Investigation of the Inverse Plasma Sheath via BIT1 PIC modelling

In a classical plasma sheath, the potential decreases from the upstream towards the wall. The absolute value of the potential drop depends on a number of parameters, such as the electron temperature and the flux of electrons emitted from the surface. The question then is whether the wall potential can ever exceed the plasma potential -- whether there is a realistic access to the so-called inverse sheath in tokamaks. We start our investigation from the work of Campanell and Umansky, reproduce their regime, and determine whether it is applicable to fusion-relevant conditions. Afterwards, we explore the theoretical conditions for accessing the inverse sheath.