Fusion Yield Research Articles

Dt nuclear fusion within a single Coulomb exploding composite nanodroplet

We present a computational study of dt fusion driven by Coulomb explosion within a single, large, heteronuclear two-component D2/T2 nanodroplet, originating from kinematic overrun effects between deuterons and tritons. Scaled electron and ion dynamics simulations have been used to explore the size dependence and the isotopic composition dependence of the intra-nanodroplet (INTRA) dt fusion yield in a composite D2n-2kT2k nanodroplet, initially consisting of an inner sphere of D2 molecules surrounded by an outer sphere of T2 molecules (n = 1.4× 108–2.0×109, k/n = 0.10–0.60, and initial radii R0 = 1100–2700 A) driven by a single, ultraintense, near-infrared, Gaussian laser pulse (peak intensity 1020 W cm-2, pulse length 25 fs). INTRA dt fusion in D2n-2kT2k nanodroplets with neutron yields of 30–90 (per nanodroplet, per laser pulse) were attained in the size domain R0 = 2000–2700 A with the optimal composition in the range of k/n = 0.2–0.4. INTRA yields in D2n-2kT2k nanodroplets are similar (within 20–40%) to those in initially homogeneous (DT)n nanodroplets of the same size. These INTRA yields are sufficiently large to warrant experimental observation in a single nanodroplet. The INTRA dt fusion can be distinguished from the inter-nanodroplet dt fusion reaction, which occurs inside and outside the macroscopic plasma filament, by the nanodroplet size dependence of the yield and by the different energies of the neutrons produced in these two channels.

Conceptual design of fast-ignition laser fusion reactor FALCON-D

A new conceptual design of the laser fusion power plant FALCON-D (Fast-ignition Advanced Laser fusion reactor CONcept with a Dry wall chamber) has been proposed. The fast-ignition method can achieve sufficient fusion gain for a commercial operation (∼100) with about 10 times smaller fusion yield than the conventional central ignition method. FALCON-D makes full use of this property and aims at designing with a compact dry wall chamber (5–6 m radius). 1D/2D simulations by hydrodynamic codes showed a possibility of achieving sufficient gain with a laser energy of 400 kJ, i.e. a 40 MJ target yield. The design feasibility of the compact dry wall chamber and the solid breeder blanket system was shown through thermomechanical analysis of the dry wall and neutronics analysis of the blanket system. Moderate electric output (∼400 MWe) can be achieved with a high repetition (30 Hz) laser. This dry wall reactor concept not only reduces several difficulties associated with a liquid wall system but also enables a simple cask maintenance method for the replacement of the blanket system, which can shorten the maintenance period. The basic idea of the maintenance method for the final optics system has also been proposed. Some critical R&D issues required for this design are also discussed.

Parameter optimization for fusion neutron yield from deuterium cluster explosion driven by intense femtosecond laser pulses

A modified model based on the Coulomb explosion model [H. Li et al., Phys. Rev. A 74, 023201 (2006)] is proposed to roughly estimate the nuclear fusion yields produced in the Coulomb explosion of deuterium cluster jet with irradiation of the intense laser pulses by taking the attenuation of laser energy absorbed by the clusters with a logarithmic-normal size distribution into account. The neutron yield generated inside the heated plasma filament, as the sum of the intercluster fusion yield and beam-target fusion yield, is calculated as a function of laser-cluster parameters such as the cluster size, the laser energy, and the focus spot radius and position. Only if these parameters match with each other can the neutron yield or the neutron conversion efficiency be maximized. The rough qualitative comparison about the variation tendency of fusion yield with laser-cluster parameters is made between our simulations and the reported measurements.

Reaching High-Yield Fusion with a Slow Plasma Liner Compressing a Magnetized Target

Dynamics of the compression of a magnetized plasma target by a heavy liner made of partially ionized high-Z material is discussed. A soft-landing (shockless) mode of the liner deceleration is analyzed. Conclusion is drawn that such mode is possible for the liners whose thickness at the time of the first contact with the target is smaller than ~10% of the initial (uncompressed) target radius. A combination of the plasma liner with one or two glide cones allows for direct access to the area near the center of the reactor chamber. One can then generate a plasma target inside the plasma liner at the optimum time. The other advantage of the glide cones is that they can be used to deliver additional fuel to the center of the target near the point of maximum compression and thereby increase the fusion yield.

Measurement of the 3He Permeability of DT-Filled Fused Silica Inertial Confinement Fusion (ICF) Targets to Study the Effects of 3He on Neutron Emission During Implosion

A set of laser implosion experiments were conducted at the OMEGA laser at the University of Rochester, Laboratory for Laser Energetics (LLE) to study the effect of 3He concentration in DT-filled target shells on fusion yield in ICF implosions.. Eleven laser fusion shells consisting of 1100-μm diameter, hollow, fused silica spheres with 4.6 to 4.7-μm-thick walls were loaded with 520 kPa of deuterium-tritium (DT) and then with 3He (101.3 or 520 kPa). The 3He permeabilities of the shells were determined by measuring the pressure rate of rise into a system with known volume. A mathematical method was developed that relied on the experimental fill pressure and time, and the rate of rise data to solve differential equations using MathCAD to simultaneously calculate 3He permeability and initial 3He partial pressure inside the shell. Because of the high permeation rate for 3He out of the shells compared to that for DT gas, shells had to be recharged with 3He immediately before being laser imploded or “shot” at LLE. The 3He partial pressure in each individual shell at shot time was calculated from the measured 3He permeability. Two different partial pressures of 3He inside the shell were shown to reduce neutron and gamma yields during implosion.

Fusion–fission hybrids for nuclear waste transmutation: A synergistic step between Gen-IV fission and fusion reactors

Energy demand and GDP per capita are strongly correlated, while public concern over the role of energy in climate change is growing. Nuclear power plants produce 16% of world electricity demands without greenhouse gases. Generation-IV advanced nuclear energy systems are being designed to be safe and economical. Minimizing the handling and storage of nuclear waste is important. NIF and ITER are bringing sustainable fusion energy closer, but a significant gap in fusion technology development remains. Fusion–fission hybrids could be a synergistic step to a pure fusion economy and act as a technology bridge. We discuss how a pulsed power-driven Z-pinch hybrid system producing only 20 MW of fusion yield can drive a sub-critical transuranic blanket that transmutes 1280 kg of actinide wastes per year and produces 3000 MW. These results are applicable to other inertial and magnetic fusion energy systems. A hybrid system could be introduced somewhat sooner because of the modest fusion yield requirements and can provide both a safe alternative to fast reactors for nuclear waste transmutation and a maturation path for fusion technology. The development and demonstration of advanced materials that withstand high-temperature, high-irradiation environments is a fundamental technology issue that is common to both fusion–fission hybrids and Generation-IV reactors.

Predictions of H-mode performance in ITER

Time-dependent integrated predictive modelling is carried out using the PTRANSP code to predict fusion power and parameters such as alpha particle density and pressure in ITER H-mode plasmas. Auxiliary heating by negative ion neutral beam injection and ion-cyclotron heating of He3 minority ions are modelled, and the GLF23 transport model is used in the prediction of the evolution of plasma temperature profiles. Effects of beam steering, beam torque, plasma rotation, beam current drive, pedestal temperatures, sawtooth oscillations, magnetic diffusion and accumulation of He ash are treated self-consistently. Variations in assumptions associated with physics uncertainties for standard base-line DT H-mode plasmas (with Ip = 15 MA, BTF = 5.3 T and Greenwald fraction = 0.86) lead to a range of predictions for DT fusion power PDT and quasi-steady state fusion QDT (≡PDT/Paux). Typical predictions assuming Paux = 50–53 MW yield PDT = 250–720 MW and QDT = 5–14. In some cases where Paux is ramped down or shut off after initial flat-top conditions, quasi-steady QDT can be considerably higher, even infinite. Adverse physics assumptions such as the existence of an inward pinch of the helium ash and an ash recycling coefficient approaching unity lead to very low values for PDT. Alternative scenarios with different heating and reduced performance regimes are also considered including plasmas with only H or D isotopes, DT plasmas with toroidal field reduced 10% or 20% and discharges with reduced beam voltage. In full-performance D-only discharges, tritium burn up is predicted to generate central tritium densities up to 1016 m−3 and DT neutron rates up to 5 × 1016 s−1, compared with the DD neutron rates of 6 × 1017 s−1. Predictions with the toroidal field reduced 10% or 20% below the planned 5.3 T and keeping the same q98, Greenwald fraction and βn indicate that the fusion yield PDT and QDT will be lower by about a factor of two (scaling as B3.5).

Conceptual design of a fast-ignition laser fusion reactor based on a dry wall chamber

The fast ignition is quite attractive for a compact laser fusion reactor, because a sufficiently high pellet gain is available with a small input energy. We designed an inertial fusion reactor based on Fast-ignition Advanced Laser fusion reactor CONcept, called FALCON-D, where a dry wall is employed for a chamber wall. A simple point model shows that the pellet gain G∼100 is available with laser energies of 350kJ for implosion, 50kJ for heating. This results in the fusion yield of 40 MJ in one shot. By increasing the repetition rate up to 30 Hz, the fusion power of 1.2 GWth becomes available. Plant system analysis shows the net electric power to be about 0.4 GWe In the fast ignition it is available to employ a low aspect ratio pellet, which is favorable for the stability during the implosion phase. Here the pellet aspect ratio is reduced to be 2 ∼ 4, and the optimization of the pulse shape for the implosion laser are carried out by using the 1-D hydrodynamic simulation code ILESTA-1D. A ferritic steel with a tungsten armour is employed for the chamber wall. The feasibility of this dry wall concept is studied from various engineering aspects such as surface melting, physical and chemical sputtering, blistering and exfoliation by helium retention, and thermo-mechanical fatigue, and it is found that blistering and exfoliation due to the helium retention and fatigue failure due to cyclic thermal load are major concerns. The cost analysis shows that the construction cost is moderate but the cost of electricity is slightly expensive.

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subclusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the case of homonuclear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuclear clusters with larger sizes are required to achieve a greater neutron yield.

Initial experiments on the shock-ignition inertial confinement fusion concept

Shock ignition is a two-step inertial confinement fusion concept where a strong shock wave is launched at the end of the laser pulse to ignite the compressed core of a low-velocity implosion. Initial shock-ignition technique experiments were performed at the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using 40-μm-thick, 0.9-mm-diam, warm surrogate plastic shells filled with deuterium gas. The experiments showed a significant improvement in the performance of low-adiabat, low-velocity implosions compared to conventional “hot-spot” implosions. High areal densities with average values exceeding ∼0.2g∕cm2 and peak areal densities above 0.3g∕cm2 were measured, which is in good agreement with one-dimensional hydrodynamical simulation predictions. Shock-ignition technique implosions with cryogenic deuterium and deuterium-tritium ice shells produced areal densities close to the 1D prediction and achieved up to 12% of the predicted 1D fusion yield.

Prediction of Net Energy Gain in Deuterium-Beam Interactions with an Inertially Confined Plasma

It is shown that deuteron beams incident on compressed, tritium-based plasma targets can undergo beam-fusion reactions at a rate greater than Coulomb scattering for a wide range of beam energies and target temperatures. As a result, energy gains of about 5 are possible. The analysis is carried out by treating the beam ions, target ions, and the electrons as separate fluids. Essential to the attainment of high gain is the inclusion of the contribution to the fusion yield from deuterons that gain scattered energy at the expense of directed energy. The results are confirmed by Monte Carlo simulations equivalent to a Fokker-Planck treatment.

Fill-Tube-Induced Mass Perturbations on X-Ray-Driven, Ignition-Scale, Inertial-Confinement-Fusion Capsule Shells and the Implications for Ignition Experiments

On the first inertial-confinement-fusion ignition facility, the target capsule will be DT filled through a long, narrow tube inserted into the shell. microg-scale shell perturbations Delta m' arising from multiple, 10-50 microm-diameter, hollow SiO2 tubes on x-ray-driven, ignition-scale, 1-mg capsules have been measured on a subignition device. Simulations compare well with observation, whence it is corroborated that Delta m' arises from early x-ray shadowing by the tube rather than tube mass coupling to the shell, and inferred that 10-20 microm tubes will negligibly affect fusion yield on a full-ignition facility.

Liner-Driven Pulsed Magnetized Target Fusion Power Plant

Magnetized Target Fusion (MTF) occupies an intermediate region between conventional Magnetic Fusion Energy (MFE) and Inertial Fusion Energy (IFE). A particular approach, extrapolated from the ongoing FRX-L experimental effort, involves the generation of a Field Reversed Configuration (FRC) suitable for translation along an axial magnetic field and cylindricalliner (i.e., converging flux conserver) implosion and pdV heating to burn conditions. The fusion gain, Q (ratio of DT fusion yield to the sum of initial liner kinetic energy plus plasma formation energy), sets the pulsed power-plant duty cycle. The modular power-plant embodiment recalls the Fast Liner Reactor (FLR) and shares stand-off and blast-mitigation features of the recent characterization of the Z-IFE. Recycle and economic remanufacture of destroyed front-end apparatus must be performed under tight cost constraints. A tin-lithium alloy is being investigated for multifunctional suitability as the liner, transmission-line, and primary coolant/breeder material. Key performance drivers are described.

Two overrun phenomena and their effects on fusion yield in the Coulomb explosion of heteronuclear clusters

Two overrun effects in the Coulomb explosion dynamics of heteronuclear clusters have been investigated theoretically by the use of a simplified electrostatic model. When the charge-to-mass ratio of light ions is higher than that of heavy ions, the light ions can overtake the heavy ions inside the cluster and acquire a higher kinetic energy. Further, if the charge density of the heavy ions is twice as high as that of the light ions, i.e. a proposed competitive parameter ζ = ρBqB/ρAqA > 2, the inner light ions can overtake those light ions on the surface of the cluster and form a shock shell during the explosion, which might drive the intracluster collision and fusion of the light ions. Different regimes of nuclear fusion are discussed and the corresponding neutron yields are estimated. Our analysis indicates that the probability of intracluster fusion is quite low even if deuterated heteronuclear clusters such as (DI)n with large size and high competitive parameter are employed. However, heteronuclear clusters are still a better candidate compared with homonuclear clusters for enhancing the total intercluster fusion yield because both a higher energy region and a higher proportion of deuterons distributing in the energy region can be created in the deuterated heteronuclear clusters.

Prospects for steady-state scenarios on JET

In the 2006 experimental campaign, progress has been made on JET to operate non-inductive scenarios at higher applied powers (31 MW) and density (nl ∼ 4 × 1019 m−3), with ITER-relevant safety factor (q95 ∼ 5) and plasma shaping, taking advantage of the new divertor capabilities. The extrapolation of the performance using transport modelling benchmarked on the experimental database indicates that the foreseen power upgrade (∼45 MW) will allow the development of non-inductive scenarios where the bootstrap current is maximized together with the fusion yield and not, as in present-day experiments, at its expense. The tools for the long-term JET programme are the new ITER-like ICRH antenna (∼15 MW), an upgrade of the NB power (35 MW/20 s or 17.5 MW/40 s), a new ITER-like first wall, a new pellet injector for edge localized mode control together with improved diagnostic and control capability. Operation with the new wall will set new constraints on non-inductive scenarios that are already addressed experimentally and in the modelling. The fusion performance and driven current that could be reached at high density and power have been estimated using either 0D or 1–1/2D validated transport models. In the high power case (45 MW), the calculations indicate the potential for the operational space of the non-inductive regime to be extended in terms of current (∼2.5 MA) and density (nl > 5 × 1019 m−3), with high βN (βN > 3.0) and a fraction of the bootstrap current within 60–70% at high toroidal field (∼3.5 T).

An Acoustically Driven Magnetized Target Fusion Reactor

We propose a new acoustic compression scheme for a MTF power plant. A strong acoustic wave is produced by piston impacts. The wave focuses in liquid PbLi to compress a pre-formed FRC plasma. Simulations indicate the possibility of building an economical 60 MWe power plant. A proof-of-principle experiment produces a small D-D fusion yield of 2000 neutrons per shot.

Target design for high fusion yield with the double Z-pinch-driven hohlraum

A key demonstration on the path to inertial fusion energy is the achievement of high fusion yield (hundreds of MJ) and high target gain. Toward this goal, an indirect-drive high-yield inertial confinement fusion (ICF) target involving two Z-pinch x-ray sources heating a central secondary hohlraum is described by Hammer et al. [Phys. Plasmas 6, 2129 (1999)]. In subsequent research at Sandia National Laboratories, theoretical/computational models have been developed and an extensive series of validation experiments have been performed to study hohlraum energetics, capsule coupling, and capsule implosion symmetry for this system. These models have been used to design a high-yield Z-pinch-driven ICF target that incorporates the latest experience in capsule design, hohlraum symmetry control, and x-ray production by Z pinches. An x-ray energy output of 9MJ per pinch, suitably pulse-shaped, is sufficient for this concept to drive 0.3–0.5GJ capsules. For the first time, integrated two-dimensional (2D) hohlraum/capsule radiation-hydrodynamics simulations have demonstrated adequate hohlraum coupling, time-dependent radiation symmetry control, and the successful implosion, ignition, and burn of a high-yield capsule in the double Z-pinch hohlraum. An important new feature of this target design is mode-selective symmetry control: the use of burn-through shields offset from the capsule that selectively tune certain low-order asymmetry modes (P2,P4) without significantly perturbing higher-order modes and without a significant energy penalty. This paper will describe the capsule and hohlraum design that have produced 0.4–0.5GJ yields in 2D simulations, provide a preliminary estimate of the Z-pinch load and accelerator requirements necessary to drive the system, and suggest future directions for target design work.

Cell membrane voltage during electrical cell fusion calculated by re-expansion method

In electrical cell fusion, two cells are first brought into contact by dielectrophoresis, and then a pulsed voltage is applied to induce reversible membrane breakdown at the contact point, by which the membranes of the two cells are reconnected to form a fusant cell. The prediction of the membrane voltage is a crucial issue for high fusion yield, however, its mathematical expression is known only for the case of an isolated cell in a uniform external field. In this paper, we employ the re-expansion method for the transient field analysis of such a multiple cell system. Each cell is modeled by an infinitesimally thin spherical insulating membrane in conducting media, on which accumulation of free charge occurs when an external field is applied. It is shown that the system has two time constants: (a) that governed by the conductivity and the permittivity of the media and (b) that of charging the membrane capacitance through the conducting media, and that the former is far shorter than the latter. Hence, the time variation due to the former is neglected to obtain a simplified expression for the membrane voltage. By expanding the potential into Legendre harmonic components and relating the coefficients for each cell based on the re-expansion method, a differential equation governing the membrane voltage buildup is obtained. The numerical calculation is performed for the axisymmetric case of two cells in contact, to which a step-wise voltage is applied. It is found that the maximum membrane voltage occurs initially at the contact point, but when the steady state is reached, it moves to the ends of the cell pair, and might lead to unsuccessful fusion. The analysis suggests that high-yield fusion may be achieved by an application of shorter pulse, or of a non-uniform field to concentrate the voltage drop at the contact point.

Perspectives on Magnetized Target Fusion Power Plants

One approach to Magnetized Target Fusion (MTF) builds upon the ongoing experimental effort (FRX-L) to generate a Field Reversed Configuration (FRC) target plasma suitable for translation and cylindrical-liner (i.e., converging flux conserver) implosion. Numerical modeling is underway to elucidate key performance drivers for possible future power-plant extrapolations. The fusion gain, Q (ratio of DT fusion yield to the sum of initial liner kinetic energy plus plasma formation energy), sets the power-plant duty cycle for a nominal design electric power [e.g. 1,000 MWe(net)]. A pulsed MTF power plant of this type derives from the historic Fast Liner Reactor (FLR) concept and shares attributes with the recent Inertial Fusion Energy (IFE) Z-pinch and laser-driven pellet HYLIFE-II conceptual designs.

Neutron production from high-intensity laser–cluster induced fusion reactions

The fusion neutron yield from a compact neutron source is studied. Laser-irradiated deuterium clusters serve as a precursor of high-energy deuterons, which react with a tritium target and produce copious amounts of neutrons in fusion reactions. The Coulomb explosion of deuterium clusters with initial radius of 5 to 20 nm irradiated by a sub-picosecond laser with intensity ranging from 1015 to 1018 W cm−2 is examined theoretically by a MD model. The dependence of the mean and maximum ion kinetic energy, ion energy distribution function and conversion efficiency of laser energy to ion kinetic energy is investigated. The fusion yield was estimated from an ion beam-target model. A high neutron yield of ∼106–107 neutrons/Joule is obtainable for peak laser intensity of 1016–1018 W cm−2, laser wavelength of 0.8–1 µm and clusters with an initial radius of ∼ 20 nm.