# An Investigation into the Behavior of Cathode and Anode Spots in a Welding Discharge
## 4 Discussion  
The results presented above on the visualization of anode and cathode spots using new methods and equipment allow us to analyze the results from a phenomenological point of view. Despite the large number of welding works presented in the scopus system, the authors use high-speed cameras and digital cameras to study the processes of droplet formation, droplet transfer, and bath formation at a macro level. Simultaneously, the exposure time ranges from 80 microseconds and beyond [1; 2; 3]. Under such shooting conditions, it is impossible to record the formation of anode and cathode spots. Additionally, researchers are only studying the diffusion binding of the welding discharge [2; 3; 18; 48]. We will specifically focus on the work associated with modeling the welding arc. For many years, arc modeling and welding modeling were essentially distinct fields. While arc models included the arc, electrode, and workpiece as boundary conditions, welding models included the workpiece and the arc as boundary conditions [1; 2; 3; 48; 52; 53]. Welding arc modeling requires solving related equations of hydrodynamics and electrodynamics, as for other applications of thermal plasmas. But most authors do not include processes in the cathode and anode parts of the welding discharge in their models. Some authors do not even say that cathode and anode spots exist, because they see the electrode and the workpiece as a solid volume [54]. In the first approximation, we already have an idea of a vacuum discharge by analogy. At the same time, the results of the visualization of anode and cathode spots in the  
Figure 19: The results of studies of the dynamics of cathode spots obtained by visualizing the reverse side of the cathode spot: (**a**) dependence of the number of cathode spots on the exposure time: 1—aluminum film; 2—copper film; (**b**) dependence of the average lifetime of the cathode spot on the thickness of the film: 1—aluminum; 2—copper; 3—siliver; (**c**) comparative histogram of the ratio of cathode spot diameters for different thicknesses of copper film (A = 250 nm, B = 350 nm): 1—the average diameter of the cathode spot on the front side; 2—the average diameter of the cathode spot on the back side; 3—the average diameter of the thermal imprint of the cathode spot on the glass. Figure 18: Reverse side of cathode spots in dynamics for a current of 20 A, copper film thickness 140 nm (frame rate 79,000 fps, exposure time 0.0037 s). welding arc require a separate analysis, taking into account the methodological features of our experiments. Let us focus on key points to discuss the results found in the scientific literature. In vacuum, as the authors of the review article [39; 40; 55] write, five modes of anode discharge can manifest themselves: (1) a low-current mode in which the anode is mostly passive and acts only as a collector of particles escaping from the cathode; (2) the second low-current mode, which may occur if the electrode material is easily sprayed (a stream of atomized atoms will be emitted by the anode); (3) the low-point mode, characterized by the appearance of one or more small luminous spots on the anode (the low points are usually much colder than the real anode spots present in the last two modes); (4) anode spot mode, in which one large or several small anode spots are present (such spots are very luminous, have a temperature close to the boiling point of the anode material at atmospheric pressure, and are an abundant source of vapors and ions); and (5) intensive mode, in which the anode spot is present, but accompanied by severe erosion of the cathode. The voltage is relatively low and quiet in two low-current and high-current modes. It is usually high and noisy in the low-point mode, but it can also be in the anode spot mode. The erosion of the anode is small, even negative, in two low-current modes and from low to moderate in the low-point mode. Severe anode erosion occurs in both the anode spot and intensive modes.