Electrode configuration under atmospheric pressure air conditions, two cylindrical electrodes made of pure Cu with a diameter of 4 mm and free length of 12 mm aligned opposite each other on a common axis, one electrode fixed, the other electrode movable along the axis with a stepper motor \u2013 the gap distance of 3 mm is reached after 50 ms, arc operation with a DC power source consisting of a signal generator Agilent 33220A and an amplifier FM1295 (FM Elektronik Berlin) in the current mode providing DC currents in the range from 0.5 to 20 A and voltages up to 100 V
\n", "procedure": "The arc is initiated by contact separation, and a constant-rate expansion of the electrode gap is achieved through precise and reproducible motion driven by the stepper motor
\n" }, "medium": { "name": "air, air-Cu, Cu vapour", "properties": "Open air with a varying admixture of Cu vapour due to electrode evaporation
\n", "procedure": "No specific gas treatment, electrode evaporation starts with arc ignition
\n" }, "target": [], "diagnostics": { "name": "electrical measurements, high-speed imaging, OES, fluid model", "properties": "Electric measurements:
\nVoltage measurements between the end contacts of both elekctrodes before and during electrode separation with a digital oscilliscope Yokogawa DLM2054.
High-speed imaging:
\nHigh-speed imaging of the arc side-on from a direction perpendicular to the arc axis with Photron Fast-Cam NOVA R3 with 1000 fps and minimum exposure time of 2 \u00b5s (without filters).
\nSpectrally selective high-speed imaging of the arc side on with Photron Fast-Cam NOVA R3 and a beam splitter (double image optics) with two narrow band metal interference filters with the centre wavelengths 514 nm and 777 nm corresponding to the CuI line at 515 nm and the OI triplet at 777 nm.
OES:
\nOptical emission spectroscopy (OES) with a 0.5 m imaging spectrograph with an entrance slit of 20 \u00b5m width and a 1200 grating coupled with a CCD camera PI-Max4:1024i and an optical mirror system to image part of the arc.
Fluid model:
\nAn 1D unified non-equilibrium fluid model as described in detail in M. Baeva et al., J. Phys. D: Appl. Phys., 58(9):095204, 2024. doi:10.1088/1361-6463/ad9f79 is used to obtain the plasma parameters in air-Cu mixture. It considers the ground state atoms and singly charged ions of Cu along with the 11-species reaction scheme for air. 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 is included.
OES:
\nRecording of one spectra side-on in each experiment for one selected time (and gap distance) with an exposure time of around 0.1 ms and over a cross section of the arc at a selected distance from the cathode by adjusting the position with a linear translation stage of the electrode configuration.