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A new simulation method that improves the conservation properties of δ f particle simulation for the collisionless Boltzmann equation is presented. When the distribution function is divided into a reference distribution specifi ed in advance and a variation distribution, the time evolution of the variation distribution is described by an advection termin the phase space and a source term associated with the reference distribution. The time evolution of the Klimontovich distribution function of the δ f method was investigated. It is shown that the errors in the Monte Carlo estimate of the source term in the δ f method deteriorate the conservation properties. In the new simulation method, errors in the Monte Carlo estimate of the source term are corrected with a complementary fl uid model. An example of the complementary fl uid model is presented for bump-on-tail instability. The simulation results are compared with those of the conventional δ f method. It is demonstrated that particle, momentum, and energy are well conserved with the new simulation method.

Neoclassical transport simulation using the δ f Monte-Carlo method is carried out to investigate the finite-orbitwidth (FOW) effect on the transport near the magnetic axis. The time evolution of the radial electric field to maintain the ambipolarity of the flux is calculated simultaneously. It is found that, in the near-axis region, the ion heat flux decreases from the value predicted by the standard neoclassical theory both in the banana and plateau regimes. Though the radial transport shows a strong dependence on the FOW effect, the ambipolar electric field profile at the steady state is similar to that calculated in the small-orbit-width limit approximation.