UM, ORVILLE...:

US physicists have confirmed that they achieved a stage in nuclear fusion called "burning plasma" last year.

There's a longstanding effort to crack fusion power because it promises an unlimited source of clean energy.

Burning plasma occurs when fusion reactions become the dominant source of heating in the process, rather than energy introduced from outside.

The stage was seen in experiments carried out at the National Ignition Facility (NIF) in California.

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