Though we may never see fusion in a device small enough to power a car, we are closer than ever to sustainable fusion power due to innovative design.
The Princeton Plasma Physics Laboratory kicked off its 33rd annual public lecture series at 9:30 a.m. on Saturday, Jan. 14. The event was part of The Ronald E. Hatcher Science on Saturday Lecture Series, which was renamed two years ago in honor of a PPPL engineer who organized the lecture series for 20 years, according to a PPPL press release. The first lecture was delivered by University professor Egemen Kolemen and was titled “Plasma Control for Energy.”
Kolemen was introduced by the head of PPPL’s Office of Communication and Public Outreach, Andrew Zwicker, who ended his introduction with a question: “How did you first get interested in science?” Kolemen told the story of how he switched fields to get a job in order to live in the same place as his wife. “A month later, she said ‘I got a postdoc at Brown, so I’m going back there,’” Kolemen said, illustrating his accidental entry into plasma physics with laughter. With the mood set for an entertaining talk, the lecture began in earnest.
The lecture dealt with three main aspects of Kolemen’s work: process control, heat dissipation, and liquid metals. The first aspect, fusion process control, is what Kolemen was originally hired to do for PPPL. To illustrate the importance of this issue, Kolemen played a clip from “Back to the Future” showing the “Mr. Fusion” device used to power a time-traveling car. Kolemen explained that process control should allow fusion to take place in a space of five or six meters in diameter, though he doubts that it would ever be possible in something as small as the Mr. Fusion. He outlined several methods for creating fusion energy, starting with the obvious example of the sun. This type of fusion energy is not attainable, though, for an obvious reason.
“You can’t reproduce that ... because, basically, you need a sun-sized machine,” said Kolemen. “There are some other methods using lasers and so forth, but the most advanced and most realistic short-term method is magnetic confinement.”
This process, coupled with reactors designed to allow plasma to flow effectively, allows scientists to contain plasma for fusion in a much smaller space. However, the confinement also creates great challenges in dealing with massive amounts of power, on the scale of 50 megawatts per square meter, according to Kolemen.
One key innovation that makes this possible is a change in the shape of heat diverter, which shifts heat dissipation from one point to several. The creation of a “snowflake”-like diverter, based on extensive simulation and optimization, represented a significant improvement over previous heat dispersion capabilities, according to Kolemen.
Apart from dissipating heat, another major problem comes from changes in plasma flow. Small disturbances can often be exacerbated by the conditions that created them, resulting in dangerous currents in the plasma during experimentation.
Kolemen described several devices that are currently used for fusion heat flux control, including one that he described as a “baseball bat” that injects pellets of lithium into the reactor to dissipate heat and energy, preventing perturbations in the plasma flow that could prove catastrophic.
One final issue with these experiments is the sheer amount of heat generated, even during typical experimental parameters. Kolemen showed a thermal video from a British experiment that showed the melting of reactor plating during an experimental run, which threatened containment of the plasma. In fact, the thermal capacity of the metal with the highest melting point, tungsten, is still significantly smaller than the temperatures reached during plasma fusion. As a result, solid materials are not likely to be feasible for use in extended fusion experiments.
If solids are not viable, only liquids are available for coating these reactors. Getting liquids to coat a three-dimensional surface evenly, however, is a challenge in and of itself. With liquid metal, however, this is less of an issue. Since the metal conducts electricity and heat, and because it is exposed to the pressure inside the reactor, the extreme force on the liquid will cause it to push up hard enough against the walls of the reactor to provide relatively even insulation, according to theory and simulation.
Kolemen outlined plans for a new liquid metal reactor, which would showcase the ability of these liquid metals to contain fusion experiments. Although these reactors wouldn’t produce plasma, they would prove that liquid metal behaves the way simulations predict.
With the assistance of a student in his lab, Kolemen demonstrated the behavior of liquid metals at room temperature using Galinstan, a liquid alloy of gallium, indium, and tin, ending the lecture on an intriguing note.
The nine-week lecture series will continue next Saturday, Jan. 21. A complete schedule of lectures is available online. Additionally, the lectures can be streamed online, and a complete record will be available at the website for PPPL.