Abstract
Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.
Highlights
The fast ignition (FI) concept [1] for inertial confinement fusion (ICF) proposes to separate the compression and ignition phases of a fuel pellet. This scheme proceeds by first compressing the pellet with an array of laser beams, and rapidly heating a localized spot on the compressed plasma with a short peta-watt laser pulse, to ignite a fusion reaction that will spread to the rest of the plasma
In the context of a FI integrated target, the magnetic mirror effect at the cone injection caused by the B-field compression at the cone tip would reduce the coupling of the relativistic electrons to the fuel. Considering these challenges, a cylindrical geometry arises as a promising option, as it allows for compression in the radial dimension and leaves a free axis to apply the external B-field and inject the fast electrons
We carried out experiments and simulations to understand fast electron transport in order to control energy deposition into a previously characterized, imploded cylindrical CH plasma magnetized with an external B-field
Summary
The fast ignition (FI) concept [1] for inertial confinement fusion (ICF) proposes to separate the compression and ignition phases of a fuel pellet. In the context of a FI integrated target, the magnetic mirror effect at the cone injection caused by the B-field compression at the cone tip would reduce the coupling of the relativistic electrons to the fuel Considering these challenges, a cylindrical geometry arises as a promising option, as it allows for compression in the radial dimension and leaves a free axis to apply the external B-field and inject the fast electrons. Long before petawatt lasers were constructed, Sweeney et al considered a class of highgain ICF targets driven by electrons or light ions with strong external B-fields in cylindrical compression [23] According to their suggestions, energy gains of 20–40 in the compressed density of 10 g cm−3 are expected using 1 MeV electron beam injection with an intensity of 45 TW cm−2 and initial B-fields of 30–60 T.
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