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Title: Diagnostics principle of microwave cut-off probe for measuring absolute electron density

Abstract

A generalized diagnostics principle of microwave cut-off probe is presented with a full analytical solution. In previous studies on the microwave cut-off measurement of weakly ionized plasmas, the cut-off frequency ω{sub c} of a given electron density is assumed to be equal to the plasma frequency ω{sub p} and is predicted using electromagnetic simulation or electric circuit model analysis. However, for specific plasma conditions such as highly collisional plasma and a very narrow probe tip gap, it has been found that ω{sub c} and ω{sub p} are not equal. To resolve this problem, a generalized diagnostics principle is proposed by analytically solving the microwave cut-off condition Re[ε{sub r,eff}(ω = ω{sub c})] = 0. In addition, characteristics of the microwave cut-off condition are theoretically tested for correct measurement of the absolute electron density.

Authors:
 [1]
  1. Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22303601
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANALYTICAL SOLUTION; COLLISIONAL PLASMA; ELECTRON DENSITY; LANGMUIR FREQUENCY; MICROWAVE RADIATION; PROBES; SIMULATION

Citation Formats

Jun, Hyun-Su, E-mail: mtsconst@kaist.ac.kr. Diagnostics principle of microwave cut-off probe for measuring absolute electron density. United States: N. p., 2014. Web. doi:10.1063/1.4892943.
Jun, Hyun-Su, E-mail: mtsconst@kaist.ac.kr. Diagnostics principle of microwave cut-off probe for measuring absolute electron density. United States. doi:10.1063/1.4892943.
Jun, Hyun-Su, E-mail: mtsconst@kaist.ac.kr. Fri . "Diagnostics principle of microwave cut-off probe for measuring absolute electron density". United States. doi:10.1063/1.4892943.
@article{osti_22303601,
title = {Diagnostics principle of microwave cut-off probe for measuring absolute electron density},
author = {Jun, Hyun-Su, E-mail: mtsconst@kaist.ac.kr},
abstractNote = {A generalized diagnostics principle of microwave cut-off probe is presented with a full analytical solution. In previous studies on the microwave cut-off measurement of weakly ionized plasmas, the cut-off frequency ω{sub c} of a given electron density is assumed to be equal to the plasma frequency ω{sub p} and is predicted using electromagnetic simulation or electric circuit model analysis. However, for specific plasma conditions such as highly collisional plasma and a very narrow probe tip gap, it has been found that ω{sub c} and ω{sub p} are not equal. To resolve this problem, a generalized diagnostics principle is proposed by analytically solving the microwave cut-off condition Re[ε{sub r,eff}(ω = ω{sub c})] = 0. In addition, characteristics of the microwave cut-off condition are theoretically tested for correct measurement of the absolute electron density.},
doi = {10.1063/1.4892943},
journal = {Physics of Plasmas},
number = 8,
volume = 21,
place = {United States},
year = {Fri Aug 15 00:00:00 EDT 2014},
month = {Fri Aug 15 00:00:00 EDT 2014}
}
  • The microwave cut-off probe for the electron density measurement in low-temperature plasmas is described in this article. It is based on the wave cutoff in an unmagnetized plasma. The measurement principle is analyzed theoretically using a model of plasma slab. Because of the high-pass characteristic of plasma, the waves above the cut-off frequency can penetrate the plasma slab, whereas the lower frequency waves are reflected from the cut-off layer. Therefore, an obvious critical point can be observed in the wave transmission spectrum. The abscissa of the critical point indicates the cut-off frequency, which is directly related to the maximum electronmore » density between transmitting/receiving antennas of the cut-off probe. The measured electron densities are in agreement with the data obtained by the Langmuir probe. Experimental results show that the microwave cut-off probe can be used to diagnose the plasmas with a wide range of parameters.« less
  • The phase resolved cut-off probe method, a precise measurement method for the electron density, was recently proposed [J. H. Kwon et al., Appl. Phys. Lett. 96, 081502 (2010)]. This paper presents the measurements of electron density using the method under various experimental conditions (different pressures, powers, chamber volumes, and discharge sources). The result shows that the method is not only in good agreement with the previous method using wave transmittance under various experimental conditions but it is also able to find the cut-off point clearly even under difficult conditions such as high pressure ({approx} 1 Torr), high discharge power, andmore » small plasma volume. The details of the experimental setup, the operating mechanism of the probe method, and the data processing procedure (algorithm) are also addressed. Furthermore, the reliability of the measurement method is investigated by using an electromagnetic field simulation with cold plasma model (CST-Drude model, Computer Simulation Technology).« less
  • The characteristics of the microwave reflection coefficient were calculated by an electronic digital computer as a function of electron density, collision frequency, and cyclotron frequency. An antomatic apparatus was constructed to measure the microwave reflection coefficient. Applying the experimental results to calculated charts of reflection coefficients, the final data on electron density and collision frequency under various magnetic fields are easily found. Charts of the reflection coefficients and descriptions of the measuring apparatus are presented. (auth)