Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Betatron radiation from direct-laser-accelerated electrons is characterized analytically and numerically. It is shown here that the electron dynamics is strongly dependent on a self-similar parameter S ( ≡ n e n c a 0 ). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field ( a 0 )fora fixed value of S . As a result, the total number of radiated photons scales as a 2 0 / √ S and the energy conversion efficiency of photons from the accelerated electrons scales as a 3 0 /S . The particle-in-cell simulations agree well with the analytical scalings. It is suggested that a tunable high-energy and high-flux radiation source can be achieved by exploiting this regime.

Abstract:

The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations.

Abstract:

A new physical model of the hosing instability that includes relativistic laser pulses and moderate densities is presented and derives the density dependence of the hosing equation. This is tested against two-dimensional particle-in-cell simulations. These simulations further examine the feasibility of using multiple pulses to mitigate the hosing instability in a Nd:glass-type parameter space. An examination of the effects of planar versus cylindrical exponential density gradients on the hosing instability is also presented. The results show that strongly relativistic pulses and more planar geometries are capable of mitigating the hosing instability which is in line with the predictions of the physical model.

Abstract:

This study explores the institution of a public holiday on September 23rd, Augustus' birthday, the related ceremonies and especially its commemoration along the centuries through epigraphical records. These documents mainly consist in Calendars, the so-called Fasti, but we also analyze inscriptions dedicated on this special day. We have noticed that this commemoration quickly became an instrument of propaganda and then one of the most important anniversaries of Rome's history, celebrated for a long time.