Cathodic arc attachment in a HID model lamp during a current step

Abstract

Changes in the cathodic arc attachment mode during a current step are studied both experimentally under well-defined and reproducible conditions, and by finite element calculations. A transition from diffuse to spot and back to diffuse attachment is observed as the response to the step. Spot formation is identified experimentally by a sharp peak in the light intensity in front of the cathode and a steep decrease in the lamp voltage. Numerical three-dimensional solutions of the thermal-conduction equation in the cathode body exposed to nonlinear surface heating give good quantitative agreement of the time course of the observed changes in attachment modes. The model that describes the heating by the near cathode layer uses a simpler equation for the ion current density than other models in the recent literature. The model describes how an excess energy flux is created in the layer in front of a spot, which cannot be transported back to the cathode by the ion current and must, therefore, be supplied to the arc. The calculated integral excess power shows a time course similar to the observed light intensity.

Understanding and modelling plasma–electrode interaction in high-pressure arc discharges: a review

“…The same question arises in the numerical calculation of a non-stationary 3D temperature distribution on an axially symmetric cathode if the temperature distribution at the initial moment (the initial condition) is axially symmetric, as is the case in the modelling of evolution of the diffuse mode on a rod cathode into a mode with a non-stationary spot [57,60,72]. In [57,60,72], this question was resolved in the same way as described above, i.e. by restricting the calculation domain to half the cathode.…”

Modelling interaction of multispecies plasmas with thermionic cathodes

“…The concept of nonlinear surface heating has become a widely accepted tool for modelling of current transfer to refractory cathodes of high-pressure arc discharges (e.g. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]; see also reviews in [7,16,17]). In previous works the case of a singlespecies plasma-producing gas was dealt with.…”

Bifurcations in the theory of current transfer to cathodes of DC discharges and observations of transitions between different modes

“…It follows that all abrupt transitions are monotonic in time. Indeed, no oscillations of arc voltage and luminosity of the cathode surface is observed in the experiments on transitions between diffuse and spot modes on arc cathodes; e.g., [14,[21][22][23]. Hence, all abrupt transitions are related to bifurcations of steady-state solutions.…”