*2.3. Electrodes*

Spiral RMF electrodes made of CuCr alloy were used. Electrode diameter was 34 mm. Contact spots at defined positions for arc initialization have been created mechanically. Figure 2 shows examples of prepared electrodes.

These initial contact spots had diameters of about 3 mm. Only the cathodes were modified in order to reduce the influence on the anode as much as possible

Figure 3 demonstrates the working principle of a RMF contact pair. When the electrode separation starts, the last connection point between the electrodes serves as an arc ignition position due to fast local overheating (bridge explosion). The arc column constricts due to the action of self-induced magnetic field. The spiral form of the contact produces an additional magnetic field, which pushes the arc toward the outer electrode boundary. As far as the constricted arc column reaches the outer boundary, the joint action of the current flow (blue tracer in Figure 3) and magnetic field (green arrows in Figure 3) causes a Lorentz force (direction is shown by red arrows in Figure 3), which rotates the arc.

**Figure 2.** Examples of CuCr electrodes used in the study. Red circles show the prepared contact spots for arc ignition, type A (**a**) and type B (**b**). The anode (**c**) was not modified.

**Figure 3.** Schematic representation of RMF contact working principle. Blue tracer shows the current flow, green arrows represent the direction of magnetic flux density, and red arrows show the direction of resulting Lorentz force.
