Bochum 2015 – wissenschaftliches Programm
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P: Fachverband Plasmaphysik
P 5: Poster Session - Low Temperature Plasmas
P 5.11: Poster
Montag, 2. März 2015, 16:30–18:30, Foyer Audimax
He-metastable densities and N2 afterglow in the pulsed constricted mode of the µAPP rf microjet (µAPPJ) — •Stefan Spiekermeier1, Stephan Chromy2, Marc Böke1, and Jörg Winter1 — 1Institut für Experimentalphysik II, Ruhr-Universität Bochum — 2IOT, RWTH Aachen
The rf-driven capacitively coupled µAPPJ is usually operated in the homogeneous α-mode. It tends to become unstable and switch to a bright local "arcing" mode (constricted mode) at high powers. In this mode, the chemical reactivity is enhanced but it will destroy the device, if it is not controlled. We have developed a technique in which the jet is repetitively driven into the constricted mode by either applying short rf-power pulses, or by triggering the transition with high power laser pulses. We have employed Broad Band Absorption Spectroscopy (BBAS) using the super-continuum radiation from a photonic fiber, pumped by a high power fs laser to measure quantitatively and space resolved the concentration of helium metastable atoms (He*). Metastable densities in the order of 1013 cm−3 have been measured in the constricted mode exceeding the metastable densities in the α-mode by two orders of magnitude. When admixing a few percent N2 to the He working gas, a confined orange afterglow is observed, extending from the nozzle of the jet for more than 20 cm. The afterglow is due to the (collisional) de-excitation of the metastable N2(A) state of the N2 molecule at an excitation energy of about 6 eV. In the constricted mode the afterglow is much more pronounced than in the α-mode.
This work is supported by DFG (FOR1123)