Student Seminars - October 2020

Friday 16 October 2020, 1.00PM to 2 PM

Speaker(s): Sid Leigh, Claudia Cobo, Liam Douglas Mann and Arun Nutter.

Neoclassical Tearing Modes: Performance-limiting plasma instabilities

Ultra-short high-intensity laser pulses interacting with underdense plasma can

accelerate electron bunches to relativistic energies via the process of laser wakefield

acceleration. While laser wakefield accelerators can sustain accelerating gradients over

a thousand times stronger than conventional accelerators, thereby having the potential

to function as compact photon sources, they are inherently unstable and susceptible to

density fluctuations. This is because any inhomogeneities may seed laser-plasma

instabilities. Measurable changes to the spectrum of the driving laser pulse occur as a

result of the laser-plasma interaction via processes such as stimulated Raman

scattering and photon acceleration which depend on the plasma density. Thus,

characterising the laser spectrum may serve as an alternative density diagnostic. This

work attempts to understand the changes to the laser spectrum through comparison of

PIC simulations and experimental results

In recent years, ramp compression using high power lasers has been demonstrated to be an effective

method of driving materials to extreme pressures as an alternative to static techniques. With the

advancement of laser pulse shaping technology, complex loading profiles can be used to reach

specific states relevant to planetary interiors. Therefore it is necessary to model the material effects of

different loading profiles to plan these experiments. However, it is prohibitively computationally

expensive to model on the spatial and temporal scale of these experiments using molecular dynamics

(MD). With the use of small simulation cells, it should be possible to replicate some important

elements of the physics of a multi-million atom non-equilibrium MD simulation of ramp compression

at a fraction of the computational cost. Preliminary results of this method will be presented

Progress in inertial fusion has been significantly hindered by the presence of

parametric instabilities, which scatter laser light and preheat fuel, reducing

compression and symmetry. Their complex nonlinear behaviour has made them

particularly difficult to model and has meant they have been omitted from many

radiation-hydrodynamics codes. I will present the preliminary results of my

parametric instability model that simulates their growth and deleterious effects in

inertial fusion relevant plasmas.

Location: Zoom