The diffusion of fast ions in Ohmic TFTR discharges

Abstract

Short duration (20 msec) neutral deuterium beams are injected into the TFTR tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. I, p. 5 11. The subsequent confinement, thermalization, and diffusion of the beam ions are studied with multichannel neutron and charge exchange diagnostics. The central fast-ion diffusion ( co.05 m2/sec) is an order of magnitude smaller than typical thermal transport coefficients.

Anomalous transport of energetic particles in ITER relevant scenarios

“…In contrast, the transport of suprathermal particles driven by microturbulence has not been a subject of concentrated research, especially following the work of a number of groups concluding that fast gyro-and orbit-averaging of the turbulent fields would render the transport negligible [4][5][6]. An apparent confirmation of these theoretical conclusions was found on early experiments at the Tokamak Fusion Test Reactor (TFTR) [7][8][9][10], where an upper limit for fast ion diffusivities was found at 0.1 m 2 · s −1 , an order of magnitude smaller than that of thermal ions. Recently, however, there has been renewed interest, triggered by experimental observations of anomalous redistribution of NBI ions at the Axial Symmetric Divertor EXperiment (ASDEX) Upgrade [11,12], at the Joint European Torus (JET) [13,14], at the Mega-Ampere Spherical Tokamak (MAST) [15,16], and at DIII-D [17,18].…”

“…The observation of a higher flux is then related to the choice of the profile gradients and similar misleading conclusions would be drawn if one chooses to study the transport in terms of D α / |D i | from Eq. (8). When dealing with theD α diffusivity from Eq.…”

Mechanisms and scalings of energetic ion transport via tokamak microturbulence

“…[8][9][10] These investigations were, in part, motivated by recent experimental investigations at ASDEX Upgrade which showed a fast radial broadening of the current profile driven by off-axis neutral beam injection in the absence of any measurable magnetohydrodynamic activity, [11] and seem to contradict earlier experimental results claiming that such an effect should not exist (see, e.g., Ref. [12]). The present paper wants to shed light on this crucial question (especially for future D-T-based experiments like ITER [13]) by studying different decorrelation mechanisms for passive tracers in a 3D turbulent environment.…”

Accurate measurements of the pitch-angle scattering of beam ions

“…7 On the other hand, the agreement between theory and experiment strongly suggests that beam deposition and orbital effects are properly treated by the TRANSP code in this regime. In the core of quiet tokamak plasmas, the deceleration, 32 pitch-angle scattering, and spatial diffusion 35 of beam ions are adequately described by the effects of Coulomb scattering.…”

“…In similar experiments on the Tokamak Fusion Test Reactor ͑TFTR͒, the measured spatial diffusion of the beam ions was very small, comparable to the expected neoclassical transport level. 35,36 Although some transport caused by neutralization and subsequent reionization does occur, the global charge exchange losses are small ͑ϳ5%͒, so the charge-exchange term in Eq. ͑1͒ is relatively unimportant.…”