ひずみのあるLangmuir探針特性からの空間電位の推定法

抄録

We have measured the electron energy distributions in He DC glow discharge under the condition of 0.5-2.5 Torr, 5-35mA, using Langmuir probe by the second harmonic method.
Distortion of the second derivative characteristic can't be neglected, because our probe is designed a large size for the measurement of the high energy part of the electron energy distribution. Therefore minimum, zero, maximum points of the second derivative exist at different probe potentials, and determination of the space potential is difficult.
In this paper, we quantified the probe circuit impedance and the ion current, and corrected the second derivative. We simulated the distortion of the second derivative due to a finite probe length and the fluctuation of the space potential. As a result, we confirmed that the inclination and the unevenness of the second derivative (which determine the shape of the electron energy distribution) appear in a high probe bias part from the maximum point of the second derivative characteristic. We found that a reference point of Druyvesteyn's principle exists at the maximum point for a distorted second derivative, and that the space potential lies at the zero point for a nondistorted characteristic.