Large-area high-density helicon plasma sources

摘要

High-density (10~(12)-10~(13) cm~(-3)) helicon plasmas produced using two different but similar devices whose diameters are very large, 40 cm and 74 cm, respectively, have been characterized. A scaling of the particle production efficiency has been investigated in detail into a low aspect ratio (the ratio of the diameter to the axial length) region down to 0.075. It has been found that reducing this ratio manifests the standing wave-like patterns of the excited radio frequency (rf) fields. Spatial profiles of the electron density and the rf wave fields are measured, showing the effectiveness of the control of these profiles by changing the magnetic field configurations near the excitation antenna. Finally, high-beta plasmas with up to β ～ 0.8, that exhibit diamagnetic character, where β is the ratio of the plasma pressure to the magnetic pressure, have been produced with low magnetic fields.