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Jul 13

Dual-pulse micronozzle acceleration of sub-GeV-class protons

Physical Review Accelerators and BeamsJul 13, 2026

Other

D. Pan, M. Murakami

Osaka University

We propose a dual-pulse micronozzle acceleration scheme that enables of laser-driven protons, mitigating the conventional trade-off between maximum energy and laser-to-proton conversion efficiency. By introducing a delay-tuned synchronization window, a compact proton front generated by a shaping prepulse is injected into, and remains copropagating with, a quasistatic axial electric field driven by a delayed main pulse in a micronozzle cavity. This phase locking maintains the relative phase between the proton bunch and the accelerating field over an extended interaction length and duration, thereby suppressing thermal debunching and prolonging the effective acceleration stage. At main-pulse intensities of the order of 10 21 W / cm 2 , sub-GeV-class proton cutoffs are achieved with a total laser-to-proton conversion efficiency of ∼ 20 % . Notably, the efficiency of the application-relevant high-energy component exceeds ∼ 13 % for protons with energies E p > 100 MeV , indicating preferential energy loading into a compact, directed proton population rather than quasithermal sheath expansion. Comparative simulations with an unconfined dual-pulse hydrogen-rod target demonstrate that this performance gain arises from the combined effects of temporal synchronization and geometric confinement, which sustain a long-lived axial accelerating channel advected downstream with the proton front. An analytical model for the synchronization condition is developed and validated against the simulation data. Three-dimensional particle-in-cell simulations support that the phase-locking mechanism and the associated spectral hardening are preserved in 3D slit-nozzle geometries, with the confined target yielding cutoff energies ∼ 60 % higher than an unconfined hydrogen rod under identical laser conditions. These results identify phase-locked acceleration in a confined laser-driven structure as a practical design principle for compact, high-yield sub-GeV-class proton drivers, with direct relevance to secondary-particle sources such as pion and muon production, accelerator-driven systems, and laser-based neutron sources.

Jul 13, 2026

Jul 7

Hybrid Simulations of the Proton Beam Instabilities in the Young Solar Wind: The Formation of Hammerhead-like Distributions

The Astrophysical JournalJul 7, 2026

Other

R. A. López, Shaaban M. Shaaban, M. Lazar, L. Pezzini, S. Poedts, H. Fichtner, P. H. Yoon

Centre for Mathematical Plasma Astrophysics, Ruhr-University Bochum, Comisión Chilena de Energía Nuclear, Universidad Andres Bello, Qatar University

Parker Solar Probe observations in the young solar wind reveal new properties of both plasma particle velocity distributions (VDs) and associated electromagnetic (EM) wave fluctuations. The quasilinear (QL) kinetic theory of plasma wave instabilities has recently shown that new hammerhead (HH) proton distributions can be generated by the relaxation of proton beams through the instabilities of right-handed (RH) polarized waves. Such RH waves have indeed been reported in association with HH distributions. In this paper, new results from hybrid simulations of proton beam–plasma systems with properties typical of those observed to excite EM-RH wave instabilities are presented. From the long-term evolution of these systems, it is found that beam relaxation is driven by instabilities and growing wave fluctuations, leading to HH-type features in the VDs. The production of these features, as well as their prominence, depends on the magnetic power of the waves generated by the instabilities and, therefore, implicitly on the available free energy, quantified by the plasma beta parameter and the relative beam drift. The simulation results capture the self-consistent evolution of the instabilities and their nonlinear development. Linear theory, together with simulations, helps identify the nature of the unstable modes and the plasma conditions under which they arise. The good agreement with QL theory further indicates that it can serve as a computationally efficient complementary framework for interpreting the associated wave–particle interactions.

Jul 7, 2026

Jul 3

Velocity-space Origins of the Pressure–Strain Interaction in Multipopulation Distributions and Its Application to Magnetic Reconnection

The Astrophysical JournalJul 3, 2026

Other

M. Hasan Barbhuiya, Paul A. Cassak, Sarah Conley, Julia E. Stawarz, Emily Lichko, Jason M. TenBarge, James Juno, Jason R. Shuster, Gregory G. Howes, Subash Adhikari

Clemson University, Bates College, Northumbria University, Princeton University, Princeton Plasma Physics Laboratory

A forefront research question is how energy evolves in weakly collisional plasmas for which departures from local thermodynamic equilibrium (LTE) are significant. The standard approach is studying the terms in the non-LTE energy evolution equation derived by taking the second moment of the Boltzmann equation, but the resultant fluid metrics do not retain information about which particles at which velocities drive energy evolution. A widely studied channel for internal energy density evolution is the pressure–strain interaction. Here, we employ the kinetic pressure–strain, a phase-space diagnostic whose velocity-space integral recovers the pressure–strain interaction to disambiguate the contributions to the pressure–strain interaction from disparate particle populations in composite phase-space densities. We develop phase-space analogs of the pressure–strain interaction decompositions to provide the phase-space origins of normal versus sheared flow. We introduce the “kinetic strain-rate” tensor, the phase-space analog of the strain-rate tensor, which we argue is needed to interpret the phase-space origins of the pressure–strain interaction. To demonstrate the utility of these quantities, we investigate them for composite electron distributions near the electron diffusion region in two-dimensional particle-in-cell simulations of antiparallel symmetric magnetic reconnection. We find that the phase-space-based diagnostics isolate the roles of distinct populations. These results contribute to a growing body of work providing new methods for quantifying phase-space energy evolution for a broad array of processes, from magnetic reconnection to collisionless shocks and turbulence, opening new pathways for answering longstanding problems of particle energization in weakly collisional plasmas.

Princeton Plasma Physics LaboratoryPrinceton University

Jul 3, 2026

Jul 1

Tokamak level performance in the optimized stellarator Wendelstein 7-X with stable peaked density profiles

Physical Review EJul 1, 2026

Other

S. Bannmann, O. Ford, S. A. Bozhenkov, T. Stange, R. Lopez-Cansino, A. Langenberg, M. Wappl, J. Brunner, G. Fuchert, T. Gonda, et al.

Max-Planck-Institute for Plasma Physics, University of Seville, Princeton Plasma Physics Laboratory

Progress towards achieving net gain from nuclear fusion is typically characterized by the triple product n T τ . Although stellarators have several benefits for a reactor, such as the inherent steady-state capability and the lack of disruptions, the maximum achieved triple product has historically lagged behind that of tokamaks. In the large optimized stellarator Wendelstein 7-X, a triple product of ( 1.10 ± 0.15 ) × 10 20 m − 3 keV s has recently been achieved and held stable for 1.9 s. This marks an important step in stellarator core plasma performance and puts it in line with H -mode performance in similar sized tokamaks. The progress in Wendelstein 7-X performance is due to the suppression of ion-temperature-gradient turbulence by strong density gradients. In the record case, these are maintained by a fine balance of the core particle transport and central fueling using neutral beam injection. The duration of the scenario was limited in time only by technical restrictions of the neutral beam injectors and control of the divertor heat loads. This paper presents the result in the context of the leading magnetic confinement devices along with details of the scenario.

Jul 1, 2026