High-resolution observation of cathode spots in a magnetically steered vacuum arc plasma source

Abstract

The properties of cathode spots in a magnetically steered vacuum arc plasma source were investigated. The cathode spots were observed with a long-distance microscope coupled to a streak camera, where the entrance slit of the camera was aligned with one of the linear sections of the steered arc source. This is a key feature that allows the observation of spots as they appear along the erosion racetrack. The trends of spot motion and patterns in the emitted light were observed with different sweep times. The streak images were analysed by fast Fourier transformation to check for the presence or absence of characteristic features like characteristic spot lifetimes, since their existence remains a disputed issue. We found that the power spectrum of the arc spot fluctuations does not show any specific frequencies or related times, rather, the spot fluctuations have a broad spectrum following a power law (spectral power density versus frequency), which is indicative for the fractal (self-similar) nature of spot processes. Moreover, we show that-at about 300 MHz under our conditions-we reach the ultimate temporal resolution limit of the method, which is associated with the finite lifetime of excited atomic and ion states. This is a fundamental limit given by the physics of atoms and ions, not a measurement flaw. The temporal resolution limit of about 3 ns also implies a spatial resolution limit of order of a few μm given that radiating species move laterally to the observation direction with at least 10 3 m s −1 .

Observation of prior light emission before arcing development in a low-temperature plasma with multiple snapshot analysis

“…In several vacuum arc studies with high-temporal resolution analysis 1,3,28 , this prior light emission was not reported. As the observation of light emission before arcing current initiation is an unprecedented finding, we www.nature.com/scientificreports/ discuss here the measurement validity in terms of the following: (i) reproducibility and consistency between inter-experimental data, and (ii) time delay of the instruments.…”

Three-dimensional hybrid simulation of vacuum arc extinction considering dynamic behavior of cathode spots

“…In the simulation, the motion direction of the cathode spot is determined by equations ( 1) and ( 2), while two other important parameters, namely the time and space step of the motion, need also to be defined. Oh et al analyzed the image of cathode spot motion using the fast Fourier transform and showed that the cathode spot did not exhibit significant lifetime characteristics and the time interval of its motion was randomly distributed [43]. Djakov and Jüttner measured the motion characteristics of a Cu cathode spot under TMF at resolutions of 10 ns and 2 µm and demonstrated that the displacement of the cathode spot within 30 ns corresponded approximately to the Gaussian distribution with the most probable value of about 5.8 µm [44].…”

Magnetised and unmagnetized axisymmetric particle-in-cell simulations of ion energy distributions in cathodic vacuum arcs

“…We attribute the spectral peak to sub-spot generation. The simulation assumes creation of a spot periodically every 16 ns for simplicity based on the forementioned trend in the noise spectra [23,24,31].…”