Coaxial Plasma Opening Switch Research Articles

Influence of Downstream Flow on Conduction Phase of Coaxial Plasma Opening Switch

Plasma behaviour and the scaling relations in a coaxial plasma opening switch (POS) using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic (MHD) equations in conjunction with the generalized Ohm's law. The vacuum region on the right of POS is included in the model and the influence of downstream flow on the conduction characteristics is discussed. It is found that with the penetration of magnetic field, the pure hydrogen plasma is pushed downstream significantly; and POS still conducts current after the magnetic field arrives at the load edge of POS, which is different from the previous experimental results in a multispecies POS. It is because that the noticeable downstream plasma in the pure hydrogen POS may continue to conduct the current, while in the multispecies POS, the downstream plasma is unimportant so that the conduction phase ends soon after the magnetic field reaches the load edge. The scaling relation obtained from the simulations including the downstream region is consistent with the experimental results.

The Energy Balance of Plasma in a Coaxial Plasma Opening Switch

The two-dimensional energy balance in a coaxial plasma opening switch (POS) is studied based on the single-fluid magnetohydrodynamic (MHD) equations coupled with the generalized Ohm's law. The energy transfers between the plasma and the magnetic field are considered during the penetration of the magnetic field as the Ohmic heating is included in the energy-balance equation. The focus is on the energy partition between the magnetic-field energy and the dissipated magnetic-field energy in a high-density POS with different rise-in-time electric currents at the generator boundary. The simulation code is tested in two cases: the constant-in-time current case and the linear rise-in-time current case. For the sinusoidally rise-in-time current similar to that of the experiments, it is shown that at the end of the conduction phase the dissipated magnetic-field energy is 36.5% of the input electromagnetic energy, which is consistent with the experimental results.

Magnetohydrodynamic Simulation of a Coaxial High-Density Plasma Opening Switch

The plasma dynamics and the magnetic-field penetration in a coaxial plasma opening switch (POS) are studied self-consistently based on the two-dimensional magnetohydrodynamic (MHD) equation conjunction with the generalized Ohm's law. The energy transfers between the plasma and the magnetic field are considered during the penetration of the magnetic field, in which both the Ohmic heating and the heat transfer are included in the energy-balance equation. The profiles of magnetic field, plasma density, and plasma temperature are simulated with the initial plasma density n0=1016 cm-3. For the high-density plasma, it is shown that the convection effect dominates the magnetic-field penetration; the plasma near the cathode is rapidly compressed by the magnetic pressure, and the temperature of the plasma in the shock region increases noticeably because of the compression effect. Furthermore, the increase of temperature in the shock region enhances the magnetic-field penetration near the cathode. The energy analysis shows that more than half of the input energy is stored as magnetic-field energy, and a significant amount of the input energy goes into the plasma thermal energy. The scaling relation between the maximal conduction current and the initial plasma density is also studied, and the simulation results agree with the theoretical law and experimental data well

Characterization of Cable Gun Plasma with a Charge Collector Array

The density, drift velocity and reproducibility of the plasma produced by a cable plasma gun array have been measured with a charge collector array. The plasma is used to prefill a coaxial plasma-opening switch with a conducting time approaching 0.4 μs. The reproducibility of the plasma source in subsequent shots is better than 5%. Near the gun nozzle and the opposite electrode, the plasma density amounts to 1015cm-3, which is 2 times to 3 times that in the gap between the two coaxial electrodes. A plasma drift velocity of about 2.4 cm/μs is observed from the time of flight of the charged particles. Both plasma density and drift velocity increase almost linearly with the rise in charge voltage.

Observation of plasma motion in a coaxial plasma opening switch with a chordal laser interferometer

Electron densities in a coaxial plasma opening switch were measured at many lines-of-sight. In the present experiment, electron density was measured by a He-Ne laser interferometer with chordal lines-of-sight. In order to observe the motion of the plasma opening switch (POS) plasma, the electron density contours during the conduction, opening, and postopening phases were drawn by combining the results of interferometer experiments. The radial and axial motion of POS plasma was investigated from the density contours. As conduction time progressed, the POS plasma moved toward downstream. At 800 ns, which corresponds to the time of opening in the current waveform, low-density region less than 10/sup 15/ cm/sup -2/ is seen at 10 mm from the cathode. After the opening was completed, the low-density gap disappeared and the shape of the corn-shape-like plasma was distorted. The interferometer experiment was followed by the additional spectroscopic experiment. The results of spectroscopic experiment were in good agreement with those of interferometer experiment.

The energy balance in the plasma of a coaxial plasma opening switch

The two-dimensional energy flow in the plasma of a coaxial plasma opening switch (POS), during the Hall-induced shock penetration of a magnetic field, is analyzed. The electron collisionality is assumed to be high enough that the dissipated magnetic-field energy becomes electron thermal energy. It is shown that that part of the magnetic-field energy (a third) that is dissipated at the cathode at the generator side of the plasma, becomes an electron kinetic energy, that is convected along the current channel. It is also shown that in the magnetized plasma magnetic-field energy flows backwards towards the generator. The third new result is that inside the shock front, electron thermal energy is converted into magnetic-field energy, contrary to the usual situation in shock waves in which field energy is converted into particle thermal energy.

Experiments on high-power ion beam generationin self-insulated diodes

Experimental results are given on high-power ion beams (HPIB) generation in a vacuumspherical focusing diode with self-magnetic insulation, obtained from the nanosecond accelerator PARUS with 0.2-TW power and 60-ns pulse duration for a matched load. When the passive plasma source of the ions was used, the efficiency of the HPIB generationwas measured to be as high as 20% for 700-kV diode voltage and 10-kA/cm2 beam density in the focal plane.The application of a coaxial plasma opening switch (POS) prior to the diode resultedin a factor-of-1.8 increase in the diode power in comparison with a match operation inthe absence of a POS.