Evaluation of Trends in Optimal Design of Pulse Transformers for Long Pulse High Power Applications

Solid state klystron modulators are typically based on oil-immersed pulse transformers due to their high performance, robustness, simplicity and straightforward design. However, the size of such transformers are highly impacted by pulse power, output voltage, pulse length, and required rise time; key parameters which are difficult to combine in long pulse high power linac applications. In this paper, pulse transformer design models for two winding configurations (single layer winding and pancake winding), including calculation of parasitic elements, are developed and validated in a 3D finite element analysis environment. These models are then employed in a global optimal design procedure used to study the evolution of pulse transformer volume as pulse length is increased from 500 μs to 4 ms while constraining maximum pulse rise time and overshoot. The impact of required pulse power, pulse rise time, and system size is also studied. The single layer winding based on standard enameled round wire is first investigated under size constraints representing a limit imposed by manufacturability and maintainability, validating the optimization procedure and demonstrating that, for this winding technique, sub-optimal rise time and therefore transformer size is attained for long pulse high power applications. Consequently, the pancake winding configuration is evaluated under the same conditions, demonstrating that, although more complex and costly, its flexibility allows a more compact design. Finally, a pulse transformer rated for pulse amplitude 115 kV, output current 25 A, pulse length 2.8 ms, and 0-99% rise time <; 300 μs is designed, demonstrating the design procedure and showcasing limitations experienced in design. Its performance is assessed in circuit simulation whereas the validity of the derived parameters is demonstrated through finite element analysis.