Berlin 2001 – scientific programme

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P: Plasmaphysik

P 9: Dense Plasmas and Plasma Diagnostic (Poster Session)

P 9.20: Poster

Tuesday, April 3, 2001, 12:30–15:00, AT2

Investigations on Electric Field Distributions in a Microwave Discharge in Hydrogen — •D. Luggenhölscher, U. Czarnetzki, and H.F. Döbele — Institut f. Laser- und Plasmaphysik, Universität Essen, 45117 Essen, Germany

Microwave discharges play an important role as plasma sources for industrial applications like surface modification and thin film deposition. The electric field distribution in the plasma determines the electron density and energy distribution and the homogeneity of the discharge. The typical amplitude of the electric field is of the order of 100 V/cm. Up to now, this low field strength was not within the reach of laser spectroscopic techniques for electric field measurements. Recently, we have developed a novel technique in atomic hydrogen that allows the measurement of low electric fields down to 5 V/cm. The electric field is determined from the Stark splitting of high Rydberg states (typically n=14-20). Here this technique is applied to a pulsed microwave discharge at 2.45 GHz in hydrogen. The spatial and temporal field distribution is investigated in a commercial plasma source (SLAN). The cylindrical discharge chamber has a diameter of 160 mm and a length of 500 mm; typical power is of the order of 1 kW at pressures of a few 10 Pa. The measurements show that both microwave and plasma microfields contribute to the electric field in the steady state case. In the pulsed mode the microwave field is dominant during the transient switch-on phase while in the off phase the micro field can be measured.