Influence of Plasma Pressure Fluctuation on RF Wave Propagation

Pressure fluctuations in the plasma sheath from spacecraft reentry affect radiofrequency（RF） wave propagation.The influence of these fluctuations on wave propagation and wave properties is studied using methods derived by synthesizing the compressible turbulent flow theory,plasma theory,and electromagnetic wave theory.We study these influences on wave propagation at GPS and Ka frequencies during typical reentry by adopting stratified modeling.We analyzed the variations in reflection and transmission properties induced by pressure fluctuations.Our results show that,at the GPS frequency,if the waves are not totally reflected then the pressure fluctuations can remarkably affect reflection,transmission,and absorption properties.In extreme situations,the fluctuations can even cause blackout.At the Ka frequency,the influences are obvious when the waves are not totally transmitted.The influences are more pronounced at the GPS frequency than at the Ka frequency.This suggests that the latter can mitigate blackout by reducing both the reflection and the absorption of waves,as well as the influences of plasma fluctuations on wave propagation.Given that communication links with the reentry vehicles are susceptible to plasma pressure fluctuations,the influences on link budgets should be taken into consideration.

A Refined Study on ECR Wave Propagation and Absorption in the Weakly Relativistic Plasma

A refined derivation of refraction and absorption of the pure O-mode and X-mode Electron Cyclotron Resonance (ECR) wave in tokamak plasma is carried out. The weakly- relativistic dielectric tensor elements are used and the results show that the refraction only changes a little, compared to that deduced from the cold-plasma dispersion relation even in the inner re- gion. Refined formulae of the wave damping rate are then obtained for both the O-mode and the X-mode fundamental waves.

Propagation of Surface Modes in a Warm Non-Magnetized Quantum Plasma System

The propagation of surface modes in warm non-magnetized quantum plasma is investigated. The surface modes are assumed to propagate on the plane between vacuum and warm quantum plasma. The quantum hydrodynamic model including quantum diffraction effect （the Bohm potential） and quantum statistical pressure is used to derive a new dispersion relation of surface modes. The new dispersion relation of surface modes is analyzed in some special interesting cases. It is shown that the dispersion relation can be reduced to the earlier results in some special cases. The results indicate that the quantum effects can facilitate the propagation of surface modes in such a semi-bounded plasma system. This work is helpful to understand the physical characteristics of the surface modes and the bounded quantum plasma.

Study on the Two-Dimensional Density Distribution for Gas Plasmas Driven by Laser Pulse

We perform an experimental study of two-dimensional（2D） electron density profiles of the laser-induced plasma plumes in air by ordinarily laboratorial interferometry. The electron density distributions measured show a feature of hollow core. To illustrate the feature, we present a theoretical investigation by using dynamics analysis. In the simulation, the propagation of laser pulse with the evolution of electron density is utilized to evaluate ionization of air target for the plasma-formation stage. In the plasma-expansion stage, a simple adiabatic fluid dynamics is used to calculate the evolution of plasma outward expansion. The simulations show good agreements with experimental results, and demonstrate an effective way of determining 2D density profiles of the laser-induced plasma plume in gas.

Generation and expansion of laser-induced plasma as a spectroscopic emission source

Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy （LIBS） has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermo-dynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.