News in Focus EUROFUSION (CC by 4.0) by (CC EUROFUSION the Joint European Torus Has Started Conducting Experiments with Tritium Fuel

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The world this week News in focus EUROFUSION (CC BY 4.0) BY (CC EUROFUSION The Joint European Torus has started conducting experiments with tritium fuel. FUEL FOR WORLD’S LARGEST FUSION REACTOR IS SET FOR TEST RUN Nuclear fusion experiments with deuterium and tritium at the Joint European Torus are a crucial dress rehearsal for the mega-experiment.

By Elizabeth Gibney experiments with tritium — a rare and radioac- its attempt to create more power from a fusion tive isotope of hydrogen. The facility is a one- reaction than is put in — something that has pioneering reactor in Britain is tenth-volume mock-up of the US$22-billion never before been demonstrated. The reactor gearing up to start pivotal tests of a ITER project and has the same dough- should heat and confine a plasma of deuterium fuel mix that will eventually power nut-shaped ‘tokamak’ design — the world’s and tritium such that the fusion of the isotopes ITER — the world’s biggest nuclear-fu- most developed approach to fusion energy. into helium produces enough heat to sustain sion experiment. Nuclear fusion is It is the first time since 1997 that researchers further fusion reactions. Athe phenomenon that powers the Sun and, if have done experiments in a tokamak with any “It’s very exciting now to, at last, get to the physicists can harness it on Earth, it would be significant amount of tritium. point where we can put into practice what a source of almost limitless energy. In June, JET will begin fusing even quantities we’ve been preparing all these years,” says In December, researchers at the Joint Euro- of tritium and deuterium, another isotope of Joelle Mailloux, who co-leads the scientific pean Torus (JET) started conducting fusion hydrogen. It is this fuel mix that ITER will use in programme at JET. “We’re ready for it.”

News in focus JET’s experiments will help scientists to fraction of a gram of tritium will be pulsed into ITER. The mass of the isotopes influences predict how the plasma in the ITER tokamak the tokamak 3–14 times a day. Each of these the conditions — such as magnetic field, cur- will behave and to craft the mega-experi- discharges will be an individual experiment rent and external heating — needed for the ment’s operating settings. “It’s the closest we with slightly different parameters, and will plasma to reach a crucial state known as con- can get to achieving ITER conditions in pres- generate between 3 and 10 seconds of useful finement. (In this state, the highest-energy ent-day machines,” says Tim Luce, chief sci- data, says Mailloux. “What we are after is phys- particles remain within the ionized gas, and entist at ITER, near Cadarache in France. The ics information that we can use to validate our that is important for sustaining the plasma’s experiments are the culmination of around understanding, and then we can apply that temperature.) “We want to explore this and two decade’s work, says Luce. ITER will begin understand why,” says Anne White, a plasma operations with low-power hydrogen reac- “It’s the closest we physicist at the Massachusetts Institute of tions in 2025. But from 2035, it will run on a Technology in Cambridge. 50:50 mix of deuterium and tritium. can get to achieving Another major difference from the 1997 Both ITER and JET, which is based at the ITER conditions in experiments is that JET has been refitted Culham Centre for Fusion Energy (CCFE) present-day machines.” so that the inner materials that protect the near Oxford, use extreme magnetic fields to machine against the effects of heat and neu- confine plasma into a ring and heat it until tron bombardment, and remove impurities fusion occurs. The temperatures in JET can to preparing the future machine,” she says. from the plasma, match those in ITER’s design. reach 100 million degrees, many times hotter Some experiments will use just tritium; Because these materials could radiate back than the Sun’s core. others will combine deuterium and tritium in into the plasma and cool it down, understand- The world’s last tokamak fusion experi- equal proportions. Both types of experiment ing how they interact with the fusion process ments with tritium also took place at JET. The are important, because a key goal is to under- is crucial. goal then was to hit peak power, and the facil- stand the effect of tritium’s larger mass on The latest generation of fusion scientists ity succeeded in achieving a record ratio of plasma behaviour (tritium has two neutrons has never worked with tritium, which makes power out to power in (known as a Q value) of in its nucleus, whereas deuterium has one and it all the more important to do the experi- 0.67. That record still stands today; 1 would be hydrogen has none). That will help in predict- ments, says Chapman. “It’s a big deal. People break-even. But this year, the aim is to sustain ing the impact of using different isotopes in are watching,” adds Luce. a similar level of fusion power for 5 seconds or more, to eke out as much data from the experiments as possible and to understand the behaviour of longer-lasting plasmas. Working with tritium poses unique chal- lenges — JET researchers have spent more WHY COVID VACCINES than two years refitting elements of their machine and preparing to handle the radioac- ARE SO DIFFICULT tive material. The isotope decays quickly, so it occurs only in trace amounts in nature and TO COMPARE is usually made as a by-product in nuclear-fis- sion reactors; the world’s supply is just 20 Despite the widespread roll-out of several vaccines, kilograms. it could be months before they can be ranked. Tritium pulses Part of the challenge of handling tritium By Heidi Ledford by limited supplies and hampered by limited is that its reactions with deuterium pro- data, says Cristina Possas, a public-health duce neutrons at a much higher rate than usuff Adebayo Adebisi knows that a researcher at the Oswaldo Cruz Foundation deuterium reactions alone. Commercial vaccine that offers 70% protection in Rio de Janeiro, Brazil. “It is not possible to reactors will capture the energy of these against COVID-19 could be a valuable compare these vaccines at this point,” she says. neutrons to generate electricity, but in JET, tool against the coronavirus pan- In Bangladesh, health economist Shafiun the high-energy particles will pepper the demic in Nigeria — especially if that Shimul at the University of Dhaka worries machine’s interior and damage diagnostic Yvaccine is cheap and doesn’t have to be stored about the risks if governments delay systems. That means that the JET team has at extremely cold temperatures. But what if vaccinations for months to build cold-chain had to move cameras and other instruments another vaccine — one that is more expensive infrastructure. “If you want to control infec- behind concrete shielding, says Ian Chapman, to buy and to store — was 95% effective? tion, you have to rely on something that is who leads the CCFE. “Should we send the less-effective vaccine contextually doable for you — it’s not only “We’ve had to refresh and renew all of to Africa? Or should we look for a way to about effectiveness,” he says. “If they wait for our processes”, from storage to handling, strengthen the cold storage?” asks Adebisi, perfection, I think it will be a long wait.” Chapman says. Once tritium experiments director for research at African Young Leaders start, neutron bombardment will make the for Global Health, a non-profit organization The ‘best’ vaccine inner facility radioactive, so it will become a based in Abuja. Given the demand for speed amid limited no-go zone for humans for 18 months. Staff These are the kinds of question facing supplies, any effort to rank the vaccines must have therefore had to get used to a mindset researchers and government leaders world- take into account not only their reported similar to that of the engineers who send craft wide, as they take stock of the emerging effectiveness, but also supplies, costs, the into space: “You can’t just go in and fix things, selection of coronavirus vaccines and try to logistics of deploying them, the durability of it has to work first time,” Chapman says. decide which will be most useful in putting the protection they offer and their ability to JET’s campaign will use less than 60 grams of an end to a pandemic that has already taken fend off emerging viral variants. Even so, many tritium, which it will recycle. Fuel containing a nearly 2.5 million lives. It is a decision shaped people might find it hard to look away from