Pierre Drobniak

• Drobniak, P. (2023). Development of a 150 MeV laser-plasma injector prototype (Doctoral dissertation, université Paris-Saclay).
• Drobniak, P., E. Baynard, C. Bruni, et al. (2023). “Random scan optimization of a
  laser-plasma electron injector based on fast particle-in-cell simulations”. In: Phys. Rev.
  Accel. Beams 26, p. 091302. DOI: 10.1103/PhysRevAccelBeams.26.091302.
• Drobniak, P., E. Baynard, K. Cassou, et al. (2023). Two-chamber gas target for laser-
  plasma accelerator electron source. arXiv: 2309.11921 [physics.acc-ph].
• Drobniak, Pierre et al. (2020). “Simulation of keyhole laser welding of stainless steel
  plates with a gap”. In: Procedia CIRP 94, pp. 731–736.

• Sjobak, Kyrre Ness; Rød-Lindberg, E; Ellingsen, Abélia; Drobniak, Pierre; Rieker, Vilde Flognfeldt & Reaz, F [Show all 8 contributors for this article] (2026). SHARP: A compact focusing system for medical applications using a diverging plasma lens. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 3266(1), p. 012014–012014. doi: 10.1088/1742-6596/3266/1/012014. Full text in Research Archive Show summary

  Abstract Cancer therapy for deep-seated tumors requires precise irradiation of a small target deep within the patient while minimizing radiation exposure to surrounding tissues. This can be accomplished with a round beam sharply converging towards a single spot, requiring a large beam size in both planes at the exit of the focusing system. Achieving this over a short distance using only quadrupole lenses is challenging; but by using a linear active plasma lens (APL) in defocusing mode, the beam can be quickly and non-destructively enlarged before focusing using quadrupoles. The position of the irradiation spot can also be scanned in three dimensions by changing magnet settings. The SHARP project will develop and test this concept. Such a system can be used with very high energy electrons (hundreds of MeV), creating a Bragg-peak-like spot using novel accelerator technology. This could lead to more compact radiotherapy facilities, not requiring a bulky infrastructure typically associated with proton radiotherapy machines. If successful, SHARP will enable precision conformal radiotherapy, spatial fractionation, and potentially be useful for FLASH radiotherapy.

• Drobniak, Pierre; Serhal, Jana; Anania, Maria Pia; Baynard, Elsa; Beck, Arnaud & Bruni, Christelle [Show all 29 contributors for this article] (2026). Validation of a Compact and Tunable Continuous Gas-Flow Laser-Plasma Target for Electron Beam Production Above 150 MeV. Applied Sciences. 16(5), p. 2312–2312. doi: 10.3390/app16052312. Full text in Research Archive Show summary

  The present article reports on the generation of stable 50 pC low-divergence electron beams above 150 MeV from laser-driven wakefield acceleration using a continuous-flow gas target prototype tested at the 60 TW Salle Jaune facility at LOA. The gas target design is meant to be easily transported and integrated as an element of the beamline with a differential pumping system offering some 10−4 mbar pressure in the rest of the line. A dedicated gas injection system allows for the control of the gas mixture concentration and gas pressure in two different regions of the target within the frame of controlled ionisation injection schemes. The measured electron beam parameters show the importance of gas density profiles and longitudinal gas mixture confinement.

• Kane, G.; Drobniak, Pierre; Beck, A.; Kazamias, S.; Kubytskyi, V. & Lenivenko, M. [Show all 11 contributors for this article] (2026). Surrogate models study for laser-plasma accelerator electron source design through numerical optimisation. Machine Learning: Science and Technology. 7(3). doi: 10.1088/2632-2153/ae6603. Full text in Research Archive
• Kalvik, Daniel; Lindstrøm, Carl A.; Peña, Felipe; Loisch, Gregor; Garland, James & Svensson, Jonas Björklund [Show all 16 contributors for this article] (2025). Ion-motion simulations of a plasma-wakefield experiment at FLASHForward. Proceedings of the International Particle Accelerator Conference. ISSN 2673-5490. p. 1442–1445. doi: 10.18429/JACOW-IPAC2025-TUPS013. Full text in Research Archive Show summary

  In plasma-based acceleration, an ultra-relativistic particle bunch—or an intense laser beam—is used to expel electrons from its propagation path, forming a wake that is devoid of electrons. The ions, being significantly more massive, are often assumed to be stationary. However, both theory and simulations suggest that any sufficiently dense electron bunch can trigger ion motion, and its effect must be taken into account. We simulate beam-driven plasma wakefields to identify key features—such as longitudinally dependent emittance growth—that could be observed in an experiment using plasma and beam parameters from the FLASHForward facility at DESY.

• Adli, Erik; Lindstrøm, Carl A.; Kalvik, Daniel; Sjobak, Kyrre Ness; Finnerud, Ole Gunnar & Chen, Jian Bin Ben [Show all 7 contributors for this article] (2025). Transverse tolerances in the plasma-wakefield acceleration blow-out regime. Proceedings of the International Particle Accelerator Conference. ISSN 2673-5490. p. 1434–1437. doi: 10.18429/JACOW-IPAC2025-TUPS011. Full text in Research Archive Show summary

  We report on recent progress in transverse instabilities and transverse tolerances for plasma-wakefield accelerators in the blow-out regime. In this regime, the transverse fields provide both strong focusing and strong deflection via transverse wakefields. The deflection effect of the wakefields on the main beam leads to limitations on the acceleration efficiency, if not mitigated. Based on comprehensive particle-in-cell simulations we summarize recent findings of the instability--efficiency relation for the blow-out regime. Ion motion and energy spread may mitigate the instability; with linac start-to-end simulations, using the recently developed ABEL framework, we demonstrate that the instability and emittance growth may be sufficiently mitigated for the colliding beams in the HALHF concept. Independent of wakefield effects, the strong focusing fields lead to very tight tolerances for the drive-beam jitter. We quantify these tolerances, using examples from HALHF start-to-end simulations. We show that the tolerances are greatly loosened by applying external magnetic fields to guide the drive-beam propagation in the plasma.

• Drobniak, P.; Baynard, E.; Beck, A.; Demailly, J.; Douillet, D. & Gonnin, A. [Show all 18 contributors for this article] (2025). Two-chamber gas target for laser-plasma electron source. Review of Scientific Instruments. ISSN 0034-6748. 96(3). doi: 10.1063/5.0226055. Full text in Research Archive Show summary

  Exploring novel target schemes for laser wakefield accelerators is essential to address the challenge of increasing repetition rates while ensuring the stability and quality of the produced electron beams. This paper introduces and discusses the prototyping of a two-chamber gas target, integrated into the beamline and operating under continuous gas flow, in the framework of ionization injection. We present the numerical fluid modeling employed to assist the density profile shaping, with a focus on gas mixing and dopant confinement. The importance of localized high-Z gas for ionization injection is demonstrated through particle-in-cell simulations using the simulated gas profiles. We describe the test bench used for prototype evaluation, specifically addressing the plasma electron density and the longitudinal distribution of species relevant to ionization injection. The lifetime of the target at 10 Hz and 60 mJ is measured for different materials, and its effect on the resulting electron beam is assessed using particle-in-cell simulations. Finally, we outline perspectives on high-power operation.

• Biagioni, A.; Bourgeois, N.; Brandi, F.; Cassou, K.; Corner, L. & Crincoli, L. [Show all 30 contributors for this article] (2025). Technical status report on plasma components and systems in the context of EuPRAXIA. Physics of Plasmas. ISSN 1070-664X. 32(11). doi: 10.1063/5.0286730. Full text in Research Archive Show summary

  The EuPRAXIA project [Walker et al., J. Phys.: Conf. Ser. 874, 012029 (2017)] aims to construct two state-of-the-art accelerator facilities based on plasma accelerator technology. Plasma-based accelerators offer the possibility of a significant reduction in facility size and cost savings over current radio frequency (RF) accelerators. The two facilities—one laser-driven, one a beam-driven—are envisioned to provide electron beams with an energy in the range of 1–5 GeV and beam quality comparable to existing RF machines. This will enable a versatile portfolio of applications from compact free-electron laser drivers to sources for medical and industrial imaging. At the heart of both facilities is the use of plasma-based accelerator components and systems, which encompass not only the accelerating medium itself but also a range of auxiliary systems such as plasma-based electron beam optics and plasma-based mirrors for high-intensity lasers. From a technical standpoint, a high-degree of control over these plasma devices will be essential for EuPRAXIA to achieve its target performance goals. The ability to diagnose and characterize these plasma devices and to simulate their operation will be further essential success factors. Additionally, compatibility with extended operation at high-repetition rates and integration into the accelerator beamline will also prove crucial. In this work, we aim to review the current status of plasma components and related systems for both laser-driven and beam-driven plasma accelerators and to assess challenges to be addressed regarding implementation at future EuPRAXIA facilities.

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• Ellingsen, Abélia; Adli, Erik; Drobniak, Pierre; Lindstrøm, Carl A.; Rød-Lindbergh, Elisabeth & Rieker, Vilde Flognfeldt [Show all 14 contributors for this article] (2026). SHARP: A Compact Focusing System for Emerging Particle Therapies using an Active Plasma Lens. doi: https:/indico.desy.de/event/51069/contributions/205605/. Full text in Research Archive Show summary

  Background: Improved control of the beam envelope in particle radiotherapy could enhance the precision of dose delivery. A novel approach is to incorporate an active plasma lens (APL) into the beamline. This compact device is used for strong and radially symmetric defocusing, giving rapid and controlled beam expansion. Such an expanded beam is of interest in itself, as it is generated by beam optics rather than through scattering, enabling large high intensity fields that may be relevant for FLASH applications. Beam expansion can also be followed by downstream refocusing to produce a sharp waist at the target. This may reduce entrance dose to healthy tissue while enhancing dose deposition at depth. Such beam geometries from a compact system could benefit precision conformal radiotherapy and spatial fractionation. The SHARP project is in the process of demonstrating these ideas experimentally with 200 MeV very high-energy electrons (VHEE), supported by simulations of beam optics and dose distributions. Materials and Methods: Experiments are being conducted at the CLEAR facility at CERN. The system combines a defocusing APL with quadrupole magnets for final focusing onto the target. Beam enlargement, without focusing, is evaluated on a downstream profile monitoring screen. The refocused beam is subsequently characterized with screens downstream of the quadrupoles. Radiation transport simulations in Geant4 are used to model dose deposition at the target and outside the focal region. Simulations with ImpactX are used for designing beam optics and assessing the influence of e.g. energy spread. Results: Beam enlargement from the APL is experimentally observed to be linear and symmetric in both transverse planes. Simulations show that quadrupoles can modify these beams into large, quasi-parallel fields for broad irradiation of higher intensity than passive scattering, which could be useful to investigate further for certain FLASH applications. For small deep targets, simulations show that increasing the APL current coupled with refocusing quadrupoles reduces focal beam size while increasing divergence, producing a sharp Bragg-like peak. Larger opening angles upstream and downstream of the target have also been confirmed experimentally. Conclusions: SHARP investigates a compact hybrid APL-quadrupole system to achieve precise focal spots and controlled dose distributions. The technique could serve as a versatile research platform for SFRT and FLASH applications. The project’s first experimental results represent a promising step towards improved dose delivery by demonstrating both controlled beam enlargement and refocusing. Ongoing work to refine the concept includes simulations and experiments of scattering in water phantoms, nonlinear APL defocusing for generating enlarged flat fields, spot scanning, and extension of the concept to protons.

• Drobniak, Pierre; Adli, Erik; Anderson, H. B.; Sjobak, Kyrre Ness; Lindstrøm, Carl A. & Dyson, A. [Show all 8 contributors for this article] (2025). Preliminary results from the CLEAR nonlinear plasma lens experiment. doi: 10.18429/JACOW-IPAC2025-MOPS027. Full text in Research Archive Show summary

  Plasma lensing provides compact focusing of electron beams, since they offer strong focusing fields (kT/m) in both planes simultaneously. This becomes particularly important for highly diverging beams with a large energy spread such as those typically originating from plasma accelerators. The lens presented here is a nonlinear active plasma lens, with a controlled focusing-strength variation purposely introduced in one transverse direction. This lens is a key element of a larger transport lattice, core of the ERC project SPARTA, which aims to provide a solution for achromatic transport between plasma-accelerator stages. We report on preliminary experimental results from the CLEAR facility at CERN, which aims to probe the magnetic field structure of the lens using an electron beam, in search of the desired nonlinearity, together with 2D plasma simulation results.

• Lindstrøm, Carl A.; Adli, Erik; Anderson, Hektor B.; Drobniak, Pierre; Kalvik, Daniel & Peña, Felipe [Show all 7 contributors for this article] (2025). The SPARTA project: toward a demonstrator facility for multistage plasma acceleration. doi: 10.18429/JACOW-IPAC2025-TUPS120. Full text in Research Archive Show summary

  Plasma acceleration is a rapidly maturing technology, but is not yet ready for large-scale applications such as linear colliders. The SPARTA project aims to develop a near-term, medium-scale plasma-accelerator facility to enable new experiments in strong-field quantum electrodynamics (SFQED)—an application that requires solving two of the most important remaining challenges in plasma acceleration: reaching high energy by using multiple accelerating stages; and achieving high beam stability. We report on progress toward the three main objectives: demonstrating a nonlinear plasma lens for achromatic beam transport between stages; developing self-stabilization and instability suppression mechanisms; and developing a conceptual design for a multistage SFQED facility.

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