Microwave-plasma in a simple magnetized torus

In a magnetized torus with no poloidal field component, a weakly ionized plasma is produced by microwaves at 2.45 GHz in the O-mode as well as the X-mode. The neutral gas pressure pg ranges from 5×10−5 to 1×10−3 mbar, ne∼1−5×1016 m−3, and Te∼2−6 eV. The O-mode is only weakly absorbed at the electron cyclotron resonance (ECR), but is partly converted to the X-mode by wall reflections. The X-mode is absorbed via the upper hybrid resonance (UHR), presumably through conversion to and absorption of electron Bernstein waves (EBW). For pg>1×10−3 mbar the EBW absorption is collisional, but for lower pg a collisionless transit particle mechanism could be responsible. Typically the spatial plasma distribution depends mainly on the major radius R, and the measured ne(R) increases monotonically with R from the ECR to an UHR near the outer wall. Te is determined by the particle balance, and is proportional to the ionization energy. The average ne is determined by power balance, and increases with wave power.