摘要:

AbstractThe current/voltage characteristics of a cylindrical Langmuir probe have been studied in Ar+/electron afterglow plasmas in helium carrier gas under truly thermal conditions at 300 K using our flowing afterglow/Langmuir probe (FALP) apparatus. The orbital motion limited (oml) ion and electron current regions of the probe characteristics have been explored over a wide range of the reduced probe voltage (up to ∼ 100) and over a wide range of electron (ne) and ion (n+) number densities (1.6 × 107to 1.5 × 1010cm−3) at a constant pressure of the He carrier gas of 1.2 Torr. The observed increase of the probe ion currents above those predicted by collisionless oml theory, resulting in an apparent increase of the measured ion number density abovenein the plasma, is explained by the enhancement in the ion current collection efficiency due to collisions of ions with neutral gas atoms in the space charge sheath surrounding the probe. The continuous change in the exponent, χ, of the power‐law dependence,i+∞V pχof the ion current,i+, on the probe voltage,Vpfrom 0.5 at the highestn+(smallest sheath) towards 1.0 at the lowestn+(large sheath) indicates that the ion current collection from the plasma changes from the oml current regime at the highn+to the continuum regime at the lown+when the ions undergo multiple collisions with the helium atoms in the space charge sheath and thus “drift”

ISSN:0863-1042    

DOI:10.1002/ctpp.2150350102

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractElectrical and optical properties of dielectric barrier Xenon discharge lamps, selectively emitting Xe 2*/172 nm vuv radiation from a multitude of transient discharge filaments have been investigated. The lamps used were uncooled and of the flat panel type with two dielectric quartz barriers and external metal electrodes. Such lamps can be considered as small scale models of much larger flat panel uv lamps. UV emission scales almost linearly with operating frequency below 10 kHz. Both uv emission and uv efficiency rise with increasing gap spacing. The specific 172 nm emission is in the range of 100 mW/cm2for frequencies close to 100 kHz (no lamp cooling). External efficiency at high specific uv emission is close to 10%. Higher external efficiencies up to 20% are possible at lower frequencies of a few kHz, but at reduced specific uv flu

ISSN:0863-1042    

DOI:10.1002/ctpp.2150350103

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractBackward waves in waveguides completely filled with magnetoactive plasma (gaseous or semiconductor plasma) have been investigated numerically. It is shown that two types of backward waves exist in such waveguides: cyclotron backward waves and waveguideHE‐modes. While the cyclotron modes are backward waves at arbitrary system parameters (plasma density, magnetic field and waveguide radius), the waveguide backward waves appear only at certain values of there parameters. In addition the cyclotron backward waves can propagate at arbitrary wave‐numberkzand at arbitrary phase velocity. The backward waveguide modes exist only at limited values ofkzand of phase velocit

ISSN:0863-1042    

DOI:10.1002/ctpp.2150350104

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe nonlinear evolution of a collisional driftwave instability is considered. Based on the two‐fluid description with ion viscosity and electric resistivity effects, first two coupled equations are derived. Iterating the latter for nearly adiabatic behaviour and a two‐dimensional geometry, a one‐field description is found which properly takes into account the damping of structures. As demonstrated by numerical simulations, this solves an old problem of collisional driftwave turbulence, since in contrast to previous considerations the unlimited growth of self‐organized structures is

ISSN:0863-1042    

DOI:10.1002/ctpp.2150350105

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractRecent experiments with high density divertor plasma operation in tokamaks and future tokamak design projects have revived interest in the much earlier work on elastic collision processes between neutral and charged components in hot plasmas. In revisiting these papers, we employ classical methods to calculate deflection functions, cross sections and collision rates for the most important of such elastic collision processes. A phyiscally motivated cut‐off procedure for the model interaction potential function is introduced. An algorithm for implementation of such processes into kinetic Monte Carlo neutral gas transport models is described, which accurately accounts also for possible singularities in the deflection function. Data fits for the relevant quantities are provided for hydrogenic and helium species. The relevance of elastic neutral‐ion collisions is illustrated by a numerical simulation of an ITER relevant divertor mo

ISSN:0863-1042    

DOI:10.1002/ctpp.2150350106

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0863-1042    

DOI:10.1002/ctpp.2150350101

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY