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  • Neutral Beam Test Facility | Lessons learned from SPIDER, a full-size negative ion source

    SPIDER finished its first test campaign in late November 2021 and is now entering an upgrade phase. During this time, the testbed will be shut down for about on [...]

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    A third 40-degree sector of the ITER vacuum vessel has exited the Hyundai Heavy Industries production line in Ulsan, Korea. Sectors representing one-third of th [...]

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    The factory acceptance test on the first ITER vacuum vessel gravity support has been successfully completed at Haneul Engineering in Gunsan, Korea. Under the 8, [...]

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  • Technology | Hail showers in ASDEX Upgrade for ITER disruption mitigation

    Just before the 2021 Christmas holiday break, the team at the ASDEX Upgrade tokamak successfully fired frozen deuterium pellet fragments into a plasma as part o [...]

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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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