Fermi accelerated particles: orbit analysis for the chaotic behavior of the magnetic field lines

Summary form only given, as follows. The "magnetic null points" of a symmetric array of permanent magnets yield a strong nonlinearity for chaotic particle motion in microwave generated plasmas (at electron cyclotron resonance). It has been shown that particles can be heated in a "shaking billiard table" configuration of the multi-cusp: low-energy particles are heated by cyclotron resonance with the wave field, while high energy particles are heated through a nonresonant transit-time mechanism. We apply a recent theory which proves that magnetic field lines are trajectories of Hamiltonian systems and develop a quasilinear theory for the dynamics of particles in presence of the chaotic behavior of the magnetic field lines. The aim of the present study is the development of a numerical technique for handling local trajectories of particles and generate symplectic maps for nontwist systems. Periodic orbits and their characteristics are found by searching symmetry lines. Hence, including the tracking of particles and of magnetic field lines, we demonstrate that the chaotic acceleration of particles and thus the anomalous resistivity found in ultrafine plasma etching experiments, is likely to occur not only in the neighborhood of magnetic field line reconnection points but also at magnetic symmetry break-up points.