Alpha-Particle-Driven Toroidal Alfvén Eigenmodes in the Tokamak Fusion Test Reactor

Alpha-particle-driven toroidal Alfv\'en eigenmodes (TAEs) have been observed for the first time in deuterium-tritium (D-T) plasmas on the tokamak fusion test reactor (TFTR). These modes are observed 100--200 ms following the end of neutral beam injection in plasmas with reduced central magnetic shear and elevated central safety factor $[q\left(0\right)>1]$. Mode activity is localized to the central region of the discharge $\left(r/a<0.5\right)$ with magnetic fluctuation level ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{B}}_{\ensuremath{\perp}}{/B}_{\ensuremath{\parallel}}\ensuremath{\sim}{10}^{\ensuremath{-}5}$ and toroidal mode numbers in the range $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2--4$, consistent with theoretical calculations of \ensuremath{\alpha}-TAE stability in TFTR.