Heat management technology for solid-state high voltage and high repetitive pulse generators:Towards better effects and reliability

Solid-state high voltage high repetitive pulse generators have a broad prospect in various applications.The high power and high-frequency operation of the pulse generator suffer from the massive heat dissipation problem,which limits the improvement of the output parameters and even affects the lifetime.This article focuses on heat management technology for high voltage high repetitive pulse generators.Firstly,the typical circuit topology of the high repetitive pulse generators was summarised.From the perspective of different application requirements,the demands of the heat management design were concluded.Moreover,the heat generation characteristics and difficulties of solid-state high voltage high repetitive pulse generators were analysed.Then,the different stateof-art cooling techniques were reviewed,and their applicability and limitations for the high voltage high repetitive generators were discussed.Finally,a flow chart for heat management design was given.

Revealing phase transitions and instabilities in pseudospark discharges

Pseudospark discharge is a low-pressure high-voltage pulsed discharge with hollow electrodes,and the overall discharge experiences several distinctive sub-phases.The instability phenomena,characterised by the sudden oscillations or distortions of discharge voltage and current,restrict the applications of pseudospark discharge.This study presents an investigation into phase transitions and instabilities in pseudospark discharge by combining the evidences from multiple discharge waveforms,time-resolved images,electron beam current profiles,2D kinetic simulation results,and the spectral line emission of cathode material.The process of a normal pseudospark discharge is firstly discussed,and the threshold conditions of the transition from the superdense glow discharge(SGD)phase to the high current phase with arc cathode spots are addressed.According to temporal profiles and voltage-current characteristics,two types and four occurrences of instabilities are distinguished:type Ⅰ—in the pre-breakdown phase;type Ⅱ-1—in the SGD phase;type Ⅱ-2—in the transition of cathode spots propagating from cathode hole edge to cathode plane;type Ⅱ-3—in the re-initiation of spots near current reversal.It is found that the instability of type Ⅰ is caused by the stepwise penetration of virtual anode plasma,and type Ⅱ is closely related to the cyclic nature and finite lifetime of cathode spots.It is induced by the fact that the decay of cathode spots is faster than the formation under certain conditions,and the existing spots are not able to provide the current required by the external circuit.Important features and the suppression methods of the instabilities are discussed based on the proposed mechanisms.