Measurement of electron densities and temperatures in the plasma boundary combining neutral beam probes and laser-induced fluorescence

A new diagnostic method using both techniques of neutral beam probing and laser-induced fluorescence (LIF) is proposed to measure electron density (10$^{11}$ - 10$^{13}$ cm$^{-3}$) and electron temperature (1 - 100 eV) of a boundary layer plasma in devices like tokamaks. The local electron density can be obtained by measuring the photon flux of the resonance line produced by electron impact excitation of an injected neutral Li-beam which is produced by laser-induced evaporation (LIE). The density of the neutral Li-beam which is necessary for the determination of the electron density is measured by LIF. The local electron temperature can be obtained by determining the attenuation of two neutral beams (Li, and Al or Ti) produced by LIE, of which the measurements are carried out by means of LIF. The applicability of this method to the TEXTOR tokamak is discussed in detail

Excitation and ionization cross-sections for He I excited states (n = 2 ÷\div 4, Δ\DeltaS = 0)

There are two types of methods for calculation of excitation and ionization of atoms and ions by electrons. A. Sophisticated $\textit{Glose coupling}$ (CC) - $\textit{type}$ methods, such as $\textit{R - matrix}$ [1] and $\textit{CCC}$ (converging elose coupling) [2]. They usually provide sufficiently accurate results. However there are some disagreements and questions in particular cases. B. Rather simple $\textit{Born - type}$ (I order) methods with possible inelusion of exchange and normalization (B). For ions Coulomb field is also ineluded (B). For ions Coulomg field is also included (CB - Coulomb-Born). Generally cross sections obtained by A-methods are preferable, but they are available for very limited number of transitions and atoms. Fast calculations of many transitions required for atomic base in diagnostic code are in fact unreliable. Therefore usage of the B-methods is necessary. Unfortunately the accuracy of calculations by simple B methods is often insufficient. To create the real data bases it is important to und erstand a physical reason of errors and to develope sufficiently simple ways of correction. One very efficient way is the method of K-matrix. It is based on I order B calculation of matrix $\textbf{K}$ for a given set of transitions. Then S-matrix and cross section $\sigma$ are calculated. The B-methods and full K-matrix approach are realized in the coupled programs $\textbf{ATOM-AKM}$ [3,4]. They can be run on PC-486 or higher and require about 10 minutes for 10 channels (transitions) in 10-20 energy points. In this paper we present results of calculations of excitation and ionization cross-sections from He I excited states (nl- n'l' for n, n' = 2 $\div$ 4 without change of spin). Different methods are used and compared. We use atomic units with Ry = 13.60 eV for energy and $\pi$a$^{2}_{0}$ for cross sections

In situ measurements of the spectral reflectance of metallic mirrors at the Hα_α line in a low density Ar–H plasma

The efficient and reliable control and monitoring of the quality of the optical properties of mirrors is an open problem in laboratory plasmas. Until now, the measurement of the reflectance of the first mirrors was based on the methods that require additional light calibration sources. We propose a new technique based on the ratio of the red- and blue-shifted emission signals of the reflected hydrogen atoms which enables the in situ measurement of the spectral reflectance of metallic mirrors in low-density Ar–H or Ar–D plasmas. The spectral reflectance coefficients were measured for C, Al, Ag, Fe, Pd, Ti, Sn, Rh, Mo, and W mirrors installed in the linear magnetized plasma device PSI-2 operating in the pressure range of 0.01-0.1 Pa. The results are obtained for the Hα line using the emission of fast atoms induced by excitation of H atoms through Ar at a plasma-solid interface by applying a negative potential U = −80, …, −220 V to the mirror. The agreement between the measured and theoretical data of reflectance is found to be within 10% for the investigated materials (except for C). The spectra also allow us to efficiently determine the material of the mirror

Properties of "detached" plasmas

The phenomenon "detached"-plasma is described and analyzed, based on detailed experimental studies in the TEXTOR tokamak, in particular by applying comprehensive edge diagnostics. The major parameters responsible for the transition to a "detached"-plasma are identified (heating power, electron density, impurity level) and can be related to a power loss via "100% radiation cooling" from low-Z impurities at the edge. The relevance for plasma-wall interaction, as evidenced e. g. by drastic changes in heat loads to the limiter, increase of particle flux to the wall, thereby enhancing the impurity release, is discussed. The great importance of considering the "detached"-plasma properties in scaling studies and additional heating effects is demonstrated by the impact of this plasma state on particle and energy confinement times and by ICRF-heating induced transitions