Study of the plasma disk generated from the head-on collision of two plasma jets

Po-Yu Chang^1*, Che-Yu Liu¹, Ming-Hsiang Kuo¹, Yen-Cheng Lin¹, Song-Yi Lin², Chih-Jui Hsieh¹, Cheng-Han Du¹, Chih-Hsien Liu¹, Yi-Zuo Pan¹

¹Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan city, Taiwan
²Department of Earth and Environmental Sciences, National Chung-Cheng University, Chia-yi County, Taiwan

* Presenter:Po-Yu Chang, email:pchang@mail.ncku.edu.tw

We are studying the dynamics of a plasma disk, which is commonly observed in the universe. For example, an accretion disk is a plasma disk rotating around a massive object in astrophysics. To generate the plasma disk in the laboratory, two counter-streaming plasma jets are first generated by a bi-conical-wire array driven by a 1-kJ pulsed-power system. The bi-conical-wire array consists of two identical conical-wire arrays facing against each other. Each of them is made of four tungsten wires with a diameter of 20 μm. The inclination angle, the diameter of the bottom and the height of conical-wire arrays are 30°, 5 mm, and 10 mm, respectively. When the pulsed current with a peak of ~135 kA and a rise time of ~1.6 μs flows through the bi-conical-wire array, the tungsten wires are vaporized and ionized by the current via ohmic heating. The azimuthal magnetic field generated by the current push the tungsten plasma toward the center. Counter-streaming plasma jets are generated when the plasma merges on the axis of the bi-conical-wire array. Finally, the plasma disk is formed when two plasma jets collide with each other at the center of the bi-conical-wire array. To observe the plasma disk, a suite of time-resolved optical diagnostics using a 5-ns Q-switch laser in 532 nm. It includes an interferometer, a shadowgraph image, a schlieren image, and a polarimeter for measuring the density, size, velocity, and magnetic fields of the plasma disk. Experimental results will be given.

Keywords: Plasma jet, Plasma disk, Pulsed-power system, Conical-wire array, Bi-conical-wire array