A powerful electron beam, used to test materials for strength and radiation resistance, initiates not one, but two waves of stress. The second wave is created by plasma in the vacuum diode of the accelerator, as discovered by scientists from MIPT and NRC "Kurchatov Institute"; the results are published in the journal Physics of Plasmas.
The testing scheme is as follows: an electron beam hits a thin near-surface layer of the target, which heats up sharply, pressure increases, and then the area expands and pressure drops. This "unloading" initiates a wave deep into the material. Previously, it was believed that this was the only source of stress, and processes in the plasma were considered insignificant.
The experiment was conducted on the high-current electron accelerator "Kalmar". A transparent target was irradiated with a beam, and waves inside were simultaneously monitored with a laser, while the plasma glow in the diode gap was monitored separately.
It turned out that the plasma lives much longer than the beam. In one of the samples, it glowed for more than 5 microseconds, while the pulse lasted 150–200 nanoseconds — a difference of tens of times. Modeling showed that when the threshold of 60 kA is exceeded, the magnetic field compresses the plasma column, pressure increases, and it additionally affects the target.
This allows for a more accurate interpretation of tests: taking into account not only heating by the beam, but also additional plasma pressure. In the laboratory, it is difficult to separate the two contributions, so the experiment must be supplemented by modeling. For reactors, space technology, and thermonuclear installations, this means a more reliable selection of materials.