Loss of energetic beam ions during TAE instabilities

H.H Duong,R.A Moyer,W.W Heidbrink,J.G Watkins,R Lee,T.W Petrie,E.J Strait

doi:10.1088/0029-5515/33/5/i06

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

Highlights

In recent years considerable progress has been made in the development of fusion energy, with tokamak experiments rapidly approaching ignition conditions
Our data firmly establish the adverse effect of toroidicity induced AlfvBn eigenmodes (TAE) modes on fast ion confinement
In the presence of violent TAE activity, losses can be as large as 70% of the injected beam power

Summary

Introduction

In recent years considerable progress has been made in the development of fusion energy, with tokamak experiments rapidly approaching ignition conditions. - devices such as the international thermonuclear experimental reactor (ITER) may use 1 MeV neutral beams for external heating and neutral beam current drive. These energetic beam ions may destabilize TAE modes, thereby possibly reducing heating and current drive efficiency. If the fast ion losses are localized, they could damage the first wall Prior experiments on both DIII-D [I] and TFTR [2] have shown that super-Alfvknic beam ion populations can destabilize TAE modes in a deuterium plasma; it is both prudent and cost effective to study TAE modes in a deuterium machine before the construction of a DT reactor. The fast ion drive term (neglecting finite gyroradius effects) is of the form

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Conclusion