Optimized tomography methods for plasma emissivity reconstruction at the ASDEX Upgrade tokamak.

The soft X-ray (SXR) emission provides valuable insight into processes happening inside of high-temperature plasmas. A standard method for deriving the local emissivity profiles of the plasma from the line-of-sight integrals measured by pinhole cameras is the tomographic inversion. Such an inversion is challenging due to its ill-conditioned nature and because the reconstructed profiles depend not only on the quality of the measurements but also on the inversion algorithm used.

Convective and diffusive energetic particle losses induced by shear Alfvén waves in the ASDEX upgrade tokamak.

We present here the first phase-space characterization of convective and diffusive energetic particle losses induced by shear Alfvén waves in a magnetically confined fusion plasma. While single toroidal Alfvén eigenmodes (TAE) and Alfvén cascades (AC) eject resonant fast ions in a convective process, an overlapping of AC and TAE spatial structures leads to a large fast-ion diffusion and loss. Diffusive fast-ion losses have been observed with a single TAE above a certain threshold in the fluctuation amplitude.

Resistive-wall-mode active rotation in the RFX-mod device.

The fundamental question of how the flow velocity of the background plasma can influence the motion of magnetohydrodynamics instabilities and, in the ultimate analysis, their stability is addressed. The growth of resistive-wall-mode instabilities in toroidal confinement devices well represents one example of such a problem. In this Letter, we illustrate a new strategy that allowed, for the first time in a reversed field pinch experiment, a fully controlled rotation of a nonresonant instability by means of a set of active coils and how the new findings compare with numerical modeling.

Fast-ion losses due to high-frequency MHD perturbations in the ASDEX upgrade Tokamak.

Time-resolved energy and pitch angle measurements of fast-ion losses correlated in frequency and phase with high-frequency magnetohydrodynamic perturbations have been obtained for the first time in a magnetic fusion device and are presented here. A detailed analysis of fast-ion losses due to toroidal Alfvén eigenmodes has revealed the existence of a new core-localized magnetohydrodynamic perturbation, the sierpes mode. The sierpes mode is a non-Alfvénic instability which dominates the losses of fast ions in ion cyclotron resonance heated discharges, and it is named for its footprint in the spectrograms ("sierpes" means "snake" in Spanish).