Nuclear Fusion: An Energy for the Future

Abstract

Nuclear fusion is one of the most important physics effects as it is the basis of power production and synthesis of nuclei in stars. The basic physics of this process is described. Based on this knowledge, the idea comes up to use this process also for power production on Earth. The physics of the possible nuclear reaction as well as the required physics parameters are described. From the power balance one receives a criterion for the fusion triple product, opening up two possible ways to achieve fusion conditions, i.e. magnetic and inertial confinement. The status of magnetic confinement fusion as well as the plans for the next step, ITER are described. Finally, an interesting physics principle to enhance fusion reactions at room temperature, i.e. muon-catalyzed fusion, is discussed. 17.1 Introduction Nuclear fusion is one of the two possible reaction types than can occur for atomic nuclei, nuclear fission being the second type which is more familiar for the public. This chapter will give a short introduction into the physics of nuclear reactions, then explain in detail nuclear fusion and its role in the universe and possibly on Earth. All nuclear reactions are based on differences in the nuclear binding energy. Figure 17.1 shows the nuclear binding energy per nucleon (proton or neutron) as a function of the nuclear mass for the nuclei bound strongest. Such graphs have been derived from measurements of the masses of the nuclei already in the beginning of the twentieth century, when it was observed that the masses of nuclei are always just a little smaller than some multiple of the hydrogen mass. After the discovery of the nuclear constituents, the proton and neutron, it became finally evident why nuclear masses should roughly be multiples of the mass of the protons and neutrons which constitute the nucleus and that the mass difference corresponds to the nuclear binding energy according to Einstein's energy-mass relation ∆E = ∆m c 2. An explanation of the coarse structure shown in Fig. 17.1 was given by Carl Friedrich von Weizsäcker in 1935 with the liquid-drop model. Based on the very limited range of the strong nuclear force he concluded that each nucleon just influences its nearest neighbors. The binding energy per nucleon would thus be constant. The smaller binding energies for smaller nuclei are then due to the relatively large surface-to-volume ratio: The nucleons at the