Ignia

Ignia holds a star in a bottle. To light it, she needs it dense enough, hot enough, for long enough.

The Physics

For a deuterium–tritium plasma to ignite, the product of density, temperature and energy confinement time must pass a threshold, lowest near 14 keV. Each fusion makes a 3.5 MeV helium nucleus, which stays to heat the plasma, and a 14.1 MeV neutron.

n T τ_E ≳ 3 × 10²¹ keV·s·m⁻³, D + T → ⁴He (3.5 MeV) + n (14.1 MeV)

• n: ion density (m⁻³)
• T: temperature (keV; 1 keV ≈ 11.6 million K)
• τ_E: energy confinement time (s)
• D, T: deuterium, tritium
• n (in the reaction): neutron

J. D. Lawson set out the criterion in 1957; on 5 Dec 2022 the National Ignition Facility put 2.05 MJ of laser light on a target and got 3.15 MJ out, a target gain of about 1.5.

Honest caveat: The lasers drew about 100 times more energy from the grid. That was target gain, not net or wall-plug gain.

On the shirt

Front: Ignia, the pixel-art character, with the title. Back: the triple product, the D–T reaction, the NIF 2022 result and the wall-plug caveat. Printed on a unisex tee.