"Long before it's in the papers"
January 27, 2015


Scientists take step toward usable fusion energy

Feb. 12, 2014
Special to World Science  

Sci­en­tists have tak­en a key step to­ward us­ing fu­sion, the pro­cess that pow­ers the Sun, to pro­duce en­er­gy, ac­cord­ing to a re­port to ap­pear Feb. 13 in the re­search jour­nal Na­ture.

Fu­sion en­er­gy is en­vi­sioned as a way to pro­duce vir­tu­ally un­lim­it­ed pow­er to supply the Earth’s needs, but no one has suc­ceeded in de­vis­ing a fu­sion pro­cess that gives out more en­er­gy than it takes in.

Two atoms, deuterium and tri­tium, fuse to­gether, form­ing a he­lium nuc­leus, a neu­tron and lots of en­er­gy. (Image courtesy F4E)

Phys­i­cists at Law­rence Liv­er­more Na­t­ional Lab­o­r­a­to­ry in Cal­i­for­nia said they suc­ceeded in at least re­leas­ing more en­er­gy through a fu­sion re­ac­tion than is ab­sorbed by the fu­el that trig­gers the re­ac­tion. 

But that en­er­gy is still only about a hun­dredth of the to­tal en­er­gy needed to set up the pro­cess in the first place, they said, most of which goes in­to com­press­ing a fu­el pel­let where fu­sion takes place.

“The next nec­es­sary step would be to achieve a to­tal gain, where en­er­gy en­ter­ing the whole sys­tem is ex­ceeded by the en­er­gy pro­duced,” the re­search­ers said in a state­ment. None­the­less, “we are clos­er than an­y­one has ev­er got­ten” to ob­tain­ing fu­sion as a vi­a­ble en­er­gy source, said Omar Hur­ri­cane, a re­searcher at the lab­o­r­a­to­ry and one of the au­thors of the re­port.

The whole pro­cess took place in a space less wide than a hu­man hair and in only the ti­ni­est frac­tion of a sec­ond—150 pi­cosec­onds, to be ex­act.

Their pro­cess used in­er­tial con­fine­ment fu­sion, which ini­ti­ates nu­clear fu­sion re­ac­tions by heat­ing fu­el pel­lets un­til they im­plode, com­press­ing the fu­el. The fu­el con­sists of deu­ter­i­um and tri­tium—iso­topes, or var­i­ant forms, of hy­dro­gen. When squeezed to­geth­er, they merge cre­at­ing a he­li­um nu­cle­us, and re­leas­ing en­er­gy along with a neu­tron, or sub­a­tom­ic par­t­i­cle.

The con­fine­ment squeezes the atoms of fu­el “to get them run­ning to­ward each oth­er at high ve­lo­city, which over­comes their mu­tu­al elec­tri­cal re­pul­sion,” said Hur­ri­cane.

The sci­en­tists said they used 192 lasers to heat and com­press a small pel­let of fu­el to the point where the fu­sion re­ac­tions take place. 

What made the pro­cess suc­cess­ful was that the sci­en­tists man­aged to in­i­ti­ate a pro­cess called “boot­strap­ping,” a sort of vi­cious cy­cle, Hur­ri­cane said. In this, “the al­pha par­t­i­cles [he­li­um nu­cle­i] that come out of that re­ac­tion start leav­ing en­er­gy be­hind and caus­ing the tem­per­a­ture to go up” with­in the ti­ny cham­ber. “When the tem­per­a­ture goes up, the re­ac­tion rate goes up, and when the re­ac­tion rate goes up, you make more al­pha par­t­i­cles.”

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Scientists have taken a key step toward using fusion, the process that powers the Sun, to produce energy, according to a paper published in the research journal Nature. Fusion energy is envisioned as a way to produce virtually unlimited power to supply the Earth’s needs, but no one has succeeded in devising a fusion process that gives out more energy than it takes in. The physicists at Lawrence Livermore National Laboratory in California said they succeeded in at least releasing more energy through a fusion reaction than is absorbed by the fuel that triggers the reaction. But that energy is still only about a hundredth of the total energy needed to set up the process in the first place, they said. Most of that goes into compressing a fuel pellet where the fusion takes place. “The next necessary step would be to achieve a total gain, where energy entering the whole system is exceeded by the energy produced,” the researchers said in a statement. Nonetheless, “we are closer than anyone has ever gotten” to obtaining fusion as a viable energy source, said Omar Hurricane, a researcher at the laboratory and one of the authors of the report. The whole process took place in a space less wide than a human hair and in only the tiniest fraction of a second—150 picoseconds, to be exact. Their process used inertial confinement fusion, which initiates nuclear fusion reactions by heating fuel pellets until they implode, compressing the fuel. The fuel consists of deuterium and tritium—isotopes, or variant forms, of hydrogen. When squeezed together, they merge creating a helium nucleus, and releasing energy along with a neutron, or subatomic particle. The confinement squeezes the atoms of fuel “to get them running toward each other at high velocity, which overcomes their mutual electrical repulsion,” said Hurricane. The scientists said they used 192 lasers to heat and compress a small pellet of fuel to the point where the fusion reactions take place. What made the process successful was that the scientists managed to initiate a process called “bootstrapping,” a sort of vicious cycle, Hurricane said. In this, “the alpha particles [helium nuclei] that come out of that reaction start leaving energy behind and causing the temperature to go up” within the tiny chamber. “When the temperature goes up, the reaction rate goes up, and when the reaction rate goes up, you make more alpha particles.”