Effects of toroidal field ripple on suprathermal ions in tokamak plasmas

Abstract

Analytic calculations of three important effects of toroidal field ripple on suprathermal ions in tokamak plasmas are presented. In the first process, collisional ripple-trapping, ions become trapped in local magnetic wells near their banana tips owing to pitch-angle scattering as they traverse the ripple on barely unripple-trapped orbits. In the second process, collisionless ripple-trapping, ions are captured (again near a banana tip) owing to their finite orbits, which carry them out into regions of higher ripple. In the third process, banana-drift diffusion, fast-ion banana orbits fail to close precisely, due to a ripple-induced ‘variable lingering period’ near the banana tips. These three mechanisms lead to substantial radial transport of banana-trapped, neutral-beam-injected ions when the quantity α*≡ε|τ|/Nqδ is of order unity or smaller.

Evidence for spatially variable beam ion diffusion in TFTR

“…Thus, the region of enhanced spatial diffusion in figure 3 coincides with the expected ripple boundary. The magnitude of the diffusion is also consistent with rough estimates based on 'ripple-plateau' diffusivity [31]. figure 3).…”

Analysis of PWI footprint traces and material damage on the first walls of the spherical tokamak QUEST

“…The toroidally asymmetric footprint traces are formed in the region existed between R = 1.0 m and 1.2 m, where the ripple factors are within 0.1-0.4%. These ripple factors are actually too small to consider the ripple effects [21]. The particle (ion/electron) orbit calculation has also suggested a toroidally uniform plasma loss over this region.…”

Numerical study of stellarator transport

“…The analytic expression for y, for an £=2 "sigmaconfiguration" is, from Eq. (12) The quantities Ppj and r B are obtained from these equations, rather than from more usual analytic expressions [5], in order to ensure that not only is flux conserved but also that Liouville's theorem is satisfied exactly at y = c) The Geometry of the Mesh-…”