D. Tsiklauri

A proton bunch flies into a plasma cloud, and leaves behind an invisible trail: an electric wave. This wave can pick up other particles and accelerate them to enormous energies. But controlling it is tricky: there are too many details in plasma behavior.

High-frequency sound focused on a single point acts like an invisible lens gathering sunlight. Inside a tumor, such a lens can raise the temperature to about 72°C in a second, like hot water from a tap, but inside living tissue. Meanwhile, surrounding healthy cells remain almost untouched.