Magnetic Drive Inertial Fusion Energy (MD-IFE)
Fusion energy has the potential to address the global energy need for baseload power generation. The US Department of Energy has recently set out several program to accelerate realization and commercialization of fusion based on the White House's Bold Decadal Vision for Fusion Energy. Within the two main approaches, magnetic and inertial confinement, MD-IFE sits within inertial fusion energy.
The MD-IFE approach
The magnetic drive approach to inertial fusion has been led by Sandia National Laboratories, and takes advantage of the high efficiency of energy delivery possible with large pulsed power drivers. This is well suited to generate large yields (500 MJ to several GJ) with each fusion shot. and to repeat shots every 10 seconds in a large scale power station. Presently, experiments on Magnetized Liner Inertial Fusion (MagLIF) are carried out one at a time on Sandia's Z Machine to optimize performance. This delivers 20 MA of current to a 6mm diameter metal cylinder which is seeded with a magnetic field, heated with a laser beam, and then rapidly compressed onto its central axis. The liner contains and rapidly heats the fusion fuel (deuterium and tritium) to high temperatures, releasing energy primarily as neutrons. These neutrons are captured in a power plant, and their energy is used to heat water to turn a steam turbine and produce electricity.
The P3 Group is working with a number of collaborators to drive MD-IFE forward. These include Sandia National Laboratories, Pacific Fusion Inc, the University of Michigan, Lawrence Livermore National Laboratory, Imperial College London, Los Alamos National Laboratory and General Atomics.
MagLIF platform: S. A. Slutz et al, Phys. Plasmas 17, 056303 (2010)
MagLIF Experimental Data: M. R. Gomez et al, Phys. Rev. Lett. 125, 155002 (2020)
Recent Performance Breakthroughs
Since the introduction of the MagLIF target in 2011, fusion performance has progressed at a remarkable rate. The figure on the right reproduces Figure 2 from Wurzel and Hsu 2022, and plots the triple product (nT𝛕) against the measured ion temperature for a wide range of experimental platforms. The premier laser-driven IFE platforms, OMEGA and NIF, show high nT𝛕 at moderate ion temperatures (few keV), with a notable exception being the NIF ignition shot N210808, with an nT𝛕 of 5.2x10^21 keV m-3 s and an ion temperature of 10 keV. This is the only point on the plot above a Lawson criterion of unity. Magnetic confinement facilities typically show significantly higher ion temperatures, triple products in the range of ~10^20 keV m-3 s, and a Lawson criterion between 0.1 and 1. The MagLIF data on the original plot showed data from Z shots in 2015 which demonstrated nT𝛕 ~3x10^20 keV m-3 s and ion temperatures approaching 3 keV. Data from 2022 (Knapp 2022) improves on these values, where the best shot gives nT𝛕 exceeding 10^21 keV m-3 s, making MagLIF the only platform other than NIF to achieve such a value. Peak ion temperatures were 3.3 keV and the Lawson criterion was close to 0.1. This breakthrough result places MagLIF and MD-IFE in an ideal position to make rapid progress on the technological challenges of energy production.
Modified from Wurzel & Hsu, Phys. Plasmas 29, 062103 (2022) with data (yellow circles) from Knapp et al, Phys. Plasmas 29, 052711 (2022)
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This excellent single shot performance needs translation to a rep-rated environment suitable for fusion energy, and this is enabled by 2 key technologies; advanced targets and scalable pulsed power drivers.
Advanced Targets
Targets on the Z machine uses external field coils to produce the seed magnetic field required. These are not compatible with rep-rated operation for energy. Advanced targets are under development in which this field is generated through the target itself by introducing a helical element to the current flow. These target also reduce load inductance, allowing higher energy deposition, and are more amenable to mass manufacture for a power plant
Scalable Pulser Power Driver Technology
The Z machine is sub-scale, in that there is insufficient electrical current to achieve fusion ignition. A power plant will use a 70MA driver capable of one shot every 10 seconds. Sandia has already developed several pulsed power architectures which could be used to construct this driver, including Linear Transformer Driver (LTD) and the Impedance Match Marx Generator (IMG)
Conceptual Design of a 70 MA ignition-scale pulsed power driver for MD-IFE (from Stygar et al, Phys. Rev. ST Accel. Beams 18, 110401 (2015)
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