Development of a reduced model for energetic particle transport by sawteeth in tokamaks*

Sawteeth are known for inducing transport and loss of energetic particles (EP), and for generating seed magnetic islands that can trigger tearing modes. Both effects degrade the plasma performance. Several theories and numerical models have been previously developed to quantify EP transport by sawteeth, with various degrees of sophistication to differentiate the response of EPs at different energies and on different orbits. The analysis is frequently limited to a single time slice. This work describes the development and initial benchmark of a framework that enables a reduced model for EP transport by sawteeth retaining the full EP phase-space information. Mode properties used in the model are consistent with the ideal MHD m/n=1/1 structure from NOVA. The model, implemented in the ORBIT particle-following code, can be used either as a stand-alone post-processor taking input data from TRANSP, or as a pre-processor to compute transport coefficients that can be fed back to TRANSP for time-dependent simulations. The advantage of the latter approach is that it enables an accurate modeling of sources, sinks and overall transport properties of EP and thermal plasma species for comprehensive studies that require detailed information of the fast ion distribution evolution over time.