Electron Induced Charging and Arcing of Multilayered Dielectric Materials

Measurements of the charge distribution in electron-bombarded, thin-film, multilayered dielectric samples showed that charging of multilayered materials evolves with time and is highly dependent on incident energy; this is driven by electron penetration depth, electron emission and material conductivity. Based on the net surface potential’s dependence on beam current, electron range, electron emission and conductivity, measurements of the surface potential, displacement current and beam energy allow the charge distribution to be inferred. To take these measurements, a thin-film disordered SiO2 structure with a conductive middle layer was charged using 200 eV and 5 keV electron beams with regular 15 s pulses at 1 nA/cm2 to 500 nA/cm2. Results show that there are two basic charging scenarios which are consistent with simple charging models; these are analyzed using independent determinations of the material’s electron range, yields, and conductivity. Large negative net surface potentials led to electrostatic breakdown and large visible arcs, which have been observed to lead to detrimental spacecraft charging effects

Low Temperature Cathodoluminescence in Disordered SiO2

Disordered SiO2 is commonly used for optical instrumentation and coatings. In space telescope applications, these materials can be exposed to low temperature (particularly for IR telescopes) and simultaneous electron fluxes from the space plasma environment. During recent charging tests of this dielectric material, a discernable glow was detected emanating from the surface of the SiO2, indicating that the incident electron beam induced a luminescent effect, termed cathodoluminescence. As the sample cooled from 300 K to 120 K, a change in the intensity and energy spectrum of the glow was observed between 250 nm and 1700 nm, demonstrating that the SiO2 cathodoluminescence is temperature dependent. Cathodoluminescence occurs when a high energy electron excites a valence band electron into the conduction band, then a transition takes place between the extended conduction states and the localized states below the mobility edge resulting from structural defects. This final electron transition is the origin of the emitted photon, hence the luminescence. As sample temperature and the thermal energy of the electrons vary, the trap state population, distribution of accessible trap states, and transitions between states also vary. A dynamic model of electrons in these localized trap states is proposed to explain the temperature dependent experimental cathodoluminescence spectra collected. Using our experimental results in conjunction with literature references, the specific structural defects in SiO2 responsible for distinct features in the cathodoluminescence spectra can be identified. From our experimental results, a simple qualitative model of disordered band theory has been developed to describe the states and electron dynamics in our SiO2 samples. Ultimately, such knowledge is important in the optimal design of space telescope optics

A new genus and species of armored scale insect (Hemiptera: Diaspididae) from Australia found in the historic Koebele Collection of the California Academy of Sciences

A new genus and species of armored scale insect (Hemiptera: Diaspididae), Protomorgania koebelei Dooley and Evans, is described and illustrated from specimens collected by Albert Koebele on Pittosporum sp. (Pittosporaceae) in Australia around the year 1900. A key to the genera of armored scale insects similar to Protomorgania and known to occur in Australia is provided

In Situ Surface Voltage Measurements of Dielectrics Under Electron Beam Irradiation

New instrumentation has been developed for non- contact, in vacuo measurements of the electron beam-induced surface voltage as a function of time and position for non- conductive spacecraft materials in a simulated space environment. The novel compact system uses two movable capacitive sensor electrodes to measure surface charge distributions on samples, using a non-contact method that has little effect on charge dissipation from sample. Design details, calibration and characterization measurements of the system are presented, with \u3c1 V to \u3e30 kV surface voltage range, \u3c0.5 V voltage resolution, and \u3c1.5 mm spatial resolution. Used in conjunction with the capabilities of an existing ultrahigh vacuum electron emission test chamber, the new instrumentation facilitates measurements of charge accumulation, bulk resistivity, effects of charge depletion and accumulation on yield measurements, electron induced electrostatic breakdown potentials, radiation induced conductivity effects, and the radial dispersion of surface voltage. Three types of measurements of surface voltage for polyimide (Kapton HNTM) serve to illustrate the research capabilities of the new system: (i) accumulation using a pulsed electron beam, while periodically measuring the surface voltage; (ii) post charging, as deposited charge dissipated to a grounded substrate; and (iii). the evolution of spatial profile resulting from an incident Gaussian beam. Theoretical models for sample charging and discharge are outlined to predict the time, temperature, and electric field dependence of the sample’s net surface voltage

In Situ Surface Voltage Measurements of Dielectrics Under Electron Beam Irradiation

New instrumentation has been developed for non-contact, in vacuo measurements of the electron beam-induced surface voltage as a function of time and position for non-conductive spacecraft materials in a simulated space environment. Used in conjunction with the capabilities of an existing ultrahigh vacuum electron emission analysis chamber, the new instrumentation facilitates measurements of charge accumulation, bulk resistivity, effects of charge depletion and accumulation on yield measurements, electron induced electrostatic breakdown potentials, radiation induced conductivity effects, and the radial dispersion of surface voltage. The novel system uses two movable capacitive sensor electrodes that can be swept across the sample to measure surface charge distributions on samples, using a non-contact method that does not dissipate sample charge. Design details, calibration and characterization measurements of the system are presented, for a surface voltage range from30 kV, voltage resolution \u3c1 \u3eV, and spatial resolutio

Report on the comparison of the scan strategies employed by the Patrick Air Force Base WSR-74C/McGill radar and the NWS Melbourne WSR-88D radar

The objective of this investigation is to determine whether the current standard WSR-88D radar (NEXRAD) scan strategies permit the use of the Melbourne WSR-88D to perform the essential functions now performed by the Patrick Air Force Base (PAFB) WSR-74C/McGill radar for evaluating shuttle weather flight rules (FR) and launch commit criteria (LCC). To meet this objective, the investigation compared the beam coverage patterns of the WSR-74C/McGill radar located at PAFB and the WSR-88D radar located at the Melbourne National Weather Service (NWS) Office over the area of concern for weather FR and LCC evaluations. The analysis focused on beam coverage within four vertical 74 km radius cylinders (1 to 4 km above ground level (AGL), 4 to 8 km AGL, 8 to 12 km AGL, and 1 to 12 km AGL) centered on Kennedy Space Center (KSC) Launch Complex 39A. The PAFB WSR-74C/McGill radar is approximately 17 km north-northeast of the Melbourne WSR-88D radar. The beam coverage of the WSR-88D using VCP 11 located at the Melbourne NWS Office is comparable (difference in percent of the atmosphere sampled between the two radars is 10 percent or less) within the area of concern to the beam coverage of the WSR-74C/McGill radar located at PAFB. Both radars provide good beam coverage over much of the atmospheric region of concern. In addition, both radars provide poor beam coverage (coverage less than 50 percent) over limited regions near the radars due to the radars' cone of silence and gaps in coverage within the higher elevation scans. Based on scan strategy alone, the WSR-88D radar could be used to perform the essential functions now performed by the PAFB WSR-74C/McGill radar for evaluating shuttle weather FR and LCC. Other radar characteristics may, however, affect the decision as to which radar to use in a given case

Containerization on Petascale HPC Clusters

Containerization technologies provide a mechanism to encapsulate applications and many of their dependencies, facilitating software portability and reproducibility on HPC systems. However, in order to access many of the architectural features that enable HPC system performance, compatibility between certain components of the container and host are required, resulting in a trade-off between portability and performance. In this work, we discuss our early experiences running three state-of-the-art containerization technologies on the petascale Frontera system. We present how we build the containers to ensure performance and security and their performance at scale.We ran microbenchmarks at a scale of 4,096 nodes and demonstrate the near-native performance and minimal memory overheads by the containerized environments at 70,000 processes on 1,296 nodes with a scientific application MILC - a quantum chromodynamics code.UT Austin-Portugal Program, a collaboration between the Portuguese Foundation of Science and Technology and the University of Texas at Austin, award UTA18-001217Texas Advanced Computing Center (TACC