Efficient 94GHz Cherenkov Radiation Source with a Multistage Energy Recovery System

We present the concept and design of an efficient (“,56% overall efficiency) megawatt (MW) coherent Cherenkov radiation source operating at 94GHz combined with a 4-stage depressed collector. The source has a highly oversized interaction region, enabling MW continuous wave radiation. Mode selection, achieved via high-order mode coupling, is mediated by a 2D periodic surface lattice (PSL) interaction cavity. The overall device efficiency is competitive with gyrotrons in the requirements for heating and current drive in fusion plasma, with further application in plasma turbulence diagnostics, biochemical spectroscopy, radar and remote sensing. These sources are scalable; both in transverse size and frequency, with strong potential to address the long-standing terahertz gap. The presented energy recovery technique has broad applicability to many electron-beam-driven devices.