A nine-electrode probe for simultaneous measurement of all terms in the ideal radial Ohm's law

A Nine-Electrode Probe (NEP) has been developed for simultaneous measurement of all terms in the ideal Ohm's law E+ U X B = 0 in the radial (r) direction in cylindrical geometry, where E is the electric field, U is the plasma flow velocity, and B is the magnetic field. The probe consists of two pairs of directional Langmuir probes ( Mach probes) to measure the axial (z) and azimuthal (theta) plasma flows, two pairs of floating Langmuir probes at different radial positions to measure the radial electric field, and two B-dot coils to measure the axial and azimuthal magnetic field. The measurement is performed in the Flowing Magnetized Plasma (FMP) experiment. Two flow patterns are identified in the FMP experiment by the NEP. The peak-to-peak values of radial electric field fluctuation is 1.5-4 times of the mean values. Comparisons of U X B vertical bar(r) and E-r show that E-r + U X B vertical bar(r) is not zero within some periods of discharge. This deviation suggests non-ideal effects in Ohm's law can not be neglected. (c) 2006 American Institute of Physics.