Every part of a fusion reactor is designed for maximum efficiency. Well, in theory, at least. In reality, the materials chosen to bring us closer to fusion don’t always perform as expected, leading to structural glitches that obstruct fusion reactions.
Diamond capsules used to safely store hydrogen fuel are no exception, but a new study offers some guidance for researchers hoping to preemptively address these material shortcomings. In a recent Matter paper, material scientists describe how the extreme pressures of fusion experiments introduce imperfections to the diamond capsule, ultimately compromising the experiment itself.
“These imperfections can disrupt the implosion symmetry, which in turn can reduce energy yield or even prevent ignition,” the researchers explained in a statement. Considering how costly and time-consuming each experimental run can be, paying close attention to understanding and improving diamond capsule designs could greatly benefit fusion projects, they added.
In theory, nuclear fusion is an energy alternative that combines two lightweight atoms to generate massive amounts of energy. Unlike nuclear fission, which splits heavy atoms to produce energy, fusion doesn’t leave harmful radioactive waste behind. But for many reasons—including the one introduced here—widespread use of fusion technology is still far out of reach. Nuclear reactors today run on fission.
Hang in there, diamond
Large facilities like the Lawrence Livermore National Laboratory’s National Ignition Facility (NIF) use diamond capsules to enclose deuterium and tritium, the two hydrogen isotopes used in fusion reactions. At the NIF, powerful lasers compress these capsules to extreme pressures. Ideally, this triggers a symmetrical implosion—the system collapses into itself—creating the high-pressure, high-temperature environment that should induce nuclear fusion.
But diamond is an “inherently brittle material,” according to the paper, which makes it difficult to study how its structure responds to intense conditions. As such, the researchers performed an experiment in which they subjected diamonds to continuous shock pressures every nanosecond or so, recording whether and how a certain amount of force affected the diamond’s crystal structure.
They found that defects arose at a pressure of about 115 gigapascals (for context, atmospheric pressure measures around 1,000 hectopascals; 1 hectopascal is equivalent to 10 million gigapascals). These ranged from “subtle crystal distortions to narrow zones of complete disorder, or amorphization,” according to the researchers. Needless to say, this isn’t good news for scientists trying to build safe, functioning nuclear fusion reactors.
To be clear, this paper doesn’t provide any easy solutions. If anything, it perhaps adds to a non-exhaustive list of problems researchers must resolve before fusion can be used to supply the world with copious amounts of energy. That might push fusion another decade into the future, but as long as scientists are hard-set on their goal to bring safe, clean energy, it’s worth the extra time.
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