Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

After the 1968 excavation, the investigations of the Roman theater of Terracina, although carried out episodically over a long period of time, were part of a unified program, at least as far as the objective was concerned: the redevelopment of the Piazza del Municipio, the ancient forum of the colony of Anxur. After seventeen excavation and restoration campaigns carried out by various teams — the most recent being the one writing these lines — extensive research work has recently made the monument fully accessible. This has made it possible to use the site as a venue for events, while at the same time underlining the urgency of its scientific publication. The excavation campaigns carried out in the area of the theater-portico over the past three decades have uncovered numerous findings: fragments of architectural decoration, a fair number of inscriptions, and parts of the sculptural ornamentation. The contextual reassessment of some of this material, along with the analysis of the wall stratigraphy, has made it possible to propose not only a reconstruction of the structure but also a detailed interpretation of the theater’s construction history. For its initial phase, both the archaeological and epigraphic records suggest a dating to the Caesarian age, followed by a phase of monumentalization, or more likely completion, during the Augustan age.

Abstract:

Recent archaeological research in the Valle Sabbia in the territory of Brescia (BS-Northern Italy) has led to the discovery of a new place of worship from the Roman era, possibly built on an ancient indigenous sanctuary. The Valle Sabbia is one of the alpine valleys of Lombardy, north of Brescia (the Colonia Augusta Civica Brixia). The territory, crossed by the river Chiese, stretches between Lake Idro and Lake Garda, in a favourable geographical position that puts it in direct contact with the plain on one side and the Alps on the other. Since 2000, campaigns of archaeological excavations have led to the discovery of different contexts that can be interpreted as sacred, with frequenting from prehistoric times to Roman times and which have as recurrent characteristic a close relationship with the surrounding landscape, with a clear preference for mountainous and wooded contexts. The most important novelties, concerning the Roman period, emerge in Villanuova sul Clisi, where on a panoramic hill overlooking the entire Valle Sabbia and Garda Lake, various wall structures have emerged that define a complex built on several levels, with a rectangular main room of about 11×4,20 m, made with large structures confining the summit plateau, and other lateral ones. The recovered materials indicate a visitation from the 1st to the 4th century A.D.: in addition to coins, fibulae and ceramics, some miniature metal ex-voto with dedications to Iuppiter Aeternus, various graffiti on plaster and a stone altar also inscribed have been uncovered.

Abstract:

Quantum speed limit (QSL) defines the theoretical upper bound on how fast a quantum system can evolve between states. It imposes a fundamental constraint on the rate of quantum information processing. For a relativistic spin-up electron in a uniform magnetic field, QSL increased with the magnetic field strength till around 1015$$10^{15}$$ Gauss, before saturating at a saturated QSL (SQSL) of 0.2407c$$0.2407c$$, where ‘c’ is the speed of light. We show that by using variable magnetic fields, it is possible to surpass this limit, achieving SQSL up to 0.4$$0.4$$–0.6c. To attain this quantum phenomenon, we solve the evolution equation of relativistic electron in spatially varying magnetic fields and find that the energies of various electron states become non-degenerate as opposed to the constant magnetic field case. This redistribution of energy is the key ingredient to accomplish higher QSL and, thus, a high information processing speed. We further explore how QSL can serve as a bridge between relativistic and non-relativistic quantum dynamics, providing insights via the Bremermann-Bekenstein bound, a quantity which constrains the maximal rate of information production. We also propose a practical experimental setup to realize these advancements. These results hold immense potential for propelling fields of quantum computation, thermodynamics and metrology.

Abstract:

The pursuit of inertial confinement fusion ignition target designs requires precise experimental validation of the conditions within imploding capsules, in particular the density and temperature of the compressed shell. Previous work has identified x-ray Thomson scattering (XRTS) as a viable diagnostic tool for inferring the in-flight compressed deuterium-tritium shell conditions during capsule implosions (Poole et al 2022 Phys. Plasmas 29 072703). However, this study focused on one-dimensional simulations, which do not account for the growth of hydrodynamic instabilities. In this work, two-dimensional DRACO simulations incorporating intermediate-mode perturbations up to Legendre mode ℓ=50 were used to generate synthetic XRTS spectra with the SPECT3D code. The analysis employed Markov-Chain Monte Carlo techniques to infer plasma conditions from these spectra. The results demonstrate that the XRTS diagnostic platform can effectively discern the in-flight compressed shell conditions for targets with varying adiabats, even in the presence of intermediate-mode perturbations. This work underscores the potential of XRTS for realistic inertial confinement fusion experiments, providing a robust method for probing the complex dynamics of fusion implosions.

Abstract:

We posit the existence of a nonthermal phase transition in iron, driven by a loss of ferromagnetic ordering on ultrafast timescales with increasing electron temperature. The transition corresponds to a solid-solid BCC to FCC phase transformation and takes place at an electron temperature of 0.62 eV while the ion lattice remains near room temperature. The BCC structure initially undergoes phonon softening during the magnetic transformation, followed by a solid-solid phase transition to the FCC structure, and a subsequent hardening of phonon modes. We present a detailed physical picture of the process, supported by finite-temperature density functional theory simulations of the phonon dispersion curves, electronic density of states, and thermodynamic free energy.