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P: Plasmaphysik
P 6: Discharges
P 6.3: Vortrag
Donnerstag, 5. April 2001, 17:00–17:15, 2053
Wave absorption and power deposition in a large volume helicon discharge with m = 1 helical antenna coupling — •Bernd Lorenz and Michael Krämer — Experimentalphysik II, Ruhr-Universität Bochum, D-44780
Helicon discharges reveal a pronounced axial asymmetry, if the rf power is launched to the plasma by helical antennas, which generate a right-turning field. This finding can be attributed to the fact that the rf power is predominantly deposited in the plasma through helicon modes with positive azimuthal mode numbers travelling in positive magnetic field direction (No-dqhelicon sideNo-dq).
The investigations have been carried out on the pulsed large-volume helicon HE-L discharge with m = 1 helical antenna coupling (tpulse≈ 2 ms, fpulse=25 or 50 Hz, PRF<3 kW, fRF=13.56 MHz, ne≤ 2· 1019 m−3, Te=3 eV, B0<0.1 T, p=0.1−2 Pa argon gas, rp=7.4 cm, Lp=110 cm). Electric probe diagnostics as well as 1 mm and 8 mm interferometry was applied to determine the plasma parameters. The rf wave field pattern was obtained from an array of movable magnetic probes.
We focussed on the formation of the helicon discharge and the helicon wave dispersion, in particular, the damping. The latter was deduced from the spatial decay of the helicon wave field which was recorded on the No-dqhelicon sideNo-dq of the antenna. Our results were compared with findings predicted by various theoretical models involving mode conversion and non-collisional damping mechanisms like electron Landau damping.
Supported by the Deutsche Forschungsgemeinschaft (SFB 191, A12).