Electron transport due to global Alfv\'en eigenmodes in NSTX

We inverstigate theoretically and numerically the possible electron transport induced by multiple instabilities of Global Alfv\'en Eigenmodes (GAE) in a toroidal plasma. Such anomalous eletron transport was observed in NSTX recently when NBI power was increased to $P_{NBI}=6MW$ in both H- and L-mode discharges. With the frequency range of $0.5-1MHz$ GAEs may resonantly interact with bulk ($\sim 1-2keV$ energy) primarily trapped electrons. Because of strong beam ion drive GAEs are not damped on electrons, but are excited to a strong amplitudes, $\delta n_{e}/n_{e}\sim 10^{-4}$. ORBIT simulations show that the overlap of electron phase space resonant structures due to multiple GAE instabilities may induce stochastic electron diffusion. Our calculations suggest that GAEs with observed amplitudes may lead to electron heat diffusivity, $\chi_{e}\ge 10m^{2}/sec$, comparable to those inferred from the power balance analysis. The above mechanism potentially could have significant implications for fusion.