ECR (Electron Cyclotron Resonance) plasma source

ECR excitation method also use microwave to heat up electrons. In ECR plasma source, permanent magnets or solenoid coils are used to generate strong magnetic field. All the free electrons will rotate with same frequency that can be calculated with the equation below: ECR equation
Once the input microwave frequency matches the electron cyclotron frequency, a resonating effect will heat up the massive number of electrons and generates plasmas.

Concept of ECR discharge plasma
Principle of ECR discharge

PIE Scientific - Remote plasma cleaner for electron microscope