Two-dimensional (2D) imaging of electron temperature perturbations provides a powerful constraint for validating theoretical models describing magnetohydrodynamic plasma behavior. In observation of Alfvén wave induced temperature fluctuations, electron cyclotron emission imaging provides unambiguous determination of the 2D eigenmode structure. This has provided support for nonperturbative eigenmode solvers which predict symmetry breaking due to poloidal flows in the fast ion population. It is shown that for Alfvén eigenmodes, and in cases where convective flows or saturated perturbations lead to nonaxisymmetric equilibria, electron plasma displacements oriented parallel to a gradient in mean temperature are well defined. Furthermore, during highly dynamic behavior, such as the sawtooth crash, highly resolved 2D temperature behaviors yield valuable insight. In particular, addressing the role of adiabatic heating on time scales much shorter than the resistive diffusion time through the additional diagnosis of local electron density allows progress to be made toward a comprehensive understanding of fast reconnection in tokamak plasmas. © 2011 American Institute of Physics.

Neutral beam injection into reversed magnetic shear DIII-D and ASDEX Upgrade plasmas produces a variety of Alfvénic activity including toroidicity-induced Alfvén eigenmodes and reversed shear Alfvén eigenmodes (RSAEs). These modes are studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and increased drive due to multiple higher order resonances. Scans of injected 80 keV neutral beam power on DIII-D showed a transition from classical to AE dominated fast ion transport and, as previously found, discharges with strong AE activity exhibit a deficit in neutron emission relative to classical predictions. By keeping beam power constant and delaying injection during the current ramp, AE activity was reduced or eliminated and a significant improvement in fast ion confinement observed. Similarly, experiments in ASDEX Upgrade using early 60 keV neutral beam injection drove multiple unstable RSAEs. Periods of strong RSAE activity are accompanied by a large (peak δS n/Sn ≈ 60%) neutron deficit. Losses of beam ions modulated at AE frequencies were observed using large bandwidth energy and pitch resolving fast ion loss scintillator detectors and clearly identify their role in the process. Modeling of DIII-D loss measurements using guiding center following codes to track particles in the presence of ideal magnetohydrodynamic (MHD) calculated AE structures (validated by comparison to experiment) is able to reproduce the dominant energy, pitch, and temporal evolution of these losses. While loss of both co and counter current fast ions occurs, simulations show that the dominant loss mechanism observed is the mode induced transition of counter-passing fast ions to lost trapped orbits. Modeling also reproduces a coherent signature of AE induced losses and it was found that these coherent losses scale proportionally with the amplitude; an additional incoherent contribution scales quadratically with the mode amplitude. © 2011 American Institute of Physics.