The Fundamental Parameter Space of Controlled Thermonuclear Fusion

Exploring the Range of Options

Image for post
Image for post
Image from Richard Siemon’s Overview of Fusion Parameter Space, 2013

Few people are aware of the many conditions under which fusion can occur. Luckily, Irv Lindemuth and Richard Siemon have written a review of fusion to help the rest of us identify the density-temperature space where fusion gain can be achieved. The analysis offers a general understanding why there is such an extreme difference between the conventional approaches to controlled fusion, MCF (which uses a giant “magnetic cage” and ICF (which uses hundreds of laser beams pointed at a small target). It also helps us see how much of the parameter space of fusion has yet to be explored.

This clarifying overview of fusion came to our attention at the Fusion Power Associates Meeting, where Dr. Lindemuth presented a talk, now available (PDF file): Fusion Parameter Space from First Principles

See also: Article by I. R. Lindemuth, R. E. Siemon, Am. J. Phys., Vol. 77, №5, May 2009. And, of course, Siemon’s Overview from which the image above is taken.

The Abstract

We apply a few simple first-principles equations to identify the parameter space in which controlled fusion might be possible. Fundamental physical parameters such as minimum size, energy, and power as well as cost are estimated. We explain why the fusion fuel density in inertial confinement fusion is more than 1011times larger than the fuel density in magnetic confinement fusion. We introduce magnetized target fusion as one possible way of accessing a density regime that is intermediate between the two extremes of inertial confinement fusion and magnetic confinement fusion and is potentially lower cost than either of these two.

Lindemuth and Siemon shine a light on magnetized target fusion, but their framework can be leveraged for plotting and comparing other approaches as well. It’s a handy document and covers a lot of the basics of fusion.

We also provide a unifying framework to make it possible for those familiar with one approach to be conversant in any other approach.

MCF and ICF

From the introduction:

The two commonly recognized paths to controlled thermonuclear fusion energy have proven to be long and costly. Physicists not working in the fusion field are generally aware of two approahes to achieving controlled fusion reactions, magnetic confinement fusion (MCF) and intertial confinement fusion (ICF), and that these approaches are embodied in two multi-billion dollar facilities known as ITER (formerly an acronym for International Thermonuclear Experimental Reactor) for magnetic confinement fusion and NIF (National Ignition Facility) for inertial confinement fusion.

Most physicists are also aware that fusion reactions occur only at high temperatures, hence the name thermonuclear fusion.

There is more limited awareness that the density of the fusion fuel (a deuterium-tritium mixture) in the two approaches differs by a factor of more than 1011. The fuel density in ITER will be about 1014ions/cm3(mass density p=4.2 x10–10g/cm3), and the hot spot of a NIF target will be greater than 1025ions/cm3(p=42g/cm3).

This very large density difference leads to different physics challenges, for example, contrast the challenge of steady state magnetic confinement of MCF with the hydrodynamic implosion stability of ICF.

The problem-solving approach is also different; MCF relies heavily on empirically determined scaling laws, and ICF relies heavily on large-scale computer simulations.

A Bridge from this article

The article was written with the goal of bridging the gap from plasma specialists to a broader audience of physicists.

It’s still written for physicists. And is behind a paywall.

We’d like to take steps to get this framework even more comprehensible and available, such that a general audience can relate to it.

Originally published at www.fusionenergyleague.org.

Fusion Energy League

We bring people and nuclei together.

Medium is an open platform where 170 million readers come to find insightful and dynamic thinking. Here, expert and undiscovered voices alike dive into the heart of any topic and bring new ideas to the surface. Learn more

Follow the writers, publications, and topics that matter to you, and you’ll see them on your homepage and in your inbox. Explore

If you have a story to tell, knowledge to share, or a perspective to offer — welcome home. It’s easy and free to post your thinking on any topic. Write on Medium

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store