NASAâ s VAriable Specific Impulse Magnetoplasma Rocket Engine (VASIMR) will provide a highly efficient propulsion source that can dramatically reduce Martian transit times, provide for more abort contingencies, and protect astronauts from space radiation with its highly radiation-absorbent hydrogen fuel. The VASIMR is still in its developmental infancy and requires many years of research before its initial operational capability. Much is still unknown about the complex plasma interactions in the exhaust. A Langmuir probe was designed, constructed, and operated to determine current density radial profiles and total particle flux at various stages in the exhaust of VASIMR. The Langmuir probe results proved that the exhaustâ s radial profile is Gaussian, experimentally validated predictions of magnetic field line dragging, and verified the ionization efficiency of VASIMR.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 144 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (M.S.)--U.S. Naval Postgraduate School, 1960. / "Controlled Thermonuclear Processes, UC-20" -t.p. "TID-4500 (15th Ed.)" -t.p. Includes bibliographical references (p. 26-27).

No description available.

The noise in the Langmuir Probe and Plasma Wave Instrument (LP-PWI) on board ESA:s future Jupiter satellite JUICE (Jupiter ICy Moons Explorer) was investigated. Thermal Johnson-Nyquist noise and shot noise, caused by fluctuations in the probe-plasma currents, were combined with the quasi-thermal noise (QTN) due to thermal fluctuations in the electric field in the plasma, using a small signal equivalent circuit model. The contributions and effects of each of the considered noise sources were examined and compared for a number of representative space plasma conditions, including the cold dense plasma of Ganymede's ionosphere and the hot tenuous plasma out in the Jovian magnetosphere. The results showed that in the cold dense plasma of Ganymede's ionosphere, the antenna was long compared to the Debye length and the quasi-thermal noise had a clearly pronounced peak and a steep high-frequency cut-off. For an antenna biased to 1 V with respect to the plasma, the shot noise due to the ambient plasma was the dominant source of noise. For a an antenna at the floating potential the photoelectron shot noise coalesced with the shot and Nyquist noises of the ambient plasma to form almost a single curve. In the hot tenuous plasma out in Jupiter's magnetosphere, the antenna was short compared to the Debye length and the QTN spectrum was much flatter, with little or no peak at the plasma frequency and a very weak high-frequency cut-off. For an antenna biased to 1 V, the shot noise due to photoelectron emission dominated at Callisto's orbital position whereas at Ganymede's and Europa's orbital positions the Nyquist and shot noises of the ambient plasma particles were the dominant noise components. For an antenna at the floating potential, the shot and Nyquist noises of the ambient plasma also dominated the output noise, except at Europa's orbital position, where the quasi-thermal noise was the largest noise component for frequencies at and above the plasma frequency. The numerical calculations were performed using MATLAB. The code was made available in a Git repository at https://github.com/eliasodelstad/irfuproj_JUICE_noise.

The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.

Langmuir probes are extensively employed to study the plasmas in space and laboratory environments. Successful measurements require a comprehensive modeling of both the plasma environment and the probe conditions in the form of current collection models. In this thesis, the surface morphology implications on the probe current collection are investigated. This problem is applied and solved in the context of a CubeSat regime. The first problem that is investigated is the consequence of surface structural variability on the current measurements. A new model for dealing with non-uniformity of the probe surface structure is developed in this paper. This model is applied to analyze the Langmuir probe data from a sounding rocket mission that was subjected to surface structural non-homogeneities. This model would be particularly useful for CubeSat platforms where elaborate probe design procedures are not feasible. The second problem that is investigated is the surface area implications on Langmuir probe measurements. It has been established that surface area ratio of the spacecraft to that of the probe needs to be sufficiently large to make successful plasma measurements. CubeSats would therefore pose a challenge for employing Langmuir-type instruments to study the space plasma. We inspect the feasibility of making plasma measurements using Langmuir probes subjected to CubeSat area constraints. This analysis is done for a forthcoming Utah State University (USU)/Space Dynamics Lab (SDL) CubeSat mission.

The rectangular pulsed plasma thruster (PPT) is an electromagnetic thruster that ablates Teflon propellant to produce thrust in a discharge that lasts 5-20 microseconds. In order to integrate PPTs onto spacecraft, it is necessary to investigate possible thruster plume-spacecraft interactions. The PPT plume consists of neutral and charged particles from the ablation of the Teflon fuel bar as well as electrode materials. In this thesis a novel application of quadruple Langmuir probes is implemented in the PPT plume to obtain electron temperature, electron density, and ion speed ratio measurements (ion speed divided by most probable thermal speed). The pulsed plasma thruster used is a NASA Glenn laboratory model based on the LES 8/9 series of PPTs, and is similar in design to the Earth Observing-1 satellite PPT. At the 20 J discharge energy level, the thruster ablates 26.6 mg of Teflon, creating an impulse bit of 256 mN-s with a specific impulse of 986 s. The quadruple probes were operated in the so-called current mode, eliminating the need to make voltage measurements. The current collection to the parallel to the flow electrodes is based on Laframboise's theory for probe to Debye length ratios between 5 and 100, and on the thin-sheath theory for ratios above 100. The ion current to the perpendicular probe is based on a model by Kanal and is a function of the ion speed ratio, the applied non-dimensional potential and the collection area. A formal error analysis is performed using the complete set of nonlinear current collection equations. The quadruple Langmuir probes were mounted on a computer controlled motion system that allowed movement in the radial direction, and the thruster was mounted on a motion system that allowed angular variation. Measurements were taken at 10, 15 and 20 cm form the Teflon fuel bar face, at angles up to 40 degrees off of the centerline axis at discharge energy levels of 5, 20, and 40 J. All data points are based on an average of four PPT pulses. Data analysis shows the temporal and spatial variation in the plume. Electron temperatures show two peaks during the length of the pulse, a trend most evident during the 20 J and 40 J discharge energies at 10 cm from the surface of the Teflon fuel bar. The electron temperatures after the initial high temperature peak are below 2 eV. Electron densities are highest near the thruster exit plane. At 10 cm from the Teflon surface, maximum electron densities are 1.04e20 ± 2.8e19 m-3, 9.8e20 ± 2.3e20 m-3, and 1.38e21 ± 4.05e20 m-3 for the 5 J, 20 J and 40 J discharge energy, respectively. The electrons densities decrease to 2.8x1019 ± 8.9e18 m-3, 1.2e20 ± 4.2e19 m-3, and 4.5e20 ± 1.2e20 m-3 at 20 cm for the 5 J, 20 J, and 40 J cases, respectively. Electron temperature and density decrease with increasing angle away from the centerline, and with increasing downstream distance. The plume is more symmetric in the parallel plane than in the perpendicular plane. Ion speed ratios are lowest near the thruster exit, increase with increasing downstream distance, but do not show any consistent angular variation. Peak speed ratios at a radial distance of 10 cm are 5.9±3.6, 5.3±0.39, and 4.8±0.41 for the 5 J, 20 J and 40 J discharge energies, respectively. The ratios increase to 6.05±5.9, 7.5±1.6, and 6.09±0.72 at a radial distance of 20 cm. Estimates of ion velocities show peak values between 36 km/s to 40 km/s, 26 km/s to 30 km/s, and 26 km/s to 36 km/s for the % J, 20 J, and 40 J discharge energies, respectively.

The noise in the Langmuir Probe and Plasma Wave Instrument (LP-PWI) on board ESA:s future Jupiter satellite JUICE (Jupiter ICy Moons Explorer) was investigated. Thermal Johnson-Nyquist noise and shot noise, caused by fluctuations in the probe-plasma currents, were combined with the quasi-thermal noise (QTN) due to thermal fluctuations in the electric field in the plasma, using a small signal equivalent circuit model. The contributions and effects of each of the considered noise sources were examined and compared for a number of representative space plasma conditions, including the cold dense plasma of Ganymede's ionosphere and the hot tenuous plasma out in the Jovian magnetosphere. The results showed that in the cold dense plasma of Ganymede's ionosphere, the antenna was long compared to the Debye length and the quasi-thermal noise had a clearly pronounced peak and a steep high-frequency cut-off. For an antenna biased to 1 V with respect to the plasma, the shot noise due to the ambient plasma was the dominant source of noise. For a an antenna at the floating potential the photoelectron shot noise coalesced with the shot and Nyquist noises of the ambient plasma to form almost a single curve. In the hot tenuous plasma out in Jupiter's magnetosphere, the antenna was short compared to the Debye length and the QTN spectrum was much flatter, with little or no peak at the plasma frequency and a very weak high-frequency cut-off. For an antenna biased to 1 V, the shot noise due to photoelectron emission dominated at Callisto's orbital position whereas at Ganymede's and Europa's orbital positions the Nyquist and shot noises of the ambient plasma particles were the dominant noise components. For an antenna at the floating potential, the shot and Nyquist noises of the ambient plasma also dominated the output noise, except at Europa's orbital position, where the quasi-thermal noise was the largest noise component for frequencies at and above the plasma frequency. The numerical calculations were performed using MATLAB. The code was made available in a Git repository at https://github.com/eliasodelstad/irfuproj_JUICE_noise.

Diagnosing the temperatures and densities of plasmas is critical to the understanding of a wide variety of phenomena. Everything from equations of state for warm dense matter (WDM) found in Jovian planets and inertial confinement fusion (ICF) to turbulent and dissipative processes in laser-produced plasmas, rely on accurate and precise measurements of temperature and density. This work presents improvements on two distinct techniques for measuring temperatures and densities in plasmas: x-ray Thomson scattering (XRTS), and Langmuir probes (LPs). At the OMEGA laser facility, experiments on warm dense matter were performed by firing lasers at an ablator foil and driving a planar shock into cryogenically cooled liquid deuterium. XRTS in the collective scattering regime was implemented to probe the matter, measuring densities of n_e ~ 4.3 x 10²³ cm^-3, temperatures of T_e ~ 12 eV and ionizations of Z ~ 1.0. Through an extension to XRTS theory for inhomogeneous systems, it was possible to extract an additional parameter, the length scale of the shock, whose value of ? ~ 1.33 nm was consistent with the predicted mean free path, and therefore the thickness of the shock. A unique triple Langmuir probe prototype was designed and tested at the Gregori group's lab at the University of Oxford. This probe was designed for a high temporal resolution of ~ 200 MHz for probing laser-produced shocks. The probes were used to measure the shock formed from ablating carbon rods in an argon gas fill. The probe yielded plasma parameters of n_e ~ 1.0 x 10¹⁷ cm^-3 , and T^e ~ 1.5 eV, consistent with measurements from interferometry and emission spectroscopy.