Comparing Particle Transport Modulation Study Methodology

Performance in fusion reactors can be dependent on a density pedestal. Pedestal shape is set by particle transport and fueling by neutral particles. The relative contributions of transport and fueling can now be disentangled by using novel edge particle source diagnostics. We expand on recently published results by further highlighting the improvements provided by forward modeling informed by edge particle source measurements over the previously typical analytical method. The analytical method involves fitting density perturbations with sinusoidal functions to develop closed form expressions for the transport coefficients from the fitted amplitude and phase but is found to be dependent on perturbations with large relative amplitude, low noise, and an approximately sinusoidal response, even when including particle source modulations. In the new method, particle transport coefficients are obtained in the pedestal region of DIII-D by utilizing edge source measurements in a time-dependent forward modeling framework with Bayesian inference to optimize the transport profiles which reproduce density profile measurements. This method allows for separation of diffusion and convection terms by exploring density profile dynamics such as gas puff modulation and is not strictly reliant on an approximately sinusoidal perturbation. Improvements in methodology are demonstrated by considering idealized synthetic data, then working up through progressively more complex scenarios.