Experimental Study on Behaviors of Low Temperature DC Plasmas in the Magnetic X-Point Simulator System, Maximus

Abstract

A multidipole chamber with a DC discharge system capable of generating magnetic X-point configuration, MAXIMUS (MAgnetic X-point sIMUlator System), is constructed. The vacuum chamber of MAXIMUS is composed of two cylindrical chambers with the total length of 2 m (2 x 1 m) and the diameter of 60cm. An LaB6 hot cathode is installed on one end of the chamber, emitting energetic electrons whose energy can be varied up to approximately 200eV. The base pressure is ~ 1 0–6 Torr, and Ar, He, or mixed H2 DC glow discharge plasmas are generated with working pressure of between 0.1 and 10.0mTorr. Langmuir probes and emissive probes are used to measure electron temperature T e, plasma density ne, and plasma potential $\phi_{\mathrm{p}}$ . Magnetic fields are measured with Hall probes. Typical plasma parameters generated in MAXIMUS are found to be $\mathrm{T}_{\mathrm{e}}\sim 1\text{eV}, \mathrm{n}_{\mathrm{e}}\sim 10^{9}$ cm-3, and $\phi_{\mathrm{p}}\sim 4\mathrm{V}$ . Plasma parameters can be controlled by neutral gas pressure, discharge voltage and discharge current. Magnetic X-point is generated by two axial copper tubes inside the MAXIMUS, which can carry DC currents up to 1kA each. The magnetic field configuration can be adjusted by changing the position of the copper tubes and by changing the driving current of each tube independently. Spatial profiles of plasma parameters are investigated in the presence of the multidipole permanent magnets and various configurations of the magnetic X-point. MAXIMUS is designed to explore fundamental properties of plasmas, effects of neutral particles around the magnetic X -point to the core plasmas, and the plasma behavior due to magnetic perturbations in magnetic X-point configuration.