Wide-range measurements of plasma density using a hairpin resonance microwave probe

Abstract

We propose a method for diagnostics of the density of weakly magnetized plasma using a resonance microwave probe, which allows decreasing the minimum measurable value of the density by three orders of magnitude, thus expanding the dynamic range of the measuring system significantly. Within the framework of this method, measurements are performed at a fixed frequency corresponding to the resonance frequency of a microwave probe in the absence of plasma, while minor variations in the resonance frequency of the system within the limits of the width of the inherent resonance are recorded by the method of amplitude-phase measurements. The paper presents a theoretical model of the measurement method and its experimental verification.

Microwave Cavity Sensor for Measurements of Air Humidity under Reduced Pressure

“…The variation is determined by the presence of gas in the cavity, which, in turn, depends on the pressure of water vapors: . According to [ 25 ], the phase shift for the signal at a frequency equal to the central frequency of the cavity in vacuum, f 0 , satisfies the relationship that has the form . Proportional (linear) measurements of the correction for the dielectric permittivity correspond to the measured small pressures P .…”

“…At a pressure below 0.01 Torr, the eigenfrequency of the cavity was 1632.6 MHz, the resonance curve bandwidth was 4.2 MHz, and the Q-factor was Q = 387. Estimations show [ 25 ] that the main contribution to the total Q-factor of the measuring system is made by the energy losses determined by the magnetic coupling of the cavity with excitation line (4) and signal reception line (5). Magnetic coupling loops are the simplest solution for cavity excitation and detection of the cavity response using coaxial cable lines.…”

“…The relative changes in the cavity eigenfrequency, which should be detected, turn out to be of the same order of magnitude. In order to detect minor frequency shifts within the limits of the resonance curve, the amplitude-phase method developed earlier in [ 25 ] is used in this paper. The experiments were performed at IAP RAS in the vacuum chamber of the Sprite setup [ 26 ].…”

Резонансный Метод Измерения Концентрации Ионосферной Плазмы На Микроспутниках

“…), что упрощает аналитическое описание электродинамической модели измерительной системы. Метод резонансного СВЧ-зонда в работах [21][22][23][24][25][26][27] получил дальнейшее развитие в плане расширения функциональных возможностей и повышения точности измерения абсолютных значений концентрации.…”

“…В настоящей работе предлагается использовать амплитудно-фазовый метод [26], позволяющий понизить минимальное измеряемое значение концентрации на три порядка от 10 6 до 10 3 cm −3 , не увеличивая длину резонатора, и тем самым расширить рабочий диапазон измерительной системы. В рамках данного метода зонд работает на фиксированной частоте, соответствующей собственной частоте резонатора без плазмы f 0 , а малые частотные сдвиги в пределах ширины резонансной кривой фиксируются посредством амплитудно-фазовых измерений.…”