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1 Crucial Non-Thermal Ignition for nearly twice as efficient again producing half the carbon emissions for the same mechanical Gaining Electrical Energy from energy of the vehicle. An example of nearly Laser Boron Fusion 100% efficiency is the conversion of chemical Heinrich Hora*, Michael Campbell, energy into electric energy in a battery where thermal losses can nearly be neglected. Shalom Eliezer, George Miley and Roland Sauerbrey** Nuclear Energy *[email protected] Ernest Rutherford discovered that atoms Abstract: Ignition of nuclear fusion reactions are built by a electron cloud surrounding a requires temperatures more than one million much smaller nucleus in the centre. The times higher than burning carbon to generate energy needed to start nuclear reactions is not energy. Recently, this has been drastically eV, as in chemistry, but more than one million changed since picosecond laser pulses with times higher. Thus, temperatures required to dozens of petawatts power have become ignite these reactions are in the order of one available. Rather than thermal pressure, the hundred million to one billion degrees. This is nonlinear forces generated by such a laser can only observed in the universe within stars. The be used to ignite a fusion reaction. This has fire that slowly burns hydrogen into helium in enabled an alternative to fission reactors for the centre of the sun is about 15 million nuclear energy generation without the degrees. In a nuclear reaction the energy problems of radioactive waste. It has opened generated by changing one chemical element the possibility of a new clean, safe, low-cost into another corresponds to a change of energy E from the mass difference M times c2 and long-lasting electrical energy supply in the 2 future. according to Einstein’s E = Mc (using the speed of light c). Energy conservation and Thermal When listing the masses of the elements Equilibrium from the heaviest natural uranium to lighter Gaining electrical energy from chemical elements, an increase of the binding energy of energy is most commonly achieved by burning the particles to the nuclei is seen. When fuel. The energy generated per molecule or changing heavier elements from uranium to atom is given in electron-volts (eV), less heavy elements, down to iron, it results in representing about a volt from chemical an energy gain. This is the energy source of batteries. Igniting petrol with a match the nuclear fission reactors. For chemical produces temperatures of several hundred up elements lighter than iron the opposite is true. to about one thousand degrees. In all cases the Reaction of light nuclei as hydrogen, helium, first law of thermodynamics holds - the total lithium, beryllium, boron etc. into heavier energy in the system is constant, whether this ones, up to iron, by fusing nuclei together, a is chemical, electrical, optical, energy of fusion energy gain is seen. mechanical motion at accelerating or slowing This happens in the universe, as mentioned down the mass of a vehicle. Thermal energy for the sun. Is there an alternative to achieving has an additional restriction in that it can only a fusion reaction without the need for flow from a higher to lower temperature and temperatures above millions of degrees? For not the other way. This limits the exchange of fission it was the most unique discovery in thermal energy conversion to an efficiency 1938 by Otto Hahn to achieve ignition at number that is determined by the difference temperatures of power stations by hitting between high and low temperature. neutrons on uranium nuclei. Neutrons are In the steam engine of James Watt, this particles like similar nuclei of hydrogen, efficiency is only a few percent of the energy however without the usual positive electric from burning coal into mechanical energy of charge. When moving the uncharged neutrons motion. For the work of a steam locomotive, a towards uranium nuclei, they are not pushed huge amount of coal has to be shovelled into back by the electric force from the uranium the fire. A petrol internal combustion engine is and can be captured by the uranium nucleus. more efficient than coal, and diesel engine is This “neutron capture” excited the new heavier uranium nucleus and caused it to split into two 2 nuclei and produce a huge amount of energy. physics can drastically change the result – a Hahn could prove this by his unique technique change from no to yes, from wrong to right – to measure the extremely small number of completely even when neglecting very tiny generated chemical elements of the new properties. This is not a gradual change as an nuclei. It could then be concluded that at the approximation, but a basic phenomenon splitting (fission) of uranium, three further discussed in detail in [4] with Richard neutrons were generated, such that a chain Feynman [5] also arguing about Steven reaction could occur creating an explosive Hawking’s or Carl Friedrich von Weizsäcker’s reaction producing the extremely high assumption of a saturation of physics and temperatures. In the case of a power station ending of physics research. In contrast, this chain reaction is controlled to maintain nonlinearity is opening a whole new manageable temperatures. dimension of discoveries and effects. For nuclear fusion as a desired source of In the case of laser ignition of a hydrogen- electrical energy a large amount of research boron reaction, mechanical energy in the was invested since 1950 for experiments that motion of a plasma is not only produced by required temperatures much higher than 10 thermal pressure but also by non-thermal million degrees. One approach is a continuous pressure due to the energy density of laser reaction in a plasma torus at extremely low pulses. This pressure generated by the density confined by very high and constant electromagnetic field of the laser is expressed magnetic fields. Examples are the Stellarator- by the nonlinear force given by the special Wendelstein experiment or the ongoing variation of the energy density of the laser worldwide $20billion ITER project. The latter pulse in the plasma. is not expected to generate energy before 2025 using the fusion of heavy and superheavy Forces and Motion of Plasma hydrogen isotopes deuterium and tritium (DT). The hydrodynamic equation for motion of Another approach is to use laser pulses for fluids like plasmas (all matter of temperatures controlled micro-reactions. The best results above thousands of degrees) began with have been achieved with the world’s biggest Leonard Euler in the eighteenth century. It laser at the National Ignition Facility (NIF) in needed the later defined electric and magnetic Livermore (California) reaching gains of about fields (Maxwell’s stress tensor) and properties one hundred times below the breakeven point of plasma, (Langmuir’s plasma frequency or of producing more fusion energy than had to the Debye-Milner length [6], all achievements be applied to start the reaction. In both cases by Nobel Laureates of the 20th century). The the required ignition temperatures are rather complicate derivation of the equation of considerably higher than 10 million degrees motion was not complete in 1966. From laser- and have been reached where local thermal plasma interaction experiments one first could equilibrium LTE was determining the derive nonlinear effects due to local changes thermonuclear fusion reactions. of the optical refractive index of plasmas resulting in the nonlinear forces. It was a merit The Fusion ignition scheme at extreme non- in the preceding equation of motion that one thermal equilibrium nonlinear term had been discovered, but the A recent experiment has confirmed a final missing two nonlinear terms were not prediction made many decades ago that fusion known before the publication [7]. can be achieved without the need for such high The completed equation of motion temperatures. Applied to a reaction of permitted a numerical study for the interaction hydrogen and boron in non-local thermal of a laser pulse of intensity 1018W/cm2 (Watts equilibrium (non-LTE) conditions, nonlinear per square centimetre) on a slab of deuterium physics [1] dominated the reaction making it plasma of density close to the critical value. viable. This need to work with non- The very general time dependent motion was equilibrium conditions was formulated for a calculated including the local variation of possible supporting the particle beams fusion temperature and density that resulted within proposal MIGMA, introduced by Meglich [2]. 1.5ps (picoseconds = millionth of a millionth The non-equilibrium aspect was highlighted of a second) in the motion of a plasma block experimentally [3] in particular how nonlinear achieving a velocity of about 109 cm/s directed 3 against the laser light. Such an ultrahigh and tritium. This produces each a harmless acceleration of more than 1020cm/s2 was one helium nucleus but also a neutron. Neutrons hundred-thousand times higher than measured decay with a half life of 14.69 minutes into a from the thermal irradiation by lasers on harmless electron and a hydrogen nucleus, but solids. For this theoretical result of 1977 before their decay, they move nearly (summarized in Fig. 8.4 of [4]), the laser unchanged through all materials over long intensities were then just available but were distances. Neutron capture can happen with many orders of magnitude longer than a any harmless stable nucleus, changing it into a picosecond – the lasers required to test this radioactive nucleus resulting in unwanted theoretical result simply didn’t exist yet. radioactive waste. In contrast, “aneutronic” A most dramatic development in laser fusion without any primary neutron generation technology was achieved with chirped pulse is possible if the usual light hydrogen H has a amplification CPA [8] which produced the fusion with the isotope 11 of boron, B-11.
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