Data assimilation system based on integrated transport simulation of Large Helical Device plasma

Abstract

A data assimilation technique is applied to the integrated transport simulation (TASK3D) of a plasma in Large Helical Device (LHD). We use the ensemble Kalman filter (EnKF) as a data assimilation method for the estimation of state variables composed of the electron and ion temperature, density, numerical coefficients of turbulence models, and NBI heat deposition. The time series data of experimentally measured temperature and density profiles are assimilated into TASK3D. The obtained electron and ion temperature profiles and temporal variations by the data assimilation system agree well with measured ones owing to the optimization of the employed turbulent transport model and the heat deposition. These results indicate the effectiveness and validity of the data assimilation approach for accurate prediction of the behavior of fusion plasmas and the possibility of advanced turbulence modeling.

Progress of statistical modelling of thermal transport of fusion plasmas

“…It is also noted here that this statistical approach can provide reasonable initial guess of transport models for conducting data assimilation [16] in which the transport models are updated and optimized to align the simulation results to experimentally measured values (such as temperatures).…”

Application of the Ensemble Kalman Smoother to Turbulent Transport Analysis in LHD Plasma

“…The smoothing calculation by EnKS can be easily performed by storing a matrix that reconstructs the ensemble members at the filtering step. To derive the matrix representation of the filtering calculation, we introduce the following matrices, X t| * = x (1) t| * , x (2) t| * ,…”

“…This assumption distinguishes the roles of k s and C s , and allows stable estimation of these terms. The standard deviation of observation noise is estimated before every filtering step to be proportional to the difference between the prediction and the observed data, whose rate is 0.8 [1].…”

“…Evaluating the employed simulation models while simultaneously considering more than one uncertainty in the simulation is difficult. To overcome this problem, we are developing a data assimilation system, ASTI [1].…”

“…In Ref. [1], a data assimilation technique, the ensemble Kalman filter (EnKF) [2] was introduced to an integrated transport simulation by TASK3D [3] for a plasma in the Large Helical Device (LHD). The electron and ion temperature profiles and temporal variations obtained by ASTI agreed well with measured values.…”