Intensification of laser-produced relativistic electron beam using converging magnetic fields for ignition in fast ignition laser fusion

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Abstract

The kilo-tesla-class converging magnetic field effects on the core heating properties and the energy and duration of relativistic electron beam (REB) required for ignition in fast ignition laser fusion has been evaluated by parametric 2D hybrid simulations where a uniformly compressed DT core with ρ = 300 g/cm3 is heated by REB with TREB = 3 MeV, IREB = 0.69 × 1020 W/cm2 and θREB = 40° under sufficiently strong magnetic field (Bext = 3 kT at the REB injection position). The kilo-tesla-class converging magnetic field can intensify REB and then enhances the core heating power drastically. As the results, the fusion ignition can be initiated by the REB with EREB ≧ 50 kJ and τREB = 10 ~ 30 ps. With increasing mirror ratio RM, the negative effect of converging field, i.e., mirror reflection, becomes significant, which enhances the REB energy required for ignition (EREB,ig = 49 kJ for RM = 3 → EREB,ig =77 kJ for RM = 20).

Section snippets

INTRODUCTION

In fast ignition (FI) scheme of laser fusion, separation of ignition spot formation from implosion process relieves the uniformity requirement to create central hot spot in implosion. Instead of isobaric configuration of imploded core in conventional central spark ignition (CSI), isochoric configuration without the central hot spark is formed through the implosion in FI scheme, which reduces the fuel mass to achieve the same areal density as that in SCI scheme and then required implosion laser

Numerical modeling and simulation condition

In this study, we use a two-dimensional (cylindrical r-z) hybrid code FIBMET [16, 17] based on one-fluid two-temperature Eulerian radiation-hydrodynamics code, which includes electron and ion thermal conductions (flux limited Spitzer Härm model [18]), radiation transport (flux-limited diffusion model), fusion reactions (DT, DD two branches and D3He reactions) and fusion-produced alpha-particle transport (Levermore-Pomraning (LP) diffusion model [19, 20]). The radiation is emitted from a hot

Simulation results and discussion

In Fig. 4, spatial profiles of plasma heating rate by REB at t = 6 ps are shown for (a) no external magnetic field case, (b) parallel field case (RM = 1), (c) RM = 3 and (d) RM = 20. In the case without external field, since the REB is diverged and separated into several filaments, the heating rate is very low. Compared with this, in the case with parallel field with Bext = 3 kT, the REB propagates without divergence (nearly parallel) due to the sufficiently strong field to trap the electrons

Concluding remarks

On the basis of 2D hybrid simulations, we have evaluated the kilo-tesla-class converging magnetic field effects on the core heating properties and the REB energy and duration required for ignition in fast ignition laser fusion by assuming a specific condition, i.e., a uniformly compressed DT core with ρ = 300 g/cm3 is heated by REB with TREB = 3 MeV, IREB = 0.69 × 1020 W/cm2 and ΔθREB = 40° under sufficiently strong magnetic field (Bext = 3 keV at the REB injection position). The main

Acknowledgements

This work was performed with the support and under the auspices of the Collaboration Research Program between the National Institute for Fusion Science (NIFS) and the Institute of Laser Engineering at Osaka University (NIFS12KUGK057, NIFS15KUGK087, NIFS18KUGK118) and the NIFS Collaboration Research Program (NIFS17KNSS098), and also supported by the Japanese Ministry of Education, Science, Sports, and Culture through Grants-in-Aid, KAKENHI(Grant No. 16H02245, 15K21767). This research used

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