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}$${S}_{0}$\ensuremath{\leftarrow}1s2p $^{1}P_{1}$ (labeled w), 1${s}^{2}$ ${}^{1}$${S}_{0}$\ensuremath{\leftarrow}1s2p $^{3}P_{1}$,2 (y,x), and 1${s}^{2}$ ${}^{1}$${S}_{0}$\ensuremath{\leftarrow}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 $^{2}\ifmmode^\circ\else\textdegree\fi{}_{3/2}$\ensuremath{\leftarrow}1s2${p}^{2}$ $^{2}D_{5/2}$ (j), 1${s}^{2}$2s $^{2}S_{1/2}$\ensuremath{\leftarrow}1s2p2s $^{2}\ifmmode^\circ\else\textdegree\fi{}_{3/2}$ (q), etc. The intensity of the resonance line w (i.e., 1${s}^{2}$ $^{1}S_{0}$\ensuremath{\leftarrow}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\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. 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.