An emissive probe is used to measure the potential of the plasma. During the heating, it emits the electron current in all directions. The emitted electrons are always found in random motion. In presence of magnetic field (strong), electrons and ions have gyro motion (or flowing in the plane perpendicular to B). In strong B case, the emitted electrons will also follow the B line and fraction of electrons will trap near the probe tip and will not come to plasma region. In such cases, the use of emissive probe may give inaccurate value of plasma potential. Could you suggest the best way to measure the plasma potential in the strong magnetized plasma (B in few Tesla).? or Could you correct my opinion on the working principle of emissive probe in strong magnetized plasma?.
Several people on tokamak COMPASS, Prague, Czech Republic, have addressed this question by comparing the measurements of an emissive Langmuir probe with ball-pen probe measurements. See e.g.:
Article Comparative measurements of the plasma potential with the ba...
Article Measurements with an emissive probe in the CASTOR tokamak
Article Direct plasma potential measurements by ball-pen probe and s...
Dear Mangilal,
Yes, definitely emissive probe can be used to measure plasma potential in magnetized plasma. However some precautions needed with probe orientation and method. Floating potential method is a better choice for plasma potential measurements even in magnetized plasmas. The errors are minimum because, probe does not draw current in this method. In case of I-V required, make sure plane of the probe parallel to the magnetic filed so that Lorentz force effects will be minimized.
Thank you Kateřina Jiráková and Vara for fruitful comments and suggestions.