arXiv subjects

Robert Holtzapple

Publications and source records attributed to Robert Holtzapple.

6 recordsLinked to original sources

arXiv2023

Energy recovery in filament-regime plasma wakefield acceleration of positron beams

Plasma wakefield acceleration using an electron filament offers stable, high-gradient, high-quality acceleration of positron beams analogous to the acceleration of electrons in the blowout regime. However, low energy-transfer efficiency is currently a limiting factor for future collider applications. We explore the addition of a secondary electron bunch in the electron filament plasma wakefield acceleration scheme to recover additional energy from the wake. Particle-in-cell simulations using HiPACE++ are used to demonstrate various energy recovery schemes. In addition to confirming the energy efficiency gains with a recovery electron beam, we also develop energy recovery schemes in the context of future plasma colliders.

physics.acc-ph↗

arXiv2023

Differential Measurement of Trident Production in Strong Electromagnetic Fields

In this paper, we present experimental results and numerical simulations of trident production, $e^-\rightarrow e^-e^+e^-$, in a strong electromagnetic field. The experiment was conducted at CERN for the purpose of probing the strong-field parameter $χ$ up to 2.4, using a 200 GeV electron beam penetrating a 400 $μ$m thick germanium crystal oriented along the $\langle 110\rangle$ axis. For the current experimental parameters we found that the trident process is primarily a two-step process, and show remarkable agreement between theoretical predictions and experimental data. This paper is an extension of the previously published paper (Phys. Rev. Lett. 130, 071601 (2023)) and features new analysis differential in the energy of the produced positron and electron in the trident process. Even for the more demanding differential analysis, we find good agreement between theoretical predictions and experimental data, while a slight discrepancy is found in the high energy tail of the trident spectrum. This discrepancy could be an indication of the direct process, but further investigation is needed due to the large uncertainties in this part of the spectrum. Finally we present a suggestion for a future experiment, aiming to probe the direct process using thin crystals.

hep-ex↗

arXiv2023

A Liquid Xenon Positron Target Concept

Positron targets are a critical component of future Linear Colliders. Traditional targets are composed of high-Z metals that become brittle over time due to constant bombardment by high-power electron beams. We explore the possibility of a liquid xenon target which is continuosly refreshed and therefore not susceptible to the damage mechanisms of traditional solid targets. Using the GEANT4 simulation code, we examine the performance of the liquid xenon target and show that the positron yield is comparable to solid targets when normalized by radiation length. Additionally, we observe that the peak energy deposition density (PEDD) threshold for liquid xenon is higher than for commonly employed metal targets, which makes it an attractive, non-toxic positron target alternative. We develop parameter sets for demonstration applications at FACET-II and future Linear Colliders.

physics.acc-ph↗

arXiv2022

Precision Measurement of Trident Production in Strong Electromagnetic Fields

We demonstrate experimentally that the trident process $e^-\rightarrow e^-e^+e^-$ in a strong external field, with a spatial extension comparable to the effective radiation length, is well understood theoretically. The experiment, conducted at CERN, probes values for the strong field parameter $χ$ up to 2.4. Experimental data and theoretical expectations using the Local Constant Field Approximation show remarkable agreement over almost 3 orders of magnitude in yield.

hep-ex↗

arXiv2022

High-resolution modeling of nonlinear Compton scattering in focused laser pulses

A semi-classical approach is used to calculate radiation emission in the collision of an electron with an intense focused laser pulse. The results are compared to predictions from the locally constant field and locally monochromatic approximations. It is found that simulations employing the semi-classical approach capture features in the energy spectra, such as subharmonics and bandwidth structure, which are beyond local approaches. The formation length is introduced as a diagnostic to select between approaches as the electron is propagated through the pulse.

physics.plasm-ph↗

arXiv2020

Radiation Reaction near the Classical Limit in Aligned Crystals

An accelerated charged particle emits electromagnetic radiation. If the driving force is sufficiently strong, the radiated energy becomes comparable to the kinetic energy of the particle and the back-action of the emitted radiation (radiation reaction) significantly alters the dynamics of the particle. The Landau-Lifshitz (LL) equation has been proposed as the classical equation to describe the dynamics of a charged particle in a strong electromagnetic field when the effects of radiation reaction are taken into account. Hitherto, the experimental problem in validating the LL equation has been to achieve sufficiently strong fields for radiation reaction to be important without quantum effects being prominent. Notwithstanding, here we provide a quantitative experimental test of the LL equation by measuring the emission spectrum for a wide range of settings for 50 GeV positrons crossing aligned silicon single crystals near the $(110)$ planar channeling regime as well as 40 GeV and 80 GeV electrons traversing aligned diamond single crystals near the $\langle100\rangle$ axial channeling regime. The experimental spectra are in remarkable agreement with predictions based on the LL equation of motion with small quantum corrections for recoil and, in case of electrons, spin and reduced radiation emission, as well as with a more elaborate quantum mechanical model. Our experiment clearly shows the inadequacy of the Lorentz force as the sole agent of force on the particles in the classical limit, due to its absence of radiative energy loss in describing the dynamics of high-energy charged particles in strong electromagnetic fields like those in aligned single crystals.

hep-ex↗