HIGH-DENSITY PLASMA PRODUCTION USING A SLOTTED HELICAL ANTENNA AT HIGH MICROWAVE-POWER

This paper presents results of high-density plasma production experime nts carried out using an optimally designed and excited slotted helica l antenna. The slotted helical antenna was excited by linearly polariz ed, right-hand polarized (RHP) and left-hand polarized (LHP) CW microw aves (f = 2.45 GHz) with power up to 2.5 kW. Two different discharges- the resonant and the non-resonant discharges-were studied. In the reso nant discharges the magnetic field at the edge of the helical antenna was equal to the ECR field, so that a resonant coupling of the electro ns and the microwaves could occur. In non-resonant discharges the valu e of the magnetic field was greater than the resonant field throughout the mirror. it was seen that the linearly polarized and RHP waves can produce about 100% ionization (at pressures approximate to 1-2 x 10(- 4) Torr; power less than or equal to 2.5 kW) for both resonant and non -resonant discharges. In most cases an enhancement over the neutral pa rticle density could be observed due to improved confinement. The reso nant discharge using LHP waves also yielded similar:results as obtaine d using the RHP and the linearly polarized waves. This result is somew hat unexpected since the LHP waves are not expected to undergo resonan ce at electron cyclotron resonance. The non-resonant discharge using L HP waves was found to be very weak (underdense). Finally, an attempt h as been made to understand the unexpected nature of the resonant disch arges using LHP waves, in terms of the modes of plasma loaded helices and waveguides.