Investigation of cathode spots and plasma formation of vacuum arcs by high speed microscopy and spectroscopy

Continuous phase transition in the region of the vacuum arc cathode spot

“…2. Figure 3 shows that a current density higher than 10 10 A / m 2 is necessary to heat the spot plasma during a few microseconds, which is in conformity with the measurements of Siemroth et al 17,25 Also, according to this figure, current densities higher than 10 11 A / m 2 are required to heat the spot during several nanoseconds, which is in accordance with the measurements of Hantzsche et al 24 Therefore, our model in Sec. II suggests a range of current density and time scale of spot heating that is in good conformity with reported experimental results.…”

“…Also, a wide range of lifetime from a few nanoseconds 16 to several microseconds has been reported for vacuum arc cathode spots. 17 During the past years, the measuring methods have been refined, which allows researchers to observe microspots and fragments. Siemroth et al have shown that the cathode spot should be considered as a multilevel organized self-similar structure, 17 and reported several microseconds for spot lifetime and 10 10 −10 11 A / m 2 for current density.…”

“…1͒. The case of an arc with a constricted cathode spot on cold cathodes is more complicated, and many theoretical 2-14 and experimental [15][16][17][18][19] works have been published in this field during recent decades. Despite many theoretical and laboratory works on the vacuum arc cathode spot, the cathode spot operation mechanism is not yet well understood, and a unified model for all cathode materials ͑containing volatile cathodes, e.g., Hg; refractory cathodes, e.g., tungsten; and cathodes that have intermediate thermophysical properties, e.g., Cu͒ has not been presented.…”

Cathodic Arc Deposition of Films

“…At the cathode of the vacuum arc the current is concentrated at a small number of discrete sites called cathode spots. The formation of cathode spots is a fundamental characteristic of the vacuum arc discharge, and the physics of the spots has been studied by a number of workers (2)(3)(4)(5)(6)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). The spot size is estimated to be in the range 1-10 microns, and the current density at the spots is of order 10 6 -10 8 A cm −2 .…”

Time evolution of plasma parameters in the jet of a low-power vacuum arc thruster

“…It is known that the cathode spots, therefore the arcs, have a complex and rich dynamics. They migrate on the cathode surface in a stochastic way both with and without the application of an external magnetic field [23][24][25][26][27]. They can also fade away and then quickly appear again somewhere else on the cathode surface.…”