Conditioning a Copper Cathode Surface by High-Voltage Subnanosecond Pulses

Within the article, a preeroded copper cathode was subjected to the impact of a series of high-voltage pulses with a duration of <tex-math notation="LaTeX">$<$</tex-math> 1 ns for surface conditioning. An effective cathode surface area was <tex-math notation="LaTeX">~</tex-math> 0.01 mm <tex-math notation="LaTeX">²</tex-math> . Preerosion of the cathode surface was performed using a series of vacuum arc discharges of microsecond duration. As a result, a well-pronounced microrelief with a typical dimension of <tex-math notation="LaTeX">~</tex-math> 5–10 <tex-math notation="LaTeX">μ</tex-math> m was formed at the cathode surface. Then, to smooth the microrelief, the cathode was placed into a vacuum setup based on a RADAN pulse generator with a pulse duration of <tex-math notation="LaTeX">$<$</tex-math> 1 ns and a pulse amplitude of up to <tex-math notation="LaTeX">$-$</tex-math> 140 kV. About 900 discharges of a subnanosecond duration were initiated. To estimate the conditioning effectiveness, the state of the cathode surface was controlled by studying the cathode field-emission characteristics and cathode surface imaging by scanning electron microscopy (SEM). The field-emission characteristic study made it possible to estimate the electric field enhancement factor <tex-math notation="LaTeX">β</tex-math> near the cathode surface before and after the conditioning. It was shown that the subnanosecond conditioning led to a decrease in <tex-math notation="LaTeX">β</tex-math> by a factor of 6–8 from <tex-math notation="LaTeX">~</tex-math> 170 after eroding to <tex-math notation="LaTeX">~</tex-math> 20–30. Employing SEM investigation of the sample surface morphology, it was found that a typical microrelief dimension was decreased from <tex-math notation="LaTeX">~</tex-math> 5–10 to <tex-math notation="LaTeX">~</tex-math> 1–2 <tex-math notation="LaTeX">μ</tex-math> m or less. That is, a proposed conditioning technique allowed significant smoothing of the cathode surface.