Jill A. Marshall

2π‐radian field‐of‐view toroidal electrostatic analyzer

We describe a new type of electrostatic charged particle analyzer based on toroidal geometry. The analyzer features a 360°×10° (polar×azimuthal) field of view and a focal length in the polar direction significantly longer than that of similar devices based on spherical geometry. Extended focal length is a requirement for matching the electrostatic energy spectrometer with a second, mass‐resolving, analyzer. Laboratory tests show that the toroid design has a large geometric factor per unit of instrument weight, good energy‐angle resolution in the particle deflection plane, and sharp (1.0° FWHM) resolution at focus in the polar angle direction. The analyzer is well suited for use in satellite‐borne mass spectrometry and also as a stand‐alone electrostatic analyzer.

Inquiry experiences as a lecture supplement for preservice elementary teachers and general education students

The study reported here was designed to substantiate the findings of previous research on the use of inquiry-based laboratory activities in introductory college physics courses. The authors sought to determine whether limited use of inquiry activities as a supplement to a traditional lecture and demonstration curriculum would improve student achievement in introductory classes for preservice teachers and general education students. Achievement was measured by responses to problems designed to test conceptual understanding as well as overall course grades. We analyzed the effect on selected student outcome measures in a preliminary study in which some students engaged in inquiry activities and others did not, and interviewed students about their perceptions of the inquiry activities. In the preliminary study, preservice elementary teachers and female students showed significantly higher achievement after engaging such activities, but only on exam questions relating directly to the material covered in the e...

Experimental tests of a toroidal electrostatic analyzer

A toroidal electrostatic analyzer of a design suitable for space plasma instrumentation has been constructed and tested. Experimental results are compared with second-order ion optical theory and are in good agreement. Verifying the ion optics of the toroid was simplified by use of a position-sensing microchannel-plate detector mounted on a positioning system with three translational degrees of freedom located at the toroid exit. The toroidal analyzer described here is the first optical element in a fully toroidal mass spectrograph intended for analysis of kilovolt magnetospheric plasmas.

Sources of field‐aligned currents in the auroral plasma

Data from the Dynamics Explorer 1 High Altitude Plasma Instrument (HAPI) and magnetometer are used to investigate the sources of field-aligned currents in the nightside auroral zone. It is found that the formula developed by S. Knight predicts the field-aligned current density fairly accurately in regions where a significant potential drop can be inferred from the HAPI data; there are, however, regions in which the proportionality between potential drop and field-aligned current does not hold. In particular, the authors note occurrences of strong upward field-aligned current associated not with inverted-V events but instead with suprathermal bursts. In addition, upward field-aligned currents are often observed to peak near the edges of inverted-V events, rather than in the center as would be predicted by Knight.

What is mathematical modelling? Exploring prospective teachers’ use of experiments to connect mathematics to the study of motion

This paper focuses on the construction, development, and use of mathematical models by prospective science and mathematics teachers enrolled in a university physics course. By studying their involvement in an inquiry-based, experimental approach to learning kinematics, we address a fundamental question about the meaning and role of abstraction in modelling when such approaches involve students encountering and resolving experimental error. We use a “tensions” framework to explore the capability of learners to make necessary connections between abstract mathematical models and physical phenomena.

CIV Experiments on ATLAS‐1

A test of the Critical Ionization Velocity (CIV) theory was made with neutral xenon releases from the Space Experiments with Particle Accelerators (SEPAC) hollow cathode plasma contactor onboard the Shuttle Orbiter Atlantis during the ATLAS-1 mission. The gas velocity perpendicular to the Earths magnetic field was essentially the orbital velocity (7.5 km/s), and thus it exceeded the CIV for xenon. The releases were observed with onboard instrumentation. A factor of 60 enhancement was seen in the Langmuir probe current. Calculations confirmed that release conditions generally satisfied criteria for CIV and predicted a maximum factor of 20 increase in plasma density. Thus, CIV effects were likely to have occurred during the ATLAS-1 experiments.

Artificial auroras in the upper atmosphere 1. Electron beam injections

Artificial electron beams from the Space Experiments with Particle Accelerators (SEPAC) on the ATLAS 1 Spacelab payload were used to stimulate auroral emissions at southern auroral latitudes. The emitted electron beams were monoenergetic at 6.25 keV and were fired in one-second pulses every fifteen seconds with currents of 1.21 A. Optical measurements of the beam were made in the vicinity of the Shuttle Orbiter by its on-board television camera and in the upper atmosphere by the Atmospheric Emissions Photometric Imager (AEPI). AEPI imaged auroral emissions in both white light and at the 427.8 nm N2+ emission line. Energy deposition calculations and the results of previous sounding-rocket experiments had suggested that emissions with scale sizes of about 130 meters would result from the artificial electron beams with the visible emissions extending from about 110 to 130 km altitudes. In the ATLAS 1 experiments the auroral imaging was performed from the Shuttle, providing a new perspective on the artificial auroras and allowing the emissions to be traced from altitudes near the 295 km Shuttle altitude down to the 110 km level along the curved magnetic field lines.

An isochronous poloidal geometry time-of-flight ion mass spectrometer for energetic space plasmas

Abstract Space missions to the outer planets of the solar system require advanced mass-spectroscopic measurements that cover an unprecedented range of particle phase space. We present here a discussion of satellite-borne mass-spectrometer design considerations and put forward a design for an isochronous time-of-flight mass spectrometer based on poloidal ion trajectories in a set of three tandem toroidal electrostatic analyzers. The proposed instrument focuses a wide range of ion energies ( ΔE / E = 0.10) and entrance angles ( ±5 ° ) over a field of view subtending 360 ° with a mass resolution M / ΔM > 20. In order to create such a large field of view, the device accepts a broad range of entrance angles in the nondispersive (azimuthal) direction of the toroids. Isochronous focusing takes place in the polar plane of the toroid, thus the optics of this device are poloidal rather than toroidal. Because of the lack of an analytical theory up to now, development has relied primarily on 3D ray tracing to find triple-focusing (angle-energy-displacement) solutions that are isochronous. The proposed device has the useful feature that it discriminates molecular species from atomic species of the same mass (e.g. CH 4 + from O + or CH 2 + from N + ).

Space Experiments with Particle Accelerators (SEPAC)

Space Experiments with Particle Accelerators (SEPAC) is a project of performing an active experiment on the Spacelab 1 in 1983 using electron and plasma beams injected into space plasma. General description, present status and future program are described.

A double-focusing toroidal mass spectrograph for energetic plasmas: II. Experimental results

Abstract We report here on experimental results from a new toroidal ion optical system that has the potential to improve significantly the angular acceptance and sensitivity of previous satellite-borne ion mass spectrometers while retaining the focusing properties required for good mass resolution. Laboratory results with single and tandem toroids show full-width acceptances of ±6° and ±25° in azimuthal and vertical directions. Second-order aberrations have been measured and are compared with analytical and ray tracing results. Terms to fourth order in vertical acceptance angle and position are also found to be important. Data were obtained with an automated two-dimensional two-axis-of-motion imaging microchannel plate detector system that greatly speeds up data acquisition and analysis.