Neoclassical Transport in the Helical Reversed-Field Pinch

Abstract

Test particle evaluation of the diffusion coefficient in a fusion plasma in the reversed-field pinch (RFP) configuration shows distinct similarities with stellarators when the plasma spontaneously evolves towards a helical shape. The almost total absence of superbanana particles at the levels of helical deformation seen in experiment (Bh/B=10%) causes transport to be proportional to collision frequency (at low collisions). This fact excludes the possibility that the minimum conceivable transport could be inversely proportional to collision frequency, which is typical of unoptimized stellarators. This result strengthens the perspectives of the helical RFP as a fusion configuration.

What is a Reversed Field Pinch?

“…Furthermore the loss of axisymmetry decreases when going towards the plasma edge, which decreases the trapped fraction of fast particles and the related transport. Finally with the amplitude of the helical field seen in experiments, super-banana orbits are present in negligible fraction, which helps fast particles to be better confined [12]. All this should prevent alpha particles to be lost rapidly to the wall.…”

Fast ion transport in the quasi-single helical reversed-field pinch

“…Volume averaged diffusion coefficients found analogous to those of Gobbin et al lacked the 1/ dependence created from superbanana orbits. 11,16 Figure 8 shows ORBIT calculated diffusivity in a SHAx state. The computed diffusivity depicted in Fig.…”

“…14,15 Research on thermal particles in the RFP's helical ripple failed to observe unoptimized stellarator-like losses. 16 The superbanana regime only became significant at experimentally unobtainable perturbation levels. Thus, at the first glance, the investigation of fast ions in the QSH state necessitates the examination of any neoclassical transport effects.…”

Three dimensional equilibrium solutions for a current-carrying reversed-field pinch plasma with a close-fitting conducting shell

“…2, a potentially favorable configuration for energy and particle confinement. 26 Previous V3FIT reconstructions performed without a conducting shell boundary condition showed a discrepancy between the observed and modeled perturbed n ¼ 5 magnetic field measured at the edge of the plasma of %60%. This large discrepancy is attributed to the measurement location.…”