Two-dimensional imaging of a helicon discharge

Two-dimensional images of the ionized argon light of a helicon discharge are made both along and across the magnetic field with various antenna configurations. Two antennas, a Nagoya type III and a helical antenna, are used to create a magnetized RF plasma with density in the range n ≤ 5× 1013 cm−3. A CCD camera with a 488 nm bandpass filter is used to image the plasma as magnetic field and power are changed. By inserting a Faraday shield, it is demonstrated that the inductive component of the antenna coupling is responsible for producing high-density plasmas. Asymmetries in the plasma profile are shown to be caused primarily by capacitive coupling, with the purely inductively coupled plasmas being symmetric and centrally peaked. Numerical calculations of antenna coupling show that the configurations having the largest antenna loading correspond to the brightest plasmas observed in the experiment, with the m = +1 mode being the most strongly coupled.