General features of experiments on the dynamics of laser-driven electron–positron beams

The experimental study of the dynamics of neutral electron–positron beams is an emerging area of research, enabled by the recent results on the generation of this exotic state of matter in the laboratory. Electron–positron beams and plasmas are believed to play a major role in the dynamics of extreme astrophysical objects such as supermassive black holes and pulsars. For instance, they are believed to be the main constituents of a large number of astrophysical jets, and they have been proposed to significantly contribute to the emission of gamma-ray bursts and their afterglow. However, despite extensive numerical modelling and indirect astrophysical observations, a detailed experimental characterisation of the dynamics of these objects is still at its infancy. Here, we will report on some of the general features of experiments studying the dynamics of electron–positron beams in a fully laser-driven setup

X-ray scattering from warm dense iron

We have carried out X-ray scattering experiments on iron foil samples that have been compressed and heated using laser-driven shocks created with the VULCAN laser system at the Rutherford-Appleton Laboratory. This is the highest Z element studied in such experiments so far and the first time scattering from warm dense iron has been reported. Because of the importance of iron in telluric planets, the work is relevant to studies of warm dense matter in planetary interiors. We report scattering results as well as shock breakout results that, in conjunction with hydrodynamic simulations, suggest the target has been compressed to a molten state at several 100 GPa pressure. Initial comparison with modelling suggests more work is needed to understand the structure factor of warm dense iron

Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (>= 1 T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of epsilon(B) approximate to 10(-3) is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets

Neptune to the Common-wealth of England (1652): the republican Britannia and the continuity of interests

In the seventeenth century, John Kerrigan reminds us, “models of empire did not always turn on monarchy”. In this essay, I trace a vision of “Neptune’s empire” shared by royalists and republicans, binding English national interest to British overseas expansion. I take as my text a poem entitled “Neptune to the Common-wealth of England”, prefixed to Marchamont Nedham’s 1652 English translation of Mare Clausum (1635), John Selden’s response to Mare Liberum (1609) by Hugo Grotius. This minor work is read alongside some equally obscure and more familiar texts in order to point up the ways in which it speaks to persistent cultural and political interests. I trace the afterlife of this verse, its critical reception and its unique status as a fragment that exemplifies the crossover between colonial republic and imperial monarchy at a crucial moment in British history, a moment that, with Brexit, remains resonant

Versatile tape-drive target for high-repetition rate laser-driven proton acceleration

We present the development and characterization of a high-stability, multi-material, multi-thickness tape-drive target for laser-driven acceleration at repetition rates of up to 100 Hz. The tape surface position was measured to be stable on the sub-micrometre scale, compatible with the high-numerical aperture focusing geometries required to achieve relativistic intensity interactions with the pulse energy available in current multi-Hz and near-future higher repetition-rate lasers ( >kHz). Long-term drift was characterized at 100 Hz demonstrating suitability for operation over extended periods. The target was continuously operated at up to 5 Hz in a recent experiment for 70,000 shots without intervention by the experimental team, with the exception of tape replacement, producing the largest data-set of relativistically intense laser–solid foil measurements to date. This tape drive provides robust targetry for the generation and study of high-repetition-rate ion beams using next-generation high-power laser systems, also enabling wider applications of laser-driven proton sources

“All things serious and sacred”: Clarendon as essayist

This is a chapter in Clarendon Reconsidered which reassesses a figure of major importance in seventeenth-century British politics, constitutional history and literature. Despite his influence in these and other fields, Edward Hyde, first Earl of Clarendon (1609–1674) remains comparatively neglected. However, the recent surge of interest in royalists and royalism, and the new theoretical strategies it has employed, make this a propitious moment to re-examine his influencecontribution. Chancellor of the Exchequer, Lord Chancellor and author of the History of the Rebellion (1702–1704), then and for long afterwards the most sophisticated history written in English, his long career in the service of the Caroline court spanned the English Revolution and Restoration. The original essays in this interdisciplinary collection shine a torch on key aspects of Clarendon’s life and works: his role as a political propagandist, his family and friendship networks, his religious and philosophical inclinations, his history- and essay-writing, his influence on other forms of writing, and the personal, political and literary repercussions of his two long exiles. Pushing the boundaries of the new royalist scholarship, this fresh account of Clarendon reveals a multifaceted man who challenges as often as he justifies traditional characterisations of detached historian and secular statesman. </p

Harrington and the oligarchs: Milton, Vane, and Stubbe

This is a chapter from Perspectives on English Revolutionary Republicanism which takes stock of developments in the scholarship of seventeenth-century English republicanism by looking at the movements and schools of thought that have shaped the field over the decades: the linguistic turn, the cultural turn and the religious turn. While scholars of seventeenth-century republicanism share their enthusiasm for their field, they have approached their subject in diverse ways. The contributors to the present volume have taken the opportunity to bring these approaches together in a number of case studies covering republican language, republican literary and political culture, and republican religion, to paint a lively picture of the state of the art in republican scholarship. The volume begins with three chapters influenced by the theory and methodology of the linguistic turn, before moving on to address cultural history approaches to English republicanism, including both literary culture and (practical) political culture. The final section of the volume looks at how religion intersected with ideas of republican thought. Taken together the essays demonstrate the vitality and diversity of what was once regarded as a narrow topic of political research. </p