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

W Cayzac,A Ortner,J Ding,C Bläser,G Malka,N Schroeter,S Busold,A Blažević,F Wagner,V Bagnoud,A Frank,G Schaumann,K Pépitone,D Pepler,D Kraus,D Jahn,A Knetsch,E Kjartansson,T Schlegel,M Ehret,S Bedacht,Simon Weih ,Nico W Neumann ,John P Helfrich ,Jan Vorberger ,Dirk O Gericke ,Stephan Sander ,Dennis Schumacher ,Patrick Fiala ,A Tauschwitz ,M Marvin Seibert ,L Hallo,Y Zobus,S Frydrych,M M Basko,O Deppert,Markus Roth

doi:10.1038/ncomms15693

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.

Highlights

The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the a-particle heating expected to trigger a burn wave in the hydrogen pellet and resulting in high thermonuclear gain
The stopping power peaks when the projectile velocity vp reaches the thermal velocity of plasma electrons and ions, respectively, that is for sffiffiffiffiffiffiffiffiffiffiffiffiffi vp % vteh;i1⁄4
Around the Bragg peak, stopping theories that include a detailed treatment of close collisions between the projectiles and the plasma electrons[16,17,18] predict 30–50% smaller energy loss than the standard perturbative models[16,17,19]

Summary

Introduction

The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the a-particle heating expected to trigger a burn wave in the hydrogen pellet and resulting in high thermonuclear gain. The effective beam charge state in the plasma, that is a crucial parameter for the stopping power, was calculated using a MonteCarlo code based on projectile electron loss and capture rates[11,19] as well as the models by Gus’kov et al.[26] and Kreussler et al.[27].

Results

Conclusion