arXiv subjects

I. Haber

Publications and source records attributed to I. Haber.

5 recordsLinked to original sources

arXiv2025

First Observation of Dispersive Shock Waves in an Electron Beam

Dispersive shock waves (DSWs) are expanding nonlinear wave trains that arise when dispersion regularizes a steepening front, a phenomenon observed in fluids, plasmas, optics, and superfluids. Here we report the first experimental observation of DSWs in an intense electron beam, using the University of Maryland Electron Ring (UMER). A localized induction-cell perturbation produced a negative density pulse that evolved into a leading soliton-like peak followed by an expanding train of oscillations. The leading peak satisfied soliton scaling laws for width^2 vs inverse amplitude and velocity vs amplitude, while the total wave-train width increased linearly with time, consistent with Korteweg--de Vries (KdV) predictions. Successive peaks showed decreasing amplitude and velocity toward the trailing edge, in agreement with dispersive shock ordering. These results demonstrate that intense charged particle beams provide a new laboratory platform for studying dispersive hydrodynamics, extending nonlinear wave physics into the high-intensity beam regime.

physics.acc-ph↗

arXiv2022

Optimization of Flat to Round Transformers with Self-fields using Adjoint Techniques

A continuous system of moment equations is introduced that models the transverse dynamics of a beam of charged particles as it passes through an arbitrary lattice of quadrupoles and solenoids in the presence of self-fields. Then, figures of merit are introduced specifying system characteristics to be optimized. The resulting model is used to optimize the parameters of the lattice elements of a flat to round transformer with self-fields, as could be applied in electron cooling. Results are shown for a case of no self-fields and two cases with self-fields. The optimization is based on a gradient descent algorithm in which the gradient is calculated using adjoint methods that prove to be very computationally efficient. Two figures of merit are studied and compared: one emphasizing radial force balance in the solenoid, the other emphasizing minimization of transverse beam energy in the solenoid.

physics.acc-ph↗

arXiv2019

Multi-Stream Instability of a Single Long Electron Bunch in a Storage Ring

A multi-stream instability is observed experimentally in a longitudinally expanding electron beam in a storage ring. The instability is observed when the beam expands such that its length is several times the circumference of the ring, and portions of the beam overlap. While portions of the beam overlap in physical space, due to the nature of the expansion process, the portions form multiple streams and remain separate in velocity space. The streams become unstable as their number increases and their separation in velocity decreases. An analytical theory predicts the onset of the instability, consistent with simulations and measurements, over a wide range of peak line-charge densities and bunch lengths. This work extends previous calculations to include the dynamic non-linear elongation of the bunch, with a given initial length, and defines an onset criterion for the filament velocity separation.

physics.plasm-ph↗

arXiv2018

Quasi-integrable optics for a small electron recirculator

This paper describes the design and simulation of a proof-of-concept quasi-integrable octupole lattice at the University of Maryland Electron Ring (UMER). This experiment tests the feasibility of nonlinear integrable optics, a novel technique that is expected to mitigate resonant beam loss and enable low-loss high-intensity beam transport in rings. Integrable lattices with large amplitude-dependent tune spreads, created by nonlinear focusing elements, are proposed to damp beam response to resonant driving perturbations while maintaining large dynamic aperture [Danilov and Nagaitsev PRSTAB 2010]. At UMER, a lattice with a single octupole insert is designed to test the predictions of this theory. The planned experiment employs a low-current high-emittance beam with low space charge tune shift (~0.005) to probe the dynamics of a lattice with large externally-induced tune spread. Design studies show that a lattice composed of a 25-cm octupole insert and existing UMER optics can induce a tune spread of \sim 0.13. Stable transport is observed in PIC simulation for many turns at space charge tune spread 0.008. A maximum spread of dnu = 0.11 (RMS 0.015) is observed for modest octupole strength (peak 50 T/m^3). A simplified model of the system explores beam sensitivity to steering and focusing errors. Results suggest that control of orbit distortion to <0.2 mm within the insert region is essential. However, we see only weak dependence on deviations of lattice phase advance (<=0.1 rad.) from the invariant-conserving condition.

physics.acc-ph↗

arXiv2018

Low Space-Charge Intensity Beams in UMER via Collimation and Solenoid Focusing

The University of Maryland Electron Ring (UMER) has operated traditionally in the regime of strong space-charge dominated beam transport, but small-current beams are desirable to significantly reduce the direct (incoherent) space-charge tune shift as well as the tune depression. This regime is of interest to model space-charge effects in large proton and ion rings similar to those used in nuclear physics and spallation neutron sources, and also for nonlinear dynamics studies of lattices inspired on the Integrable Optics Test Accelerator (IOTA). We review the definition of space-charge intensity, show a comparison of space-charge parameters in UMER and other machines, and discuss a simple method involving double collimation and solenoid focusing for varying the space-charge intensity of the beam injected into UMER.

physics.acc-ph↗