Seth Putterman started from studying the behavior of plasma for reasons of national security. Extremely fast hypersonic missiles heat and ionize the surrounding air, forming a cloud of charged particles called plasma that absorbs radio waves and makes it difficult for operators on the ground to communicate with the missiles – a problem Putterman sought to solve. Then it occurred to him: The same plasma physics applies to our sun.
The UCLA scientist and his colleagues have now created what Putterman calls “our sun in a jar,” a 1.2-inch glass sphere filled with plasma, which they have used to model processes such as those that cause solar flares. These are explosive bursts of energy that are sometimes accompanied by the release of a fast blob of plasma that can wreak havoc on orbiting satellites and power grids on the ground. “The steps we’re making will impact modeling so there can be a warning and determination of space weather precursors,” said Putterman, the senior author of a study in Physical assessment letters describe their experiments.
The sun is actually a swirling inferno of plasma made up of rotating, electrically charged gas particles – mainly electrons and hydrogen atoms stripped of their electrons. (Stellar plasma is somewhat different from the low-density plasma used in tokamak fusion reactors.) Researchers have long tried to better understand solar flares, especially when a particularly large chunk of plasma is launched toward Earth.
The team’s experiments began by putting some partially ionized sulfur gas in a glass bulb, then bombarding it with low-frequency microwaves — similar to the kind used in a microwave oven — to excite the gas and heat it up to about 5000 degrees Fahrenheit. They found that a 30 kHz pulse from the microwaves creates a sound wave that exerts a pressure that causes the hot gas to contract. This sound wave pressure creates a kind of “acoustic gravity” and causes the fluid to move as if it were in the sun’s spherical gravitational field. (The experiment’s gravitational field is about 1,000 times stronger than Earth’s.) This generates plasma convection, a process in which warm liquid rises and cooler, denser liquid sinks toward the core of the glass sphere. In this way, the team became the first humans on Earth to create something similar to the spherical convection normally found in a star’s interior.
Their project was first funded by DARPA, the Pentagon’s advanced research arm, for its applications to hypersonic vehicles. It then received the support of the Air Force Research Laboratory, as space weather can interfere with aircraft and spacecraft. But astronomers think it could also tell us something fundamental about the sun’s behavior. “I think it’s really important to start simulating solar convection in the lab and, through that, understand the sun’s mysterious solar cycle,” said Tom Berger, executive director of the Space Weather Technology, Research and Education Center at NASA. the University. of Colorado in Boulder, who was not involved in the study.
Berger refers to an approximately 11-year cycle in which the inner convection zone of the sun somehow becomes more active, causing the outer layer, or corona, to generate more frequent and intense flares and plasma explosions called coronal mass ejections. It’s hard to probe the sun’s inner regions, Berger says, though NASA is trying to do it with a spacecraft called the Solar Dynamics Observatory, which uses sound waves to map the sun’s surface and make inferences about it. plasma below.
Others in the field also praise Putterman and his colleagues’ research, but note that it has limitations. “It is an exciting and innovative development. It’s done smartly. Simulating the internal dynamics of a star in a lab has always been a challenge,” said Mark Miesch, a researcher at the NOAA Space Weather Prediction Center and the University of Colorado.
