Ultrahigh Acceleration of Plasma Blocks by Nonlinear Forces for Side-On Laser Ignition of Solid Density Fusion Fuel

A fundamental difference of very high intensity laser interaction with plasmas from solid targets appears with lasing at picosecond (ps) pulse durations in contrast to pulses of nanosec- onds (ns). This can be seen from the more than 10,000 times higher acceleration with ps pulse du- rations than with thermal pressure determined interaction. A ps pulse duration produces instantly acting high-efficiency nonlinear (ponderomotive) electrodynamic force dominated acceleration in contrast to heating with longer pulses. The ps pulses accelerate high-density plasma blocks. This can be used by a new scheme of side-on driven laser fusion with generating a flame ignition in uncompressed fusion fuel of solid density resulting in a reaction velocity of more than 2000 km/s for DT.     

Study of the Ignition Requirements and Burn Characteristics of Aneutronic Fusion in Degenerate Plasma

The reactions such as; D?+?³ He and p?+?¹¹B are aneutronic fusion reactions that, in characteristic conditions create degenerate plasma. The electronic stopping power of degenerate plasma is smaller than the classical plasma, because some transitions between the electron states are forbidden. The equations that predict the behavior of these plasmas are different from the classical ones, and this is the main factor in decreasing the ignition temperature of the plasma. In this research, the nuclear fusion in deuterium–helium with a small seeding born, D/³ He/¹¹B, is considered using a time dependent model based on nuclear reactions, including ion-electron collisions, Bremsstrahlung losses and mechanical expansion. The effect of the initial born concentration on ignition temperature and energy gain is analyzed with calculating the effect of radiation loss in ignition temperature.     

Study of thorium–uranium based molten salt blanket in a fusion–fission hybrid reactor

Not only solid fuels, but also liquid fuels can be used for the fusion–fission symbiotic reactor blanket. The operational record of the molten salt reactor with F–Li–Be was very successful, so the F–Li–Be blanket was chosen for research. The molten salt has several features which are suited for the fusion–fission applications.The fuel material uranium and thorium were dissolved in the F–Li–Be molten salt. A combined program, COUPLE, was used for neutronics analysis of the molten salt blanket. Several cases have been calculated and compared. Not only the influence of the different fuels have been studied, but also the thickness of the molten salt, and the concentration of the ⁶Li in the molten salt.Preliminary studies indicate that when thorium–uranium–plutonium fuels were added into a F–Li–Be molten salt blanket and with a component of 71% LiF–2% BeF₂–13.5% ThF₄–8.5% UF₄–5% PuF₃, and also with the molten salt thickness of 40 cm and natural concentration of ⁶Li, the appropriate blanket energy multiplication factor and TBR can be obtained.The result shows that thorium–uranium molten salt can be used in the blanket of a fusion–fission symbiotic reactor. The research on the molten salt blanket must be valuable for the design of fusion–fission symbiotic reactor.     

A Review of Confinement Requirements for Advanced Fuels

The energy confinement requirements for burning D-³He, D-D, or P-¹¹B are reviewed, with particular attention to the effects of helium ash accumulation. It is concluded that the DT cycle will lead to the more compact and economic fusion power reactor. The substantially less demanding requirements for ignition in DT (the n_{e E} T required for ignition in DT is smaller than that of the nearest advanced fuel, D-³He, by a factor of 50) will allow ignition, or significant fusion gain, in a smaller device; while the higher fusion power density (the fusion power density in DT is higher than that of D-³He by a factor of 100 at the same plasma pressure) allows for a more compact and economic device at fixed fusion power.     

Preliminary study of high neutron flux fusion heating

A heating scheme for nuclear fusion is proposed based on the availability of a high flux, low energy neutron source. The heat is derived in the reaction ⁶Li (n, T) ⁴He resulting from the incidence of a low energy neutron beam on a sample of ⁶Li D. The energy release per reaction, Q = 4.6 MeV, is converted through electron Coulomb collisions thereby quickly dissociating the solid sample to the plasma state. For 10⁻³ eV neutrons it is estimated that this dissociation occurs in 7 ms for an incident flux of 10¹⁷ cm⁻² · s⁻¹. The possibility of further driving the heated fuel to fusion is also discussed.     

Fusion Generated Fast Particles by Laser Impact on Ultra-Dense Deuterium: Rapid Variation with Laser Intensity

Nuclear fusion D+D processes are studied by nanosecond pulsed laser interaction with ultra-dense deuterium. This material has a density of 10²⁹ cm^?3 as shown in several previous publications. Laser power is <2 W (0.2 J pulses) and laser intensity is <10¹⁴ W cm^?2 in the 5–10 μm wide beam waist. Particle detection by time-of-flight energy analysis with plastic scintillators is used. Metal foils in the particle flux to the detector remove slow ions, and make it possible to convert and count particles with energy well above 1 MeV. The variation of the signal of MeV particles from D+D fusion is measured as a function of laser power. At relatively weak laser-emitter interaction, the particle signal from the laser focus varies as the square of the laser power. This indicates collisions in the ultra-dense deuterium of two fast deuterons released by Coulomb explosions. During experiments with stronger laser-emitter interaction, the signal varies approximately as the sixth power of the laser power, indicating a plasma process. At least 2 × 10⁶ particles are created by each laser pulse at the maximum intensity used. Our results indicate break-even in fusion at a laser pulse energy of 1 J with the same focusing, in approximate agreement with theoretical results for ignition conditions in ultra-dense deuterium. Radiation loss at high temperature will however require higher laser energy at break-even.     

Scattering of 14.1 MeV Neutrons by 6Li, 7Li, 9Be, 10B and 11B

Using a time-of-flight spectrometer, the differential cross sections were measured for the elastic and inelastic scattering of 14.1 MeV neutrons by ⁶Li, ⁷Li, ⁹Be, ¹⁰B and ¹¹B. In the case of elastic scattering by ⁷Li and ¹⁰B, correction was applied to subtract the contribution of inelastic scattering from the unresolved first excited state, after which, the elastic scattering data were compared with predictions based on the optical model. The potential parameters derived with a seven-parameter search yielded angular distributions agreeing with the present experimental data. The expressions for these parameters are presented as a function of mass number.

The experimental data on inelastic scattering were analyzed with the distorted wave Born approximation. The deformation parameters were estimated to be nearly equal to or larger than unity for these nuclei.     

Controlling Energy Flow and Loss in p<Superscript>6</Superscript>Li Fusion Plasma

The proton-Lithium-6 (p⁶Li) fusion reaction is significant because it produces energy through charged particles. By selecting this reaction, the problems of tritium processes and 14 MeV neutron fluxes will be reduced. One of the main concerns for p⁶Li plasma is the control of energy flow and loss that occur in fusion reactor. The calculations of energy balance are essential for investigating the energy flow and loss in p⁶Li plasma. It has a fundamental role for describing the material conditions in this plasma. Energy production must compete with inevitable losses in plasma. The losses perform a principal role in determining the operating temperature of thermonuclear plasma. Some losses of energy can be minimized by the suitable selection of designing parameters while some are intrinsic in reactant system. Calculations of energy flow and loss suggest an operating point at 800 keV for p⁶Li plasma. The effect of electron temperature on ion–electron energy transfer and the bremsstrahlung losses is reviewed. It is indicated that the bremsstrahlung radiation losses resulting from large mean electron energies are a serious difficulty for p⁶Li fusion reactor. It would be highly desirable to reduce the electron temperature below their normal equilibrium values. If the ion–electron energy transfer be reduced from the classical value, the electron temperature and thus bremsstrahlung radiation losses would be reduced substantially and as a result the performance of a p⁶Li fusion reactor would be improved significantly. Meanwhile, the bremsstrahlung radiation losses can be minimized with suitable mixture for p⁶Li plasma in a fusion reactor.     

Stopping force and straggling of 0.6–4.7 MeV H,He and Li ions in the polyhydroxybutyrate foil

Stopping force and straggling of 0.6–3.5 MeV ¹H ions, 2.0–4.7 MeV ⁴He ions and 1.4–4.4 MeV ⁷Li ions in the polyhydroxybutyrate (PHB) foil were measured by means of a transmission technique. The measured stopping forces are in well agreement with the SRIM 2008 calculation and the ICRU Report tables, except for the lower energy region. The obtained energy loss straggling deviates from the Bohr’s value by as much as 23.6% for the energies under study. The validity of the Bragg’s rule has also been demonstrated in the stopping force and straggling for ¹H, ⁴He and ⁷Li ions in the PHB foil.     

Measurement of thick-target gamma-ray production yields of the 7Li(p,p′)7Li and 7Li(p, γ)8Be reactions in the near-threshold energy region for the 7Li(p,n)7Be reaction

The gamma-ray production reactions, ⁷Li(p, p′)⁷Li and ⁷Li(p, γ)⁸Be, occur along with the neutron production reaction ⁷Li(p, n)⁷Be in a p-Li neutron source. These gamma-ray production reactions contribute to a patient's absorbed dose in boron neutron capture therapy (BNCT) when using a neutron beam from the ⁷Li(p, n)⁷Be reaction. The present work experimentally determined the thick-target gamma-ray production yields of the ⁷Li(p, p′)⁷Li and ⁷Li(p, γ)⁸Be reactions at incident proton energies of 1.670 and 1.870 MeV. The present results were compared with previous measurements. The gamma-ray production yield of ⁷Li(p, p′)⁷Li was measured to be 30%–50% smaller than as reported by previous studies. For the ⁷Li(p, γ)⁸Be reaction, the present thick-target yield is 30% smaller than one estimated from cross-section data measured in previous studies. The results must be included in future dose evaluation for BNCT using a p–Li neutron source.     

Effects of lithium burn-up on TBR in DEMO reactor SlimCS

Lithium in a breeding blanket is burned up through neutron nuclear reactions in fusion DEMO reactors. Effects of decrease of solid breeder materials due to lithium burn-up on tritium breeding ratio (TBR) are not systematically calculated in the past. For the SlimCS blanket design, TBR is calculated taking into account the lithium burn-ups by one dimensional Sn radiation transport calculation code ANISN in this study. The ⁶Li burn-ups are 8–79% after 10-year operation. TBR due to ⁶Li decreases to 40% of the initial one in some layer, while it increases in some layers. The TBR integrated over all the blanket decreases to around 96% of the initial one. The study makes it clear that the reduction of the TBR due to the lithium burn-up is not so large.     

Implanted boron profiles in silicon

¹⁰B and ¹¹B implants into amorphous Si, with energies ranging from 50 keV to 2 MeV and 10 keV to 1 MeV respectively, were profiled by the nuclear reactions ¹⁰B(n, α)⁷Li and ¹¹B(p, γ)¹²C. The projected range R_p and straggling ΔR_p agree within a few percent with recent calculations due to Ziegler, Biersack and Littmark (ZBL). These results show that the ZBL electronic stopping power is adequate to reproduce range parameters resulting from MeV implantations.     

Electronic stopping power for 7Li, 11B, 12C, 14N and 16O at energies 0.4 to 2.1 MeV/nucleon in Ta and Au,and for 12C at energies 0.4, 0.8 and 1.4 MeV/nucleon in 18 elemental solids

Stopping powers have been measured for 0.4 to 2.1 MeV/nucleon beams of ⁷Li, ¹¹B, ¹²C, ¹⁴N and ¹⁶O in Au and of ⁷Li, ¹²C and ¹⁴N in Ta. The results are compared with the predictions of an empirical model. By application of the Doppler-shift attenuation method, the measured electronic stopping powers for ¹²C in Ta and Au are used to deduce the mean lifetime 58 ± 5 fs for the 4.439 MeV level in ¹²C. Deviations of the electronic stopping power from the predictions of the empirical model have been studied for ¹²C at energies 0.4, 0.8 and 1.4 MeV/nucleon in 18 Z = 14–82 elemental solids by application of the Doppler-shift attenuation method and the lifetime value of the 4.439 MeV level.     

Criteria for neutron fusion

The reaction ⁶Li(n, α) T is studied as a possible mechanism for driving a fuel pellet of ⁶LiD to fusion temperatures through bombardment with low energy neutrons. The criterion Jt 10²³ for fusion by this scheme is derived where J is incident neutron current (cm⁻² · s⁻¹) and t is time (s). The possibility of fusion through implosion is also examined. Ablation pressure exerted by products of the Li(n, α) T reaction is found to be independent of the cross section of this reaction. The index of refraction of neutrons in the neV to eV range indicates total absorption on a sample of ⁶Li.     

Investigation of excited states of 7Li by means of thermal neutron capture

Capture of unpolarized thermal neutrons has been used to gain information on the ⁷Li level scheme. Two reactions have been investigated. Firstly, a study has been made of the decay scheme of ⁷Li through the ⁶Li(n, γ)⁷Li reaction. Three γ-transitions were observed and placed. The binding energy value of this reaction turned out to be Q = 7251.02(9) keV. Secondly, investigation of radiation from excited Li produced by the ¹⁰B(n,α)⁷Li reaction, made it possible to deduce a more precise lifetime of the 478 keV level of ⁷Li; namely τ = 102 ± 5 fs. This value is compared with existing data; it agrees with previous less accurate independent values and an average could be made in order to reduce the error further. As a byproduct the analysis of the peak shape of the 478 keV transition offered a new method for estimating the size of boron grains embedded in other materials.     

Fusion neutron induced radioactive emissions from surfaces

Neutron induced direct nuclear recoil sputtering ratios have been measured for a variety of 14.8 MeV (d, t) neutron induced reactions in Nb, Mo, V and 316 SS. Absolute recoil sputtering ratios for forward and backward sputtering are reported. Forward sputtering ratios are typically in the range of 10^?9–10^?7 recoil atoms per (d, t) neutron while backward sputtering ratios are usually several orders of magnitude lower. Some of the implications of radioactive particle ejection in the first wall region of fusion reactors are discussed. It is shown that radioactivity ejected into the fusion reactor coolant channels by direct nuclear recoil and by lattice dynamic neutron sputtering, may have a significant effect on the design and maintenance of fusion reactors.     

Development of technology for recovering lithium from seawater by electrodialysis using ionic liquid membrane

Tritium fuel for fusion reactors is produced by reacting lithium-6 (⁶Li) with neutrons in tritium breeders. This study demonstrates a method for Li recovery from seawater, wherein Li does not permeate from the anode side to the cathode side through an ionic liquid N,N,N-trimethyl-N-propylammonium–bis(trifluoromethanesulfonyl) imide. Almost all Li ions remain on the anode side (seawater), whereas the other ions in the seawater permeate to the cathode side through the ionic liquid with an applied electric voltage of 2–3 V.     

Confirmation of Track Formation in Cellulose Nitrate Detector by Lithium Particles from 10B(n, α)7Li Reaction

Two experiments were performed, which confirmed that the lithium particles produced by the ¹⁰B(n, α)⁷Li reactions form etchable latent tracks in cellulose nitrate resin. The first experiment was made on a pair of resin detector plates sandwiching between them a boron-bearing layer. Upon irradiation and etching, the tracks appearing on the two plates were found to constitute matching pairs, some of which appeared to be shorter than others, suggesting their correspondence respectively to the ⁷Li and α particles generated by the ¹⁰B(n, α)⁷Li reaction. This surmise was further confirmed by a second experiment, in which the pairing of etch-pits was examined between the two faces of a film detector of thickness below the range of a but above that of ⁷Li particles. The ratio between paired and single etch-pits counted in a unit area of the two faces of film after irradiation and etching proved to be quite close to the value derived by calculation based on the assumption that ⁷Li as well as α particles leave etchable tracks on the resin with 100% efficiency, whereas the observed ratio distinctly differed from the corresponding calculation undertaken assuming that α particles alone contributed to the track formation.

This finding is consistent with the estimations of etchable track formability obtained by applying criteria given in three independent theoretical studies found in published literature.     

Nuclear Spin-Polarized Proton and 11B Fuel for Fusion Reactors: Advantages of Double Polarization in the 11 B(p, α)8 Be * Fusion Reaction

A previously developed general formalism has been used to calculate the yield and the angular distributions of outgoing particles for fusion reactions when the projectile and target nuclei are both polarized. The case of D–³He is compared with earlier calculations and experiments and a new study for the case of fully polarized protons and ¹¹B in the ¹¹ B(p, α)⁸ Be ^* reaction is presented. The conditions which produce a gain in the yield and the angular distributions which affect the production of fusion energy are presented.