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  • Cryolines | Another day, another spool

    Having wedged his body and equipment into the cramped space between the ceiling and the massive pipe, a worker is busy welding two cryolines spools. A few metre [...]

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  • Image of the week | Bearings unveiled

    The construction teams are in the last stages of preparing the Tokamak pit for the first major operation of ITER machine assembly: the lowering of the cryostat [...]

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    While ITER will never breed tritium for its own consumption, it will test breeding blanket concepts—the tools and techniques that designers of future DEMO react [...]

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  • Fusion world | Japan and Europe complete the assembly of JT-60SA

    The JT-60SA fusion experiment in Naka, Japan, is designed to explore advanced plasma physics in support of the operation of ITER and next-phase devices. After s [...]

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  • Manufacturing | Thermal shield milestone in Korea

    Six years after the start of fabrication, Korean contractor SFA has completed the last 40° sector of vacuum vessel thermal shield. The stainless steel panels, c [...]

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Of Interest

See archived entries

The physics behind the transition to H-mode

PPPL physicists Seung-Hoe Ku, Robert Hager, Choong-Seock Chang, and Randy Michael Churchill. (Photo by Elle Starkman) (Click to view larger version...)
PPPL physicists Seung-Hoe Ku, Robert Hager, Choong-Seock Chang, and Randy Michael Churchill. (Photo by Elle Starkman)
H‐mode—or the sudden improvement of plasma confinement in the magnetic field of tokamaks by approximately a factor of two—is the high confinement regime that all modern tokamaks, including ITER, rely on.

It was observed for the first time rather by accident (read more here) and to this day the physics behind H-mode remains not fully understood.

Scientists at the Princeton Plasma Physics Laboratory (PPPL) in the US have made a step in the direction of elucidating the phenomenon by simulating, for the first time, the spontaneous transition of turbulence at the edge of a fusion plasma to H-mode.
The research was achieved with the extreme-scale plasma turbulence code XGC developed at PPPL in collaboration with a nationwide team. This massively parallel simulation, which reveals the physics behind the transition, utilized most of a supercomputer's power—running for three days and using 90 percent of the capacity of Titan at the Oak Ridge Leadership Computing Facility (the most powerful supercomputer for open science in the US).

"After 35 years, the fundamental physics of the bifurcation of turbulence into H-mode has now been simulated, thanks to the rapid development of the computational hardware and software capability," said C.S. Chang, first author of the April Physical Review Letters paper [118, 175001 (2017)] that reported the findings. Co-authors included a team from PPPL, the University of California, San Diego, and the MIT Plasma Science and Fusion Center. Seung-Hoe Ku of PPPL performed the simulation.

Read the full report by John Greenwald on the PPPL website.



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