arXiv subjects

Ryland Goldman

Publications and source records attributed to Ryland Goldman.

3 recordsLinked to original sources

arXiv2026

Building a Start-to-End Model of the CESR Injector Linac

The CESR injector linac supplies positrons to the Cornell Electron Storage Ring in six stages: a thermionic cathode, a 150 kV DC gun, a prebuncher, four electron linac sections, a tungsten positron converter, and four positron linacs. We present a start-to-end model of the full chain, built in Python from open-source codes. WarpX is used for the space-charge-dominated cathode, gun, prebuncher, and electron linacs, Geant4 for positron production, and Impact-T for the positron linacs. The beam reaches the converter at 146 MeV and the recaptured positrons are accelerated to 250 MeV. Stage configurations are written in YAML to allow algorithmic adjustment by Xopt for ML optimization.

physics.acc-ph↗

arXiv2025

Moderator Simulation for the Compact Positron Source at NLCTA

Positron moderation is a key part of the production of slow positrons. This paper examines G4beamline simulations of various moderator designs and the addition of a radiofrequency cavity to increase the efficiency of the moderator. A setup consisting of a 100 MeV electron beam incident on a 7 mm tungsten target, a 5 T adiabatic matching device, a 5-cell L-band RF cavity, and a single-crystal tungsten moderator leads to a 39.3x improvement in the number of positrons moderated over a common thin-foil polycrystalline moderator without the AMD and cavity. We also present a novel calculation method for determining the stopping distribution of low-energy positrons in a thin foil, modifying the Makhovian distribution with an exponential ramp to account for edge effects.

physics.acc-ph↗

arXiv2025

Start-To-End Simulations of a Compact, Linac-Based Positron Source

Slow positrons are increasingly important to the study of material surfaces. For these kinds of studies, the positrons must have low emittance and relatively high brightness. Unfortunately, fast positron sources like radioactive capsules or linac driven sources have broad energy and angular spread, which make them difficult to capture and use. Moderators are materials that produce slow, mono-energetic positrons from a fast positron beam. Since their efficiencies are typically less than $10^{-3}$ slow $e^+$ per fast $e^+$, research into how to maximize efficiency is of great interest. Previous work has shown that using a linac, one can decelerate the fast positron beam in order to greatly increase moderation efficiency. We present here start-to-end simulations using G4beamline to model a 100 MeV electron beam incident upon a Tungsten target, focused by an adiabatic matching device, and decelerated by a 1.3 GHz, 5-cell pillbox cavity. We show that by decelerating the positrons after their creation we can increase the number of positrons under 500 keV by 15 times, translating to a 16.3 times improvement in moderation efficiency, and therefore leading to a brighter positron source.

physics.acc-ph↗