Abstract
ABSTRACTBootstrap current in stellarators is usually very small since they operate solely with the magnetic confinement provided by the external currents. Since plasma pressure gradients are always present, the bootstrap current is always finite, but the magnetic design can be optimized to minimize it. In the heliac configuration, there is no optimization and therefore it is important to estimate the actual bootstrap current generated by given pressure profiles. Here, we use the configuration of the TJ-II heliac to calculate the bootstrap current for various density regimes using the kinetic code DKES. We compute the mono-energetic transport coefficients and to find first the thermal ambipolar diffusion coefficients and the corresponding radial electric field and then the respective bootstrap current. This is made taking experimental density and electron and ion temperature profiles. In spite of the convergence problems of DKES at low collisionality, we can obtain bootstrap current values with acceptable uncertainties, without using Monte Carlo methods. The resulting rotational transform is used to obtain the rational surfaces' location and predict the transport barriers observed in the experiments.
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