Scientific Achievement
Laser-driven ion accelerators (LDIA) offer compact acceleration of proton beams due to their ultra-high accelerating gradients; however, the large divergence and broad energy spread of LDIA beams pose significant beam-transport challenges, which limit their use in applications.
Now, a team of researchers from the BELLA Center and Fusion Science & Ion Beam Technology (FS&IBT) Program in the Accelerator Technology & Applied Physics (ATAP) Division at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a suite of compact, permanent-magnet-based beam transport systems optimized for laser-driven proton beams.
The work offers a practical approach to overcoming current limitations of transporting proton beams through optimized, permanent-magnet transport systems, thereby paving the way for the broader deployment of LDIA facilities.
Significance and Impact
This work addresses the longstanding challenge of efficiently transporting highly divergent, broad-energy-spread laser-accelerated proton beams in a compact space while enabling beam delivery for diverse applications, including radiobiology, materials science, and high-energy-density physics.
By laying the groundwork for designing the beam transport system recently utilized at the BELLA interaction point 2 (iP2) beamline, the research serves as a blueprint for the wider particle accelerator community in overcoming the significant challenges of transporting laser-driven ion beams. Furthermore, the tools and designs presented here will enable future laser-driven ion accelerator facilities to better serve the diverse needs and applications of users.
Research Details
This study employed a combination of high-order particle tracking simulations using the COSY INFINITY code and custom tools in MATLAB software to model and optimize various beam transport system configurations. Simulations of the beam transport must be performed at high order, as nonlinear effects are significant due to the large beam divergence and energy spread of LDIA beams.
Simulated beam spectrum (left) and profile (right) at different target locations z=−200 mm (top) and z=+500 mm (bottom) relative to the 30 MeV focal location for the quartet design shown in the lead image of this article. This shows the target location can be used to tune the system to deliver different beam energies.
The permanent magnet quadrupoles (PMQs) and dipoles used in this study were designed using the RADIA code to ensure feasibility and performance. The choice to use PMQs was made due to the high field gradient achievable in a compact geometry when arranged in a Halbach array, as well as for their high reliability and compatibility with high repetition rate operation of an LDIA source.
Beam transport performance was assessed based on particle tracking simulations to estimate the collection efficiency, beam spot size, energy acceptance, and proton intensity, using a representative input beam modeled for BELLA iP2 conditions. The tools and methods developed here allowed rapid iteration and optimization of transport designs tailored for different scientific use cases.
Tailoring laser-driven proton beams for different applications
Illustration of the 1.0 m quartet with two dipole magnets from Sec. 2d with magnetic dispersion along the x axis (dipole field oriented along y) for E0=30 MeV proton beam. The red, green, and blue lines show the envelopes of 0.85 E0, E0, and 1.15 E0 proton beams, respectively. The half angle of the traces are 28.5 mrad for x and 32.5 mrad for y planes. The dipole magnets are shown in blue.
The researchers evaluated a range of transport configurations, including doublets, triplets, quartets, and mirrored systems, focusing on their ability to deliver LDIA beams with a desirable energy spread, spot size, and intensity. Notably, the study demonstrated that by varying the placement of the fixed-field permanent magnets, these systems could effectively accommodate different energy ranges and application needs, all while remaining within stringent spatial constraints. Various configurations were explored, and their performances were analyzed so that users could choose the optimized configuration for their applications.
Design of beam transport for radiobiology at BELLA iP2
For the BELLA Center’s new laser iP2 beamline, a compact high-energy proton beam transport system is essential for applications of the laser-accelerated proton beams. This study culminated in the design and implementation of a compact transport system tailored explicitly for radiobiological experiments, enabling the first in vivo irradiation studies with laser-driven protons at iP2. This collimating system achieved uniform dose delivery of 10 MeV protons to biological targets, supporting ultra-high dose rate radiobiology studies and opening new avenues for cancer therapy research with LDIA sources.
Contact: Jared De Chant and Kei Nakamura
Researchers: Jared De Chant, Kei Nakamura, and Lieselotte Obst-Heubl (BELLA Center); and Qing Ji (formerly in FS&IBT, and now in ATAP’s Berkeley Accelerator Controls & Instrumentation program)
Funding: The work was supported by Laboratory Directed Research and Development funding from Berkeley Lab, provided by the Director and the U.S. Department of Energy Office of Science, Offices of Fusion Energy Sciences, High Energy Physics, and LaserNetUS.
Publication: J. De Chant, K. Nakamura, Q. Ji, L. Obst-Huebl, S. Barber, A. M. Snijders, C. G. R. Geddes, J. van Tilborg, A. J. Gonsalves, C. B. Schroeder, and E. Esarey. “Modeling and design of compact, permanent-magnet transport systems for highly divergent, broad energy spread laser-driven proton beams,” Phys. Rev. Accel. Beams 28, 033501 (2025). https://doi.org/10.1103/PhysRevAccelBeams.28.033501
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