arXiv subjects

C. Hansel

Publications and source records attributed to C. Hansel.

7 recordsLinked to original sources

arXiv2026

First results from the E302 efficiency$\unicode{x2013}$instability experiment at the FACET-II facility

The beam-breakup (BBU) instability in plasma accelerators is seeded by a transverse offset between the driver and a trailing bunch. The BBU instability induces oscillations in the trailing bunch, which are detrimental to its beam quality. When the instability is large, assuming little mitigation from ion motion and energy spread, the beam suffers emittance growth, and charge can be kicked transversely out of the plasma channel. The detrimental effect on beam quality is substantially worse at high efficiencies, which places constraints on the achievable power efficiency in applications such as linear colliders, where maintaining the beam quality is required. In this paper, we present the first experimental signatures of the BBU instability in data taken in the E302 experiment at the FACET-II facility at SLAC National Accelerator Laboratory. We use a specific beam-optical setup and a novel method to probe for transverse instabilities on diagnostic screens downstream of a magnetic dipole spectrometer. We complement the analysis with full 3D particle-in-cell (PIC) simulations of the plasma interaction using similar driver and trailing bunch parameters on a simulated FACET-II spectrometer.

physics.acc-ph↗

arXiv2023

Generation of meter-scale hydrogen plasmas and efficient, pump-depletion-limited wakefield excitation using 10 GeV electron bunches

High repetition rates and efficient energy transfer to the accelerating beam are important for a future linear collider based on the beam-driven plasma wakefield acceleration scheme (PWFA-LC). This paper reports the first results from the Plasma Wakefield Acceleration Collaboration (E300) that are beginning to address both of these issues using the recently commissioned FACET-II facility at SLAC. We have generated meter-scale hydrogen plasmas using time-structured 10 GeV electron bunches from FACET-II, which hold the promise of dramatically increasing the repetition rate of PWFA by rapidly replenishing the gas between each shot compared to the hitherto used lithium plasmas that operate at 1-10 Hz. Furthermore, we have excited wakes in such plasmas that are suitable for high gradient particle acceleration with high drive-bunch to wake energy transfer efficiency -- a first step in achieving a high overall energy transfer efficiency. We have done this by using time-structured electron drive bunches that typically have one or more ultra-high current (>30 kA) femtosecond spike(s) superimposed on a longer (~0.4 ps) lower current (<10 kA) bunch structure. The first spike effectively field-ionizes the gas and produces a meter-scale (30-160 cm) plasma, whereas the subsequent beam charge creates a wake. The length and amplitude of the wake depends on the longitudinal current profile of the bunch and plasma density. We find that the onset of pump depletion, when some of the drive beam electrons are nearly fully depleted of their energy, occurs for hydrogen pressure >1.5 Torr. We also show that some electrons in the rear of the bunch can gain several GeV energies from the wake. These results are reproduced by particle-in-cell simulations using the QPAD code. At a pressure of ~2 Torr, simulations results and experimental data show that the beam transfers about 60% of its energy to the wake.

physics.acc-ph↗

arXiv2023

Modeling betatron radiation using particle-in-cell codes for plasma wakefield accelerator diagnostics

The characterization of plasma wakefield acceleration experiments using emitted photons from betatron radiation requires numerical models in support of instrumentation of single-shot, double-differential angular-energy spectra. Precision characterization for relevant experiments necessitates covering a wide energy range extending from tens of keV through 10~GeV, with an angular resolution on the order of $100 \;\mu\text{rad}$. In this paper, we present a numerical model for betatron radiation from plasma accelerated beams, that are based on integration of Lienard Wiechert (LW) potentials for computed particle trajectories. The particle trajectories are generated in three different ways: first, by particle tracking through idealized fields in the blowout regime of PWFA; second, by obtaining trajectories from the Quasi-static Particle-in-Cell (PIC) code QuickPIC; and third, by obtaining trajectories from the full PIC code OSIRIS. We performed various benchmarks with analytical expressions and the PIC code EPOCH, which uses a Monte-Carlo QED radiation model. Finally, we present simulations of the expected betatron radiation for parameters from the Facility for Advanced Accelerator Experimental Tests II (FACET-II) PWFA and plasma photocathode experiments.

physics.acc-ph↗

arXiv2021

Chromatic Dynamics of an Electron Beam in a Plasma Based Accelerator

We present a theoretical investigation of the chromatic dynamics of the witness beam within a plasma based accelerator. We derive the single particle motion of an electron in an ion column within a nonlinear, blowout wake including adiabatic dampening and adiabatic variations in plasma density. Using this, we calculate the evolution of the beam moments and emittance for an electron beam. Our model can handle near arbitrary longitudinal phase space distributions. We include the effects of energy change in the beam, imperfect wake loading, initial transverse offsets of the beam, and mismatch between the beam and plasma. We use our model to derive analytic saturation lengths for the projected, longitudinal slice, and energy slice emittance under different beam loading conditions. Further, we show that the centroid oscillations and spot sizes vary between the slices and the variation depends strongly on the beam loading. Next, we show how a beam evolves in a full plasma source with density ramps and show that the integral of the plasma density along the ramp determines the impact on the beam. Finally, we derive several simple scaling laws that show how to design a plasma based injector to produce a target beam energy and energy spread.

physics.acc-ph↗

arXiv2021

Plasma Wakefield Accelerators with Ion Motion and the E-314 Experiment at FACET-II

A future plasma based linear collider has the potential to reach unprecedented energies and transform our understanding of high energy physics. The extremely dense beams in such a device would cause the plasma ions to fall toward the axis. For more mild ion motion, this introduces a nonlinear perturbation to the focusing fields inside of the bubble. However, for extreme ion motion, the ion distribution collapses to a quasi-equilibrium characterized by a thin filament of extreme density on the axis which generates strong, nonlinear focusing fields. These fields can provoke unacceptable emittance growth that can be reduced through careful beam matching. In this paper, we discuss the rich physics of ion motion, give a brief overview of plans for the E-314 experiment at FACET-II which will experimentally demonstrate ion motion in plasma accelerators, and present results of particle-in-cell simulations of ion motion relevant to the E-314 experiment.

physics.acc-ph↗

arXiv2021

Modeling Betatron Radiation Diagnostics for E-310 -- Trojan Horse

The E-310 experiment at the Facility for Advanced Accelerator Experimental Tests II (FACET-II) at SLAC National Accelerator Laboratory aims to demonstrate the creation of high brightness beams from a plasma photocathode. Betatron radiation will be measured by a Compton spectrometer, currently under development at UCLA, to provide single-shot, nondestructive beam diagnostics. We give a brief overview of this spectrometer as well as double differential spectrum reconstruction from the spectrometer image and beam parameter reconstruction from this double differential spectrum. We discuss three models for betatron radiation: an idealized particle tracking code which computes radiation from Li\'enard-Wiechert potentials, a quasi-static particle-in-cell (PIC) code which computes radiation from Li\'enard-Wiechert potentials, and a full PIC code which computes radiation using a Monte Carlo QED method. Spectra computed by the three models for a simple case are compared.

physics.acc-ph↗

arXiv2020

Nonlinear equilibria and emittance growth in plasma wakefield accelerators with ion motion

The plasma wakefield accelerator may accelerate particles to high energy in a future linear collider with unprecedented acceleration gradients, exceeding the GeV/m range. Beams for this application would have extremely high brightness and, subject to the intense plasma ion-derived focusing, they would achieve densities high enough to induce the plasma ions to collapse into the beam volume. This non-uniform ion density gives rise to strong nonlinear focusing which may lead to deleterious beam emittance growth. The effects of ion collapse and their mitigation has been investigated recently through particle-in-cell simulations, which show that by dynamically matching the beam to the focusing of the collapsed ion distribution, one may avoid serious emittance growth. We extend this work by exploring the near-equilibrium state of the beam-ion system reached after the ions have collapsed, a condition yielding the emittance growth mitigation observed. We show through PIC simulations and analytical theory that in this case a dual electron beam-ion Bennett-type equilibrium distribution is approached. Here, the beam and ion distributions share nearly the same shape, which generates nonlinear transverse electromagnetic fields. We exploit a Bennett-type model to study beam phase space dynamics and emittance growth over time scales much longer than permitted by PIC simulations through use of a 2D symplectic tracking code with Monte Carlo scattering based on Moliere's theory of small angle multiple scattering. We find that while phase space diffusion due to parametric excitations of the beam size due to plasma non-uniformity is negligible, scattering from collapsed ions gives rise to manageable emittance growth in the case of a linear collider. The implications of these results on experiments planned at FACET-II are examined.

physics.acc-ph↗