ELI summer school, August 26 – 30, 2019

Academic research on the inertial confinement in Europe

V. T. Tikhonchuk Centre Intenses et Applications, University of Bordeaux – CNRS – CEA, Talence, France ELI-Beamlines, Institute of Physics, CSR, Dolní Břežany, Czech Republic Principles of initial confinement fusion for energy production (IFE)

IFE is a pulsed process: the energy is released in periodic pellet explosions • Standard power plant produces 1 GW = 1 GJ/s: 1 GW = 10 explosions in 1 s = 250 kg TNT/s = 3 mg DT/s • Typical target mass is 1 mg corresponds to a sphere R = 1 mm at normal density ρ = 0.25 g/cc

Ignition conditions are imposed by the : ρR > 0.3 g/cm2 at T = 5 keV It cannot be satisfied at normal conditions: compression and heating are needed • compression of the total fuel mass by using the ablation pressure: recoil effect • heating of a small part of the fuel: creation of a spark (hot spot) • combustion of the residual fuel

August 30, 2019 Academic research on ICF in Europe 2 Three steps of the ICF process:

• compression of the total fuel mass by using the ablation pressure: recoil effect • heating of a small part of the fuel: creation of a spark (hot spot) • combustion of the residual fuel

• implosion time 10 ns • driver energy 1 MJ • ignition time 30 ps • 300 • acceleration 1013g • final energy 50 kJ • radius 100 µm • fusion energy • pressure 100 Mbar • efficiency 5% • pressure 300 Gbar 300 MJ • implosion velocity ~ • energy 10 kJ 400 km/s

August 30, 2019 Academic research on ICF in Europe 3 Two basic approaches: direct and indirect drive

direct drive indirect drive

ablator DT ice  DT gas R

R ~ 1 mm  ~ 0.2 mm

• indirect drive is motivated by the national defence programs: less efficient but considered to be more reliable • direct drive: academic program is motivated by energy production and modelling extreme states of matter in laboratory

August 30, 2019 Academic research on ICF in Europe 4 Only few large scale installations exist in the world

direct drive indirect drive

OMEGA LMJ NIF 60-beams, 30 kJ, 30 TW 176-beams, 1.4 MJ, 400 TW 192-beams, 1.8 MJ, 500 TW

direct drive: fast ignition Academic programs benefit a free access to the national MJ facilities on a competitive basis within ~15% of the

GEKKO XII available shots 12-beams, 10 kJ, 10 TW SHENGUANG-III 48-beams, 180 kJ, 60 TW August 30, 2019 Academic research on ICF in Europe 5 Update on the indirect drive experiments Indirect Drive ignition experiments are conducted on NIF since 2009 Several approaches are considered: Major problems: • low adiabat (low foot) implosions (2010 – 2012) • low energy coupling to the hot spot • medium adiabat (high foot) implosions with plastic • hydrodynamic instability of the and HD carbon ablators imploding shell • low gas fill hohlraums (symmetry control) • low energy coupling to hohlraum

O Hurricane et al, Phys Plasmas 2019 Significant progress but still far from ignition

August 30, 2019 Academic research on ICF in Europe 6 Outline

. Direct drive ignition program and role of the European scientific community . Alternative approaches to inertial fusion: fast and shock ignition . Recent developments in the fast ignition approach: magnetic guiding of electrons . Strong shock generation experiments in the planar and spherical geometry: role of hot electrons . Near future plans

August 30, 2019 Academic research on ICF in Europe 7 Direct drive approach: more efficient energy deposition

The ignition conditions impose a relation between the hot spot pressure and energy .⁄ By using relations between the energy pressure and radius:

~~/ ~~~/

the ignition criterion reads:

Higher energy deposition in the hot spot with the direct drive approach results in lower compression ratio CR ~ 22 compared to CR ~30‐40 for the indirect drive

R Betti et al, Phys Rev Lett 2015 SP Regan et al 2019

August 30, 2019 Academic research on ICF in Europe 8 Program for the direct drive to 2020

The Rochester group is leading the International Direct Drive Program curves: scaled fusion yield for 1.9 MJ • Improve coupling of laser energy to the hot spot • Improve symmetry of implosions on OMEGA ) • Demonstrate scaled performance on NIF 14 (×10

yield

areal density (mg/cm2) Collaborations: • LLNL: LPI, target design, • NRL: imprint, CBET control V Goncharov et al PPCF 2018 • LANL: high Z, EoS, opacities V Gopalaswamy et al Nature 2019 • EUROPE: physics, alternative schemes August 30, 2019 Academic research on ICF in Europe 9 Alternative ignition schemes: fast and shock ignition

Alternative ignition schemes separate the implosion and ignition phases: the implosion phase is common with the standard direct drive approach, but the ignition is non‐isobaric • shock ignition: the central hot spot pressure is boosted with a special intense laser spike (the scheme selected by the European ICF project HiPER, collaboration with LLE) • fast ignition: the ignition spark is initiated with an intense of electron or ion beam driven by a multi‐PW laser pulse (ILE, Osaka) Spike : Converging Shock

v. 54, no.5 Hot Spot

Fuel

Major issues: Major issues: • transport of hot electrons or • generation of a strong converging ions to the core shock • high energy PW laser pulse • control of the hot electron preheat Review on alternative ignition schemes: Nuclear Fusion 54, No. 5, 2014 August 30, 2019 Academic research on ICF in Europe 10 Fast Ignition Approach

August 30, 2019 Academic research on ICF in Europe 11 Fast ignition scheme: recent results

Fast ignition approach requires less laser energy injected in the hot spot Central ignition Fast ignition ~~ (isobaric) (isochoric) High ρ (1000 g/cm3) Main fuel

Low ρ (100 g/cm3) High ρ (a part of fuel) hot spark Fast ignition project with electron beams is led by the Japanese team, ILE, Osaka: The laser facility contains: • 12 beam 3.5 kJ ns GEKKO system • 4 beam 2.5 kJ ps LFEX

R Kodama et al, Nature 2002 Nuclear Fusion 54, No. 5, 2014 Major issue: high energy & strong divergence of electrons August 30, 2019 Academic research on ICF in Europe 12 Magnetic field assisted fast ignition scheme

GEKKO experimental campaigns in 2016 ‐ 2018 proposed three significant improvements in the integrated fast ignition experiment

• A thin shell is replaced with a solid ball to improve the implosion stability

100 µm Gold cone

• The LFEX contrast is strongly improved: suppression of super‐hot electrons • A capacity‐coil laser driven parallel magnetic field is applied for the electron guiding

Bz

S Sakata et al, Nature Comm 2018

August 30, 2019 Academic research on ICF in Europe 13 Solid ball compression

The areal density of 100 mg/cm2 is achieved with a Gaussian GEKKO‐XII pulse and 200 µm diameter solid ball

undriven -400ps

#38964 #38989

-260ps -160ps #38989

Temporal evolution of ρR 100 μm 100 μm #38995 #38983 With a tailored laser pulse the areal density of 2.7 g/cm2 can be achieved on NIF X‐ray shadows of fuel core H Sawada et al. Appl Phys Lett 2016 August 30, 2019 Academic research on ICF in Europe 14 Strong magnetic field generation with a laser

A capacitor‐coil target allows generation of magnetic fields ~ 5‐6 MG in a 1 mm3 volume current B In experiments on LULI200 and GEKKO‐XII a set of three complementary diagnostics has been used: • B‐dot probes • proton deflectometry • Faraday rotation

J JSantos et al. NJP 2015 V T Tikhonchuk et al. Phys Rev E 2017

August 30, 2019 Academic research on ICF in Europe 15 Demonstration of the electron beam guiding

Experiment on LULI2000 demonstrates an electron beam collimation in the magnetic field: CTR diagnostic of transmitted electrons

1.5×1019 W/cm2

w/out B‐field with B‐field

• the electron beam width is reduced by 3 times • the electron peak density is raised by 12 times • smoothing of electron beam filaments • reduced emittance 2 times

S Fujioka et al, Phys Plasmas 2016 M Bailly‐Grandvaux et al, Nature Comm. 2018

August 30, 2019 Academic research on ICF in Europe 16 Integrated experiment on fast ignition Experiment on GEKKO‐XII demonstrates good implosion and core heating up to 3 keV B-generation coil

Cone

Dense core

• 3 GEKKO beams for the magnetic field generation • 6 GEKKO beams for the ball compression • Core density of 6 ‐ 11 g/cm3 was obtained • 4 LFEX beams for the electron beam generation at the heating laser pulse injection timing • 3 GEKKO beams for the implosion diagnostics • Spectrum emitted from Li‐ and He‐like Cu ions indicates a 3 keV temperature of the • Cu‐doped oleic‐acid bead heated region • Coupling efficiency ~5 –8%, energy H Sawada et al, Appl Phys Lett 2016 deposition 50 J, pressure ~1 Gbar S Sakata et al, Nature Comm 2018

August 30, 2019 Academic research on ICF in Europe 17 Shock Ignition Approach

August 30, 2019 Academic research on ICF in Europe 18 Shock Ignition scheme

An intense laser spike launches a strong shock at the end of implosion phase which . . provides a pressure boost in the central hot spot ~ ~ 200 TW 10 PW/cm2 Major issues: Laser Pulse • Strong shock generation • Control of high energy electrons • Definition of optimal ignition conditions • Effects of the irradiation anisotropy • Development of appropriate num. tools • Robust target design radius

time Ignition

V Shcherbakov, Sov J Plasma Phys 1983 R Betti et al. PRL 2007 X Ribeyre et al. PPCF 2009 August 30, 2019 Academic research on ICF in Europe 19 Shock pressure generation with hot electrons Spike pulse intensity ~ 1016 W/cm2 implies strong LPI effects: param. inst. & hot electrons

Ablation pressure is evaluated from the quasi‐stationary energy flow balance

/ / ≅. The shock pressure enhanced by hot electrons / / ≅. but for a short time / / ≅ Double role of hot electrons: • medium energy < 50‐80 keV depose their energy behind the shock front enhance its pressure • higher energy electron preheat the fuel and reduce the shock strength S. Guskov et al, Phys Rev Lett 2012 X. Ribeyre et al, Phys Plasmas 2013 E. Llor Aisa et al, Phys Plasmas 2015 August 30, 2019 Academic research on ICF in Europe 20 Laser energy deposition model: thick rays

New approach of paraxial complex geometrical optics describes the laser intensity in corona and takes into account the cross beam energy transfer, the ponderomotive force, excitation of parametric instabilities and hot electron generation = ∥ Ray centroid Front curvature/Ray width Standard ray tracing Beam width ⁄ ⁄ Beam curvature ⁄ , ⁄

Wave front equation in the ray reference frame

Y A Kravtsov, N A Zhu, Theory of Diffraction, 2010 A Colaitis et al, Phys Rev E 2014

August 30, 2019 Academic research on ICF in Europe 21 Non-linear LPI processes with thick rays

New approach of paraxial complex geometrical optics describes the laser intensity in corona and takes into account: • speckled intensity distribution • cross beam energy transfer (CBET) • ponderomotive force • excitation of parametric instabilities Stimulated • hot electron generation and transport Raman Scattering and Two Plasmon Decay Resonance absorption

CBET

Cross beam A Colaitis et al, Phys Rev E 2015, 2016 energy transfer

August 30, 2019 Academic research on ICF in Europe 22 Influence of hot electrons on the target design

Hot electron preheat may affect the shock ignition target parameters

DT ice 211 µm

DT gas 833 µm

Standard HiPER target do not withstand the hot electron preheat

with hot electrons

Ignition window from standard Dramatic increase of radiation losses due simulations with collisional absorption to internal ablation is responsible for the A Colaitis et al, Phys Plasmas 2016 temperature inhibition and non‐ignition August 30, 2019 Academic research on ICF in Europe 23 Influence of hot electrons on the target design

Hot electron preheat may affect the shock ignition target parameters

DT ice 211 µm

DT gas 833 µm

Standard HiPER target do not withstand the hot New target design has been proposed for the electron preheat NIF experiment: hot electron driven shock

with hot electrons

Ignition window from standard Dramatic increase of radiation losses due simulations with collisional absorption to internal ablation is responsible for the A Colaitis et al, Phys Plasmas 2016 temperature inhibition and non‐ignition WL Shang et al, PRL 2017 August 30, 2019 Academic research on ICF in Europe 24 Quest for strong shock generation

Experiments at several European facilities (LULI 2000, LIL and PALS) and at OMEGA attempted to achieve shock pressures needed for shock ignition: > 300 Mbar • Planar geometry: intensities > 1016 W/cm2 @ 1w but small spot size, large lateral losses –maximum pressure 110 Mbar @ 3w 3×1015 W/cm2 (LIL) • Demonstration of the hot electron preheat • Spherical geometry: lower intensities but higher shock pressure, shock pressure amplification due to hot electrons

low intensity Back VISAR scattered high intensity SOP light

B. Batani et al. Nuclear Fusion 2014 A. Colaitis et al. Phys Rev E 2016 G. Cristoforetti et al. EPL 2017 Model of NONLINEAR laser absorption provides good R. Nora et al, Phys Rev Lett 2015 shock timing and HOT ELECTRON fraction W. Theobald, Phys Plasmas 2015

August 30, 2019 Academic research on ICF in Europe 25 LIL campaign: shock drive in a hemispherical target

Planar geometry at 10 kJ energy level  Effect of the optical laser smoothing on shock pressure generation  Effect of hot electrons on shock pressure generation  Bipolar shock generation

 Formation of a planar shock front by the target shaping  Validation of the numerical tools  X‐ray radiography of the shock front

 LIL smoothing is efficient @ 3 ω  Low backscattered energy @ 3×1015 W/cm2  Estimated ablation pressure ≤ 110 Mbar

S Baton et al. Phys Rev E 2017

August 30, 2019 Academic research on ICF in Europe 26 OMEGA experiment on strong shock generation

Series of experiments on strong shock generation on OMEGA in spherical geometry The shock amplitude is evaluated from the measured laser energy absorption and the X‐ray flash delay

. Laser intensity ~ 6×1015 W/cm2 @ 351 nm . Measured laser absorption and hot electron number and energy . Higher local intensities achieved with a non‐smoothed laser energy distribution . Correlation of HE production and SRS

R. Nora et al, Phys Rev Lett 2015 . Stronger shock in the shots with SSD off W. Theobald, Phys Plasmas 2015 August 30, 2019 Academic research on ICF in Europe 27 Hot electron generation and SRS

Hot electron generation is correlated with SRS . Correlation of the hot electron generation and SRS in different ablators . Anti‐correlation of the hot electron generation with the flash time . The temperature of hot electrons remains constant . Enhanced SRS and hot electron production in the CH ablator

SSD on SSD off

The hot electrons are produced by SRS and contribute to a stronger shock pressure E. Llor Aisa et al, Phys Plasmas 2017 W. Theobald et al, Phys Plasmas, 2017 August 30, 2019 Academic research on ICF in Europe 28 Modeling of the strong shock experiment on OMEGA

Laser absorption, hot electron parameters and the flash time are in good agreement with the CHIC simulations (f = 4%) • Experimental absorption 71%

shock pressure • Calculated absorption 69% without HE with HE • Hot electrons in experiment: 8% @ 80 keV shock pressure • Hot electron calculated: 7% @ 60 keV • Experimental flash time 2439±5 ps • Simulation with hot electrons 2436 ps ablation pressure ablation pressure

Generation of hot electrons increases without HE the shock pressure by 100 Mbar: laser driven shock with HE / / ⁄ ⁄ hot electron driven shock / / Hot electrons enhance the shock pressure but preheat E. Llor Aisa et al, Phys Plasmas 2017 the target and reduce the shock strength W. Theobald et al, Phys Plasmas 2017

August 30, 2019 Academic research on ICF in Europe 29 Shock ignition dedicated experiment on LMJ-PETAL

First shock generation experiment at the high laser energy (>40 kJ) and high intensity (>8×1015 W/cm2) in the planar geometry

29U 28U • Characteristics of generated hot electrons • CBET effects N • Effects of the laser beam smoothing on the hot electron generation and shock amplitude • Expected HE conversion ~4%, average energy ~50 keV (SRS) • Expected shock pressure 220 Mbar

28L 300 µm Ti, Ag, Pt Ka layers TW 1,3 ns 4.4 12 kJ CH 3 ns 0.4 3 kJ 0246(ns) S Baton et al LMJ‐PETAL User Meeting, 2 quads used for X‐ray ns backlighter (Fe) October 2018 to observe the propagation of the shock August 30, 2019 Academic research on ICF in Europe 30 Hydro simulations with the PCGO module

Target and laser irradiation design for the shock ignition relevant conditions

• Corona: Te = 7‐8 keV, Ln = 80 – 200 µm • CBET effects • Effects of the hot electron generation Expected HE conversion: • SRS ~10%, average energy ~45 keV • SRS ~1.5%, average energy ~90 keV

S Baton et al LMJ‐PETAL User Meeting, October 2018 Three LMJ shots in April 2019

August 30, 2019 Academic research on ICF in Europe 31 Near future for ICF:

• LMJ commissioning • Approach to higher repetition rates • Novel target designs (magnetic fields) • Looking for the inertial fusion energy

August 30, 2019 Academic research on ICF in Europe 32 LMJ program status

LMJ full scale will have 176 beams ‐> 44 quadruplets > 22 bundles energy 1.4 MJ at 351 nm with maximum power 400 TW • Operational commissioning in October 2014 with 8 beams with maximum energy 25 kJ • 500 laser shots including 150 shots on target in 4 years • PETAL commissioned in October 2017, first academic experiment in December 2017

2022 J.L. Miquel, LaserLab Forum 26 2019 August 30, 2019 Academic research on ICF in Europe 33 LMJ ignition roadmap

LMJ in the construction phase operates in 2 shifts: 4 months of plasma experiments and 8 months of construction –mounting, qualification, activation • activation of plasma diagnostics: from 10 actually to 30 diagnostics in 2022 • improvement of the focusing quality and the shot cycle time • 40 laser shots on target per year, 10 shots for the academic community • 6 academic experiments are selected, new call in 2020

Precision control LMJ: • beam energy 7% • temporal shape 20% • synchronization 28 ps • pointing accuracy 52 µm • shot cycle time 7 h

PETAL characteristics: • beam energy 400 J • pulse duration 700 ps • focal spot size ~ 50 µm • intensity ~ 1019 W/cm2

JL Miquel, E Prene, Nuclear Fusion 2019 August 30, 2019 Academic research on ICF in Europe 34 Preparation of high rep-rate operation at ELI-BL

ELI‐Beamlines facility prepares L4 laser for high repetition rate operation in the ns mode • laser line at 527 nm 800 J, 5 ns pulse duration is under preparation • time interval between shots ~10’ – about 100 shots per day • experiment on EoS of silicates and enstatites is planned for the beginning 2020 • international collaboration team: Czech – Germany – France –USA

Program for 2019: • construction of the beam line • design of the experiment • design of the target support and Kick‐off meeting Nov. 27 2018 pointing system User meeting April 5 2019 • mass target fabrication First shots in fall 2020 • design and fielding of diagnostics https://www.eli‐beams.eu/ • management of debris

August 30, 2019 Academic research on ICF in Europe 35 Novel target designs: MagLIF

Difficulties with ICF experiments on NIF motivated new more robust target designs and approaches MagLIF scheme implies the use high current Z‐pinches for the radial magnetic compression and plasma preheat with intense laser pulse: • more stable implosion • smaller compression • large energy available in high pulsed power systems • lower energy gain 10‐30 T 100‐300 eV CR = 20‐30 actual Z –machine experiments Sub‐scale Peak current 19 MA experiments are Magnetic field 10 T ongoing at OMEGA Laser energy 2.5 kJ Yield DD 2×1012 n µm

Needed for ignition Peak current 30 MA

Magnetic field 30 T Position, Hansen et al: PPCF, 2018 Laser energy 10 kJ Slutz ey al: Phys Plasmas, 2010 Convergence 25 Time, ps August 30, 2019 Academic research on ICF in Europe 36 Novel target designs: multiple shells

Difficulties with ICF experiments on NIF motivated new more robust target designs and approaches Multi‐layered targets imply the Direct drive approach provides better energetic efficiency: Be use high‐Z metallic shells for shell 150 kJ ‐> Cu shell 88 kJ ‐> Au shell 40 kJ (input hot spot the fuel compression energy in the current NIF implosions is 5 kJ)

• more stable implosion • Use of metals strongly increases payload Mshell/Mfuel ~ 100, • stronger compression lower ignition temperature 2.5 keV • much larger payload • Lower implosion velocity < 200 km/s more stable • lower energy gain compression • Volume ignition instead of hot spot ignition • Use metallic shells resembles the nuclear weapon designs • Complicated target technology • First experiments have been started at OMEGA

Molvig et al: PRL, 2016, Phys. Plasmas 2018 Merritt et al, Phys Plasmas 2019 August 30, 2019 Academic research on ICF in Europe 37 Pathways to the Energy from Inertial Fusion

Ultimate goal of IFE is design and construction of a plant The most advanced power plants projects are LIFE (USA), HiPER (Europe) and KOYO‐F (Japan)

Many serious challenges need to be addressed before the commercial use of IFE: • demonstration of ignition and high energy gain • design of high rep‐rate reliable lasers and experiments • design of final optics and construction materials capable to withstand high neutron, radiation and thermal fluxes, high temperatures and pulsed mechanical load • mass production of cheap targets, target injection & tracking • efficient energy recovery LIFE: Fusion Sci. Tech. v.60, 2011 • tritium inventory, breeding& handling HiPER Project: www.‐laser.org • integrated power plant design, safety and security KOYO‐F: Fusion Sci. Tech. v.56, 2009 August 30, 2019 Academic research on ICF in Europe 38 Major axes for achieving the ignition conditions

The International Direct Drive program addresses the major issues related to the direct drive ignition • laser plasma interaction (LPI) and laser energy coupling to plasma • target design and achieving a high implosion velocity • control of the target adiabat: laser prepulse, radiation transport and hot electron generation • control of hydrodynamic instabilities: quality of target surface, adiabat shaping, laser imprint, laser beam power balance, beam energy transfer (CBET) mitigation • hot spot control, cold‐hot fuel mix European contribution: • improvement of the physics of laser plasma modelling: LPI, PDD, imprint control • small scale SI experiments, collaborative experiments on GEKKO, OMEGA and NIF • improving theoretical models, LMJ‐PETAL experiments • improving electron and ion transport: contribution to fast ignition

August 30, 2019 Academic research on ICF in Europe 39 THANK YOU for YOUR ATTENTION

August 30, 2019 Academic research on ICF in Europe 40