Ripple loss of suprathermal alpha particles during slowing-down in a tokamak reactor

Abstract

The slowing-down process of suprathermal alpha particles in a rippled toroidal field is investigated by means of an orbit-following Monte-Carlo code. It is found that numerical results on the collisionless ripple loss agree fairly well with the theoretical predictions. The collisional diffusion coefficient for non-ergodic banana particles in a field ripple is derived. The ripple-enhanced power loss of alpha particles during slowing-down amounts to 10% of their total power in a reactor-grade tokamak with a toroidal-field ripple of 𝛅 ∼ 1%. The fraction of particle loss is 1.5 to 1.8 times as large as that of power loss. The ripple-enhanced banana drift dominates the alpha-particle loss process.

The effect of toroidal field ripple on confined alphas in TFTR DT plasmas

“…Although both theory and computational simulation predict negligible TF ripple induced alpha particle losses in a fusion reactor where the ripple amplitude is less than 1 -2% [3,4], these losses are localized and may cause serious first-wall hest load problems in a reactor even if the losses are kept to a few percent [5]. In addition, there is some evidence that sawteeth [6,7] and other magnetohydrodynamic (MHD) instabilities [8] may transport alphas into the ripple loss regions and potentially increase the losses well above this level.…”

Energetic particle transport in compact quasi-axisymmetric stellarators

“…Guiding center code simulations which follow the motion of an ensemble of particles in toroidal magnetic coordinates over an energy slowing down time are a wellknown method for the analysis of fast particle loss from tokamak experiments [9][10][11][12][13][14][15] . We here make use of a new stellarator version of the Monte Carlo ORBIT 16 guiding center code, ORBITMN, to assess the loss rate of plasma ions, both thermal and energetic, in promising quasi-axisymmetric stellarator designs.…”

Design Optimization Study of the JT-60 Superconducting Coil Modification

“…The design of the toroidal field ripple compensation was carried out using FEMAG code [8] which was originally developed at JAERI, and the improvement of the fast ion losses was evaluated by the OFMC code [9]. Fig.…”