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In this article, extension of the He beam diagnostic, which is routinely applied in fusion devices for the characterization of the edge electronic parameters-ne and Te-and their profile, to the measurement of ion temperature and plasma rotation is proposed. The theoretical background for these new applications is reviewed and examples of their use in TJ-II are provided. Also, the shortcomings and their possible solutions are addressed. Finally, the field of application of the technique to other beam-based diagnostics is discussed. [ABSTRACT FROM AUTHOR]

The secondary electron emission (SEE) coefficient by electron impact of Li, W and stainless steel (SS) surfaces exposed to a glow discharge is evaluated and analyzed in the energy range of Ee<200 eV. While the values of the SEE coefficient for SS and W show a small increase with respect to their vacuum value, an enhancement of this parameter up to a factor of 6 has been deduced for clean Li surfaces. Experiments with different plasma gas discharges (He, Ar and H2) are undertaken in order to address the possible mechanisms related to such enhancement. No major effect of the bombarding ion mass or incident electron flux is observed. The implications of these findings on the use of Li as a plasma-facing component in fusion devices are addressed. [ABSTRACT FROM AUTHOR]

Evidence of the strong contribution of electrons with energies up to the cathode fall potential was found in low-pressure He dc glow discharge plasmas (3-8 mTorr), in agreement with expectations from the estimates of the mean free path of electron-neutral inelastic collisions. A simple gridded probe, of the retarding field analyzer type, was applied to the characterization of the full electron energy distribution function (EEDF) in He plasmas with significant contribution from suprathermal electrons (up to 3.5%). The inferred EEDFs were cross-checked with results from the He line ratio diagnostic and good agreement was found at several values of pressure and plasma current. [ABSTRACT FROM AUTHOR]

He and Li beams have been installed and set into operation at the TJ-II stellarator with the aim of measuring electron temperature and density profiles in the edge and scrape-off layer regions of the plasma. The effusive thermal Li beam penetrates up to a normalized effective radius of ρ=0.6–0.7 in typical electron cyclotron heated plasmas. Density profiles deduced from the Li beam are wider than those obtained from extrapolation of the profile measured by Thomson scattering. The He beam is a pulsed supersonic one. Simultaneous detection of three emission lines (667.2, 706.5, and 728.1 nm) is made with a set of three photomultipliers. First He beam measurements of n[sub e] and T[sub e] in TJ-II are presented and the agreement among results of different plasma edge diagnostics is discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A description and transport analysis (energy and particles) of neutral beam heated plasmas is shown for two almost identical magnetic configurations except for a ≈1% difference in their rotational transform, .... Due to the low magnetic shear of TJ-II magnetic fields, such difference takes the low order rational ... = 8/5 to the plasma edge in one of them, while in the other the 8/5 value is near the edge but inside the plasma. A transport transition happens at lower density and plasma energy for the configuration that includes the ... = 8/5, which exhibits better particle confinement already before the transition. [ABSTRACT FROM AUTHOR]

The core electron temperature (Te0) of neutral beam heated plasmas is determined in TJ-II stellarator by using soft x ray detectors with beryllium filters of different thickness, based on the method known as the foil absorption technique. Te0 estimations are done with the impurity code IONEQ, making use of complementary information from the TJ-II soft x ray tomography and the VUV survey diagnostics. When considering the actual electron density and temperature profile shapes, an acceptable agreement is found with Thomson scattering measurements for 8 different magnetic configurations. The impact of the use of both neutral beam injectors on the Te0 measurements is addressed. Also, the behaviour of Te0 during spontaneous profile transitions is presented. [ABSTRACT FROM AUTHOR]

The well known He beam diagnostic, able to provide profiles of the electronic plasma edge parameters, has undergone a significant improvement by the application of supersonic expansion techniques in the last years. The use of pulsed fast piezoelectric valves was initiated in the TJ-IU and implemented in the TJ-II stellarators. In its former configuration the repetition rate of the beam was ultimately limited in the expansion chamber by the pressure buildup. In the actual upgraded version, however, a repetition rate up to 200 Hz can be achieved, and the recording of the electron temperature and density profiles with millisecond resolution is possible. In the present work, the technical development of the diagnostic required for optimized performance is described. In addition, the validation of the collisional–radiative model needed for the reconstruction of the edge profiles and the analysis of the complementary information given by the beam attenuation is also addressed. [ABSTRACT FROM AUTHOR]

The response of transport in low density (line average ) plasmas to electron cyclotron resonance heating (ECH) power, 100 kW ≲ QECH ≲ 400 kW, is documented for the TJ-II Heliac-type stellarator. Radially resolved electron heat balance shows no significant differences between boron or lithium coating of the vacuum chamber walls. The main trends in electron heat transport are found to be similar to other stellarator/heliotron devices and are compatible with neoclassical calculations in the bulk of the plasma. According to our calculations the heat fluxes are anomalous near the edge, ρ ≳ 0.8 where ρ is the normalized minor radius, but the uncertainties there are large. Particle transport in the density gradient region, ρ ≈ 0.8, has little sensitivity to the variation of heating power and is compatible with neoclassical predictions. Neoclassical transport of particles and electron heat is found to be dominant in the gradient regions of typical ECH plasmas of the TJ-II Heliac. [ABSTRACT FROM AUTHOR]