Production of Large Diameter, High-Density Helicon Plasma with Short Axial Length Using a Flat Spiral Antenna

A large diameter (73.8 cm), high-density helicon plasma with a short axial length (81 cm) has been successfully produced using a flat spiral antenna. The electron plasma density can reach ~ 6*10^12cm^-3 with the input rf power of < 4 kW. The stronger the degree of magnetic field convergence is from the antenna to the bulk plasma region, the lower the minimum input rf power required is to obtain a helicon plasma. This signifies the important role of the magnetic field structure near the antenna and is similar to the previous result obtained with a helicon plasma of a much longer axial length of 486 cm.