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.
Highlights
Recent experiments with the tilted DIII-D neutral beam injection (NBI), which significantly vary 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 [1]
To validate the AE critical EP density gradient profiles determined from the GYRO linear growth rates, the critical profiles are inserted in the ALPHA EP density transport code reviewed in the appendix
Our overall conclusion is that the AE critical EP density gradient stiff EP transport model determined by the recipe γAE > γITG/TEM presented in section 3, is in good agreement with the NBI fast ion pressure profile inferred from MSE constrained equilibrium EFIT reconstructions for the on-axis NBI deposition DIII-D discharge 146102 [figure 6(a)]
Summary
Recent experiments with the tilted DIII-D (off-axis) neutral beam injection (NBI), which significantly vary 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 [1]. This paper attempts to quantitatively validate the proposed AE critical gradient stiff transport model against data from the on-axis NBI DIII-D shot 146102 using the ALPHA EP density transport code [5] This discharge was part of the on-axis to off-axis beam deposition scan carried out in [1] in which the resulting fast ion profiles were found to be relatively insensitive to the beam deposition profile. The ALPHA code combines the low-n stiff EP critical density gradient AE transport (normally most unstable at the mid-core radii) with the Angioni et al [7, 8] energy independent high-n ITG/TEM density transport model which controls the central core EP density profile. For convenience of the reader, the appendix summarizes (and corrects) the formulation of the ALPHA code first given in [5] and the Angioni model [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
