On Monday, a paper was released that describes some confusing results from the National Ignition Facility, which uses a lot of very energetic lasers focused on a small target to begin a fusion reaction. Over the past few years, the facility has passed some key milestones, including ignition of fusion and creating what’s termed a burning plasma.
Now, researchers have analyzed the properties of the plasma as it experiences these high-energy states. And to their surprise, they found that burning plasmas appear to behave differently from those that have experienced ignition. At the moment, there’s no obvious explanation for the difference.
Ignition vs. burning
In the experiments, the material being used for fusion is a mix of tritium and deuterium, two heavier isotopes of hydrogen. These combine to produce a helium atom, leaving a spare neutron that’s emitted; the energy of the fusion reaction is released in the form of a gamma ray.
The fusion process is triggered by a short, extremely intense burst of laser light that targets a small metallic cylinder. The metal emits intense X-rays, which vaporize the surface of a nearby pellet, creating an intense wave of heat and pressure on the pellet’s interior, where the deuterium and tritium reside. These form a very high-energy plasma, setting the conditions for fusion.
If everything goes well, the energy imparted ignites the plasma, meaning that no additional energy is needed for the fusion reactions to continue for the tiny fraction of a second that passes before the whole thing blows apart. At even higher energies, the plasma reaches a state called burning, where the helium atoms that are forming carry so much energy that they can ignite the nearby plasma. This is considered critical because it means the rest of the energy (in the form of neutrons and gamma rays) can potentially be harvested to produce useful power.
While we have detailed models of the physics that goes on under these extreme conditions, we need to compare those models to what’s going on inside the plasma. Unfortunately, given that both the plasma and the materials that formerly surrounded it are in the process of exploding, that’s a significant challenge. To get a picture of what might be going on, researchers have turned to one of the products of the fusion reaction: the neutrons it emits, which can pass through the wreckage and be picked up by nearby detectors.
Taking a temperature
The physics of the fusion reaction produces neutrons with a specific energy. If fusion happened in a material where the atoms were stationary, all of the neutrons would come out with that energy. But obviously, the atomic nuclei in the plasma—the tritium and deuterium—are moving about violently. Depending on how they’re moving relative to the detector, these ions may impart some additional energy to the neutrons, or subtract a bit.
This means that, instead of coming out as a sharp line at a specific energy, the neutrons come out at a range of energies that form a broad curve. The peak of that curve is related to the motion of the ions in the plasma, and thus the temperature of the plasma. Further details can be extracted from the shape of the curve.
Between the ignition point and the burning point, we seem to have an accurate understanding of how the temperature of the plasma relates to the velocity of the atoms in the plasma. The data from the neutrons lines up nicely with the curve that’s calculated from our model predictions. Once the plasma switches over to burning, however, things no longer match. It’s like the neutron data finds a completely different curve and follows along that instead.
So, what might explain that different curve? It’s not that we have no idea; we have a bunch of them and no way to tell them apart. The team that analyzed these results suggests four possible explanations, including unexpected kinetics of individual particles in the plasma or a failure to account for details in the behavior of the bulk plasma. Alternatively, it could be that the burning plasma extends over a different area, or lasts a different amount of time, than we’d predict.
In any case, as the authors state, “Understanding the cause of this departure from hydrodynamic behavior could be important for achieving robust and reproducible ignition.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
