Calibration of the fir polarimeter on TFTR tokamak

The results of the first Faraday rotation measurement on the TFTR tokamak are presented. Data are reported on ohmic-as well as neutral-beam-heated plasmas including solid pellet injections. The procedure and the results of the calibration, are described. The effects of various errors in the measurements as well as the problem of cross coupling laser beams are studied.     

Observation of anomalous momentum transport in tokamak plasmas with no momentum input

Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas through analysis of the time evolution of core impurity toroidal rotation velocity profiles. Following the L-mode to EDA (enhanced D(alpha)) H-mode transition, the ensuing cocurrent toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core. The steady state toroidal rotation velocity profiles are relatively flat and the momentum transport can be simulated with a simple diffusion model. Velocity profiles during edge localized mode free (ELM-free) H-modes are centrally peaked, which suggests the addition of inward momentum convection. In all operating regimes the observed momentum diffusivities are much larger than the neoclassical values.     

Observation of photonuclear processes in the TFR tokamak

The existence of photonuclear processes in T.F.R. is established by two experiments. Firstly a gamma spectrometry of the activated molybdenum limiter is made. Secondly the neutron flux measurements are compared with the theoretical $\text{NZ}\text{A}$ dependence of the photonuclear processes.     

Turbulent transport in tokamak plasmas with rotational shear

Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, indicating an optimal E×B shear value for plasma confinement. Local maxima in the momentum fluxes are observed, implying the possibility of bifurcations in the E×B shear. The critical temperature gradient for the onset of turbulence increases with flow shear at low flow shears; at higher flow shears, the dependence of heat flux on temperature gradient becomes less stiff. The turbulent Prandtl number is found to be largely independent of temperature and flow gradients, with a value close to unity.