Index of content:
Volume 78, Issue 7, July 2007
- NUCLEAR PHYSICS, FUSION AND PLASMAS
Mirror Langmuir probe: A technique for real-time measurement of magnetized plasma conditions using a single Langmuir electrode78(2007); http://dx.doi.org/10.1063/1.2754392View Description Hide Description
A new method for the real-time evaluation of the conditions in a magnetized plasma is described. The technique employs an electronic “mirror Langmuir probe” (MLP), constructed from bipolar rf transistors and associated high-bandwidth electronics. Utilizing a three-state bias wave form and active feedback control, the mirror probe’s characteristic is continuously adjusted to be a scaled replica of the “actual” Langmuir electrode immersed in a plasma. Real-time high-bandwidth measurements of the plasma’s electron temperature, ion saturation current, and floating potential can thereby be obtained using only a single electrode. Initial tests of a prototype MLP system are reported, proving the concept. Fast-switching metal-oxide-semiconductor field-effect transistors produce the required three-state voltage bias wave form, completing a full cycle in under . Real-time outputs of electron temperature, ion saturation current, and floating potential are demonstrated, which accurately track an independent computation of these values from digitally stored characteristics. The MLP technique represents a significant improvement over existing real-time methods, eliminating the need for multiple electrodes and sampling all three plasma parameters at a single spatial location.