Letter of Intent: Nuclear Fusion Reactions from laser-accelerated fissile ion beams

Transcription

1 Letter of Intent: Nuclear Fusion Reactions from laser-accelerated fissile ion beams Peter G. Thirolf, LMU Munich D. Habs, H. Ruhl, J. Schreiber, LMU Munich, MPQ Garching T. Dickel, H. Geissel, W. Plass, C. Scheidenberger Justus-Liebig Univ. Giessen + GSI Darmstadt Outline: motivation: nucleosynthesis of heavy elements r process path: waiting point N=126 ultra-dense laser-accelerated ion beams novel reaction mechanism: fission-fusion experimental requirements at ELI-NP

2 Motivation: Astrophysics The 11 Greatest Unanswered Questions of Physics: ( US National Research Council's board on physics and astronomy) 1. What is Dark matter? 2. What is Dark Energy? 3. How were the Heavy Elements from Iron to Uranium made? 4. What is the mass of the neutrino? 5. Where do the ultrahigh-energy particles come from? 6. Is a new theory of light and matter needed to explain what happens at very high energies and temperatures? 7. Are there new states of matter at ultrahigh temperatures and densities? 8. Are protons unstable? 9. What is gravity? 10. Are there additional dimensions? 11. How did the Universe begin?

3 solar abundance Solar Elemental Abundances Z 26 (Fe): thermonuclear fusion in stars Z > 26 : neutron capture slow: s process fast: r process (n capture much faster than b decay) mass number

4 r process scenarios physical conditions: - temperature ~ K - neutron density > cm -3 - neutron-to-seed ratio must be high (~ 100): scenario?? (i) (core collapse) supernovae - m > 9 m solar - reverse b decay: p + e - n + n e - neutron degeneracy pressure -> infall reverted to outward shock wave - nucleosynthesis in n-driven winds - but: n wind depletes neutron flux remnant of SN 1987A: (ii) neutron star mergers (10-5 /yr/galaxy) - decompression of ejected neutron star material

5 Nucleosynthesis of Heavy Elements - modelling the r process path (far in terra incognita ): - masses and lifetimes needed for ~ 1000 neutron-rich isotopes - measured masses, lifetimes required for model testing

6 r process: waiting point N=126 r process: - path for heavy nuclei far in terra incognita - expected from fission-fusion Au, Pt, Ir,Os - waiting point N=126: bottleneck for nucleosynthesis of actinides - last region of r process close to stability

7 Nuclear Mass Model Predictions from: K. Blaum, Phys. Rep. 425 (2006) 1 data badly needed for extremely neutron-rich isotopes

8 Radiation Pressure Ion Acceleration high-intensity driver laser + thin solid target foil: electr. ions electrons driver laser ions nm foil - hole-boring regime of RPA - 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 nm foil Eion I Laser ~ x density of conventionally accelerated ion beams relativ. electrons/ ions at solid density

9 Stopping Power Reduction? Bethe-Bloch for individual ion: de dx Z e mev ln e k 2 4 eff 4 n e 2 2 mev 2 D kdv ln p binary collisions k D = Debye wave number long-range collective interaction p = plasma frequency potential 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 : may allow for thick reaction targets for fusion reactions requires R&D: stopping range measurements

10 Exp. Scheme for Fission-Fusion Production target Reaction target 232 Th: ~ 50mm 232 Th: 560 nm ~ 1 mm Fission fragments conventional stopping: high-power, high-contrast laser: J, 32 fs ( PW) W/cm 2 focal diam. ~ 3 mm collective stopping: CD 2 : 520 nm 232 Th: 560 nm ~ 1 mm CH 2 ~ 70 mm 232 Th: ~ 5 mm Fission fragments Fusion products Fusion products CD 2 : 520 nm

11 Reaction Scheme: Fission-Fusion 1. Fission: beam (~ 7 MeV/u): H, C, 232 Th target: C, 232 Th H, C Th F L + F H : target-like fission fragments 232 Th + C F L + F H : beam-like fission fragments F L F H 232 Th: <A L> ~ 91, DA L ~ 14 amu (FWHM) DAL ~ 22 amu (10%) <Z L > ~ 37.5 (Rb,Sr) 2. Fusion: light fission fragments (beam) + light fission fragments (target) PACE-4: (Z=35,A=102) + (Z=35, A=102): E lab = 270 MeV (E* = 65 MeV) 190 Yb (Z=70,N=126): 2.1 mb 189 Yb ( N=125): 15.8 mb 188 Yb ( N=124): 61.7 mb 187 Yb ( N=123): 55.6 mb

12 Fission-Fusion Yield / Laser Pulse laser acceleration (300 J, e~10%): normal stopping reduced stopping 232 Th C protons 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 targeted D. Habs, PT et al., Appl. Phys. B 103, 471 (2011)

13 Towards N=126 Waiting Point r process path: - known isotopes ~15 neutrons away from r-process path (Z 70) s fisfus measure: - masses, lifetimes, structure - lifetime measurements: already with ~ 10 pps x key nuclei 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 r-process loops?

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

15 Experimental layout characterization of reaction products - decay spectroscopy precision mass measurements: e.g. Penning trap or MR-TOF mirror high power short-pulse laser APOLLON target precision mass measurements gas stopping cell cooler/buncher concrete shielding (gas-filled) separator

16 Experimental Approach various challenges require staged approach: - laser ion acceleration of heavy species via RPA - optimization of target structure, target shape, rep-rate capabilities - characterization of stopping range for laser-driven ion bunches, investigation/characterization of potential collective effects - optimize conditions for laser-driven nuclear reactions will be addressed also at CALA facility in Garching - development of reaction product identification and characterization: (wide acceptance) separator for fusion products decay spectroscopy for short-lived species (e.g. fast tape station) setups for precision mass measurements important ingredient: theoretical support and guidance

17 Experimental ELI-NP Laser clean rooms experimental areas area E1: laser-induced nuclear reactions fission-fusion driver laser parameters used: - 2x 150 J/pulse - ca. 30 fs (~ 2x 8 PW) - ca W/cm 2 facility infrastructure: - handling of radioactive targets

18 Requirements for ELI-NP: Floorspace layout (very prelim.) productionseparation area 18 m measurement area 12 m 12 m concrete shielding recoil separator: - wide momentum acceptance - gas-filled? 15 m

19 Conclusions novel laser ion acceleration (RPA) of heavy species: - generation of ultra-dense ion bunches - enables fission-fusion reaction mechanism fusion between 2 neutron-rich fission fragments - reduction of electronic stopping? - may lead much closer towards N=126 r-process waiting point ELI-NP: unique infrastructure - superior opportunities to conventional radioactive beam facilities - many individual development steps to go for final goal, each of them forefront science Thank you for your attention

20 Cost Estimate component cost estimate: - laser target chamber : ~ 250 keur (incl. optics, vacuum, diagnostics) - recoil separator : ~ 5000 keur - tape station : ~ 150 keur - decay detectors : ~ 150 keur - buffer gas cell : ~ 300 keur - mass analyzer (MR-TOF) : ~ 300 keur - electronics, control, data acquisition : ~ 200 keur personnel: total: ~ 6.35 MEUR - priority: 1 postdoc position for design of recoil separator