Alex Seaton: 'PIC simulations of Stimulated Raman Scattering in ICF'

Abstract:

Stimulated Raman Scattering (SRS) is one of several laser-plasma instabilities that affect Inertial Confinement Fusion (ICF). Of these, it is particularly detrimental to ICF performance as it is able to both reflect a significant fraction of the laser’s energy and generate hot electrons that preheat the fuel, reducing the level of compression that can be achieved. Recently it has been shown that, for an indirect-drive laser configuration, regions of the laser beam with high intensity known as ‘speckles’ are able to drive coherent bursts of SRS on a picosecond timescale with instantaneous reflectivity greater than 100%. Detailed 2D and 3D particle-in-cell (PIC) simulations have demonstrated that this occurs due to self-organised interactions between speckles. In this talk I will discuss these results and progress made towards investigating whether the effect occurs in a direct-drive configuration.

Liz Tindale: 'Solar cycle impact on variability in fast and slow solar wind'

 

Abstract: Both fast and slow solar wind exhibit variability across a wide range of spatiotemporal scales, with evolving turbulence producing fluctuations on sub-hour timescales and the irregular solar cycle modulating the system over many years. Minute-resolution in-situ satellite observations spanning the last two solar cycles now support the use of statistical techniques to probe variation over all these scales. In particular, we use the data quantile-quantile (DQQ) plot as a model-independent method for tracing changes in the statistical distribution of solar wind plasma parameters over solar cycles 23 and 24. Without any assumptions regarding the functional form of the distribution, we can use this method to determine whether the underlying distribution is multi-component, within which range of values the data is best described by each component, and whether the moments or functional form of each component change over time. In fast and slow solar wind, the distribution is multi-component: the majority of data is drawn from a lognormal distribution, as expected in a turbulent medium; extremal values depart from this regime, exhibiting unique evolutions in fast and slow wind within each solar cycle. Lastly we apply the DQQ method to commonly used solar wind-magnetosphere coupling parameters, and demonstrate their differing sensitivities to solar cycle variation.