Laser Ion Acceleration: Status and Perspectives for Fusion

Transcription

1 Laser Ion Acceleration: Status and Perspectives for Fusion Peter G. Thirolf, LMU Munich Outline: laser-particle acceleration fission-fusion mechanism: with ultra-dense ion beams towards r-process path at N=126 new large-scale laser infrastructure for nuclear physics: ELI-Nuclear Physics (Extreme Light Infrastructure)

2 Laser particle acceleration mechanisms - high-power (100 TW PW ), short-pulse (few fs) lasers - focused intensity on target: W/cm 2 Electron acceleration (gas jet) LWFA (laser wake-field acceleration) Ion acceleration (thin foil) RPA (radiation-pressure acceleration) accelerated electrons wakefield bubble laser pulse field ~ TV/m PV/m E e GeV E ion 50 MeV/u charge ~ pc E/E ~ 1-2% (e - ) ~ 10-20% (ion) ε~10-5 mm mrad A. Pukhov et al., Appl. Phys. B 74, 335 (2002) J. Faure et al., Nature 431, 541 (2004). A. Henig et al., PRL 103 (2009)

3 Radiation Pressure (Ion) Acceleration electr. ions electrons ions driver laser nm foil nm foil relativ. electrons/ ions at solid density - cold compression of electron sheet, followed by electron breakout - dipole field between electrons and ions - ions + electrons accelerated as neutral bunch (avoid Coulomb explosion) - solid-state density: e/cm 3 classical bunches: 10 8 e/cm 3 ~ x density of conventionally accelerated ion beams

4 Collective Stopping Power Reduction Bethe-Bloch for individual ion: de dx = Z e mev ln e k 2 4 eff 4πne 2 2 mev 2 D + kdv ln ω p binary collisions k D = Debye wave number long-range collective interaction ω p = plasma frequency reduction of atomic stopping power for ultra-dense ion bunches: - plasma wavelength (~ 5 nm) «bunch length (~560 nm): only binary collisions contribute - snowplough effect : first layers of ion bunch remove electrons of target foil - predominant part of bunch: screened from electrons (n e reduced) reduction of de/dx : avoids ion deceleration below V C : allows for thick reaction targets for fusion reactions

5 Exp. Scheme for Fission-Fusion conventional stopping: Production target Reaction target 232 Th: 560 nm 232 Th: ~ 50µm W/cm 2 focal diam. ~ 3 µm high-power, high-contrast APOLLON laser: 2x 150 J, 21 fs (2x 7.1 PW) ~ 1 mm Fission fragments Fusion products W/cm 2 focal diam. ~ 5 µm CD 2 : 520 nm CH 2 ~ 70 µm

6 Exp. Scheme for Fission-Fusion collective stopping: Production target Reaction target 232 Th: 560 nm 232 Th: ~ 5 mm W/cm 2 focal diam. ~ 3 µm high-power, high-contrast APOLLON laser: 2x 150 J, 21 fs (2x 7.1 PW) ~ 1 mm Fission fragments Fusion products W/cm 2 focal diam. ~ 5 µm CD 2 : 520 nm

7 Reaction Scheme: Fission-Fusion 1. Fission: beam (~ 7 MeV/u): d, C, 232 Th target: p, C, 232 Th d, C Th F L + F H : fission fragments in target 232 Th + p,c F L + F H : fission fragments of beam F L F H 232 Th: <A L> ~ 91, A L ~ 14 amu (FWHM) AL ~ 22 amu (10%) <Z L > ~ 37.5 (Rb,Sr) 2. Fusion: light fission fragments of beam + light fission fragments of target - F L + F L < A Z> : nuclei close to N=126 waiting point - F L + F H 232 Th : original nuclei - F H + F H unstable

8 Fission-Fusion Yield / Laser Pulse laser acceleration (300 J, ε=10%): normal stopping reduced stopping 232 Th : C : deuterons : beam-like light fragments target-like light fragments fusion probability F L (beam) + F L (target) neutron-rich fusion products (A ) laser development in progress: diode-pumped high power lasers: increase of repetition rate in progress

9 r process: waiting point N=126 r process: - path for heavy nuclei far in terra incognita - astrophysical site(s) still unknown: core collapse SN II, neutron star merger? Au, Pt, Ir,Os - waiting point N=126: bottleneck for nucleosynthesis of actinides - last region of r process close to stability

10 Towards N=126 Waiting Point r process path: - known isotopes ~15 neutrons away from r process path (Z 70) x σ fisfus 0.1 key nuclei measure: - masses, lifetimes, structure - β-delayed n emission prob. P ν,n - lifetime measurements: already with ~ 10 pps visions: - test predictions: r process branch to long-lived (~ 10 9 a) superheavies (Z 110) search in nature? - improve formation predictions for U, Th - recycling of fission fragments in (many) r process loops?

11 Experimental layout characterization of reaction products - decay spectroscopy high power short-pulse laser APOLLON detector transport system mirror target concrete shielding (gas-filled) separator

12 Experimental layout characterization of reaction products - decay spectroscopy Penning trap mass measurements Penning trap mass measurements ( m/m= 10-8 ) mirror high power short-pulse laser APOLLON target gas stopping cell cooler/buncher concrete shielding (gas-filled) separator

13 Staged Experimental Approach exploratory experiments needed: Study RPA laser ion acceleration of heavy elements: efficiency, target shaping, yields Study atomic stopping power of dense ion bunches test concept of collective reduction of stopping power quantify range enhancement Perform fission-fusion experiments optimize Th beam energy measure A,Z,N distributions of A L: does neutron transfer help to broaden mass distributions? characterize fusion products by decay studies implement isotopic separation gradually approach N=126

14 ELI: Extreme Light Infrastructure ELI: - new EU-funded scientific infrastructure - devoted to scientific research with high-intensity lasers - laser-matter interaction: 5 orders of magnitude higher than today's laser intensity Pillars of ELI 1. physics with ultrashort laser pulses: Szeged 2. laser acceleration: electrons, ions; applications: Prague 3. nuclear physics (ELI-NP): Bucharest Project: - ELI in total: ca. 740 MEUR from EU structural funds - ELI-NP: ca. 280 MEUR - facility to be operational end of 2015 (EU budget requirement)

15 ELI-Nuclear Bucharest high-power laser (20 PW): - laser acceleration, - high field physics electron linac (600 MeV) : γ beam - E < 19 MeV, E/E < 10-3, > γ/s 120 m Laser clean rooms experimental areas laser-induced nuclear reactions fission-fusion 110 m

16 Conclusions laser particle acceleration is world-wide rapidly growing field presently reached: e - : < 1 GeV, ions: < 50 MeV/u, E/E : e - ~ 1-2%, ions ~ 10-20% novel laser ion acceleration mechanism (RPA): - generation of ultra-dense ion bunches - enables fission-fusion reactions fusion between 2 neutron-rich fission fragments - collective reduction of electronic stopping? - may lead much closer towards N=126 r-process waiting point realization of these schemes: ELI-Nuclear Physics: new laser research infrastructure - unique perspectives for: photonuclear physics, exotic ions, high-field physics

17 Thanks to the Collaboration: D. Habs (LMU, MPQ) T. Tajima (LMU) J. Schreiber (LMU, MPQ) M. Gross (LMU) A. Henig (LMU) D. Jung (LMU) D. Kiefer (LMU) G. Korn (MPQ) F. Krausz (MPQ, LMU) J. Meyer-ter-Vehn (MPQ) H.-C. Wu (MPQ) X.Q. Yan (MPQ, Univ. Beijing) M. Hegelich (LANL) V. Liechtenstein (Kurchatov Inst., Moscow) Thank you for your attention!

18 Laser Electron Acceleration Wakefield bubble acceleration: courtesy: M. Geissler (Belfast)