Laser-stimulated photodetachment of electrons from the negatively charged dielectric substrates

It is shown experimentally that the photodetachment yield of surplus electrons created by plasma-induced charging of non-conductive surfaces of dielectric materials depends on the initial surface charge density and do not correlate with the tabulated affinity values of these materials. This unexpected result obtained using laser-stimulated photodetachment for fused silica, boron nitride, and alumina, is critically important for the understanding of charging and discharging dynamics, secondary electron emission, and photoemission effects affecting plasma-wall interactions relevant to surface and capacitively coupled discharges, dusty plasmas, electrostatic probe diagnostics and applications for plasma processing of materials, plasma propulsion and gas breakdown

Determination of positive anode sheath in anodic carbon arc for synthesis of nanomaterials

Abstract In the atmospheric pressure anodic carbon arc, ablation of the anode serves as a feedstock of carbon for production of nanomaterials. It is known that the ablation of the graphite anode in this arc can have two distinctive modes with low and high ablation rates. The transition between these modes is governed by the power deposition at the arc attachment to the anode and depends on the gap between the anode and the cathode electrodes. Probe measurements combined with optical emission spectroscopy are used to analyze the voltage drop between the arc electrodes. These measurements corroborated previous predictions of a positive anode sheath (i.e. electron attracting sheath) in this arc, which appears in both low and high ablation modes. However, the positive anode sheath was determined to be ∼3–8 V, significantly larger than ∼0.5 V predicted by previous models. Thus, there are apparently other physical mechanisms not considered by these models that force the anode sheath to be electron attracting in both ablation regimes. Another key result is a relatively low electron temperature (∼0.6 eV) obtained from OES using a collisional radiative model. This result partially explains a higher arc voltage (∼20 V) required to sustain the arc current of 50–70 A than predicted by existing simulations of this discharge.</jats:p

MACHINE LEARNING-ASSISTED EVALUATION OF COMPLEX BALLISTIC ARMOUR PERFORMANCE

MACHINE LEARNING-ASSISTED EVALUATION OF COMPLEX BALLISTIC ARMOUR PERFORMANC

ADAPTIVE EXPERIMENTAL OPTIMISATION FOR SAMPLE-EFFICIENT ARMOUR DESIGN

We present a Bayesian optimisation methodology intended to support a human expert in the design of armour systems for which limited prior knowledge/data exists and within a limiting, pre-defined experimental budget. We apply the methodology to design an armour configuration consisting of multiple plates, with multiple materials, at varying orientations and spacing, for protection against 12.7 mm APM2 and 20 mm FSP threats. The full-factorial design matrix for the defined solution space exceeds 17,500 possible solutions. With an objective to minimise system weight, we identify a solution within 102 ballistic tests (44 design iterations) that provides a weight reduction of 11.4% over expert-designed reference configurations and a mass efficiency of 1.5 relative to a monolithic RHA Class 1. The value of the demonstrated methodology is expected to increase with increasing armour (or threat) complexity