Low Emittance Positron Beam Generation: A Comparison Between Photo-production and Electro-Production

TL;DR

This paper compares photo-production and electro-production methods for generating low emittance positron beams, analyzing efficiency, beam quality, brightness, and energy deposition to inform accelerator applications.

Contribution

It provides a detailed comparison of the two main positron production methods, including yield, beam quality, and brightness, with new insights into their efficiencies and characteristics.

Findings

Photo-production yield up to 7.6%

Electro-production yield up to 200%

Analysis of beam emittance and brightness

Abstract

Positron beams, both polarized and non-polarized, low and high energy have a wide range of applications and many methods can be used to produce them. In this paper we analyse the two main methods used to produce positrons for accelerator applications, the "traditional" electro-production and the more recent "photo-production". After having determined the best target material, the positron production yield is determined for various target thickness and primary beam energy. Production efficiency up to about 7.6% and 200% are achievable for photo-production and electro-production respectively. Then the quality, i.e. the emittance and the normalized emittance of the produced beam is evaluated; the proposed "Gruber" correction for calculating the normalized emittance is considered too. The brightness of the obtained beams is calculated, relating it to the intrinsic temporal lengthening of the positron beam. The time structure of the primary beam is preserved for long bunches down to the ps scale. A very preliminary evaluation of the energy deposition in the target and its effect is done. The polarization is not take, so far, into account.