Quantitative Modeling of Fast Ion Transport by NTMs in Integrated TRANSP Simulations

A new analysis tool for determining the experimental island width (W) [1] was integrated with the TRANSP-”Kick” reduced transport model [2] to study Neoclassical Tearing Mode (NTM) driven fast ion (FI) transport with no free parameters for the first time. Initial tests are encouraging with the model quantitatively predicting measured neutron rates over a broad range of DIII-D plasmas. The model retains all TRANSP functionality and self-consistently predicts the NTM impact on beam torque, current drive and heating. These effects depend on the location and width of FI phase space resonances which is not accounted for by the ad-hoc anomalous beam diffusivity model of TRANSP. FI transport was found to be significant when resonances overlap, resulting in a transport threshold at W~5cm. This model also shows that 3/2 (2/1) NTMs broaden (peak) the beam driven core current profile, which may contribute to flux pumping in hybrid plasmas.

[1] L. Bardóczi et al, PoP 23, 052507 (2016)

[2] M. Podestà, PPCF 56, 055003 (2014)