The inertial electrostatic confinement (IEC) is a concept for electrostatically confining high-energy fuel ions in potential well. In ideal IEC plasmas, the ions converge toward the center of the device, and their space charge forms a virtual anode. The IEC fusion system has intrinsic potential for earlier practical use of fusion energy as a compact and economical neutron/proton source. To improve further the device performance, it is important to understand the physics of the IEC plasmas. In the device several kinds of ion-neutral collisions occur, e.g. elastic-scattering, ionization, charge exchange (CX) in parallel with the fusion reaction. Especially, the charge exchange reaction changes accelerated ions to fast-neutral which can cause fusion reaction with background neutral gas. In previous researches, it has been shown that the fusion reaction between the fast-neutral and background gas is comparable with those between ion and background gas [1, 2]. We have previously examined correlation between the ion distribution function and neutron production rate between ion and background gas in spherical IEC devices [3]. The energy distribution of fast-neutral would also be influenced by the shape of the ion distribution function. In this paper, we investigate the fast-neutral distribution function (neutron production rate) for various ion distribution functions and device parameters.
We assume the spherical IEC device. Within the spherical cathode, the potential structure is determined by solving the Poisson-Equation, and the Child-Langmuir radial potential is assumed outside the spherical cathode region. The Boltzmann-Equation for the fast-neutral is solved considering the fast-neutral generation and loss by CX reactions, together with the particle transport loss from the device. We evaluate the Doppler-shift wavelength of the hydrogen specific H_αline by using the obtained fast-neutral distribution and compare it with previous experiment[4].It is shown that the shape of the fast-neutral distribution function is sensitively affected by the shape of the ion distribution function and device parameters.

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