Efficient Cherenkov source exploiting two-dimensional periodic surface structure and multi-stage depressed collector*

We present the detailed design of powerful, efficient sources based on novel two-dimensional periodic surface lattice (2D-PSL) structures.  The 2D-PSL interaction cavities are scalable, both in frequency and in transverse size^1,2, with potential to deliver the high-frequency, continuous-wave (CW), megawatt (MW) radiation needed for RF heating and current drive in fusion tokamaks. To meet these requirements, the cylindrical 2D-PSL cavity diameter must be at least 9 times greater than the free-space source wavelength.  The 2D corrugations of the PSL interaction cavity mediate a Cherenkov interaction with a complex high-order coupled eigenmode, composed of volume and surface waves, ensuring modest beam and wave power density. 

 

To achieve nuclear fusion, hundreds of 1MW, CW sources are needed.  Energy efficiency is therefore paramount.  Maximum energy extraction is achieved by optimizing the non-linear dynamics of the system, ensuring that the radiation generated from different parts of the large diameter, annular electron beam is coherently synchronized.  The overall efficiency can be increased by recovering electron energy from the spent beam using a multi-stage depressed collector.  Here, we demonstrate the ability to efficiently generate MW, CW radiation at high frequencies, with a slow wave technique.

 

Sources based on 2D-PSLs have additional applications in many areas where enhanced power is needed at sub-THz and THz frequencies.  Important applications include: plasma scattering and turbulence diagnostics, advanced spectroscopic techniques such as enhancing nuclear magnetic resonance using dynamic nuclear polarization (DNP-NMR), radar, remote sensing and communications.