Spatio-Temporal Measurements of Elevated Ion Temperatures in a Z- Pinch Fusion Plasma using Ion Doppler Spectroscopy

Recent measurements by Thomson scattering on the FuZE Z-pinch device showed elevated electron temperature coincident with fusion neutron production, with a peak Te = 1–3 keV [1]. A complementary measurement was carried out on FuZE using ion Doppler spectroscopy to characterize the ion temperature. The timing of the spectrometer collection gate was varied with respect to the peak neutron pulse over a series of discharges to reconstruct the temporal evolution of the ion temperature inferred from Doppler broadening of the C V 227 nm impurity line. The data show similar trends as were observed with the electron measurements, with peak Ti = 1–4 keV, but delayed in time with respect to the electron temperature. A detailed analysis of ion-electron energy equilibria and advection of impurities suggest that carbon is heated via a two-stage electron-deuterium-ion channel, after Ti and fusion reactions have begun to decrease. The introduction of cold impurities into the plasma may contribute to this delay, which is investigated with high-speed videography.



[1] B. Levitt, et al., Phys. Rev. Lett. 132, 155101 (2024).