Observation of Weak Impact of a Stochastic Magnetic Field on Fast-Ion Confinement

Abstract

Fast ions are observed to be very well confined in the Madison Symmetric Torus reversed field pinch despite the presence of stochastic magnetic field. The fast-ion energy loss is consistent with the classical slowing down rate, and their confinement time is longer than expected by stochastic estimates. Fast-ion confinement is measured from the decay of d-d neutrons following a short pulse of a 20 keV atomic deuterium beam. Ion confinement agrees with computation of particle trajectories in the stochastic magnetic field, and is understood through consideration of ion guiding center islands.

Study on the creation and destruction of transport barriers via the effective safety factors for energetic particles

“…The idea is heavily inspired from what was dubbed the ion guiding center safety factor in Ref. 12. As we shall see, using this point view, most of the behaviors observed in Ref.…”

“…SO thanks D. F. Escande for bringing his attention to the paper of Fiksel et al 12 SO and XL are grateful to M.…”

“…12 and we consider the notion of an effective safety factor in our cylindrical torus (periodic cylinder) for a particle orbit given by…”

“…9 In fact it has been shown that when the energy is sufficiently large the effective location of the resonance which was destroying the magnetic structure can be displaced and even disappear as we shall discuss later on. [12][13][14] To be more specific, when we consider only particles with small energy whose motion is mostly one along a magnetic field line and some gyration around it. Then, the qualitative structure (e.g.…”

Preferential confinement and field-aligned acceleration of energetic ions in a reversed field pinch

“…A substantial overlap of magnetic islands typically makes the magnetic field in the RFP stochastic and limits electron and thermal ion confinement times to around 1 ms [8]. The confinement of fast ions is insensitive to the stochastic field of the RFP and is understood from the decoupling of the fast ion orbits from the magnetic perturbations [9,10]. In the RFP, with a magnetic field strongest at the magnetic axis and a dominant poloidal field over much of the minor 040001-2 radius, the drift-altered fast ion guiding center remains on a flux surface.…”