Open AccessStochastic Orbit Loss of Neutral Beam Ions From NSTX Due to Toroidal Alfven Eigenmode Avalanches
Author(s) -
D S Darrow,
E. D. Fredrickson,
N N Gorelenkov,
M Gorelenkova,
S Kubota,
S S Medley,
M Podesta,
L Shi
Publication year - 2012
Language(s) - English
Resource type - Reports
DOI - 10.2172/1057474
Subject(s) - physics , pitch angle , toroid , atomic physics , ion , beam (structure) , plasma , orbit (dynamics) , range (aeronautics) , torus , phase space , computational physics , optics , nuclear physics , materials science , geometry , geophysics , engineering , mathematics , quantum mechanics , composite material , thermodynamics , aerospace engineering
Short toroidal Alfven eigenmode (TAE) avalanche bursts in the National Spherical Torus Experiment (NSTX) cause a drop in the neutron rate and sometimes a loss of neutral beam ions at or near the full injection energy over an extended range of pitch angles. The simultaneous loss of wide ranges of pitch angle suggests stochastic transport of the beam ions occurs. When beam ion orbits are followed with a guiding center code that incorporates plasma's magnetic equilibrium plus the measured modes, the predicted ranges of lost pitch angle are similar to those seen in the experiment, with distinct populations of trapped and passing orbits lost. These correspond to domains where the stochasticity extends in the orbit phase space from the region of beam ion deposition to the loss boundary