Plasma contactor research, 1990

Emissive and Langmuir probes were used to measure plasma potential profiles, plasma densities, electron energy distributions, and plasma noise levels near a hollow cathode-based plasma contactor emitting electrons. The effects of electron emission current (100 to 1500 mA) and contactor flowrate (2 to 10 sccm (Xenon)) on these data are examined. Retarding potential analyzer (RPA) measurements showing that high energy ions generally stream from a contactor along with the electrons being emitted are also presented, and a mechanism by which this occurs is postulated. This mechanism, which involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice, results in a region of high positive space charge and high positive potential. Langmuir and RPA probe data suggests that both electrons and ions expand spherically from this potential hill region. In addition to experimental observations, a simple one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and is shown to agree qualitatively with these observations. Experimental results of the first stage of bilateral cooperation with the Italian Institute of Interplanetary Space Physics (IFSI CNR) are presented. Sharp, well-defined double layers were observed downstream of a contactor collecting electrons from an ambient plasma created in the IFSI Facility. The voltage drop across these double layers was observed to increase with the current drawn from the ambient plasma. This observation, which was not as clear in previous IFSI tests conducted at higher neutral pressures, is in agreement with previous experimental observations made at both Colorado State University and NASA Lewis Research Center. Greater double layer voltage drops, multiple double layers, and higher noise levels in the region near the double layers were also observed when a magnetic field was imposed and oriented perpendicular to the line joining the contactor and simulator

Space plasma contractor research, 1988

Results of experiments conducted on hollow cathode-based plasma contractors are reported. Specific tests in which attempts were made to vary plasma conditions in the simulated ionospheric plasma are described. Experimental results showing the effects of contractor flowrate and ion collecting surface size on contactor performance and contactor plasma plume geometry are presented. In addition to this work, one-dimensional solutions to spherical and cylindircal space-charge limited double-sheath problems are developed. A technique is proposed that can be used to apply these solutions to the problem of current flow through elongated double-sheaths that separate two cold plasmas. Two conference papers which describe the essential features of the plasma contacting process and present data that should facilitate calibration of comprehensive numerical models of the plasma contacting process are also included

Ion extraction capabilities of two-grid accelerator systems

An experimental investigation into the ion extraction capabilities of two-grid accelerator systems common to electrostatic ion thrusters is described. This work resulted in a large body of experimental data which facilitates the selection of the accelerator system geometries and operating parameters necessary to maximize the extracted ion current. Results suggest that the impingement-limited perveance is not dramatically affected by reductions in screen hole diameter to 0.5 mm. Impingement-limited performance is shown to depend most strongly on grid separation distance, accelerator hole diameter ratio, the discharge-to-total accelerating voltage ratio, and the net-to-total accelerating voltage ratio. Results obtained at small grid separation ratios suggest a new grid operating condition where high beam current per hole levels are achieved at a specified net accelerating voltage. It is shown that this operating condition is realized at an optimum ratio of net-to-total accelerating voltage ratio which is typically quite high. The apparatus developed for this study is also shown to be well suited measuring the electron backstreaming and electrical breakdown characteristics of two-grid accelerator systems

An Analysis of the Location of White Light Flares in the Sun\u27s Atmosphere

When flares occur in the Sun’s atmosphere, electromagnetic radiation in all wavelengths is emitted. Flares observed at visible wavelengths are called white light flares. Little is known about white light flares since the radiation from the Sun in the visible range greatly outshines what is produced during solar flares. Since white light flares are hard to see, it is not clear in what part of the solar atmosphere they occur. The point of this research is to identify where in the corona white light emission in produced during a flare. Depending on what will be discovered affects the validity of solar flare theories, particularly the Standard Flare Model, that have been a foundation in heliophysics. To answer this question a catalog of flares has been constructed as well as a code created in SunPy to obtain images of the flares from the catalog for further analysis of the location of white light flares

Development of Reagents for Application of At-211 to Targeted Radionuclide Therapy of Cancer

This grant covered only a period of 4 months as the major portion of the award was returned to DOE due to an award of funding from NIH that covered the same research objectives. A letter regarding the termination of the research is attached as the last page of the Final Report. The research conducted was limited due to the short period of this grant, but the results obtained in that period are outlined in the Final Report. The studies addressed in the research effort were directed at a problem that is of critical importance to the in vivo application of the alpha-particle emitting radionuclide At-211. That problem, low in vivo stability of many astatinated molecules, severely limits the use of At-211 in therapeutic applications. The advances sought in the studies were expected to expand the types of biomolecules that can be used as carriers of At-211, and provide improved in vivo targeting of the radiation dose compared with the dose delivered to normal tissue