Monte-Carlo calculation of perpendicular neutral-beam injection in helical systems

The effect of a helical field ripple on the slowing-down process of the fast ions created by neutral injection is investigated numerically. For this purpose, the guiding-center orbits are followed in a model magnetic field without plasma current, on the assumption that the slowing-down process is to...

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Bibliographic Details
Published in:Nuclear fusion 1981-09, Vol.21 (9), p.1067-1077
Main Authors: Hanatani, K, Wakatani, M, Uo, K
Format: Article
Language:English
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Summary:The effect of a helical field ripple on the slowing-down process of the fast ions created by neutral injection is investigated numerically. For this purpose, the guiding-center orbits are followed in a model magnetic field without plasma current, on the assumption that the slowing-down process is to be classical. Optimum injection angles in two types of helical magnetic traps are compared. One is the Heliotron-E configuration with a large rotational transform and deep helical ripple; the other one is the conventional stellarator field with a small rotational transform and shallow helical ripple. In contrast to the stellarator, the heating efficiency as calculated for Heliotron-E does not decrease monotonically when the injection angle is perpendicular to the toroidal direction; a heating efficiency of above 70% was obtained for perpendicular injection into a high-density plasma with negligible charge-exchange loss. The difference in heating efficiency versus injection angle between heliotron and conventional stellarator fields is explained by a difference in drift motion of the helically trapped fast ions.
ISSN:0029-5515
1741-4326
DOI:10.1088/0029-5515/21/9/002