A copper wire thinner than a human hair sat inside one of the most powerful X-ray facilities on Earth. Then a laser hit it, and for roughly 2.5 trillionths of a second, each copper atom lost 22 of its 29 electrons, collapsing into a screaming-hot plasma before the whole thing began cooling and recombining almost as fast as it formed.
The experiment, carried out at the European XFEL facility in Hamburg, Germany, captured one of the most extreme ionization events ever recorded in a laboratory. The results, published in Nature Communications in early 2026, offer a time-resolved look at how solid metal transforms into superheated plasma and snaps back, all within a window so brief that light itself travels less than a millimeter.
What the team actually did
Researchers at the HED-HiBEF instrument used a pump-probe approach. First, the ReLaX high-intensity optical laser slammed into a copper wire target, dumping enough energy to blast atoms apart. Then, at precisely timed delays, the European XFEL fired resonant X-ray pulses tuned to approximately 8.2 keV through the expanding debris. That specific energy allowed the team to fingerprint individual charge states of copper ions inside the dense, rapidly evolving material.
The charge state they zeroed in on was Cu22+, sometimes called nitrogen-like copper because it retains only seven electrons, the same number as a neutral nitrogen atom. Reaching that level of ionization means ripping away 22 electrons from each copper atom, a feat that requires extraordinary energy density concentrated in an extraordinarily short burst.
According to a summary from the Helmholtz Association of German Research Centres, ionization peaked at about 2.5 picoseconds after the laser pulse and had largely vanished by roughly 10 picoseconds. That entire lifecycle, from violent stripping to the start of electron recombination, played out in less than one hundred-trillionth of a second.
How hot, and how do they know?
Institutional reporting from the Helmholtz Association describes the resulting plasma as reaching “million-degree” temperatures. Plasma physicists, however, distinguish between electron temperature, ion temperature, and effective radiation temperature, and in a dense, fast-evolving system like this one, those numbers can diverge significantly. The press description is best understood as a qualitative marker of extreme conditions rather than a single thermometer reading.
The measurement technique itself is on firmer ground. An arXiv preprint describing diagnostic capabilities at HED-HiBEF independently confirmed that resonant absorption measurements of specific copper charge states using the ReLaX laser have been implemented and validated at the instrument. That means the team was not relying on a single indirect signal. Multiple diagnostics cross-checked whether the observed X-ray absorption genuinely corresponded to highly charged copper ions embedded in dense plasma.
The Nature Communications paper is open-access, so the full dataset, error bars, and theoretical modeling are available for independent scrutiny. Anyone can examine how the authors translated X-ray absorption features into specific charge states and how they estimated uncertainties on timing and plasma density.
Where the 10,000 volts figure fits in
The voltage figure in the headline draws from a related but distinct line of plasma research: exploding-wire experiments. In those setups, a capacitor bank charged to around 10 kV drives massive current through a thin metal filament, vaporizing it and triggering the onset of plasma formation. One such study, published in the journal Metals, used platinum and iron filaments rather than copper, and its configuration differs fundamentally from the XFEL’s laser-driven approach.
Both methods produce plasmas from metal targets, but the energy delivery mechanisms are not the same. Exploding-wire experiments push electrical current through the bulk of a wire over nanoseconds to microseconds. The XFEL experiment focused an optical laser onto a tiny region of copper for just picoseconds, achieving far higher energy densities in a far smaller volume. Separate research published in Scientific Reports has documented the macroscopic dynamics of copper wire explosions, including how the wire expands, fragments, and emits light, confirming that copper is a well-studied and reproducible medium for plasma generation. But that work examined the big picture of the explosion, not the charge-state-specific, picosecond-resolution probing that makes the European XFEL results distinctive.
In short, 10,000-volt capacitor discharges can push metal into a plasma state, and the XFEL laser can push copper far deeper into that state with far greater precision. They share a subject but occupy different experimental regimes. The headline pairs these two threads because both illustrate the raw physics of metal-to-plasma transitions, but readers should understand that the 10,000-volt figure describes the exploding-wire method, not the energy input of the XFEL laser that produced the Cu22+ observation.
Why it matters beyond the lab
Highly charged ions like Cu22+ are not just laboratory curiosities. Similar conditions exist in the interiors of stars, in the accretion disks around black holes, and in the plasma that future fusion reactors will need to confine and control. Understanding exactly how atoms lose and regain electrons on picosecond timescales feeds directly into models of those environments.
Until now, most knowledge of extreme ionization states came from steady-state or slower experiments that could not capture the transient dynamics. The European XFEL’s ability to freeze-frame the process at 2.5-picosecond resolution opens a window that theorists have long wanted but experimentalists could not provide. If the technique scales to other elements and higher charge states, it could become a standard tool for benchmarking the atomic physics codes used in astrophysics and inertial confinement fusion research.
What remains incomplete in public reporting
Several details remain unresolved in publicly available summaries as of May 2026. The exact pulse energy, duration, and focal spot size of the ReLaX laser during these shots are detailed in the full paper but not in press releases, making direct comparisons to other high-intensity laser facilities difficult without digging into the publication.
Shot-to-shot reproducibility is another open question for general readers. The pump-probe technique builds its time series from many nominally identical laser shots, each probed at a different delay. Variations in laser focus, target alignment, or wire manufacturing could introduce differences that get averaged out in the final analysis. The Nature Communications paper addresses these quantitatively, but the institutional summaries necessarily compress that nuance.
Finally, broader implications for astrophysical modeling or fusion science, while plausible, have not yet been demonstrated in follow-up work. The experiment proves the diagnostic capability. Whether it reshapes our understanding of stellar interiors or reactor plasmas depends on what comes next from this team and others who now have the technique in hand.
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*This article was researched with the help of AI, with human editors creating the final content.
