Fusion Reactors: Inertial Confinement

The National Ignition Facility (NIF) at Lawrence Livermore Laboratory is exp­erimenting with using laser beams to induce fusion. In the NIF device, 192 laser beams will focus on single point in a 10-meter-diameter target chamber called a hohlraum. A hohlraum is "a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity" (Science & Engineering Encyclopaedia).

At the focal point inside the target chamber, there will be a pea-sized pellet of deuterium-tritium encased in a small, plastic cylinder. The power from the lasers (1.8 million joules) will heat the cylinder and generate X-rays. The heat and radiation will convert the pellet into plasma and compress it until fusion occurs. The fusion reaction will be short-lived, about one-millionth of a second, but will yield 50 to 100 times more energy than is needed to initiate the fusion reaction. A reactor of this type would have multiple targets that would be ignited in succession to generate sustained heat production. Scientists estimate that each target can be made for as little as $0.25, making the fusion power plant cost efficient.

Like the magnetic-confinement fusion reactor, the heat from inertial-confinement fusion will be passed to a heat exchanger to make steam for producing electricity.

Applications of Fusion

The main application for fusion is in making electricity. Nuclear fusion can pro­vide a safe, clean energy source for future generations with several advantages over current fission reactors:

Abundant fuel supply - Deuterium can be readily extracted from seawater, and excess tritium can be made in the fusion reactor itself from lithium, which is readily available in the Earth's crust. Uranium for fission is rare, and it must be mined and then enriched for use in reactors.

Safe - The amounts of fuel used for fusion are small compared to fission reactors. This is so that uncontrolled releases of energy do not occur. Most fusion reactors make less radiation than the natural background radiation we live with in our daily lives.

Clean - No combustion occurs in nuclear power (fission or fusion), so there is no air pollution.

Less nuclear waste - Fusion reactors will not produce high-level nuclear wastes like their fission counterparts, so disposal will be less of a problem. In addition, the wastes will not be of weapons-grade nuclear materials as is the case in fission reactors.

NASA is currently looking into developing small-scale fusion reactors for powering­ deep-space rockets. Fusion propulsion would boast an unlimited fuel supply (hydrogen), would be more efficient and would ultimately lead to faster rockets.

For more information on nuclear fusion reactors and related topics, check out the links on the next page.

Cold fusion

In 1989, researchers in the United States and Great Britain claimed to have made a fusion reactor at room temperature without confining high-temperature plasmas. They made an electrode of palladium, placed it in a thermos of heavy water (deuterium oxide) and passed an electrical current through the water. They claimed that the palladium catalyzed fusion by allowing deuterium atoms to get close enough for fusion to occur. However, several scientists in many countries failed to get the same result.

But in April 2005, cold fusion got a major boost. Scientists at UCLA initiated fusion using a pyroelectric crystal. They put the crystal into a small container filled with hydrogen, warmed the crystal to produce an electric field and inserted a metal wire into the container to focus the charge. The focused electric field powerfully repelled the positively charged hydrogen nuclei, and in the rush away from the wire, the nuclei smashed into eachother with enough force to fuse. The reaction took place at room temperature. See Coming in out of the cold: Cold fusion, for real (csmonitor.com) to learn more.