Microwave discharge in H₂: influence of H-atom density on the power balance

Abstract

We investigate a source of H atoms generated by a low-pressure surface wave discharge (2.45 GHz). We study the influence of microwave power both on the discharge characteristics on the H atom density, which has been measured by actinometry. Dissociation levels of H2 are much higher (75%) at low microwave power than at high power (10%). Unlike what has been found in oxygen surface wave plasmas, discharge characteristics depend strongly on microwave power, due to an important coupling between discharge equilibrium and kinetics of the atomic hydrogen. These results are explained taking into account the effect of discharge tube wall temperature on atomic recombination. The wall recombination probability gamma is estimated as a function of the microwave power: it ranges from 6*10-3 to 6*10-2, which is very high in comparison with values determined previously under post-discharge conditions.

Travelling-wave-sustained discharges

“…As it was mentioned in Section 2, the behaviour of the SWSDs in hydrogen contradicts the usual feature observed in all the other gases experimentally studied, namely extension in length of the discharge with the increase of the applied power without changes of the axial gradient of the plasma density. The experiments [129] in hydrogen discharges show something different: the axial profile of the electron concentration is different for each given value of the applied power and its gradient becomes smaller when the applied power is higher. As the discussions on the results from the model presented here show, this peculiar behaviour of the axial profile of the electron concentration in SWSDs in hydrogen is due to the mechanism of self-consistency of hydrogen discharges which is based on the important role of the atom yield in these discharges.…”

“…The increase of the discharge length with the increase of the applied power without changes of the axial gradient of the plasma density, observed in many experiments, was also considered as a general feature of the SWSDs. However, results from experiments in hydrogen [129] do not permit such a statement any more. The experiments furthermore show complicate behaviour of the axial plasma density variations in the vicinity of the wave launcher [4] as well as a fast drop of the plasma density at the discharge end [130].…”

Diagnostics of the magnetized low-pressure hydrogen plasma jet: Molecular regime

“…Later the technique was used for monitoring hydrogen atoms with argon as an actinometer. [47][48][49] This requires a mixture of additional components to a minimum concentration to be able to detect the emission of the correspondent spectral lines. This inevitably will lead to a certain perturbation of the plasma properties.…”

Determination of the degree of dissociation in an inductively coupled hydrogen plasma using optical emission spectroscopy and laser diagnostics

“…They are used in materials treatments such as reduction of oxides on surfaces and deposition of thin films [5].…”