Ph. Lauber, I.G.J. Classen, D. Curran, V. Igochine, B. Geiger, S. da Graca, M. Garcia-Munoz, M. Maraschek, P. McCarthy and the ASDEX Upgrade Team

2012

September

Nuclear Fusion

NBI-driven Alfvénic modes at ASDEX Upgrade

Published

Scopus: 19 ()

52

9

094007

094007

A large variety of electromagnetic modes excited by NBI-generated energetic ions are observed in the early phase of many discharges at ASDEX Upgrade. In addition to the well-known reversed shear Alfvén eigenmodes (RSAE) and the toroidal Alfvén eigenmodes (TAE), a set of modes around 70 kHz is observed as recently described in [7]. The modes were identified to be beta-induced Alfvén eigenmodes (BAE) connected with the appearance of the q = 2 and the q = 1.5 surface during the current ramp-up phase. In the view of ITER, these BAEs may occur in scenarios with q ≈ 2 (scenario 4) and therefore add significantly to the transport of energetic ions due to RSAEs and TAEs. Experimentally, the combination of ECE, soft-x-ray and magnetic measurements allows for a very reliable mode position and mode structure determination. The measurements are compared with linear gyrokinetic calculations employing the LIGKA code that uses a fully kinetic model to describe fast-particle-driven modes in general tokamak geometry.

10.1088/0029-5515/52/9/094007