Particles Confinement Properties in Low Aspect Ratio L=1 Helical Systems.

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The L=1 helical axis systems applying the control methods of effective toroidal curvature term defined as the sum of usual toroidal curvature term and one of the nearest satellite harmonics of helical field term, have been studied to improve particles confinement properties. If we consider a compact system, a small period number N and low aspect ratio system is desirable. In generally, particles transport properties of compact system become worse due to usual toroidal effect. We have been studied by the same methods described in our paper, and we have improved particles transport by controlling the effective curvature term. It has been found that improving of particle confinement has observed, and the optimal structure of magnetic field in case of low aspect ratio case has been discussed. The transport properties of small N systems will be worse than that in the larger N systems. But, the magnetic well control is comparatively easy and device becomes compact. So, we have investigated the collisionless test particles confinement and velocity space loss region for the four type devices. The maximum test particles energy is set at 10KeV. We can see that the particle confinement becomes worse in low N ( low coil aspect ratio) case as expected. But, the low N case, especially N=5 case, the particle confinement is influenced by the pitch modulation parameter a^* and shows that the transport of a^* =-0.2 case is improved confinement properties. These results are consistent with the neo-classical theory. On the other hand, the high aspect ratio cases show that the efficiency of improvement is not so large in our particle tracing calculation.