Time-resolved measurements of nonthermal x-ray emission of Ti xxi lines in electron-cyclotron-heated tokamak plasmas

Observations of the heliumlike titanium spectra with 20-ms temporal resolution during electron cyclotron heating (ECH) of Doublet III tokamak plasma have been made. Several prominent lines in the heliumlike spectra are observed: 1$s^2$ ${}^1$ $S_0$←1s2p ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ (labeled w), 1$s^2$ ${}^1$ $S_0$←1s2p ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$,2 (y,x), and 1$s^2$ ${}^1$ $S_0$←1s2s ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ (z). In addition, the dielectronic satellite lines from the autoionizing lithiumlike ionization states are also observed, e.g., 1$s^2$2p ${}_{}{}^2{}_{}{}^{}°_{3/2}^{}{}_{}{}^{}$←1s2$p^2$ ${}_{}{}^2{}_{}{}^{}D_{5/2}^{}{}_{}{}^{}$ (j), 1$s^2$2s ${}_{}{}^2{}_{}{}^{}S_{1/2}^{}{}_{}{}^{}$←1s2p2s ${}_{}{}^2{}_{}{}^{}°_{3/2}^{}{}_{}{}^{}$ (q), etc. The intensity of the resonance line w (i.e., 1$s^2$ ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$←1s2p ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$) is found to be extremely sensitive to the ECH power. Ion temperatures rise from the Ohmic phase to steady-state ECH phase in 20–40 ms at an electron density of 6×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}3}$. Time-resolved line ratios G=(x+y+z)/w, R=z/(x+y), and j/w are also presented. Detailed analysis of the observed spectra is carried out, based on the relevant atomic and plasma effects, and it is concluded that there exists a significant departure from a Maxwellian distribution of electrons in the present ECH plasmas, which are also dominated by nonequilibrium ionization.