Time-resolved spatial profiles of Zeff in JIPP T-II tokamak plasmas have been determined from the measurement of bremsstrahlung in the visible spectral region. The effective ion charge Zeff increases at the plasma centre and decreases at the plasma periphery in the high-electron-density regime. The emissions from low ionization states of light impurities increase notably in the region of lower electron temperatures in this regime. As a result, impurities accumulate in the plasma centre in the high-density regime. The results obtained with respect to the plasma periphery support the interpretation of the behaviour of the impurities, which is based on VUV spectroscopic studies.
The empirical scaling of the electron thermal diffusivity, Xe, is investigated for more than 100 beam-heated discharges. These discharges include two major features: 1) high-temperature and highdensity plasma (T e (O)«Tj(O)« 2.5-3 keV at n ^ (5-7) X 10 13 cm" 3 , P NB i £ 4 MW), which will be the basis for the breakeven experiments in the next-generation tokamaks, 2) three types of discharges, i.e. good and poor confinement divertor discharges and limiter discharges. -All kinds of discharges (good heating and poor heating divertor discharges, limiter discharges) have fhe same functional form in x e within ~ 40% at 0.25 a < r <0.65 a, where Xe in the simplest expression scales as Xe a Vn e -The * on t n e r m a l diffusivity, Xi, is consistent with the assumption that the neoclassical Xi can be applicable to our three kinds of discharges. For discharges with different heating efficiency, there is no systematic difference, in the adjustable multiplier, to the neoclassical theory by Hinton-Hazeltine for an ion collisionality of v*= 0.02-0.5.
A magnetic analysis to determine the plasma cross-sectional shape and equilibrium parameters in the superconducting tokamak TRIAM-1M is discussed using magnetic data obtained in ohmic discharges. First, it is shown that the eddy currents in the tokamak structures should be taken into account. Two magnetic analysis codes are applied. One is the SHP code in which the plasma current is replaced by several filamental loop currents and the other is the FITEQ code in which the plasma current density is consistent with the MHD equilibrium. The magnetic fields due to eddy currents are expanded into multipole fields. The central safety factor q(0) is fixed at 1.0. The eddy currents reduce the vertical field by 10%. Taking account of them, the accuracy of the magnetic analysis is improved and estimation of the stored thermal energy in a plasma becomes possible. The SHP code has the difficulty that the local plasma surface position can be distorted by the eddy current magnetic field. In addition, it is also noted that the pressure profile analysed by the FITEQ code is consistent with the Thomson scattering measurement and that the energy confinement characteristics are consistent with the neo-Alcator scaling.
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