XXXVII international conference on plasma physics and CF, February 8 – 12, 2010, Zvenigorod.
eVALUATING THE Effect of laser excitation of atomic beam on THE charge-exchange recombination spectroscopy in ITER
S.N. Tugarinov, M.B. Kadomtsev, M.G. Levashova,V.S. Lisitsa
TPI RRC "Kurchatov Institute", Moscow, Russia,
Weinvestigatetheefficiencyof charge-exchange recombination spectroscopy ofimpuritiesintokamakplasmasboth inthe standard scheme and in the case of additionalexcitationofneutralatomicbeambya Lyman-αlaser, using thedata oncharge-exchange cross-sections by Olson et al. [1,2] and the model [3] for the cascade population of atomic levels. Itisshownthat (i) underconditionsoflaserexcitationofatomicbeamthecharge-exchangepopulationfromatomiclevel ni=2 ofneutralbeamatomseffectivelyproduces highlyexcitedatomicstates ofhighlychargedimpurity ions, that gives a noticeable increase of the measurable line intensity, (ii) on the other hand, with decreasing charge of the impurity ion there is an abrupt drop of both total and partial cross-sections of the charge-exchange recombination -- for Не at typical energy of diagnostic atomic beam, Е100 keV,almost by the order of magnitude, (iii) the suggested analytical formulas for the net rates of spectral line excitation are applicable for arbitrary Z. We made a detailed comparison with the results from [4].
Theestimatesofnetratesofopticalspectrallineexcitationof impurities duetocharge-exchangefromexcitedstatesofhydrogenatomsare based on the Bohr-Lindhard asymptotic results for thecharge-exchange at high energies, which allow the derivation of a universal analytic formula to obtain the netrate (in atomic units) ofopticalspectrallineexcitation for arbitrary impurity due to charge-exchange from =2 to the level n in impurity ion under conditions typical for ITER:
= 3 ln()(1)
where is velocity of beam atoms. Theoptimalvaluesofbeamenergyarefound, whichgivethemaximumeffect of the charge exchange from hydrogen excited states. Anoticeableeffectcanbeobservedat the ions of moderate and high atomic number impurities. E.g., for (fully stripped) ironionsthemeasuredsignalenhancementdueto charge-exchange is about factor of 2, whereas for tungsten ions it goes up to 25. Thus, laserexcitationappearstobeefficientfor impurity ions with high enough charge, starting from iron nuclei.
References
[1].CorneliusK.R., WojtkowskiK., OlsonR.E. J. Phys.B., 2000, 33, 2017-2035
[2].HoekstraR.etal. PlasmaPhys. Control. Fusion, 1998, 40, 1541-1550
[3].KadomtsevM.B., LevashovaM.G. andLisitsaV.S., JETP, 2008, 106 (4), 635-649
[4].TugarinovS.N. etal. PlasmaPhysicsReports, 2004, 30, (2), 128–135
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