Two clever tricks for taming fusion's most violent instability

A nitrogen gas puff silenced plasma edge explosions and boosted performance

A plasma that was spiking violently 300 times per second went completely quiet — and held more energy — after scientists puffed in a little nitrogen gas.

The EAST tokamak at the Institute of Plasma Physics in Hefei, China, ran one experiment where scientists injected a small amount of nitrogen gas — mixed with deuterium, the fuel — at the plasma edge. Within about 0.8 seconds, violent energy bursts that had been rattling the machine 300 times per second went completely quiet. And they stayed quiet for a full second after the gas injection stopped. Think of a pressure cooker that keeps popping its lid every few milliseconds: you add something that lets steam escape gently and continuously instead, and the lid stops popping entirely. The pressure inside actually rises, stably. Those bursts are called ELMs — edge-localized modes — sudden eruptions from the hot plasma edge. In a real power plant they'd hit the surrounding metal walls like a blowtorch firing hundreds of times per minute, eventually destroying them. Suppressing ELMs is one of fusion's most urgent near-term engineering problems. What made this result unusual is the double win: the plasma stored about 25% more energy at the same time, with the H98 factor — a standard score comparing actual performance to a benchmark, where 1.0 means meeting expectations — rising from 0.9 to 1.2. A team simulation using the CGYRO code suggested a specific turbulent wave at the plasma edge, called a dissipative trapped electron mode, is what keeps the ELMs suppressed. The catch is significant: this is a single plasma shot. One discharge, number 153901. The CGYRO simulations were run in linear mode, meaning small disturbances were modelled but the full chaos of plasma turbulence was not. Whether nitrogen seeding works reliably across different conditions, on larger machines, or for longer durations is an open question. One impressive shot is a starting point, not a solution.

A reprogrammable chip now watches DIII-D's plasma and predicts trouble in microseconds

A computer chip installed inside a fusion reactor's control system is now making predictions about plasma instabilities in 4.4 microseconds — roughly a thousand times faster than a nerve impulse.

A team at SLAC National Accelerator Laboratory and General Atomics installed a specialised chip — an FPGA, a type of hardware you can reprogram after it leaves the factory — directly inside the plasma control system of the DIII-D tokamak in San Diego. The chip runs a small neural network, the same class of pattern-recognition software that identifies faces on your phone. It watches 160 sensor channels simultaneously, all reading the plasma's behaviour 1 million times per second, and flags when an ELM — a violent plasma edge burst — looks likely. It makes that call in 4.4 microseconds. Think of it as a smoke detector that doesn't just shriek an alarm, but can automatically nudge the stove dial before the pan catches fire. Speed is the whole point. ELMs develop on timescales where human reaction is physically impossible. The only way to prevent wall damage is an automated system that sees trouble forming and adjusts the plasma controls — gas injection, heating power, magnetic fields — before the burst happens. What makes this system particularly flexible: you can swap in a completely new neural network model without physically rebuilding or rewiring the hardware. The same chip can be retrained for a different task, like identifying which confinement regime the plasma is in, and reloaded on the fly. The honest caveat here is that this paper describes an engineering deployment, not a validated control result. The team at SLAC and General Atomics explicitly states that full performance statistics are coming in a follow-up publication. The chip is installed and working. Whether the ELM forecast model it runs is accurate enough to safely act on — how often it's right, how often it raises a false alarm — remains to be shown.

Both stories today circle the same bottleneck: ELMs, the violent edge bursts that would gradually destroy the walls of any real fusion power plant. The EAST result says you can chemically quiet them — with a nitrogen puff — and actually improve plasma performance at the same time. The DIII-D result says you can build a system fast enough to see them coming and, eventually, react. These aren't competing approaches. A future reactor will almost certainly need both: something to detect trouble in microseconds, and a toolkit of responses to pull from. What I want you to take away is the stage we're at: 'this worked in one experiment' and 'this chip is now installed and running.' Neither is a solved problem. But they're pointed at the same wall, from two different directions, and that's how hard engineering problems tend to get cracked.

The EAST team's obvious next step is reproducing this nitrogen result across multiple discharges and scanning conditions — watch for follow-up papers from ASIPP Hefei in the next few months. For DIII-D, the SLAC group has explicitly promised a second paper with actual ELM forecasting accuracy numbers; that's the one to wait for before drawing conclusions about whether this ML approach is ready for real control decisions. The bigger marker on the calendar: ITER's assembly is grinding forward, and ELM control solutions need to be demonstrated convincingly before that machine's full-power operations, currently targeted for the early 2030s.

• Wikipedia: Edge-localized modes explained
• Wikipedia: Field-programmable gate arrays (what an FPGA actually is)