Fast lithium‐beam spectroscopy of tokamak edge plasmas

Institut für Allgemeine Physik, Technische Universität Wien, Austria
Review of Scientific Instruments (Impact Factor: 1.61). 09/1993; 64(8):2285 - 2292. DOI: 10.1063/1.1144460
Source: IEEE Xplore


Plasma‐wall interaction and impurity transport processes in the outermost region of magnetically confined hot plasmas (the so‐called plasma edge) must be well understood for successful development of future thermonuclear fusion reactors. To this goal, sufficiently detailed edge plasma diagnostics are in great demand. By injecting a fast Li beam into the edge plasma region, a great number of information can be obtained with excellent space and time resolution. This so‐called Li‐beam plasma spectroscopy gives access not only to edge plasma density profiles from the collisionally excited Li atoms, but also to the impurity concentration and temperature profiles via line emission induced by electron capture from the injected Li atoms by the impurity ions. Full utilization of all capabilities requires a reliable data base for the atomic collision processes involving injected Li atoms and plasma constituents (i.e., electrons, hydrogen ions, and relevant impurities in their various charge states), since a precise modeling of Li beam attenuation and excited‐state composition has to be made for evaluating desired plasma properties from the related spectroscopical measurements. The most recent methodical improvement permits a fully consistent determination of absolute edge plasma density profiles by measuring only relative LiI line emission profiles. This is of special interest for investigating rapid edge plasma density fluctuations in connection with, e.g., ELMs, L‐H mode transition, turbulence or edge cooling by impurity injection. This paper describes the capabilities of Li‐beam edge plasma spectroscopy by way of illustrative examples from measurements at the tokamak experiment TEXTOR.

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    • "Thermal helium beams have been successfully used for measuring electron temperature and -density in tokamak edge plasmas [1]. Fast lithium beams are widely used for diagnosing the density profile [2] in the plasma edge. It has been proposed to use beam emission spectroscopy from fast helium beams as density-and temperature diagnostics, for covering a wider range than either for thermal helium beam or fast lithium beam diagnostics [3]. "
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    ABSTRACT: Summary Visible HeI beam emission profiles have been measured at JET using 70 and 130 kV pure and doped He beams in a radially swept high clearance L-mode plasma. The measured spectra are very clean with good spatial coverage. Altogether, the profiles of 7 different lines could be measured in plasmas with 1.5 ≤ Zeff ≤ 2.1. These profiles will be used to develop a reversion code extracting density- and temperature profiles from the He beam emission profiles.
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    ABSTRACT: For the purpose of neutral‐lithium beam tokamak–plasma diagnostics we have developed a compact, high current (several tens of mA/cm<sup>2</sup>) 2.45‐GHz electron cyclotron resonance (ECR) Li<sup>+</sup> plasma ion source in coaxial geometry, coupled to a helium‐buffered lithium feeding system working according to the heat pipe principle. The accel–decel‐type ion extraction system features either seven holes or one single aperture. First experimental results for the extractable Li<sup>+</sup> and He<sup>+</sup> ions in both cw and pulsed‐mode operations are presented.
    Review of Scientific Instruments 05/1994; DOI:10.1063/1.1145074 · 1.61 Impact Factor
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    ABSTRACT: A fast neutral lithium beam has been installed on the TEXT tokamak for beam emission spectroscopy studies of the edge plasma electron‐density profile. The diagnostic was recently upgraded from ten to twenty spatial channels, each of which has two detectors, one to measure lithium beam signal and one to monitor plasma background light. The spatial resolution is 6 mm, and the temporal resolution is designed to be as high as 10 ms for studies of transient events including plasma density fluctuations. Initial results are presented from the ten‐channel system: Edge electron densities unfolded from the LiI (2 s <sup>2</sup>S–2 p <sup>2</sup>P) 670.8 nm emission profile have the same general time dependence as the line‐averaged density measured by microwave interferometry. © 1995 American Institute of Physics.
    Review of Scientific Instruments 02/1995; DOI:10.1063/1.1146487 · 1.61 Impact Factor
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