Fast ignition inertial fusion energy using laser-driven ion beams - PowerPoint Presentation

1. Fast ignition inertial fusion energy using laser-driven ion beamsLA-UR-22-21549Inertial Fusion Energy Science & Technology Strategic Planning WorkshopVirtual Meeting23 Feb. 2022Presented by Brian Albright, Los Alamos National Laboratory

2. Thanks to contributors Farhat Beg (UCSD), Todd Ditmire (Focused Energy, LLC, U. Texas at Austin), Evan Dodd (LANL), Juan Fernández (LANL), Cort Gautier (LANL), Brian Haines (LANL), Chengkun Huang (LANL), John Kline (LANL), Ari Le (LANL), Scott Luedtke (LANL), Markus Roth (Focused Energy, LLC), Sasi Palaniyappan (LANL), Alex Seaton (LANL), Lin Yin (LANL) Obst-Huebl, L. et al.Lawrence Berkeley National LaboratoryBELLA PW 1 Hz Laser Experiments for Short Pulse Laser-based Ion Fast Ignition for IFEWilks, S.C. et al.Lawrence Livermore National LaboratoryShort Pulse Laser based Ion Fast Ignition for IFEAlbright, B. et al.Los Alamos National LaboratoryFast ignition inertial fusion energy using laser-driven ion beamsWorkshop white papers on IFI:

3. Fast ignition initiated by a laser-driven ion beam is a promising path to inertial fusion energy In ion fast ignition* (IFI), cold, dense DT fuel is assembled using conventional drivers (lasers, pulsed power, heavy ion beams)Then, a high-current ion beam resulting from the interaction of a high-power laser with a target is focused onto a small volume within the fuel (hot spot), heating the fuel isochoricallyFusion burn in the hot spot propagates to the surrounding fuel, leading to the possibility of high fractional burn-up and high gain (G~100)Indirectly driven proton-driven fast ignition concept**M. Roth et al., Phys. Rev. Lett. 86, 436 (2001)S. Atzeni et al., Nucl. Fusion 42, L1 (2002)M. Key et al., Fusion Sci. & Tech. 49, 440 (2006)J. C. Fernandez et al., Nucl. Fusion 54, 54006 (2014)

4. Ion fast ignition has several advantages (and a few disadvantages) compared with other approaches to IFEAdvantagesLower fuel symmetry and temporal pulse shaping requirements than conventional hot spot ignitionFuel compression and heating are decoupled, providing flexibility and different paths for optimizationModular – we can mature the critical components (fuel assembly, ion beam generation & transport) independently before requiring investment in an integrated facilityDisadvantagesSomewhat higher hot spot rRh and Th needed to igniteIon fast ignition drivers are currently not high TRLThough there are no obvious show stoppers, R&D investment is needed to assess the feasibility and develop toward a working prototypeFig. 2. Parameter space for a fusion hot spot within compressed DT fuel, according to an analytic model that balances alpha heat deposition and losses from PdV, thermal conduction, and radiation [S. Atzeni and J. Meyer-Ter-Vehn, The Physics of Inertial Fusion (Oxford; Oxford University Press; 2004).]In rough numbers, rR = 0.5 g/cm2, 10 keV

5. The first challenge for ion fast ignition is the DT fuel assemblyCold DT fuel properties are set by the required gain and efficiencyGain G ~ 100, as needed for IFE generallyICF fuel burnup efficiency*: For IFI power production, this implies a DT fuel density of ~500 g/cm3, rR of cold fuel of 3-5 g/cm2 and a cold fuel mass of 450-2000 µg DT fuel compression for fast ignition† is quite different from the explored ICF design spaceShock followed by ramp drive for isentropic compression (possibly higher pulse contrast than conventional ICF) Longer implosion time scales Zooming probably needed for efficient compression  *Lindl, Phys. Plasmas 2, 3933 (1995)Candidate target composition and laser drive for fast ignition implosion [Clark and Tabak, Nucl. Fusion 47, 1146 (2007)]

6. The desired hot spot properties set the requirements for the ion beamsA minimum rRh of 0.5 g/cm2 implies that for 500 g/cm3 fuel, Rh 10 µmthe hot spot radius may be larger, depending on how well we ultimately can focus the ion beamTo raise the DT fuel to ignition conditions (~10 keV), the minimum ion beam energy delivered to the hot spot is of order several kJ (though this increases as Rh3)This energy must be delivered in to beat disassembly and losses to conduction and radiationHave to do this at ~10Hz (high-energy, high-average-power requirements for short pulse system) see S. Wilks’s white paper for a discussion of this issue along with some candidate technologies In rough numbers, rR = 0.5 g/cm2, 10 keV

7. Broadly speaking, two classes of ion beams (and, thus, targets) have been considered for ion fast ignitionLaser-driven protons/deuteronsLaser-driven high-Z ions (C6+, Al13+, …)

8. The first approach, using laser-driven proton/deuteron beam, is more matureThis approach uses target-normal sheath acceleration (TNSA)*, producing high-current, laminar, charge- and current-neutralized p or d beams with mean energy ~3-10 MeV The TNSA proton energy spectrum is well suited for ion fast ignitionthe fast part of the spectrum arrives first, heats the target plasma and lowers the ion stopping power, enabling better transport of the lower energy part of the beamIon beam focusing is accomplished by the use of a curved (e.g., hemispherical) laser targetP. K. Patel et al., Phys. Rev. Lett. 91, 125004 (2003)46 µm FWHM* S. Hatchett et al. Phys. Plasmas 5, 2076 (2000); R. Snavely et al. PRL 85, 2945 (2000); A. Maksimchuk et al. PRL 84, 4108 (2000); S. Wilks et al., Phys. Plasmas 8, 542-549 (2001); Hegelich et al. PRL 89, 085002 (2002)M. Roth et al. PPCF 44, B99 (2002) Measured TNSA proton energy spectrum

9. Electrodynamics in the cone (and the resultant effects on the ion beam) complicate ion beam focusingElectric fields and plasma-filling complicate the electrodynamics of sheath acceleration of ions in cone geometryIt’s been shown that these fields can improve focusability, though further R&D is needed to see if this can be harnessed for IFI-scale driversT. Bartal et al., Nature Physics 8, 139 (2011)

10. High TNSA proton conversion efficiency (h>5%) is also desirableHigh efficiency lowers requirements for short-pulse laser energy Typical flat-foil TNSA conversion efficiencies (laser to protons) are a few percentIncreasing conversion efficiency is an active area of research e.g., nanostructured targets* may increase conversion efficiencies by 3x or more, though with attendant target fabrication challengesFurther R&D is needed to determine the limitations of ion conversion efficiency at IFI scale in focusing geometry Nano-structured laser target, affording higher conversion efficiency [S. Vallières et al. Sci. Reports 11, 2226 (2021)] *Purvis et al. Nature Photonics (2013), Bailly-Grandvaux et al. Phys. Rev. E 021201R (2020), Dozières et al. PPCF 61, 065016 (2019), Xie et al. Phys. Plasmas 27, 123108 (2020), Vallières et al. Sci. Reports 11, 2226 (2021)

11. The other approach, using high-Z ions (e.g., C6+, Al13+) is promising, though less matureIon beams made from high-Z ions (e.g., 400 MeV C6+) are another possibility for IFIlaser converter target is outside the capsule (no cone)higher average ion energy than in TNSAquasi-monoenergetic beams requiredThis approach to IFI requires alternative acceleration mechanisms that are at lower TRLbreak out afterburner, radiation pressure acceleration, ion solitary wave acceleration, etc.*most of these require high pulse contrast and external, thin (sub-µm) converter targets (additional target challenge) ion beam focusing has not been demonstrated experimentally  *J. C. Fernández et al., Nucl. Fusion 54, 54006 (2014) op. cit.

12. Experimentally, many of the IFI desiderata have been demonstrated with high-Z beams, though not simultaneously500 MeV1GeV C6+ from DLC target(IWASP on CR39)Energy (MeV)Angle (degrees)Off axis COn axis C2D VPIC, Cprotons500 MeVDLC target (TP on CR39)1 GeVDLC target (TP on CR39)C6+ beams with the required energies have been demonstrated1 B. M. Hegelich, et al., Nuclear Fusion 51, 083011 (2011); D. Jung et al., PoP 20, 083103 (2013)

13. Palaniyappan et al. Nature Communications 6, 10170 (2015)A narrow ion energy spectrum has been demonstratedHigh conversion efficiency (7%) has been demonstratedJung et al. New Journal of Physics 15, 023007 (2013)Experimentally, many of the IFI desiderata have been demonstrated with high-Z beams, though not simultaneously

14. Nominal IFI facility requirements for different IFE scenarios are ambitious, though not infeasible Design 1Design 2Design 3Assembled fuel density (g/cc)500500500Assembled fuel radius R (µm)6080100DT fuel rR (g/cm2) 3.04.05.0DT fuel mass (µg)45010702090Eshortpulse (kJ)200200200Elongpulse (kJ) 31012403000Yield (MJ)51145320Gain G100100100Rep-rate (Hz) 101010Electrical conv. efficiency e0.40.40.4Burn-up wall capture efficiency b1.251.251.25Driver efficiency h0.10.10.1Pgrid (MWe) 2005801300 Pdriver = (Eshortpulse + Elongpulse) * Rep-rate p=1/ehbG B. Albright et al. “Fast ignition inertial fusion energy using laser-driven ion beams,” LA-UR-22-20681, white paper for Inertial Fusion Energy Science & Technology Strategic Planning Workshop

15. Summary: Fast ignition initiated by a laser-driven ion beam is a promising path to inertial fusion energy IFI energy production design figures of merit and targets: DT fuel assembly at 500 g/cc and rR = 3-5 g/cm2Ion beam generation with >5% laser-to-ion conversion efficiency for ion energy delivered to the hot spotRep-rated high-energy, high-average-power, short-pulse and long-pulse laser operation at 10 Hz with driver efficiency 10% Relatively small energy of the long-pulse driver relative to a conventional laser-fusion design, reflecting an advantage of only having to compress the fuelThe energy of the drivers has a large lever arm in the design performance. These energies have a relatively high uncertainty rooted in the uncertainty in the underlying physics of fuel compression and focused ion-beam generation. The impact on driver energy, especially short-pulse, may be an effective research prioritizing metric