ENERGETIC PARTICLE TRANSPORT AND ALPHA-DRIVEN INSTABILITIES IN ADVANCED CONFINEMENT D-T PLASMAS ON TFTR

摘要

This paper reviews the physics of fusion alpha particles and energetic neutral beam ionsrnstudied in the final phase of TFTR operation, with an emphasis on observations in Reversed magneticrnShear (RS) and Enhanced Reversed Shear (ERS) D-T plasmas. Energy-resolved measurements of thernradial profiles of confined, trapped alphas in RS plasmas exhibit reduced core alpha density withrnincreasing alpha energy, in contrast to plasmas with normal monotonic shear. The measured profiles arernconsistent with predictions of increased alpha loss due to stochastic ripple diffusion and increased firstorbitrnloss in RS plasmas. In experiments in which a short tritium beam pulse is injected into a deuteriumrnRS plasma, the measured D-T neutron emission is lower than standard predictions assuming first orbitrnloss and stochastic ripple diffusion of the beam ions. A microwave reflectometer measured the spatialrnlocalization of low-toroidal mode number (n), alpha-driven Toroidal Alfvén Eigenmodes (TAEs) in D-TrnRS discharges. Although the observed ballooning character of the n=4 mode is consistent with predictionsrnof a kinetic-MHD stability code, the observed anti-ballooning nature of the n=2 mode is not. Furthermore,rnthe modeling does not show the observed strong dependence of mode frequency on n. These alpha-drivenrnTAEs do not cause measurable alpha loss in TFTR. Other Alfvén frequency modes with n=2-4 seen inrnboth D-T and D-D ERS and RS discharges are localized to the weak magnetic shear region near qmin. Inrn10-20% of D-T discharges, normal low-n MHD activity causes alpha loss at levels above the first orbitrnloss rate.