J.H. Newman

Absolute and angular efficiencies of a microchannel‐plate position‐sensitive detector

This paper presents a characterization of a commercially available position‐sensitive detector of energetic ions and neutrals. The detector consists of two microchannel plates followed by a resistive position‐encoding anode. The work includes measurement of absolute efficiencies of H+, He+, and O+ ions in the energy range between 250 and 5000 eV, measurement of relative detection efficiencies as a function of particle impact angle, and a simple method for accurate measurement of the time at which a particle strikes the detector.

Differential cross sections for scattering of 0.5-, 1.5-, and 5.0-keV hydrogen atoms by He, H2, N2, and O2

This paper reports measurements of absolute scattering cross sections, differential in angle, for collisions of ground state oxygen atoms with He, N{sub 2}, and O{sub 2}. Data are presented for scattering of 0.5-, 1.5-, and 5.0-keV oxygen atome projectiles in the range of laboratory frame angles between 0.06{degree} and 5{degree}. These measurements provide information relevant to calculations of the aeronomic consequences of O{sup +} precipitation in the earths upper atmosphere.

SINGLE AND MULTIPLE IONIZATION OF SULFUR ATOMS BY ELECTRON IMPACT

Abstract In 1979 significant concentrations of singly and multiply charged sulfur ions were observed in the Io torus. Attempts to model these observations revealed a need for new fundamental cross section data. In response, laboratory measurements of the cross-sections for single, double, triple and quadruple ionization of sulfur atoms by electron impact are presented for collision energies from threshold to 500 eV.

Double ionization of atomic oxygen by electron impact

Abstract Laboratory measurements of the cross-sections for double ionization of atomic oxygen by electrons are presented for energies from threshold to ∼ 400 eV. A maximum cross-section of about 5.6 × 10−18 cm2 is observed at an electron energy of approx. 200 eV. Absolute cross-sections are obtained from measurements of the ratio of the cross-sections for double and single ionization, coupled with absolute cross-sections for single ionization previously measured by other investigators. The possible effects of excited oxygen reactants are examined, and the reported cross-sections are considered to be characteristic of ground state oxygen atoms.

Metal-organic hybrid metamaterial THz imaging band translators

We investigate the feasibility of negative photoresist as a structural material in metal-organic hybrid THz imaging detectors using SU-8. We will discuss design of metamaterials for MEMS-based terahertz (THz) thermal sensors and design and microfabrication process for building SU8-based MEMS THz focal plane arrays. Metamaterials of this kind, exhibiting absorption properties comparable to those of resonant metamaterials made using traditional thin films, coupled with the applicability of SU-8 as a structural material, offer possibilities for quick, simple microfabrication of focal plane arrays of THz imaging detectors. SU-8 is a low-cost material that can quickly be spun onto a substrate at a wide range of thicknesses and photolithographically patterned into a variety of structures. This removes the need for both PECVD deposition and plasma etching, dramatically increasing the speed and lowering the cost of production of such FPAs. We further investigate feasibility of use of such detectors as band translators rather than traditional bimaterial devices. Translators would be optically probed with an infrared (IR) camera. Individual pixels would absorb THz radiation, heat up and the thermal image would be projected onto an infrared camera, effectively translating the image from THz into IR.

Characterization of a shape memory alloy interference coupling

A versatile and heretofore unutilized coupling is obtained by press-fitting a hollow nickel titanium shape memory alloy (SMA) shaft into a steel hub. This produces an SMA interference coupling that is distinct from other SMA actuators by the method in which the SMA is used. Press-fitting the hollow SMA shaft in its detwinned martensitic phase into a steel hub creates a joint capable of holding parts such as emergency doors, satellite solar panels, or tamper locks securely together until commanded release. Release is accomplished by heating the SMA to its activation temperature. The resulting decrease in diameter of the hollow SMA shaft allows it to easily slip out of the hub, releasing the part. Load testing of the SMA interference coupling showed ultimate strengths about twice that of traditional press-fit coupling strength calculations. The coupling can be designed to be a simple mechanism of very small size, on the order of one cubic centimeter, capable of achieving coupling strengths in excess of 4000 N (900 lbf).