First Observation of Alpha Particle Loss Induced by Kinetic Ballooning Modes in TFTR Deuterium-Tritium Experiments

A correlation between the measured alpha particle loss and high frequency ( $\ensuremath{\sim}100--200$ kHz) magnetohydrodynamic (MHD) modes has been observed in some high \ensuremath{\beta} ( $\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}$ plasma pressure/magnetic pressure) DT plasmas in TFTR. These modes are localized around the peak plasma pressure gradient and have ballooning characteristics. Particle simulation shows that the loss is due to wave-particle resonances. Linear instability analysis indicates that the plasma is unstable to the kinetic MHD ballooning modes driven by strong local pressure gradients.