In tokamak experiments, equilibrium reconstruction codes are used to calculate the location of the last closed flux surface, to map diagnostic information, and to derive important properties like current density and safety factor. At JET, the equilibrium code EFIT is automatically executed after each discharge. For speed and robustness, intershot EFIT is based on magnetic probe measurements only. As a consequence, the intershot profiles of the safety factor can be wrong for a variety of plasma scenarios. Internal diagnostic information, the pitch angle as measured with the motional stark effect, Faraday rotation angles, as well as pressure profile information can increase the accuracy of the EFIT equilibrium. In this paper, the accuracy of the internal diagnostics at JET and their impact on the EFIT results are discussed in detail. The influence of control parameters like the form of the test functions for and on the equilibrium is investigated. The from this analysis agrees with information from magnetohydrodynamics analysis (e.g., Alfvén cascades and sawtooth analysis) to within 10%–15%.
Accuracy of EFIT equilibrium reconstruction with internal diagnostic information at JETa)
For a full listing of names and affiliations of the JET-EFDA Contributors, see A. T. Macrander, Rev. Sci. Instrum. 79, 10F701 (2008).
See the Appendix of M. L. Watkins et al., Fusion Energy (2006), Proceedings of the 21st International Conference of Chengdu (2006), IAEA (2006).
M. Brix, N. C. Hawkes, A. Boboc, V. Drozdov, S. E. Sharapov, JET-EFDA Contributors; Accuracy of EFIT equilibrium reconstruction with internal diagnostic information at JET. Rev. Sci. Instrum. 1 October 2008; 79 (10): 10F325. https://doi.org/10.1063/1.2964180
Download citation file: