Correlation Between Fluctuating Electron Temperature and Fluctuating Space-Potential Challenges the Probe Determination of Turbulent Electric Field Spectrum

The measurement of plasma potential and electric field by the traditional Langmuir probe method can contain a significant qualitative error due to a spurious effect from temperature fluctuations that appear in the temperature-potential cross phase. This error is separate from any systematic error in the floating potential amplitude due to cross-correlated temperature and potential fluctuations not averaging out. Conditions under which electron temperature fluctuations significantly and insignificantly affect the measurement of electric field fluctuations in plasma are considered for both effects. Actual measurements illustrate the obtained conclusions are presented. Correct direct measurement of plasma’s space potential fluctuations requires that the amplitude of electron temperature fluctuations (in eV) be at least ten times smaller than the space potential fluctuation amplitude (in volts).