In a chamber that looks like a metal barrel, a current of four hundred thousand amps discharges in two hundred nanoseconds. Inside is a ring of argon plasma, compressed by its own magnetic field like a hand squeezing a snowball. This is a Z-pinch: the plasma is squeezed toward the axis and heats up. But until now, no one had seen exactly how the gas moves inside that snowball — simultaneously in all three directions: along the axis, around it, and across it.
At the Llampüdkeñ facility, the plasma was probed with lasers from three sides at once. Light scattered off electrons revealed the velocities. It turned out that near the axis, the gas flows along the axis at 60–70 kilometers per second, faster than a bullet, but only if the external magnetic field is weak. Crank the field up to 0.1 tesla, and this flow nearly freezes: the velocity drops to plus or minus 20 kilometers per second. It's as if a strong hand were holding the snowball from flattening into a pancake.
The plasma rotation also surprised. Previously, it was only noticed at the edge, but now it's clear: the vortex penetrates the entire column, only spinning slower near the axis and faster toward the edge, following a smooth curve reminiscent of a drain vortex profile. Moreover, rotation appears even if there is no initial radial magnetic field: it is born spontaneously during compression. And if such a field is added externally, the rotation intensifies.
These measurements are like reading the pulse of an explosion. Now we can see where the compression energy goes: part of it is spent not on heating but on accelerating the gas along the axis and on rotation. If we learn to control these flows, plasma can be compressed more efficiently, and that's a direct path to compact fusion energy sources, where plasma is held not by walls but by magnetic fields.
Argon used in such experiments is the same gas that glows violet in neon signs, only there it's mixed with neon.