Experimental discrimination of ion stopping models near the Bragg peak in highly ionized matter

TLDR

Ion stopping in dense plasmas governs α‑particle heating in inertial confinement fusion, yet experimental data are scarce and limited to high velocities, leaving large uncertainties near the Bragg peak. The study reports experimental data at low projectile velocities near the Bragg peak to probe ion stopping. We measured ion stopping at low projectile velocities near the Bragg peak. Our precise measurements disprove several standard stopping‑power models for typical inertial‑fusion velocities while supporting theories that account for strong ion‑electron collisions.

Abstract

Abstract The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the α-particle heating expected to trigger a burn wave in the hydrogen pellet and resulting in high thermonuclear gain. However, measurements of ion stopping in plasmas are scarce and mostly restricted to high ion velocities where theory agrees with the data. Here, we report experimental data at low projectile velocities near the Bragg peak, where the stopping force reaches its maximum. This parameter range features the largest theoretical uncertainties and conclusive data are missing until today. The precision of our measurements, combined with a reliable knowledge of the plasma parameters, allows to disprove several standard models for the stopping power for beam velocities typically encountered in inertial fusion. On the other hand, our data support theories that include a detailed treatment of strong ion-electron collisions.