Assessment of the effect of parallel temperature gradients in the JET SOL on T_e measured by divertor target Langmuir probes

Abstract Higher than expected electron temperatures (T_e) are often measured by divertor Langmuir probes (LP) in high recycling and detached regimes in JET and other tokamaks. As a possible mechanism to explain this discrepancy, we investigate the effect of penetration of fast, almost collisionless electrons connecting the hot upstream scrape-off layer (SOL) region to the divertor targets in JET. We simulate the electron velocity distribution function (EVDF) near the divertor targets using a simple 1D kinetic model using parallel SOL profiles from EDGE2D-EIRENE simulations. The resulting EVDF is used to construct synthetic LP current-voltage (IV) characteristics and evaluation of T_e is performed in the same way as for experimental data. Results indicate that the process does not explain the anomalously high T_e values estimated from the target probe measurements if the EDGE2D-EIRENE simulated parallel profiles are a good representation of reality.