Interaction of energetic particles with large and small scale instabilities

Abstract

Beyond a certain heating power, measured and predicted distributions of NBI driven currents deviate from each other even in the absence of MHD instabilities. The most reasonable explanation is a redistribution of fast NBI ions on a time scale smaller than the current redistribution time. The hypothesis of a redistribution of fast ions by background turbulence is discussed. Direct numerical simulation of fast test particles in a given field of electrostatic turbulence indicates that for reasonable parameters fast and thermal particle diffusion can indeed be similar. -High quality plasma edge density profiles on ASDEX Upgrade and the recent extension of the reflectometry system allow for a direct comparison of observed TAE eigenfunctions with theoretical ones as obtained with the linear, gyrokinetic, global stability code LIGKA. These comparisons support the hypothesis of TAE-frequency crossing the continuum at the plasma edge in ASDEX Upgrade H-mode discharges. -A new fast ion loss detector with 1 MHz time resolution allows frequency and phase resolved correlation between the observed losses and low frequency magnetic perturbations such as TAE modes and rotating magnetic islands.Whereas losses caused by TAE modes are known to be due to resonances in velocity space, by modelling of the particle drift orbits we were able to explain losses caused by magnetic islands as due to island formation and stochasticity in the drift orbits.

Mechanisms and scalings of energetic ion transport via tokamak microturbulence

“…[9]. Moreover, they can be applied to try to understand and interpret recent experimental observations [11] concerning the efficiency of neutral beam injection. A thorough discussion of the latter problem will be presented elsewhere.…”

“…While there exists a large number of publications about particles with large gyroradii in 2D turbulence, [1][2][3][4][5][6][7] the study of fast particles in a turbulent background in 3D toroidal geometry has (re-)gained attention only quite recently. [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]).…”

“…This was, in part, motivated by recent experimental results [11] concerning the efficiency of neutral beam injection, and the need to explain them. In the present section, however, we would like to investigate in which way the D(E) behavior is modified if the test particles only have a small parallel velocity component such that they are trapped on the outer side of the torus, moving along banana orbits.…”

Suprathermal ion transport in simple magnetized torus configurations

“…200, which are relevant to fusion-related neutral beam experiments. 39 We emphasize that our study has focused on injection at R ¼ R 0 . We remark that it is possible to vary T e by changing the injection location.…”

Assessment of the ITER high-frequency magnetic diagnostic set

“…This value is well below the ITER requirement of |ıB MEAS /B POL | ∼ 10 −4 , as the latter is of similar order to the threshold in mode amplitude that is expected to cause stochastic fast ion transport [3]. Note also that values of |ıB MEAS | ∼ mG are routinely measured by HF pick-up coils in all major tokamaks such as JET [4], ASDEX-U [5], MAST [6], DIII-D [7], JT60U [8], i.e. for modes which are far away from the stochasticity threshold.…”