International Fusion Materials Irradiation Facility
The International Fusion Materials Irradiation Facility ( IFMIF ) is a planned since the 1990s research facility which is designed to test materials for their suitability for use in potential fusion reactors. In a fusion reactor meet very many neutrons with very high energy on the wall material. In order to investigate the damage caused by this load and compare with calculations, IFMIF is to produce a high neutron flux corresponding particle with a particle accelerator. It is a joint project of the EU, Japan, Russia and the United States under the auspices of the International Atomic Energy Agency. The project is currently (2014) in the so-called Engineering Validation and Engineering Design Activities ( EVEDA ) phase. About the location of the plant is not yet decided.
Material problem of fusion reactors
Some structural components of the reactor must - in addition to high thermal stress - a high neutron exposure for sufficiently long time ( eg two years ) to withstand. Is it, for example, steel is the displacement damage that accumulates in this life, in the "first wall ", ie the zones adjacent to the fusion plasma Blanket parts, in the order of 50 dpa. A similarly important damage is the evolution of gas (hydrogen and helium) by neutron reactions in the material (see reactor materials ).
So far, these stresses can be experimentally simulated only imperfectly. Neutron irradiation in high flux research reactors use only limited because the energy spectrum of the neutrons is not as high up enough as in a fusion reactor. Experiments with implantation of self- - ions while the target material is shot with high energy on the same material, for example tungsten on tungsten ions - resulting dislocations, but not concomitant gas evolution.
Materials whose strength properties even after enough of that damage, can not be developed without irradiation experiments under realistic conditions. An experimental fusion reactor like ITER does not provide these conditions, for he will not run continuously, but in relatively short experimental phases with intervening pauses. However, the structural material is to be developed for the construction of the prototype DEMO, ie at the end of the life of ITER, already ready.
Concept of IFMIF
Neutron source
To provide with currently existing technology a suitable neutron source IFMIF will use neutrons, which are triggered by fast deuterons in lithium. Two parallel next to each other high-current linear accelerator data per one deuteron beam of 40 MeV and 125 milliamperes; the two beams overlap each other on the target, a 2.5 cm thick layer of flowing, liquid lithium. In this layer, the deuterons are stopped completely. The lithium is pumped in a closed circuit through a radiator to dissipate the heat inevitably suffer great performance. At the high deuteron energy neutrons are released mainly by the ( d, n) stripping reaction. They therefore do not occur isotropically, but preferably to the front of the target from. There the test cell with the Betrahlungsproben.
The measured in a Zyklotronexperiment neutron energy spectrum differs in shape significantly from the fusion reactor spectrum, but is good in terms of material damage thus comparable.
Test cell
The test cell is divided into a high flow area of 500 cm3 close to the target, a larger underlying cash flow and an even greater low-flow zone. In the high- flow zone in ferrous materials, according to calculations from 20 to 55 dpa ( location dependent ) per year irradiation achieved .. you should take miniaturized structural material samples. In the medium and low flow zones, for example Neutronenvervielfacher and nesting materials can be tested (see Blanket ). As months and years long exposures are necessary, the test cell needs a powerful cooling system that can be also quickly switched to heating to in unforeseen failures of the accelerator to keep the temperature of the sample constant.
The structural materials to be tested include the in-progress low activating steels, but for example also CFC ( carbon fiber carbon composite, carbon fiber-reinforced carbon), SiC / SiC ( silicon carbide siliziumkarbidfaserverstärktes ) and tungsten as the material for divertor plates.