Theory developments

In the last recent years, we have obtained analytical results on stellarator neoclassical theory that are the basis for the goals of this task and for some of the numerical goals of task (2). In [Calvo-17], we derived orbit averaged low collisionality neoclassical equations that rigorously retain the component of the magnetic drift tangent to …

Development and benchmarking of KNOSOS code for multi-species plasmas of arbitrary geometry

Following the recent theoretical results discussed in the theory section, we have developed the numerical code KNOSOS (KiNetic Orbit-averaging SOlver for Stellarators) [Velasco-18, Calvo-18]. KNOSOS is the first radially-local code to rigorously retain the tangential magnetic drift in the calculation of ion neoclassical transport. In [Velasco-18] we proved that this is crucial in order to …

Optimization of neoclassical transport

The viability of the stellarator programme as an alternative to tokamaks in the path towards the fusion reactor relies on our capability to design magnetic configurations whose neoclassical radial energy transport is as low as that of tokamaks. Stellarator configurations are typically designed including the minimization of the effective ripple [Nemov-99] as an optimization criterion. …

Influence of global effects and neoclassical physics on stellarator turbulence and zonal flow dynamics

Under this task, we would like to understand what is the correct computational approach (perhaps depending on plasma parameters) to study stellarator plasma turbulence and zonal flow dynamics in multispecies plasmas. Influence of global effects on zonal flow dynamics The flows produced by the component of the turbulent fluctuating electric potential that is constant on …

Turbulent transport of impurities

Impurity accumulation is considered to be a crucial issue in the path towards a fusion-grade stellarator reactor. The reason is that stellarator operation scenarios usually display a negative radial electric field that, according to standard neoclassical theory, should cause an inwards impurity pinch roughly proportional to the charge number Z. This impurity accumulation is observed …