Helicon plasma studies

Summary form only given. Helicon plasma sources are recognized as sources of high density plasma. These sources are characterized by an axial magnetic field and an inductive antenna that is used to generate helicon waves which penetrate into the core plasma and heat electrons away from the walls. Even though these sources have been studied extensively some aspects of their operation are still unknown-the design of these sources is still an art form. There are axially short, large radii, low field systems and axially long, radially small, high field systems. This report concentrates on the latter type. Peak densities of 2-3/spl times/10/sup 13/ cm/sup -3/ are obtained on our test system which is a 120 cm long, 10 cm diameter cylindrical glass tube filled with argon at 7 mTorr. The axial magnetic field is 1 kG. RF power of 300-700 Watts at 13.56 MHz is applied to a 3 turn, 15 cm long, spiral antenna that is located near one end of the system. A Nagoya III antenna and a double half-turn antenna have also been studied. A grounded limiter/end plate is located near the antenna. The densities are measured using Langmuir probes with RF fluctuation suppression circuits and confirmed with 70 GHz microwave interferometry. The density increases from less than 1/spl times/10/sup 12/ cm/sup -3/ to 2/spl times/10/sup 13/ cm/sup -3/ as the power is increased from 150 to 300 Watts. Antenna coupling measurements show that increased coupling cannot account for the increased density. More efficient electron heating or changes in the losses or a combination of these must be invoked to account for the density increases.