Estimation of turbulent transport coefficients by the conditional variance method

A novel approach for estimating turbulent transport coefficients in fusion devices is presented. The diagnostic method is established on the analysis of the conditional variance of one-point time series of density or temperature fluctuations. It is tested on data obtained from probe measurements in the edge of the tokamak ASDEX Upgrade and the stellarator Wendelstein 7-X, and on synthetic data from the gyrofluid transport model GEMR. The approach demonstrates a remarkable degree of accuracy, typically within a factor of two of the actual transport measured by more difficult means. It is a simple and accurate way of evaluating turbulent particle and heat transport coefficients that does not require measurements of the velocity fluctuations.