Plasma Welll Interaction Physics in Ignitor

The introduction of a proper divertor in meaningful fusion burn experiments is at times advocated with the argument that it addresses the rcactor relevant issue of ash and impurity control and it allows easier access to the H-mode regime. On the other hand, a divettor decreases the volume available for the plasnna and introduces structutes that have to withstand high thermal wall loadings and the effects of disruptions in a high magnetic field environment. Other related questions are whether the density profiles that characterize the H-regime, for which a divertor is introduced, are optimal for ignition, whether the divertor has indeed led to cleaner core plasmas than those produced in limiter devices , and whether other means to remove the alfa-particles produced by fusion reactions, e.g. during their slowing down, are more appropriate even in principle. In the Ignitor operating scenario of reference, ignition can be reached by ohmic heating only. The edge conditions are characterized by relatively low temperatures and high densities. In high density regimes , an extensive series of experiments has observed a low level of impurity in the plasma core, thanks to both reduced sputtering from the wall and improved screening properties of the adjacent plasma. Radiation losses gain importance in dissipating the power leaving the main plasma and the whole scrape off layer contributes in dispersing the energy of the particles impinging on the material walls, even without the introduction of additional impurities. Therefore, the extended limiter solution, with the plasma wetting a large fraction of the first wall surface, has been preferred over that of a traditional divertor configuration.