Cao Jinxiang

Characteristics of the Plasma During Chemical Vapor Deposition for Diamond Growth

During the course of diamond growth by dc plasma chemical vapor deposition and microwave plasma chemical vapor deposition, characteristics of the plasma were measured by Langmuir single probe, double probe, emission spectrometer and microwave interferometer. The relationships between plasma parameters and the concentration of hydrocarbon, the power, pressure and the gas flow rate are discussed.

Study of microturbulence on the KT-5 tokamak by CO2 laser scattering

We report our observation of low frequency (LF) density fluctuation of microturbulence in KT-5 tokamak. Broad frequency and wavenumber power spectra are observed. The density fluctuation frequencies are found to be around a few hundred kHz, and at higher frequencies the fluctuation level rolls off as n2(f) ∝ f-β with β = 1 - 3. The wavenumber power spectrum S(κ) can be fitted into S(κ) ∝ κ-α with α around 3.0.

Excitation of surface plasmons at the boundary of overdense plasma

The excitation of surface plasmons (SPs) with a strip grating at the boundary of an unmagnetized overdense plasma has been investigated theoretically and experimentally. An incident electromagnetic radiation was p-polarized at the frequency of 5 GHz. Experiments showed that when the plasma density was four times higher than the critical density with the grating present, and the SPs could be excited at the boundary of the overdense plasma. Contribution of the glass layer in the formation of the SP dispersion relation was examined. When the incident electromagnetic radiation was coupled into SPs the coupling order with the effective permittivity was simulated qualitatively. We find that the existence of SPs at the boundary of overdense plasma indicates that the reflection coefficient of the incident electromagnetic radiation reaches its minimum and even becomes total absorption. In this work the plasma density was diagnosed by a Langmuir double probe.

Experimental Studies of Low-Pressure Plasma Jet by Means of Langmuir Probes and Emission Spectra

An investigation was made into the argon plasma jet that expanded in a low-pressure vacuum chamber. The spatial distributions of the parameters of the plasma jet with different supplied powers were measured using a ten-channel Langmuir probe array. The chemical species in the plasma jet were identified by emission spectroscopy. The electron excitation temperatures at two positions, 10 cm and 50 cm downstream from the nozzle exit were calculated, respectively, by the Boltzmann plot method.

Optimization of Langmuir Probe System Parameters in a Stationary Laboratory Plasma

In order to obtain creditable data an applicable method to optimize parameters of the Langmuir probes and circuits in a stationary laboratory device is investigated and an experimental criterion of the probe dimension is developed. To obtain the electron temperature and density the Electron Energy Distribution Function (EEDF) approach with less computing time and more accurate results is applied, instead of the conventional slope approach. Moreover the influence of the vessel wall materials on the plasma density is discussed briefly, indicating that the dielectric wall is helpful to enhancing the electron density.

Theoretical and Experimental Study of Scattering of a Plane Wave by an Inhomogeneous Plasma Sphere

Scattering of electromagnetic waves by an inhomogeneous plasma sphere has been studied theoretically and experimentally. The offset angles of electromagnetic waves caused by the plasma sphere have been observed experimentally. The effects of the electromagnetic wave frequency and plasma density on the offset angle are discussed. The plasma density is estimated with the offset angle.

Full-wave Analyses of Scattering of Electromagnetic Wave from the Weakly Ionized Plasma in Plane Geometry

The purpose of the present work is to present a full-wave analysis of scattering from the weakly ionized plasma in the plane geometry. We have yielded an approximate solution in an analytic form to the electromagnetic wave scattering from the weakly ionized plasma. In the normal and oblique incidence, the analytic solution works well, as compared with the exact solution and the solution based on the Wenzell-Kramers-Brillouin-Jeffreys (WKBJ) approximation to the uniform density profile.

Experimental investigation of the plasma wake of a blunt cone

The flow field of a plasma wake is studied by analysing the saturated ion current of multiple scanning probes with the method of chaos dynamics. The laminated structure of the near-wake is verified. It is observed at x > 250 mm (x is the axis along the flow field) that the far-wake flow field is similar to the free flow field, and turbulent structure exists in the near-wake, but there is no turbulence in the far-wake. The spatially intermittent character of the flow field can be discovered, which seems to produce some relationship between the spatially intermittent character and the turbulence. The results show that the analytic method of chaos dynamics is sensitive to a non-periodic signal.

Wavelet Analysis of Fluctuation of Plasma Density in Hypersonic Flow

By use of wavelet transform, a high frequency fluctuation is identified in the presence of low frequency disturbance through the zoned wavelet energy spectrum. The high frequency fluctuation of the plasma density may be stimulated by an ion-acoustic instability. These results can help to study the mechanism of the perturbation of plasma density in hypersonic wake.

Experimental Investigation of Reflectometry as a Density Fluctuation Diagnostic

In this paper, a controlled laboratory experiment to investigate the response properties of reflectometry to the density fluctuations is presented. The reflectometer signal is observed to be highly spatially localized in the plasma. The quantitative measurement has demonstrated that the signal originates about one free space wavelength of the probe wave in front of the critical layer and this position is independent of the fluctuation wavenumber. It is also found that the sensitivity of transverse response to wavenumbers is different from that of longitudinal response.