A Radially Movable Laser-Heated Emissive Probe

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.