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ITER's vacuum vessel port plugs are critical components that seal the plasma chamber and allow experiments to take place in a high vacuum environment.

The Russian Domestic Agency—responsible for supplying four test stands for the vacuum, heat and functional testing of the port plugs before their installation on the machine—has contracted with the Russian firm Cryogenmash for the development of the technology.

The team at Cryogenmash is currently testing the sealing flanges that will secure the port plugs on the test stand and running tests on the gaskets to arrive at a final choice of technology and material. Vacuum and leak tests were run recently with results that surpassed expectations.

Watch a five-minute video of the work underway courtesy of ITER Russia.

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Physicist Fatima Ebrahimi from the Princeton Plasma Physics Laboratory (PPPL) has for the first time used advanced models to accurately simulate key characteristics of the cyclic behaviour of edge-localized modes (ELMs), a particular type of plasma instability.

The findings could help physicists more fully comprehend the behaviour of plasma, the hot, charged gas that fuels fusion reactions in doughnut-shaped fusion facilities called tokamaks, and more reliably produce plasmas for fusion reactions. The findings could also provide insight into solar flares, the eruptions of enormous masses of plasma from the surface of the sun into space.

ELMs occur around the outer edge of high-confinement, or H-mode, plasmas due to strong edge currents. Ebrahimi used a computer simulation code known as NIMROD to show how ELMs go through a repeated cycle in which they form, develop, and vanish.

The model demonstrates that ELMs can form when a steep gradient of current exists at the plasma edge. The gradient develops when the plasma moves suddenly up or down, creating a bump in the current and forming an edge current sheet. The instability then forms a current-carrying filament that moves around the tokamak, producing electrical fields that interfere with the currents that caused the ELMs to form. With the original currents disrupted, the ELM dies. "In a way," Ebrahimi said, "an ELM eliminates its own source — erases the bump on the edge current — by its own motion."

Ebrahimi's findings are consistent with observations of cyclic behaviour of ELMs in tokamaks around the world. These include Pegasus, a small spherical device at the University of Wisconsin; the Mega Ampere Spherical Tokamak (MAST) in the United Kingdom; and the National Spherical Torus Experiment (NSTX), the flagship facility at PPPL before its recent upgrade. The research could also improve understanding of solar eruptions, which are accompanied by filamentary structures similar to those produced by ELMs. Her next step will involve investigating the impact of differences in plasma pressure on the cyclic behaviour of ELMs.

Read the full article on the PPPL website.

The elements of the ITER divertor that will directly face the hot plasma must withstand a heat load that is estimated at ten times that of a spacecraft re-entering Earth's atmosphere.

Procuring parties Russia (divertor dome), Japan (divertor outer targets) and Europe (divertor inner targets) are all engaged in multiyear qualification programs that include prototype fabrication and high heat flux testing.

The European Domestic Agency made the choice of contracting with three separate manufacturers for the development of small-scale inner vertical target prototypes that are 1/19th of the actual scale needed for ITER. In the first stage of the pre-qualification program the prototypes were successfully tested in high heat flux conditions; the next step will now be to develop full-scale prototypes. This phase—which involves the three manufacturers plus a fourth, pre-qualified supplier—is expected to last approximately three years.

Read the full article on the European Domestic Agency website.