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Fusion Progress Validates A 40-Year Quest

A 10-quadrillion-watt burst at Lawrence Livermore is good news for LLE as well

When researchers at Lawrence Livermore National Laboratory this week announced they had ignited a burst of more than 10 quadrillion watts of fusion power, it was cause for celebration at the University of Rochester’s Laboratory for Laser Energetics as well.

The announcement validates the laser-driven implosion techniques that the two labs have closely collaborated on, as a way to assess the viability of the nation’s nuclear weapons stockpile and perhaps even pave the way for an abundant supply of clean energy.

Even skeptics were impressed by the results of the August 8 experiment. In a story in the New York Times, for example, Stephen Bodner, a retired plasma physicist who has long been a critic of Lawrence Livermore’s National Ignition Facility (NIF), expressed surprise, adding, “they have come close enough to their goal of ignition and break-even to call it a success.”

Says Riccardo Betti, LLE’s chief scientist and a leading expert in the field, “This really clears up a lot of the concern about the ability to ignite thermonuclear fuel in the lab, or that we would need much bigger lasers to do it. This is a major step forward.”

Since the early 1970s, scientists have pursued the possibility of using high-power lasers to compress thermonuclear material long enough, at high enough temperatures to trigger ignition — resulting in an output of fusion energy many times greater than the energy required for ignition. The entire process of compression and ignition, which occurs in nanoseconds, is called inertial confinement fusion (ICF).

A news release from Lawrence Livermore said the Aug. 8 experiment was enabled by focusing 192 gigantic lasers onto a target the size of a BB, producing a hot spot the diameter of a human hair, which then generated more than 10 quadrillion watts of fusion power for 100 trillionths of a second.

“This advancement puts researchers at the threshold of fusion ignition, an important goal of the NIF, and opens access to a new experimental regime.” the news release stated.

More promisingly, the fusion reactions for the first time appeared to be self-sustaining, meaning that the torrent of particles flowing outward from the hot spot at the center the pellet heated surrounding hydrogen atoms and caused them to fuse as well, the New York Times reported.

Betti is particularly optimistic because only minor adjustments to the apparatus and fuel target at (NIF) were required to dramatically increase the energy yields within a short time frame.

“It’s not some magic thing that they did,” Betti says. “That’s what you would expect when you get close to triggering the thermal instability that occurs at full ignition; even small changes to the experimental setup can produce big changes in fusion yield once ignition occurs.” That bodes well for even bigger fusion yields in the future, he says.

The increase in fusion energy output places scientists much closer to replicating the complex physical processes that drive nuclear weapon performance, for example. Even larger energy gains from the ignition experiments will be needed for properly assessing the nuclear stockpile. “It needs more tweaking and better understanding,” Betti says, “but we are not far from completing the job. The LLE fusion scheme could get us there since it is devised to achieve the highest possible energy gains with laser fusion ”

However, major hurdles remain in the quest to use inertial confinement fusion as a source of abundant, clean energy. “Proving that you can make energy is one thing; putting it on a power grid is a humongous step, requiring engineering that is probably as big of a task, if not bigger, than the physics milestone that has just been achieved,” Betti says.

“It’s really hard to even attempt to assess what a reasonable timetable would be.”

Ignition at Lawrence Livermore was achieved by “indirect drive,” meaning its high-energy lasers were directed at and into a small box, or holhraum, made of gold, with a fuel capsule of deuterium and tritium inside. The laser beams heat the gold, causing it to emanate X-rays, which drive the implosion of the fuel.

LLE, which uses the 60 less powerful lasers of the OMEGA facility, primarily employs “direct drive,” meaning laser beams converge directly on the fuel capsule.

But the underlying principles are similar enough that experiments at Rochester can help inform what Livermore is doing, and vice versa by extrapolation.

“And when we extrapolate our experiments to NIF laser energies, we are not that far from ignition either,” Betti says.

“So a lot of the fundamental physics is settled and now it’s a just a question of making improvements to determine the maximum fusion yield that we can get out of the National Ignition Facility. Will it be a few megajoules, or tens of megajoules? And what about the direct drive that we do at Rochester? Can we get tens of megajoules or hundreds of megajoules at the laser energies of NIF?. Those are the questions from now on.”

Mike Campbell, the director of LLE, adds, “This is a great achievement for the entire field and even though accomplished at LLNL with NIF, scientists and engineers from the broad ICF community have contributed to this success. Research on OMEGA played a critical role in developing the physics and diagnostics that enabled this achievement. We are very proud to be a member of this community and look forward to even greater fusion performance in the future.””

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