Scientific Achievement
Researchers from the Advanced Modeling Program (AMP) and the BELLA Center in the Accelerator Technology & Applied Physics (ATAP) Division at Berkeley Lab have proposed and demonstrated, in self-consistent numerical simulations, an innovative technique to boost the energy of an intense ion beam using a hollow-channel laser-plasma device while maintaining key beam quality parameters.
Significance and Impact
High-intensity ion beams promise to significantly impact applications ranging from fundamental research to industry and society. These include ion sources for next-generation hadron colliders, neutrino factories, nuclear physics, drivers for fusion energy, radiotherapy, secondary radiation generation for materials research and security applications, and testing the radiation hardening of spacecraft. Ion beam sources leveraging laser-plasma interaction (LPI) can produce such beams. However, the achievable beam energies need to be higher for the requirements of some of these applications. The work presented here demonstrates how to advance the impact of LPI sources by introducing plasma-based booster stages that increase the beam energy while preserving beam quality.
Research Details
Laser-driven ion acceleration can provide ultra-intense, highly energetic ion bunches that could democratize access to ion accelerators because of its relatively compact footprint. Accelerating fields of 10s of TV/m in plasma—four to five orders of magnitude larger than the damage threshold of established radiofrequency accelerator technology—make this possible. Despite significant progress, reaching the particle energy needed for many applications has been challenging. Demonstrated methods using a single laser pulse to accelerate ions from a plasma source have reached ~150 MeV for protons, which is still in the sub-relativistic regime and just short of the requirements of some of the most pivotal applications (e.g., radiotherapy for humans requires 200-250 MeV to reach deep tissue in the body).
Theoretical Demonstration of a Hollow-Channel MVA Booster Stage
Researchers at ATAP are proposing a multi-stage approach that uses compact, laser-driven plasma stages to boost the energy of proton beams stepwise to the desired values. The specific laser-plasma acceleration mechanism employed here, called magnetic vortex acceleration (MVA), stands out from other laser-ion acceleration mechanisms as it provides both acceleration and focusing fields for ions. This approach makes it an ideal candidate for the staging of refocused ion beams. As a source, earlier WarpX simulation studies showed that MVA at the new BELLA iP2 beamline could reach proton energies of up to 125 MeV. Moreover, MVA can relax laser contrast and target fabrication requirements, enhancing its feasibility and potential for practical realization.
The twist: modifying MVA targets by adding a pre-formed hollow channel disables unwanted acceleration of plasma particles from the booster itself (dark current) and leaves only the energy boost of a carefully timed incoming particle beam.
Self-Consistent WarpX Simulations Show Preservation of Beam Quality
The researchers showed that their flexible booster stage can boost the beams’ energy independent of their initial energy by adjusting the delay between the beam and the driving laser pulse. For instance, a proton beam with an initial energy of 80 MeV could be boosted to 400 MeV in just five consecutive stages (energy gain increases with proton velocity from 50 MeV to 80 MeV per stage) using laser drivers with parameters that could readily be provided by a laser like the BELLA PW laser system (if multiple equally powerful pulses were simultaneously available).
WarpX simulation of a laser-plasma accelerator, using cutting-edge algorithmic methods such as mesh refinement (green box) to zoom the spatial resolution around the accelerated electron beam (white). (Credit: Berkeley Lab)
Key to enabling this study is the open-source particle-in-cell code WarpX, the 2022 Gordon Bell-Prize winning plasma simulation code spearheaded by the AMP team and their collaborators. In their simulations, the researchers first mapped the phase space of the booster stage to see if it provides suitable temporal and spatial (jitter) tolerances for accepting existing intense ion beams. Then, they numerically demonstrated that a high-charge (200 pC, 19 kA) intense proton bunch generated by an LPI source (filtered to 5% initial energy spread) can be boosted in energy (from 80 MeV to 130 MeV in a single stage), without the loss of charge and, critically, maintaining low energy spread (5% to 7%) and very low normalized beam emittance (20 nm to 23 nm). Emittance preservation through maintaining focusability in space and time is crucial for subsequent staging. Charge preservation is critical for the envisioned applications and is ensured by a high interaction cross-section and efficiency, with many particles reaching the desired energy. By achieving previously unattainable bunch energy and preserving the quality of the accelerated ion bunch while using current and near-term laser facility capabilities, this work can open doors to numerous scientific and practical applications. BELLA iP2 experiments investigate this fundamental MVA mechanism.
Contact: Marco Garten and Axel Huebl
Researchers: Marco Garten, Stepan Bulanov, Sahel Hakimi, Lieselotte Obst-Huebl, Chad Mitchell, Carl Schroeder, Eric Esarey, Cameron G. R. Geddes, Jean-Luc Vay, and Axel Huebl
Funding: DARPA via Northrop Grumman Corporation, ECP, DOE FES (through LaserNet US), computing times at OLCF and NERSC through ASCR Leadership Computing Challenge (ALCC) program and NERSC ERCAP FES-ERCAP0024250.
Publication: M. Garten, S. Bulanov, S. Hakimi, L. Obst-Huebl, C. Mitchell, C. B. Schroeder, E. Esarey, C. G. R. Geddes, J.-L. Vay, and A. Huebl. “Laser-plasma ion beam booster based on hollow-channel magnetic vortex acceleration,” Phys. Rev. Research, accepted on June 12, 2024, https://doi.org/10.1103/PhysRevResearch.6.033148
For more information on ATAP News articles, contact caw@lbl.gov.
