Ion Temperature Sensitive Effect in Transient Langmuir Probe Response
MASSACHUSETTS INST OF TECH CAMBRIDGE FLUID MECHANICS LAB
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A theory is presented for a method, recently proposed by Hester and Sonin, of determining the ion temperature in a plasma by measuring the transient current response of a highly negative, cylindrical Langmuir probe under conditions where collection is collision-free and the ratio of probe radius to Debye length is small. The ion component of the current does not approach its final steady-state value monotonically, but exhibits a strong, ion temperature dependent overshoot in the first few ion-plasma periods following the biasing of the probe. Analytical formulae are derived for a Maxwellian plasma, and convenient graphical results are presented. The possible masking of the overshoot by a transient displacement current is discussed and found to be often negligible. For other conditions an alternative measuring method is suggested in which the contribution of the displacement current cancels out.
- Plasma Physics and Magnetohydrodynamics