Plasma-wali 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.
A b s W t -A superconducting magnet usssmbly Bar Been built for rm ECR (Electron Cyclotron Resonarm$ Ion sowce at the 88~inch cyclohoti at LBL'. Three 34-cm ID solenoids provide axhl plasma cotijintw" and U sexfupole ussembly in the solenoid bore provides radial stabill@. Two large solenoid8 are spaced SO em. npwi with a smaller opposing solenoid bedween. The sexlupole ussembly is 92 cm long with winding inner diameter of 20 cm. and outer diameter of 27.2 em. Tfis design goat is fo achieve afield on axis of 4 T und 3 T a t the mirrors with 0.4 T behvees and a sexfapole field of 2.0 T at IS-cm diumeter iti the confinement volume. Emfr solenoid uses rectrsngrrlar conductor wtth mpper/'SC ratio of 4; flie three coils are wet-wound on a one-piece aluminlrm bobbin with aluminum bnndti!g for rudiui suppord. The sexapole uses rectangular conductor with copper/SC ratio of 3. EacR of the 6 eoik is wet-wound with filled epoxy ori a metal pole; the ends of the pole are ahminum and the central 34-cm h lron to augment the sextupokfldd. The a& coils me assembled on a 2O-cni4lD stainless steel hrbe with a I.4-cm thick 30.0.cm OD aluminum tribe over the assembly for striictural support. Thin metal bludders are exparrded adtnut!ially behveen each coil axially ab the ends to pre-load the assembly, The sexhrpob assembbflts inside lire solenoid bobtin, wlikb provMes support for the magnetic forces. The magnet exceeds design requirements with ni inim um training.
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