Laser-driven discharges and electromagnetic fields

When high intensity lasers interact with solid targets, hot electrons are produced that can exit the material and leave behind a positive electric charge. As this accumulated charge is neutralised by a cold return current, radiation is emitted with characteristics dependent on laser and target properties. This thesis examines how electromagnetic radiation is emitted in experiments with long-pulse and short-pulse lasers. Radiofrequency electromagnetic pulses emitted during ps-duration laser interactions can disrupt scientific measurements and damage electronic equipment close to the target. A study of electromagnetic pulses produced by the Vulcan laser is presented. Strong fields exceeding 100kV/m and 0.1mT were measured 1.5m from the target using conducting probes. Scaling of the EMP field with laser and target parameters shows qualitative agreement with target charging models. A novel EMP mitigation scheme is presented using a dielectric spiral target holder. Experimental results are used to benchmark a frequency-domain dipole antenna model of EMP emission that connects charging physics to EMP fields measured at an arbitrary distance from the target. In a separate experiment, coil targets were driven with three ns laser beams from the Vulcan laser, generating multi-tesla quasi-static magnetic fields. Dual-axis proton deflectometry was used to measure electric and magnetic fields around the coils. Results suggest that wire electric fields of order 0.1GV/m develop on a 100ps timescale. Maximum currents of 10kA were observed towards the end of the laser drive for 1mm- and 2mm-diameter loop targets, corresponding to an axial magnetic field of B_0=12T in the 1mm loops. Deflectometry results agree well with a plasma diode model, whereas B-dot probe measurements of the magnetic field were approximately 10x larger. Analytic and computational modelling of charged particle motion in electric and magnetic fields is presented. Prospects for an all-optical platform for magnetized high energy density physics experiments are discussed

Police Crime & Less-than-Lethal Coercive Force: A Description of the Criminal Misuse of TASERs

This study explores and describes the nature and character of cases that involve the criminal misuse of TASERs by police officers through a content analysis of newspaper articles. The news-based content analysis identified 24 police officers who were arrested for crimes that involved inappropriate use of TASERs over a 65 month period from January 2005 through May 2010. Data on these cases are presented in terms of: a) the arrested officer, b) victim characteristics, and c) the situational context of these events. The news-based content analyses were used to identify and describe some factors that were common among these events, especially in regard to the actions and motivations of the arrested officers and how the situational context appeared to influence the criminal misconduct of officers. The findings indicate that the cases examined did not involve much, if any, situational risk to the officer. The criminal misuse of TASERs seems more likely to involve suspects who are already handcuffed, or even citizens who are clearly not criminals at all

Computational Thinking Integration into Middle Grades Science Classrooms: Strategies for Meeting the Challenges

This paper reports findings from the efforts of a university-based research team as they worked with middle school educators within formal school structures to infuse computer science principles and computational thinking practices. Despite the need to integrate these skills within regular classroom practices to allow all students the opportunity to learn these essential 21st Century skills, prior practice has been to offer these learning experiences outside of mainstream curricula where only a subset of students have access. We have sought to leverage elements of the research-practice partnership framework to achieve our project objectives of integrating computer science and computational thinking within middle science classrooms. Utilizing a qualitative approach to inquiry, we present narratives from three case schools, report on themes across work sites, and share recommendations to guide other practitioners and researchers who are looking to engage in technology-related initiatives to impact the lives of middle grades students

Research Brief One-Sheet No.5: Police Criminal Misuse of Conductive Energy Devices

The purpose of the research is to explore and describe the nature and character of arrest cases that involve the criminal misuse of TASERS by police officers through a content analysis of news articles. The research specifically focuses on factors that were common among the arrest events involving CEDs, especially with regard to the actions and motivations of the arrested officers and how the situational context appeared to influence the criminal misconduct of police officers

Extending the family of hybrid layered fluoride perovskites

We acknowledge support from the University of St Andrews, the China Scholarship Council (201606280032, PhD studentship to TL), and the China Postdoctoral Science Foundation (2022M710619).The family of hybrid layered fluoride perovskites has been extended, based on the only previously reported example (enH2)MnF4 (en = 1,2-diaminoethane), to include further divalent transition metals and longer chain diamines. The compounds (enH2)BF4, (B = Co, Ni) and (bnH2)BF4, (bn = 1,4-diaminobutane, B = Mn, Co) adopt the same space group (P21/c) as (enH2)MnF4, whereas (pnH2)BF4, (pn = 1,3-diaminopropane, B = Mn, Co) adopt the space group Pnma. Key differences in these structure types are shown to depend on the parity of the number of carbon atoms in the linear amine, which may be considered a structure-directing agent. Magnetic measurements on selected samples indicate differences in magnetic order that can be understood in terms of both the transition metal and the molecular species. All samples exhibit antiferromagnetic correlations but can in some cases develop a canted spin ferromagnetic component due to anisotropic exchange interactions. An additional compound, (bn)Ni2F4, has also been isolated, which exhibits a unique layered structure with bn acting as a ligand rather than in cationic formPeer reviewe

Perovzalates : a family of perovskite-related oxalates

Authors would like to thank the University of St Andrews (studentship to AJB) and the EPSRC (doctoral studentship to RC: DTG012 EP/K503162-1) for funding.A family of hybrid Perovskite-oxalates (“Perovzalates”) of general composition AILi3MII(C2O4)3 (A = K+, Rb+, Cs+; M = Fe2+, Co2+, Ni2+) are presented. All eight new compounds are isostructural with the previously reported examples NH4Li3Fe(C2O4)3 and KLi3Fe(C2O4)3, crystallising in the rhombohedral space group Rc, with a ∼11.3–11.6 Å, c ∼14.8–15.2 Å. In contrast to other families of “hybrid perovskites” such as the formates, these compounds can be regarded as closer structural relatives to inorganic (oxide) perovskites, in the sense that they contain direct linkages of the octahedral sites via bridging oxygen atoms (of the oxalate groups). It is of note, therefore, that monoatomic cations as large as Cs+ can be incorporated into the perovskite-like A sites of this structure type, which is not feasible in traditional ABO3 perovskites; indeed CsLi3Ni(C2O4)3 appears to exhibit the ‘mostly tightly bound’ 12-coordinate Cs+ ion in an oxide environment, according to a bond valence analysis.PostprintPeer reviewe

Electromagnetic pulse emission from target holders during short-pulse laser interactions

For the first time, a global model of electromagnetic pulse (EMP) emission connects charge separation in the laser target to quantitative measurements of the electromagnetic field. We present a frequency-domain dipole antenna model which predicts the quantity of charge accumulated in a laser target as well as the EMP amplitude and frequency. The model is validated against measurements from several high-intensity laser facilities, providing insight into target physics and informing the design of next-generation ultra-intense laser facilities. EMP amplitude is proportional to the total charge accumulated on the target, but we demonstrate that it is not directly affected by target charging time (and therefore the laser pulse duration), provided the charging time is shorter than the antenna characteristic time. We propose two independent methods for estimating the charging time based on the laser pulse duration. We also investigate the impact of target holder geometry on EMPs using cylindrical, conical, and helical holders

Constraining the ISM Properties of the Cloverleaf Quasar Host Galaxy with Herschel Spectroscopy

We present Herschel observations of the far-infrared (FIR) fine-structure (FS) lines [C II]158 μm, [O I]63 μm, [O III]52 μm, and [Si II]35 μm in the z = 2.56 Cloverleaf quasar, and combine them with published data in an analysis of the dense interstellar medium (ISM) in this system. Observed [C II]158 μm, [O I]63 μm, and FIR continuum flux ratios are reproduced with photodissociation region (PDR) models characterized by moderate far-ultraviolet (FUV) radiation fields with G_0 = 0.3–1 × 10^3 and atomic gas densities n_H = 3–5 × 10^3 cm^(−3), depending on contributions to [C II]158 μm from ionized gas. We assess the contribution to the [C II]158 μm flux from an active galactic nucleus (AGN) narrow line region (NLR) using ground-based measurements of the [N II]122 μm transition, finding that the NLR can contribute at most 20%–30% of the observed [C II]158 μm flux. The PDR density and far-UV radiation fields inferred from the atomic lines are not consistent with the CO emission, indicating that the molecular gas excitation is not solely provided via UV heating from local star formation (SF), but requires an additional heating source. X-ray heating from the AGN is explored, and we find that X-ray-dominated region (XDR) models, in combination with PDR models, can match the CO cooling without overproducing the observed FS line emission. While this XDR/PDR solution is favored given the evidence for both X-rays and SF in the Cloverleaf, we also investigate alternatives for the warm molecular gas, finding that either mechanical heating via low-velocity shocks or an enhanced cosmic-ray ionization rate may also contribute. Finally, we include upper limits on two other measurements attempted in the Herschel program: [C II]158 μm in FSC 10214 and [O I]63 μm in APM 08279+5255

A hybrid fluoride layered perovskite, (enH2)MnF4

We acknowledge the University of St Andrews and the China Scholarship Council (studentship to TL) and the EPSRC (DTG: EP/K503162/1) for a studentship (to RC). The are no conflicts of interest to declare.The title compound is the first example of a layered fluoroperovskite containing an interlayer organic cation. Preliminary magnetic characterisation is reported, and structural relationships to related layered perovskites are discussed.PostprintPostprintPeer reviewe