Newswise — When ITER, the international fusion experiment kicks off in 2025, a top priority will be avoiding or mitigating violent disruptions that can severely damage the giant machine. Scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have successfully built and simulated a prototype of a new device to mitigate the consequences of a damaging disturbance before it can proceed.
Risk of disruptions
The risk of disruption concerns all donut-shaped facilities called “tokamaks”, devices widely used in the global effort to harvest the fusion energy on Earth that powers the sun and stars. Tokamaks confine the state of matter called plasma that powers fusion reactions with powerful magnetic fields and heats it to many times the temperature of the sun to fuse atomic nuclei, or ions, in the plasma and release great energy . The goal is to provide a safe and clean source of energy to generate the world’s electricity.
Disturbances occur when the magnetic bottle used to confine the hot plasma becomes unstable, causing large electromagnetic forces and thermal loads to slam against the walls of the vessel. The cylinder is like a gas balloon in which the gas slowly escapes. A mitigation system cannot stop the disturbance, which is like a sudden tear in the skin of the balloon, but only alter the course of the disturbance to minimize damage to reactor components.
Electromagnetic particle injector
The simulated railgun-like device, called an “electromagnetic particle injector” (EPI), is designed to alleviate the problem by firing a high-velocity projectile of material that will radiate energy into the plasma core at the first sign of a disturbance. The payload will cool and stop the reaction in a controlled manner to prevent damage to the walls of the reactor chamber.
The researchers modeled the pellet injector with a PPPL fusion code that describes plasma as an electrically conducting fluid. “It was a very difficult simulation,” said physicist Cesar Clauser, a postdoctoral researcher at Lehigh University assigned to PPPL and first author of a paper describing the modeling process in nuclear fusion. “This work marks an important step towards the study, modeling and planning of disturbance mitigation systems that will be extremely important for future fusion devices.“, Clauser said.
The pellet injector could serve as an alternative to the mitigation system currently planned for ITER, which aims to demonstrate the feasibility of replicating fusion energy on Earth. Current plans to control ITER disturbances call for smashing frozen gas-propelled gas pellets against a metal plate to spread shards of cooling by fusion reaction into the edge of the plasma.
ten times faster
However, “The electromagnetic system is 10 times faster,” said Roger Raman, a University of Washington physicist on a long-term assignment at PPPL, a lead designer of PPE and co-author of the paper. . The bullet-shaped high-speed projectile could create a near-instantaneous response to the initial warning of a disturbance that could unfold in one to two thousandths of a second, Raman said, a period known as the scale of heat soak time.
Plans now include testing the injector, which is under development at PPPL, on the flagship National Spherical Torus Experiment (NSTX-U) at the lab when the facility is back online. The injector could also be tested on other tokamaks. “The simulations need to be validated by comparison with experiments,” said Steve Jardin, head of the macroscopic stability group at the PPPL Theory Department, co-author of the paper and co-developer of the PPPL code that the researchers pushed to their limits to produce the simulation.
Research so far suggests that the injector has the potential to counter the disruptions that threaten to occur on ITER. Future simulations, Clauser said, will focus on the payload responses of more focused plasma configurations.
PPPL, at Princeton University’s Forrestal Campus in Plainsboro, NJ, is dedicated to creating new knowledge about the physics of plasmas – ultra-hot, charged gases – and developing practical solutions for creating energy of merger. The lab is operated by the University for the U.S. Department of Energy Office of Science, which is the largest supporter of basic physical science research in the United States and works to address some of the most pressing challenges From our era. For more information, visit energy.gov/science.