In operation since 1983, JET was explicitly designed to study plasma behaviour in conditions and dimensions approaching those required in a fusion reactor. Today, its primary task is to prepare for the construction and operation of ITER, acting as a test bed for ITER technologies and plasma operating scenarios.
In the past years, JET has been upgraded to become more ITER-like in order to conduct dedicated studies for ITER. One main upgrade was to equip the vessel with an inner wall made of the same materials planned for ITER – beryllium and tungsten. Together with upgraded heating power, this ITER-like wall enables scientists to develop plasma scenarios that resemble as closely as possible those planned for ITER. Already JET experiments have helped ITER make the decision to begin operation with a full tungsten divertor, thus substantially reducing investment costs.
In certain modes of operation fusion plasmas can develop potentially harmful instabilities. Examples are disruptions, powerful events during which the plasma very rapidly loses all its energy, or Edge Localised Modes (ELMs), which are short plasma outbursts which thrust large heat and particle loads onto the vessel wall. In powerful devices like ITER such events are a potential risk for the vessel wall and must be mitigated. JET develops various methods to predict and mitigate these plasma instabilities in ITER-like regimes of plasma operation.
Deuterium-tritium (D-T) plasmas produce more fusion power and will therefore be the fuel for fusion power plants. ITER will carry out its ultimate experiments with D-T plasmas. Usually fusion laboratories operate with D-D plasmas. JET is the only device operating that has been licensed for tritium. After a successful experimental campaign in 2015-2016 JET is currently preparing for the deuterium-tritium (DT) experiments in 2021.