Dynamics of Fusion in Plasmas

Abstract

We investigate the possibility of gaining energy from nuclear fusion reactions using different mixtures of D, T and 6 Li. First, a plasma in equilibrium is studied at different densities and temperatures. In a second, highly non equilibrium case, the plasma is at high densities and excitation energies. While the first case could lead to an energy gain especially when coupled to an accelerator, in the second case the energy given to the system might be larger than the output energy even for a D+T plasma. This is due to the small number of particles which can be treated numerically. Furthermore, there is a possible double counting between the elementary fusion cross section and the exact Coulomb potential used in the calculations. §1. Introduction A way of producing energy is by means of nuclear fusion reactions. Such reactions naturally occur in stars and essentially consist of fusion of light elements such as Deuterium (D), Tritium (T), 3He and so on. 1) Reactions involving D+T have a large efficiency and are mostly studied and proposed as a way to produce energy. 2) However, there are some shortcomings for such a proposal. While D can be found easily in water, T is radioactive, very dangerous to handle and must be produced via n+Li reactions. Furthermore in D+T reactions, 14 MeV neutrons are produced which are of damage to the reactors and generate large quantities of radioisotopes. Even though, using low activation materials, the neutrons damage could be reduced, it would be better to avoid T as a main fuel ingredient. Alternatives have been proposed 3) such as D + 3 He 4) or p+ 11 B in Colliding Beam Fusion Reactors-CBFR. 5) There are essentially two routes studied nowdays to produce energy. In the first one a plasma is confined through strong magnetic fields at a given temperature θ and density ρ. This is like a boiling pot where from time to time some nuclear fusion occurs and energy is produced. In order to get more energy output than input, the θ and/or ρ must be very high. In such conditions, the plasma becomes highly chaotic and even turbulences set in. The confining fields are not strong enough to hold the plasma for a very long time.A completely different route to fusion is through the use of lasers. 6) One or more powerful lasers are used to compress and ignite a pellet of fuel. 7) Problems as confinement are avoided, however the time of compression is short, thus it might be difficult to gain energy from such a method even using the D+T fuel.Because of the many uncertainties discussed above, theoretical simulations are highly desirable in order to shed some light on the matter. Simulations exist based on hydrodynamics or kinetic approaches. 1), 6) Such approaches deal very often with the atomic or macroscopic (from the nuclear point of view) dynamics of the plasma. typeset using PTPT E X.cls Ver.0.89

Fusion hindrance effects in laser-induced non-neutral plasmas

“…This work investigated how the cross-section of nuclear fusion reactions at ultra-low energy ( 10 keV) can be modified in a positively charged environment. The direction and importance of those variations critically depends on the reactants and plasma conditions, as can be seen by comparing equations (20), (40) and (42). In particular, it was found that primary (and beambeam) reactions are hindered by the analyzed environment, while secondary (and beam-target) 16 10 −6 fusions are moderately enhanced.…”

“…It is even conceivable that a positive charge may persist in the hotspot for some time after the whole target already became globally neutral, if a sufficient amount of relatively slow electrons can be found lingering in the external regions. These electrons would be either previously emitted from the surface and then caught back, or formed with a mechanism as the one in [20] mentioned above. Any effect due to a charged hotspot is anyway expected to fade away in experiments where the bang time is significantly delayed.…”

“…Note that the chosen parametrization for U has a relevance in determining the reactants spatial distribution for the average. For instance, equation (20) is an average, at fixed x and r 0 , on different x directions, followed by an (here trivial) average on r 0 , which produces an equal distribution for r + and r − positions. Taking instead an average at fixed r + and different x directions, followed by an average on r + in the sphere, would imply that r + is (on average) found nearer to the sphere center than r − , resulting in a non-zero U .…”

Model-independent determination of the astrophysicalSfactor in laser-induced fusion plasmas

“…Our densities are much larger than those obtained in confinement devices (of the order of 10 12 atoms/cm 3 ), but smaller than those reached at NIF so far (a few times solid density). Medium modifications of the crosssection might be more important of course in high density environments, thus some effects in our density regime might be very important [26].…”

Constrained molecular dynamics simulation of the quark-gluon plasma

“…An important ingredient of our approach is a constraint to satisfy the Pauli principle. The approach dubbed Constraint Molecular Dynamis (CoMD) as been successfully applied to relativistic and non relativistic [3,4] heavy ion collision and plasma physics as well [5].…”