The engineering of a fusion reactor will require solution of a number of serious technological problems, as we have seen above. ITER will take decades to build and operate, and it is not designed to solve many of these problems. It is therefore prudent to build smaller machines specially designed for technology development so that this work can proceed in parallel with ITER. Many proposals have been made for a fusion development facility (FDF). A few of these will be described here.

IFMIF: International Fusion Materials Irradiation Facility

A favorite proposal of the European Union, together with Japan, is the IFMIF, a large linear accelerator that has been in the planning stage for 16 years. A diagram of it is shown in Fig. 9.30. As you can see, this is a large installation. The accelerator occupies a building of several hundred meters in length. It is designed to produce neutrons with energies matching those that would enter a tokamak blanket. This is done by accelerating to 40 MeV a beam of deuterons onto a target of liquid lithium. Reactions like the reverse of that in Fig. 9.10 would occur: a deuteron on lithium-6 would produce beryllium and a neutron, and a deuteron on lithium-7 would produce beryllium and two neutrons. The neutrons would then be used to bombard different materials to see how they stand up.

The key parameters for assessing radiation damage are neutron flux, neutron fluence, and dpa. Flux is how many neutrons per second go through each square meter. Fluence is how many have gone through the area during the whole life of the material. Dpa measures the damage, either per year or for the whole life. The flux produced by IFMIF is comparable to that expected in ITER, and about four times less than that in DEMO. The dpa per year in IFMIF is comparable to that in DEMO (about 30) and much larger than at in ITER.5 The fluence cannot compare with that in DEMO, but could duplicate that in the limited life of ITER.

The IFMIF will cost about $700M [22]. It has been severely criticized because only small samples, a few square centimeters in size, can be tested. This is entirely inadequate to test the large components of ITER and DEMO, especially the blanket modules.

Ion Source

High Energy Beam Transport

Fig. 9.30 Diagram of the International Fusion Materials Irradiation Facility [A. Moslang (Karlsruhe), Strategy of Fusion Materials Development and the Intense Neutron Source IFMIF]

Fusion Ignition Tokamaks

Proposals to build small but powerful tokamaks to test burning plasmas were made well before ITER. In the late 1980s, a Compact Ignition Tokamak was initiated in the USA, but was soon canceled. In 1999, Dale Meade at Princeton designed a 10-T, 2-m diameter tokamak call Fusion Ignition Research Experiment (FIRE), but this was never funded. These early ideas were based on the hope that very high magnetic fields produced without superconductivity could be used to achieve igni­tion on a small scale. This philosophy, promulgated by Bruno Coppi at the Massachusetts Institute of Technology, resulted in the Alcator tokamaks at M. I.T. and the Ignitor in Italy. In 2010, Italy and Russia signed an agreement to build a 13-T Ignitor-type tokamak to study burning plasma physics before ITER is fin­ished. These small, pulsed machines cannot expose the steady-state problems that ITER will face. Engineering problems such as tritium breeding and plasma exhaust can be studied only with sufficient neutron flux. There are several proposals for large machines designed specifically for problems not tackled by ITER which will run simultaneously with ITER. None of these has been funded so far.