Ion-temperature determination with a baffled Langmuir probe

An electrostatic Langmuir probe for real-time measurements of parameters in magnetized plasma is tested in fully ionized, barium, Q-machine plasma. The small-diameter, long-length, tungsten wire sensor, i.e., the probe tip, oriented with its cylindrical axis perpendicular to the magnetic field (B), is partially shielded by ceramic baffles, or masks, that form sensor-access slots between the baffles. Adjusting the azimuthal orientation of the slots, by rotating the probe about its cylindrical axis, changes the fraction of proximity gyro-orbiting electrons, relative to the fraction of proximity gyro-orbiting ions, that can access the recessed sensor along the magnetic field. Thus, the ratio between the electron and ion saturation currents, I_e ^sat and I_i ^sat, can be adjusted without having affected the probe bias voltage V_b. When optimally shielded (I_e ^sat/I_i ^sat=1), accurate, real-time measurements of space potential V_s can be acquired. When maximally shielded (I_e ^sat/I_i ^sat≪1), accurate, real-time measurements of ion temperature T_i can be acquired. Subtracting the floating potential V_f of an optimally shielded baffled probe from V_f of a maximally shielded baffled probe yields T_i (and its fluctuation phase) in real time.