JET is the largest and most powerful tokamak in the world and currently the only machine capable of operating with the deuterium-tritium fuel mix of future commercial reactors. In operation since 1983, JET was explicitly designed to study plasma behaviour in conditions and dimensions approaching those required in a fusion reactor. Thanks to a very sturdy and flexible original design the machine has been able to evolve with the advancements in fusion research and to remain state-of-the-art to this day. 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 core of the machine is the vacuum vessel where the fusion plasma is confined by means of strong magnetic fields and plasma currents (up to 4 tesla and 5 mega amperes). In the current configuration the major and minor radii of the plasma torus are 3 metres and 0.9 metres respectively, and the total plasma volume is 90 cubic metres. A divertor at the bottom of the vacuum vessel allows escaping heat and gas to be exhausted in a controlled way. Since 2011 the first wall of the vacuum vessel has been made of beryllium and tungsten, mirroring the material choices of ITER. Other important features of JET are:
- A flexible and powerful plasma auxiliary heating system, consisting of Neutral Beam Injection (34 megawatts), Ion Cyclotron Resonance Heating (10 megawatts) and Lower Hybrid Current Drive (7 megawatts).
- An extensive diagnostic suite of around 100 individual instruments capturing up to 18 gigabytes of raw data per plasma pulse.
- A high frequency pellet injector for plasma refuelling and for ELM pacing studies.
- A massive gas injection valve for plasma disruption studies.
- Capabilities to operate with tritium fuel – unique among today’s tokamaks
- Beryllium handling facilities, allowing use of beryllium plasma-facing components.
- Remote handling facilities that allow advanced engineering work to be performed inside the vacuum vessel without the need for manned access.