Orbit tomography in constants-of-motion phase-space

作者：M. Rud, D. Moseev, F. Jaulmes, K. Bogár, Yiqiu Dong, Per Christian Hansen, J. Eriksson, H. Järleblad, M. Nocente, G. Prechel, Bernard Reman, Bo Simmendefeldt Schmidt, A. Snicker, L. Stagner, A. Valentini, M. Salewski · 发表于：Nuclear Fusion · 年份：2024 · DOI：10.1088/1741-4326/ad4bf4 · 被引用次数：14 · 研究领域：Atomic and Subatomic Physics Research、Laser-Plasma Interactions and Diagnostics、Magnetic confinement fusion research

Abstract Tomographic reconstructions of a 3D fast-ion constants-of-motion phase-space distribution function are computed by inverting synthetic signals based on projected velocities of the fast ions along the diagnostic lines of sight. A spectrum of projected velocities is a key element of the spectrum formation in fast-ion D-alpha spectroscopy, collective Thomson scattering, and gamma-ray and neutron emission spectroscopy, and it can hence serve as a proxy for any of these. The fast-ion distribution functions are parameterised by three constants of motion, the kinetic energy, the magnetic moment and the toroidal canonical angular momentum. The reconstructions are computed using both zeroth-order and first-order Tikhonov regularisation expressed in terms of Bayesian inference to allow uncertainty quantification. In addition to this, a discontinuity appears to be present in the solution across the trapped-passing boundary surface in the three-dimensional phase space due to a singularity in the Jacobian of the transformation from position and velocity space to phase space. A method to allow for this apparent discontinuity while simultaneously penalising large gradients in the solution is demonstrated. Finally, we use our new methods to optimise the diagnostic performance of a set of six fans of sightlines by finding where the detectors contribute most complementary diagnostic information for the future COMPASS-Upgrade tokamak.