摘要:

AbstractAn instability is triggered in a weakly magnetized discharge plasma by the application of a positive voltage step to a planar collector immersed into the plasma column with its surface perpendicular to the magnetic field lines. Time developement of the plasma density after the application of the pulse is measured by a Langmuir probe. Radial and axial velocity of the plasma density perturbation are measured. Radial velocity is consistent with the increase of the plasma potential in the current channel. Axial velocity is very high. It is interpreted as phase velocity of radial quasiperiodic motion of the plasma in and out of the current channel. Response time of the collector current to the applied voltage step is measured versus different parameters. Experimental results are in agreement with a qualitative model presented in previous work [1] where the observed instability is modeled as a two dimensional potential relaxation instability (PRI). Minor improvements of the previous model are proposed. A rarefaction pulse that moves towards the collector is found as the initial stage of the instability.

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360602

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractFor the first time there have been analyzed profiles of electric‐field‐sensitivenaspectral lines of the Li‐like impurity ions CIV, NV, OVI emitted by a hot dense plasma of a plane current sheet. Theoretical profiles of these lines have been calculated with an allowance for Anomalous Electric Fields (AEF). By comparing the experimental and theoretical profiles of the lines it has been established for the first time that in the plane current sheet there were developed AEF of rms strengthsF0≈ (100–120) kV/cm in the time interval from τ = −0.2 μs to τ = 0 (the time τ was counted from the instant of the maximum intensity of the spectral line OVI 5291 Å). These results have been backed up by a similar analysis of the experimental profiles of the spectral line HeII 4686 Å of the primary gas of the discharge. The AEF reached these strengths at the same instant of time, τ = −0.2 μs, when electron and ion temperatures reached their maxima:Te≫ 100 eV,Ti≈ 300 eV. The instant τ = −0.2 μs corresponds to a transition from the metastable stage to the explosive phase of the current sheet evolution. At this time the ratio of the AEF energy density to the thermal energy density of the plasma was § ≡F20/[8π/NeTe+NiTi)] ≈ 10−3, which exceeded a similar ratio for the thermal wa

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360603

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe dispersion properties of the slow electromagnetic surface waves propagating across external magnetic field in planar metallic waveguides with plasma and dielectric filling on the harmonics of the electron cyclotron frequency are studied in this paper. The external steady magnetic field is supposed to be directed perpendicularly to the waveguide wall. Dielectric layer separates semibounded plasma from the metallic wall. The analytical research is carried out using the kinetic description for plasma particles, the mirror reflection model for the interaction between particles and plasma boundary. Skin depth of the surface cyclotron waves (SCW) is much greater than electron Larmor radius. Effect of the following parameters of the waveguide structures: dielectric constant and thickness of the dielectric layer, plasma density value and number of the cyclotron harmonics, on the SCW dispersion is examined both analytically and numerically.

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360604

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractInfluence of cathode materials (Ti, Al, Cu, TiN), ambient gases (Ar, N2,p= 0.1‐1 Pa) and the arc current itself on the motion and the velocity of cathode spots in an arc coating process have been investigated with the help of a new high speed framing camera. It was found, that the cathode material causes different spot currents but in general the spot arrangement and the motion on the surface are similar. Surface contaminations due to ambient gases affect this dynamics in several ways. Insulating layers like AIN can drastically increase the instantaneous spot velocity, for example from<5 m/s on Al up to 170 m/s on AIN contaminated areas. TiN layers with a high conductivity increase the spot mobility at first. But at nearly completely contaminated surfaces (simulated by a TiN cathode), the mobility is strongly decreased. The values change from an average velocity of 6.3 m/s with a diffusion constant of 54 cm2/s (Ti, 0.01 Pa) to 2 m/s and 6.4 cm2/s at TiN.The course of the instantaneous spot velocity during the spot splitting phase was investigated too. The instantaneous spot velocity of each of the two new spots originated from the starting spot is relatively high (30–40 m/s) within the first 50 μs. The cathode material and the ambient gases are of slight influence in this phase. The movement is directed. In the further development the instantaneous spot velocity is decreasing to values under 5–10 m/s. The motion is now more and more random. Additionally it could be proved, that the lower stability limit for a stable discharge is strongly connected with the spot current, which depends on discharge cond

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360605

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractDielectric barrier discharges in Xe and Ne/Xe, He/Xe mixtures are investigated with regard to the ranges of existence of various discharge types over a wide range of parameters (total gas pressurep, electrode distanced, frequencyfand mixture ratioX). The discharges were explained in more detail because of the bistable behaviour and the transfered charges, partly of the peak current and the maximum of the visible radiation pulse. The time behaviour of the discharge was observed, too. In this paper a distinction of various discharge types could be achieved by the similarity parametersf/pandpd. The charge carriers remaining in the volume and long‐living plasma species could be identified as essential mechanisms for the development of various types of discharges. The influence of space charges on the bistable behaviour could be shown indirectl

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360606

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractTime resolved absolute density measurements of the 1s5 (metastable) and 1s4 (resonance) level in the positive column of a pulsed xenon gas discharge for gas pressures between 1 and 40 Torr and currents between 100 and 300 mA are presented. The densities ranged from 1 × 1011to 5 × 1012cm−3and were found to be ten times larger in the afterglow than in the active part of the discharge. The enhanced radiation obtained in the afterglow in the near infrared regions as well as in the VUV region is caused by a dissociative recombination and formation of excimer sta

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360607

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe optical emission spectra in the wavelength region 200–800 nm produced by electron impact on the silicon‐organic molecules TMS (tetramethylsilane) and HMDSO (hexamethyldisiloxane) under controlled single‐collision conditions have been analyzed. Absolute emission cross sections from threshold to 200 eV impact energy were determined for a variety of emission features. For both targets, the CH(A2Δ → X2Π) emission, the so‐called CH „4300 Å”︁ band, was found to have the largest emission cross section with values (at 100 eV) of 5.5 × 10−19cm2and 6.1 × 10−19cm2for TMS and HMDSO, respectively. Relatively high onset energies of 28.0 ± 1.5 eV (TMS) and 33.1 ± 1.5 eV (HMDSO) were measured for these emissions. Weaker emission features in both spectra were identified as CH bands corresponding to the B2∑−→ X2Π transition (the CH „3900 Å”︁ system) and the C2∑ → X2Π transition, and as the atomic Si line emissions at 253 nm and 288 nm. Near‐threshold studies indicate an onset for the Si emissions of 29.0 ± 2.0 eV (TMS) and 44.6 ± 2.0 eV (HMDSO). Absolute cross sections and appearance energies were also determined for the strongest lines of the hydrogen Balmer series for both targets. The comparatively high onset energies and small emission cross sections for all observed emissions indicate that single‐step dissociative excitation processes are unlikely to play a dominant role in low‐te

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360608

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

ISSN:0863-1042    

DOI:10.1002/ctpp.2150360601

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY