The behavior of the energetic particle in a helical axis heliotron device, Heliotron J[1], has been investigated. When the hydrogen neutral beam is injected into deuterium plasmas at an acceleration voltage of 28 keV, energetic protons up to 20 keV and deuterium up to 5keV are observed, while the bulk (D) ion temperature is estimated to be 0.3keV. Since the present CX-NPA system can not detect the CX-flux having the same pitch angle as the injected neutral beam, the bean components (E, E/2, E/3) are not observed clearly. The decay of the CX-flux having energy range of 2-3 keV is much faster than the other energy ranges. Although the mechanism of this observation is under investigation, it is considered that some loss mechanism might exist. From the theoretical calculation, it has been pointed out that controlling Fourier components of magnetic field plays a key role in the particle confinement[2]. In order to investigate the dependence of the energetic particle confinement on a Fourier component of the magnetic field, toroidal mirror ratio (bumpiness component), the behavior of the charge exchange neutral particle has been studied by changing the bumpiness component. The 1/e decay time of CX-flux after the NBI turned-off decreases with increasing the bumpiness. To understand the experimental result, the non-collisional orbit calculation for ion guiding center has been carried out. The calculation predicts that the main part of the detection area of CX-NPA is dominated by the direct loss in the high bumpiness case, while CX-NPA observes the passing particles in the low bumpiness case. Then the decrease in the decay time with bumpiness component may be attributed to the change in the loss cone shape. In order to investigate the effect of controlling the bumpiness component on the particle confinement in more detail, the system is being upgraded to enable to change the viewing angle in the toroidal and poloidal direction.

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