Study of lithium influx, radiation, transport and influence on plasma parameters in the T-10 tokamak

Abstract

An investigation of lithium influx to plasma, radiation, transport, and its influence on plasma parameters is carried out using spectroscopy and transport modeling methods. The lithium source in the discharge of the T-10 tokamak is a moving Li-limiter based on a tungsten capillary-pore system (CPS). A strong dependence is found between the Li influx to plasma on the distance between the Li-limiter and plasma current boundary in the scrape-off layer (SOL) region. It is shown that if the Li-limiter is located on the radius of the chamber wall (r ≈ 40 cm), lithium influx to plasma is at a low level with a value ∼2·1018 s−1 and the Li nuclei concentration in the plasma does not exceed ∼0.5% of electron density ne with the effective charge value Zeff ≈ 1.2. If the Li-limiter is moved to the current radius (aL = 30 cm), lithium influx to plasma reaches ∼3 · 1020 s−1, which leads to a formation of lithium plasma with the density limit of (the Greenwald density limit) with a Zeff value of ≈2.9 and ≈10% of the remaining deuteron density. In this case, the lithium radiation losses power estimated in Li-plasma is extremely low and does not exceed ≈15% of ohmic power. All obtained results are interpreted using transport models. Changing the lithization level of the chamber walls can significantly reduce the level of C, O, and W impurities and greatly affect the Zeff values. The dependencies of energy confinement times in the electron and ion components on the value of the averaged electron density are investigated in regimes with significantly varying Zeff values. The paper presents the computational analysis of the lithium radiation power at the plasma periphery and in the SOL as a function of boundary conditions, transport characteristics, and confinement times of lithium ions.