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Anode Tufting

Bright anode tufting is readily seen in mercury arc rectifiers when the current load is high: -

Mercury Arc Rectifier

Invented in 1902 by Peter Cooper Hewitt, a mercury-arc rectifier provides power for industrial equipment and high-voltage DC power transmission. It's basically an AC to DC converter. Today, the rectifiers are solid state diodes and thyristors. Mercury metal is expensive and toxic.

Anodes can clump together and retain identity, a bit like the bunching of grass or hair, hence the term 'tuft.' The Sun is just a small anode on the cosmic scale, and its photosphere is packed with bright granulations, which are tufts of anodes:

Solar granulations - anode tufts

In arc mode plasma, the sizes and voltages of the anode tufts depend on the electric current density. The tufts appear and disappear to maintain the right balance between positive ions and electrons in the total current.

Anode tufting disappears where the current density over an particular area drops. It’s then not intense enough to require the shielding created by the plasma double layer. At these locations, anode tufting collapses, and we can then see right into the anode. As no arc mode plasma discharge are occurs, the locations look darker than the surrounding areas. These locations are starspots or, in the Sun’s case, sunspots.

Red giant stars are large anodes, so tufts aren't needed to carry electric current over them, hence why a red chromospheric anode glow dominates these huge stars:

Betelgeuse in the constellation of Orion - an example of an anodic red giant

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