Advanced impurity measurement for deuterium-tritium-burning plasmas using pulsed CO2 laser collective Thomson scattering

Knowledge of the dynamics and concentration of impurities in the plasma cor e is crucial to the development of a deuterium-tritium (DT) tokamak fusion reactor. In this article, we first describe an advanced diagnostic techniqu e to measure the impurities, thermalized helium density, and the deuterium- to-tritium density ratio in DT-burning plasmas. The measurement is made by small-angle collective Thomson scattering using a high-power pulsed CO2 las er and heterodyne receiver system. The component of scattered laser power n early perpendicular to the magnetic field gives rise to ion cyclotron modul ation of the scattered spectrum. Scattered spectrum of expected impurities (Ar, Be, and He ash) are presented for the International Thermonuclear Expe rimental Reactor plasmas. The method for the determination of the helium as h density and deuterium-to-tritium ratio are also proposed. Modulation spec tra as a function of frequency for different magnetic-field angles are conf irmed. Experimental requirements to measure a scattered spectrum with fine details resulting from ion cyclotron oscillations are also discussed. (C) 2 000 American Institute of Physics. [S0034-6748(00)00411-1].