A transmission-line microwave interferometer for plasma electron density measurement

Abstract

We present both the theoretical analysis and proof-of-principle experimental results of a novel transmission-line microwave interferometer for measurements of plasma electron density. The principle of this technique is the same as conventional microwave interferometers except that the sensing microwave propagates along a transmission-line structure. For this study, the transmission-line is a circular coaxial dielectric waveguide operated at 2.4 GHz. A microwave module consisting of a microwave source and a phase detector has also been developed for detecting the phase of the microwave propagating through the transmission-line. Good agreement of phase measurements between the microwave module and a microwave network analyser has been demonstrated. The electron density measured by the interferometer is also consistent with the results from a Langmuir probe.

Dual-role plasma absorption probe to study the effects of sheath thickness on the measurement of electron density

“…The surface waves are excited in the antenna region, and a resonator of surface waves is formed along the plasmasheath boundary at radius r s = r 0 + s. The theoretical model in the antenna region consists of the metal rod, the sheath layer and the plasma layer. According to [15], the dispersion relation of surface waves can be expressed as…”

“…where β = 2π/λ denotes the axial wave number, p = 1 − ω 2 pe /ω 2 and sh are the relative permittivities in the plasma and the sheath, respectively. The surface waves correspond to the slow wave modes [15], i.e. ω/β < c/ √ sh .…”

Experimental and Simulational Studies on the Theoretical Model of the Plasma Absorption Probe

“…Since PAP is of axially symmetric geometry, the transverse magnetic (TM) modes are expected to exist for the propagation of surface waves. The dispersion relation of surface waves for the electromagnetic theoretical model can be derived by following the conventional procedures [14,15] . Hence only a brief description is given in this paper.…”

Analysis of uncertainty of electron density and temperature using laser Thomson scattering in helicon plasmas

“…A lot of diagnostic methods and their reliability (or uncertainty) have been suggested to measure plasma parameters accurately. [1][2][3][4][5][6][7][8] Among the diagnostic methods, the laser Thomson scattering (TS) method is believed to be a promising diagnostic method as a standard of the low temperature plasma metrology, because its basic measurement principle is very simple and it is not affected by the noises from plasma source (RF noise, magnetic field noise, and so on). 1,9,10) Although the laser Thomson Scattering method has been known for its high measurement accuracy, [11][12][13][14][15][16][17][18][19] there can be also large uncertainty in plasma parameter measurements depending on the input quantities in the measurement model such as a scattering signal or a stray light signal.…”