Different operational regimes in a helicon plasma source

Abstract

The characterization of a helicon plasma source has been done in argon plasmas using a rf compensated Langmuir probe. It is now well known that helicon discharges exhibit three modes of operation: a capacitive mode (known as the E mode), which is a low-density mode (around 109 cm−3), an inductive mode (known as the H mode) with higher densities (1010 cm−3), and a helicon-wave sustained mode (known as the W mode) with very high densities (1011–1012 cm−3). By increasing the injected power, the transitions between these modes can be observed and correspond to sudden increases of the plasma density and of the glow brightness. In this article the performances of the helicon source in terms of density and plasma potential are presented and discussed. Transitions between the different coupling modes are observed and explained thanks to two phenomenological models and a good agreement is found between the experimental values and the model results. It has been shown that the main parameter, which determines the coupling mode, is the plasma density, which depends on the rf power and the gas pressure. So the transition between E and H modes is observed when the density reaches a critical value: for this value the skin depth δ is equal to the radius of the Pyrex tube. A similar result has been shown for the H–W transition: a minimum density, the value of which depends on the magnetic field amplitude, is necessary to observe the first longitudinal helicon-wave mode. This value is also directly linked with the geometry of the reactor and of the antenna.

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

“…The experimental set-up was previously described 60,70,71 . Briefly, an HOPG surface is centered in the diffusion chamber of a low-pressure helicon plasma reactor.…”

In‐plane and out‐of‐plane defects of graphite bombarded by H, D and He investigated by atomic force and Raman microscopies

“…Samples were disposed on a DC biased sample holder and exposed to hydrogen, deuterium and helium RF plasmas (0.2 Pa, 100 W in the case of hydrogen and deuterium, and 0.4 Pa and 60 W in the case of helium) during 15 min using the set up described in. [54,55] Due to the plasma sheath, ions are oriented perpendicular to the sample. Mass spectrometry measurements show that the dominant ion in the hydrogen (deuterium) plasma is H 2 + (D 2 + ):~90% of the total ion amount.…”

Positive sheath behaviour in low pressure Argon plasma

“…The matching box is an L type with a 0-2000 pF tune capacitor and a 0-1000 pF load capacitor and is controlled manually. The total volume of the reactor is around 10 l [12]. A base pressure lower than 10 À5 Pa (penning gauge limit) is achieved in the chamber by mean of a 150 l/s turbomolecular pump.…”

“…The experimental set-up is described in [12]. It is an helicon reactor, (PHISIS, plasma helicon to irradiate surfaces in situ) which consists of an upper source chamber and a lower diffusion chamber.…”