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The Max Planck Institute for Plasma Physics is reporting that physicists have, for the first time, explained the sudden formation of high-confinement mode (H-mode) in tokamaks using simulations based purely on fundamental physical principles. First observed in 1982 on the ASDEX tokamak in Garching, H-mode dramatically improves plasma energy confinement and is considered essential for future fusion devices, including ITER. Yet despite decades of experimental and theoretical work, scientists had not fully understood why the transition occurs at a specific heating power.

Led by Wladimir Zholobenko, IPP researchers performed advanced “flux-driven” edge simulations with the GRILLIX code, allowing the plasma to evolve naturally as heating power increased step by step. Unlike earlier models, the transition was not imposed but emerged self-consistently from turbulence dynamics. Simulating just 50 milliseconds of plasma evolution required a year of supercomputer time.

The simulations show that after a gradual buildup of turbulence, heat transport at the plasma edge abruptly reverses. Within 100 microseconds, the characteristic H-mode pedestal—a steep pressure and temperature gradient—forms. The transition is linked to a sudden shift from drift-wave turbulence to kinetic ballooning modes, along with a rapid reorganization of microscopic fluctuations. The model even predicts a brief inward heat flow before transport stabilizes.

Based on conditions from ASDEX Upgrade, the simulation shows that it reproduces exactly those effects that can also be observed in experimental results. However, the researchers have not yet been able to achieve satisfactory quantitative agreement—in other words, the actual measurements from ASDEX Upgrade are either above or below the simulated results.“We haven't reached our goal yet, but the simulations provide insight into what is still missing,” says Dr Zholobenko. The aim is to end up with a simulation model that can predict the experimental parameters at which H-mode occurs in fusion facilities that have not yet been built.

The findings were published in Physical Review Letters. 

See the original report on the IPP website.

Since 2019, ITER Japan has been publishing a manga series that brings the ITER project to life for a broad audience. 

The story follows Japanese student Taiyô Tenna, who discovers ITER while on a world tour after meeting a French student in Aix-en-Provence. His journey continues through an internship experience at ITER, and then as he returns to Japan to learn more about the advanced fusion technologies developed by Japan’s Domestic Agency for the project. In the eighth volume, just released, he has become a staff member at the National Institutes for Quantum Science and Technology (QST), where he learns about ITER's new baseline scope and schedule and the ways in which Japan's flagship fusion device, JT-60SA is participating.

Explore all volumes of the ITER manga series on the ITER Japan website or download Volume 8 from ITER's Publication Centre. Editions are available in Japanese, English, French and ... Provençal.

Registration is open now for the third ITER Public-Private Fusion Workshop that will be organized on 28 and 29 April 2026 at the ITER site in Saint Paul-lez-Durance, France.

For the past two years, ITER has opened its doors to private sector fusion companies for joint workshops on areas of mutual interest and mechanisms for positive engagement. This year’s theme—“Fusion: a Joint Quest”—reflects the reality that progress toward fusion energy is neither linear nor uniform, but pursued through multiple technical approaches, institutional models, and timelines. Across public and private efforts alike, divergent visions coexist with genuinely complementary strengths—in science, engineering, manufacturing, and systems integration.

See the detailed agenda on the workshop website under Program (scroll down). On the day before or after the workshop—Monday, 27 April and/or Thursday, 30 April—participants may arrange consultations with ITER experts, customized tours of the ITER worksite, and opportunities for networking and discussion with fellow attendees.

Register to attend the third ITER Public-Private Fusion Workshop here.