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News & Media

Latest ITER Newsline

  • Heating | A pinch of moondust in the ITER plasma

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  • Delivery | 2,000 km through canals, locks and tunnels

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  • Monaco Fellows | A hand in shaping ITER

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  • On site | Drone survey on a perfect day

    There are days in winter when the skies over Provence are perfectly transparent. Snowy peaks 200 kilometres away appear close enough to be touched and farms, co [...]

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  • AAAS conference | ITER on the world science stage

    With more than 120,000 members globally, the American Association for the Advancement of Science (AAAS) is billed as the world's largest scientific society. The [...]

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Of Interest

See archived entries

Colour me a plasma

Phil Dooley, EFDA

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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