Collective Instabilities Research Articles

Neutrino quantum kinetics in a core-collapse supernova

Our understanding of neutrino flavor conversion in the supernova core is still preliminary, despite its likely relevance to the neutrino-driven supernova mechanism. We present multi-angle and multi-energy numerical simulations of neutrino quantum kinetics within a spherically symmetric shell in the proximity of the region of neutrino decoupling. We rely on inputs from a one-dimensional core-collapse supernova model with a mass of 18.6 M ⊙ and find that, at early post-bounce times (t pb ≲ 0.5 s), no crossing is present in the angular distribution of the electron neutrino lepton number and flavor conversion is triggered by slow collective instabilities. Angular crossings appear for t pb ≳ 0.5 s and fast flavor conversion leads to flavor equipartition, with the spectral energy distribution of ν e (ν̅e) and ν x (ν̅ x ) becoming comparable. Notably, flavor equipartition is not a generic outcome of fast flavor conversion, rather it is a consequence of the relatively similar properties of neutrinos of different flavors characterizing the late accretion phase. Artificially tweaking the collision term to introduce an electron lepton number angular crossing for t pb ≲ 0.5 s, we observe that flavor equipartition is not achieved. While our findings are restricted to a specific supernova model, and they only take into account the feedback of the neutrino background on the flavor conversion, they suggest a rich phenomenology in the supernova core as a function of the post-bounce time which needs to be further explored to assess its impact on the explosion mechanism.

Boundary of the Distribution of Solar Wind Proton Beta versus Temperature Anisotropy

The frequency distribution of solar wind protons, measured in the vicinity of Earth’s orbit, is customarily plotted in (β ∥, T ⊥/T ∥) phase space. Here, T ⊥/T ∥ is the ratio of perpendicular and parallel temperatures, and β ∥ = 8π nT ∥/B 2 is the ratio of parallel thermal energy to background magnetic field energy, the so-called “parallel beta,” with ⊥ and ∥ denoting directions with respect to the ambient magnetic field. Such a frequency distribution, plotted as a two-dimensional histogram, forms a peculiar rhombic shape defined with an outer boundary in the said phase space. Past studies reveal that the threshold conditions for temperature anisotropy–driven plasma instability partially account for the boundary on the high-β ∥ side. The low-β ∥ side remains largely unexplained despite some efforts. Work by Vafin et al. recently showed that certain contours of collisional relaxation frequency, ν pp, when parameterized by T ⊥/T ∥ and β ∥, could match the overall shape of the left-hand boundary, thus suggesting that the collisional relaxation process might be closely related to the formation of the left-hand boundary. The present paper extends the analysis by Vafin et al. and carries out the dynamical computation of the collisional relaxation process for an ensemble of initial proton states with varying degrees of anisotropic temperatures. The final states of the relaxed protons are shown to closely match the observed boundary to the left of the (β ∥, T ⊥/T ∥) phase space. When coupled with a similar set of calculations for the ensemble in the collective instability regime, it is found that the combined collisional/collective effects provide the baseline explanation for the observation.

Impedance modelling and single-bunch collective instability simulations for the SuperKEKB main rings

The SuperKEKB is an electron-positron collider consisting of two storage rings: the 4 GeV-positron low-energy ring and the 7 GeV-electron high-energy ring. The impedance of the rings has been modeled using electromagnetic simulation codes and used to study the single-bunch collective instabilities. The wake potentials are exported from the impedance model and included in a particle tracking simulation code, PyHEADTAIL. In this paper, we review the impedance modeling and the results of the collective instability simulations.

Impedance driven collective effects in CEPC

The Circular Electron Positron Collider is a double ring lepton collider covering beam energy from 45 GeV (Z) to 180 GeV (tt-bar). Beam coupling impedance and the collective effects that are triggered by the impedance are important subjects when targeting high machine performance of an electron positron collider. A robust impedance model is required for the instabilities evaluations as well as to investigate their possible mitigations. Meanwhile, a thorough investigation on the collective effects is essential to identify the critical issues on the beam instabilities. In this paper, a detailed impedance model has been built for the collider ring and dominant impedance contributors have been identified by evaluating the effective impedances. The potential collective instabilities driven by the impedance are also discussed.

Studies of FCC-ee Single Bunch Instabilities with an Updated Impedance Model

The design of the FCC-ee collider is ongoing with the goal of optimizing beam parameters and developing various accelerator systems. As a result, the modelling of coupling impedance is continuously evolving to take into account the design of the collider vacuum chamber and hardware components. Concurrently, estimates of collective effects and instabilities are being continually updated and refined. This paper presents the current FCC-ee impedance model and reports the findings of the single-bunch instability studies. Additionally, some potential mitigation techniques for these instabilities are discussed.

Upgrade the impedance model in RCS of CSNS

The Rapid Cycling Synchrotron (RCS) in the China Spallation Neutron Source (CSNS) is a high-intensity proton accelerator that is susceptible to collective instabilities and performance limitations due to its impedance. With impedance study of key components and new component installations, the impedance model should be updated. This article presents a comprehensive estimate of the coupling impedance and outlines the impedance model of the RCS.

Concatenation of Two Different Integrable Systems is Not Integrable

Aims/Objectives: Nonlinear, completely integrable Hamiltonian systems representing charged particle motion in external electromagnetic fields hold promise for models of novel intensity frontier particle accelerators. The main reason is the combination of large regions of stable orbits with damping of collective instabilities by conservative relaxation. Intensity frontier particle accelerators are essential for discovery science in particle and nuclear physics, and a host of industrial and security applications.Study Design: Mathematical proof.Methodology: Tools of Hamiltonian dynamics and differential geometry.Results: Realistic system lattices include additional sections or inserts that themselves may be integrable (such as linear optics, phase trombones, thin lenses, kicks, etc.). However, in general the full system fails to remain integrable.Conclusion: The non-integrability proof is presented and some consequences of integrability failure are explored.

Coherent propagation of spin-orbit excitons in a correlated metal

Collective excitations such as plasmons and paramagnons are fingerprints of atomic-scale Coulomb and exchange interactions between conduction electrons in metals. The strength and range of these interactions, which are encoded in the excitations’ dispersion relations, are of primary interest in research on the origin of collective instabilities such as superconductivity and magnetism in quantum materials. Here we report resonant inelastic x-ray scattering experiments on the correlated 4d-electron metal Sr2RhO4, which reveal a spin-orbit entangled collective excitation. The dispersion relation of this mode is opposite to those of antiferromagnetic insulators such as Sr2IrO4, where the spin-orbit excitons are dressed by magnons. The presence of propagating spin-orbit excitons implies that the spin-orbit coupling in Sr2RhO4 is unquenched, and that collective instabilities in 4d-electron metals and superconductors must be described in terms of spin-orbit entangled electronic states.

Abstract 4742: Familial adenomatous polyposis epigenetic landscape as a precancer model of colorectal cancer

Abstract Aberrant shifts in DNA methylation have long been regarded as an early biomarker for cancer onset and progression. However, it is unclear when methylation aberrance starts and how it interacts with other epigenomic modifications. To address how epigenomic changes occur and interact during the transformation from normal healthy colon tissue to malignant colorectal cancer (CRC), we collected 51 samples from 15 familial adenomatous polyposis (FAP) and non-FAP colorectal cancer patients. We generated 30-70x of whole-genome enzymatic methylation sequencing (WGEM-seq) data via the novel Ultima Genomics ultra high-throughput sequencing platform. We observed hypermethylation and hypomethylation emerge early in the malignant transformation process in gene promoters and distal regulatory elements. We performed multifaceted analysis on methylation alterations with whole-genome sequencing (WGS), transposase accessibility (ATAC-seq), high-resolution chromatin accessibility (Tri-C), and gene expression (RNA-seq) data. Our multidimensional analysis demonstrates how collectively epigenomic alterations have affected gene expression throughout normal colon mucosa, benign and dysplasia polyps to adenocarcinoma. Epigenomic changes start as early as benign polyps, followed by other epigenomic shifts, including bivalent domains. Various epigenomic aberrances are associated with concomitant gene expression level changes. Our integrative analysis of multi-epigenomics data implicates collective and cumulative epigenomic instability in the early onset of colon carcinogenesis. Citation Format: Hayan Lee, Gat Krieger, Tyson Clark, Yizhou Zhu, Aziz Khan, Casey R. Hanson, Aaron Horning, Edward D. Esplin, Mohan Badu, Kristina Paul, Roxanne Chiu, Bahareh Bahmani, Stephanie Nevins, Annika K. Weimer, Ariel Jaimovich, Christina Curtis, William Greenleaf, James M. Ford, Doron Lipson, Zohar Shipony, Michael P. Snyder. Familial adenomatous polyposis epigenetic landscape as a precancer model of colorectal cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4742.

Mesoscopic Klein-Schwinger effect in graphene

Strong electric field annihilation by particle–antiparticle pair creation, also known as the Schwinger effect, is a non-perturbative prediction of quantum electrodynamics. Its experimental demonstration remains elusive, as threshold electric fields are extremely strong and beyond current reach. Here, we propose a mesoscopic variant of the Schwinger effect in graphene, which hosts Dirac fermions with an approximate electron–hole symmetry. Using transport measurements, we report on universal one-dimensional Schwinger conductance at the pinchoff of ballistic graphene transistors. Strong pinchoff electric fields are concentrated within approximately 1 μm of the transistor’s drain and induce Schwinger electron–hole pair creation at saturation. This effect precedes a collective instability towards an ohmic Zener regime, which is rejected at twice the pinchoff voltage in long devices. These observations advance our understanding of current saturation limits in ballistic graphene and provide a direction for further quantum electrodynamic experiments in the laboratory.

A Study of the Collective Beam Instabilities in the Damping Ring of the VEPP-5 Injection Complex

A Study of the Collective Beam Instabilities in the Damping Ring of the VEPP-5 Injection Complex

Acoustic waves in the Jovian dusty magnetosphere: a brief review and meta-analysis

The omnipresence of dust particulates in space and astrophysical plasmas has been attracting numerous researchers to study the collective excitation and propagation dynamics of different eigen-mode structures in diversifed astrocosmic circumstances for years. It includes planetary rings, interplanetary space, cometary tails, asteroid zones, planetary atmospheres, etc. The ubiquitous charged dust particulates possess collective degrees of dynamic freedom resulting in the excitation of relatively low-frequency modes, such as dust-ion-acoustic waves (DIAWs), dust-acoustic waves (DAWs), dust-Coulomb waves (DCWs), and so forth. An interesting prevalency of dusty plasma stability research lies in the Jovian magnetosphere (i.e., Jovian plasmas), embedded inside the supersonic solar wind. A brief review of the updated research works on dust-acoustic waves and related collective instability dynamics in the presence of trapped plasma particles is presented herein. The key aim of the proposed explorative meta-analysis is rooted in outlining concisely the main up-to-date investigations on such collective instability processes chronologically. An especial attention is given primarily to the thermostatistical distribution laws of the constitutive lighter electrons and ions against the heavier positively charged dust grains (microspheres). The trapping mechanism of both the lighter species (electrons+ions) is another additive feature revisited here properly. Finally, we clearly extrapolate a number of futuristic directions in light of sensible novelties with a wider scope, both horizontally as well as vertically.

New Developments in Relativistic Magnetohydrodynamics

Relativistic magnetohydrodynamics (RMHD) provides an extremely useful description of the low-energy long-wavelength phenomena in a variety of physical systems from quark–gluon plasma in heavy-ion collisions to matters in supernova, compact stars, and early universe. We review the recent theoretical progresses of RMHD, such as a formulation of RMHD from the perspective of magnetic flux conservation using the entropy–current analysis, the nonequilibrium statistical operator approach applied to quantum electrodynamics, and the relativistic kinetic theory. We discuss how the transport coefficients in RMHD are computed in kinetic theory and perturbative quantum field theories. We also explore the collective modes and instabilities in RMHD with a special emphasis on the role of chirality in a parity-odd plasma. We also give some future prospects of RMHD, including the interaction with spin hydrodynamics and the new kinetic framework with magnetic flux conservation.

Shock Waves in Weakly Relativistic e-p-i Plasma: Application to Plasma Created by Ultraintense Short Pulse Laser

In this article, the role of the positrons shock waves generation in weakly relativistic laser-created plasma is investigated. The plasma considered is generated on the rear face of a target, irradiated by a high intensity short pulse laser, in the framework of target normal sheath acceleration (TNSA) mechanism. This plasma is composed of Boltzmann distributed positrons, hot and cold super-thermal electrons, and dynamic ions. Kinematic viscosity among the plasma constituents has been also considered. With the purpose of studying the behavior of nonlinear ion acoustic shock waves (IASHWs), the reductive perturbation method (RPM) has been employed and Korteweg-de Vries Burgers equation has been derived. It was observed that different plasma parameters (namely, electrons super-thermality, number of positrons, ion temperature, kinematic viscosity, etc.) have a real impact on the propagation of IASHWs. As electron–positron plasmas with ion possessing relativistic velocities are often detected in laboratory experiments, astrophysical, and space environments, the present work will help to explain the different types of collective processes and instabilities in regions where e-p-i plasmas can exist.

Structural Principles in Liquids and Glasses: Bottom-Up or Top-Down

The conventional approach to elucidate the atomic structure of liquid and glass is to start with local structural units made of several atoms, and to use them as building blocks to form a global structure, the bottom-up approach. We propose to add an alternative top-down approach in which we start with a global high-temperature gas state and then apply interatomic potentials to all atoms at once. This causes collective density wave instability in all directions with the same wavelength. These two driving forces, local and global, are in competition and are mutually frustrated. The final structure is determined through the compromise of frustration between these two, which creates the medium-range-order. This even-handed approach on global and local potential energy landscapes explains the distinct natures of short-range order and medium-range order, and strong temperature dependence of various properties of liquid.

Theoretical formulation of multiturn collective dynamics in a laser cavity modulator with comparison to Robinson and high-gain free-electron laser instability

The study of collective beam instabilities has long been an important and active research topic in particle accelerators. The collective effects are typically divided into two categories: the short-range single-bunch instabilities and the long-range multibunch or multiturn instabilities. Robinson instability can be the mostly encountered long-range multiturn instability. We recently explored a collective multiturn instability driven by the short-range coherent undulator radiation in the laser cavity modulator of a steady-state microbunching (SSMB) storage ring. In this paper, we formulate and compare such an instability with the Robinson instability. Considering the radiation slippage effect and the finite duration, the functional form of the radiation wakes is essentially different from that of the Robinson case. We also relate a special case of the newly explored instability to the high-gain free-electron laser process and find that a similar cubic dispersion equation can be obtained. The discussions and comparisons presented in this paper may shed light on the underlying physical mechanisms of the collective beam dynamics in the laser cavity modulator of an SSMB storage ring.

CoSyR: A novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamics code is developed based on a Lagrangian method for the calculation of the particles’ radiation near-fields using wavefront/wavelet meshes via the Green’s function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in 2D/3D simulations at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. The current 2D implementation of CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed. Extension of the core algorithms to 3D is possible and planned.

Space charge effects for collective instabilities in circular machines

Coulomb fields of charged particle beams in circular machines determine, together with wake fields, modes of the collective beam oscillations, for both transverse and longitudinal degrees of freedom. Recent progress in these two areas of beam dynamics is discussed.

Background-enhanced collapse instability of optical speckle beams in nonlocal nonlinear media

We study the focusing dynamics of incoherent wave-packets (speckle beams) in the presence of a nonlocal nonlinear response in the framework of the nonlocal nonlinear Schrödinger (NLS) equation. In the highly nonlocal regime, we show that the speckle beam develops a collective incoherent collapse instability — at variance with a conventional collapse that is inherently a coherent object, here it is the incoherent beam as a whole that develops a collapse. More specifically, we study the impact of a homogeneous incoherent background on the development of the incoherent collapse instability. Despite the fact that the homogeneous background is modulationally stable, we show that it significantly strengthens the formation of the incoherent collapse instability. Our theoretical analysis is based on a wave turbulence formulation of the Vlasov equation, which allows us to introduce an effective hydrodynamic model that is subsequently solved by the method of characteristics. A quantitative agreement is obtained between the simulations of the NLS equation, the Vlasov equation and the hydrodynamic model, without using adjustable parameters. The interaction between the background and the collapsing structure is described by means of a coupled system for the singular and smooth components of the solution of the Vlasov equation. The theory reveals that the mechanism underlying the background-induced collapse enhancement is due to a transfer of momentum from the background to the collapsing structure, while there is no ‘mass’ exchange among them. Furthermore, we show that a strong background level significantly boosts the collapse dynamics. Our work should stimulate the development of nonlinear experiments aimed at observing the incoherent collapse phenomenon in nonlinear thermal media. From a broader perspective, these investigations pave the way for the study of novel forms of global incoherent collective behaviors in wave turbulence, such as the formation of incoherent rogue waves.

Collective Neutrino Flavor Instability Requires a Crossing.

Neutrinos in supernovae, neutron stars, and in the early Universe may change flavor collectively and unstably, due to neutrino-neutrino forward scattering. We prove that, for collective instability to occur, the difference of momentum distributions of two flavors must change sign, i.e., there is a zero crossing. This necessary criterion, which unifies slow and fast instabilities, is valid for Hamiltonian flavor evolution of ultrarelativistic standard model neutrino occupation matrices, including damping due to collisions in the relaxation approximation. It provides a simple but rigorous condition for collective flavor transformations that are believed to be important for stellar dynamics, nucleosynthesis, and neutrino phenomenology.