The containment properties of alpha particles during the slowing-down process in an axisymmetric tokamak reactor are studied by using Monte-Carlo calculations, in which the pitch-anglescattering effects are included. The loss of alpha particles during slowing-down is found to be safely negligible in a pure DT plasma, but increases proportionally to the effective charge number of the plasma and cannot be ignored in a highly contaminated plasma (Z e ff > 4), compared with the loss of 3.5-MeV particles.
The electrostatic potential well in inertial electrostatic confinement (IEC) is studied using two approaches. First, the equilibrium potential profile is obtained by solving the charge neutrality condition, i.e. ni=ne, assuming the appropriate distribution functions for the ions and the electrons. The formation of a double well structure is demonstrated, with a depth depending upon the ratio between the focus radii of the electrons and the ions. The correlations between the well depth and the volume integrated neutron production due to deuterium-deuterium (DD) reactions are obtained. Second, in order to study the stability of the well, the dynamic behaviours of the potential well are calculated by performing time advancing numerical simulations on the basis of the particle in cell method. Single, double and triple wells, depending on the amount of injected ion current, are observed to be formed for ions with a monoenergetic distribution. The well in the centre of the multiwell structure is unstable and oscillates with a period much longer than the inverse ion plasma frequency. A double well structure can be formed even for ions with a spread out energy distribution when the ion current is larger than the threshold value. The time averaged neutron production by DD fusion events is proportional to a power of the ion current involved in forming the double well structure. The results strongly suggest that the high neutron production rate should be attributed to not only the well depth but also the unstable behaviour of the potential, i.e. the intermittent peaking of the density in the centre region. A numerical simulation reveals that IEC possesses a favourable dependence of fusion reactions on the injected ion current for the application to a neutron source or a fusion reactor
A Monte Carlo simulation code is developed for ion cyclotron range of frequencies (ICRF) hearing in helical systems, which takes into account finite beta effects, complicated orbits of high energetic particles, Coulomb collisions and interactions between particles and the applied waves. The code is used to investigate ICRF minority heating in the Large Helical Device (LHD). The configuration of the magnetic fields changes significantly due to finite beta effects in the LHD. The resonance layer position is found to be crucial to the heating efficiency as the plasma beta increases. When the strength of the resonance magnetic field is set to the value at the magnetic axis, a higher heat efficiency is obtained and no clear difference of the heat efficiency due to finite beta effects is found in the high ICRF wave power region. However, the radial profile of the power transferred to majority ions and electrons from minority ions changes because of the deformation of the trapped particle orbits due to the finite beta effects. The heat efficiency is improved if the radial electric field, Er, is positive (Er is directed radially outward) and it is also improved by supplying 3He minority ions rather than proton minority ions
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