GEnerating extreme NEutrons for achieving controlled r-process nucleosyntheSIS

Project Information

GENESIS

Grant agreement ID: 787539

DOI

10.3030/787539

Project closed

EC signature date 26 July 2018

Start date 1 January 2019

End date 31 December 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 3 494 784,00

EU contribution

€ 3 494 784,00

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 4 - GENESIS (GEnerating extreme NEutrons for achieving controlled r-process nucleosyntheSIS)

Reporting period: 2023-07-01 to 2024-12-31

Summary of the context and overall objectives of the project

The overarching goal of the GENESIS project is to test, through laboratory experiments, the models of nucleosynthesis of heavy elements in the Universe, in particular the so-called “r-process” of nucleosynthesis, which proceeds through the multiple absorption of neutrons in heavy elements in order to increase their mass. The project was thus laid out to work in two complementary directions: (1) the production of extreme brightness neutron beams, such that we can beat the very low cross-section of neutron absorption in nuclei, and realize multiple absorption at once, and (2) the generation of laboratory plasmas that can be quantitatively scaled-down to astrophysical ones, in particular mature stars and supernovae, which are thought to be the site of heavy element nucleosynthesis, once exposed to extreme fluxes of neutrons (as resulting e.g. from a merger event, or a supernova explosion). For these aspects of the project, high-power lasers have been used as the driver, since the underlying idea of the project is that: (i) our estimates showed that lasers, and in particular the upcoming generation developing the unprecedented power level of 10 PW, had the potential to produce neutron beams with fluxes many orders-of-magnitude higher than the existing ones (produced by conventional accelerators), and (ii) lasers have shown to be capable of producing scaled-down astrophysical plasmas of a wide variety. These two directions have been actively pursued since the start of the project, on 01/01/2019, and major progress has been obtained in both.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The overall strategy of the project is to combine (1) extreme neutron fluxes, with (2) astrophysically-relevant scaled plasmas, both produced by high-power lasers [CHE19]. To implement this strategy, we worked in parallel in two directions: (i) simulating how to optimize the generation of neutrons using multi-PW lasers, in preparation for experimental implementation, and (ii) perform experiments, using the new “Apollon” laser facility. We have also had already good progress in the production of astrophysical-relevant plasmas using high-power lasers, which is promising in order to achieve injection of high-brightness neutron beams in relevant environments.
The concrete achievements obtained during the project are multi-fold: (1) we could characterize the high-flux neutron beams [LEL20,LEL21,BUR23,LEL24] produced by high-intensity, PW-scale lasers, such as the "Apollon" laser facility in France [BUR21b,YAO24,YAO25] or other similar lasers [LEL24b,YAO24b,HIG24], (2) we could also initiate nuclear astrophysics-relevant measurements [LEL23]. We have also (3) benchmarked our codes against these measured neutron fluxes [MAR22b], which allowed us to foresee the way we could reach the neutron flux necessary for the end goal of the project [HOR24]. In parallel, we have also (4) made very significant progress in modelling in the laboratory analogues of interstellar media [HIG19,MAR21,YAO21,YAO22a,YAO22b,MAR22a,FAZ22,BOL22,YAO23,SLA24] and the formation of stars [REV19,FIL19,KHI19,BUR20,REV21,BUR21a,FIL21,BUR22], i.e. the matter that will be the cradle of future nucleosynthesis events.
In short, the project was a success. It allowed to characterise the required ultra-brilliant neutron beams that can be produced by PW-scale lasers. This characterisation allowed us then to assess how we could produce the sought-after heavy elements. Our conclusion [HOR24] is that such production is within reach, on the condition of increasing the repetition rate of the laser facility. At present, the repetition rate is one shot per minute. To produce enough heavy elements, so that their nuclear properties can be measured, we would need to increase that repetition rate to 10 Hz. This is technically doable, but would require the authorisation of the nuclear safety authority. This is envisioned by the laboratory management of the "Apollon" laser facility, once the facility will settle on routine delivery of beam to users.
In terms of dissemination, on top of the numerous publications listed below, a wide audience video describing the project and its objectives has been made, which can be found at: https://www.youtube.com/watch?v=M-UkowEvgOY.

[BOL22] Nat. Comm. 13, 6426 (2022)
[BUR20] Astronomy & astrophysics 642, A38 (2020)
[BUR21a] Astronomy & Astrophysics 648, A81 (2021)
[BUR21b] Matter and Radiation at Extremes 6 (2021)
[BUR22] A&A 657, A112 (2022)
[BUR23] Rev. Sci. Inst 94, 083303 (2023)
[CHE19] Matter and Radiation at Extremes 4, 054402 (2019)
[FAZ22] A&A, 665 (2022) A87
[FIL19] Matter and Radiation at Extremes 4, 064402 (2019)
[FIL21] Scientific Reports 11, 8180 (2021)
[HIG19] Communication Physics 2, 60 (2019)
[HIG24] J. of Plasma Phys. 90 (3), pp.905900308 (2024)
[HOR22] Scientific Reports 12, 19767 (2022)
[HOR24] Phys. Rev. C 109, 025802 (2024)
[KHI19] Phys. Rev. Lett. 123, 205001 (2019)
[LEL20] J. of Instrumentation 15, P04002 (2020)
[LEL21] Review of Scientific Instruments 92, 113303 (2021)
[LEL23] http://arxiv.org/abs/2309.16340
[LEL24] European Physical Journal Plus 139, 1035 (2024)
[LEL24b] Phys. Plasmas 31, 093106 (2024)
[MAR21] Monthly Notices of the Royal Astronomical Society 500, 2302–2315 (2021)
[MAR22a] Phys. Rev. Lett. 128, 115101 (2022)
[MAR22b] Matter and Radiation at Extremes 7, 024401 (2022)
[REV19] High Energy Density Physics 33, 100711 (2019)
[REV21] Nat. Comm. 12, 762 (2021)
[RUY20] Nature Phys. 16, 983–988 (2020)
[SLA24] Nat. Comm. 15, 10065 (2024)
[YAO21] Nat. Physics 17, 1177–1182 (2021)
[YAO22a] Matter and Radiation at Extremes 7, 014402 (2022)
[YAO22b] Matter and Radiation at Extremes 7, 026903 (2022)
[YAO23] Journal of Plasma Physics, 89(1), 915890101 (2023)
[YAO24] Appl. Sci. 14(14), 6101 (2024).
[YAO24b] Matter and Radiation at Extremes 9, 047202 (2024)
[YAO25] Phys. Plasmas 32, 043106 (2025)

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

For the first axis of the project, we tested in simulations, in order to generate extreme neutron fluxes (in the range rendering heavy elements nucleosynthesis possible), how to: (i) use multi-PW lasers to produce high-charge, high-energy protons, and then (ii) convert these protons into neutrons in a high-Z converter, using the spallation mechanism which is well know in nuclear physics and commonly employed in conventional accelerators.
Within the project, we examined the neutron yield from spallation as a function of the converter target material and the projectile proton energy, in a range within the reach of present or near-future laser systems. For this purpose, we have used the FLUKA 3D Monte Carlo code to simulate the nuclear reactions induced during irradiation of a convertor target by a mono-kinetic and mono-directional proton beam. With this, we know what optimal material to use for the neutron converter. The next steps was to see how to optimize the proton generation with multi-PW lasers in order to obtain the highest neutron fluxes. Again, this is done through simulations, but we validated that part with the experiments performed during the project. We thus researched, utilising large scale particle-in-cell and Monte Carlo simulations, a neutron source which relies on the laser-driven proton acceleration on the primary target and conversion of these protons into the neutrons in the secondary high-Z neutron converter. Inspired by the trends in the community, we investigated the use of the double layer primary targets for proton acceleration where the laser pulse is first focused in the near-critical front layer before hitting its rear solid density layer with a significantly higher intensity but a smaller spot size.

As mentioned above, the nominal power level of 10 PW, at a high-repetition rate of 10 Hz, at which we plan to work for producing the extreme neutron beam simulated above is not yet available (it is now at a lower power of 4 PW and a lower repetition rate of 1 shot/minute), but planned for the near future. Thus, we started by commissioning the "short focal length" area (SFA) of the new Apollon laser facility (Saclay, France) with the first available laser beam, at a level of 0.4 PW (10 J average on-target energy with pulse durations of 25 fs). It was the first time this experimental area was used for high-power shots on targets. The commissioning went well and allowed ramping up the power in 2023 to 4 PW, which allowed us to perform the last set of experiments for the project. In all these experiments, a range of diagnostics was in place: An imager, working in X-ray range, of the zone heated by the laser on the target demonstrated a good focusing of the laser at full power, with a heated spot of 4.5 µm in diameter. Solid targets as thin as 2 µm in thickness were irradiated by intense laser pulse without damaging them by the pedestal preceding the main pulse, which corresponds to a good temporal contrast characteristics. Emissions of electrons, ions and high energy electromagnetic radiation were recorded, showing good laser-target coupling and an overall performance that is very consistent with what have been reported by similar international facilities. Neutrons were quantitatively measured, which was the main point of the project, and which allowed us to obtain the estimates aimed at in the project of producing heavy elements.

For the second axis of the project, we have worked actively on the generation of laboratory plasmas that can be quantitatively scaled-down to astrophysical ones. This was pursued in two main axes: (1) the use of strong magnetic fields to both (i) make laboratory plasmas more astrophysically-relevant plasmas, as well as (ii) confine them, with in view the better ability to have them be well coupled to the neutron beams we produce - these are star-scaled plasmas, and (2) the production of supernovae-scaled plasmas, so that we could explore the two possible sites were nucleosynthesis is hypothesized to take place, star mergers or supernovae. We have already in the recent past devoted quite some effort to show that we could produce star-scaled plasmas in the laboratory. We pursued this effort by investigating how high-strength magnetic fields, produced by Helmholtz-type coils surrounding the laser-driven plasmas, could be used to improve the variety of star systems we could have the laboratory plasmas scaled to, as well as to confine the plasmas. In parallel to investigate how to produce star-scaled plasmas, we have also investigated how to generate quantitatively scalable supernovae plasmas in the laboratory. On all these accounts, significant results were obtained: we showed that we could quantitatively reproduce exploding supernova envelopes interacting with the ambient medium. An important by-product of the project was that we were able to reproduce the first stage of particle acceleration in these systems, which represents the first step of cosmic-rays production. Hence, in this axis, the project allowed to answer some pending questions pertaining to the quantitative production of cosmic-rays, which has impact on the formation of stellar systems and exoplanets.

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