Skip to content
Try: plasma ITER tokamak
↑↓ to navigate Enter to select Esc to close

Inertial Confinement Fusion

Inertial confinement fusion (ICF) is a method in which a small fuel pellet is instantaneously compressed and heated by powerful lasers or similar drivers, so that fusion reactions occur during the very brief time the fuel holds its shape through inertia.

Simple Definition (High School)

Section titled “Simple Definition (High School)”

Whereas magnetic confinement “gently holds plasma in a magnetic cage,” inertial confinement is a “get it done in an instant” approach. A tiny ball of fuel about the size of a grain of rice is blasted from all directions by powerful lasers fired simultaneously. The surface of the ball then explodes outward, and the recoil creates a strong inward pressure toward the center, squeezing the fuel together all at once. This inward compression is called implosion. At the moment the center becomes hotter and denser than the core of the Sun, fusion ignites, and the reaction finishes before the fuel can fly apart. What confines the fuel is not a magnetic field, but inertia itself: the fact that matter cannot move suddenly.

Precise Definition (Undergraduate and Above)

Section titled “Precise Definition (Undergraduate and Above)”

In inertial confinement, to obtain enough reactions during the time τ\tau that the fuel holds its shape through inertia, the shortness of the confinement time is compensated by overwhelmingly high density nn. In satisfying the nτn \tau that appears in the Lawson criterion, magnetic confinement takes a low-density, long-duration approach, while inertial confinement takes the exact opposite strategy of ultra-high density and extremely short duration. In implosion, the fuel is compressed to several hundred to about a thousand times solid density, ignited in a high-temperature region (the hot spot) formed at the center, and the reaction burns outward into the surrounding cold fuel.

There are two ways to deliver the energy. Direct drive shines the lasers directly onto the pellet surface; it is energetically efficient but makes it difficult to keep the irradiation uniform. Indirect drive places the pellet inside a small metal cylinder (a hohlraum) and heats the inner wall of the cylinder with lasers, causing the implosion via the X-rays that are generated; it offers superior uniformity. The National Ignition Facility (NIF) in the United States uses indirect drive.

Role in Fusion Research

Section titled “Role in Fusion Research”

Inertial confinement is one of the two major approaches to fusion, alongside magnetic confinement. In December 2022, NIF achieved ignition, extracting more fusion energy than the laser energy put in, for the first time in human history, demonstrating that fusion is scientifically feasible. This achievement was a major milestone for fusion research as a whole, heightening interest in the engineering challenges of turning inertial confinement into a source of electricity.

Learn More

Section titled “Learn More”
Section titled “Related Terms”