account for LPIs and the changes they cause. This makes it very difficult to account for their effects, precluding the design of experiments with sufficient accuracy for energy gain.

In an attempt to address this problem, which is particularly important in the context of Shock Ignition, EPSRC has awarded a three year, £1.3 mllion grant lead by Dr. Robbie Scott (CLF) in conjunction with co-PI's Prof. Nigel Woolsey (University of York), and Prof. Tony Arber (University of Warwick). The project is being performed within a wider international collaboration involving the AWE, the University of Bordeaux (Prof. Dimitri Batani, Prof. Vladimir Tikhonchuk, Dr. Alexis Casner), General Atomics (Dr M. Wei), UCSD (Prof. F. Beg), MIT (Prof. C. Li), and the Laboratory for Laser Energetics, Rochester, USA (Prof. Riccardo Betti, Dr. Wolfgang Theobald, Dr S. Regan).

“Over the next 3 years our team - and international collaborative partners - will perform a robust evaluation of the viability of the shock ignition approach to laser fusion. Current theoretical models indicate the shock ignition approach would require a significantly smaller, and cheaper, laser system than existing laser fusion ignition facilities." Dr. Robbie Scott said about this project.

Through a combination of dedicated laser-plasma interaction experiments and innovative code developments, the goal is to create a benchmarked, world-leading simulation code capability by including the effects of LPIs within the UK's 'Odin' radiation-hydrodynamics code. This will enable academic users of the CLF to design and interpret their experiments with unprecedented accuracy, and ultimately enable a robust evaluation of the viability of the shock ignition approach to laser fusion, and the energy-scale of the laser this would require.

Robbie continued, “This represents a real opportunity for UK science to develop the first step towards a low capital-cost, carbon-free, base-load electricity generation platform."

Dr Robbie Scott, who has been at the STFC for 14 years, originally worked in ISIS as a mechanical design and analysis engineer, designing the neutron-producing core of ISIS Target Station 2. Jointly with ISIS and the CLF, he then began a PhD in laser-plasma physics within the Plasma Physics Group at Imperial College London. The goal of this was to determine whether laser fusion could be harnessed as the ultimate pulsed neutron source in ISIS. However it became clear that there were many interesting physics challenges which have to be tackled before this can become a reality, which lead him down the path towards his current work with laser fusion simulations and experiments.

Robbie commented out his transition to theoretical physics in laser fusion, “Laser fusion research inspires me as, not only is the science fascinating, but perhaps even more importantly for me, its application offers a genuine solution to global warming, which is probably the single greatest challenge facing mankind today."

Contact: Towrie, Helen (STFC,RAL,CLF)