Copper Loses 22 Electrons in Million-Degree Plasma
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- HZDR researchers combined an X-ray free-electron laser with the high-intensity optical laser ReLaX at the HED-HiBEF experiment station at the European XFEL in Schenefeld, near Hamburg, to observe copper ionization in unprecedented detail.
- An intense laser pulse of approximately 250 trillion megawatts per square centimeter struck a copper wire about one-seventh the thickness of a human hair, instantly vaporizing it into plasma at several million degrees.
- Using a pump-probe method with 25- and 30-femtosecond pulses, the team tracked copper atoms losing up to 22 electrons (Cu²²⁺), with peak ionization occurring at roughly 2.5 picoseconds before recombination neutralized the ions within about 10 picoseconds.
- The X-ray pulse energy was precisely tuned to 8.2 kiloelectronvolts — the resonant absorption point for Cu²²⁺ ions — letting researchers count these heavily stripped ions over time via their characteristic emitted X-rays.
- Dr. Lingen Huang and Prof. Tom Cowan led the work; Cowan explained that the initial laser pulse triggers an electron wave that cascades through neighboring copper atoms, knocking out more electrons until the wave loses energy and recombination begins.
- The findings, published in Nature Communications, are aimed at refining simulations for laser fusion reactors, where similarly hot plasmas are heated by the same kind of electron-wave mechanism.
Why it matters: Laser fusion reactor design depends on accurately modeling how matter behaves in million-degree plasmas, but the ionization dynamics have been too fast to observe precisely. By resolving the 22-electron-stripping process down to the picosecond, the HZDR team gives fusion engineers concrete data to anchor their simulations — tightening the inputs to a technology racing toward viability.
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