Maximum entropy reconstruction of poloidal magnetic field and radial electric field profiles in tokamaks*

The Laser-driven Ion beam trace probe (LITP) [1, 2] is a new diagnostic method for measuring poloidal magnetic field (B$_{\mathrm{p}})$ and radial electric field (E$_{\mathrm{r}})$ in tokamaks. LITP injects a laser-driven ion beam into the tokamak, and B$_{\mathrm{p}}$ and E$_{\mathrm{r}}$ profiles can be reconstructed using tomography methods. A reconstruction code has been developed to validate the LITP theory, and both 2D reconstruction of B$_{\mathrm{p}}$ and simultaneous reconstruction of B$_{\mathrm{p}}$ and E$_{\mathrm{r}}$ have been attained [2]. To reconstruct from experimental data with noise, Maximum Entropy and Gaussian-Bayesian tomography methods were applied and improved according to the characteristics of the LITP problem. With these improved methods, a reconstruction error level below 15{\%} has been attained with a data noise level of 10{\%}. These methods will be further tested and applied in the following LITP experiments. [1] X. Y. Yang et al. Rev. Sci. Instrum. 85(11), 11E429 (2014). [2] X. Y. Yang et al. Rev. Sci. Instrum. 87(11), 11D610 (2016).