Survivability of dust in front of guard limiter of the lower hybrid wave antenna on EAST tokamak

Abstract The fast electrons induced by plasma–lower hybrid wave (LHW) interactions near the guard limiter of the LHW antenna on the EAST tokamak not only enhance the limiter corrosion and dust production, but also alter the dust transport. Based on the shifted orbital motion limited model accounting for a flowing Maxwellian background plasma, this work investigates the tungsten dust transport in the sheath in front of the guard limiter of the LHW antenna, after the sheath structure is obtained using the one-dimensional particle-in-cell code, in which the fast electron component and electron emission from the tungsten material surface are included. It is shown that the fast electron concentration has a substantial impact on the dynamic characteristics of dust in the sheath, since the presence of the fast electrons enhances the heat flux to the dust, and the enhancement is stronger at higher fast electron concentrations. When the fast electron concentration is small, the dust can survive or survive partially in the sheath and then enter the edge plasma region, although it may lose part of its mass while crossing the sheath. Conversely, the dust quickly reaches the boiling temperature, and then melts and disappears in the sheath at high fast electron concentrations. The results indicate that the dust is accelerated to melt by the fast electrons and potentially mitigates the degradation of the plasma performance, compared to when it transits the sheath of Maxwellian plasma. Furthermore, the dust survival probability in the sheath of plasma containing fast electrons is also determined by the dust size and injection velocity. Large-radius dust with a high injection velocity is more likely to survive and cross the sheath, while dust with a small injection velocity may redeposit easily on the material surface due to the stronger electric force when the fast electron component is presented.