Index of content:
Volume 86, Issue 12, 15 December 1999
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
86(1999); http://dx.doi.org/10.1063/1.371741View Description Hide Description
Dealing with the collisionless plane sheath of a capacitively coupled high frequency (hf) discharge a two-point boundary value problem of the standard form is elaborated for a set of ordinary differential equations. The numerical solution yields that the direction of the electric field is reversed in a short interval of the period if the hf amplitude exceeds a threshold. The sheath model hitherto often used is extended to include the effect of the field reversal in a relatively simple way. At the electrode various boundary conditions are taken into account. It is shown that the different screening of the time-averaged component and of the high frequent components of the electric field near the electrode and in the interior of the sheath is the physical reason for the occurrence of the field reversal. In front of the electrode, the field reversal decreases the electron density and the electron current and causes an additional step in the displacement current. Apparently, recent experiments known from the references confirm the theoretical results.
86(1999); http://dx.doi.org/10.1063/1.371742View Description Hide Description
A radial multichannel pseudospark switch is integrated into a plasma focus system designed to generate soft x rays to determine switch durability in a long-term test. The operating parameters correspond to a repetition rate of up to 2 Hz, stand-off voltages of 10 kV and peak currents of 200 kA. Only minimal electrodeerosion is witnessed after a serial test of 180 000 shots where the electrode surfaces are inspected after every 25 000 shots. The good condition of electrode surfaces suggests the possibility of an additional 200 000 shots, implying that for the given parameter range the lifetime of the multichannel pseudospark is at least four times longer than that of traditional high-current switches such as spark gaps. In a comparative test the performance of the multichannel pseudospark switch is evaluated against a multichannel spark gap. The results of these investigations show that the low-erosive pseudospark is well suited to substitute for spark gaps in high-current applications.