The SST-1tokamak belongs to a new generation of tokamaks with the major objective being steady state operation of an advanced configuration plasma.
Traditionally the tokamaks have operated with a `transformer' action -- with plasma acting as a secondary, thus having the vital `self-generated' magnetic field on top of the `externally-generated' (toroidal and equilibrium) fields. This is a pretty good scheme in which creation, current-drive and heating are neatly integrated and remained a choice of the fusion community for many years untill the stage came to heat the plasma to multi-keV temperatures. Heating was then accomplished separately by Radio Frequency (RF) waves and/or energetic Neutral Beam Injection (NBI).
Subsequently, excellent control got established on tokamak plasma performance by controlling the plasma-wall interaction processes at the plasma boundary so the plasma duration was limited primarily by the `transformer pulse length'. However, for relevance to future power reactors it is essential to operate these devices in a steady state mode. The very idea of steady state operation presents a series of physics and technology challenges! For example, the excellent plasma performance which was accomplished earlier, was with the surrounding material wall acting as a good `pump' of particles, a fact which may not be true in steady state.
So one has to try and accomplish an equally good performance in presence of a possibly `saturated' wall. Secondly, a host of engineering and technical considerations spring up. The magnets must be superconducting type, otherwise the power dissipation in conventional (resistive) types can reach uneconomical levels. They have to be specially designed to remain superconducting inspite of their proximity to the other `warm' objects (like vacuum vessel etc.). The heat and particle exhaust must be handled in steady state with specialized tiles and active cooling. The advanced, so-called double null divertor plasma configuration has to be maintained through efficient feedback control avoiding plasma disruptions over long discharge durations.
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