Abstract
We have developed 1D analytic and 2D fully electromagnetic models of radial transmission-line impedance transformers. The models have been used to quantify the power-transport efficiency and pulse sharpening of such transformers as a function of voltage pulse width and impedance profile. For the cases considered, we find that in the limit as $\ensuremath{\Gamma}\ensuremath{\rightarrow}0$ (where $\ensuremath{\Gamma}$ is the ratio of the pulse width to the one-way transit time of the transformer), the transport efficiency is maximized when the impedance profile is exponential. As $\ensuremath{\Gamma}$ increases from zero, the optimum profile gradually deviates from an exponential. A numerical procedure is presented that determines the optimum profile for a given pulse shape and width. The procedure can be applied to optimize the design of impedance transformers used in petawatt-class pulsed-power accelerators.
Highlights
Radial transmission-line impedance transformers provide an efficient method of combining the outputs of as many as several hundred traditional Marx generators or linear-transformer-driver (LTD) modules to produce a petawatt-level power pulse [1]
II and III, we investigate the power-transport efficiency and other characteristics of the transformer of the two published accelerator designs
We find in semianalytic theory and 2D simulation that an impedance transformer can provide reasonable voltage transformation and high transmission efficiency for pulsed-power applications
Summary
Radial transmission-line impedance transformers provide an efficient method of combining the outputs of as many as several hundred traditional Marx generators or linear-transformer-driver (LTD) modules to produce a petawatt-level power pulse [1]. In a recently published design of a petawatt-class z-pinch accelerator [1], LTD modules are used to drive monolithic water-insulated radial transmission lines with an exponentially increasing impedance. In the complex 3D convolution, the LTD electrodes connect to two levels of transformers at a given azimuth At their outputs, the impedance transformers are connected to magnetically insulated transmission lines (MITLs). The transformers serve as passive high-pass filters that reduce the amplitude of any low-frequency prepulse that might exist, and in addition, compress slightly the electrical power pulse This characteristic may reduce the need for additional pulse sharpening components and make an accelerator design more compact.
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