Large volume electron cyclotron resonance plasma generation by use of the slotted antenna microwave source

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Abstract
A new electron cyclotron resonance plasma source, the slotted antenna (SLAN) is presented. The microwave power is coupled to the plasma inside a quartz bell jar by ten equally spaced slot antennae positioned equidistantly around the inside wall of a cylindrical ring cavity. A total of 10 SmCo magnet stacks are positioned between each two slots yielding the required 87.5 mT magnetic field strength for electron cyclotron resonance inside the plasma excitation volume. The source plasma ignition/extinction performance and operational range for different atomic (Ar, He) and molecular gases (O2, N2) were studied in detail. Due to the external magnetic field either in toroidal or hybrid symmetry, a shift of the minimum ignition pressure from 0.4 to 2×10−3 mbar and the minimum extinction pressure from 4×10−3 to 2×10−4 mbar for argon was observed. The radial and downstream ion density as well as electron temperature were measured by double-Langmuir-probe techniques. Microwave power coupled to the source was varied from 600 to 2000 W and pressure was ranged from 2×10−4 to 10−2 mbar. Typical data achieved for 1000 W microwave power are ion density 2.8×1011 cm−3 at a pressure of 5×10−3 mbar, corresponding to an ionization ratio of 1.3% (center of SLAN).

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