Hypervelocity Dust Storm Launched With a Coaxial Plasma Gun

Snowplow model is the main method to describe the acceleration process of coaxial plasma gun in the prefill mode, which can directly give the analytical expression of plasma velocity versus time. So it has become an important reference in the design of device structure for different application requirements. Through the measurements of current, magnetic and optical signals, the characters of current during the discharge and the motion of plasmoid are investigated. The variation of discharge current with time is close to the damping sine, which is an underdamping solution of RLC equivalent discharge circuit. The measured current is used to calculate the theoretical velocity instead of the sinusoidal one to eliminate the error of magnetic pressure. The variation of plasma velocity with discharge voltage and chamber pressure is consistent with that predicted by solving the equation of plasma motion under snow plough model, but the acceleration process is not. At the initial stage of the discharge, due to the low sweep efficiency, the plasma is accelerated to a higher velocity than the predicted one, the increase in voltage and the decrease in pressure further enhanced the effect. With the extension of the acceleration distance, due to the friction resistance between plasma and electrodes, the acceleration slows down and the velocity stars to fall below the predicated value, the saturation of plasma velocity at the nozzle is found. The friction resistance term is added to the equation of plasma motion. Compared with the deviation range of 26.8~53.6% of the existing model, the difference between the theoretical and the measured speed under different voltages and pressures is only 3.1~8.4% after adding the friction resistance term. The optimization of snow plow model greatly improves the accuracy of velocity prediction and provides an effective reference for the design of device structure and the calculation of energy efficiency.

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Analysis and optimization of acceleration model in coaxial plasma gun in pre-fill mode

Zhang,

Sun,

et al. 2023

Experimental study on coaxial gun pulse discharge plasma density change in transport process

Yang¹,

Zhang²,

Yan³

et al. 2017

Coaxial gun discharge plasma with high density and velocity has a number of potential applications in fusion energy, plasma refueling, disruption mitigation in tokamaks, plasma space propulsion, acceleration of dust particles to hypervelocity etc., and thus has become an important research topic in fields of nuclear physics and aerospace engineering. In this paper, we report the experimental investigation on electrical and transport characteristics of coaxial gun discharge plasma. Based on electrical and optical diagnoses, the discharge voltage, discharge current and axial velocity of plasma transport are measured. Meanwhile, the emission spectrum technology is employed to measure the Stark broadening of H spectral line and then plasma density is calculated. The experimental results show that the discharges in the coaxial gun present a feature of multiple discharges and blow-by instability phenomena are observed by photomultiplier acquired signals. In addition, the plasma velocity and density in the transport process are not constant. It is found that the axial plasma velocity in the transport process decreases due to mass gain caused by the snowplow model and the change tendency of plasma density in the transport process is dependent on various settings. A systematic study has been carried out for exploring plasma density change in transport process, and different experimental parameters are adopted in order to further analyze the physical mechanism of plasma density change in transport process. When the air pressure in the coaxial gun is changed from 4.0 Pa to 10 Pa, for 1.08 kJ applied power energy, an obvious difference appears in transport properties of plasma density, i.e., plasma density increases gradually in 4.0 Pa air while it increases first and then decreases in 10 Pa air. However, the plasma density increases continually in air pressure of 10 Pa when the power energy is increased to 7.68 kJ. Moreover, when the working gas is replaced with argon and discharge setting is 4.0 Pa pressure and 1.08 kJ applied power energy, the plasma density decreases continually in the transport process. The distinct behaviors, as analyzed, are mainly caused by plasma energy transformation difference in the transport process. As it is known, the plasma movement at high velocity in coaxial guns can ionize neutral particles and consume its energy, which results in the increasing plasma density and the decreasing electron and ion temperatures in the transport process. Then, a maximum density is present in the transport process when the electron and ion temperatures are lower than that at which gas ionization occurs. The axial location of maximum density changes with applied power energy, working gas pressure and species, which means that plasma energy transformation and density change properties in transport process strongly rely on different external parameters. The study provides some insight into how to better apply the coaxial gun discharge plasma to practical engineering field.

Comparative study of positive and negative pulsed discharge plasma characteristics of coaxial gun

Yu¹,

Qi²,

Zhao³

et al. 2020

The coaxial gun plasma generated by pulsed discharge possesses the characteristics of high speed and high density, and has potential application value in the field of fusion, space propulsion and astrophysics. In this paper, the effect of positive and negative pulsed discharges on plasma characteristics are investigated and a theoretical model for analyzing the morphology of positive and negative pulsed current sheets is proposed. Positive and negative pulsed discharges are realized by changing the direction of the rectifier diode in the pulse power supply to change the direction of the recharging current. Through theoretical analysis, and measurements by using photodiode, Pearson probe, magnetic probe, HD camera, fast-framing camera and RGB image processing, the plasmas generated by positive and negative pulsed discharges are compared and investigated. Most of experimental diagnoses concentrate on investigating the plasma behavior in the coaxial gun muzzle on a microsecond-order time scale. Because radial and axial transport characteristics of plasma change little, we think, the plasma characteristics in the muzzle still depend on the characteristics of plasma in the coaxial gun. Therefore, the conclusion of the theoretical analysis of the current sheet in the coaxial gun is still valid for the plasma in the muzzle. The theoretical analysis shows that the positive pulsed current sheet presents a parabolic shape and the negative pulsed current sheet displays a convex shape, which makes the negative pulsed current sheet sweep more efficiently and a large amount of plasma is concentrated near the inner electrode, namely the cathode, so the negative pulsed plasma is denser. For the positive pulsed plasma, near the inner electrode the plasma is thin and the magnetic pressure is powerful, and near the outer electrode, the plasma is dense and the magnetic pressure is weak. Therefore, the positive pulsed plasma is faster in movement speed but easier to split, and because of its dispersion, its transport stability is not so good as that of the negative pulsed plasma. The experimental results accord with the theoretical analyses. The final conclusion shows that under the same discharge parameters, the positive pulsed discharge produced plasma is faster in movement speed but more likely to split, and the negative pulsed discharge created plasma is denser in density and more stable. Therefore, for obtaining a higher density plasma, the negative pulsed discharge is recommended, and for achieving a high-speed plasma source, the positive pulsed discharge is advised to be adopted.