The autograph method was used to investigate the arc spot motion over a virgin tungsten cathode under a magnetic field of H=0.1-0.7 T in the current range 2-50 A. The cathode spot (CS) has been found to start dividing at a current of a few amperes. The current density measured at the moment of CS death is (1.2+or-0.5)*1011 A m-2 for a cold cathode and (3+or-1)*1010 A m-2 for a hot one. The CS lifetime is 25-50 ns for a cold cathode and it increases to 150-200 ns for a heated one. Neither the current density nor the CS lifetime depends on current. Estimates have shown that the erosion rate decreases with current and increases with temperature. The backflow electron current from the CS plasma is invoked to account for the experimental evidence.
This article suggests an alternative mechanism for electron emission from the ferroelectric ceramic cathode. This mechanism involves the concept of vacuum breakdown initiation from metal-dielectric cathodes that comprises two stages: the field emission through metal- dielectric-vacuum conjunction followed by the processes resulting in an uncompleted surface discharge. The electron emission thus occurs from the low-density surface plasma.
This letter reports efficient treatment of NO emission with a transient, nonequilibrium plasma created by pulsed corona discharge. The transient plasma (≈50 ns) is found to reduce NO emission by 50% in a flow of 2–25 l/s with energy cost ≈10–20 eV/molecule, corresponding to a fraction of source power of ≈5%. The efficiency of NOx reduction is a complex function of parameters that include pulse width, pulse polarity, current density, repetition rate, and reactor design. It was found that the best efficiencies are correlated with a low current density (0.2 A/cm2)and high repetition rate (1 kHz) under high flow rate. Careful optimization of all these parameters is required to reach cost effective NOx reduction.
High frequency fluctuations (up to 50 MHz) in the ion current arc voltage and plasma floating potential have been studied, together with the influence of the surface history on these fluctuations for arc currents ranging from 2 to 50 A. In the process of surface conditioning by repeated arcs, the amplitude of fluctuations increases. The fluctuations of a signal from the grounded probe situated at a distance of
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