The electron emission from a field emission trigger unit was matched to the requirements for the simultaneous ignition of all channels in a radial multichannel pseudospark switch for a large parameter range of the pseudospark discharge. In such trigger unit the electrons are extracted from the surface of a high-e material by field emission after applying a pulsed voltage. Electron emission occurs in a pressure range from 1-50 Pa, where the pseudospark discharge is operated. The access to low working gas pressures (

The microscopic structure and the spatial distribution of the cathode spots in a radial multichannel pseudospark switch have been investigated by means of scanning electron microscopy. Current pulses of about 15 my s duration and peak amplitudes up to 340 kA have been applied. When using stainless steel and copper as electrode material cathode spots of type I and type II are observed. These cathode spots appear in groups (macrospots) with a diameter of several 100 mu m. Assuming that the lifetime of the macrospots corresponds to the half period time of the current pulse the distribution of the cathode spots within the macrospots can be explained by a retrograde motion of the spots with a velocity of several 100 m/s in the self-magnetic field of the discharge current. Furthermore, the spatial distribution of the cathode spots within the macrospots can be interpreted by assuming a splitting and a repulsion of the cathode spots. The electrode phenomena show that the discharge current is d istributed over a large area which is prerequisite for low erosion and long lifetime operation of the switch

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 electrode erosion 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.

Analysis of discharge mechanism in especially designed pseudosparks that facilitate pseudospark characteristic low-erosive conduction at very high currents is presented. The alternate formulation of criterion for transition to arc discharge phase developed here enables us to account for the emergence of arcs at each aperture after a threshold electric charge is transmitted in these devices. The use of a large number of apertures is found to have no influence on discharge condition that initiates arc formation at individual apertures.

No abstract