Extension and optimisation of the EPOCH code

Plasmas are fully ionized gasses that arise naturally at high temperatures. They are the most common state of matter in the Universe but the high temperatures usually required make them rare on Earth. For engineering, terrestrial applications plasmas are important as the basic fuel for any potential fusion reactor. These rely on heating a gas of hydrogen isotopes to 100's of millions of degrees Centigrade. Such attempts to achieve fusion using lasers at the National Ignition Facility (NIF) in California have encountered problems. One of the potential causes of this lack of performance on NIF is the deleterious influence of electrons accelerated to higher than the ambient electron temperature, so called hot-electrons. These are caused by complex laser-plasma interactions. Any modeling of such processes must follow the full kinetics of the plasma - that is follow the motion of millions of individual particles evolving in the plasma under the influence of the electro-magnetic force. The most common sort of computer code that does this is called a particle-in-cell (PIC) code.

This project aims to complete a software refresh and update of the existing UK community PIC code EPOCH. This code has been established as a leading PIC code over the last few years since the first major releases of the code were publicized. The growing UK and international community of users, currently over 400, has defined a set of new physics packages and optimisations to EPOCH that will establish it as a leading PIC code research tool for many years to come. It is proposed to recruit a young researcher; train them in research software engineering and PIC codes and over two years complete the full refresh.

The new science that the upgraded EPOCH will allow us to undertake includes at scale simulations of the laser-plasma problems in NIF, hot-electron acceleration in advance fusion concepts such as shock ignition and fast ignition. Beyond fusion EPOCH can be used to simulate experiments designed to build compact electron and proton (hadron) accelerators, the latter with an aim of delivering a device for medical hadron therapy. At the more exotic end of plasma research are ideas based around the Extreme Light Infrastructure ELI - a multi-national collaboration based around several EU cites which use the most powerful lasers ever built. At these intensities the electron relativisitic mass approaches that of the proton and QED effects allow the generation of gamma-rays for nuclear physics research and dense electron-positron pair plasmas. All of these experiments require PIC codes to design targets and interpret results. EPOCH will deliver that capability to the UK. Currently EPOCH is being used for many of these applications but the refresh proposed here takes PIC codes into a new realm of fidelity and opens new science not accessible with the existing code.

There is a growing need for well-trained research software engineers (RSE) in UK academia, industry and the financial sector. This project will train a new researcher in RSE skills working in a team of programmers on a major, well-established project. They will also gain experience working with international partners and travelling to, and presenting at, major computing conferences. This immediate uplift in the UK RSE skill base, while only one person, has a clear impact on UK economy.

A grand long-term challenge of much of the research that will use the EPOCH code is that it may help international efforts to achieve power from fusion. If successful these reactors have the potential to change the world's energy market, freeing us from the constraints of fossil fuel supply and directly addressing the problems of electricity supply without carbon dioxide emission. For the UK this could also guarantee a security of energy supply independent of regions that currently control the fossil fuel market.

Others using EPOCH in the UK are working on using laser-plasmas to produce compact electron and hadron accelerators. The hadron accelerators main application drive is that it offers a potential route to a compact ion source for medical hadron therapy.