Deuterium

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Deuterium is the stable heavy hydrogen isotope that supplies the other half of the deuterium-tritium fuel. Unlike tritium it is abundant and unproblematic: it occurs naturally in water at roughly one part in 6,400 hydrogen atoms and is separated at industrial scale for heavy-water reactors and other uses. Fuel masses are strikingly small — JET's record 69.26 MJ pulse used about 0.2 milligrams of fuel in total. Deuterium is included in this Journey chiefly as a contrast: it is the half of the fuel cycle that is genuinely solved, which sharpens how unsolved the tritium half is. Deuterium-only operation, used by ITER in its early phases and by machines such as EAST and Wendelstein 7-X, produces negligible fusion power and is a way of studying plasma physics without a tritium licence.

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