Magnetized Liner Inertial Fusion Concept Research Articles

Preliminary exploration of MagLIF concept and feasibility analysis on PTS facility

Magnetized Liner Inertial Fusion (MagLIF) concept has promising potentials for future energy source (Phys.Plasmas, 2014, 21:072711), it is widely applicable to large-scale pulsed power generators such as the Primary Test Stand (PTS) facility (10 MA, 100 ns). In this context, we’ve developed a zero-dimensional (0D) MagLIF simulation code basing on magneto-hydrodynamic (MHD) equations and Deuterium-Tritium (DT) fusion models. Relationships between fusion products and initial setups (magnetic field Bz0, preheat temperature T0 and so on) are explored using this code, results show optimal parameters existing under given inputs, which are very helpful for future experimental designs. Specifically, according to our simulations, critical driving current (＞21.2 MA) is essential for fuel (50∶50 DT) energy to reach breakeven, which infers that PTS facility may not be suitable for integrated MagLIF experiments. Series of calculations are performed to confirm this inference, and more practical aluminum liner experiments are proposed and designed.

Enhancing performance of magnetized liner inertial fusion at the Z facility

The Magnetized Liner Inertial Fusion concept (MagLIF) [Slutz et al., Phys. Plasmas 17, 056303 (2010)] is being studied on the Z facility at Sandia National Laboratories. Neutron yields greater than 1012 have been achieved with a drive current in the range of 17–18 MA and pure deuterium fuel [Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)]. We show that 2D simulated yields are about twice the best yields obtained on Z and that a likely cause of this difference is the mix of material into the fuel. Mitigation strategies are presented. Previous numerical studies indicate that much larger yields (10–1000 MJ) should be possible with pulsed power machines producing larger drive currents (45–60 MA) than can be produced by the Z machine [Slutz et al., Phys. Plasmas 23, 022702 (2016)]. To test the accuracy of these 2D simulations, we present modifications to MagLIF experiments using the existing Z facility, for which 2D simulations predict a 100-fold enhancement of MagLIF fusion yields and considerable increases in burn temperatures. Experimental verification of these predictions would increase the credibility of predictions at higher drive currents.

Preliminary investigation on the use of low current pulsed power Z-pinch plasma devices for the study of early stage plasma instabilities

This article addresses key features for the implementation of low current pulsed power plasma devices for the study of matter dynamics from the solid to the plasma phase. The renewed interest in such low current plasma devices lies in the need to investigate methods for the mitigation of prompt seeding mechanisms for the generation of plasma instabilities. The low current when driven into thick wires (skin effect mode) allows for the simultaneous existence of all phases of matter from solid to plasma. Such studies are important for the concept of inertial confinement fusion where the mitigation of the instability seeding mechanisms arising from the very early moments within the target’s heating is of crucial importance. Similarly, in the magnetized liner inertial fusion concept it is an open question as to how much surface non-uniformity correlates with the magneto-Rayleigh–Taylor instability, which develops during the implosion. This study presents experimental and simulation results, which demonstrate that the use of low current pulsed power devices in conjunction with appropriate diagnostics can be important for studying seeding mechanisms for the imminent generation of plasma instabilities in future research.

Recent laser upgrades at Sandia’s Z-backlighter facility in order to accommodate new requirements for magnetized liner inertial fusion on the Z-machine

The Z-backlighter laser facility primarily consists of two high energy, high-power laser systems. Z-Beamlet laser (ZBL) (Rambo et al., Appl. Opt. 44, 2421 (2005)) is a multi-kJ-class, nanosecond laser operating at 1054 nm which is frequency doubled to 527 nm in order to provide x-ray backlighting of high energy density events on the Z-machine. Z-Petawatt (ZPW) (Schwarz et al., J. Phys.: Conf. Ser. 112, 032020 (2008)) is a petawatt-class system operating at 1054 nm delivering up to 500 J in 500 fs for backlighting and various short-pulse laser experiments (see also Figure 10 for a facility overview). With the development of the magnetized liner inertial fusion (MagLIF) concept on the Z-machine, the primary backlighting missions of ZBL and ZPW have been adjusted accordingly. As a result, we have focused our recent efforts on increasing the output energy of ZBL from 2 to 4 kJ at 527 nm by modifying the fiber front end to now include extra bandwidth (for stimulated Brillouin scattering suppression). The MagLIF concept requires a well-defined/behaved beam for interaction with the pressurized fuel. Hence we have made great efforts to implement an adaptive optics system on ZBL and have explored the use of phase plates. We are also exploring concepts to use ZPW as a backlighter for ZBL driven MagLIF experiments. Alternatively, ZPW could be used as an additional fusion fuel pre-heater or as a temporally flexible high energy pre-pulse. All of these concepts require the ability to operate the ZPW in a nanosecond long-pulse mode, in which the beam can co-propagate with ZBL. Some of the proposed modifications are complete and most of them are well on their way.

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.

Characterizing the Plasmas of Dense $Z$ -Pinches

This mini-tutorial summarizes the plasma characteristics important for the $Z$ -pinch research, with an emphasis on high-density collisional plasmas. It begins with the discussion of the most basic plasma properties related to collisionality and magnetization and then proceeds to more complex phenomena associated with magnetic field evolution in a highly dynamical plasma. Plasma transport properties are discussed mostly in conjunction with the Magnetized Liner Inertial Fusion concept. Issues of interplay of the classical and anomalous transport in a plasma whose pressure is higher than the magnetic pressure are elucidated. Differences in magnetic reconnection in weakly versus highly collisional plasmas are discussed. Kinetic effects and the role of microturbulence are mentioned in conjunction with the formation of high-energy tails in the particle distribution functions and the generation of particle beams. The discussion is based on the order-of-magnitude estimates suitable for initial orientation in the problem. The two appendixes contain some auxiliary material.

Demonstration of thermonuclear conditions in magnetized liner inertial fusion experimentsa)

The magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the pressure requirements of inertial confinement fusion. The first experiments to test the concept [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] were conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z system. Despite an estimated implosion velocity of only 70 km/s in these experiments, electron and ion temperatures at stagnation were as high as 3 keV, and thermonuclear deuterium-deuterium neutron yields up to 2 × 1012 have been produced. X-ray emission from the fuel at stagnation had widths ranging from 50 to 110 μm over a roughly 80% of the axial extent of the target (6–8 mm) and lasted approximately 2 ns. X-ray yields from these experiments are consistent with a stagnation density of the hot fuel equal to 0.2–0.4 g/cm3. In these experiments, up to 5 × 1010 secondary deuterium-tritium neutrons were produced. Given that the areal density of the plasma was approximately 1–2 mg/cm2, this indicates the stagnation plasma was significantly magnetized, which is consistent with the anisotropy observed in the deuterium-tritium neutron spectra. Control experiments where the laser and/or magnetic field were not utilized failed to produce stagnation temperatures greater than 1 keV and primary deuterium-deuterium yields greater than 1010. An additional control experiment where the fuel contained a sufficient dopant fraction to substantially increase radiative losses also failed to produce a relevant stagnation temperature. The results of these experiments are consistent with a thermonuclear neutron source.

Pulsed-coil magnet systems for applying uniform 10–30 T fields to centimeter-scale targets on Sandia's Z facility

Sandia has successfully integrated the capability to apply uniform, high magnetic fields (10-30 T) to high energy density experiments on the Z facility. This system uses an 8-mF, 15-kV capacitor bank to drive large-bore (5 cm diameter), high-inductance (1-3 mH) multi-turn, multi-layer electromagnets that slowly magnetize the conductive targets used on Z over several milliseconds (time to peak field of 2-7 ms). This system was commissioned in February 2013 and has been used successfully to magnetize more than 30 experiments up to 10 T that have produced exciting and surprising physics results. These experiments used split-magnet topologies to maintain diagnostic lines of sight to the target. We describe the design, integration, and operation of the pulsed coil system into the challenging and harsh environment of the Z Machine. We also describe our plans and designs for achieving fields up to 20 T with a reduced-gap split-magnet configuration, and up to 30 T with a solid magnet configuration in pursuit of the Magnetized Liner Inertial Fusion concept.

Experimental demonstration of fusion-relevant conditions in magnetized liner inertial fusion.

This Letter presents results from the first fully integrated experiments testing the magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)], in which a cylinder of deuterium gas with a preimposed 10 Taxial magnetic field is heated by Z beamlet, a 2.5 kJ, 1 TW laser, and magnetically imploded by a 19 MA, 100 ns rise time current on the Z facility. Despite a predicted peak implosion velocity of only 70 km = s, the fuel reaches a stagnation temperature of approximately 3 keV, with T(e) ≈ T(i), and produces up to 2 x 10(12) thermonuclear deuterium-deuterium neutrons. X-ray emission indicates a hot fuel region with full width at half maximum ranging from 60 to 120 μm over a 6 mm height and lasting approximately 2 ns. Greater than 10(10) secondary deuterium-tritium neutrons were observed, indicating significant fuel magnetization given that the estimated radial areal density of the plasma is only 2 mg = cm(2).

Design of magnetized liner inertial fusion experiments using the Z facility

The magnetized liner inertial fusion concept has been presented as a path toward obtaining substantial thermonuclear fusion yields using the Z accelerator [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)]. We present the first integrated magnetohydrodynamic simulations of the inertial fusion targets, which self-consistently include laser preheating of the fuel, the presence of electrodes, and end loss effects. These numerical simulations provided the design for the first thermonuclear fusion neutron-producing experiments on Z using capabilities that presently exist: peak currents of Imax = 18–20 MA, pre-seeded axial magnetic fields of Bz0=10 T, laser preheat energies of about Elas = 2 kJ delivered in 2 ns, DD fuel, and an aspect ratio 6 solid Be liner imploded to 70 km/s. Specific design details and observables for both near-term and future experiments are discussed, including sensitivity to laser timing and absorbed preheat energy. The initial experiments measured stagnation radii rstag<75 μm, temperatures around 3 keV, and isotropic neutron yields up to YnDD=2×1012, with inferred alpha-particle magnetization parameters around rstag/rLα=1.7 [M. R. Gomez et al., Phys. Rev. Lett. (submitted)].

Beryllium liner implosion experiments on the Z accelerator in preparation for magnetized liner inertial fusion

Multiple experimental campaigns have been executed to study the implosions of initially solid beryllium (Be) liners (tubes) on the Z pulsed-power accelerator. The implosions were driven by current pulses that rose from 0 to 20 MA in either 100 or 200 ns (200 ns for pulse shaping experiments). These studies were conducted in support of the recently proposed Magnetized Liner Inertial Fusion concept [Slutz et al., Phys. Plasmas 17, 056303 (2010)], as well as for exploring novel equation-of-state measurement techniques. The experiments used thick-walled liners that had an aspect ratio (initial outer radius divided by initial wall thickness) of either 3.2, 4, or 6. From these studies, we present three new primary results. First, we present radiographic images of imploding Be liners, where each liner contained a thin aluminum sleeve for enhancing the contrast and visibility of the liner's inner surface in the images. These images allow us to assess the stability of the liner's inner surface more accurately and more directly than was previously possible. Second, we present radiographic images taken early in the implosion (prior to any motion of the liner's inner surface) of a shockwave propagating radially inward through the liner wall. Radial mass density profiles from these shock compression experiments are contrasted with profiles from experiments where the Z accelerator's pulse shaping capabilities were used to achieve shockless (“quasi-isentropic”) liner compression. Third, we present “micro-Ḃ” measurements of azimuthal magnetic field penetration into the initially vacuum-filled interior of a shocked liner. Our measurements and simulations reveal that the penetration commences shortly after the shockwave breaks out from the liner's inner surface. The field then accelerates this low-density “precursor” plasma to the axis of symmetry.

Magnetically Driven Implosions for Inertial Confinement Fusion at Sandia National Laboratories

High current pulsed-power generators efficiently store and deliver magnetic energy to z-pinch targets. We review applications of magnetically driven implosions (MDIs) to inertial confinement fusion. Previous research on MDIs of wire-array z-pinches for radiation-driven indirect-drive target designs is summarized. Indirect-drive designs are compared with new targets that are imploded by direct application of magnetic pressure produced by the pulsed-power current pulse. We describe target design elements such as larger absorbed energy, magnetized and pre-heated fuel, and cryogenic fuel layers that may relax fusion requirements. These elements are embodied in the magnetized liner inertial fusion (MagLIF) concept [Slutz <etal xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> “Pulsed-power-driven cylindrical liner implosions of laser pre-heated fuel magnetized with an axial field,” Phys. Plasmas, 17, 056303 (2010), and Stephen A. Slutz and Roger A. Vesey, “High-Gain Magnetized Inertial Fusion,” Phys. Rev. Lett., 108, 025003 (2012)]. MagLIF is in the class of magneto-inertial fusion targets. In MagLIF, the large drive currents produce an azimuthal magnetic field that compresses cylindrical liners containing pre-heated and axially pre-magnetized fusion fuel. Scientific breakeven may be achievable on the Z facility with this concept. Simulations of MagLIF with deuterium-tritium fuel indicate that the fusion energy yield can exceed the energy invested in heating the fuel at a peak drive current of about 27 MA. Scientific breakeven does not require alpha particle self-heating and is therefore not equivalent to ignition. Capabilities to perform these experiments will be developed on Z starting in 2013. These simulations and predictions must be validated against a series of experiments over the next five years. Near-term experiments are planned at drive currents of 16 MA with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm D}_{2}$</tex></formula> fuel. MagLIF increases the efficiency of coupling energy ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$=$</tex></formula> target absorbed energy/driver stored energy) to targets by 10–150 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$X$</tex></formula> relative to indirect-drive targets. MagLIF also increases the absolute energy absorbed by the target by 10-50 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$X$</tex> </formula> relative to indirect-drive targets. These increases could lead to higher fusion gains and yields. Single-shot high yields are of great utility to national security missions. Higher efficiency and higher gains may also translate into more compelling (lower cost and complexity) fusion reactor designs. We will discuss the broad goals of the emerging research on the MagLIF concept and identify some of the challenges. We will also summarize advances in pulsed-power technology and pulsed-power driver architectures that double the efficiency of the driver.

Effects of magnetic shear on magneto-Rayleigh-Taylor instability

The magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] consists of a cylindrical metal liner enclosing a preheated plasma that is embedded in an axial magnetic field. Because of its diffusion into the liner, the pulsed azimuthal magnetic field may exhibit a strong magnetic shear within the liner, offering the interesting possibility of shear stabilization of the magneto-Rayleigh-Taylor (MRT) instability. Here, we use the ideal MHD model to study this effect of magnetic shear in a finite slab. It is found that magnetic shear reduces the MRT growth rate in general. The feedthrough factor is virtually independent of magnetic shear. In the limit of infinite magnetic shear, all MRT modes are stable if bu &amp;gt; 1, where bu is the ratio of the perturbed magnetic tension in the liner’s interior region to the acceleration during implosion.