Harvey Fraser

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Project: Modelling charged-particle transport and heating in fusion plasmas

Important to the study and development of Inertial Confinement Fusion (ICF) is the research of charged-particle transport and heating in fusion plasmas. Now that ignition has been demonstrated repeatedly at the National Ignition Facility (NIF), understanding the properties of dense plasmas where net gain is achieved is vital to further increasing this ratio in order to make fusion a viable source of energy. During the process of deuterium-tritium (D-T) fusion, the hydrogen isotopes react to form a helium-4 nucleus (or alpha particle) as well as a neutron and releasing energy to be harnessed for electricty generation. A significant change in composition of a fusion plasma caused by this reaction for high burn-fractions will affect the equations of state of dense plasmas. Energy transferred to the helium nuclei produced must be re-deposited back into the plasma by the stopping power of the charged particles through a process known as alpha-heating in order to sustain the fusion reaction. This project will aim to improve modelling capabilities for dense plasmas in order to better predict the behaviour of fusion plasmas in high-gain and high-burn environments.

During my 1st year, I have researched the properties of ion beams for beam-driven ICF. A dense plasma is modelled using a simple framework of an isotropic and homogeneous electron gas with the beam particles represented by a delta-function. The Boltzmann equation was used to derive a general expression for a beam property and then specified to calculate the momentum and energy. By studying the rate of change of their components, an estimate for the spread of the beam particles was determined. In the low-velocity limit, the beam properties are accurately described by using a statically-screened potential whereas at higher velocities, the Bethe result reproduces the expected behaviour. Without having to calculate the full T-matrix solution, a velocity-dependent screening length, which imitates the dynamic screening effects at high velocities whilst retaining the low velocity behaviour, can interpolate between these results. A more realistic beam model was represented by using an ensemble of delta-functions to better reflect the spread of the beam over time. I presented a poster on this research at the Direct Drive and Fast Ignition Workshop 2025.

Acknowledgements: Research funded via iCASE by EPSRC and in co-operation with First Light Fusion (FLF).