V. A. Kadetov

Characterization of stationary and pulsed inductively coupled RF discharges for plasma sterilization

Sterilization of bio-medical materials using radio frequency (RF) excited inductively coupled plasmas (ICPs) has been investigated. A double ICP has been developed and studied for homogenous treatment of three-dimensional objects. Sterilization is achieved through a combination of ultraviolet light, ion bombardment and radical treatment. For temperature sensitive materials, the process temperature is a crucial parameter. Pulsing of the plasma reduces the time average heat strain and also provides additional control of the various sterilization mechanisms. Certain aspects of pulsed plasmas are, however, not yet fully understood. Phase resolved optical emission spectroscopy and time resolved ion energy analysis illustrate that a pulsed ICP ignites capacitively before reaching a stable inductive mode. Time resolved investigations of the post-discharge, after switching off the RF power, show that the plasma boundary sheath in front of a substrate does not fully collapse for the case of hydrogen discharges. This is explained by electron heating through super-elastic collisions with vibrationally excited hydrogen molecules.

Phase resolved measurement of anisotropic electron velocity distribution functions in a radio-frequency discharge

Oscillating radio-frequency (RF) electric fields penetrating into a plasma lead to a corresponding oscillation of the electron velocity distribution function. Here we report on the first time measurement of this oscillation by Thomson scattering in a low-pressure inductively coupled plasma. The local current density is inferred by combining the oscillation amplitude with the plasma density, also resulting from Thomson scattering. The results are compared with a novel emission spectroscopic technique, RF modulation spectroscopy, which also provides direct determination of the electron oscillation velocity.

Thomson scattering in low temperature helium plasmas of a magnetic multipole plasma source

Measurements of electron density and temperature of helium plasmas in a cw running magnetic multipole plasma source by repetitively laser-pulsed 90° Thomson scattering are reported. This is the first experiment in which this technique has been applied to such plasmas. Measurements are performed at a helium gas pressure of pg = 5 Pa, the discharge voltage was Ud = 100 V, the discharge current was 5 A ≤ Id ≤ 30 A, and the cathode heating current was 80 A ≤ Ih ≤ 140 A. Electron energy distribution functions obtained from the Thomson scattering spectra are studied. The obtained plasma parameters are electron temperature 1.5 eV ≤ kTe ≤ 5 eV and density 1012 cm−3 ≤ ne ≤ 4 × 1012 cm−3, respectively. The sensitivity of detection of the experiment is in the range of 109 electrons and the accuracy of the electron temperature and electron density are specified to 15% and 20%, respectively. In addition, the neutral density and helium gas temperature are obtained from the Rayleigh component of the scattered spectra. Langmuir probe measurements are performed under the same plasma conditions and a comparison of the results with Thomson scattering shows good agreement between the two diagnostics.

Plasma diagnostics by laser spectroscopic electric field measurement

Laser spectroscopic electric field measurements have the potential to become a versatile tool for the diagnostics of low-temperature plasmas. From the spatially and temporally resolved field distribution in the sheath close to electrodes or surfaces in general, a broad range of important plasma parameters can be inferred directly: electron temperature; ion density distribution; displacement-, ion-, electron-diffusion current density; and the sheath potential. Indirectly, the electron and ion energy distribution functions and information on the ion dynamics in the sheath can also be obtained. Finally, measurements in the quasi-neutral bulk can also reveal even the plasma density distribution with high spatial and temporal resolution. The basic concepts for analysis of the field data are introduced and demonstrated by examples in hydrogen discharges.

Diagnostics for the Dynamics of Power Dissipation in Technologically used Plasmas

Radio frequency (rf) discharges are widely used for technological applications. Despite this, power dissipation mechanisms in these discharges are not yet fully understood. The limited understanding is mainly caused by the complexity of underlying phenomena and very restricted experimental access. Recent advances in phase resolved optical emission spectroscopy (PROES) in combination with adequate modeling of the population dynamics of excited states allow deeper insight into underlying fundamental processes. This paper discusses the application of PROES in a variety of rf‐discharges, such as: capacitively coupled plasmas (CCP), dual‐frequency CCP (2f‐CCP), inductively coupled plasmas (ICP), and magnetic neutral loop discharges (NLD).