E×B Penning Discharge: Coherent Plasma Structures and Cross-Field Transport

The E×B Penning discharge is a surrogate for the Hall thruster. Its axial magnetic field and radial electric field are perpendicular, so the electron drift is in the same direction for both the Penning discharge and the Hall Thruster. Plasma configurations where the magnetic and electric fields are perpendicular are called Hall plasmas, and are also used in magnetrons as well as Hall thrusters and Penning discharge devices.

The Penning discharge however has a large, open chamber which is ideal for introducing probes without disturbing the plasma. The device is suitable for studying spoke instabilities as well as for testing new probe models in stable or unstable plasmas. Depending on the operating parameters of the Penning discharge, for gas pressures of 0.1-10 mTorr of Xenon or Argon and a magnetic field of 10-150 Gauss, the plasma can be subject to the enhacement of electron cross-field transport and compared to classical collisional transport. Measuring the plasma potential is needed for the characterization of particle transport but such measurements of complex, flowing are magnetized plasmas can be challenging. Magnetized plasmas and typically subject to low and high frequency oscillations due to instabilities and plasma fluctuations lead to oscillating potential distributions in time and space.

Penning cross-field configuration with an RF cathode.

Xenon plasma in Penning discharge device with electron beam and probes.

Diagnostics for the Penning discharge include:

  • Langmuir probes (with reference probe) for temperature, density and plasma potential measurements.
  • Emissive probes for plasma potential measurements.
  • Novel magnetically-insulated baffled probe for plasma potential measurements.
  • Three planar probes for measuring ion densities.
  • Fast camera for 50kHz imaging of the plasma's visible light emission.

Penning Discharge Configuration

  • Low temperature DC-RF E × B beam-plasma disccharge with a negatively based cathode 20-100V with respect to ground chamber.
  • Current: 1.0-3.0A.
  • Pressure: 0.1-1.0mTorr.
  • Magnetic Field: 10-100G.
  • Electron density ne= 1010-1012cm-3.
  • Electron temperature Te= 1-10eV.