The electrode configuration includes a cathode made of cadmium (Cd) and an anode made of tungsten (W) with lengths of 10mm and a diameter of 100 \u03bcm each. The length of the plasma region varies from 20 \u03bcm up to 160 \u03bcm during the contact separation.
\n", "procedure": "An electric contact of a wire (anode) is established on the rough surface of a metal block (cathode). The wire is pulled away from the surface which initiates an electric discharge. The main discharge develops in metal vapour at distances between 20 \u03bcm and \u223c 200 \u03bcm (the so-called microdischarges). The wire moves further away from the surface, the released heat causes a thermochemical reaction, which can lead to the formation and the development of a flame front.
\n" }, "medium": { "name": "air-H2_Cd, air, H2, Cd vapour", "properties": "The plasma is assumed to contain electrons and heavy particles of Cd atoms and singly charged Cd+ ions in their ground states. Admixture of air/H2 appears after the main microdischarge.
\n", "procedure": "Spark ignition occurs during the contact separation at a constant current of 60 mA. Initially the spark is ignited in the metal vapour of Cd. Later on the gas characterising the explosive atmopshere (a mixture air/H2) is supposed to mix with the metal vapour.
\n" }, "target": { "name": "Cd cathode, W anode", "properties": "Melting and evaporation of the cathode made of Cd. Thermo-field emission from the Cd cathode with precomputed values of the electric current density as a function of the electric field and the temperature on the cathode " }, "diagnostics": { "name": "fluid model, voltage measurement, OES, electrical measurements", "properties": "A unified non-equilibrium fluid in one dimension is used to obtain the plasma parameters in Cd metal vapour. It considers the ground state atoms and singly charged ions of Cd. The model solves the equations for conservation of species, energy of electrons and heavy particles (atoms, molecules, ions), the Poison equations for the electric potential, the heat transfer in the electrodes for a current level controlled by an external circuit. A collisional-radiative model for the population of the excited states of Cd atoms can be considered in a second step.
\nThe electrical characteristics of the discharge have been studied and quasi-stationary current-voltage characteristics have been obtained by using a setup that includes a DC control system, oscilloscope, providing the electrical parameters with a time step of 1.6 \u03bcs, long distance microscope, image intensifier, and a high-speed camera.
\n", "procedure": "The model equations are solved using a fully coupled approach. The plasma domain is resolved in 1600 mesh elements and 300 elements are used for the electrodes. The electric current in the model has a constant value of 60mA. A steady-state solution is sought for a gap length of 20 \u03bcm to mimic the initial two phases of contact opening. Then, a deforming mesh approach is applied to simulate the moving electrode. The discharge gap was increased
\n140 from 20 \u03bcm up to 160 \u03bcm with a speed of 0.14m/s.
\nThe discharge length is measured along the line connecting the strongly emitting anode and cathode areas. The length is defined as the distance between the endpoints, which represent the half of the maximum emission intensity. The discharge width is taken along lines that are perpendicular to the central line. Here again, the value at the half-maximum of the emission intensity is considered. Over 600 measurements for 15 discharges were carried out with a current of 60 mA.