Effect of length of outer electrode on plasma characteristics in coaxial gun

Song Jian; Li Jia-Wen; Bai Xiao-Dong; Zhang Jin-Shuo; Yan Hui-Jie; Xiao Qing-Mei; Wang De-Zhen

doi:10.7498/aps.70.20201724

Abstract

The dense plasma produced by a coaxial gun possesses an extremely high velocity (~100 km/s), electron density (~10¹⁶ cm^–3) and energy density (~1 MJ/m²), which has great potential applications in fusion energy, astrophysics and aerospace physics. Through the measurements of electrical and optical signals, as well as the temporal and spatial evolution of the ejected plasma, the plasma characteristics of two different outer electrodes in length are investigated. As the outer electrode is lengthened, the axial velocity, the collimation and the propagation distance of plasma are all enhanced while the electron density and the optical intensity decrease, this can be ascribed to the extension of plasma column formed by Z-pinch on the central electrode during the discharge. When moving across the end of the inner electrode, the plasma sheet can be stretched into a bow shape due to the Coulomb and Lorentz force. With the appearance of axial current, part of the plasma sheet near the head of the inner electrode converges toward the center, and then generates a plasma column with much higher electron density and temperature. On the one hand, the extending of the plasma column can match the outer electrode in length and therefore the plasma column gains longer accelerating time in the coaxial gun resulting in the growing of ejected velocity. On the other hand, it also brings higher losses of the charged particles and recombination rates between the plasma and the wall of electrodes, resulting in the decrease of electron density and optical intensity. Moreover, the axial kinetic energy, the electron density and the radial Lorentz force of ejected plasma are jointly responsible for the collimation and the attenuation characteristics in its propagation. As the axial velocity and electron density increase, the axial kinetic energy of ejected plasma increases, which induces a longer propagating distance. In contrast, with the electron density and radial Lorentz force growing, the density gradient and thermal expansion of ejected plasma are enhanced correspondingly, leading the energy density to decrease and finally the propagating distance to shorten. In conclusion, a high collimation plasma jet trends to generate in a high axial velocity, electron density and with a relatively long outer electrode.

Keywords:

Authors and contacts

1.
Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams of the Ministry of Education, School of Physics, Dalian University of Technology, Dalian 116024, China
2.
Space Environment Simulation Research Infrastructure, Harbin Institute of Technology, Harbin 150006, China

Corresponding author: Song Jian, songjian@dlut.edu.cn ; Xiao Qing-Mei, qmxiao@hit.edu.cn ;

Funds: Project supported by the National Natural Science Foundation of China (Grant No. 51807020), the National Key R&D Program of China (Grant No. 2017YFE0301206), and the Fundamental Research Funds for the Central University of Ministry of Education of China (Grant No. DUT20RC(4)008)

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References

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Cited By

图 1 实验装置图

Figure 1. Schematic diagram of experimental equipment.

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图 2 不同长度外电极同轴枪在充电电压为5 kV, 气压为10 Pa放电条件下的电压、电流以及光电流波形　(a) 短外电极; (b) 长外电极

Figure 2. Typical electrical and optical signals of discharge in a coaxial gun with (a) short and (b) long external electrode. V = 5 kV and P = 10 Pa.

DownLoad: Full-Size Img PowerPoint

图 3 气压10 Pa时, 同轴枪放电等离子体速度随充电电压的变化

Figure 3. The variation of plasma velocity with the charging voltage of the coaxial gun at 10 Pa.

DownLoad: Full-Size Img PowerPoint

图 4 高速相机拍摄的同轴枪放电等离子体图像, 充电电压5 kV, 气压10 Pa, 曝光时间为5 μs　(a) 短外电极; (b) 长外电极

Figure 4. High-speed camera photographs of discharge in a coaxial gun with (a) short and (b) long outer electrode. V = 5 kV, P = 10 Pa, the exposure time is 5 μs.

DownLoad: Full-Size Img PowerPoint

图 5 短外电极同轴枪放电中的等离子体片发展过程

Figure 5. Development of plasma sheet during discharge in a coaxial gun with short outer electrode.

DownLoad: Full-Size Img PowerPoint

图 6 长外电极同轴枪放电中的等离子体片发展过程

Figure 6. Development of plasma sheet during discharge in a coaxial gun with long outer electrode.

DownLoad: Full-Size Img PowerPoint

图 7 同轴枪在气压为10 Pa的放电条件下, 电子密度随充电电压的变化

Figure 7. The variation of electron density with the charging voltage of the coaxial gun at 10 Pa.

DownLoad: Full-Size Img PowerPoint

图 8 数码相机拍摄的不同外电极长度条件下的放电照片　(a) 短外电极; (b) 长外电极. 气压为10 Pa, 充电电压为7 kV, 曝光时间为1 s

Figure 8. Digital camera photographs of discharge in a coaxial gun with (a) short and (b) long outer electrode. P = 10 Pa, V = 7 kV, the exposure time is 1 s.

DownLoad: Full-Size Img PowerPoint

图 9 同轴枪在气压为10 Pa的放电条件下, 扩散角随充电电压的变化

Figure 9. The variation of diffusion angles with the charging voltage of the coaxial gun at 10 Pa.

DownLoad: Full-Size Img PowerPoint

map

[1]	Marshall J 1960 Phys. Fluids 3 134
[2]	Hagerman D C, Osher J E 1963 Rev. Sci. Instrum. 34 56 Google Scholar
[3]	Subramaniam V, Raja L L 2017 Phys. Plasmas 24 062507 Google Scholar
[4]	Cheng D Y 1971 AIAA J. 9 1681 Google Scholar
[5]	Cassibry J T, Thio Y C F, Markusic T E, Wu S T 2006 J. Propul. Power 22 628 Google Scholar
[6]	Wang M Y, Choi C K, Mead F B 1992 9th Symp on Space Nuclear Power Systems Albuquerque NM, January 12–16, 1992 p30
[7]	Bellan P M, You S, Hsu S C 2005 Astrophys. Space Sci. 298 203 Google Scholar
[8]	Bellan P M 2005 Phys. Plasmas 12 058301 Google Scholar
[9]	Golingo R P, Shumlak U, Nelson B A 2005 Phys. Plasmas 12 062505 Google Scholar
[10]	Ticos C M, Wang Z H, Wurden G A, Kline J L, Montgomery D S 2008 Phys. plasmas 15 103701 Google Scholar
[11]	Parks P B 1988 Phys. Rev. Lett. 61 1364 Google Scholar
[12]	Underwood T C, Loebner K T, Cappelli A 2017 High Energy Density Phys. 23 73 Google Scholar
[13]	Hart P J 1962 Phys. Fluids. 5 38 Google Scholar
[14]	Chow S P, Lee S, Tan B C 1972 J. Plasma Phys. 8 21 Google Scholar
[15]	Cheng D Y 1970 Nucl. Fusion 10 305 Google Scholar
[16]	Witherspoon F D, Case A, Messer S J, Bomgardner R, Phillips W, Brockington S, Elton R 2009 Rev. Sci. Instrum. 80 083506 Google Scholar
[17]	Hart P J 1964 J. Appl. Phys. 35 3425 Google Scholar
[18]	Milanese M M, Niedbalski J, Moroso R L 2007 IEEE Trans. Plasma Sci. 35 808 Google Scholar
[19]	Lie T N, Rhee M J, Chang C C 1967 AIAA 67 1
[20]	Michels C J, Ramins P 1964 Phys. Fluids 7 71 Google Scholar
[21]	张俊龙, 杨亮, 闫慧杰, 滑跃, 任春生 2015 64 075201 Google Scholar Zhang J L, Yang L, Yan H J, Hua Y, Ren C S 2015 Acta Phys. Sin. 64 075201 Google Scholar
[22]	Gloersen P, Gorowitz B 1966 AIAA J. 4 436 Google Scholar
[23]	Hsu S C, Awe T J, Brockington S, Case A, Cassibry J T, Kagan G, Messer S J, Stanic M, Tang X, Welch D R, Witherspoon F D 2012 IEEE Trans. Plasma Sci. 40 1287 Google Scholar
[24]	余鑫, 漆亮文, 赵崇霄, 任春生 2020 69 035202 Google Scholar Yu X, Qi L W, Zhao C X, Ren C S 2020 Acta Phys. Sin. 69 035202 Google Scholar
[25]	赵崇霄, 漆亮文, 闫慧杰, 王婷婷, 任春生 2019 68 105203 Google Scholar Zhao C X, Qi L W, Yan H J, Wang T T, Ren C S 2019 Acta Phys. Sin. 68 105203 Google Scholar
[26]	漆亮文, 赵崇霄, 闫慧杰, 王婷婷, 任春生 2019 68 035203 Google Scholar Qi L W, Zhao C X, Yan H J, Wang T T, Ren C S 2019 Acta Phys. Sin. 68 035203 Google Scholar
[27]	Berkery J W, Choueiri E Y 2006 Plasma Sources Sci. Technol. 15 64 Google Scholar
[28]	Chow S P, Lee S, Tan B C 1972 J. Plasma Phys. 1 21
[29]	Chen Y H, Lee S 1973 Int. J. Electron. 35 341 Google Scholar
[30]	Lie T N, Ali A W, Mclean E A, Kolb A C 1967 Phys. Fluids 10 1545 Google Scholar
[31]	Markusic T E, Thio Y C F 2002 38th AIAA Joint Propulsion Conference Indianapolis, Indiana, July 7–10, 2002 p1

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