Lawrence Berkeley National Laboratory

Three machine learning techniques (multilayer perceptron, random forest and Gaussian process) provide fast surrogate models for lower hybrid current drive (LHCD) simulations. A single GENRAY/CQL3D simulation without radial diffusion of fast electrons requires several minutes of wall-clock time to complete, which is acceptable for many purposes, but too slow for integrated modelling and real-Time control applications. The machine learning models use a database of more than 16Â 000 GENRAY/CQL3D simulations for training, validation and testing. Latin hypercube sampling methods ensure that the database covers the range of nine input parameters (, and) with sufficient density in all regions of parameter space. The surrogate models reduce the inference time from minutes to ms with high accuracy across the input parameter space.