Inductive Radio-frequency Discharge Research Articles

Validity of Electron Temperature Measurement by Using Boltzmann Plot Method in Radio Frequency Inductive Discharge in the Atmospheric Pressure Range

The validity of electron temperature measurement using the Boltzmann plot method was investigated in a radio frequency (rf) inductive discharge in the atmospheric pressure range. Since the Boltzmann plot method requires local thermal equilibrium (LTE), the parameter regions of electron temperature and electron density, in which the Boltzmann plot method is applicable, were analyzed in terms of a comparison of the spontaneous emission and collisional excitation to the excited states. It is observed that in our rf-inductive plasma near the atmospheric pressure range the Boltzmann plot method does not provide an exact measurement of electron temperature because of relatively low electron density, which does not satisfy the calculation criteria. An alternative method employing a combination of the Stark broadening measurement and the Saha-Boltzmann equation was demonstrated to more accurately determine the plasma parameters (electron temperature and electron density).

Measurement of vibrational, gas, and rotational temperatures of H2 (X1Σg+) in radio frequency inductive discharge plasma by multiplex coherent anti-Stokes Raman scattering spectroscopy technique

Translational, rotational, and vibrational temperatures of H2 in radio frequency inductive discharge plasmas at pressures and power release ranges, respectively, of 0.5–8 torr and 0.5–2W∕cm3 have been measured by using multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopy. Computational codes have been developed to determine the rotational and vibrational temperatures and to analyze H2 CARS spectrum for nonequilibrium conditions. The results show a decrease of the vibrational temperature from 4250 to 2800 K by increasing the pressure from 0.5 to 8 torr and a corresponding increase of the rotational temperature from 525 to 750 K.

Electron cyclotron resonance in a weakly magnetized radio-frequency inductive discharge.

The evolution of the electron energy distribution function (EEDF) over a weak magnetic field range is investigated in magnetized radio-frequency (rf) inductive discharges under a collisionless regime where an anomalous skin effect and electron cyclotron resonance (ECR) can occur. A significant change in the low-energy range of the EEDF is found in the ECR condition during the evolution. The observed result reveals the low-energy electrons are efficiently heated by the rf ECR in the presence of the anomalous skin effect. The calculated result of the electron distribution based on kinetic theory is in good agreement with the experiment.

Nonlinear Forces Acting on Electrons in an Inhomogeneous Radio-Frequency Field of an Inductive Discharge

Accounting for the combined effects of the ponderomotive and thermal forces, an improved expression for the ambipolar potential is deduced. It is shown that in weakly ionized radio-frequency inductive discharges the thermal force far exceeds the ponderomotive force.

Inductively-coupled dusty plasma

The results of experimental research of behaviour of microparticles in plasma of inductive radio-frequency discharge are presented. The experiments were performed in inert gases with monodisperse and polydisperse particles. The discharge was initiated by radio-frequency power supply at 27 and 100 MHz. There are presented different kinds of dusty particle structures and conditions of their formation.

Hysteresis and the E-to-H transition in radiofrequencyinductive discharges

Typical inductive discharges, such as are used for plasma processing, exhibit two modes of operation: the true inductive discharge known as the H mode, and a weak capacitive discharge known as the E mode. Experimentally, the transition between these modes as the coil current is increased is clear and is marked by a large increase in discharge power, plasma density and optical emission occurring as the H mode appears. According to simple theory, this transition and the reverse transition occur at a single well defined current. In practice, this is usually not the case. The E-to-H transition occurs at a larger coil current than the H-to-E transition, and a range of currents between these values supports either E or H mode. This effect is called hysteresis. In this paper we show that hysteresis can be understood to arise from nonlinear effects, most notably in the electron power balance equation. We survey various mechanisms that can produce hysteresis and attempt to provide quantitative estimates of their significance.

Ion sources for medical accelerators

Advanced injector systems for proton synchrotrons and accelerator-based boron neutron capture therapy systems are being developed at the Lawrence Berkeley National Laboratory. Multicusp ion sources, particularly those driven by radio frequency, have been tested for these applications. The use of a radio frequency induction discharge provides clean, reliable, and long-life source operation. It has been demonstrated that the multicusp ion source can provide good-quality positive hydrogen ion beams with a monatomic ion fraction higher than 90%. The extractable ion current densities from this type of source can meet the injector requirements for both proton synchrotron and accelerator-based boron neutron capture therapy projects.

Magnetic induction and plasma impedance in a cylindrical inductive discharge

An inductive radio frequency discharge in the cylindrical configuration is modelled as a transformer with the inductive coil taken as the primary circuit and the plasma as the secondary circuit. The mutual inductance between the primary and secondary circuit, the self-inductance of the plasma and the impedance of the plasma are determined theoretically and related to the properties of the plasma evaluated using a global (volume-averaged) discharge model for argon plasma. The azimuthal electric field and the axial magnetic field profile within an inductive discharge in the cylindrical configuration are determined assuming a parabolic electron density profile.

Ion-ion neutralization of iodine in radio-frequency inductive discharges of Xe and I2 mixtures

Xe/I 2 low-pressure electric discharges are being developed as efficient, long-lived ultraviolet lighting sources. In this work the kinetics of low pressure, 0.5–5 Torr, radio-frequency inductively excited discharges sustained in Xe and I2 were investigated to determine the source of radiating states. The diagnostics applied in this study include optical absorption and emission spectroscopy, microwave interferometry, and microwave absorption. We found that in time modulated discharges, the emissions from excited states of atomic iodine decays with time constants of hundreds of microseconds. These observations are consistent with those states being populated by ion-ion neutralization. Electron-ion recombination leading to excited states appears not to be an important source of emission.

On the E - H mode transition in RF inductive discharges

In inductively coupled radio frequency (RF) plasmas a mode transition between a low-power mode with dominant capacitive coupling (E-mode) and a high-power mode with dominant inductive coupling (H-mode) has been frequently reported in the literature. We investigate this transition, which results in an increase of the light emission by up to two orders of magnitude. Furthermore we observe a hysteresis of this mode transition. Two major aspects of the transition are addressed in this paper. First we propose an explanation for the discontinuous character of the mode transition. The analysis is based on a simple, electrodynamic model of the inductive discharge. This analysis shows that a certain minimum maintenance RF coil current is required for the operation of an inductive discharge and that the skin effect of the RF field is essential for stable discharge operation. This point is supported by experimental observations. In the second part of the paper we present a simple, self-consistent analytic description of the discharge, which enables us to calculate the minimum maintenance RF coil current. The theoretical results are found to be in reasonable agreement with the measured minimum maintenance coil currents.

Simulation of kinetic effects in inductive discharges

We show that, under certain conditions of practical interest, radio frequency inductive discharges can exhibit kinetic effects arising from the random thermal motion of electrons. The electrical response of the plasma is altered in this kinetic regime. More power is dissipated than is expected from cold plasma theory and the spatial distributions of the induced currents and fields change. Moment- or fluid-based simulations do not normally include these kinetic effects, but we show that the introduction of an appropriate viscosity into the moment equations can make them accurate in the kinetic regime.

Radio frequency inductive discharge source design for large area processing

Abstract

The electron-energy distribution function in a shielded argon radiofrequency inductive discharge

The electron-energy distribution function (EEDF) and its integrals such as plasma density and effective electron temperature have been measured in an inductively coupled plasma. The EEDFs were measured together with electrical discharge characteristics over a wide range of argon gas pressure between 1 mTorr and 1 Torr. The discharge was maintained by an internal induction coil, which was electrostatically shielded to provide a purely inductive discharge. All measurements were related to RF power dissipated in the plasma. Non-Maxwellian EEDFs were found that differ significantly from those found in capacitive RF discharges and in inductive discharges without or with only partial electrostatic shielding.