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同轴枪放电可以产生高速度、高密度及高能量密度的等离子体射流，在等离子体空间推进、天体物理和高温核聚变等研究领域具有广泛的应用。基于同轴枪的实际应用，等离子体速度、密度、纯净度是评估等离子体特性的重要参量。本实验通过对等离子体光电流信号和发射光谱的测量及放电图像的拍摄，研究了不同放电电流和气压对同轴枪放电等离子体的动力学特性、电子密度与杂质发射光谱的影响。实验结果表明：气压为10 Pa，放电电流为30-70 kA时，等离子体在枪内的加速时间随电流的增大而缩短，等离子体中阳极和阴极杂质光谱均随电流的增大而增强；放电电流为40 kA，气压为10-70 Pa时，等离子体加速时间随气压的增大而增长，等离子体中阴极杂质光谱强度随气压的增加不断降低，而阳极杂质光谱强度却是逐渐增加的，不过其增长速率逐渐减小。分析认为，不同放电电流和气压决定了等离子体获能、加速特性及电子密度，协同影响金属杂质特性。同轴枪喷口处发生等离子体箍缩效应与高密度电弧在枪内加速时间是影响阳极烧蚀的重要因素，阴极材料的杂质是离子轰击溅射产生的，主要依赖于离子携带的能量。The coaxial gun discharge could produce plasma jet with high velocity, high density and high energy density, which has a wide range of applications in plasma space propulsion, simulation of the interaction between edge local mode and wall materials in ITER, fuel injection in magnetic confinement fusion devices, and laboratory astrophysics, etc. In the pre-filled discharge mode, the plasma current sheet is formed near the insulating layer surface and moves toward the end of the coaxial gun under Lorentz force. Plasma velocity, density and purity characteristics are very important research contents for the actual application of coaxial gun. Emission spectrometry as a non-interference method can be used to diagnose a variety of plasma physical properties. In this experiment, the effects of different discharge currents and gas pressure on the plasma dynamics, electron density and impurity emission spectra of coaxial gun discharge plasma are studied through the measurement of plasma photocurrent, emission spectra and the shooting of discharge images. The experimental results show that the acceleration time of the plasma in the gun decreases with the increase of the current in 30~70 kA when the gas pressure is 10 Pa, the spectra of anode and cathode impurities in plasma increase with the current amplitude. When the discharge current is 40 kA and the gas pressure is in 10~70 Pa, the acceleration time of plasma increases with the increase of gas pressure, and the spectral intensity of the cathode impurity in the plasma decreases with the increase of the pressure, while the spectral intensity of the anode impurity increases gradually, but its growth rate decreases continuously. According to the analysis, the presence of metallic impurities originating from the electrode material limits the jet velocity of the plasma and is the main cause of the deviation from theoretical value. The plasma pinch effect at the nozzle of coaxial gun and the acceleration time of high-density arc in the gun are important factors affecting anode ablation. The impurity of cathode material is produced by ion bombardment sputtering, which mainly depends on the energy attached to ions. Therefore, a reasonable choice for discharge parameters is the key factor to obtain optimal plasma characteristics during the discharge of the coaxial gun.
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Keywords:
- coaxial gun /
- plasma /
- photocurrent /
- emission spectrum
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