Daniel Kalvik

• Finnerud, Ole Gunnar; Adli, Erik; Ariniello, R; Corde, S; Dalichaouch, T N & Emma, C [Show all 21 contributors for this article] (2026). First results from the E302 efficiency–instability experiment at the FACET-II facility. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 3266(1). doi: 10.1088/1742-6596/3266/1/012001. Full text in Research Archive Show summary

  Abstract The beam-breakup (BBU) instability in plasma accelerators is seeded by a transverse offset between the driver and a trailing bunch. The BBU instability induces oscillations in the trailing bunch, which are detrimental to its beam quality. When the instability is large, assuming little mitigation from ion motion and energy spread, the beam suffers emittance growth, and charge can be kicked transversely out of the plasma channel. The detrimental effect on beam quality is substantially worse at high efficiencies, which places constraints on the achievable power efficiency in applications such as linear colliders, where maintaining the beam quality is required. In this paper, we present the first experimental signatures of the BBU instability in data taken in the E302 experiment at the FACET-II facility at SLAC National Accelerator Laboratory. We use a specific beam-optical setup and a novel method to probe for transverse instabilities on diagnostic screens downstream of a magnetic dipole spectrometer. We complement the analysis with full 3D particle-in-cell (PIC) simulations of the plasma interaction using similar driver and trailing bunch parameters on a simulated FACET-II spectrometer.

• 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.

• Foster, Brian; Adli, Erik; Barklow, Timothy L.; Berggren, Mikael; Boogert, Stewart & Chen, Jian Bin Ben [Show all 24 contributors for this article] (2025). Proceedings of the Erice workshop: A new baseline for the hybrid, asymmetric, linear Higgs factory HALHF. Physics Open. 23. doi: 10.1016/j.physo.2025.100261. Full text in Research Archive Show summary

  The HALHF collaboration has discussed a new baseline for the project, taking into account comments from the accelerator community on various aspects of the original design. In particular, these concerned the practicality of the dual-purpose linac to accelerate both colliding positron bunches and the drive beams required for the plasma linac. In addition, many other aspects of the project were also considered; the discussion and conclusions are documented in this paper. Finally, a new baseline is outlined that has been optimised and addresses several weaknesses in the original design, has higher luminosity, reduced centre-of-mass energy boost and additional features such as two interaction points and positron polarisation as well as electron polarisation. Although HALHF has become longer and more expensive, it remains significantly smaller and cheaper than other mature Higgs factory designs currently under discussion.

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• 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.

• Chen, Jian Bin Ben; Adli, Erik; Drobniak, Pierre; Finnerud, Ole Gunnar; Hørlyk, Eir Eline & Kalvik, Daniel [Show all 9 contributors for this article] (2025). ABEL: The adaptable beginning-to-end linac simulation framework. doi: 10.18429/JACOW-IPAC2025-TUPS012. Full text in Research Archive Show summary

  We introduce ABEL, the Adaptable Beginning-to-End Linac simulation framework developed for agile design studies of plasma-based accelerators and colliders. ABEL’s modular architecture allows users to simulate particle acceleration across various beamline components. The framework supports specialised codes such as HiPACE++, Wake-T, ELEGANT, GUINEA-PIG and CLICopti, which facilitate precise modelling of complex machine components. Key features include simplified models for addressing transverse instabilities, radiation reactions, and ion motion, alongside comprehensive diagnostics and optimisation capabilities. Our simulation studies focus on the HALHF plasma linac, examining tolerances for drive beam jitter, including effects of self-correction mechanisms. Simulation results demonstrate ABEL's ability to model emittance growth under transverse instability and ion motion, highlighting the framework’s adaptability in balancing simulation fidelity with computational efficiency. The findings point towards ABEL’s potential for advancing compact accelerator designs and contribute to the broader goals of enhancing control and precision in plasma-based acceleration.

• Peña, Felipe; Adli, Erik; Drobniak, Pierre; Kalvik, Daniel; Sjobak, Kyrre Ness & Lindstrøm, Carl A. (2025). Development of an achromatic spectrometer for a laser-wakefield-accelerator experiment. doi: 10.18429/JACOW-IPAC2025-TUPM096. Full text in Research Archive Show summary

  The large gradients of plasma-wakefield accelerators promise to shorten accelerators and reduce their financial and environmental costs. For such accelerators, a key challenge is the transport of beams with high divergence and energy spread. Achromatic optics is a potential solution that would allow staging of plasma accelerators without beam-quality degradation. For this, a nonlinear plasma lens is being developped within the SPARTA project. As a first application of this lens, we aim to implement an achromatic spectrometer for electron bunches produced by a laser-wakefield accelerator. We report on progress in designing such an experiment.

• Lindstrøm, Carl A.; Adli, Erik; Chen, Jian Bin Ben; Drobniak, Pierre; Hørlyk, Eir Eline & Kalvik, Daniel [Show all 28 contributors for this article] (2025). Updated baseline design for HALHF: the hybrid, asymmetric, linear Higgs factory. doi: 10.18429/JACOW-IPAC2025-MOCD1. Full text in Research Archive Show summary

  Particle physicists aim to construct a electron–positron Higgs factory as the next major particle collider. However, the high associated costs motivate the development of more affordable collider designs. Plasma-wakefield acceleration is a promising technology to this end. HALHF is a proposal for a Higgs factory that utilizes beam-driven plasma-wakefield acceleration to accelerate electrons to high energy with high gradient, while using radio-frequency acceleration to accelerate positrons to a lower energy. This asymmetry sidesteps a major difficulty in plasma acceleration: that of accelerating positrons with high efficiency and quality. Since publication, several challenges were identified in the original baseline design. We summarize the updated baseline design, which addresses these challenges, and describe the parameter- and cost-optimization process used to arrive at this design.

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