A plasma diode appears resistive to an external observer at the magnetized electron series resonance (MESR). The authors derive the MESR resonant frequencies from an equivalent circuit model using ...linear cold plasma theory. The noise current from a decaying plasma is predicted to exhibit the MESR resonant frequencies and is verified by observing the spectra of the noise currents in 1d3v simulations. The spectra compare well with the theoretical values, which depend on the (central) plasma density and the sheath thickness. The latter is obtained from the (warm) plasma simulations.
The possibility of the improvement in performance of a nonequilibrium disk magnetohydrodynamics (MHD) generator by externally applying a radio frequency (RF) electromagnetic field (RF preionization) ...was examined experimentally. The MHD power generation experiments were carried out using a shock-tube driven disk MHD generator with the RF induction coils for the two inlet stagnation temperatures of 2275(/spl plusmn/75) K and 2650(/spl plusmn/50) K. As a result, under the conditions of both high and low stagnation temperatures, the output power was increased by the RF preionization. The increase was markedly observed for the low inlet stagnation temperature, where the plasma could not be produced only by the Joule heating attributed to a self-excited electromotive force. For the high inlet stagnation temperature, the plasma state in the MHD channel was improved by the RF preionization, leading to the increase in the output power. For the low inlet stagnation temperature, the marked increase in the output power by the preionization was not only because applying the RF electromagnetic field triggered the plasma production by the Joule heating attributed to a self-excited electromotive force but also because the plasma with the high electrical conductivity was produced in the more upstream region of MHD channel by the Joule heating attributed to the RF electromagnetic field.
The results of the investigation of electrical breakdown in neon filled diode at 13.3 mbar pressure in function of distances between electrodes (0.1 < d < 20 mm), using electrical breakdown time ...delay method, are presented in this paper. The Paschen curve, as well as the electrical breakdown time delay mean values, and discharge formative time dependence of distance between electrodes are analyzed. The electrical breakdown time delay distributions and Laue diagrams, both as the functions of the distances between electrodes, were used in consideration. The shapes of the established distributions indicate the complex nature of the discharge formation mechanism. The results also indicate that on the right hand side of the Paschen curve (pd > 15 mbar · cm) the transition regime between Townsend and streamer mechanism of electrical breakdown is dominant.
In this paper, important laboratory experiments in closed-cycle magneto-hydrodynamic (MHD) generator plasmas are discussed. The following aspects are treated: electron temperature elevation and ...nonequilibrium ionization, fluctuations and nonuniformity, streamers as the nonlinear appearance of ionization instability, inlet relaxation, and fully ionized seed as a concept to suppress ionization instability. Conclusions are presented on electrical transport parameters in nonuniform plasmas, streamer fine structure, streamer velocity, streamer initiation in relation to inlet relaxation, and the fully ionized seed concept.
In a magnetohydrodynamics (MHD) power generation with a frozen inert gas plasma (FIP), the effect of the nonuniformity of the inlet plasma in the direction perpendicular to walls on the performance ...and the comparison of the performance with r-/spl theta/ two-dimensional (2-D) numerical simulations are examined with r-z 2-D ones. The inlet nonuniformity of an ionization degree is kept throughout the channel and even in the boundary layer the state of the FIP is realized without an ionization instability. When the inlet ionization degree near the walls is higher than that in the main flow, the enthalpy extraction ratio decreases because the strong MHD interaction near the wall leads to the development of the boundary layer. On the other hand, it increases for the inverse distribution at the channel inlet, even if the introduced total inlet ionization degree is the same. In comparison with the results obtained from the r-/spl theta/ simulation, the development of the boundary layer results in the deterioration of the performance, and the optimal condition shifts to the low inlet ionization degree and the high load resistance.
It is widely assumed that thermionic current flow through a plasma is limited by a "space-charge limited" (SCL) cathode sheath that consumes the hot cathode's negative bias and accelerates upstream ...ions into the cathode. Here, we formulate a fundamentally different current-limited mode. In the "inverse" mode, the potentials of both electrodes are above the plasma potential, so that the plasma ions are confined. The bias is consumed by the anode sheath. There is no potential gradient in the neutral plasma region from resistivity or presheath. The inverse cathode sheath pulls some thermoelectrons back to the cathode, thereby limiting the circuit current. Thermoelectrons entering the zero-field plasma region that undergo collisions may also be sent back to the cathode, further attenuating the circuit current. In planar geometry, the plasma density is shown to vary linearly across the electrode gap. A continuum kinetic planar plasma diode simulation model is set up to compare the properties of current modes with classical, conventional SCL, and inverse cathode sheaths. SCL modes can exist only if charge-exchange collisions are turned off in the potential well of the virtual cathode to prevent ion trapping. With the collisions, the current-limited equilibrium must be inverse. Inverse operating modes should therefore be present or possible in many plasma devices that rely on hot cathodes. Evidence from past experiments is discussed. The inverse mode may offer opportunities to minimize sputtering and power consumption that were not previously explored due to the common assumption of SCL sheaths.
In an magnetohydrodynamic (MHD) generator using a frozen inert gas plasma (FIP), the availability of a frozen argon plasma, the influence of plasma uniformity at the generator inlet on the ...performance, and the feasibility of a large-scale generator are numerically examined by /spl gamma/-/spl theta/ two-dimensional simulation. The FIP is produced by pre-ionizing inert gas without an alkali metal seed at the generator inlet, then the ionization degree of the plasma is kept almost constant in the whole of the channel because of considerable slow recombination of the inert gas just like frozen reaction plasma. It is found that not only helium, but also argon frozen plasma MHD generation is realized, although highly accurate control of inlet ionization degree is necessary for argon. It is important to reduce the nonuniformity of plasma properties at the generator inlet in order to raise the maximum enthalpy extraction ratio. Even for the large-scale generator with 1000-MW thermal input, the ionization degree is kept almost constant in the whole of the channel and the high performance is obtainable. This result is extremely attractive for the FIP MHD generator.
The classical Pierce model consists of a one-dimensional plasma-filled diode into which a monoenergetic electron beam is injected. Particle-in-cell (PIC) simulations are performed with the BIT1 code, ...involving a large number of superparticles. The evolution of slightly perturbed uniform equilibria into the related nonlinear attractor states for a broad range of $\alpha$ values, where $\alpha\,=\,\omega_{{\rm pe}}d/u_0$ is the diode control parameter, is investigated. A period-doubling route to chaos in the classical Pierce diode for $\alpha$ slightly below $5\pi$ is analyzed in detail.
The generation of electricity using direct electrostatic and magnetohydrodynamic (MHD) conversion of the plasma-particle energy of small to midsize chemically assisted microwave or glow discharge ...plasma (CA-plasma) power sources in the range of a few hundred Watts to several tens of kilowatts for microdistributed commercial applications (e.g., household, automotive, light industry, and space-based power) is studied for the first time. In the determination of the effect of plasma parameters on conversion efficiency, careful attention was paid to the unique plasma conditions of low-pressure, low-ionization fraction, and nonthermal ion energies that are much greater than that of the thermal ions of traditional MHD but much lower than those of a fully ionized plasma typically generated for fusion experiments. The density of plasma ions and neutrals and their cross sections for processes such as charge exchange were also considered. The most important parameters were found to be charged-particle density and energy, as well as the large inventory of neutral gas atoms and molecules. Momentum and charge exchange of plasma ions with the large background fraction of neutrals represents a limitation to conversion efficiency. Two conversion technologies were examined in some detail. We considered the possibility of converting a CA-plasma using adaptations of a member of the broad category of electromagnetic direct converters previously developed for recovery and conversion of the high energy particles lost from tandem mirror and magnetically confined plasmas, and an MHD converter previously developed for conversion of high pressure combustion gases to electricity. While it was found that both conversion techniques performed well under ideal conditions for conversion of plasma to electricity showing conversion efficiencies of >50%, the tight coupling of plasma cell and converter, size limitations, particle energy, and the substantial inventory of relatively low energy neutrals may substantially reduce the efficacy of direct electrostatic converters under these conditions. However, MHD conversion of CA-plasmas appears feasible at /spl sim/50% efficiency with a simple compact design.
