Browsing by Author "Hechtfischer, U."
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- Investigating near-anode plasma layers of very high-pressure arc dischargesPublication . Almeida, N. A.; Benilov, M. S.; Hechtfischer, U.; Naidis, G. V.Numerical and experimental investigation of near-anode layers of very high-pressure arcs in mercury and xenon is reported. The simulation is performed by means of a recently developed numerical model in which the whole of a near-electrode layer is simulated in the framework of a single set of equations without simplifying assumptions such as thermal equilibrium, ionization equilibrium and quasi-neutrality and which was used previously for a simulation of the near-cathode plasma layers. The simulation results support the general understanding of similarities and differences between plasma–cathode and plasma–anode interaction in high-pressure arc discharges established in preceding works. In particular, the anode power input is governed primarily by, and is approximately proportional to, the arc current. In the experiment, the spectral radiance from the electrodes and the near-electrode regions in xenon arcs was recorded. The derived total anode power input and near-anode plasma radiance distribution agree reasonably well with the simulation results.
- Stability of very-high pressure arc discharges against perturbations of the electron temperaturePublication . Benilov, M. S.; Hechtfischer, U.We study the stability of the energy balance of the electron gas in very high–pressure plasmas against longitudinal perturbations, using a local dispersion analysis. After deriving a dispersion equation, we apply the model to a very high–pressure (100 bar) xenon plasma and find instability for electron temperatures, Te, in a window between 2400 K and 5500-7000 K, depending on the current density (106 –108 A/m2 ). The instability can be traced back to the Joule heating of the electron gas being a growing function of Te, which is due to a rising dependence of the electron atom collision frequency on Te. We then analyze the Te range occurring in very high–pressure xenon lamps and conclude that only the near-anode region exhibits Te sufficiently low for this instability to occur. Indeed, previous experiments have revealed that such lamps develop, under certain conditions, voltage oscillations accompanied by electromagnetic interference, and this instability has been pinned down to the plasma-anode interaction. A relation between the mechanisms of the considered instability and multiple anodic attachments of high-pressure arcs is discussed.