High Frequency Plasma Confinement (original) (raw)

Spectral measurements in the plasma of microwave and magnetron discharges

Journal of Physics: Conference Series, 2019

Spectroscopic methods were used to study the parameters of a low-power (≤ 100 W) magnetron discharge plasma, as well as a low-pressure microwave discharge (6–40 Pa) in argon. It is shown that in the magnetron discharge the concentration of atoms and ions of the buffer gas (Ar) and the target material (Cu) decreases exponentially with distance from the target cathode and in the first case it occurs much more sharply. The temperature of electrons in a plasma stream, which is emitted by a discharge burning near the surface of the cathode, was estimated from the relative intensity of the spectral lines according to the LTE model and the coronal model. The values obtained in both cases were close, lying near 1 eV, and the temperature remained almost constant with the distance from the cathode. The electron temperature in the microwave discharge turned out to be almost constant over the cross section of the plasma column, while the concentration near the microwave emitter was 2–3 times hi...

Physics of Radio-Frequency Plasmas

2009

Low-temperature radio frequency plasmas are essential in various sectors of advanced technology, from micro-engineering to spacecraft propulsion systems and efficient sources of light. The subject lies at the complex interfaces between physics, chemistry and engineering. Focusing mostly on physics, this book will interest graduate students and researchers in applied physics and electrical engineering. The book incorporates a cutting-edge perspective on RF plasmas. It also covers basic plasma physics including transport in bounded plasmas and electrical diagnostics. Its pedagogic style engages readers, helping them to develop physical arguments and mathematical analyses. Worked examples apply the theories covered to realistic scenarios, and over 100 in-text questions let readers put their newly acquired knowledge to use and gain confidence in applying physics to real laboratory situations.

Special issue on recent developments in plasma sources and new plasma regimes

Journal of Physics D: Applied Physics

To cite this article: Yuri Akishev et al 2019 J. Phys. D: Appl. Phys. 52 130301 View the article online for updates and enhancements. Recent citations Modification of the electric field distribution in a diffuse streamer-induced discharge under extreme overvoltage Alexandra Brisset et al -This content was downloaded from IP address 64.137.113.104 on 30/05

Fundamental investigations of capacitive radio frequency plasmas: simulations and experiments

Plasma Physics and Controlled Fusion, 2012

Capacitive radio frequency (RF) discharge plasmas have been serving hi-tech industry (e.g. chip and solar cell manufacturing, realization of biocompatible surfaces) for several years. Nonetheless, their complex modes of operation are not fully understood and represent topics of high interest. The understanding of these phenomena is aided by modern diagnostic techniques and computer simulations. From the industrial point of view the control of ion properties is of particular interest; possibilities of independent control of the ion flux and the ion energy have been utilized via excitation of the discharges with multiple frequencies. 'Classical' dual-frequency (DF) discharges (where two significantly different driving frequencies are used), as well as discharges driven by a base frequency and its higher harmonic(s) have been analyzed thoroughly. It has been recognized that the second solution results in an electrically induced asymmetry (electrical asymmetry effect), which provides the basis for the control of the mean ion energy. This paper reviews recent advances on studies of the different electron heating mechanisms, on the possibilities of the separate control of ion energy and ion flux in DF discharges, on the effects of secondary electrons, as well as on the non-linear behavior (self-generated resonant current oscillations) of capacitive RF plasmas. The work is based on a synergistic approach of theoretical modeling, experiments and kinetic simulations based on the particle-in-cell approach.

The effect of ambipolar electric fields on the electron heating in capacitive RF plasmas

Plasma Sources Science and Technology, 2014

We investigate the electron heating dynamics in electropositive argon and helium capacitively coupled RF discharges driven at 13.56 MHz by particle-in-cell simulations and by an analytical model. The model allows one to calculate the electric field outside the electrode sheaths, space and time resolved within the RF period. Electrons are found to be heated by strong ambipolar electric fields outside the sheath during the phase of sheath expansion in addition to classical sheath expansion heating. By tracing individual electrons we also show that ionization is primarily caused by electrons that collide with the expanding sheath edge multiple times during one phase of sheath expansion due to backscattering toward the sheath by collisions. A synergistic combination of these different heating events during one phase of sheath expansion is required to accelerate an electron to energies above the threshold for ionization. The ambipolar electric field outside the sheath is found to be time modulated due to a time modulation of the electron mean energy caused by the presence of sheath expansion heating only during one half of the RF period at a given electrode. This time modulation results in more electron heating than cooling inside the region of high electric field outside the sheath on time average. If an electric field reversal is present during sheath collapse, this time modulation and, thus, the asymmetry between the phases of sheath expansion and collapse will be enhanced. We propose that the ambipolar electron heating should be included in models describing electron heating in capacitive RF plasmas.

Numerical Studies of the Low Pressure RF Plasma

ANU, 1990

A one-dimensional, electrostatic particle-in-cell code with non-periodic boundary conditions is used to simulate a low pressure capacitive rf plasma created between two planar electrodes. Ion and electron motion is included and ionising collisions by energetic electrons allow a steady state to be reached and maintained. Realistic values of mi/me are used but there is no attempt to model a real gas and, except for ionisation, no binary collision processes are considered. The simulation plasma is generated by driving one boundary with a sinusoidal rf voltage at a frequency of 10 MHz. The effects of scaling on the steady state, the structure and the impedance of the resulting discharge are investigated. Changes resulting from varying the amplitude of the driving voltage are examined and scaling laws for the plasma potential, electron density and power loss obtained. Sheath heating is shown to be the main electron heating process and power balance is checked. The structure of the rf sheath obtained in the simulation is compared to theoretical models of both the current driven and the voltage driven sheath. Disagreement in the maximum sheath width between the simulation and the model is ascribed to neglect of the period of sheath collapse and the use of an idealised electron density profile in the model. Sheath scaling is shown to underlie the variation of electron density and temperature with rf voltage. The electron sheath interaction is examined and found to differ considerably from current theoretical models. In the range of parameters investigated, it is essential to consider the distortion of the electron velocity distribution in the sheath. A beam-like distribution is observed when the sheath velocity changes rapidly near the time of sheath collapse and an instability develops when electrons are accelerated into the plasma as the sheath expands.

Thermal ionization instability of an air discharge plasma in a microwave field

Technical Physics, 2007

Results are presented from experimental studies of the initial stage of an air discharge initiated in a linearly polarized quasi-optical microwave beam. The discharge was excited at an air pressure at which the electron-neutral collision frequency in the discharge plasma was considerably higher than the circular frequency of the electromagnetic field and at a microwave field amplitude close to the threshold field for air breakdown. The experiments revealed relatively bright plasma channels stretched along the microwave electric field. The development rate of these channels and their characteristic transverse dimensions are estimated. A comparison of the experimental data and theoretical estimates indicates that the channels observed arise due to the onset of thermal ionization instability in the microwave discharge plasma.

Sheath impedance effects in very high frequency plasma experiments

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1996

The frequency dependence ͑13.56-70 MHz͒ of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive argon discharge. Reduced sheath impedance at very high frequency allows high levels of plasma power and substrate ion flux while maintaining low levels of ion energy and electrode voltage. The lower limit of ion bombardment energy is fixed by the sheath floating potential at high frequency, in contrast to low frequencies where only the radio frequency voltage amplitude is a determinant. The capacitive sheaths are thinner at high frequencies which accentuates the high frequency reduction in sheath impedance. It is argued that the frequency dependence of sheath impedance is responsible for the principal characteristics of very high frequency plasmas. The measurements are summarized by simple physical descriptions and compared with a particle-in-cell simulation.