A steady-state plasma in a quadrupole magnetic field

Plasma from a duoplasmatron is injected along the axis of a linear quadrupole. Peak number densities of about 5 x 109 cm-3 and temperatures of about 10 eV are achieved. The lifetime is about 100 μs; losses occur mainly at the ends, transverse losses being negligible. This hot plasma is embedded in a cold plasma (0.5-1 eV) part of which drifts upstream towards the source. It is suggested that this arises from the action of a positive sheath at the far end of the device, maintained by an excess electron current from the source. Density and potential fluctuations are observed throughout the plasma but are large only in a zone bounded approximately by the critical surface and the surface of minimum field line length. (author)