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A thrust power of a gas-driven laser-propulsion system is obtained through interaction with a propellant gas heated by a laser energy. Therefore, understanding the nonequilibrium nature of laser-produced plasma is essential for increasing available thrust force and for improving energy conversion efficiency from a laser to a propellant gas. In this work, a time-dependent collisional-radiative model for air plasma has been developed to study the effects of nonequilibrium atomic and molecular processes on population densities for an air-driven type laser propulsion. Many elementary processes are considered in the number density range of 1012/cm3≤N≤1019/cm3 and the temperature range of 300 K≤T≤40,000 K. We then compute the unsteady nature of pulsively heated air plasma. When the ionization relaxation time is the same order as the time scale of a heating pulse, the effects of unsteady ionization are important for estimating air plasma states. From parametric computations, we determine the appropriate conditions for the collisional-radiative steady state, local thermodynamic equilibrium, and corona equilibrium models in that density and temperature range. [ABSTRACT FROM AUTHOR]

In high density and low temperature peripheral plasmas of JT-60 U, i.e. detached divertor plasmas, C III and C IV lines were observed by a visible and VUV spectrometers in order to investigate dominant radiators, radiation power and particle balance between the radiators. An emission peak was found between the inner strike and the X-point. With increasing electron density, the emission peak moved to the X-point with a constant electron temperature of ∼7 eV. In the case the emission peak was located on the X-point, the dominant radiators in the emission peak were C2+ and C3+, which contributed 30% and 60% to the total radiative power. It was found that C3+ was produced by the ionization of C2+ and the volume recombination of C4+ at a similar rates. However, the loss flux of C3+ was lower by two orders of magnitude than the C3+ production flux, indicating that another loss mechanism such as transport loss around the X-point was significant. [ABSTRACT FROM AUTHOR]

The properties of the secondary plasma created inside the ITER Neutral Beam Injector (NBI) neutraliser, through the interaction of the high energetic hydrogen beam with the molecular hydrogen gas, have been analysed. Starting from the results of our OBI-2 PIC Monte-Carlo numerical code, detailed kinetic of the hydrogen plasma has been studied using a Collisional-Radiative model. In this model, the electron distribution function is determined by solving a Boltzmann equation, whereas main plasma species are derived from balance equations. This paper presents preliminary results obtained in a 0D geometry, boundary conditions bing introduced through effective rates for gain and loss of particles at the neutraliser walls. It has been found that the main ion specie is H2+, essentially coming from the ionisation of the target gas. The electron energy distribution function is not maxwellian and its mean energy is about 5 eV. The plasma-wall interactions yield a strong contribution, in particular regarding the density of molecular ion H3+. Assuming several independent slices of plasma along the negative ions beam axis, the axial profile of the secondary plasma has been analysed. It has been found that the density and mean energy profiles of the plasma electrons are directly related to the plasma potential profile, which in turn closely follows the gas density one. [ABSTRACT FROM AUTHOR]

A laser-based technique for the direct testing of the predictions of the Collisional-Radiative Model, of application to the analysis of the supersonic He beam diagnostic, is presented. The time evolution of the populations of some relevant excited levels upon the laser pumping of one of them is simulated by solving the corresponding system of coupled differential equations. Good sensitivity of the changes induced by the laser interaction to the particular values of the relevant collisional rate constants is observed for both, the singlet and triplet systems of the He atom. The available experimental set-up and some previous results are also shown, and the required improvements for its application to the TJ-II plasma conditions are addressed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]