ORIGIN OF RADIATION EMISSION INDUCED BY FUSION REACTION-PRODUCTS

The excitation of collective modes at the harmonics of the cyclotron frequency of the He-4 population produced in D-T fusing plasmas has been predicted by a detailed analysis that includes the important effects of the confinement geometry and confirmed by the first experiments on D-T plasmas. These modes are shown to be spatially localized in a narrow layer centered around a surface near the edge of the plasma column that is consistent with that inferred from the value of the magnetic field corresponding to the observed cyclotron frequency. The radial width of the layer is compatible with the relatively narrow width of the peaks of radiation emission. The outermost edge of the plasma column is reached by the alpha-particles having magnetically trapped orbits of relatively large amplitude and a distribution anisotropy in velocity space of the type needed to drive the considered modes unstable. The relevance of the proposed interpretation to both analyze and interfere with the alpha-particle distribution is pointed out.