Dramatic advances in powerful, high-intensity lasers are making it viable for scientists to pursue what was once thought impossible: creating fusion energy based on hydrogen-boron reactions. And an Australian physicist is in the lead, armed with a patented design and working with international collaborators on the remaining scientific challenges.

In a paper in the scientific journal Laser and Particle Beams today, lead author Heinrich Hora from the University of New South Wales in Sydney and international colleagues argue that the path to hydrogen-boron fusion is now viable, and may be closer to realization than other approaches, such as the deuterium-tritium fusion approach being pursued by U.S. National Ignition Facility (NIF) and the International Thermonuclear Experimental Reactor under construction in France.

"I think this puts our approach ahead of all other fusion energy technologies," said Hora, who predicted in the 1970s that fusing hydrogen and boron might be possible without the need for thermal equilibrium. Rather than heat fuel to the temperature of the Sun using massive, high-strength magnets to control superhot plasmas inside a doughnut-shaped toroidal chamber (as in ITER), hydrogen-boron fusion is achieved using two powerful lasers in rapid bursts, which apply precise non-linear forces to compress the nuclei together.

Hydrogen-boron fusion produces no neutrons and, therefore, no radioactivity in its primary reaction. And unlike most other sources of power production - like coal, gas and nuclear, which rely on heating liquids like water to drive turbines - the energy generated by hydrogen-boron fusion converts directly into electricity. But the downside has always been that this needs much higher temperatures and densities - almost 3 billion degrees Celsius, or 200 times hotter than the core of the Sun.

However, dramatic advances in laser technology are close to making the two-laser approach feasible, and a spate of recent experiments around the world indicate that an 'avalanche' fusion reaction could be triggered in the trillionth-of-a-second blast from a petawatt-scale laser pulse, whose fleeting bursts pack a quadrillion watts of power. If scientists could exploit this avalanche, Hora said, a breakthrough in proton-boron fusion was imminent.

"It is a most exciting thing to see these reactions confirmed in recent experiments and simulations," said Hora, an emeritus professor of theoretical physics at UNSW. "Not just because it proves some of my earlier theoretical work, but they have also measured the laser-initiated chain reaction to create one billion-fold higher energy output than predicted under thermal equilibrium conditions."

Together with 10 colleagues in six nations - including from Israel's Soreq Nuclear Research Centre and the University of California, Berkeley - Hora describes a roadmap for the development of hydrogen-boron fusion based on his design, bringing together recent breakthroughs and detailing what further research is needed to make the reactor a reality.

An Australian spin-off company, HB11 Energy, holds the patents for Hora's process. "If the next few years of research don't uncover any major engineering hurdles, we could have prototype reactor within a decade," said Warren McKenzie, managing director of HB11.

"From an engineering perspective, our approach will be a much simpler project because the fuels and waste are safe, the reactor won't need a heat exchanger and steam turbine generator, and the lasers we need can be bought off the shelf," he added.

The project, named DE-STAR (Directed Energy System for Targeting of Asteroids and exploRation), envisions a large phased-array laser in Earth orbit to deflect asteroids, comets, and other NEOs endangering the planet. There is also a much smaller, though similar system being considered, called DE-STARLITE, that could travel alongside the target, slowly deflecting it from nearby over a long period.

According to the authors of these proposals, their goal was to create an orbital planetary defense system capable of heating the surface of potentially hazardous objects to the point of vaporization. They emphasize that vaporization on the surface of an object continually ejects vaporized material, creating a reactionary force that pushes the object into a new path. This can be accomplished by lasers deployed on spacecraft stationed near the asteroid.

The system should be capable of projecting a laser at a distant asteroid with sufficient flux to heat a spot on the surface and vaporize solid rock. Currently, high-powered lasers deliver sufficient energy density to melt and vaporize any known material.

(a) Concept diagram of an orbiting DE-STAR engaged in multiple tasks including asteroid diversion, composition analysis, and long-range spacecraft power and propulsion. (b) Visualization of a laser beam with relevant physical phenomenon …more

"Generally speaking, the technology is available today. The main challenge with building a full DE-STAR is the necessary scale to be effective," Qicheng Zhang of the University of California, Santa Barbara, one of the authors of the project, told Astrowatch.net.

Zhang and his colleagues claim that if DE-STAR had a 330-feet-wide phased laser array, it could divert volatile-laden asteroids 330 feet in diameter by initiating engagement at about two million miles. However, DE-STARLITE, being a much smaller and less expensive system, is the more practical option. For instance, a 20 kW version of DE-STARLITE operating for 15 years could deflect an Apophis-size (1,066 feet) asteroid at a distance equal to Earth's diameter. A 1 MW version could deflect all known threats up to 1,640 feet in diameter with five-year laser activity.

"The bigger the NEO, the longer the time needed. The bigger the laser, the shorter the time needed. With a very small 20 kW DE-STARLITE, a 300-meter-wide (1,000 foot) asteroid can be deflected in 15 years. Smaller asteroids can be deflected in under a year, after the spacecraft's arrival at the asteroid," Zhang said.

According to the scientists, DE-STARLITE would be ineffective at deflecting targets on short notice due to the time required for transit to the target asteroid. Thus the DE-STAR system seems to be a last line of defense on short notice.

A full stand-off system like DE-STAR is still considered as a possibility for the more distant future for its ability to rapidly respond to identified threats. It could also provide one of the few options for defense against long-period comets, which modern technology is often incapable of reaching by spacecraft.

An orbiting DE-STAR of adequate size would have the capability of reacting to small or moderately sized objects that are discovered with limited time to react. However, the researchers note that actual effectiveness of a deflection mission depends strongly on the target. A mission optimized for one target may be ineffective when applied to another, even one of the same size and composition.

"It depends on the exact circumstances. If, say, a 100-meter-wide asteroid were found today on a collision course with Earth next week, directed energy would not be a viable solution as that would require a very large laser array that would be far bigger than an equally effective single-use impactor or explosive. If, on the other hand, we find that same asteroid 30 years before impact, directed energy would be very effective, even with 10 kW lasers which are far below the power of many lasers in possession by the U.S. military today," Zhang explained.

The concepts of DE-STAR and DE-STARLITE show that the directed energy method could be a promising technology for planetary defense. It could save our planet from small- to mile-class hazardous objects. With the recent technology advancements it is now feasible to consider the methods based on laser ablation as one of the most relevant and effective techniques of asteroid deflection.