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The Helias (Helical Advanced Stellarator Reactor configuration [1,2] is one of the leading candidates for a steady-state fusion reactor. This configuration is an extrapolation of the Wendelstein 7-X configuration [3] to reactor dimensions.The basic physical features of the Helias reactor configuration (HSR) are the following: Its capability to confine an MHD-stable plasma up to <B>+5%, the low neoclassical losses which are not prohibitive to ignition, the good confinement properties of highly energetic a-particles. In this paper we consider the problem of a-particle confinement, namely collisionless a-particles with an energy of 3.5 MeV.The confinement of fusion a-particles is of great interest for the reactor. It has been shown that in tokamaks with secondary ripples of the magnetic field due to the discreteness of the toroidal field coils, trapped particle orbits become stochastic [4,5]. Therefore, radial transport of these particles increases. The flux of highly energetic a-particles to the first wall of a slightly rippled tokamak is highly non-uniform in the poloidal angular coordinate [6]. This effect has been observed experimentally in TFTR [7]. Stellarator magnetic field is inherently three-dimensional and can lead to much more complicated particle behaviour. This is especially apparent in the processes of particle trapping-detrapping in the field ripples. In the case of Helias, the confinement of highly energetic a-particles depends strongly on the parameter B (the ratio of the thermal to magnetic energy in the confinement region). It was shown that the prompt losses of a-particles decrease considerably (less than 10%) for <B>=5%. The reason is that finite plasma pressure produces a true minimum-B configuration in which the majority of reflected a-particles are confined for at least one slowing-down time [8]. In this article we analyze the coil-ripple effects on a-particle orbits. The position of lost a-particles, footprints on the first wall of HSR is anot

Additional information

Authors: BEIDLER C D, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);HERRNEGGER, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);KISSLINGER J, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);WOBIG H, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);ZOLOTUHKIN A V, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE)
Bibliographic Reference: Article: Guiding Center Studies of Collisionless alpha-particles in a helias configuration, (1999)
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