Description
We present the concept of high-power (kilowatt to megawatt) sub-THz Cherenkov oscillators employing complex two-dimensional periodic surface lattice (2D PSL) interaction cavities for the production of coherent radiation. These sources can be tailored for diverse stationary and non-stationary regimes. When operating in the steady-state regime, these sources are especially attractive for applications in plasma physics including enhanced plasma turbulence diagnostics and potentially as current drive sources for future fusion tokamaks.
Backward-wave electron beam driven sources are traditionally designed with cavity diameters comparable to the radiation wavelength which ensures phase and spectral coherence but limits the output power at shorter wavelengths, scaling approximately as P∼1/f^2. The cylindrical interaction volume can be increased, while suppressing parasitic mode excitation, by introducing a shallow two-dimensional periodic corrugation along the cavity wall. This corrugation mediates the formation of a hybrid eigenmode composed of coupled volume and surface wave components, which under optimum operating conditions, becomes the dominant mode excited by the hollow annular electron beam.
A key advantage of these sources is that the operating frequency is primarily determined by the lattice parameters, rather than the magnetic field, allowing operation with modest axial guide fields. Simulations indicate that >90% of the output power can be concentrated in a single high-order 〖HE〗_(m,1) mode, where m is the number of azimuthal periods of the cylindrical interaction structure.
Particle-in-cell simulations demonstrate the potential of these sources to deliver high-power, narrowband radiation, with the maximum output power determined by both the desired pulse length and the D/λ ratio of the cavity. Although very high values of D/λ are theoretically possible, this leads to increasingly constrained coupling conditions and also requires the electron beam to be positioned closer to the wall to intercept the rapidly decaying surface field.
We present the progress towards the realisation of Cherenkov sources based on 2D surface lattice structures. The scalability in both frequency and transverse cavity size make these sources a promising solution for bridging the long-standing THz gap, with important applications in plasma science.