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[en] Runaway electrons represent a serious problem for the reliable operation of the future experimental tokamak ITER. Due to the multiplication factor of exp(50) in the avalanche even a few seed runaway electrons will result in a beam of high energetic electrons that is able to damage the machine. Thus suppression of runaway electrons is a task of great importance, for which we present here a systematic study of runaway electrons following massive gas injection in TEXTOR. Argon injection can cause the generation of runaways carrying up to 30% of the initial plasma current, while disruptions triggered by injection of helium or of mixtures of argon (5%, 10%, 20%) with deuterium are runaway free. Disruptions caused by argon injection finally become runaway free for very large numbers of injected atoms. The appearance/absence of runaway electrons is related to the fraction of atoms delivered to the plasma centre. This so-called mixing efficiency is deduced from a 0D model of the current quench. The estimated mixing efficiency is 3% for argon, 15% for an argon/deuterium mixture and about 40% for helium. A low mixing efficiency of high-Z impurities can have a strong implication for the design of the disruption mitigation system for ITER. However, a quantitative prediction requires a better understanding of the mixing mechanism
[en] Studies of two-beam coherent induced optical anisotropy has been performed for the cadmium sulphide nanocrystallites (NC) embedded within the different polymer matrices. The NC were fabricated by the modified electrolytical method and have been embedded into different polymer matrices: PC, PMMA, PVA. The phototreatement was performed by two space split coherent beams generated by 120 fs laser with pulse energy 23 nJ. The phototreatment has been durated several minutes until the clear diffraction grating has been observed. The monitoring of the laser induced gratings and of the anisotropy was performed using the cw 1150 nm continuous wave He–Ne laser with power about 30 mW. Varying the polarization of the laser coherent femtosecond beams we have found that the optimal gratings has been achieved for 45° polarizations between the beams. The control of the maximal laser induced gratings has been done using optically polarized method. The effect is not completely reversible and there remain some changes after switching off of the phototreatment. The anisotropy has been monitored by Senarmont method. The role of different polymers on the output photo stimulated birefringence was explored. This method may be promising for the design and engineering of optical triggers in the femtosecond laser pulse duration.