Effect of argon and oxygen gas concentration on mode transition and negative ion production in helicon discharge

Abstract

In this paper, the effect of mixing of argon and oxygen gas on the mode transition and negative ion production in the helicon discharge is investigated. In the source chamber of the experimental setup, argon–oxygen gas mixture plasma is produced by applying RF power from 100 W to 2000 W at an applied magnetic field of 0.03 T. In this experiment, the total flow rate is kept at 200 SCCM, corresponding to the working pressure of 4–5 × 10−1 Pa. The mode transition to helicon discharge is investigated by varying the concentration of these two gases. To the best of our knowledge, the literature survey indicates this to be the first study of the influence of the mixing of oxygen–argon gas on the mode transition from the inductive to the helicon mode. It is observed that an increase in the concentration of oxygen gas in the discharge shifts mode transition toward higher RF power values, indicating the influence of the nature of the working gas on the transition to the inductive as well as to the helicon mode. The variation of the electron density and temperature is explained in terms of particle and power balance equation. In the source and in the downstream expansion chamber, the effect of the concentration of argon gas on the negative ion production in oxygen discharge is also studied, and the results are explained in terms of various reactions involved in the production and loss of negative ions.

Plasma sheath with multi‐species of positive ions and surface produced negative ions

“…For all cases of investigation, we keep Ψ p = 5 and 𝛾 = 15, unless mentioned otherwise. The value of Ψ s can be determined for different 𝛼 0 , following the Equation (23). For a simple electronegative plasma, the equation has a multi-valued solution in the range 1.569 < 𝛼 0 < 4.951.…”

“…[12][13][14][15][16][17] The electronegative plasma sheath under different conditions has already been widely explored. [18][19][20][21][22][23] However, with the advent of fusion research, interest has grown to study the electronegative sheath with negative ion emitting wall. [5,9,24,25] It has been shown earlier [5,14,26] that if the temperature ratio of the electrons and volume negative ions exceed a value of 5 + √ 24, the sheath edge electric potential becomes multi-valued with respect to the electronegativity.…”

Changing pattern of N2 dissociation in N2–Ar RF plasma during E–H mode transition

“…A half-helical antenna is wrapped around the source chamber to deliver the applied RF power into the system. The complete description of the system is discussed elsewhere [36,39]. After production of the plasma in the source chamber, it is allowed to expand in the expansion chamber.…”

E-H mode transitions and high-energy electron characteristics of helical antenna coupled plasma

“…They showed that regardless of whether there is a magnetic field, the metastable state is an important feature affecting ionization. The presence of a static axial component of the magnetic field also affects plasma properties [30,31], which results in a plasma anisotropy that complicates discharges. Generally, the metastable state is believed to be produced through the collisions of high-energy electrons with ground-state particles [32,33].…”