Cherenkov oscillators based on multi-dimensional interaction cavities hold strong promise to address the long-standing “terahertz gap”^1-4.  Sources delivering substantive power in the 0.1-10THz range are urgently needed for applications in fusion energy (sources for plasma heating and current drive in tokamaks, turbulence diagnostics for fusion plasma), enhancing Nuclear Magnetic Resonance using Dynamic Nuclear Polarisation (DNP-NMR) for biochemical spectroscopy and drug discovery, non-destructive testing, radar, remote sensing, and security.

Sources based on a backward-wave interaction with an electron beam are typically designed with cavity diameters comparable to the radiation wavelength, ensuring phase and spectral coherence of the output radiation but restricting the power at high frequencies, P ~ 1/f^2. The  interaction volume can be increased, without parasitic mode excitation, by implementing novel interaction structures with a shallow two-dimensional periodic corrugation.  The corrugation mediates the formation of a cavity eigenmode, composed of coupled volume and surface waves, providing the mode selection required for stable operation. Coherent radiation is generated by the Cherenkov interaction of the eigenmode and a hollow electron beam.

By exploring the non-linear dynamics of the system over a wide range of control parameters and modifying the electromagnetic dispersion near the point of interaction, we demonstrate the potential for sub-THz and THz sources operating in both the steady-state (stationary) and transient slippage (non-stationary) regimes. 

Simulations of sources exploiting cylindrical cavities with diameters exceeding 9 times  λ show the potential for diverse operation regimes: short pulse, steady-state sources offering 10’s of megawatts (MW) of power, high average power (0.5-2.5MW) “quasi-continuous” wave and continuous-wave sources and ultra-short pulse superradiant sources delivering 100’s of megawatts of instantaneous power.