Target Division

Spallation sources are devices designed to produce neutrons using reactions with the same name. To produce spallation reactions, it is necessary to accelerate a proton through a series of electromagnetic fields in the accelerator until it acquires a high level of kinetic energy. At that moment, it is made to collide with the atom of a heavy material (normally mercury, lead or tungsten) to bring about the nuclear reaction which generates the neutrons.

The place where the proton collision takes place is known as the target and it can be considered to be the center of the neutron source. These targets are highly complex engineering devices where an enormous amount of heat is generated from the interaction of the protons with the material. In some cases, more heat is generated per unit of volume than in the fuel bars of a nuclear reactor, so the challenge posed to engineers is comparable. The target at ESS is one of these cases.

The target is formed of a succession of tungsten blocks located inside a wheel that is 2.5 meters in diameter where the proton beam hits in a radial direction. Inside the wheel is a series of channels with helium circulating around them at high speed to extract the heat generated during spallation. The wheel spins at ~0.5 Hz so that each time the accelerator is triggered it hits a different part of the wheel and distributes the heat around the whole perimeter.

Finally, and following a long process of negotiation, the ESS technical team decided that ESS-Bilbao should be the institution in charge of designing the target. The project has a budget of €8.4 million and covers the design, manufacture and assembly of both the target and its auxiliary movement systems (axis, rotary seal, bearings and engine). As for the timeline, work is to begin immediately and will be finished by the start of 2019 with the delivery of the target to the ESS facilities in Lund (Sweden).

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