The need for new energy sources is pressing. Global warming and climate change mean that it is essential to reduce our dependence on the burning of fossil fuels for electricity generation. Renewable sources, such as solar, wind and tidal power, are unlikely to satisfy the world's ever-increasing energy needs over the coming decades. One alternative that has been pursued for some time is controlled thermonuclear fusion - the same energy source that powers the Sun. Fusion involves heating the fusion fuel, isotopes of hydrogen (deuterium and tritium), to tens of millions of degrees centigrade so that the nuclei can overcome their Coloumb repulsion and fuse together, via the strong nuclear force, to form helium nuclei and neutrons. Clearly, no vessel can withstand direct contact with matter at such temperatures and it has to be confined in some manner.
Laser beams have the capability of delivering enormous energy densities to target when they are focused to small spots. The electric field in the laser pulse focus can approach a billion volts per centimetre or more. Any material placed within a field of this magnitude will be ionised within one or two oscillations, generating hot dense plasma (defined as a cloud of charged particles that exhibit collective behaviour) almost instantaneously. The pressure associated with the generation of this plasma is enormous - millions of atmospheres. If laser pulses (or intense X-rays generated from close-by secondary sources) are applied to the outer surface of a spherical shell containing fusion fuel frozen onto its inner surface, plasma generated at the outer surface will rapidly expand into the surrounding vacuum, while the remainder of the shell implodes inwards at high velocity, in order to conserve momentum. This rocket effect compresses the fuel to high density and confines it due to its own inertia. At the same time that plasma is generated at the surface of the fuel, however, a strong shock is driven through the shell material before it starts to accelerate. If one allows a number of strong shocks of increasing amplitude to travel through the fusion fuel and to converge at the centre of the fuel close to peak compression, then it is possible to form a hot spot region, surrounded by much colder and denser fusion fuel region. The temperature and density in hot spot region causes deuterium and tritium to fuse there to produce alpha particles and neutrons. When sufficient numbers of alpha particles stop and release their energy inside the hot spot itself, then the plasma enters the self-heating/bootstrap regime. The next stage is when the heating begins to propagate into the surrounding fuel region, known as the burning regime. The ignition regime is entered when the heating starts to raise the temperature in the dense fuel to that of the hot spot itself. Finally, when the burn wave propagates throughout the fusion fuel and disassembles, it enters the full propagating burn regime.
Remarkable progress has been made over the past few years using the National Ignition Facility in the United States to explore this concept at full-scale. In 2014, scientists there have entered the hot-spot alpha particle self-heating regime for the first time and, in 2021, are on the cusp of entry into the burning plasma regime. The strategic goal of my research is to determine how to reduce the drive energy requirement in order to minimise costs for applications to fusion energy and defence. I am working on novel concepts to extend our understanding and predictive modelling capability. In the next few years, we will gain a better understanding of the underlying physics and devise novel solutions to current barriers.
I am also working on new concepts in laser- and beam-driven particle accelerators, ultra-bright X-ray sources and physics at extreme intensities. My team is versatile and combine experiment, modelling and state-of-the-art computer simulations to explore these fascinating topics.