Nuclear Fusion Achieves Energy Gain

Popular Science

Popular Science

For the first time, scientists at the National Ignition Facility (NIF) in Livermore, California have successfully produced more energy with a fusion reaction than was used to start it.

Fusion is the process that hydrogen nuclei undergo inside of stars due to the intense heat and pressure found there; if fusion reactions could be mastered for commercial use, the technique would be incredibly efficient and entirely renewable, providing us with enough energy to sustain our current usage for billions of years. Scientists have been trying for decades to create a self-sustaining fusion reaction with an overall gain in energy, a process called ignition.

NIF is funded by the U.S. Department of Energy’s National Nuclear Security Administration and has been in operation since 2009. The facility describes how its laser-driven approach begins on its website:

A weak laser pulse—about 1 billionth of a joule—is created, split, and carried on optical fibers to 48 preamplifiers that increase the pulse’s energy by a factor of 10 billion, to a few joules. The 48 beams are then split into four beams each for injection into the 192 main laser amplifier beamlines.

From there, the 192 laser beams are split into quads of 2×2 arrays and pass through a final optics assembly, where they are converted from infrared to ultraviolet light and aimed at a gold chamber, which converts the lasers’ energy into X-rays. Four of these pulses squeeze a small fuel pellet containing deuterium and tritium (isotopes of hydrogen), causing the pellet to implode and undergo fusion. By the time the process has completed, the original lasers have traveled 1500 meters over the course of 1.5 microseconds.

Though NIF researchers have successfully achieved an energy gain by adjusting the laser setup to hit the gold chamber in three pulses, heating it faster, there are still a few roadblocks ahead. While their experiment, which produced 15 kJ of energy, used 10kJ of fuel, the laser setup itself, the total energy input was around 2 MJ (yes, megajoules). Much of the energy is lost along the way in the conversion of light, so the team still has a long way to go, but this is an important milestone on the road toward ignition.

Even if the team does reach its goal of ignition, there are still engineering issues that need to be resolved to make it a practical energy source: creating the fuel and setting up the lasers is a burdensome process and the intense laser blasts degrade the machine too quickly for long-term commercial use.

If all of the above issues can be solved, the world certainly has a brighter energy future ahead than would otherwise be the case.


The Universe has been Measured to 1% Accuracy

Courtesy: Lawrence Berkeley National Laboratory

Courtesy: Lawrence Berkeley National Laboratory

At the 223rd meeting of the American Astronomical Society in Washington, DC, astronomers announced that the distance between galaxies in the universe has been measured with 1% accuracy. The feat was achieved by the BOSS (Baryon Oscillation Spectroscopic Survey) team with the Sloan Foundation Telescope in New Mexico. The principal investigator of BOSS, Professor David Schlegel of the Lawrence Berkeley National Laboratory, had the following to say:

I now know the size of the universe better than I know the size of my house.

Twenty years ago astronomers were arguing about estimates that differed by up to 50%. Five years ago, we’d refined that uncertainty to 5%; a year ago it was 2%.

Baryon acoustic oscillations (BAOs) were used as a metric to measure distances between galaxies; BAOs are the remnants of pressure waves that moved through the universe in its early stages. The behavior of BAOs in the early universe shaped the layout of galaxies that we have today. The BOSS team used these waves to precisely measure large distances from far away, allowing the team to calculate vast intergalactic distances to within 1% accuracy.

The distances from this study will provide a standard in astronomy for years to come, which will allow astronomers to determine the nature of fundamental cosmic forces. The data have already indicated that dark energy is a cosmological constant – a force whose strength is not affected by variances in space or time.

The data also indicate that the universe is extremely flat, which has implications for whether or not the universe is infinite:

While we can’t say with certainty, it’s likely the universe extends forever in space and will go on forever in time. Our results are consistent with an infinite universe.

-Prof. Schlegel

When the survey is completed (estimated for June), it will have collected high-quality spectra of 1.3 million galaxies and 160,000 quasars.

One percent accuracy will be the standard for a long time to come.