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P: Fachverband Plasmaphysik

P 23: Plasma Wall Interaction II

P 23.5: Vortrag

Donnerstag, 8. März 2018, 11:45–12:00, A 0.112

Determination of the Cs distribution along a line of sight by the Zeeman splitting in an inhomogeneous magnetic field — •Christian Wimmer, Maria Lindauer, Ursel Fantz, and the NNBI Team — Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching

A Tunable Diode Laser Absorption Spectroscopy (TDLAS) is installed in a pulsed-driven (plasma pulses up to one hour) low-temperature, low-pressure hydrogen plasma, into which caesium is evaporated, for the determination of the neutral Cs density and its temperature. Permanent magnets are attached to the side walls creating an inhomogeneous magnetic field (field strength of 3–30 mT) along the chosen line of sight. The laser is tuned over the resonance transition of Cs at 852 nm in order to obtain the Doppler-broadened spectrum. A clear Zeeman-splitting appears at the high field strength, i.e. close to the side walls, whereas no significant splitting occurs at the lower B-field strength in the center. By analyzing the measured Zeeman-split spectra, it could be observed that neutral Cs is depleted in the central part of the line of sight during long plasma pulses, whereas the Cs density stays considerably high close to the side walls. Cs is used in this ion source for the surface-conversion of hydrogen atoms to negative ions, with the main conversion surface being located close to the center of the line of sight. With this new insight, the vanishing of the correlation of the Cs density with the performance of the ion source can be explained.