Determination of the mean energy of fast electron losses in LHCD scenarios at WEST*

Fast electrons are produced at WEST during lower hybrid current drive discharges. Characterizing the loss of fast electrons is important to quantify the current drive efficiency and estimating the power deposited on the plasma-facing components. In this contribution a new method to obtain the mean energy of fast electron losses is presented. The method is based on measuring the thick-target emission of tungsten in the divertor region produced by fast electron losses interacting with the target. The measurements are carried out by a versatile multi-energy hard x-ray detector. The tungsten spectra are modeled by a Monte Carlo code which simulates the interaction between an electron beam and a solid target. The mean energy of the fast electron losses is determined through the comparison between the experimental and synthetic emission. The results show that fast electron losses at WEST have an average energy of 130 keV and represent only a small fraction of the total heat flux at the target.