AU2022218565A1 - Device and procedure for the production of ife (inertial fusion energy) - Google Patents

Abstract

The present application relates to a method for producing neutronic and aneutronic fusion energy by a neutronic and/or 5 aneutronic nuclear fusion reaction, and the generation of secular electric and magnetic fields, the method comprising irradiating a target (10) of a nano-structured material with a laser pulse, wherein the laser pulse has a laser carrier frequency o, a pulse duration, and a spot size, and wherein 0 the laser pulse is at least partially absorbed by the nano structured material, wherein the target (10) comprises a surface (15) with a plurality of nano-rods (12) extending from the surface (15). The present application further relates to a corresponding system and target (10). 5 (Fig. 1) 1/2 CNCIO CC c0 (I0 CN~ KLL CNNLLO

Description

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KLL CNNLLO DEVICE AND PROCEDURE FOR THE PRODUCTION OF IFE (INERTIAL FUSION ENERGY)

[0001] This application claims priority from European patent application 21193867.5, filed 30 August 2021 and European patent application 21211940.8, filed 2 December 2021, the entire contents of which is incorporated by reference.

TECHNICAL FIELD

[0002] The present invention relates to a method, a system and a target in the field of producing neutronic and aneutronic fusion energy by a neutronic and/or aneutronic nuclear fusion reaction, in other words ignition of an aneutronic reaction, namely, a fusion reaction, i.e., conversion of laser energy into fusion energy and fusion products by means of triggering fusion reactions, and secular electric and magnetic fields. The conversion is achieved by irradiating a target of a nano structured material with a laser pulse so that the laser pulse is at least partially absorbed by the nano-structured material.

BACKGROUND

[0003] Fusion energy relies on the merging of light nuclei to form a heavier nucleus, where the reduced mass of the reaction 2 product is transformed to energy according to E=mc . Among the reactions known today, combinations of the isotopes Deuterium and Tritium, also called D-T or DT, offer the best cross section and the lowest ignition temperature. The nuclear fusion reaction of DT results in a massive production of fast neutrons around 14.1 MeV which are then used for energy production by transforming their kinetic energy via absorption into heat in a surrounding blanket. The downside of the corresponding nuclear reaction is that the energetic neutrons which are difficult to shield can also damage some of the material that is used in a reactor confinement vessel.

[0004] Further known is a lean neutronic (aneutronic) fusion reaction of Boron-11 and a proton, also called PB-11, which results in charged reaction products, following the equation p+B11 - 3 ax + 8.9 MeV, and significantly fewer neutrons than the above-mentioned combinations of Deuterium and Tritium. A disadvantage of this lean neutronic fusion reaction is that it requires far higher temperatures of around 570 keV to reach energy producing fusion burn. Direct ignition of PB-11 was considered unlikely using conventional thermonuclear approaches.

[0005] There are two general concepts to ignite nuclear fusion for using its energy in electric power generation: Magnetic Fusion Energy, abbreviated MFE, and Inertial Fusion Energy, abbreviated IFE.

[0006] In MFE, microwaves, electricity and neutral particle beams heat a stream of hydrogen gas. This heating turns the gas into a low-density plasma which is then squeezed and confined over longer times in a very strong magnetic field obtained from magnets. This allows fusion to occur. Today's state of the art-shape for such a magnetically confined plasma is a donut shape also known as toroid. A corresponding reactor is called a tokamak, and a prominent publicly funded reactor of this kind is part of the ITER project, which is planned to be operational in 2035.

[0007] On the other hand, Inertial Fusion Energy is distinguished from the above-mentioned Magnetic Fusion Energy particularly in that the fusion fuel is compressed to high densities in a very short time and maintained at fusion densities and temperatures by its own inertia. The most common approach to IFE is based on lasers as driver technology for compressing the fuel.

[0008] Laser driven IFE offers the prospect of a comparably versatile system, where modifications on one part of the system do not always affect other parts. This allows decoupling of the design of the fusion reactor from the driving laser system. Today, generally two types of fusion strategies are known, namely, Hot Spot and Fast Ignition.

[0009] As to Hot Spot, unlike MFE, laser driven IFE relies on the fusion of light nuclei in an extremely dense, high pressure, high temperature plasma hot spot where the nuclear fusion burn wave, due to its own inertia, outruns the disassembly of the fuel. In conventional D-T inertial fusion, ignition and propagating burn occurs when a sufficient temperature of, for example, 5-10 keV, is reached within a sufficient mass of DT fuel. The necessary conditions for propagating D-T burn are achieved by an appropriate balance between the energy gain and loss mechanisms. When the rate of fusion energy gain exceeds the rate of energy loss for a sufficient period of time, in the order of picoseconds, ignition occurs.

[0010] To achieve central hot spot ignition, a highly symmetric, high velocity spherical implosion is desired, where the incoming shock waves finally overlap, first compressing the fuel and then heating it up at the moment of maximum compression. This has been studied in experiments at the National Ignition Facility, Lawrence Livermore National Laboratory, Livermore, California, USA, also called NIF, and significant progress has been made resulting in the highest neutron yield in any IFE experiment.

[0011] Results from 2021 show a fusion yield of 1.3MJ, which corresponds to a conversion efficiency of energy out to laser energy in of roughly 70 %, up from 0.1% efficiency in 2011. In its latest experiments, NIF has also seen initial signs of alpha heating for the first time ever in a laboratory setting, i.e., the energy generated by alpha particles stimulating additional fusion reactions in the cold fuel exceeds the kinetic energy delivered by the implosion.

[0012] The NIF used a 1.8 MJ flashlamp-pumped, neodymium-doped phosphate glass laser system with 192 beam lines at the third harmonic of the glass laser transition frequency. The pulse length was around 8 nanoseconds with a special pulse shape.

[0013] The targets designed for indirect hotspot ignition at NIF feature four essential components: a capsule with fill tube, deuterium and tritium (D-T) fuel in form of a frozen layer inside the fuel capsule, a cylinder the size of a pencil eraser known as a "hohlraum" enclosing the capsule, and thermal control hardware. The capsule needs to have a precise spherical shape with surfaces smooth to the nanometer level. Once assembly is complete, the target is integrated with a cryogenic target positioning system and placed at the target chamber center. The temperature of the target needs to be held in the range of 18 to 20 Kelvin, as is described at https://lasers.llnl.gov/about/how-nif-works/beamline/targets.

[0014] Fast Ignition strategies, on the other hand, have been researched extensively, particularly at the NIF and the LFEX facility in Osaka, Japan. This approach uses a combination of two laser pulses. First, a long laser pulse causes an implosion and compression of the fuel because compressing the fuel reduces the amount of heat needed. Next, a shorter, fast laser pulse induces ignition. This reduces the amount of energy delivered in each of the two steps. The longer pulse can be "shaped" to be more efficient, reducing the overall energy needed and thereby in requiring smaller lasers.

[0015] M. Tabak, et al., Phys. Plasmas 1, 1626 (1994) proposes Fast Ignition as an approach to increase the gain, reduce the drive energy, and relax the symmetry requirements for compression. The idea is to first pre-compress the cold fuel to an intermediate density, and to subsequently ignite it with a separate short-pulse high-intensity laser or particle (electron or ion) pulse. According to Inertial Fusion Science and Applications 1999, edited by C. Labaune, W. J. Hogan, and K. A. Tanaka (Elsevier, New York /Amsterdam, 1999), Fast Ignition is being studied by many groups worldwide. Achievements to-date include attaining a conversion efficiency of 10% of laser light into a proton beam and focusing the beam to better than 50pm a spot size, as is disclosed, e.g., by Hegelich et al., Experimental demonstration of particle energy, conversion efficiency and spectral shape required for ion-based fast ignition, Nucl. Fusion 51 083011 (2011), R. SNAVELY et al. Phys. Rev. Lett.85, 2945(2000), and M. Key et al., Fast Ignition: Physics Progress in the US Fusion Energy Program and Prospects for Achieving Ignition.

[0016] The vast majority of these approaches are based on D-T fuel with the above-mentioned disadvantages. A different option is using a PB-11 (pB) fuel. Hora et al., Matter and Radiation at Extremes 2, 177 (2017) suggest that the barrier for igniting pB fuel can be lowered by exploiting new plasma physics. The phenomenon of "non-thermal" fusion reactions, i.e., fusion reactions that are not induced in a thermonuclear regime but make use of non-equilibrium, non-thermal distributions, were demonstrated by Belyaev, V., et al., Observation of neutronless fusion reactions in picosecond laser plasmas, Physical review. E, Statistical, nonlinear, and soft matter physics, 2005. 72: p. 026406; Labaune, C., et al., Laser-initiated primary and secondary nuclear reactions in Boron-Nitride, Scientific Reports, 2016. 6: p. 21202; D. Margarone, et. al, Generation of a-Particle Beams With a Multi-kJ, Peta-Watt Class Laser System, Frontiers in Physics, 2020; Korn, G., Margarone, D. & Picciotto, A. (2014), Boron Proton Nuclear Fusion Enhancement Induced in Boron-doped Silicon Targets by Low-contrast Pulsed Lasers, IZEST ELI-NP Conf. Paris, 17-18 September 2014; Picciotto, A., et al., Boron-Proton Nuclear-Fusion Enhancement Induced in Boron-Doped Silicon Targets by Low-Contrast Pulsed Laser, Physical Review X, 2014, 4: p. 031030; and Margarone, D., et al., Advanced scheme for high-yield laser driven nuclear reactions, Plasma Physics and Controlled Fusion, 2014, 57(1): p. 014030. These results extended from the observation that these pB reaction gains are many orders of magnitude higher. In particular, the results of Korn, Picciotto and Margarone achieved one billion times higher reaction yields.

[0017] To allow non-thermal (non-equilibrium) fusion concepts, two technologies are key: laser systems that reach a sufficiently high intensity, peak power, contrast and pulse length, and nanostructured fuel pellets ("targets") that enable efficient laser absorption and control of non-linear optical effects.

[0018] It has been 55 years since the demonstration of the laser and the first proposal to use focused laser light to initiate thermonuclear (TN) fusion. Understandable optimism led to early hopes and claims that breakeven (fusion energy out greater than laser energy in) was only a few years away. However, it is only in recent years that laser and target technologies and understanding of the related physics have advanced to a point where laser-driven fusion energy can be seen as a realistic option for the future.

[0019] One important development in laser technology is the increase of peak power. Initial jumps of several orders of magnitude in peak power came with discovering Q-switching and mode-locking. Progress slowed until the late 1980s. D. Strickland and G. Mourou, Opt. Commun. 56, 219 (1985) explains the development of the technique of chirped pulse amplification (CPA). CPA along with other developments led to the first well-defined 100 TW class laser systems in the mid 1990s. Further development in pulse shaping technology, new gratings for the pulse compression and beam focusing technology subsequently opened the way to PW-class laser systems with ultra-high intensities and ultra-short pulse lengths.

[0020] Another important innovation was the world's first high average power PW-class laser system HAPLS, installed at the ELI-Beamlines facility in the Czech Republic. This laser uses a single-aperture, diode-pumped solid-state laser (DPSSL) to pump the laser medium. This diode-pumped system allows the operation at 10 Hz, i.e. 10 laser shots per second, significantly broadening the possibilities for potential commercial applications of these high energy laser systems if compared to previous laser systems.

[0021] Novel technologies like Optical Parametric Chirped Pulse Amplification (OPCPA) now open the path to 100 PW to Exawatt laser systems with super high temporal contrast, allowing commercial applications like laser-driven inertial fusion.

[0022] Fuel pellets for laser-driven inertial fusion can be of various shape and form. Cryogenic D-T targets as being used for hotspot ignition have been discussed above. However, with the continuous innovation in nanotechnology and the ability to finetune ever more granular target structures, novel, nanostructured non-frozen targets can be produced. Specifically, different approaches for surface structured targets can be chosen for largely increased laser absorption.

[0023] Bargsten, Volumetric creation of ultra-high-energy density plasma by irradiation of ordered nanowire arrays, Master Thesis at Colorado State University (2016) discloses ordered nanowire arrays (nanorods) showing beneficial properties for laser absorption and the creation of immense plasma densities. Fedeli et al, Ultra-intense laser interaction with nanostructured near-critical plasmas, Scientific Reports 8:3834 (2018); DOI: 10.1038/s41598-018 22147-6, discloses that the presence of nanorods strongly reduces the effect of pulse polarization, and enhances the energy absorbed by the ion population, while leading to a significant decrease of the electron temperature with respect to a homogeneous near-critical plasma.

[0024] There have also been experiments with amorphous pB based targets using PW-class laser systems. Margarone et al., Generation of a-Particle Beams With a Multi-kJ, Peta-Watt Class Laser System, Front. Phys., September 2020, https://doi.org/10.3389/fphy.2020.00343 discloses an alpha particle flux of 109 and a laser absorption efficiency of 7%.

[0025] Patent literature in the above technical field comprises US 2018/0322962 Al, US 2004/0213368 Al, US 4 199 685 A, US 2017/0125129 Al and US 2020/0321135 Al.

[0026] The thermonuclear approach to fusion is a quasi equilibrium approach based on neutron rich reaction chains. They typically have the lowest activation energies or, in the terminology of equilibrium physics, require the lowest temperature for fusion to set in. One problem is that most of the fusion energy yield by neutron rich reactions is consumed by the neutrons which cannot be confined within the burning hot spot.

[0027] Further, these neutrons are difficult to shield and can lead to an activation of the reactor chamber wall, leading to high maintenance costs and radioactive waste.

[0028] Also, all neutron rich reaction chains using D-T fuel face the problem of handling Tritium, which is unstable, radioactive and rare, making a possible commercialization difficult.

[0029] The main advantage of equilibria is that there is little net energy transfer amongst the components which are in equilibrium with each other. A disadvantage, however, is that the reactivity of equilibria is extremely small. Due to hard temporal limitations for the reacting system, the reaction rate has to be large in order to burn a sizable fraction of the fuel.

[0030] So far, it is tried to enhance the fusion rate by massive material compression, which tends to shift the main share of the costs into a viable thermal fusion concept to fusion target implosion. The latter comes along with a new yet unresolved range of problems, including Rayleigh Taylor Instabilities and laser-plasma instabilities.

[0031] Aneutronic reaction chains such as p-B or others do not have to deal with the problem of energetic neutrons. However, they require very high ignition temperature under classical thermonuclear conditions. They also face the problem of massive material compression. These problems prevent successful commercialization of fusion technology based on p-B fuel as the associated laser system costs for reaching these high temperatures and high compression levels are above any reasonable amount that would allow to provide electricity at competitive prices.

[0032] Non-thermal (i.e., non-equilibrium) approaches based on p-B fuel, i.e. approaches that act outside of the thermonuclear regime, do not rely on neutron rich reactions but on efficient ways to generate non-thermal distributions that can sustain long enough. Non-thermal ionic distributions are therefore a prerequisite for fusion with advanced fuels. Up to now non-equilibrium fusion concepts have little track record. The physics of converting laser energy into fusion products like charge particles is quite different and challenging. However, with the advent of efficient energetic ultra-short optical laser pulses and the capabilities to manufacture nanostructured targets, it is now possible follow non-equilibrium routes into fusion.

SUMMARY OF THE INVENTION

[0033] In view of the above, an objective of the present invention is to efficiently trigger fusion reactions non thermally, with high reactivity in a broad range of relative centre of mass kinetic energies between the fusion partners and thereby obtaining an economically viable path to energy production based on aneutronic fuels via efficient conversion of a driver energy in fusion products and therefore fusion energy.

[0034] The objective is solved by a method according to claim 1, a system according to claim 12, and a target according to claim 23. Preferred features of the disclosure are subject of the dependent claims.

[0035] According to the invention, a method for ignition of an aneutronic reaction, in particular a fusion reaction, non thermally, or for producing secular electric and magnetic fields, comprises irradiating a target of a nanostructured material with a laser pulse, wherein the laser pulse has a laser carrier frequency o, a pulse duration, and a spot size, and wherein the laser pulse is at least partially absorbed by the nanostructured material. According to the present disclosure, the target comprises a surface with a plurality of nano-rods extending from the surface, wherein the nano-rods have a distance D, height h and a diameter d.

[0036] In principle many aneutronic reactions can be ignited using this concept. It works best if the mass difference of the fusing nuclei is bigger. Due to the fs-acceleration process, lighter ions are much faster brought to high energies. Protons, due to the lowest mass of all ions, are therefore best accelerated.

[0037] According to the invention, a system for igniting non thermally a fusion reaction, triggering a neutronic and/or an aneutronic nuclear fusion reaction, or for producing a secular electric and magnetic field comprises a target of a nanostructured material and a laser device for emitting a laser pulse, wherein the laser pulse has a laser carrier frequency o, a pulse duration, and a spot size, and can at least partially be absorbed by the nanostructured material, wherein the target comprises a surface with a plurality of nano-rods extending from the surface.

[0038] According to the invention, a target of a nano structured material for absorbing a laser pulse having a laser carrier frequency o, a pulse duration, and a spot size for igniting non-thermally a fusion reaction or for producing secular electric and magnetic fields comprises a surface with a plurality of nano-rods extending from the surface.

[0039] Essentially, aneutronic fusion reactions, such as p+Bli - 3a + 8.9 MeV, i.e. pBil fusion, or secular electric and magnetic fields, in nanostructured materials can be triggered or produced, respectively, by short ultra-intense optical laser radiation extending to the UV and VUV spectral range. The nanostructured material is supposed to work as an ultra fast and efficient absorber for the laser, while efficiently accelerating the ions and due to quantum effects enhance the fusion reactivity also for lower centre of mass kinetic energies of fusion partners due to massive collective screening effects.

[0040] Laser deposition in these materials is very efficient and electrons tend to over-heat. For example, nanostructured proton-boron composite material can absorb ultra-short optical laser pulses almost entirely, which leads to electrons being rapidly expelled from the nano-structures and to consecutive Coulomb explosion. This generates a non-thermal, i.e. non equilibrium, distribution for fusion-relevant ions within femtoseconds that are sufficient for pB fusion.

[0041] Since the laser induced relative velocities between protons and boron ions are large, the reactivity is large, which in turn allows for lower average densities in the system. Since laser-deposition and fusion in the nanostructured absorber are fast, instabilities are avoided. Hence, there is reduced experimental complexity that is more easily manageable, and significantly less laser energy is required for converting the laser energy into fusion products, making the total system cost economically viable as a converter and or ignitor.

[0042] One underlying physical model is in essential parts of quantum nature. Due to large electric and magnetic fields induced by the absorbed short pulse laser energy in the nanostructured material of the target, the Coulomb barriers for fusion processes are shielded. Consequently, the effective tunnelling length for protons through the shielded Coulomb barrier is increased. This leads to fusion cross sections in the system which are enhanced by orders of magnitude even at smaller center-of-mass kinetic energies between the fusing ionic components. Since the shielded cross sections in the absorber are enhanced, fusion takes place over a much larger centre of mass kinetic energy range including smaller energies therefore enhancing fusion reactivities, gain and fusion energy output.

[0043] In addition, the nanostructured material has an interesting scaling behaviour with the wavelength of the laser pulse. For shorter wavelengths the concept proposed here continues to work. However, working at half the laser wavelength means that four times the critical plasma density in the nanostructured material can be afforded, leading to sixteen times the fusion yield within the same time window. This allows for highly efficient conversion of laser energy into fusion products and therefore can lead to ignition (break-even) and gain.

[0044] The present concept is based on high peak-power laser pulses with high contrast and intensity, wherein the laser pulses preferably are femtosecond optical laser pulses.

[0045] The nanostructured target enables fast and highly efficient optical laser absorption (>90%) without parametric instabilities. The absorption is hence significantly higher than the typical absorption efficiency seen in other laser based ignition approaches.

[0046] The nanostructured target irradiated with high intensity short laser pulses leads to non-thermal distribution functions due to efficient Coulomb explosions for fusion relevant materials that involve all ions and, consequently, to very large reactivities. In case of a pB reaction, because there is a substantial mass gap between protons and boron ions, large relative velocities between both are created.

[0047] Since reactivities in the proposed concept are large, lower average densities are permissible. Therefore, an optical laser pulse can propagate through the nanostructured material at almost speed of light, which implies that the pulse never interacts with corrupted nanostructured material. Hence, the laser pulse can generate non-thermal distributions of fusion relevant ions until it is almost depleted.

[0048] The nanostructured material can be adapted to the laser pulse allowing to control the shape of the distribution functions that are created.

[0049] Irradiating of the nanostructured material of the target by a laser pulse can lead to rapid evacuation and over heating of electrons. Strong collective fields can be formed by the expelled overheated electrons. These fields can lead to significant screening of the Coulomb barriers that immensely increase the fusion rates for pB at lower centre of mass kinetic energies to several barns, even above thermonuclear fusion rates for DT.

[0050] An advantage of the concept is that this process can be controlled through the variation of different technical parameters:

[0051] Firstly, the relative velocity (i.e., center-of-mass kinetic energy) between protons and boron ions can be controlled through the design of the nanostructured material and the laser pulse.

[0052] Secondly, shorter wavelengths for the laser pulse results in a massive improvement for fusion yield. Operating at half the wavelength means sixteen-fold the fusion yield in the same time window.

[0053] Thirdly, the average density of the nanostructured material and the wavelength of the laser pulse can be optimized to maximize fusion power and fusion yield.

[0054] The present concept can work as a converter or even ignitor for a subsequent burn to reach high energy gain factors. It is also possible to operate the target at shorter yet still optical wavelengths of the laser pulse leading to significant enhancement of fusion power and yield.

[0055] The converter ignitor concept is based on very fast processes through efficient and fast laser deposition in the nanostructured material of the target leading to high relative energies of fusion relevant ions and high reactivity, thereby enabling low density operation that avoids instabilities. In addition, there is no or reduced requirement to compressing the nanostructured converter to very high densities.

[0056] Since the laser induced processes in target are fast, they can be included into a low compression concept while there is perfect control when to ignite the target.

[0057] The method based on ultrafast high intensity laser deposition described in the present disclosure is significantly faster than traditional fusion approaches, thus avoiding instabilities. Further, this concept works in a broader range of center-of-mass energies and significantly less laser energy can be applied to achieve ignition, which may be decisive for using fusion energy in commercial electric power generation.

[0058] Preferably, the nano-rods of the target are cylindrical each having a rod-diameter and a rod-length. In this context, cylindrical nano-rods means that the nano-rods which extend from a common base of the target, which preferably is a flat surface, are bounded by a cylindrical surface and a top base. The nano-rods can be right cylinders or oblique cylinders, and the top bases can be circular disks, ovals or polygons. The nano-rods are preferably periodically and symmetrically grown.

[0059] The rod-length is, in this context, the height of the cylindrical rod, i.e., the perpendicular distance between its top base and the common base.

[0060] Advantageously, the nano-rods of the target are regularly arranged along one first direction, which is a linear direction or a circular direction, so that adjacent nano-rods are spaced along the first direction by a first rod distance. For the nano-rods to be regularly arranged along a direction, the first rod-distance is substantially the same or an integer multiple for a plurality of nano-rods of the target, preferably for at least 50% of the nano-rods of the target, most preferably for at least 90% of the nano-rods of the target along that direction.

[0061] In the present context, a rod-distance is defined as the lateral distance between the lateral centres of two rods.

[0062] Further advantageously, the nano-rods of the target are regularly arranged along two perpendicular directions so that adjacent nano-rods are spaced along a first direction of the two perpendicular directions by a first rod-distance and along a second direction of the two perpendicular directions by a second rod-distance. For the nano-rods to be regularly arranged along a direction, the first and second rod-distances are substantially the same or an integer multiple for a plurality of nano-rods of the target, preferably for at least 50% of the nano-rods of the target, most preferably for at least 90% of the nano-rods of the target along that direction. However, the first rod-distance along the first direction can be different from the second rod-distance along the second direction. The first and second directions can be arranged perpendicularly in a cartesian coordinate system, but also in a circular coordinate system or other coordinate systems.

[0063] Using cylindrical rods facilitates using technical parameters to optimize fusion yield. Such technical parameters are the rod-diameter, the rod-length, and the distances between adjacent rods. This is advantageous over the prior art based on, for example, amorphous targets.

[0064] The absorbing target works at a range of parameters. However, to maximize fusion yield, it is preferred that the target and laser properties are aligned. According to the fundamental scaling behaviour of the target, fusion yield significantly increases with shorter wavelength. Hence, preferably, the first rod-distance, and further preferably also the second rod-distance, as the case may be, is greater or equals AR 2 nie 2 /Eomew 2 , wherein R is the radius of the rod, ni is the average ion density, e is the charge of an electron, 8o is the electric field constant, me is the electron mass, and o is the laser carrier frequency.

[0065] In other words, the rod-distance is proportional to 1/o, i.e. the laser carrier frequency. Hence, if o is doubled, the distance between adjacent nano-rods in two perpendicular directions is halved, the density of nano-rods per area is four times as large which means that four times as many nano rods with the same electron release capability can be admitted in the target. This means that the fusion power is then about 16-times as large, while the amount of fusion material is four-fold as high. In summary, decreasing the wavelength by a 4 factor x increases the fusion yield by a factor of x

.

[0066] As to the rod-diameter, the intensity of the laser, including its focal spot, is preferably be taken into consideration when determining the rod-diameter of the nano rods.

[0067] The rod-length is preferably determined by how far the laser can propagate into the target until it has fully depleted its energy.

[0068] According to a preferred embodiment, the nanostructured material comprises boron and/or boron compounds containing other materials such as boron nitride and/or hydrogen containing materials. Alternatively, or additionally, it is preferred that the nano-structured material comprises amorphous material or layers of different materials. Further alternatively, or additionally, the nanostructured material preferably comprises nano-rods of alternating materials, in particular of boron and gold, respectively. Materials including protons, boron, deuterium, tritium and gold in arbitrary concentration are also preferred.

[0069] The material composition of the nanostructured targets can vary. One option is to only use fusion-relevant material, for example boron or boron nitride. A second option is to grow nano-rods having different layers. The different layers can contain a mix of fusion-relevant material and material that can, for example, induce ultraviolet light radiation in the 100 nm spectrum to further enhance fusion yield. As the efficiency of the nano-structured material scales with shorter wavelength, introducing materials that can generate photons of a shorter wavelength than the laser pulse can make the overall system more efficient.

[0070] The material composition of the nanostructured targets can also comprise DT, or it is possible to include a non nanostructured DT composition surrounding a nanostructured target serving as the ignitor with and without compression of DT. The alphas from the ignitor would initiate burn in the outer non-compressed or pre-compressed material.

[0071] The nano-structured material and a space in between and surrounding the nano-rods can comprise a neutronic fuel and/or an aneutronic fuel.

[0072] According to a preferred embodiment, the laser pulse is a femtosecond optical to VUV laser pulse. Other laser pulses are generally possible, but short femtosecond optical to VUV laser pulses are advantageous over, for example, nanosecond laser pulses because instabilities are avoided, and the process works in strong non-equilibrium due to the very short time scale.

[0073] A particularly preferred fusion reaction comprises p+B"1 -> 3ax + 8.9 MeV. Further, it is preferred that the secular magnetic field has a magnetic B-field strength of 1 MT to 100 MT.

[0074] Further advantages and additional features of the disclosure become apparent from the set of claims and the following description.

BRIEF DESCRIPTION OF THE FIGURES

[0075] Fig. 1 illustrates a perspective view of a preferred target.

[0076] Figs. 2a and 2b illustrate a top view of the preferred target of Fig. 1.

[0077] Fig. 3 illustrates a side view of the preferred target of Fig. 1.

[0078] Fig. 4 is an exemplary graph illustrating fusion cross sections for thermonuclear pB and thermonuclear DT fusion reactions in comparison to the fusion cross sections of a preferred non-thermal pB fusion reaction.

[0079] Fig. 5 is an exemplary graph illustrating the fusion cross sections of a preferred non-thermal pB fusion reaction.

[0080] Fig. 6 is an exemplary isocontour plot illustrating Q of the fusion energy yield and in particular the scaling behaviour of Q normalized to the initial energy in the ionic distributions after laser energy deposition of a preferred non-thermal pB fusion reaction as a function of $ and nBR.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0081] In the following description, same or corresponding elements and features are referenced by the same or corresponding reference signs and a repetitive description thereof is avoided.

[0082] Fig. 1 illustrates a perspective view of a preferred target 10. A common base 14 is, in the illustrated embodiment, square shaped and has a flat upper surface 15 from which a plurality of nano-rods 12 extend perpendicularly from the common base 14. The nano-rods 12 are regularly arranged along a first direction X and a second direction Y, wherein the first direction X and the second direction Y are perpendicularly oriented with respect to each other in a cartesian sense. Alternative arrangements of perpendicular directions are, for example, according to circular coordinates, i.e., along a radius with respect to an origin, and a circumference about this origin.

[0083] Figs. 2a and 2b illustrate a top view of the preferred target 10 of Fig. 1, wherein Fig. 2a illustrates a total top view of the target 10, and Fig. 2b a detailed view of the illustration of Fig. 2a, namely, the top right corner including four of the nano-rods 12 illustrated in Fig. 2a. The top view of Fig. 2a more clearly illustrates that the nano rods 12 are regularly, i.e., periodically, arranged along the first and second directions X and Y. Fig. 2a also illustrates a first target side length D and a second target side length D'. As illustrated, it is preferred that the nano-rods 12 are regularly arranged over the total of the first and second target side lengths D and D'. Fig. 2b highlights that a first rod-distance B between adjacent nano-rods in the first direction X is equal to a second rod-distance B' between adjacent nano-rods in the second direction Y. Although the first and second rod-distances B, B' can differ from each other, it is preferred that the first rod-distance B is the same as the second rod-distance B' for at least 50% of the nano-rods 12 of the target 10, further preferably for at least 90% of the nano-rods 12 of the target 10. A rod-diameter A is smaller than the first and second rod-distances B, B'.

[0084] Fig. 3 illustrates a side view of the preferred target 10 of Fig. 1. In this side view according to Fig. 3, the nano rods 12 are shown to have a rod-length C which is measured perpendicularly to the surface 15 of the common base 14 and between the surface 15 and a top base 16 of the nano-rods 12. The nano-rods 12 illustrated here are right cylinders but can also be non-cylindrically shaped or oblique cylinders. However, the illustrated shape of the nano-rods is preferred.

[0085] The first and second target side lengths D and D' of the target 10 can preferably be determined by a size of a focal spot of the laser used for the ignition, and the necessary amount of material around it to get gain well above one. As the nano-structured material has areal scaling properties, increasing D and D' and the focal spot of the laser also increases the total fusion yield. Another parameter for variation is the composition of the target material as described before.

[0086] The nanostructured material of the target 10 can comprise boron nitride. Additionally, and alternatively, the nanostructured material can comprise amorphous material or layers of different materials, in particular including a material for inducing ultraviolet light radiation. In particular, the nanostructured material can comprise nano-rods 12 of alternating materials, in particular of boron and gold, respectively, which means that every second nano-rod 12 along the first and second directions X and Y comprises boron and every alternating second nano-rod 12 along the first and second directions X and Y comprises gold.

[0087] A system for ignition of a non-thermal fusion reaction also comprises a laser device, which is not illustrated and which is configured for emitting a laser pulse, wherein the laser pulse has a laser carrier frequency o, a pulse duration, and a spot size, and which can at least partially be absorbed by the nano-structured material of the target 10. An intensity 2 of the laser pulses measured in W/cm can be varied through increasing the pulse energy, the pulse length or the focus spot size of the laser device. Further, the wavelength of the laser pulse can be varied.

[0088] It is preferred that the target 10 and laser properties are aligned. According to the fundamental scaling behaviour of the target 10, fusion yield significantly increases with shorter wavelength. Hence, preferably, the first rod-distance B and the second rod-distance B' of the target 10 is greater or equals AnR 2 nie 2 /Eomew 2 , wherein R is the radius of the rod, ni is the average ion density, e is the charge of an electron, 8o is the electric field constant, me is the electron mass, and o is the laser carrier frequency.

[0089] The intensity of the laser, including its focal spot, then determines the diameter of the nano-rods. The rod length is determined by how far the laser can propagate into the target until it has fully depleted its energy. In the following, four Examples of preferred technical parameters for the system of the laser device and target 10 are shown:

[0090] Example 1: Laser system: Wavelength 1060 nm 2 Intensity 1022 W/cm

[0091] Nano-rods 12 of target 10: Rod-diameter A 120 nm Rod-length C 2-100 pm First rod-distance B 2500 nm Second rod-distance B' 2500 nm

[0092] Example 2: Laser system: Wavelength 1060 nm 2 Intensity 1020 W/cm

[0093] Nano-rods 12 of target 10: Rod-diameter A 100 nm Rod-length C 2-100 pm First rod-distance B 400 nm Second rod-distance B' 400 nm

[0094] Example 3: Laser system: Wavelength 210 nm

2 Intensity 1022 W/cm

[0095] Nano-rods 12 of target 10: Rod-diameter A 100 nm Rod-length C 2-100 pm First rod-distance B 400 nm Second rod-distance B' 400 nm

[0096] Example 4: Laser system: Wavelength 210 nm 2 Intensity 1021 W/cm

[0097] Nano-rods 12 of target 10: Rod-diameter A 20 nm Rod-length C 2-100 pm First rod-distance B 10 nm Second rod-distance B' 10 nm

[0098] Fig. 4 is an exemplary graph illustrating cross sections for thermonuclear pB and thermonuclear DT fusion reactions in comparison to the cross section of a preferred non-thermal pB fusion reaction. A first curve 18 shows the progress of a cross section of a thermonuclear pB fusion reaction over the center-of-mass energy. A second curve 20 shows the progress of a cross section of a thermonuclear DT fusion reaction over the center-of-mass energy. A third curve, i.e. a range of an area illustrated as hatched, 22 shows the progress of a cross section of a preferred non-thermal pB fusion reaction over the center-of-mass energy. The cross section of the third curve 22 is significantly higher, in particular for low center-of-mass energies than the first and second curves 18 and 20. Rapid evacuation and over-heating of electrons and the induced field distribution in the nano structured target 10 leads to significant screening of the Coulomb barrier that immensely increases fusion rates for pB also at low relative energies.

[0099] Fig. 5 is an exemplary graph illustrating the fusion cross sections of a preferred non-thermal pB fusion reaction. A first curve 24 shows a cross section of a non-thermal pB fusion reaction for screening energy Es=O MeV. A second curve 26 shows a cross section of a non-thermal pB fusion reaction for screening energy Es=l MeV. A third curve 28 shows a cross section of a non-thermal pB fusion reaction for screening energy Es= 3 MeV.

[0100] Between the nano-rods strong electric and magnetic fields are generated by the ultra-short high-intensity driver laser. This leads to shielded cross sections for nuclear fusion. Shielded nuclear fusion cross sections of pB fusion are significantly enhanced at low relative energies, leading to a significantly higher reactivity at technical parameters which are particularly relevant to commercial fusion energy.

[0101] The electric field effects suppressing the Coulomb barriers can be accounted for with the help of the relative energy Eg and the screening energy Es of the fuel constituents.

[0102] Fig. 6 is an exemplary isocontour plot illustrating Q of the fusion energy yield and in particular the scaling behaviour of Q normalized to the initial energy in the ionic distributions after laser energy deposition of a preferred non-thermal pB fusion reaction as a function of $ and nBR.

[0103] For the present invention, the following formula can be derived for the ratio Q of the fusion energy yield normalized to the initial energy in the ionic distributions after laser energy deposition:

Q =f -6f= fr/, wherein eg+cS 6Gkl

n__Rtot R Ski fl tav) _ EGkl

1+nRkR,to t ~t 1+nRk ~

wherein P is the sum of the relative energy and the shielding energy.

[0104] Further sE is the energy release of an elementary nuclear fusion reaction and -Sk is the Gamov energy of the fuel comprising the fuel constituents k and 1. In case of pB as the fuel, k=p and l=B hold andCGpB, the Gamov energy of pB, is 2.3xlO 7 eV.

[0105] This shows that, if the electrons in the nano structured material do not cool significantly due to radiation reaction, collisional energy exchange between electrons and ions is inhibited due to electron overheating by the laser in addition to low plasma densities in the nano-structure that also prevent collisions. Then At scales with the volume of the target 10. Larger volumes of the target 10 lead to larger At. At the same time, At scales weakly with the wavelength of the laser pulse since only radiation reaction after energy deposition is of concern. Hence, the wavelength of the laser pulse can be increased and, simultaneously, the nano-structure be adapted such that Eq ~ 500keV holds true after laser deposition.

[0106] The present invention can be applied to various use cases. First, it can serve as a converter from laser energy to fusion energy and fusion products for various burn materials including neutron rich or aneutronic fusion reactions, where the burn materials can be placed at predefined locations in the convertor and where arbitrary fuel mixes can be utilized. As a spark plug, the convertor can be surrounded with compressed or uncompressed amorphous fuel materials, that are subsequently ignited by the strong flux of fusion products like for instance alpha particles in the case of pBi" fusion, that come from the convertor. Second, the invention can serve as a nanoscopic integrated particle accelerator, producing protons, neutrons, alpha particles, and electrons with high fluxes, high powers, and high kinetic energies. Third, the nano-structured material can be used as a source for novel diagnostics and strong x-ray generation.

LIST OF REFERENCE SIGNS

10 target 12 nano-rod 14 common base 15 surface 16 top base 18 cross section of thermonuclear pB fusion reaction 20 cross section of thermonuclear DT fusion reaction 22 cross section of non-thermal pB fusion reaction 24 cross section of non-thermal pB fusion reaction for screening energy Es=O MeV 26 cross section of non-thermal pB fusion reaction for screening energy Es=l MeV 28 cross section of non-thermal pB fusion reaction for screening energy 8s= 3 MeV A rod-diameter B first rod-distance B' second rod-distance C rod-length D first target side length D' second target side length X first direction Y second direction

Claims (32)

1. A method for producing neutronic and aneutronic fusion energy by a neutronic and/or aneutronic nuclear fusion reaction, or for generating secular electric and magnetic fields, the method comprising irradiating a target (10) of nano-structured material with a laser pulse, wherein the laser pulse has a laser carrier frequency o, a pulse duration, and a spot size, and wherein the laser pulse is at least partially absorbed by the nano-structured material, wherein the target (10) comprises a surface (15) with a plurality of nano-rods (12) extending from the surface (15).

2. The method according to claim 1, wherein a portion or all of the nano-rods (12) of the target (10) are cylindrically or conically shaped while having a circular, elliptical, rectangular, or polygonal base, each having a medium rod diameter (A) and a rod-length (C).

3. The method according to claim 1 or 2, wherein the nano rods (12) of the target (10) are regularly arranged along one first direction (X), which is a linear direction or a circular direction, so that adjacent nano-rods (12) are spaced along the first direction (X) by a first rod-distance (B).

4. The method according to claim 1 or 2, wherein the nano rods (12) of the target (10) are regularly arranged along two perpendicular directions (X, Y) so that adjacent nano-rods (12) are spaced along a first direction (X) of the two perpendicular directions by a first rod-distance (B) and along a second direction (Y) of the two perpendicular directions (X, Y) by a second rod-distance (B').

5. The method according to claim 3 or 4, wherein the first rod-distance (B), and preferably also the second rod-distance (B'), is greater or equals JrcR 2 nie 2 /omeW 2 ,

wherein R is the radius of the rod, ni is the average ion density, e is the charge of an electron, 8o is the electric field constant, me is the electron mass, and o is the laser carrier frequency.

6. The method according to any one of claims 1 to 5, wherein the nano-structured material comprises boron and/or boron nitride and/or hydrogen containing material, in particular wherein the nano-structured material also comprises DT inside and between the nano-rods, in particular wherein the nano-structured material is surrounded by non-nanostructured DT compound, in particular wherein the nano-structured material and a space in between and surrounding the nano-rods comprises a neutronic fuel and/or an aneutronic fuel.

7. The method according to any one of claims 1 to 6, wherein the nano-structured material comprises amorphous material or layers of different materials, in particular including a material for inducing ultraviolet light radiation.

8. The method according to any one of claims 1 to 7, wherein the nano-structured material comprises nano-rods (12) of alternating materials, in particular containing protons, boron, deuterium, tritium and gold, respectively.

9. The method according to any one of claims 1 to 8, wherein the laser pulse is a femtosecond optical to VUV laser pulse.

10. The method according to any one of claims 1 to 9, wherein the fusion reaction comprises p+B" -> 3ax + 8.9 MeV.

11. The method according to any one of claims 1 to 9, wherein the secular magnetic field has a magnetic B-field strength of 1 MT to 100 MT.

12. A system for triggering a neutronic and/or an aneutronic nuclear fusion reaction, or for producing a secular electric and magnetic field, the system comprising a target (10) of a nano-structured material and a laser device for emitting a laser pulse, wherein the laser pulse has a laser carrier frequency o, a pulse duration, and a spot size, and can at least partially be absorbed by the nano-structured material, wherein the target (10) comprises a surface (15) with a plurality of nano-rods (12) extending from the surface (15).

13. The system according to claim 12, wherein a portion or all of the nano-rods (12) of the target (10) are cylindrically or conically shaped while having a circular, elliptical, rectangular, or polygonal base each having a medium rod diameter (A) and a rod-length (C).

14. The system according to claim 12 or 13, wherein the nano rods (12) of the target (10) are regularly arranged along one first direction (X), which is a linear direction or a circular direction, so that adjacent nano-rods (12) are spaced along the first direction (X) by a first rod-distance (B).

15. The system according to claim 12 or 13, wherein the nano rods (12) of the target (10) are regularly arranged along two perpendicular directions (X, Y) so that adjacent nano-rods (12) are spaced along a first direction (X) of the two perpendicular directions by a first rod-distance (B) and along a second direction (Y) of the two perpendicular directions (X, Y) by a second rod-distance (B').

16. The system according to claim 14 or 15, wherein the first rod-distance (B), and preferably also the second rod-distance (B'), is greater or equals rR 2 nie 2 /EomedW, wherein R is the radius of the rod, ni is the average ion density, e is the charge of an electron, 8o is the electric field constant, me is the electron mass, and o is the laser carrier frequency.

17. The system according to any one of claims 12 to 16, wherein the nano-structured material comprises boron, and/or boron nitride and/or hydrogen containing material, in particular wherein the nano-structured material also comprises DT inside and between the nano-rods, in particular wherein the nano-structured material is surrounded by non-nanostructured DT compound, in particular wherein the nano-structured material and a space in and between the nano-rods comprises a neutronic fuel and/or an aneutronic fuel.

18. The system according to any one of claims 12 to 17, wherein the nano-structured material comprises amorphous material or layers of different materials, in particular including a material for inducing ultraviolet light radiation.

19. The system according to any one of claims 12 to 18, wherein the nano-structured material comprises nano-rods (12) of alternating materials, in particular comprising protons, boron, deuterium, tritium, and gold, respectively.

20. The system according to any one of claims 12 to 19, wherein the laser pulse is a femtosecond optical to VUV laser pulse.

21. The system according to any one of claims 12 to 20, wherein the fusion reaction comprises p+B" -> 3ax + 8.9 MeV.

22. The system according to any one of claims 12 to 20, wherein the secular magnetic field has a magnetic B-field strength of 1 MT to 100 MT.

23. A target (10) of a nano-structured material for absorbing a laser pulse having a laser carrier frequency o, a pulse duration, and a spot size for triggering fusion reactions or for producing a secular electric and magnetic field, wherein the target (10) comprises a surface (15) with a plurality of nano-rods (12) extending from the surface (15).

24. The target (10) according to claim 23, wherein a portion or all of the nano-rods (12) of the target (10) are cylindrically or conically shaped while having a circular, elliptical, rectangular, or polygonal base each having a medium rod-diameter (A) and a rod-length (C).

25. The target (10) according to claim 23 or 24, wherein the nano-rods (12) of the target (10) are regularly arranged along one first direction (X), which is a linear direction or a circular direction, so that adjacent nano-rods (12) are spaced along the first direction (X) by a first rod-distance (B).

26. The target (10) according to claim 23 or 24, wherein the nano-rods (12) of the target (10) are regularly arranged along two perpendicular directions (X, Y) so that adjacent nano-rods (12) are spaced along a first direction (X) of the two perpendicular directions by a first rod-distance (B) and along a second direction (Y) of the two perpendicular directions (X, Y) by a second rod-distance (B').

27. The target (10) according to claim 25 or 26, wherein the first rod-distance (B), and preferably also the second rod 2 distance (B'), is greater or equals JjR nie 2 /EomeW 2 , wherein R is the radius of the rod, ni is the average ion density, e is the charge of an electron, 8o is the electric field constant, me is the electron mass, and o is the laser carrier frequency.

28. The target (10) according to any one of claims 23 to 27, wherein the nano-structured material comprises boron and/or boron nitride and/or hydrogen containing material, in particular wherein the nano-structured material also comprises DT inside and between the nano-rods, in particular wherein the nano-structured material is surrounded by non-nanostructured DT compound, in particular wherein the nano-structured material and a space in and between the nano-rods comprises a neutronic fuel and/or an aneutronic fuel.

29. The target (10) according to any one of claims 23 to 28, wherein the nano-structured material comprises amorphous material or layers of different materials, in particular including a material for inducing ultraviolet light radiation.

30. The target (10) according to any one of claims 23 to 29, wherein the nano-structured material comprises nano-rods (12) of alternating materials, in particular containing protons, boron, deuterium, tritium and gold, respectively.

31. The target (10) according to any one of claims 23 to 30, wherein the fusion reaction comprises p+B"1 -> 3ax + 8.9 MeV.

32. The target (10) according to any one of claims 23 to 30, wherein the secular magnetic field has a magnetic B-field strength of 1 MT to 100 MT.