Spectroscopic Studies of Low-Current (Single-Spot) Short Vacuum Arcs in Axial Magnetic Field

Abstract

Measurements of radiation intensity spatial distribution for different copper ionization states (CuI, CuII, and CuIII) were carried out in short (8 and 4 mm long) low-current vacuum arcs with copper electrodes. The arc current was I = 60 A = I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> [where I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> is the mean current per cathode spot (CS)]. That is, the single-spot arcs were investigated. The spatial and temporal resolutions were 0.5 mm and 50 μs, respectively. The external axial magnetic field induction was 0 ≤ B ≤ 0.1 T . The studies have shown that the plasma state and the column shape and structure in short arcs are determined not only by cathode processes. In the near-anode region of the arc, changes take place both inside the arc channel and in the “coat” of weakly ionized plasma that surrounds it. The interaction of the high-speed ions of the CS plasma jet (PJ) with the anode forms a flow of atoms from the anode surface part to which the arc is attached. The atoms are ionized in the immediate vicinity of its surface. This increases the plasma concentration and decreases the average charge of ions in the near-anode part of the arc, as compared with the average charge of the CS PJ.