In a significant breakthrough, researchers in the United States have demonstrated a novel method of sustaining electrical currents in nuclear fusion experiments with the successful use of a “helicon current drive.”
The advancement could help overcome a major obstacle in the quest to develop reactors that can operate continuously, according to new findings that appeared in the journal Physical Review Letters.
Achieved by a team of scientists at General Atomics in San Diego, the achievement relies on the use of powerful radio waves to drive electrical currents through extremely hot plasma, the electrically charged gas in which fusion reactions take place.
Maintaining Continuous Plasma Currents
The experiments were conducted using DIII-D, a doughnut-shaped research reactor known as a tokamak, which relies on powerful magnetic fields to confine plasma at the extreme temperatures required for atomic nuclei to fuse and release energy.
A significant challenge that conventional tokamaks face involves their reliance on a central electromagnetic coil, which allows them to generate electrical current within their confined plasmas. This works similarly to a transformer, in that the coil induces a current as changes occur in its magnetic field.
However, once the coil reaches the limits of its operational range, the reactor is forced to interrupt operations in order to reset the system, preventing the process from continuing indefinitely. Because of this, researchers have searched for alternative methods of achieving continuous plasma currents without having to rely on the central coil.
Demonstrating Helicon Current Drive
Overcoming these longstanding issues requires an alternative approach, which is why researchers have been exploring novel methods of maintaining plasma currents that do not rely on the use of a central coil.
In the recent study, the team led by physicist Jeff Lestz chose to use a new technique known as a helicon current drive, which leverages radio waves directed in certain ways as a way to transfer energy and momentum over to electrons within the plasma.
To achieve this, the radio waves are propelled using a special antenna, which the team used to direct them around the tokamak reactor, thereby allowing them to penetrate toward the plasma’s core.
Electrons moving at suitable speeds will interact with the waves, which assists them in sustaining an electrical current while not depending entirely on the conventional transformer system.
The researchers then demonstrated that the waves could effectively carry energy deep inside the plasma by using what they call a megawatt-level helicon system. Additionally, they monitored changes in the plasma’s magnetic structure, which were consistent with the generation of additional electrical current—offering proof that the novel method was working as planned.
The Path to Continuous Fusion
“Taken together, these experimental results represent strong evidence for the first definitive observation of auxiliary current drive due to helicon waves on any device,” the researchers write in their recent study.
The team’s findings offer one of the most significant experimental demonstrations of an approach long investigated by fusion researchers.
While the recent experiment does not confirm the production of continuous fusion power, it signals a promising new means of addressing one of the technological challenges that future reactors will likely face.
In the future, the team envisions their helicon current drive could be developed and scaled for practical use, which would offer a major advantage in helping tokamaks achieve and maintain stable plasma conditions that longer operational durations will require.
Ultimately, capabilities like these could be poised to help bring accessible fusion energy one step closer to being a practical reality in the years ahead.
The team’s study, “First Experimental Evidence of Helicon Current Drive,” appeared in Physical Review Letters.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.