Abstract

In recent discharges on DIII-D, neutron measurements indicated absorption of the fast wave by energetic deuterium beam ions when the fourth harmonic resonance is on axis, but little or no interaction for the fifth harmonic. In this work, a geometric optics code is used to quantify the beam ion absorption of fast waves as the frequency (or on-axis harmonic resonance) is varied. Isotropic and anisotropic Maxwellians are used to model the beam ion distribution. Wave power flow in this harmonic range has been found to exhibit a strong poloidal and toroidal behavior in its initial transits across the plasma. Absorption along the rays is calculated using the fully thermal and magnetized treatment. Competing with the beam ions for absorption are the minority hydrogen and background electrons. The modeling results are only in partial agreement with experimental observations, indicating that more detailed physics may need to be included.

Highlights

  • Fast magnetosonic waves have been studied extensively on DIII-D for electron heating, current drive and profile control

  • In neutral beam heated discharges, it was observed that application of fast wave power could result in the delay of sawteeth onset and, in some cases, enhanced neutron flux from D-D reactions, indicating wave interaction with energetic beam ions

  • For the 5th harmonic case (B), no similar activities have been observed. It is the purpose of this paper to evaluate the strength of beam-wave interactions in these discharges using a model that can be incorporated into the ONETWO predictive and time-dependent transport code

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Summary

Introduction

Fast magnetosonic waves have been studied extensively on DIII-D for electron heating, current drive and profile control. In neutral beam heated discharges, it was observed that application of fast wave power could result in the delay of sawteeth onset and, in some cases, enhanced neutron flux from D-D reactions, indicating wave interaction with energetic beam ions. The CURRAY ray tracing code [2] is used to analyze fast wave propagation and absorption in the plasma.

Results
Conclusion

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