Loss of energetic beam ions during TAE instabilities

Abstract

Toroidicity induced Alfven eigenmodes (TAE) are observed in the DIII-D tokamak when energetic beam ions ( approximately 75 keV) are used to destabilize the mode. Measurements of the neutron emission indicate that up to 70% of the injected power is lost during strong TAE activity. Measurements of the poloidal distribution of fast ion losses suggest that the losses are greatest near the vessel midplane. Fast ion losses in discharges with combined fishbones and TAE bursts are 1.5 to 2 times greater than losses in fishbone discharges without TAB activity. The scaling of fast ion losses with MHD mode amplitude exhibits no threshold in the mode amplitude, suggesting that mode particle pumping is the dominant loss mechanism