Predictions of the Transport-limited Fusion Alpha Profile in ITER

We present a simple 1D transport model prediction for the alpha density profile in an ITER burning plasma. Thermal species profiles, which provide the basis for the alpha birth and collisional slowing-down rates, come from a recent ITER H-mode prediction using the EPED model for the pedestal and a quasilinear microturbulent model in the core [1]. The model includes the fusion source, an effective sink into a population of helium ash, and diffusive transport due to both microturbulence and alpha-driven Alfv\'en eigenmodes (AEs). Where applicable, we assume the local distribution maintains the classical slowing-down form. The microturbulent (passive) contribution to alpha transport is given by combining the known absolute energy flux appropriate for a $Q=10$ scenario with the GYRO simulation-fitted model for the quasilinear transport ratio given in Ref.~[2]. A ``stiff" transport model gives the alpha-driven AE component. In this model, {\it local} AEs drive the alpha gradient to the {\it local} mode stability threshold determined by fully realistic GYRO simulations. Both the stiffness [3] and locality [4] of AE transport are supported by previous work. We compare the impact on the AE stability threshold of using Maxwellian versus slowing-down forms for the alpha distribution. In general, the AEs are found to re-distribute fusion alphas within the plasma core, but the Alfv\'en avalanche does not appear to propagate to the loss boundary. Microturbulence can drive modest alpha losses at the edge.\par \vskip3pt \noindent [1] J.E.\ Kinsey et al., Nucl.\ Fusion {\bf 51}, 083001 (2011)\par \noindent [2] C.~Angioni et al., Nucl.\ Fusion {\bf 49}, 055013 (2009)\par \noindent [3] E.M.\ Bass and R.E.\ Waltz, Phys.\ Plasmas {\bf 17}, 112319 (2010)\par \noindent [4] E.M.\ Bass and R.E.\ Waltz, Phys.\ Plasmas {\bf 20}, 012508 (2013)