ABSTRACT
There is always competition between different transport mechanisms in plasma. To simulate tokamak scrape-off-layer (SOL) like situation 110experimentally, a tabletop experiment (CPS) is set up in the plasma research laboratory of Ravenshaw University, Cuttack. It is worth noting that matter and energy can be transported effectively across magnetic field lines in a tokamak SOL region and cause damage to the walls. This convective transport is a major issue needs to be addressed. In our system convective transport of plasma in form of blob from bulk plasma produced from a gas injected washer plasma gun, is simulated by adjusting the base pressure of the system (CPS). It is well known that mean free path of charged particles decrease with increase in base pressure. After coming out from plasma gun the plasma is shaped into a structure having finite diameter. It is observed from probe as well as fast imaging data that when the classical ion-neutral and neutral-neutral mean free path is smaller than that of diameter of plasma plume convective transport of plasma in form of blob, is observed. It is well known that classical ionneutral and neutral-neutral mean free path are basically neutral density (base pressure) dependent, when temperature of plasma does not change appreciably. It is because at low base pressure where mean free path of charged species/neutrals are higher than plasma dimension, there is no source of energy formation/transfer, whereas at higher base pressure where mean free path of charged species/neutrals are smaller than that of plasma dimension collisionality in plasma increases and charge particles and fast neutrals in plasma produces fresh ions/excited species in the plasma plume that sustains plasma even after the energy source (plasma gun) is switched off. This increased lifetime of plasma (more than pulse width of pulse forming network (PFN)) provided space for convective transport in form of blobs, similar to that of SOL region detachment phenomenon in tokamaks.
