Image of sun_plasma.jpg
Image courtesy of NASA

The ultimate energy source

Fusion occurs when two atomic nuclei are joined together. To fuse the atoms, the force that repels them as they come together must be overcome. Accelerators accomplish this by forcing molecules to collide with one another at very high temperatures (high temperatures are simply molecules moving at high speeds).

When light nuclei are involved, fusion can produce more energy than was required to start the reaction. This process is the force that powers the Sun, whose source of energy is an ongoing fusion chain reaction.

As an unconfined event, fusion was first developed for use in nuclear weapons. Fusion’s great potential as a new energy source depends on scientists’ ability to harness its power in laboratory events. The Z machine is central to that effort.

The major challenge for fusion researchers is to figure out a way to contain hot plasma — hot enough to melt any container –long enough to extract useful energy.

Paths to fusion

One approach, used at ITER in southern France, involves confining low-density plasma for a relatively long time — as much as 20 minutes — using magnetic fields, which don’t melt. This approach is known as magnetic confinement fusion.

The other major approach works under the premise that another way to use plasma is to create it in a series of bursts of energy. The trick then is to get as much energy as possible out of small, high-density plasma fusion targets before they expand and cool. This is what is known as inertial confinement fusion, and this is the main approach used at Z.

Inertial confinement fusion’s target is a BB-sized fuel capsule placed inside a container about the size of a spool of thread. An enormous pulse of power is focused for a few nanoseconds on the fuel capsule containing a mixture of hydrogen isotopes (deuterium and tritium). The source of power is often a laser, or in the case of the Z machine, a Z pinch. Whatever the source, the intense burst of power causes the target to implode, compressing the material in it and heating it to temperatures near those at the center of the Sun. If the heat and pressure are intense enough, the conditions should ignite a fusion reaction.

For years, Z’s fusion work was primarily for weapons effects simulations, weapons physics, and other scientific purposes, but there is a synergy between that kind of research and the potential energy applications of fusion.

Fusion research for weapons and fusion research for energy share many of the same basic physics issues, and high-yield fusion in the laboratory would translate into progress in both areas.

MagLIF: a new approach

Z machine researchers are working on magnetized liner inertial fusion (MagLIF), a new and exciting approach to fusion, never tried before.

MagLIF aims to generate fusion energy by using magnetic fields to crush a fuel-filled metal cylinder, called a liner. The process, called inertial confinement fusion, is similar to the approach taken at Lawrence Livermore National Laboratory’s National Ignition Facility, but distinguishes itself by using magnetic fields, rather than lasers, to compress the fuel.

Scientists have begun the first MagLIF experiments and have their sights set on reaching the goal of creating a burning plasma for stewardship applications.

Computer simulations/calculations indicate MagLIF can eventually achieve scientific breakeven on the Z machine.

Z researchers know that the drive energy and fuel type necessary to achieve scientific breakeven will require infrastructure improvements over the next few years.

Scientists expect to determine the viability of this concept within the next three years.