High Gradient High Shunt Impedance Accelerating Structure

Conventional traveling wave or pi-phase advance standing wave structures use coupling of the microwave power through the beam pipe. This feature constrains the cavity shunt impedance (efficiency) to relatively small values. As microwave power flows through the accelerating cells in such structures, the probability of breakdown in high gradient operation is greatly increased. Euclid Techlabs LLC proposes to develop a high gradient high efficiency accelerating structure based on a distributed microwave coupling approach invented at SLAC. These structures include one or more parallel waveguides which are loaded by accelerating cavities. In this configuration accelerating cavities are fed independently and completely isolated at the beam pipe. This approach allows maximizing the shunt impedance and enables high gradient operation because there is no microwave power flowing through the accelerating cavity. In Phase I we will design and build a proof-of-principle prototype of a distributed coupling accelerating structure. The only step left to Phase II because of limited time in Phase I will be the brazing of the structure. We will perform cold tests of the unbrazed structure to measure its basic accelerating properties. The main performance metric in Phase I is the demonstration of high shunt impedance (~100 MOhm/m). Future free electron lasers and colliders require high gradient and high efficiency accelerating structures. The accelerator proposed here satisfies both requirements and offers a reduced manufacturing cost compared to modern high gradient structures. The proposed approach will find immediate applications in industry because the high shunt impedance relaxes the requirements on the peak power of the microwave source for the accelerator.