Performance of solenoids vs. quadrupoles in focusing and energy selection of laser accelerated protons

TL;DR

This paper compares solenoids and quadrupoles for focusing and energy selection of laser-accelerated protons, deriving an analytical model and validating it with simulations, to determine their suitability at different energies.

Contribution

It introduces an analytical scaling for solenoid versus quadrupole performance in proton focusing, supported by TRACEWIN simulations and energy selection analysis.

Findings

Solenoids require pulsed or superconducting operation above a few MeV.

Quadrupoles can operate conventionally at higher energies.

Triplet systems have only 25% lower transmission than solenoids.

Abstract

Using laser accelerated protons or ions for various applications - for example in particle therapie or short-pulse radiographic diagnostics - requires an effective method of focusing and energy selection. We derive an analytical scaling for the performance of a solenoid compared with a doublet/triplet as function of the energy, which is confirmed by TRACEWIN simulations. The scaling shows that above a few MeV a solenoid needs to be pulsed or super-conducting, whereas the quadrupoles can remain conventional. The transmission of the triplet is found only 25% lower than that of the equivalent solenoid. Both systems are equally suitable for energy selection based on their chromatic effect as is shown using an initial distribution following the RPA simulation model by Yan et al.\cite{yan2009}.