Development and validation of a critical gradient energetic particle driven Alfven eigenmode transport model for DIII-D tilted neutral beam experiments. (30th October 2015)

• Record Type: Journal Article
• Authors: Waltz, R.E.; Bass, E.M.; Heidbrink, W.W.; VanZeeland, M.A.
• Is Part Of: Nuclear fusion. Volume 55:Number 12(2015:Dec.)
• Publication Date: 2015-10-30
• Subjects: energetic particles -- Alfven eigenmodes -- critical gradient -- transport; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/0029-5515/55/12/123012
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: Recent experiments with the DIII-D tilted neutral beam injection (NBI) varying the beam energetic particle (EP) source profiles have provided strong evidence that unstable Alfven eigenmodes (AE) drive stiff EP transport at a critical EP density gradient [Heidbrink et al 2013 Nucl. Fusion 53 093006]. Here the critical gradient is identified by the local AE growth rate being equal to the local ITG/TEM growth rate at the same low toroidal mode number. The growth rates are taken from the gyrokinetic code GYRO. Simulation show that the slowing down beam-like EP distribution has a slightly lower critical gradient than the Maxwellian. The ALPHA EP density transport code [Waltz and Bass 2014 Nucl. Fusion 54 104006], used to validate the model, combines the low-n stiff EP critical density gradient AE mid-core transport with the Angioni et al (2009 Nucl. Fusion 49 055013) energy independent high-n ITG/TEM density transport model controling the central core EP density profile. For the on-axis NBI heated DIII-D shot 146102, while the net loss to the edge is small, about half the birth fast ions are transported from the central core r / a < 0.5 and the central density is about half the slowing down density. These results are in good agreement with experimental fast ion pressure profiles inferred from MSE constrained EFIT equilibria.