It is increasingly clear that real-time control is expected to play a crucial role in experiments based on magnetically confined plasma. From the early years of fusion research where the experimental scenario was ‘hard-wired’ and used elementary electronic control over a few key parameters, research has moved towards a completely different setup. The very fast response of today’s computing and control systems gives the opportunity of extensive real-time control and data analyses. Real-time tools can not only precisely tailor key plasma parameters and keep them under control, but can also run several consecutive experiments within a single plasma discharge. This latter feature is very significant now that JET’s plasma discharges may last tens of seconds – and will be in future superconducting facilities where plasmas could potentially extend over tens of minutes.

JET represents today the most spectacular experiment in terms of real-time control of a plasma. On JET, scientists leading the experimental sessions, are able to control a number of parameters in the same time, and space resolution, providing flexibility in experimental output between each plasma discharge.

Real-time measurements of neutrons, magnetic flux, plasma temperature, density, helicity, electromagnetic radiation (X-ray, UV, visible and IR) provide inputs for real-time analysis of magnetic fields, confinement, spectral lines, chemical composition, and profiles of temperature, density and current. There are over 500 signals involved, updating every few milliseconds and travelling over a high speed digital computer network (ATM), similar to those used by telephone companies in their backbone exchanges, designed to deliver sets of signals (datagrams) from different sources to the appropriate destinations.

Magnetic coils, gas valves, Neutral Beam Injectors (NBI), pellet injectors, Ion Cyclotron Resonance Heating (ICRH) and Lower Hybrid Current Drive (LHCD) systems can all act as actuators in JET. Two examples can give an idea of how challenging the task is: the control of the heat power load and the extreme plasma shape control.

The control of the power applies in particular to the X-point configuration. Here the particles escaping from the plasma and, following the field lines outside the separatrix, collide with the walls in two points called “strike points”. This highly concentrated energy flow, delivering most of the energy output from the plasma, needs to be directed onto the divertor, where the thermalmechanical design and properties of the material can sustain the high thermal load (see fig. 1). Nevertheless, a prolonged and focused heat load could damage even the divertor and, to prevent such damage, the only possible solution is spreading the heat by sweeping the strike points over a wider area of the divertor. That means that it is the real-time control of the magnetic configuration which guarantees the integrity of the machine.

A further example is the implementation of the so-called Extreme Shape Control (XSC). In order to obtain reference scenarios with high quality H-mode plasmas at a plasma density close to the Greenwald density (for example through high triangularity and elongation) the control system at JET has been recently modified to maintain the plasma shape in the presence of large disturbances (e.g. giant edge localised mode [ELMs] and large variations of bp and/or li). The system has been successfully installed and commissioned during the last experimental campaign and proven during a set of high triangularity ITB discharges with bp up to 1.5 (fig. 2) and/or bli up to 0.5.

In conclusion, as one of the recent tools developed in JET, the real-time equilibrium, together with real-time electron and ion temperature and current profiles measurements, has dramatically enhanced the experimental work on the integration of advanced tokamak scenarios and, in particular, the development of techniques to control in real-time the q and pressure profiles simulta-neously in real-time.

All these examples show the increasing role of real-time control at JET and demonstrate that this is an asset with an important role in exploring and preparing new scenarios for the first phase of the ITER operations.


An instability that often occurs in short periodic bursts during the H-mode in divertor tokamaks. It causes transient heat and particle loss into the divertor which can be damaging. Small ELMs are useful for impurity/ density control.