Characteristics of Rf-Produced, High-Density Plasma with Very Small Diameter

To investigate characteristics of helicon plasma with a very small diameter, we have developed the Small Helicon Device (SHD) and measured the electron density under various conditions over a wide range of radio frequencies. Using a tube with inner diameter of 20 mm, an electron density ne of ~ 10 13 cm near the antenna region was obtained with an excitation frequency f of 7 MHz, rf power Prf of ~ 1000 W, and axial magnetic field in the magnet coil region B of 560 G. In the case of an inner diameter of 5 (10) mm under conditions of f = 12 (7) MHz, Prf ~ 1000 W, and B = 280 G, ne of ~ 10 11 cm was succesfully achieved even away from the antenna region.