Cutoff probe using Fourier analysis for electron density measurement

Abstract

This paper proposes a new method for cutoff probe using a nanosecond impulse generator and an oscilloscope, instead of a network analyzer. The nanosecond impulse generator supplies a radiating signal of broadband frequency spectrum simultaneously without frequency sweeping, while frequency sweeping method is used by a network analyzer in a previous method. The transmission spectrum (S21) was obtained through a Fourier analysis of the transmitted impulse signal detected by the oscilloscope and was used to measure the electron density. The results showed that the transmission frequency spectrum and the electron density obtained with a new method are very close to those obtained with a previous method using a network analyzer. And also, only 15 ns long signal was necessary for spectrum reconstruction. These results were also compared to the Langmuir probe's measurements with satisfactory results. This method is expected to provide not only fast measurement of absolute electron density, but also function in other diagnostic situations where a network analyzer would be used (a hairpin probe and an impedance probe) by replacing the network analyzer with a nanosecond impulse generator and an oscilloscope.

Fast measurement of a pulsed plasma using a Fourier cutoff probe

“…Each tip was 1 cm long and about 2 mm apart from each other. While a network analyzer is normally used to produce a transmission spectrum, a method employing a Fourier cutoff probe (FCP) [33] was used in this experiment, because the frequency sweeping time of the network analyzer is much slower than the variation of the pulsed plasma. The FCP uses an impulse signal source (DG645, Stanford Research Systems) and an oscilloscope (X8600A, LeCroy) to measure the transmission of an impulse signal.…”

“…In this paper, we proposed a new and fast method for pulsed plasma measurement using a Fourier cutoff probe. The cutoff probe, which can be used even in processing plasmas, molecular plasmas, mixed gas plasma, and dual frequency plasma, using Fourier analysis, the FCP, can measure pulsed plasmas with higher time resolution of up to 15 nano-seconds [33] by delivering a delay with respect to the pulse trigger. This method also reduces the time consumption for measurement compared to other diagnostics such as the Langmuir probe.…”

“…Recently, a new method to provide a transmission spectrum in a short time was developed. [33] This method uses a cutoff probe with a short impulse. The short impulse has a broadband spectrum in a short length signal.…”

Crossing Frequency Method Applicable to Intermediate Pressure Plasma Diagnostics Using the Cutoff Probe

“…While a full discussion of this point is beyond the scope of this paper, two solutions are briefly given as follows. The first is to remove the cavity resonance peaks through the time-gating method as in [ 57 ], which does not use continuous sinusoidal signals but pulse signals and removes the detection signals that include the cavity information in the time domain. The second approach is to choose an alternative reference signal, such as one of the pressure conditions shown in Figure 4 a.…”

Effect of an inhomogeneous electron density profile on the transmission microwave frequency spectrum of the cutoff probe

“…Among the various types of microwave probes that have been proposed, the CP has proved a reliable [21], reproducible [22], and precise instrument to measure electron density [10], sheath width [23], and electron-neutral collision frequency [24]. Besides, various types of the CP itself have been developed for particular applications, such as the reactance CP [12], phase-resolved CP [25], Fourier CP [26], and ring-type CP [27]. These outstanding accomplishments are attributed to physical models, namely circuit models [28], transmission line models [29]), and commercial three-dimensional (3D) full E/M wave simulation (microwave studio, computer simulation technology (CST)), which all share a special assumption: homogeneous electron density between CP tips.…”