A fast modular pulsed power source for a pulsed electron beam device

Summary

The pulsed electron beam device GESA investigated at the Institute for Pulsed Power and Microwave Technology (IHM) at Karlsruhe Institute of Technology (KIT) generates an intense electron beam for surface modification of metals. The beam is created by means of an explosive emission cathode in a triode configuration. The anode-cathode current in the triode can be controlled via the voltage applied to the triode’s control grid. Due to the inherent dynamics of the cathode plasma the impedance of the triode is not constant over time, leading to electron beam instabilities for certain modes of operation. This challenge is currently addressed by replacing the formerly used combination of spark gap based pulse generator and passive grid control by a new modular semiconductor-based pulse generator including active grid control. This approach enables an easy adjustment of pulse length to up to 100 µs and current to up to 600 A. The resulting requirements for the generator include a variable output voltage of up to 120 kV with a ripple of less than 1 %. Therefore, the generator is designed as semiconductor-based Marx generator with a stage voltage of 1 kV. In addition, the pulse rise time has to be below 100 ns for a homogeneous cathode plasma ignition. Charging the parasitic capacitance of the cathode results in hard switching conditions for the employed IGBT switches, demanding for a special gate drive circuit to speed up commercial devices. Droop compensation is achieved by consecutive adding of active stages during the pulse, requiring a total number of 150 stages. For efficient implementation, each stage is equipped with a microcontroller-based control circuit, providing exact timing of the switching process. The communication between the stages is performed by means of a fast optical bus. So far, the circuitry for one stage has been designed. This work presents selected features of the design and measurements in a small generator assembly.

Additional informations

Keywords

Pulsed Power, Semiconductor-based Marx generator, Power electronics, Fast switching