Speaker
Description
See the full abstract here http://ocs.ciemat.es/EPS2019ABS/pdf/I5.102.pdf
Lausanne, Switzerland An extensive study of quasi-axisymmetric equilibria has been conducted, from which a highly promising magnetic field design has been found by exploiting ROSE (Rose Optimizes Stellarator Equilibria) [1] - an optimization code for 3D magnetic plasma equilibria. The results of this design study and the characteristics of the new configuration [2] are presented. Quasi-axisymmetric fields have small neoclassical particle losses thanks to a magnetic field strength which is independent of the toroidal Boozer coordinate. This toroidal symmetry causes quasi-axisymmetric stellarators to share many neoclassical properties with tokamaks such as a substantial bootstrap current, which produces positive rotational transform and thus helps to confine the plasma. In addition to the advantage of steady-state operation, there is experimental evidence that sufficient vacuum rotational transform can prevent certain types of disruptions - a major challenge for tokamaks.
The ROSE code optimizes the plasma boundary calculated with VMEC based on a set of physical and engineering criteria. Various aspect ratios, number of field periods and rotational-transform profiles have been investigated. As an evaluation of the design, the bootstrap current [3], ideal MHD stability [4], fast-particle losses [5], and the existence of islands [6] are examined. To the best of our knowledge, we have obtained better fast-particle loss-fraction rates than any previous quasi-axisymmetric configuration.
This study could form the basis of the design of a compact, MHD-stable, two-field-period stellarator with particularly good fast-particle confinement. As an extension to the optimization, which mainly concerned plasma physical properties, a new approach will also be presented that includes coil properties in the optimization procedure, which is one of the most demanding issues in stellarator design.
[1] M. Drevlak, et al., Nucl. Fusion, 59 (2018) 016010
[2] S. Henneberg, et al., Nucl. Fusion, 59 (2019) 026014
[3] Y. Turkin, et al., Phys. Plasmas 18 (2011) 022505
[4] C. Schwab, Phys. Fluids 5 (1993) 3195
[5] M. Drevlak, et al., Nucl. Fusion 54 (2014) 073002
[6] J. Loizu, et al., Phys.Plasmas 23 (2016) 112505
