MegaWatt Microwave Pulse Chopper

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

My work was in the design, fabrication, testing, and characterization this "pulse chopper". 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.

I published a paper on this pulse chopper which can be seen here, and a paper on the accelerator testing results is currently in review at Applied Physics Letters. This work also resulted in the Best Student Poster Award at PPPS 2019 and Best Student Poster Award at NAPAC 2019.

Top: The actually pulse chopper (laser not shown). The Silicon wafer is held in a housing at center-front. Microwaves enter the switch as a long pulse from the left waveguide and the short, "chopped", pulse leave through the waveguide at top-right.
Bottom: The Megawatt Gyrotron Lab at the MIT PSFC. The Pulse Chopper can be seen at left, within the black laser enclosure.