A Simulation of the Photoionization of H- Together with the Subsequent Tracking of the Liberated Electrons

TL;DR

This paper presents a MATLAB simulation of photoionization of H- ions and electron tracking to optimize beam profile measurements in Fermilab's PIP-II LINAC, aiding in non-intercepting beam diagnostics.

Contribution

It introduces a novel simulation combining electromagnetic modeling and electron tracking for laserwire beam diagnostics in a superconducting LINAC.

Findings

Simulation accurately predicts liberated electron positions.

Optimizes electron collection mechanisms for laserwire diagnostics.

Supports non-intercepting beam profile measurements.

Abstract

The Proton Improvement Plan - II (PIP-II) is a new linear accelerator (LINAC) complex being built at Fermilab. It is based on superconducting radiofrequency cavities and will accelerate H- ions to 800 MeV kinetic energy before injection into the existing Booster ring. Measurements of the profile of the beam along the LINAC must be done by non-intercepting methods due to the superconducting cavities. The method chosen is photoionization of a small number of H- by a focused infrared laser, aka laserwire. The number of ionized electrons is measured as a function of laser position within the H- beam. To aid in the design of the collection mechanism, a simulation was written in MATLAB with input from the commercial electromagnetic simulation, CST. This simulation calculates the number and positions of the liberated electrons and tracks them through the magnetic collection and H- beam fields to the collection point. Results from this simulation for various points along the LINAC will be shown.