Plasma measurements in the space plasma operation chamber (SPOC)

Plasma with a temperature and density similar to the ionospheric plasma is produced in the Space Plasma Operation Chamber (SPOC). SPOC, constructed at NCKU in 2009, is a research plasma device designed for the calibration and testing of satellite/rocket-borne instruments and for studying space plasma processes. It is a cylindrical chamber 2 meters in diameter and 3 meters in length. The vacuum pressure inside the SPOC can reach 10^-8 Torr. The plasma in this large vacuum space is produced by two back-diffusion type plasma sources installed at the center of the chamber side doors. The sources produce ions of controllable drifting energy from a few ten eV to several hundred eV, these ions, together with the thermal electrons emitted from nickel cathodes, collide with neutral molecules at a pressure of 10^-4 Torr in the chamber and form the plasma environment. The plasma density varies from 10³ to 10⁶ cm^-3, and the neutral density is ~ 1012 cm^-3. The electrons have a Maxwellian distribution with a temperature in the range 1000-3000 K. The ions have two component distributionsP: one is the drift-Maxwellian component with temperature close to the neutral particle temperature (room temperature), and the other is a small ion beam component. We have developed several space instruments for testing in the SPOC. This paper describes the SPOC machine and its capabilities for plasma experiments and space environmental tests. The plasma environment in the SPOC is measured by the Langmuir probe, the retarding potential analyzer, and the electron temperature and density probe. Results measured by different instruments are compared and discussed. The thermal and beam components of the ion energy distributions at different positions and the electron temperature and density spatial distributions are shown and discussed. The SPOC can be used to develop space-borne instruments and plasma thrusters, check the performance of instruments before flight, check whole payload systems in the plasma and vacuum environment, and conduct basic plasma experiments related to space sciences.