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

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.

Axial profiles of argon helicon plasma by optical emission spectroscope and Langmuir probe

We present the axial profiles of argon helicon plasma measured by a local optical emission spectroscope(OES) and Langmuir RF-compensated probe. The results show that the emission intensity of the argon atom lines(750 nm, 811 nm) is proportional to the plasma density determined by the Langmuir probe. The axial profile of helicon plasma depends on the discharge mode which changes with the RF power. Excited by helical antenna, the axial distribution of plasma density is similar to that of the external magnetic field in the capacitive coupled mode(E-mode). As the discharge mode changes into the inductively coupled mode(H-mode), the axial distribution of plasma density in the downstream can still be similar to that of the external magnetic field, but becomes more uniform in the upstream. When the discharge entered wave coupled mode(W-mode), the plasma becomes nearly uniform along the axis, showing a completely different profile from the magnetic field. The W-mode is expected to be a mixed pattern of helicon(H) and Trivelpiece-Gould(TG) waves.

Study of double-chamber air arc plasma torch and the application in solid-waste disposal

Arc plasma can be applied in hazardous solid waste disposal for higher temperature than common heating methods,but some practical issues exist in practical engineering application.In this study,an air arc plasma torch with double chambers and magnetic controlling is designed to realize wide variable power and long electrode life.The detailed characteristics and laws of the air arc are studied.The condition parameters of arc current(I),air flow rate(G)and the structure parameters of inlet area ratios and electrode diameters influence both the arc voltage and arc root positions.The arc rotating driven by magnetic field effectively lengthens the electrode life.The gasification process and product of organic wastes by air plasma are influenced largely by the waste compositions and the air flow rate.A furnace structure with more even atmosphere and longer residence time should be considered for better gasification.Oxygen-deficient environment is important to suppress NOxformation during the application of air plasma.Inorganic solid wastes can be melt by the air plasma and cooled down to form compact vitreous structures in which heavy metals can be locked and the leaching rates significantly decrease down.