Ramona Gstrein

University of Innsbruck, Innsbruck, Tyrol, Austria

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Publications (4)1.94 Total impact

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    ABSTRACT: Emissive probes are standard tools in laboratory plasmas for the direct determination of the plasma potential. Usually they consist of a loop of refractory wire heated by an electric current until sufficient electron emission. Recently emissive probes were used also for measuring the radial fluctuation-induced particle flux and other essential parameters of edge turbulence in magnetized toroidal hot plasmas [R. Schrittwieser et al., Plasma Phys. Controlled Fusion 50, 055004 (2008)]. We have developed and investigated various types of emissive probes, which were heated by a focused infrared laser beam. Such a probe has several advantages: higher probe temperature without evaporation or melting and thus higher emissivity and longer lifetime, no deformation of the probe in a magnetic field, no potential drop along the probe wire, and faster time response. The probes are heated by an infrared diode laser with 808 nm wavelength and an output power up to 50 W. One probe was mounted together with the lens system on a radially movable probe shaft, and radial profiles of the plasma potential and of its oscillations were measured in a linear helicon discharge.
    The Review of scientific instruments 09/2008; 79(8):083508. · 1.52 Impact Factor
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    ABSTRACT: We report on experimental investigations of the change of the electron saturation current of a dc-heated emissive probe with the probe heating current. According to the simple theory of the emissive probe, the electron saturation current should not be affected by emission. However, in many experiments a variation of the electron saturation current with the emission current was observed. We consider two possible reasons for such variations: (a) the influence of the space charge around the probe shaft, (b) the change of the work function of the probe surface material due to heating. We tried to find sufficient experimental evidence for supporting one or the other (or both) of these two explanations. We used two different types of plasma to validate the results: a cylindrical magnetron plasma and the non-magnetized plasma of a DP machine. From our experiments follows that the electron saturation current of the emissive probe is affected by the space charge effect as well as it depends on the probe wire material.
    Czechoslovak Journal of Physics 09/2006; 56:B932-B937. · 0.42 Impact Factor
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    ABSTRACT: Emissive probes are standard tools in laboratory plasmas for the direct determination of the plasma potential. Usually they consist of a loop of refractory wire heated by an electric current until sufficient electron emission. We have developed and investigated various types of emissive probes which were heated by a focused infrared laser beam. Such a probe has several advantages: higher probe temperature without evaporation or melting and thus higher emissivity and longer lifetime, no deformation of the probe in a magnetic field, no potential drop along the probe wire, faster time response. The probes are heated by an infrared diode laser with 808 nm wavelength and an output power up to 50 W.
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    ABSTRACT: We report on a systematic investigation of electron-emissive probes in a DP-machine plasma. The rationale are perturbing effects observed with emissive probes in various plasmas and with emissive probes of various designs. These effects might impair the accuracy of emissive probes as diagnostic tools for the direct determination of the plasma poten-tial. The two effects are a deviation of the floating potential of an emissive probe from the plasma potential even for a strongly heated probe and a variation of the electron saturation current with the probe heating. We have therefore tested conventional emissive wire probes with different wire diameters and materials and different loop lengths in the Innsbruck DP-machine.