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A double flush-mounted probe method is proposed to analyze the characteristics of intermediate-pressure plasmas (10–100 Pa) by a sheath criterion. The analytical model mainly focuses on the effect of the ion drift velocity in the sheath edge and then provides a correction factor for the measured ion-collection current. The reduction of the ion current is attributed to ion–neutral collisions leading to the modified Bohm velocity. To validate this method, the ion density is calculated and compared with that measured by two types of cylindrical probes, and the results agree well with the data measured by other probes. On the basis of this work, the double flush-mounted probe can be adopted to diagnose plasma parameters accurately, without a reference electrode, in collisional and certain complex plasma environments, such as the reentry plasma sheath. [ABSTRACT FROM AUTHOR]

A new configuration of a resonant-cavity electrode microwave discharge device is developed in this work. In the device, a hollow electrode antenna is used for microwave transporting, and a well-designed resonant-cavity could enhance the absorption of the microwave power. A quartz cover is adopted to seal the vacuum and insulate the antenna from plasma, which greatly reduces the heat accumulation on the antenna. A magnetic field coil made by multiple-turn enameled wires is designed which could generate a strong magnetic field based upon a low-current power supply. In the plasma chamber, a distinctive L-shape probe is designed to measure the parameter distribution, and the two-dimensional parameters can be measured with the simple structure. In addition, the characteristic parameters such as electron density and temperature are measured in the chamber with a single probe, and the electron density distribution and spectrum are compared in argon and xenon plasma, which suggests that the microwave plasma device has good adaptability and functionality. [ABSTRACT FROM AUTHOR]

In this work, an experimental design for generation of the controllable electron density gradient is achieved through a large area oxide coated cathode and two stainless meshes. The large area oxide coated cathode is adopted to produce a large area, uniform and high density plasma, and these two metal meshes are specially designed to control the density and potential of the plasma. A boundary layer with independent electron density gradient and uniform plasma potential is subsequently generated. The controllable electron density gradient can be achieved, and the accompanied electric field can be compensated simultaneously using this design, which could be potentially extended to study the excitation of the plasma instabilities when the strong plasma density gradient exists. [ABSTRACT FROM AUTHOR]

A new approach for investigating ionosphere chemical depletion in the laboratory is introduced. Air glow discharge plasma closely resembling the ionosphere in both composition and chemical reactions is used as the artificially created ionosphere. The ionospheric depletion experiment is accomplished by releasing chemicals such as SF6, CCl2F2, and CO2 into the model discharge. The evolution of the electron density is investigated by varying the plasma pressure and input power. It is found that the negative ion (SF6-, CCl2F2-) intermediary species provide larger reduction of the electron density than the positive ion (CO2+) intermediary species. The negative ion intermediary species are also more efficient in producing ionospheric holes because of their fast reaction rates. Airglow enhancement attributed to SF6 and CO2 releases agrees well with the published data. Compared to the traditional methods, the new scheme is simpler to use, both in the release of chemicals and in the electron density measurements. It is therefore more efficient for investigating the release of chemicals in the ionosphere. [ABSTRACT FROM AUTHOR]

In this work, a double flush-mounted probe for measuring plasma parameters was designed and fabricated. The method to determine the plasma density and electron temperature using a floating double flush-mounted probe was characterized. To validate this method, the measurement results in an argon glow discharge plasma, including the electron density and temperature measurements, were compared with those obtained using a single probe and a double probe. Results indicate that the electron density measured using the double flush-mounted probe agrees well with those measured using other probes; the effective electron temperature values are also consistent within the admissible error range. These results suggest that the double flush-mounted probe can be used for accurate measurements at low pressure DC plasma discharges and also can be applied to other complex plasmas such as tokamaks, in the boundary-layer region without a reference electrode.

In this work, the design and construction of the Keda Space Plasma EXperiment (KSPEX), which aims to study the boundary layer processes of ionospheric depletions, are described in detail. The device is composed of three stainless-steel sections: two source chambers at both ends and an experimental chamber in the center. KSPEX is a steady state experimental device, in which hot filament arrays are used to produce plasmas in the two sources. A Macor-mesh design is adopted to adjust the plasma density and potential difference between the two plasmas, which creates a boundary layer with a controllable electron density gradient and inhomogeneous radial electric field. In addition, attachment chemicals can be released into the plasmas through a tailor-made needle valve which leads to the generation of negative ions plasmas. Ionospheric depletions can be modeled and simulated using KSPEX, and many micro-physical processes of the formation and evolution of an ionospheric depletion can be experimentally studied.

A comparison is made between plasma parameters measured by a flush-mounted probe (FP) and a cylindrical probe (CP) in argon glow discharge plasma. Parameters compared include the space potential, the plasma density, and the effective electron temperature. It is found that the ion density determined by the FP agrees well with the electron density determined by the CP in the quasi-neutral plasma to better than 10%. Moreover, the space potential and effective electron temperature calculated from electron energy distribution function measured by the FP is consistent with that measured by the CP over the operated discharge current and pressure ranges. These results present the FP can be used as a reliable diagnostic tool in the stable laboratory plasma and also be anticipated to be applied in other complicated plasmas, such as tokamaks, the region of boundary-layer, and so on.