Abstract:Electromagnetic scattering in accelerating reference frames inspires a variety of phenomena, requiring employment of general relativity for their description. While the 'quasi-stationary field' analysis could be applied to slowly-accelerating bodies as a first-order approximation, the scattering problem remains fundamentally nonlinear in boundary conditions, giving rise to multiple frequency generation (microDoppler shifts). Here a frequency comb, generated by an axially rotating subwavelength (cm-range) wire and split ring resonator (SRR), is analyzed theoretically and observed experimentally by illuminating the system with a 2GHz carrier wave. Highly accurate 'lock in' detection scheme enables factorization of the carrier and observation of more than ten peaks in a comb. The Hallen integral equation is employed for deriving the currents induced on the scatterer at rest and a set of coordinate transformations, connecting laboratory and rotating frames, is applied in order to predict the spectral positions and amplitudes of the frequency comb peaks. Unique spectral signature of micro-Doppler shifts could enable resolving an internal structure of the scatterers and mapping their accelerations in space, which is valuable for a variety of applications spanning from targets identification to stellar radiometry.

Refractory metal plasma generated by a vacuum arc was used to deposit thin films with different arc currents I. The deposition rate V dep was measured for electrode configurations including a planar Zr cathode and a planar W anode; cylindrical W or Mo electrode pairs and a cylindrical Nb cathode closed by a BN plate and a W or Nb shower-head cup anode or with one-hole Ta cup anode. V dep for a Mo electrode pair with I = 275 A at a distance L = 110 mm from the electrode axis reached 2.2 µm/min, 60 s after arc ignition. For the W electrode pair V dep was ∼1 µm/min at 80 s (I = 200 A and L = 110 mm), while for W film deposition with shower-head anode V dep was ∼0.6 µm/min (I = 200 A and L = 60 mm). For Nb films deposited with the closed electrode configuration, V dep was 0.3 µm/min at 30 s after arc ignition (I = 275 A and L = 80 mm from the anode front).Index Terms-Metallic plasma, refractory electrode, thin film, vacuum arc.

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An inductive-based power supply (240μH, 50kA) was used for the investigation of the foil explosion process in the time range of 0.05ms<texpl<0.2ms. The foil current for these experiments was set between 10kA and 27kA. The foil thickness was 10μm and its length was 5cm. Images of the exploding foil captured by a fast framing camera show that the radiation of the exploding foil discharge starts on the voltage rise. The peak voltage Vpeak decreases with an increasing time to explosion and a decreasing current density: Vpeak=2.8kV at j=9.1MA∕cm2 and Vpeak=1.75kV at j=5.3MA∕cm2. A phenomenological model was suggested for the experimental data interpretations. Contrary to the previous model, we assume that the breakdown initiates with cathode spots instead of a breakdown by a bulk discharge. We suggest that the plasma appearance is related to the ejection of a metal vapor during the metal boiling. The high temperature of the vapor permits ignition of the cathode spots even at a low electric field. It results in the arcing in the metal vapor and bypassing the liquid pieces of the foil.

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