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Plasma Sci. Technol. ›› 2018, Vol. 20 ›› Issue (7): 075402.doi: 10.1088/2058-6272/aab4f1

• Low Temperature Plasma • Previous Articles     Next Articles

Study of axial double layer in helicon plasma by optical emission spectroscopy and simple probe

Gao ZHAO (赵高)1, Wanying ZHU (朱婉莹)1, Huihui WANG (王慧慧)1, Qiang CHEN (陈强)2, Chang TAN (谭畅)3 and Jiting OUYANG (欧阳吉庭)1,4   


  1. 1 School of Physics, Beijing Institute of Technology, Beijing 100081, People’s Republic of China
    2 Laboratory of Plasma Physics & Materials, Beijing Institute of Graphic Communication, Beijing 102600, People’s Republic of China
    3 Shanxi Key Laboratory of Plasma Physics and Applied Technology, Xi’an Aerospace Propulsion Institute, Xi’an 710100, People’s Republic of China  
  • Received:2017-10-20 Published:2018-03-07
  • Supported by:

    This study is supported by National Natural Science Foundation of China (No. 11475131).


In this work we used a passive measurement method based on a high-impedance electrostatic probe and an optical emission spectroscope (OES) to investigate the characteristics of the double layer (DL) in an argon helicon plasma. The DL can be confirmed by a rapid change in the plasma potential along the axis. The axial potential variation of the passive measurement shows that the DL forms near a region of strong magnetic field gradient when the plasma is operated in wave-coupled mode, and the DL strength increases at higher powers in this experiment. The emission intensity of the argon atom line, which is strongly dependent on the metastable atom concentration, shows a similar spatial distribution to the plasma potential along the axis. The emission intensity of the argon atom line and the argon ion line in the DL suggests the existence of an energetic electron population upstream of the DL. The electron density upstream is much higher than that downstream, which is mainly caused by these energetic electrons.

Key words: helicon discharge, double layer, plasma diagnosis, plasma potential