ACADEMIA

Engineer Goretti Sevillano proposes control methods for this source currently being developed

This is not nuclear fission that is currently in use, but nuclear fusion, which many regard as the main energy source of the future. Among others, the ITER project (the third most expensive in history) is seeking to turn this venture into reality and is making use of the Tokamak reactor for this purpose. Reactors of this type and the plasma used in them to carry out fusion have a number of control problems, and to solve them the electronics engineer Goretti Sevillano has come up with some tools in her thesis defended at the University of the Basque Country (UPV/EHU). Her thesis is entitled Herramientas para el control del plasma en reactores Tokamak de fusión nuclear: integración Astra-Matlab y control en tiempo real (Tools for plasma control in Tokamak nuclear fusion reactors: Astra-Matlab integration and control in real time), and she has also had two papers published on the subject in the journals Informatica and Energy.

What happens in fission is that the nucleus of an atom is split; this is in stark contrast to fusion in which two lightweight atoms join together. Sevillano explains that the latter could generate more energy than fission, on which nuclear power stations are currently based. But that is not all. "In fission reactions there is a risk of explosion, but not in fusion, so nothing like what took place in Chernobyl or Fukushima would ever happen. What is more, the waste generated in fission has a very long life and is radioactive; but this is not the case in fusion. Likewise, the fuels are more accessible. Uranium or plutonium is used in fission, and its access is not so widespread; but in fusion, helium or tritium, which can be obtained from water or earth, are used," she explains. So her PhD thesis is another step along the path to fusion.

ASTRA-Matlab

Among all the reactors it is the Tokamaks studied by this researcher which are best placed in the race to obtain efficient energy from nuclear fusion. Sevillano has detailed how they function: "The materials used in fusion must have certain specific features, and these materials have to be turned into plasma. At the same time, the plasma has to be restricted to a limited space to enable the reaction to be generated and the energy to be used. To achieve this, magnetic confinement is applied in the case of the Tokamaks." In other words, the magnetic field creates lines that act as a wall to keep the plasma in the space where it is meant to remain. But the plasma and the device itself have several problems that have yet to be solved, and Sevillano has worked on some of them.

"To develop Tokamaks, many of the plasma's parameters must be controlled, as well as the whole device itself; the currents that are going to be used, the voltage, the intensity, etc. Until all these things are controlled, it will not be possible to use these machines to produce marketable energy," the researcher points out. In connection with this, Sevillano has embedded a code known as ASTRA into the Matlab software; ASTRA is frequently used to simulate the behaviour of Tokamak reactors, and the embedding of this code into Matlab will facilitate the development of controllers suited to these devices. The control problems are of several kinds, but in this case some very specific parameters relating to the plasma have been explored in depth. "Control of the parameters is necessary to obtain the maximum energy possible from the plasma, and the amount of this energy that can be extracted is calculated on the basis of the current: the greatest amount of current possible has to be maintained during the longest time possible. That is why these parameters have to be controlled by means of the control, in turn, of the numerous coils and voltages within the structure," she adds.

Sevillano points out that this PhD thesis has produced only a single branch of what would be a complete tree. "All I have achieved is no more than a step towards doing more things. The aim of all these tasks is to design a machine capable of generating marketable energy within the ITER project," she explains. It is a long-term task: they have been working on nuclear fusion for the last 50 years and they calculate they will obtain some results around the year 2050.