Comparative analysis of the plasma parameters of ECR and combined ECR+RF discharges in the TOMAS plasma facility

Context. As is well known, coronal mass ejection (CME) propagation often results in the fragmentation of the solar atmosphere on smaller regions of density (magnetic field) enhancement (depletion). It is expected that this type of fragmentation may have radio signatures. Aims. The general aim of the present paper is to perform a comparative analysis of type III solar and narrow-band type-III-like radio burst properties before and during CME events, respectively. The main goal is to analyze radio observational signatures of the dynamical processes in solar corona. In particular, we aim to perform a comparison of local plasma parameters without and with CME propagation, based on the analysis of decameter radio emission data. Methods. In order to examine this intuitive expectation, we performed a comparison of usual type III bursts before the CME with narrow-band type-III-like bursts, which are observationally detectable on top of the background type IV radio bursts associated with CME propagation. We focused on the analysis of in total 429 type III and 129 narrow-band type-III-like bursts. We studied their main characteristic parameters such as frequency drift rate, duration, and instantaneous frequency bandwidth using standard statistical methods. Furthermore, we inferred local plasma parameters (e.g., density scale height, emission source radial sizes) using known definitions of frequency drift, duration, and instantaneous frequency bandwidth. Results. The analysis reveals that the physical parameters of coronal plasma before CMEs considerably differ from those during the propagation of CMEs (the observational periods 2 and 4 with type IV radio bursts associated with CMEs). Local density radial profiles and the characteristic spatial scales of radio emission sources vary with radial distance more drastically during the CME propagation compared to the cases of quasistatic solar atmosphere without CME(s) (observational periods 1 and 3). Conclusions. The results of the work enable us to distinguish different regimes of plasma state in the solar corona. Our results create a solid perspective from which to develop novel tools for coronal plasma studies using radio dynamic spectra.

Download Full-text

The Formation and Behavior of Particles in Silane Discharges

MRS Proceedings ◽

10.1557/proc-557-3 ◽

1999 ◽

Vol 557 ◽

Cited By ~ 1

Author(s):

Alan Gallagher

Keyword(s):

Growth Rate ◽

Film Growth ◽

Particle Density ◽

Plasma Chemistry ◽

Particle Growth ◽

Rf Plasma ◽

Electrode Gap ◽

Plasma Parameters ◽

Rf Discharges ◽

And Behavior

AbstractParticle growth in silane RF discharges, and the incorporation of particles into hydrogenated-amorphous-silicon (a-Si:H) devices is described. These particles have a structure similar to a-Si:H, but their incorporation into the device is believed to yield harmful voids and interfaces. Measurements of particle density and growth in a silane RF plasma, for particle diameters of 8-50 nm, are described. This particle growth rate is very rapid, and decreases in density during the growth indicate a major flux of these size particles to the substrate. Particle densities are a very strong function of pressure, film growth rate and electrode gap, increasing orders of magnitude for small increases in each parameter. A full plasma- chemistry model for particle growth from SiHm radicals and ions has been developed, and is outlined. It yields particle densities and growth rates, as a function of plasma parameters, which are in qualitative agreement with the data. It also indicates that, in addition to the diameter >2 nm particles that have been observed in films, a very large flux of SixH,, molecular radicals with × >1 also incorporate into the film. It appears that these large radicals yield more than 1% of the film for typical device-deposition conditions, so this may have a serious effect on device properties.

Download Full-text

Pecvd RF Discharge Models Review

MRS Proceedings ◽

10.1557/proc-165-3 ◽

1989 ◽

Vol 165 ◽

Cited By ~ 2

Author(s):

Alan Garscadden

Keyword(s):

Kinetic Models ◽

Plasma Chemistry ◽

Plasma Electron ◽

Secondary Emission ◽

Rf Discharge ◽

Data Sets ◽

Plasma Parameters ◽

Rf Discharges ◽

Ion Collisions ◽

Boundary Interaction

AbstractThis paper presents a concise and subjective summary of the rapid progress that has been made in the understanding of the essential features of RF discharges. The paper concentrates on introducing the important concepts used in modeling the rf discharge. The discharges have been modeled from several distinctly different approaches. These include circuit, beamdiffusion, plasma fluid or continuum, and particle kinetic models. The treatments have their usefulness depending on the application. The circuit models give easily parameterized results, power deposition, and phase angles between voltage and current, however, they do not describe the important plasma chemistry and the source terms for deposition and etching. The newer continuum models efficiently give self-consistent plasma parameters for higher pressure discharges but synergistic ion and neutral interactions with surfaces are difficult to include. The particle kinetic models can include many effects without approximations, however they need extensive data sets and long computer run times. The coupling of improved diagnostics and the different theories has resulted in a convergence of their conclusions. There are four distinct energy-gain mechanisms in the RF discharge : a bulk plasma excitation; electron beam excitation resulting from secondary emission from ion collisions with the electrodes; wave-riding acceleration on the sheath oscillation (collisional: Kushner); and a noncollisional plasma electron-sheath boundary interaction (Godyak). The relative contributions are sensitive functions of the gas mixture, pressure, frequency and RF voltage.

Download Full-text