Two-Frequency Notch Filters for Sub-THz Plasma Diagnostics

Modern Electron Cyclotron Resonance Heating (ECRH) systems in fusion plasma research take advantage of multi-frequency gyrotrons. This means that the frequency band of some millimeter-wave diagnostics contains more than one narrowband gyrotron-frequency line, which needs to be suppressed. Compact standard-waveguide notch filters, based on coupled waveguide resonators with rectangular cross section, are presented, which can provide very high suppression of several gyrotron frequencies providing low insertion loss in the pass band.