Towards a bayesian equilibrium reconstruction using JET’s microwave diagnostics

For the JET tokamak, standard equilibrium reconstructions find solutions of the Grad-Shafranov equa tion (GSE) given diverse constraints on plasma pressure and/or magnetic field [1]. The most basic recon struction neglects plasma pressure entirely and constraints the magnetic field via measurements of pick up coils surrounding the plasma. A more advanced reconstruction exploits polarimetry and motional stark-effect diagnostics which provide information about the magnetic field inside the plasma. These conventional approaches provide different results, estimating to some extent the systematic uncertainties of the reconstruction. An alternative approach uses Bayes’ theorem to estimate the flux surface geometry via current tomography without solving the GSE [2]. The results obtained are consistent with the underlying physics model and with uncertain data measured by magnetic and motional-stark-effect diagnostics. In preparation for a Bayesian approach involving the GSE, the work presented tests probabilistically re sults of the standard reconstruction of the axisymmetric equilibrium of an Ohmic JET plasma, relying on data measured with two broadband ECE diagnostics and an extra-ordinary (X-) mode reflectometer [3].