Bfm Bert Pots

Collective scattering of CO2-laser light from ion-acoustic turbulence

The spectral density function S(k,w) associated with spontaneous turbulence in a current‐driven plasma of medium density (n e = 1019−10220 m −3) is measured with the scattering of the radiation of a cw low‐power CO2‐ laser (P i ≃2 W, l i = 10.6 mm). Optical homodyne detection has been used. A remarkable result is that the level of fluctuations with wave vectors k∥B is close to thermal; B is the magnetic field for plasma confinement. The level of fluctuations with k⊥B is several orders of magnitude larger than the thermal level. The phase velocity of these fluctuations is equal to the ion‐acoustic velocity. A power law spectrum of the form n e /n e ∼w−2 has been found. It is consistent with the spectrum below 1 MHz as measured by optical probes.

An experimental study of the ion energy balance of a magnetized plasma

The authors report on an experimental study of the ion energy balance of the magnetized and current-driven plasma of a hollow cathode discharge. The balance appears to be classical. At the axis of the plasma column the electron-ion Coulomb interaction is in equilibrium with the ion-neutral interaction. The authors find no significant influence on the energy balance by the spontaneously appearing plasma turbulence.

A collisional radiative model for the argon ion (laser) system with an experimental test

Abstract A collisional radiative model for the argon ion system has been set up. In this model collisional data of Zapesochnyi et al. for the 4p group and of Rubin and Sobolev for the other groups have been used. Absorption of resonance radiation has been included in the model. The population densities of the 4p group with upper laser levels and the 4s group with lower laser levels have been calculated with this model as functions of the elecron temperature and density. We also measured these group densities and the electron temperature and density in a continous hollow cathode are discharge and compared them with the model data at the relevant temperature and density. This method may be qualified as a direct comparison between model and experiment by excluding an indirect determination of the electron temperature and density by a calculation. We found over three decades of excited level densities that the model predicts densities which are a factor 3 too large for the 4p group and a factor 3–8 for the 4s group. Possible reasons for this discrepancy are discussed.

On the Pressure Balance and Plasma Transport in Cylindrical Magnetized Arcs

Abstract Magnetized current-carrying plasmas exhibit usually significant E x B rotation velocities which often approach the ion thermal velocity. It is shown both experimentally and theoretically that this rotation in combination with inertia, viscosity and friction leads to an important reduction of the radial transport. If the radial electric field component is directed inward an inwardly directed force on the ions is set up. On the other hand, turbulence leads to enhanced transport especially at higher values of the electron Hall parameter. Also this effect is observed in this experiment and is shown to be in accordance with measured turbulence levels.