News
Striking the Perfect Balance
Researchers are using the NCCS’s leadership computing systems to model heat and particle loss in a fusion reactor, paving the way for a clean, abundant form of energy. A team led by Jeff Candy of General Atomics is using the NCCS systems to focus on the ionized gas—known as plasma—that serves as a reactor’s fuel. The plasma generates energy when hydrogen atoms within it collide, creating high-energy alpha particles and neutrons. Eventually, the reactor reaches a temperature ten times that of the sun.
According to Candy, the plasma is turbulent, and this turbulence is extremely difficult to simulate. It causes the reactor to lack “perfect containment”— as the alpha particles heat the plasma, turbulence carries some of the heat away and eventually throws out the particles—but it is also necessary.
The key, says Candy, is to know the rate at which the plasma is leaking heat and particles. With that knowledge, researchers can find “optimum turbulence,” the perfect balance of heat and alpha-particle production and loss.
Candy’s team is pursuing this perfect balance with his revolutionary GYRO code, which, among other things, calculates electromagnetic fluctuations in fusion plasmas. The code simulates a tokamak, which is a doughnut-shaped fusion reactor such as the international ITER project and leading research reactors.
The team is also developing a new type of code designed to advance the quest for optimum turbulence. The new code will predict the operating temperatures and densities in a reactor by designing a feedback loop that uses multiple GYRO calculations.
“Gyrokinetic simulations are a bit like a black box,” Candy explains. “You tell it what the densities and temperatures are, and it will tell you how violent the turbulence is. By introducing feedback schemes, you find the unique temperatures and densities for which heat loss balances heat production. That’s never been done before using gyrokinetic simulations.” Fortunately, he said, the project is able to take full advantage of the growing computing power offered at the NCCS. While the simulations will take up to 100 times the processing power of previous work, the GYRO code is able to take advantage of the thousands of processors available on the center’s state-of-the-art supercomputers.