Microwave Tube Fault-Current Model for Design of Crowbar Protection

TL;DR

This paper introduces a flexible dc fault current model for microwave tube protection, incorporating non-linearity and rectifier effects, verified experimentally to improve crowbar design for high-energy plasma applications.

Contribution

It proposes a novel dc fault current model based on Joules Integral energy, accounting for system non-linearity and rectifier effects, enhancing crowbar protection design.

Findings

The model accurately predicts fault current behavior.

Experimental verification confirms the model's effectiveness.

A crowbar was built to limit energy below 10J.

Abstract

Many applications that use high energy plasma are realized using Microwave tubes (MWT) that operate at peak power in the range of hundreds of MW and frequency in GHz. One failure mode of the MWT is due to the excess energy in the tube during internal arcing events. Crowbar is used to protect the MWT by diverting the energy during fault. To compute the energy released into the MWT, the dc fault current model and the MWT model are essential. An equivalent fuse wire model is utilized for the MWT for the crowbar applications. The paper proposes a model for the dc fault current, the analysis for which is based on Joules Integral energy concept. The model provides flexibility to choose a range of practically observed reactance to resistance ratio (X/R) of transformer and also allows the use of a range of dc current limiting resistances that are utilized in the High Voltage (HV) power supply circuits in Microwave applications. The non-linearity of the system due to the multipulse diode rectifier is also considered by introducing a correction factor in the model. This paper shows that the same correction factor can be applied for both dc side parallel and series connected rectifier circuits. Both dc fault current and MWT models are verified experimentally. Using the model a 10kV , 1kA crowbar is built to limit the energy in MWT below 10J.