Abstract
Reversed shear Alfvén eigenmode (RSAE) activity in DIII-D is stabilized by electron cyclotron heating (ECH) applied near the minimum of the magnetic safety factor (qmin) in neutral beam heated discharges with reversed-magnetic shear. The degree of RSAE stabilization, fast ion density and the volume averaged neutron production (Sn) are highly dependent on ECH deposition location relative to qmin. While discharges with ECH stabilization of RSAEs have higher Sn and more peaked fast ion profiles than discharges with significant RSAE activity, neutron production remains strongly reduced (up to 60% relative to TRANSP predictions assuming classical fast ion transport) even when RSAEs are stabilized.
Highlights
Future burning plasma experiments will be subject to the excitation of Alfvenic instabilities by several fast ion sources including both fusion born alpha particles as well as 1 MeV neutral beam ions [1,2]
It has been observed that electron cyclotron heating (ECH) deposition near qmin in a reversed shear discharge stabilizes the Reversed shear Alfven eigenmode (RSAE), while deposition near the magnetic axis or simultaneously on adjacent sides of qmin does not stabilize the modes
Analytic estimates of the local RSAE minimum frequency based on equilibrium profiles indicate that fm is below fTAE, at later times when qmin has evolved and the stabilization persists
Summary
Future burning plasma experiments will be subject to the excitation of Alfvenic instabilities by several fast ion sources including both fusion born alpha particles as well as 1 MeV neutral beam ions [1,2]. The ability of these instabilities to cause fast ion transport is well documented [3] as are both the deleterious effects and potentially positive aspects of this transport [4]. Discharges with reduced AE activity have up to 50% higher fast ion density near the magnetic axis as measured by Doppler shifted D-alpha emission
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