Historical research guide · 0797 · 2012
High-Gain Magnetized Inertial Fusion
Stephen A. Slutz · Roger A. Vesey
In one minute
Stephen Slutz and Roger Vesey, at Sandia National Laboratories, take the fusion scheme built around Sandia’s Z machine and show in simulation how it could reach the yields an actual power plant needs. The scheme, magnetized liner inertial fusion, wraps deuterium-tritium fuel in a metal cylinder, magnetizes it, warms it with a laser and then crushes the cylinder with a huge pulse of current. Magnetizing the fuel holds the heat in and keeps the fast helium nuclei from escaping, which is what makes ignition reachable at a gentle squeeze. The new ingredient here is a layer of frozen deuterium-tritium ice lining the inside of the cylinder. The simulations show a burn wave leaving the hot centre and eating outward into that cold dense ice, provided the hot spot is dense enough to start it. At a drive current of 60 million amps the simulated energy gain passes 100, and at 70 million amps it passes 1000.
Connection
Chapter 12 treats fusion as the near-term door the vacuum programme opens onto, and this paper is the design study that puts a number on it: a pulsed-power machine of the kind Sandia already runs, plus a ring of deuterium-tritium ice, returning a hundred times the energy the liner absorbs. Gain here is a fuel-burning reactor returning more than it draws, which is a separate question from drawing energy from the vacuum.
From the source
Magnetizing the fuel substantially eases the plasma conditions needed for significant fusion yield, which is what makes ignition reachable with the slow implosion and modest radial squeeze a cylindrical liner gives you — the point of the magnetized liner inertial fusion concept the authors published in Physics of Plasmas 17, 056303 in 2010.Abstract, first two sentences
Adding a cryogenic layer of deuterium-tritium ice inside the liner turns the scheme from a batch burn into a propagating one: the simulations show a burn wave moving radially out of the magnetized hot spot into the surrounding much denser cold fuel, provided the hot spot reaches sufficient areal density.Abstract, third and fourth sentences
For a drive current of 60 million amps the simulated gain exceeds 100, which the authors state is more than adequate for fusion energy applications, and for 70 million amps the simulated gain exceeds 1000.Abstract, final two sentences
The magnetic field is a two-sided knob and there is an optimum: inhibiting radial heat conduction and holding the alpha particles in lowers the hot-spot areal density needed for ignition, while too strong a field slows the burn wave moving into the cold fuel — so the high-gain design lowers the initial axial field to about 10 tesla, where the gas-only design used about 30.Authors’ companion Sandia presentation SAND2011-5344C, radial-propagation slides and summary slide
The cost of the extra ice layer is modest: the laser preheat energy rises to roughly 22 kilojoules, and the authors’ own gain threshold for inertial fusion energy — set by the electricity conversion efficiency, the recirculated power fraction and the driver efficiency of a magnetic implosion — is a gain of about 50, which the simulated designs clear by a wide margin.Authors’ companion Sandia presentation SAND2011-5344C, high-gain requirement and summary slides
The measurement that would settle the design is the instability behaviour of the liner surface: two-dimensional simulations say short-wavelength magneto-Rayleigh-Taylor growth is the most damaging feature and that root-mean-square surface roughness of less than about 20 nanometres may be required, and the authors call for three-dimensional simulation and further experiment to fix the real tolerance.Authors’ companion Sandia presentation SAND2011-5344C, magneto-Rayleigh-Taylor slides and summary slide
The way in
https://doi.org/10.1103/PhysRevLett.108.025003How to cite it
Stephen A. Slutz, Roger A. Vesey (2012) High-Gain Magnetized Inertial Fusion doi:10.1103/PhysRevLett.108.025003