Magneto-inertial Fusion Research Articles

The Role of Magnetized Liner Inertial Fusion as a Pathway to Fusion Energy

We discuss the possible impacts of a new magnetized liner inertial fusion concept on magneto-inertial fusion approaches to fusion energy. Experiments in the last 1.5 years have already shown direct evidence of magnetic flux compression, a highly magnetized fusing fuel, significant compressional heating, a compressed cylindrical fusing plasma, and significant fusion yield. While these exciting results demonstrate several key principles behind magneto-inertial fusion, more work in the coming years will be needed to demonstrate that such targets can scale to ignition and high yield. We argue that justifying significant investment in pulsed inertial fusion energy beyond target development should require well-understood, significant fusion yields to be demonstrated in single-shot experiments. We also caution that even once target ideas and fusion power plants have been demonstrated, historical trends suggest it would still be decades before fusion could materially impact worldwide energy production.

Case and Development Path for Fusion Propulsion

This paper discusses the importance of fusion propulsion for interplanetary space travel, illustrates why the magnetoinertial fusion parameter space may facilitate the most rapid, economic path for development, justifies the choice of pulsed Z pinch, and provides a potential development path leading up to a technical readiness level 9 system. Round trips of less than one year to Mars are only possible using fusion propulsion systems. Such a system will require an onboard nuclear fission reactor for reliable startups, and so fission and fusion developments for space are mutually beneficial. The paper reviews the more than 50 year history of fusion research and summarizes results from a recent study of the fusion parameter space for terrestrial power, which suggests magnetoinertial fusion can provide the smallest, most economical approach for a fusion propulsion system. Emerging experimental data and theory show pulsed Z-pinch fusion solves some of the most deleterious instabilities and scales to fusion breakeven within reach of current pulsed power facilities. The paper illustrates a potential development path to a technical readiness level 9 flight system, starting from an assumed technical readiness level 2 for the current state of fusion propulsion.

Note: Experimental platform for magnetized high-energy-density plasma studies at the omega laser facility.

An upgrade of the pulsed magnetic field generator magneto-inertial fusion electrical discharge system [O. Gotchev et al., Rev. Sci. Instrum. 80, 043504 (2009)] is described. The device is used to study magnetized high-energy-density plasma and is capable of producing a pulsed magnetic field of tens of tesla in a volume of a few cubic centimeters. The magnetic field is created by discharging a high-voltage capacitor through a small wire-wound coil. The coil current pulse has a duration of about 1 μs and a peak value of 40 kA. Compared to the original, the updated version has a larger energy storage and improved switching system. In addition, magnetic coils are fabricated using 3-D printing technology which allows for a greater variety of the magnetic field topology.

Understanding fuel magnetization and mix using secondary nuclear reactions in magneto-inertial fusion.

Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during deuterium-deuterium fusion and can undergo secondary deuterium-tritium reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall deuterium-tritium to deuterium-deuterium neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions also are shown to provide an upper bound for the volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs.

Numerical simulation of an experimental analogue of a planetary magnetosphere

Recent improvements to the Omega Laser Facility's magneto-inertial fusion electrical discharge system (MIFEDS) have made it possible to generate strong enough magnetic fields in the laboratory to begin to address the physics of magnetized astrophysical flows. Here, we adapt the MHD code AstroBEAR to create 2D numerical models of an experimental analogue of a planetary magnetosphere. We track the secular evolution of the magnetosphere analogue and we show that the magnetospheric components such as the magnetopause, magnetosheath, and bow shock, should all be observable in experimental optical band thermal bremsstrahlung emissivity maps, assuming equilibrium charge state distributions of the plasma. When the magnetosphere analogue nears the steady state, the mid-plane altitude of the magnetopause from the wire surface scales as the one-half power of the ratio of the magnetic pressure at the surface of the free wire to the ram pressure of an unobstructed wind; the mid-plane thickness of the magnetosheath is directly related to the radius of the magnetopause. This behavior conforms to Chapman and Ferraro's theory of planetary magnetospheres. Although the radial dependence of the magnetic field strength differs between the case of a current-carrying wire and a typical planetary object, the major morphological features that develop when a supersonic flow passes either system are identical. Hence, this experimental concept is an attractive one for studying the dynamics of planetary magnetospheres in a controlled environment.

Investigation into Fusion Feasibility of a Magnetized Target Fusion Reactor: A Preliminary Numerical Framework

The efforts to engineer devices to produces conditions suitable for nuclear fusion on earth have made significant leaps and bounds in recent years due to improved technology and engineering methods. Magnetized target fusion, or magneto-inertial fusion, involves the inertial compression of a pre-magnetized plasma, using high magnetic fields to insulate the plasma, thereby allowing slower and lower convergence compression than achievable by inertial techniques alone. One particular form of MTF (suggested by general fusion) involves using an intense pressure wave transmitted through a dense medium, growing in intensity due to focusing, and finally reaching a plasma and compressing it. Our model consists of a spherically symmetric domain with moving boundaries that we solve numerically through a coordinate transformation and a flux-limited finite volume method. Our work ventures towards a proof of concept, both of a mathematical technique to solve nonlinear conservation laws with moving boundaries and of the notion that current designs being considered show potential for successful fusion conditions. Our work also includes a sensitivity analysis to estimate the optimal conditions for such a reactor.

Possible energy gain for a plasma-liner-driven magneto-inertial fusion concept

A one-dimensional parameter study of a Magneto-Inertial Fusion (MIF) concept indicates that significant gain may be achievable. This concept uses a dynamically formed plasma shell with inwardly directed momentum to drive a magnetized fuel to ignition, which in turn partially burns an intermediate layer of unmagnetized fuel. The concept is referred to as Plasma Jet MIF or PJMIF. The results of an adaptive mesh refinement Eulerian code (Crestone) are compared to those of a Lagrangian code (LASNEX). These are the first published results using the Crestone and LASNEX codes on the PJMIF concept.

Low radioactive and hybrid fusion – A path to clean energy

Aneutronic/low radioactive fuel is the way to clean and cheap energy of the future. An alternative scheme using compact toroids – field-reversed configuration or spheromak – may be applied for the reactor based on any magnetic confinement system. Even more, any fusion concept, including hybrid magneto-inertial fusion might use advantages of D–3He fuel. Advanced fuel, including helium-3 – based fusion plasma and alternative systems are reviewed. Different schemes of reactors, near-term technology and non-electric applications are discussed.

Addressing Short Trapped-Flux Lifetime in High-Density Field-Reversed Configuration Plasmas in FRCHX

The objective of the field-reversed configuration heating experiment (FRCHX) is to obtain a better understanding of the fundamental scientific issues associated with high-energy density laboratory plasmas (HEDLPs) in strong, closed-field-line magnetic fields. These issues have relevance to such topics as magneto-inertial fusion, laboratory astrophysical research, and intense radiation sources, among others. To create HEDLP conditions, a field-reversed configuration (FRC) plasma of moderate density is first formed via reversed-field theta pinch. It is then translated into a cylindrical aluminum flux conserver (solid liner), where it is trapped between two magnetic mirrors and then compressed by the magnetically driven implosion of the solid liner. A requirement is that, once the FRC is stopped within the solid liner, the trapped flux inside the FRC must persist while the compression process is completed. With the present liner dimensions and implosion drive bank parameters, the total time required for implosion is ${\sim}{\rm 25}~\mu{\rm s}$ . Lifetime measurements of recent FRCHX FRCs indicate that trapped lifetimes following capture are now approaching ${\sim}{\rm 14}~\mu{\rm s}$ (and therefore, total lifetimes after formation are now approaching ${\sim}{\rm 19}~\mu{\rm s}$ ). By separating the mirror and translation coil banks into two so that the mirror fields can be set lower initially, the liner compression can now be initiated 7–9 $\mu{\rm s}$ before the FRC is formed. A discussion of FRC lifetime-limiting mechanisms and various experimental approaches to extending the FRC lifetime will be presented.

Current state, problems, and prospects of thermonuclear facilities based on the magneto-inertial confinement of hot plasma

Magneto-inertial fusion (MIF) is an original technique of inertial thermonuclear fusion, where spherical and cylindrical gas or plasma configurations are compressed under the action of an external magnetic field. We present a brief review of recent data on laser- and plasma jet-driven MIF systems and possible ways they can be applied. This work also presents problems of and prospects for the application of such approaches.

Modified helix-like instability structure on imploding z-pinch liners that are pre-imposed with a uniform axial magnetic field

Recent experiments at the Sandia National Laboratories Z Facility have, for the first time, studied the implosion dynamics of magnetized liner inertial fusion (MagLIF) style liners that were pre-imposed with a uniform axial magnetic field. As reported [T. J. Awe et al., Phys. Rev. Lett. 111, 235005 (2013)] when premagnetized with a 7 or 10 T axial field, these liners developed 3D-helix-like hydrodynamic instabilities; such instabilities starkly contrast with the azimuthally correlated magneto-Rayleigh-Taylor (MRT) instabilities that have been consistently observed in many earlier non-premagnetized experiments. The helical structure persisted throughout the implosion, even though the azimuthal drive field greatly exceeded the expected axial field at the liner's outer wall for all but the earliest stages of the experiment. Whether this modified instability structure has practical importance for magneto-inertial fusion concepts depends primarily on whether the modified instability structure is more stable than standard azimuthally correlated MRT instabilities. In this manuscript, we discuss the evolution of the helix-like instability observed on premagnetized liners. While a first principles explanation of this observation remains elusive, recent 3D simulations suggest that if a small amplitude helical perturbation can be seeded on the liner's outer surface, no further influence from the axial field is required for the instability to grow.

Particle-in-cell simulations of laser beat-wave magnetization of dense plasmas

The interaction of two lasers with a difference frequency near that of the ambient plasma frequency produces beat waves that can resonantly accelerate thermal electrons. These beat waves can be used to drive electron current and thereby embed magnetic fields into the plasma [Welch et al., Phys. Rev. Lett. 109, 225002 (2012)]. In this paper, we present two-dimensional particle-in-cell simulations of the beat-wave current-drive process over a wide range of angles between the injected lasers, laser intensities, and plasma densities. We discuss the application of this technique to the magnetization of dense plasmas, motivated in particular by the problem of forming high-β plasma targets in a standoff manner for magneto-inertial fusion. The feasibility of a near-term experiment embedding magnetic fields using lasers with micron-scale wavelengths into a ∼1018 cm−3-density plasma is assessed.

Recent magneto-inertial fusion experiments on the field reversed configuration heating experiment

Magneto-inertial fusion (MIF) approaches take advantage of an embedded magnetic field to improve plasma energy confinement by reducing thermal conduction relative to conventional inertial confinement fusion (ICF). MIF reduces required precision in the implosion and the convergence ratio. Since 2008 (Wurden et al 2008 IAEA 2008 Fusion Energy Conf. (Geneva, Switzerland, 13–18 October) IC/P4-13 LA-UR-08-0796) and since our prior refereed publication on this topic (Degnan et al 2008 IEEE Trans. Plasma Sci. 36 80), AFRL and LANL have developed further one version of MIF. We have (1) reliably formed, translated, and captured field reversed configurations (FRCs) in magnetic mirrors inside metal shells or liners in preparation for subsequent compression by liner implosion; (2) imploded a liner with interior magnetic mirror field, obtaining evidence for compression of a 1.36 T field to 540 T; (3) performed a full system experiment of FRC formation, translation, capture, and imploding liner compression operation; (4) identified by comparison of 2D-MHD simulation and experiments factors limiting the closed-field lifetime of FRCs to about half that required for good liner compression of FRCs to multi-keV, 1019 ion cm−3, high energy density plasma (HEDP) conditions; and (5) designed and prepared hardware to increase that closed-field FRC lifetime to the required amount. Those lifetime experiments are now underway, with the goal of at least doubling closed-field FRC lifetimes and performing FRC implosions to HEDP conditions this year. These experiments have obtained imaging evidence of FRC rotation, and of initial rotation control measures slowing and stopping such rotation. Important improvements in fidelity of simulation to experiment have been achieved, enabling improved guidance and understanding of experiment design and performance.

Analysis of the Compression and Heating of Magnetized Plasma Targets for Magneto-Inertial Fusion

This paper deals with the analysis of the possible use of magneto-inertial fusion (MIF) to create a neutron source. We consider the configuration of the target in the form of an axially symmetric magnetic trap with magnetic “plugs” or so-called “probkotron”. Heating and compression of a plasma target in the magnetic field is studied numerically. Parameters of the neutron source based on plasma-jet driven magneto-inertial fusion with a cylindrical target are given.

Analysis of the Compression and Heating of Magnetized Plasma Targets for Magneto-Inertial Fusion

Analysis of the Compression and Heating of Magnetized Plasma Targets for Magneto-Inertial Fusion

Numerical Simulation of Merging Plasma Jets Using High-$Z$ Gases

Some initial numerical studies of merging plasma jets for magneto-inertial fusion (MIF) and high-energy-density laboratory plasmas have been performed, focusing on the study of jet propagation and plasma liner formation. Being heavier for a fixed number density and with more radiation cooling, high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> materials can keep low jet transverse Mach number, and they are preferred in our studies as plasma jet and liner materials, while four-jet mergings of hydrogen and helium are briefly studied for comparison. Because of the advantages of high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> plasma jets for the MIF application in which we are particularly interested, we focus mainly on argon and xenon in this paper. The plasma jets propagate with an initial velocity of 50-100 km/s, and number density is in the range 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The merging jets are several centimeters in diameter. The hybrid particle-in-cell code LSP is used to perform the simulations, using an advanced fluid algorithm with equation-of-state model and a radiation transport model. Simulation results for several configurations and different numbers of the merging jets are compared and discussed. The results show that, with same number density, jet velocity, and temperature, merging using more jets achieves higher density, such as an amplification ratio of 115 for 16 jets and 38.5 for 4 jets, and much higher than that of hydrogen and helium in four-jet merging. During these mergings, the electron pressure reaches up to 10, 22.5, and 33.5 bar, respectively.

Nonlinear compressions in merging plasma jets

We investigate the dynamics of merging supersonic plasma jets using an analytic model. The merging structures exhibit supersonic, nonlinear compressions which may steepen into full shocks. We estimate the distance necessary to form such shocks and the resulting jump conditions. These theoretical models are compared to experimental observations and simulated dynamics. We also use those models to extrapolate behavior of the jet-merging compressions in a Plasma Jet Magneto-Inertial Fusion reactor.

Project Icarus: Analysis of Plasma jet driven Magneto-Inertial Fusion as potential primary propulsion driver for the Icarus probe

Hopes of sending probes to another star other than the Sun are currently limited by the maturity of advanced propulsion technologies. One of the few candidate propulsion systems for providing interstellar flight capabilities is nuclear fusion. In the past many fusion propulsion concepts have been proposed and some of them have even been explored in detail, Project Daedalus for example. However, as scientific progress in this field has advanced, new fusion concepts have emerged that merit evaluation as potential drivers for interstellar missions. Plasma jet driven Magneto-Inertial Fusion (PJMIF) is one of those concepts. PJMIF involves a salvo of converging plasma jets that form a uniform liner, which compresses a magnetized target to fusion conditions. It is an Inertial Confinement Fusion (ICF)–Magnetic Confinement Fusion (MCF) hybrid approach that has the potential for a multitude of benefits over both ICF and MCF, such as lower system mass and significantly lower cost. This paper concentrates on a thermodynamic assessment of basic performance parameters necessary for utilization of PJMIF as a candidate propulsion system for the Project Icarus mission. These parameters include: specific impulse, thrust, exhaust velocity, mass of the engine system, mass of the fuel required etc. This is a submission of the Project Icarus Study Group.

On the structure of plasma liners for plasma jet induced magnetoinertial fusion

The internal structure and self-collapse properties of plasma liners, formed by the merger of argon plasma jets, have been studied via 3-dimensional numerical simulations using the FronTier code. We have shown that the jets merger process is accomplished through a cascade of oblique shock waves that heat the liner and reduce its Mach number. Oblique shock waves and the adiabatic compression heating have led to the 10 times reduction of the self-collapse pressure of a 3-dimensional argon liner compared to a spherically symmetric liner with the same pressure and density profiles at the merging radius. We have also observed a factor of 10 variations of pressure and density in the leading edge of the liner along spherical surfaces close to the interaction with potential plasma targets. Such a non-uniformity of imploding plasma liners presents problems for the stability of targets during compression.

Sharp Interface Algorithm for Large Density Ratio Incompressible Multiphase Magnetohydrodynamic Flows

A numerical algorithm and the corresponding paralleled implementation for the study of magnetohydrodynamics (MHD) of large density ratio, three-dimensional multiphase flows at low magnetic Reynolds numbers have been developed. The algorithm employs the method of front tracking for the propagation of material interfaces and the embedded interface method for solving elliptic-parabolic problems associated with approximations of incompressible fluids and low magnetic Reynolds numbers. The use of embedded interface method supports arbitrary discontinuities of density and other physics properties across interfaces and significantly improves methods that smear interface discontinuities across several grid cells. The numerical algorithm has been implemented as an MHD extension of FronTier, a parallel front tracking hydrodynamic code, verified using asymptotic solutions and validated through the comparison with experiments on liquid metal jets. The FronTier-MHD code has been used for simulations of liquid mercury targets for the proposed muon collider / neutrino factory, ablation of pellets in tokamaks, and processes in hybrid magnetoinertial fusion.