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  • Fuelling fusion | The magic cocktail of deuterium and tritium

    Nuclear fusion in stars is easy: it just happens, because the immense gravity of a star easily overcomes the resistance of nuclei to come together and fuse. [...]

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  • 360° image of the week | The cryoplant

    Cryogenics play a central role in the ITER Tokamak: the machine's superconducting magnets (10,000 tonnes in total), the vacuum pumps, thermal shields and so [...]

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  • Central solenoid assembly | First sequences underway

    What does it take to assemble the magnet at the heart of ITER? Heavy lifting, unerring accuracy, and a human touch. The central solenoid will be assembled from [...]

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  • Assembly | The eyes of ITER

    Supervisors ensure compliance and completion as machine and plant assembly forges ahead. In Greek mythology, Argus was considered an ideal guardian because his [...]

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  • Component repairs | Removing, displacing and disassembling

    A good repair job starts with a cleared workbench, the right tools on hand and a strong vise. This axiom, true for odd jobs in a home workshop, is also true for [...]

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Of Interest

See archived entries

Colour me a plasma

Each element has its own colour, corresponding to the gaps between its electrons' energy levels. The human classification of today's plasma colour as salmon, or peach, or burnt sienna is quite irrelevant. But a fun discussion to have, nonetheless. (Click to view larger version...)
Each element has its own colour, corresponding to the gaps between its electrons' energy levels. The human classification of today's plasma colour as salmon, or peach, or burnt sienna is quite irrelevant. But a fun discussion to have, nonetheless.
Something that surprises many people when they see their first plasma pulse on a screen in the control room, is that the plasma is invisible. There is a bit of glow around the edges, and the divertor—the bottom area of the vessel where the plasma touches the tiles—glows red hot. But the core of the plasma, at something like 100 million degrees, is completely transparent.

This is a desirable characteristic — it means that there is no energy being lost via radiation. It comes about because the atoms of the hydrogen fuel have been completely stripped of their electrons, or ionised. When attached to a nucleus at lower temperatures, these electrons absorb and emit light as they jump between the energy levels, but once they are detached that mechanism is disabled, so no light is absorbed or emitted.

To become this transparent, of course all the electrons must be detached. There is a pink glow around the edges because the plasma is cooler and so some electrons are attached, but generally for deuterium and tritium atoms, their single electron is easily removed. But for all other elements, with more electrons, it is harder to remove every last one and therefore to completely prevent energy leaking out through in the form of radiation.

Read the full article at EFDA.


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