Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session KI3: Magnetized-Liner Inertial Fusion |
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Chair: Matthew Weis, Sandia National Laboratory Room: OCC Oregon Ballroom 204 |
Tuesday, November 6, 2018 3:00PM - 3:36PM |
KI3.00001: Improved Stability and Reproducibility of Magnetized Liner Inertial Fusion Implosions Invited Speaker: David Ampleford The Magnetized Liner Inertial Fusion (MagLIF) approach uses a pulsed-power-driven low-Z liner to compress a pre-magnetized, pre-heated fuel to reach fusion conditions. As with all inertial confinement fusion schemes, implosion stability is a key factor in the success of MagLIF. Since the first MagLIF experiments, there has been evidence of non-uniform implosions, with a quasi-helical stagnation column and significant variations in x-ray brightness along the height of the column. Recent experiments varied the aspect ratio of the liner and demonstrated a change in stagnation structures, consistent with an instability being seeded on the outer surface of the liner. To minimize the electro-thermal instability, a likely seed for magneto-Rayleigh Taylor growth, we incorporated a CH coating on the outer surface of the beryllium liner. Using this coating we achieved a stagnation column with negligible helical structure and minimal axial variation in x-ray brightness. The first data from a one-dimensional neutron imager also showed quasi-uniform neutron emission along the stagnation column. By creating a quasi-uniform stagnation column, we improved stagnation reproducibility, with <15% shot-to-shot variability in ion temperature, DD yield, and, importantly for magneto-inertial schemes, magnetization. Building on this reproducible platform we will discuss experiments that have started to make controlled changes, including experiments that show an increase in ion temperature and yield at stagnation with increased pre-magnetization. |
Tuesday, November 6, 2018 3:36PM - 4:12PM |
KI3.00002: Demonstration of High-Energy, Low-Mix Laser Preheat for MagLIF Invited Speaker: Adam Harvey-Thompson The Magnetized Liner Inertial Fusion (MagLIF) platform on the Z Facility has demonstrated thermonuclear fusion yields by imploding a cylindrical liner filled with D2 fuel that is preheated with a 0.53 μm, multi-kJ laser and pre-magnetized with an axial Bz = 10-30 T magnetic field. The challenge of fuel preheat is to efficiently deposit >1 kJ of energy into the underdense (ne/nc < 0.1) fuel over a ~10 mm target length without introducing deleterious mix. To achieve this goal, we have developed new diagnostic capabilities to measure laser-energy deposition and contaminants introduced during fuel preheat. In addition, we also developed more efficient laser heating protocols using numerical simulations and offline (separate to the Z chamber) laser experiments. The offline experiments measure backscatter from laser—plasma instabilities (LPI) and constrain energy deposition via a multi-frame shadowgraphy diagnostic that observes the blast-wave produced in the gas. Laser heating protocols are then tested in integrated MagLIF experiments that quantify the preheat-induced mix by using mid-Z coatings applied to various surfaces of the target. This talk will summarize the significant progress that has been made in developing new diagnostics and new MagLIF preheat protocols over the past 2 years. Our results show that >1 kJ of preheat energy can be coupled to the fuel without introducing contaminants and without significant LPI backscatter by applying DPP smoothing and pulse shaping the beam with a low-energy (20 J), early pre-pulse. These efforts have culminated in the highest neutron yield (1.1e13±20%) recorded to date in a MagLIF experiment. |
Tuesday, November 6, 2018 4:12PM - 4:48PM |
KI3.00003: Megagauss-level premagnetization field production in helically-wound auto-magnetizing liners for Magnetized Liner Inertial Fusion (MagLIF) Invited Speaker: Gabriel Alan Shipley Pulsed-power driven auto-magnetizing (AutoMag) liners [1] are cylindrical tubes composed of discrete helical conduction paths separated by electrically insulating material. AutoMag liners generate Bz > 100 T axial premagnetization field (pre-implosion) for the MagLIF magneto-inertial fusion concept. Initially, helical current in the AutoMag liner produces Bz in the cold fuel within the liner during a 200 ns, 1-2 MA current prepulse. After the fuel is magnetized, a rapidly rising main current pulse induces an electric field in the liner that is sufficient to force dielectric breakdown of the insulating material between helices. Liner current then reorients from helical to predominantly axial (ceasing Bz production) and the z-pinch liner implodes as the current rises to 20 MA in 100 ns. Proof-of-concept experiments on the 600 kA, 100 ns risetime Mykonos accelerator demonstrated the efficacy of the AutoMag field generation mechanism [2]. Recent AutoMag experiments on the Z Facility confirmed production of Bz > 100 T during a 2 MA prepulse and furthermore used radiography to determine the liner’s implosion integrity. Despite initially having a 3D density and conductivity topology, radiography data shows that AutoMag liners on Z implode with a high level of cylindrical symmetry. [1] Slutz et al., Phys. Plasmas 24, 012704 (2017). [2] Shipley et al., Phys. Plasmas 25, 052703 (2018). |
Tuesday, November 6, 2018 4:48PM - 5:24PM |
KI3.00004: Laser-Driven Magnetized Liner Inertial Fusion on OMEGA Invited Speaker: Jonathan Davies Laser-driven magnetized liner inertial fusion (MagLIF) has been developed on the OMEGA Laser System in a joint SNL-LLE project funded by ARPA-E. MagLIF relies on compressing cylindrical, magnetized, and preheated plasma to achieve fusion with inertial confinement. The magnetic field reduces electron heat flow into the shell (liner), allowing compressional heating at implosion velocities < 200 km/s, and confines the alpha particles, replacing the radial areal density requirement for ignition with a BR requirement of 0.6 T m. Preheating to > 100 eV reduces the fuel convergence ratio required to achieve fusion temperatures to < 30. MagLIF experiments on Z have achieved temperatures of 3 keV, BR of 0.4 T m, and DD neutron yields of 1013. However, these are the only MagLIF experiments being carried out. Laser-driven MagLIF on OMEGA is providing the first experimental data on scaling, with 1000× less drive energy and targets 10× smaller in linear dimensions. OMEGA also allows more shots than Z with better diagnostic access and a greater dynamic range. OMEGA targets are 0.6-mm-outer-diam, 20-μm-thick, D2-filled plastic cylinders. MIFEDS (magneto-inertial fusion electrical discharge system) provides an axial magnetic field up to 28 T (the highest to date). A single OMEGA beam preheats the D2 up to 200 eV, and then 40 OMEGA beams delivering 14 kJ compress the target. A full overview of the project will be given, from the initial point design process, preheat experiments, compression optimization experiments, up to the most recent fully integrated experiments. |
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