Results of anode heat-flux and anode fail measurements from a multimegawatt self-field quasi-steady magnetoplasmadynamic (MPD) thruster are presented. Measurements were obtained with argon and helium propellants for a variety of currents and mass flow rates. Anode heat flux was directly measured with thermocouples attached to the inner surface of a hollowed section. Anode falls were determined both from floating probes and through heat flux measurements. Comparison of data acquired through either method shows excellent agreement. Anode falls varied between 4-50 V with anode power fractions reaching 70 percent with helium at 150 kW, and 50 percent with argon at 1.9 MW. The anode fall was found to correlate well with electron Hall parameters calculated from triple Langmuir and magnetic probe data collected near the anode. Two possible explanations for this result are proposed: (1) the establishment of large electric fields at the anode to maintain current conduction across the strong magnetic fields; and (2) anomalous resistivity resulting from the onset of microturbulence in the plasma. To investigate the latter hypothesis, electric field, magnetic field, and current density profiles measured in the vicinity of the anode were incorporated into Ohm's law to estimate the electrical conductivity. Results of this analysis show a substantial deviation of the measured conductivity from that calculated with classical formulas. These results imply that anomalous effects are present in the plasma near the anode.

Anode power deposition in magnetoplasmadynamic thrusters

: Theoretical studies indicate that a variety of microscopic and macroscopic plasma instabilities can significantly affect the performance of the magnetoplasmadynamic (MPD) thruster, yet experimental evidence for their existence is extremely limited. The objective of this research was to provide experimental evidence for the existence of microinstabilities in a 10-kW-class, self-field MPD thruster. The lower- bound of the range of thruster operating currents investigated in this study was set by the requirement that the electromagnetic thrust component be much greater than the electrothermal thrust component. The upper-bound of the operating current was set by the initial observation of high-frequency thruster voltage oscillations, which is usually associated with the onset of excessive thruster erosion. Experimental evidence for two microinstabilities was obtained in the near-field plume of the thruster: 1) the generalized lower hybrid drift instability and 2) the electron cyclotron drift instability.

Microinstabilities in a 10-Kilowatt Self-Field Magnetoplasmadynamic Thruster

In this work the effects of Hydrogen and Argon ions on Aluminum samples and the spatial distribution of the ions in 2.5 kJ SBUPF1 Mather type plasma focus device in different distance from the anode top have been investigated. For each gas the pressure and operation voltage have been determined to have maximum ion density. Aluminum samples were placed at different distances above the anode. Irradiated samples have been analyzed with SEM technique for morphological and surface study of samples. Melting and surface evaporation effects and generation of cracks were seen in these samples. The result of ions patterns on these samples can be used to determine ions spatial distribution on top of the anode region. The EDX spectroscopy and the SRIM calculations have been done to determine the composition of samples and the penetration depth of the ions in the samples respectively.

Investigation of Spatial Distribution of Hydrogen and Argon Ions and Effects of them on Aluminum Samples in a 2.5 kJ Mater Type Plasma Focus Device

The instantaneous plasma structure of the SPHEX spheromak is determined here by numerically processing data from insertable Rogowski and magnetic field probes. Data is presented and compared for two modes of gun operation: with the central electrode biased positively and negatively. It is found that while the mean-, or even instantaneous-, field structure would give the impression of a roughly axisymmetric spheromak, the instantaneous current structure does not. Hundred per cent variations in J measured at the magnetic axis can be explained by the rotation of a current filament that has a width equal to half of the radius of the flux-conserving first wall. In positive gun operation, current leaves the filament in the confinement region leading to high wall current there. In negative gun operation, wall current remains low as all injected current returns to the gun through the plasma. The plasma, in either instance, is strongly asymmetric. We discuss evidence for the existence of the current filament in other gun-driven spheromaks and coaxial plasma thrusters.

Instantaneous current and field structure of a gun-driven spheromak for two gun polarities

A new concept for generation of thrust for space propulsion is introduced. Energetic thrust is generated in the form of plasmoids (confined plasma in closed magnetic loops) when magnetic helicity (linked magnetic field lines) is injected into an annular channel. Using a novel configuration of static electric and magnetic fields, the concept utilizes a current-sheet instability to spontaneously and continuously create plasmoids via magnetic reconnection. The generated low-temperature plasma is simulated in a global annular geometry using the extended magnetohydrodynamic model. Because the system-size plasmoid is an Alfvenic outflow from the reconnection site, its thrust is proportional to the square of the magnetic field strength and does not ideally depend on the mass of the ion species of the plasma. Exhaust velocities in the range of 20 to 500 km/s, controllable by the coil currents, are observed in the simulations.

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An Alfvenic reconnecting plasmoid thruster

Publisher Summary This chapter discusses the plasma problems in electrical propulsion. The involvement of plasma physics and technology in the area of space propulsion has occurred because (1) with the exception of nuclear explosions, the electrical or electromagnetic acceleration of conducting matter is the only feasible way of bringing rocket exhausts to the very high velocities necessary for deep space flight with payloads of men and their support equipment; (2) Ionized gas, or plasma, is the most convenient conducting material to use, as by virtue of its usually low density, it can be brought to the requisite velocities without the expenditure of prohibitive increments of energy. Several excellent developments of the rationale for electrical propulsion are available. The field of electric propulsion is concerned with plasma of medium to heavy elements, fairly well ionized, and having electron and ion densities in the range of 10 11 -10 15 /cm 3 .

16. Plasma Problems in Electrical Propulsion

This volume is devoted to the understandings of law developed from the mid17th century to the end of the 19th century by jurists and legal philosophers working in the civil-law tradition.1 This makes the volume complementary to Michael Lobban’s Volume 8 of this Treatise, where the same subject matter and the same period are covered, but from a common-law perspective instead. This peculiar combination of subject matter and period has made it necessary for us as volume editors to make certain choices in treating the civil-law tradition: These choices concern the volume’s overall design as well as the framing of its single chapters. Which is to say that the thinkers and schools of thought covered are not arranged along a strictly chronological line of development, nor is there an attempt to show how different thinkers and schools of thought have offered different solutions to the same basic questions, concerning the nature, the distinctive traits, and the function of law, since that would not have made it possible to bring out how complex the development was that legal thought went through during the arc of time in question: Such a development cannot be reduced to a linear sequence of theories and ideas, for it is instead broken up by significant discontinuities. One need only recall here, by way of example, how an understanding of law still tied to the late-medieval world eclipsed during this period, making it possible for modern legal science to progressively take hold; or how the institutions of the Ancien Régime fell apart and the modern state became fully established politically as well as administratively; or how legal pluralism survived in Europe until the end of the 18th century, when legal monism came into being with the 19th-century codifications. This makes it necessary—as we take into view the jurists’ and legal philosophers’ understandings of law in the historical period in question—to speak of different epochs of development rather than of different stages within the same epoch. Add to this that the discontinuities just mentioned were marked by different characteristics, came to pass at different times, and had entirely different consequences depending on which levels legal discourse, which areas of cultural influence, and which parts of the legal system we are considering. Let us take a few examples to briefly consider, in the first place, what this means with respect to the different levels of legal discourse. There was the discourse of the practical jurists on the one hand and that of the theoretical ones on the other. And it can be observed in this regard that, while the jurists’

Ralph H. Lovberg

Papers

16. Plasma Problems in Electrical Propulsion

Preface to Volume 9