Magnetoplasmadynamic Research Articles

Electrode Configuration Effect on the Performance of a Two-Dimensional Magnetoplasmadynamic Arcjet

Thrust performance and internal plasma flowfield of a 1-MW class self-field magnetoplasmadynamic (MPD) arcjet were measured to evaluate their dependence on the cross-sectional geometry of the electrodes. A multichannel two-dimensional MPD arcjet in quasisteady operation was used to visualize the two-dimensional flowfield and reveal the correlation between the internal flowfield and the thrust performance. The experimental results for six different electrode configurations show that the thrust performance strongly depends on the thruster chamber cross-sectional geometries for the 7sp range of interest, 1000-3000 s. The cathode length determined the engine performance, regardless of the anode geometry. In particular, the convergent-divergent anode with a short cathode showed the best performance. The superior acceleration mechanism of the short cathode was explained on the basis of two-dimension al plasma distributions such as discharge current contours and plasma density obtained by Mach-Zehnder interferometry. A dense plasma region near the tip of the short cathode was observed and subsequent expansion guided by the diverging nozzle can enhance aerodynamic acceleration, which contributes to large thrust generation.

Distribution of ionized carbon during simulated plasma disruption using spectroscopy

In the present study, the behavior of ionized carbons during a simulated plasma disruption is investigated with the magneto-plasma-dynamic (MPD) arc jet. The MPD arc jet was improved to generate the high heat flux. The temporal and spatial distributions of the ionized carbons were measured by emission spectroscopy. The effect of heat load was evaluated using two pulses, i.e. the original and improved MPD arc jet. The C II and C III distributions were obtained for the two pulses. The emission intensities were strongly related to the evaporated flux of carbon.

Instabilities in MPD thruster flows: 2. Investigation of drift and gradient driven instabilities using multi-fluid plasma models

The investigation of magnetoplasmadynamic (MPD) instabilities in connection with the performance of MPD thrusters has received increased attention for several years. A systematic investigation of macroscopic drift and gradient driven instabilities at the Institut für Raumfahrtsysteme (IRS), carried out since 1987, showed that the occurrence of acoustic wave and space charge instabilities was possible. The calculation of the linear development of instabilities using a three-fluid theory of the plasma flow will be presented. Furthermore, in order to identify the instabilities found in the three-fluid formalism, two-fluid and one-fluid models are investigated and links established. When possible, analytical approximations for the unstable roots of the linear dispersion relation are derived, giving the explicit dependence of the oscillation frequencies and growth rates on the wavevector and the various plasma parameters.

Quasisteady Ablative Magnetoplasmadynamic Thruster Performance with Different Propellants

This paper discusses quasisteady, ablative, magnetoplasmadynamic (MPD) thruster operation and performance. Quasisteady MPD thrusters operate with instantaneous power levels of a few megawatts during pulses (shots) that last approximately 1 ms. The MPD thruster used during this study consisted of coaxial electrodes with radially positioned bars of propellant that passed through the sidewall of the anode near the cathode tip. Four different polymer propellants were investigated: 1 ) polytetrae uoroethylene (Tee ont), 2) ethylene-tetrae uoroethylene resin (Hye ont), 3) polyethylene, and 4 ) ethylene-chlorotrie uoroethylene resin (Halart). Voltage, current, ablated propellant mass, jet velocity, and impulse bit were measured for e ve different values of energy per shot in the 1666‐ 3000 J range for each propellant. Polyethylene exhibited different electrical behavior (higher discharge voltages and impedances ) compared with the other three propellants that showed the typical features of high-ionization regime operation. Polytetrae uoroethylene provided the highest thrust and thrust-to-power ratio e gures, whereas ethylene-tetrae uoroethylene resin had the lowest values of these parameters. Polyethylene exhibited the highest exhaust velocity.

準定常ＭＰＤチャンネル内のプラズマの加速過程

Plasma diagnostic measurement and flowfield analysis in a quasi-steady coaxial magnetoplasmadynamic (MPD) channel realizing a one-dimensional flowfield were conducted for understanding blowing acceleration. Axial variations of current, electron temperature and electron number density in an MPD channel were measured, and these experimental results for Ar roughly agreed with analyzed ones. As a result, it was expected, from the axial profiles of Lorentz forces inferred from the measured current distributions and the calculated plasma velocities, that there existed two acceleration zones near the inlet and outlet at high magnetic Reynolds numbers. Furthermore, it was predicted from numerical analysis that nonequilibrium ionization process enhanced electromagnetic acceleration through the channel.

Numerical Analysis of a Two-Dimensional Magnetoplasmadynamic Arcjet

The effect of electrode cone guration on thrust characteristics of a two-dimensional magnetoplasmadynamic (MPD) arcjet was numerically investigated. A simple magnetohydrodynamics (MHD) model was developed and the numerical results were compared with the experimental data for several electrode geometries. To understand the features of the e owe eld, we introduced a magnetosonic Mach number, which is dee ned as local velocity divided by a propagation speed of the MHD disturbance. Based on the magnetosonic Mach number distribution of the e owe eld, the model can explain the thrust characteristics of the MPD arcjet, especially the superiority of a short cathode under various anode cone gurations. Because the electromagnetic thrust is unaltered for the same anode cone guration, the electrothermal component of thrust makes a difference between the long and the short cathodes. With a short cathode cone guration, the large heat deposition near the cathode tip, which is inevitable to MPD arcjets, can be cone ned in the submagnetosonic region where the local e ow is accelerated to magnetosonic velocity. Then the thermal deposition into the submagnetosonic region can be efe ciently recovered through transmagnetosonic acceleration, resulting in a large thrust generation.

Characterization of a low-power steady-state magnetoplasmadynamic device for non-propulsive applications

The design, construction and operation of a low-power (5 - 15 kW) steady-state magnetoplasmadynamic (MPD) device is described. Its performance when operated on argon, nitrogen and oxygen-bearing gases is detailed, and typical operational data for runs with argon given, together with a current - voltage characteristic for the device. The electrode supports are water cooled; water temperature measurements show that thermal equilibrium is reached, thus enabling the anode and cathode power sinks to be determined and the device efficiency to be estimated. These figures are similar to those obtained from another device also operated in the tens of kilowatts power range. Electrode erosion and passivation mechanisms encountered in the device are described for the different propellants. Analysis of the cathode shows that the majority of the erosion occurs at the relatively cool cathode root and backplate. Passivation of the actively cooled anode due to deposited layers, when operated on oxygen-bearing gases, is discussed. Non-propulsive applications of such an MPD device for materials processing or for atomic oxygen production are discussed, together with proposed modifications to lengthen run times.

Performance and Acceleration Process of Quasisteady Magnetoplasmadynamic Arcjets with Applied Magnetic Fields

A quasisteady magnetoplasmadynamic (MPD) arcjet with an applied magnetic Ž eld was investigated to improve the thruster performance and understand the complex acceleration mechanisms with both the self-induced and applied magnetic Ž elds. The MPD arcjet was operated with hydrogen, a mixture of nitrogen and hydrogen simulating hydrazine, and argon at discharge currents of 3 – 18 kA in high speciŽ c impulse levels around a critical discharge current predicted from the rules of Alfven’s ionization velocity or minimum input power. The application of axial magnetic Ž elds achieved higher thrust efŽ ciencies than those for only the self-induced magnetic Ž eld at constant speciŽ c impulses, and still achieved stable operations at higher speciŽ c impulses with less electrode erosion. The following guidelines were suggested to achieve higher thruster performance: 1) the axial magnetic Ž eld strength must be smaller than the azimuthal self-Ž eld strength in the main discharge region near the cathode tip, and 2) the applied magnetic Ž eld lines must expand gradually downstream for smooth expansion of plasma. Furthermore, the measured pressures on the electrodes and the current distributions in the discharge chamber showed that the overall thrust measured by a pendulum method increased, in spite of a decrease in the electromagnetic pumping thrust and a small contribution of Hall acceleration. Thus, an additional thrust component because of the axial magnetic Ž eld, such as that caused by swirl acceleration, is expected to exist.

Optimal Control of Quasi-One-Dimensional Self-Field Magnetoplasmadynamic Arcjet Flowfields

The e owe eld of a self-e eld magnetoplasmadynamic (MPD) arcjet was analyzed to establish the optimum geometry that produces the highest possible thrust for specie ed operating conditions. A set of simplie ed assumptions, within a quasi-one-dimensional framework, was used to establish how the optimum e owe eld was coupled to the thruster geometry. The resultant distribution of discharge current was smooth without any prominent concentration along the electrodes. The approach employed a purely mathematical method of engineering optimal control to suggest design guidelines for MPD arcjet thrusters within the idealized constraints. The optimum was found to be a slowly convergent and quickly divergent geometry that maximized the exit velocity for a e xed electrical input power.

Parameter Change of Magneto-Plasma-Dynamic Arc-Jet Plasma on a Flow-Facing Plate

Electron temperature and density of plasma flow, which was obtained from a magneto-plasma-dynamic (MPD) arc jet, were measured by the triple-probe method. In order to apply the MPD arc jet to thin-film processing, the changes in the plasma parameters on a processing substrate were investigated.

Mechanisms of anode power deposition in a low pressure free burning arc

Anode power deposition is a dominant power loss mechanism for arcjets and magnetoplasmadynamic (MPD) thrusters. In this study, a free burning arc experiment was operated at pressures and current densities similar to those in arcjets and MPD thrusters in an attempt to identify the physics controlling this loss mechanism. Use of a free burning arc allowed for the isolation of independent variables controlling anode power deposition and provided a convenient and flexible way to cover a broad range of currents, anode surface pressures, and applied magnetic field strengths and orientations using an argon gas. Test results showed that anode power deposition decreased with increasing anode surface pressure up to 6.7 Pa and then became insensitive to pressure. Anode power increased with increasing arc current, while the electron number density near the anode surface increased linearly. Anode power also increased with increasing applied magnetic field strength due to an increasing anode fall voltage. Applied magnetic field orientation had an effect only at high currents and low anode surface pressures, where anode power decreased when applied-field lines intercepted the anode surface. The results demonstrated that anode power deposition was dominated by the kinetic energy of the current-carrying electrons acquired over the anode fall region. Furthermore, the results showed that anode power deposition can be reduced by operating at increased anode pressures, reduced arc currents, anode current densities, and applied magnetic field strengths, and with magnetic field lines intercepting the anode.

Microinstabilities in a 10-kilowatt self-field magnetoplasmadynamic thruster

Abstract : 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.

Time-resolved plasma diagnostic by laser-diode spectroscopy

A tunable diode laser has been used as a light source for line-of-sight absorption and Doppler-shift measurements. We have applied the method to perform plasma diagnostics in a magneto plasma dynamic (MPD) pulsed propulsor device and of an Ar/sup +/ laser tube plasma. Spectrally resolved argon absorption lineshapes of transitions of neutral and single ionized argon were recorded. A high temporal resolution (a few microseconds) is achieved by fast tuning the laser frequency at a repetition rate greater than 100 kHz. From the recorded spectra, we deduce the dynamics of the neutral components of the plasma in the thruster. We also demonstrate the possibility of direct ion diagnostics by the observation of ionic transitions, using red diode lasers in an Ar/sup +/-laser commercial tube.

Calculation of nonlinear drift instabilities in magneto-plasmadynamic thruster flows

This paper presents the latest results from calculations of the nonlinear development of instabilities in magneto-plasmadynamic (MPD) thruster flows. Linear instability analysis carried out at the Institut fur Raumfahrtsysteme of the Universitat Stuttgart yielded three basic instabilities for stationary MPD thruster flows: a space charge instability, an acoustic wave instability and an electron drift instability. Nonlinear analysis using the quasi-analytical method (QAM) developed by the authors not only yields these instabilities in the lower orders of the QAM hierarchy but also shows their nonlinear evolution in the higher order development, particularly that of the space charge instability which is actually shown to lead to current chopping. Calculation results for the normalized current density and electric field strength as functions of time for various relative gradients are presented.

Thrust Formula for Applied-Field Magnetoplasmadynamic Thrusters Derived from Energy Conservation Equation

A thrust formula for applied-field magnetoplasmadynamic (MPD) thrusters has been derived from the energy conservation equation for the propellant plasma flow by assuming that the work done by electromagnetic forces is converted into kinetic energy of the exhaust plasma. Three acceleration mechanisms, 1) generalized Hall acceleration, 2) swirl acceleration, and 3) self-magnetic acceleration are taken into account. This formula enables theoretical calculation of thrust of an applied-field MPD thruster from controllable thruster operation parameters, and estimation of the contributions of the respective acceleration mechanisms.

電磁プラズマ加速アークジェットのセラミックコーティングへの応用

A magneto-plasma-dynamic (MPD) arcjet generator, in which plasma generated is accelerated by the electromagnetic interaction between the discharge current and the magnetic field induced by it, is a simple, efficient, and reliable device suitable for material processing. A quasi-steady MPD arcjet was studied to examine fundamental operational characteristics and plasma features. The MPD arcjet was operated for discharge currents of 3-25 kA with working gases of Ar, H2, N2 and NH3. Three different discharge modes of diffuse, spot and gross erosion existed in the MPD arc, and a qualitative explanation of their nature was presented. As a result, the MPD arcjet was found to produce high-velocity, high-temperature, high-density, large-area plasmas. For applications of MPD arcjets to ceramic coatings, an ablation-type MPD arcjet with a cathode covered with ceramic materials was developed. In 100-shot operations for Ar at 5-10 kA, the ablation rates of the ceramic covers ranged from 1.1 to 7.5 mg/shot. The MPD plasma spraying showed that a dense uniform ceramic film with above 1200 Vickers hardness was deposited. From the XPS spectra, the peak area ratio of Si/Al for the coating film almost equaled that for the raw ceramic material, and the valence numbers of Al and Si did not change. Consequently, the MPD arcjet was found to have a high potential for material processing.

Non‐MHD influences on the magnetospheric current system

The dynamics of critical magnetospheric boundary regions is examined through combined particle and fluid simulations. The particle simulations focus on the dynamics of the magnetopause whose structure is shown to be determined by the differential penetration of magnetosheath ions and electrons. The magnetosheath electrons with their small gyroradius have only limited penetration and give rise to a sharp peak in the current density, producing a well‐defined magnetopause current sheet. The magnetosheath ions penetrate further, where they intermix with magnetospheric plasma producing the magnetopause boundary layer. An ambipolar electric field is set up by this differential penetration which draws some of the magnetospheric ions out into the current layer and beyond. In addition, the ambipolar electric field sets up surface currents along the flanks of the magnetopause. These surface currents and their analogues in the magnetotail are shown to play a major role in (1) mapping of currents into the ionosphere and (2) determining the reconnection rate at the magnetopause and magnetotail current sheets by the effective resistivity they produce on these current sheets. These surface currents which are neglected in present MHD treatments are explicitly included in a modified set of single fluid equations, called magnetoplasma dynamics (MPD). The MPD description is able to remove the need for assuming an artificial resistivity while, at the same time providing, a comprehensive description of the currents that map into the ionosphere as well as the various current sheets attached to the different magnetospheric boundary layers. Important results include (1) the mapping of region 1 and 2 currents into the noon and midnight sectors of the ionosphere, (2) their equatorward motion during the southward turning of the interplanetary magnetic field, (3) their temporary enhancement at pseudobreakup, and (4) their enhancement and poleward expansion at substorm onset.

Applications of Quasi-Steady Magneto-Plasma-Dynamic Arcjets to Ceramic Coatings

For applications of quasi-steady magneto-plasma-dynamic (MPD) arcjets to material processing, an MPD arcjet with a cathode covered with ceramic materials was developed. In 100-shot operations at 5-10 kA, the ablation rates of the ceramic covers ranged from 2.5 to 5.0 mg/shot. The front velocities of ablated Al atoms inferred with a streak camera were much higher than velocities of 200-500 m/s for conventional plasma torches for material processing. This is effective for deposition of rigid films adhering strongly to substrate surfaces. The SEM photographs showed that a dense uniform film was deposited near the center of the substrate. From the XPS spectra, the peak area ratio of Ti/Al for the coating film almost equaled that for the cross section, and the valence numbers of Al and Ti did not change.

Injected propellant ionization in MPD thrusters

A model is presented for the selfmagnetized, weakly ionized preionization region at the entrance to a magnetoplasmadynamic (MPD) accelerator. The model is steady, one-dimensional and inviscid, and assumes supersonic flow of argon plasma with zero current in the region. Heavy particle temperature is constant, and electron temperature Te is determined by ambipolar diffusion and by photoand electron-impact ionization processes. The plasma continuity, momentum and energy equations are integrated numerically with appropriate boundary conditions, giving a region width Ax ranging from 3 to 17 mm, depending on density, and a degree of ionization a increasin from an initial value of inlet. The electron temperature rises monotonically from Te=lOOOK to Te~18,000'K, a level sufficient to sustain MPD accelerator operation. The total electrostatic potential across Ax is AV=12.5+0.6 V. Reducing the injected particle flux Qo increases Ax, until a critical Qo is reached below which no solutions exist. W a=IO-' to a = 4 f 2 ~ 1 0 3 at the MPD accelerator NOMENCLATURE j IRoss L n no nn Pe qe Qci

Application of a quadruple probe technique to MPD thruster plume measurements

A new quadruple Langmuir probe diagnostic technique is applied to the plume of a pulsed magnetoplasmadynamic (MPD) thruster with argon propellant. The probe permits simultaneous measurement of electron temperature Te, density ne, and ion flow velocity u in the exhaust stream. For distances of 3-25 cm from the thruster face, Te is 8-1.5 eV, ne is 4.8-1.2 x 10 m~, and u is 0.7-1.8 x 10 m/s. The measurements suggest that the plume is well-collimated, and that the ion temperature is significantly higher than the electron temperature, consistent with an ion-conduction model of the thruster.