Measurement of the Electron Distribution Function in the Loss Cone of an ECR-discharge by Using a Double Retarding Field Analyzer

A double retarding field analyzer (DRA) was used for measuring electron distribution functions (EDFs) in the loss cone of an electron-cyclotron-resonance (ECR) discharge run in mixtures of He and N2. By integrating along ϵ = const lines, where ϵ = E‖ + E⟂ is the kinetic energy, the true electron energy distribution function F(ϵ) in the loss cone of the ECR discharge was determined. The shape of F(ϵ) transforms from an exponential functions to a power law when changing plasma parameters like mixture ratio, total pressure and mirror ratio.