Dissipated electrical power and electron density in an RF atmospheric pressure helium plasma jet

Abstract

Atmospheric pressure plasmas have great potential, especially for biomedical applications, due to the large number of reactive species produced. In particular with regard to these applications, the comparability of processes through appropriate control of plasma parameters is essential for treatment safety. Here we present a method for the operando determination of absolute absorbed power in an RF atmospheric pressure helium plasma discharge using miniaturized probes. A detailed error analysis demonstrates the reliability of the measured power values. With the help of a global model, the sheath width and electron density (4 × 1016–11 × 1016 m−3) are derived from these power measurements and compared to literature. The results and thus the validity of the electrical model are confirmed by a second, independent characterization method using optical emission spectroscopy and time-averaged imaging.

Characterization of an RF-driven argon plasma at atmospheric pressure using broadband absorption and optical emission spectroscopy

“…Finally, the sheath width was determined by the difference in the number of pixels when the intensity drops to 61% of the intensity at the sheath edge. 30,45 The sheath edge is marked by a horizontal gray dashed line in Fig. 9.…”

“…An independent determination of n e is obtained by the analysis of an equivalent electrical circuit for a homogeneous RF plasma as reported in 30,43 . This method is based on a simplified homogeneous RF discharge model without considering sheath effects (stochastic and ion heating), 44,45 while isolating the influence of the bulk plasma and the sheaths.…”

“…The rates of electron-neutral momentum transfer (ν m ) for argon and helium at atmospheric pressure are 4.03 × 10 12 s −1 and 1.52 × 10 12 s −1 , respectively. 46 Using the measured sheath capacitance X s , the sheath width can be estimated as follows: 30,44 s…”

“…The electron temperature and density are determined from continuum radiation emission spectroscopy and compared with the electron density obtained from a previously reported electrical impedance measurement approach. 30 The experimental setup, optical diagnostics and a detailed procedure to determine the electron temperature and density as well as the absolute densities from the measured absorption data are described before we present the results. The estimated electron properties and the spatially distributed densities of atoms in the metastable and resonant states of Ar across the plasma gap allow to discuss the production and destruction mechanisms of the excited atoms of Ar in detail.…”

Vacuum ultraviolet spectroscopy of cold atmospheric pressure plasma jets

“…One electrode is powered by a sinusoidal RF voltage at a frequency of 13.56 MHz and the other electrode is grounded. Typically absorbed powers are of the order of 1 W. [ 22 ] The APP jet is operated at gas flow rates of typically 1.4 slm of pure helium (He) or argon (Ar) with optional small admixtures (<1%) of argon or molecular gases such as oxygen (O 2 ) or nitrogen (N 2 ). In this study, 5.0 purity gases were used.…”