The Concept

In order to test some designs for future particle accelerators, you need a very short pulse of very high power microwaves. It's easy to make a pulse that's either short or high power, but both is much more challenging. I developed a "pulse chopper" to generate very short pulses (<10 ns) from longer, high-power pulses, which are generated by a gyrotron in our lab.

My Research

I designed, fabricated, tested, and characterized the pulse chopper over my first two years of graduate school. The chopper uses a laser to temporarily turn a microwave-transparent wafer of silicon into a microwave-reflecting mirror. During the few nanoseconds the silicon is reflective, the reflected microwave pulse can be directed into particle accelerator structures and the results measured. We have successfully used this to test an accelerator cavity developed at SLAC up to >225 MV/m. Typical accelerator cavities can achive <100 MV/m.

The pulse chopper has since be implemented in a new project for the NIH to enhance the resolution of medical spectroscopy. Nanosecond-duration high power pulses of 250 GHz microwaves are generated for use in pulsed dynamic polarization magnetic resonance imaging (PDNP-NMR) to study tissue samples.

I published a paper on the pulse chopper which can be seen here, and the results of the SLAC structure testing has been published here. This work resulted in the Best Student Poster Award at PPPS 2019 and Best Student Poster Award at NAPAC 2019.