  Recently, theoretical analysis has identified plasma microinstabilities as
the primary mechanism responsible for anomalous heat transport in tokamaks. In
particular, the microtearing mode (MTM) has been credited with the production
of intense electron heat fluxes, most notably through a thin self-organized
boundary layer called the pedestal. Here we exploit a novel, time-dependent
analysis to compile explicit experimental evidence that MTMs are active in the
pedestal region. The expected frequency of pedestal MTMs, calculated as a
function of time from plasma profile measurements, is shown in a dedicated
experiment to be in excellent agreement with observed magnetic turbulence
fluctuations. Further, fast perturbations of the plasma equilibrium are
introduced to decouple the instability drive and resonant location, providing a
compelling validation of the analytical model. This analysis offers strong
evidence of edge MTMs, validating the existing theoretical work and
highlighting the important role of MTMs in regulating electron heat flow in
tokamaks.
