Fluid description of the energy absorption in microwave discharges: a new perspective

Centro de Física dos Plasmas, IST, Av. Rovisco Pais, 1049-001 Lisboa Codex, Portugal

Corresponding author: llalves@alfa.ist.utl.pt

Received: 30 October 2003
Revised: 12 January 2004
Accepted: 18 February 2004
Published online: 7 April 2004

Abstract

The paper discusses the wave-plasma energy coupling in cylindrical microwave discharges produced in argon, operating at frequency 2.45 GHz, average electron densities between 5×10¹¹−3×10¹² cm⁻³ and pressures from 10⁻³ to a few torr. The study focus on a special propagation mode called surface wave (SW), whose field distribution presents a maximum intensity near the discharge wall. Moreover, the influence of the space-charge sheath in the discharge energy deposition is carefully analysed. Simulation results show that the absorption of energy from the SW occurs in two different modes (convection and friction) depending on pressure, and that the transition between them is observed around 10 mtorr pressure, regardless of the electron density. The paper proposes a definition for the discharge yield, which can be of interest in optimizing the operation conditions of gas discharges for applications.