Thomson-scattering diagnostics of plasmas produced in a miniature microwave discharge ion engine

A study was conducted to measure plasma properties by laser Thomson scattering (LTS) to understand the physics inside this engine. The photon-counting method with a double monochromator was used to overcome the difficulties of applying the method to the plasma produced in the miniature microwave ion engine. Microwave power at 2.45 GHz was fed through a coaxial line and into an antenna in the engine. The screen grid and the ion source body were biased at +1500 V relative to ground and the acceleration grid was biased at -300 V. The primary electrons were confined in the mirrorlike magnetic field formed between the central and front yokes, gaining energy from microwave emission by electron cyclotron resonance heating. Two small holes to inject the laser and another hole collect scattering light were made to measure the plasma inside the discharge chamber.