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Wetted-foam layers are of significant interest for inertial confinement fusion capsules, due to the control they provide over the convergence ratio of the implosion, and the opportunity this affords to minimize hydrodynamic instability growth. However, the equation of state (EOS) for fusion relevant foams is not well characterized, and many simulations rely on modelling such foams as a homogeneous medium with the foam average density. To address this question, an experiment was performed using the the VULCAN Nd:glass laser at the Central Laser Facility. The aim was to measure the principal Hugoniot of TMPTA plastic foams at 260 mg/cm3 , corresponding to the density of liquid DT-wetted-foam layers, and their ‘hydrodynamic equivalent’ capsules. A VISAR was used to obtain the shock velocity of both the foam and an α-quartz reference layer, while streaked optical pyrometry provided the temperature of the shocked material. The measurements confirm that, for the pressure range accessed, this material can indeed be well described using the equation of state of the homogeneous medium at the foam density.

Following indirect-drive experiments which demonstrated promising performance for low convergence ratios (below 17), previous direct-drive simulations identified a fusion-relevant regime which is expected to be robust to hydrodynamic instability growth. This paper expands these results with simulated implosions at lower energies of 100 kJ and 270 kJ, and ‘hydrodynamic equivalent’ capsules which demonstrate comparable convergence ratio, implosion velocity and in-flight aspect ratio without the need for cryogenic cooling, which would allow the assumptions of 1D-like performance to be tested on current facilities. A range of techniques to improve performance within this regime are then investigated, including the use of two-colour and deep ultraviolet laser pulses. Finally, further simulations demonstrate that the deposition of electron energy into the hotspot of a low convergence ratio implosion through auxiliary heating also leads to significant increases in yield. Results include break-even for 1.1 MJ of total energy input (including an estimated 370 kJ of short-pulse laser energy to produce electron beams for the auxiliary heating), but are found to be highly dependent upon the efficiency with which electron beams can be created and transported to the hotspot to drive the heating mechanism.

The orbital angular momentum (OAM) of light is one of the most intriguing properties of electromagnetic radiation. Although OAM is more commonly associated with the mechanical movement of massive particles, researchers have shown that, under certain conditions, laser beams can carry it. This is not merely a theoretical proposition, this idea was almost immediately experimentally proven by showing that OAM can be transferred between light and matter. This has, in turn, spurred an ever-increasing interest in leveraging the interesting proprieties of the OAM of light for various technological applications. This work focuses on the effect that OAM has on high-intensity laser interactions. High-intensity lasers have been a boon to scientific� investigations in their own right. They have allowed us to experimentally research astrophysical phenomena inside of laboratories, opened the possibility to tabletop particle accelerators and gotten us closer to useful fusion energy sources. More recently, we have been able to reach extreme intensities that allow us to probe the most fundamental interactions in the universe. Predictions that had been theorized decades ago by the pioneers of the quantum theory of matter are now close to being experimentally verifiable. In the coming chapters, I look at the fundamental nature of the OAM of light and the many discussions it has spurred. I then show that it modifies an interaction known as vacuum photon-photon scattering where beams of light can interact with each other in the absence of any mediating matter violating the constraints established by the classical theory of electromagnetism. OAM provides an extra signal that makes this light-light interaction more identifiable in an experiment. On a more practical note, I continue to look specifically at high-intensity lasers and how they can be manipulated to produce high-intensity OAM-carrying beams and how said beams can be characterized.

The study of parametric instabilities has played a crucial role in understanding energy transfer to plasma and, with that, the development of key applications such as inertial confinement fusion. When the densities are between $0.108n_c\lesssim n_e\lesssim 0.138n_c$ and the electron temperature is $T_e=$2.5 keV, anomalous hot electrons with kinetic energies above 100 keV are generated. Here, a new electron acceleration mechanism - the anti-Stokes Langmuir decay instability cascade of forward stimulated Raman scattering - is investigated. This mechanism not only explains anomalous energetic electron generation in indirectly driven inertial confinement fusion experiments (and, with that, future mitigation strategies for experiments on the National Ignition Facility), it also provides a new way of accelerating electrons to higher energy for applications such as novel X-ray sources., Comment: 19 pages, 21 figures

Raman back-scatter from an under-dense plasma can be used to compress laser pulses, as shown by several previous experiments in the optical regime. A short seed pulse counter-propagates with a longer pump pulse and energy is transferred to the shorter pulse via stimulated Raman scattering. The robustness of the scheme to non-ideal plasma density conditions is demonstrated through particle-in-cell simulations. The scale invariance of the scheme ensures that compression of XUV pulses from a free electron laser is also possible, as demonstrated by further simulations. The output is as short as 300 as, with energy typical of fourth generation sources.