Turbulent transport of beam ions

Abstract

The radial redistribution of energetic ions by background turbulence is investigated by means of linear and nonlinear gyrokinetic simulations with the GENE code [T. Dannert and F. Jenko, Phys. Plasmas 12, 072309 (2005)]. The fast particles are described by an asymmetric and anisotropic Maxwellian distribution function, and they are treated as passive tracers. It is found that there can be a significant fast ion diffusivity for particle energies up to about 10 times the thermal energy, with details depending on the properties of the magnetic geometry and of the microinstabilities driving the turbulence. This finding provides a possible explanation of experimental results concerning the efficiency of neutral beam current drive reported recently from ASDEX Upgrade [S. Günter et al., Nucl. Fusion 47, 920 (2007)].

Anomalous transport of energetic particles in ITER relevant scenarios

“…Our findings have been shown to be in qualitative agreement with those presented in Refs. [29,31,41], and quantitative discrepancies are due to the difference in the parameters chosen.…”

“…We note that these pitch angles are characteristic of tangentially injected NBI distributions and ICRH distributions, respectively. For passing ions, a D v ≃ E −1 decay is expected [29][30][31]. For deeply trapped particles, i.e.…”

“…The extension to a velocity space resolved analysis by means of the GENE code [2,28] was undertaken in Ref. [29], where a 1/E decay of the particle diffusivity of high energy passing particles was observed in the presence of small scale turbulence. This scaling shows how micro-turbulence can affect NBI ions, whose energies for present days experiments can be 10 to 20 times larger than the electron temperature.…”

Assessment of turbulent beam ion redistribution in tokamaks through velocity space-dependent gyrokinetic analyses

“…However, a series of experimental [5,6], theoretical [7] and numerical investigations [8][9][10] demonstrated that this conclusion might not hold for energetic ions created by neutral beam injection: in general, transport can be significant for particles characterized by 'intermediate' energies (E/T e 10) and small Larmor radii.…”

Combination of fast-ion diagnostics in velocity-space tomographies

“…Several types of modes affect ions in only part of velocity space, for example sawteeth [35][36][37][38], Alfvén eigenmodes [6,[39][40][41][42][43] and neoclassical tearing modes [4,5]. Turbulent transport of fast ions also depends on the ion energy [44][45][46][47]. Additionally, velocityspace tomography could be used to monitor phase-space engineering of fast-ion velocity distribution functions which has enabled control of sawteeth and neoclassical tearing modes [48].…”