Emittance Growth in Linear Induction Accelerators

TL;DR

This paper investigates the causes of emittance growth in linear induction accelerators used in radiography, identifying beam mismatch as a primary factor affecting source spot size and resolution.

Contribution

It analyzes potential causes of emittance growth in DARHT's LIAs using PIC simulations, highlighting beam mismatch as a key issue.

Findings

Beam mismatch likely causes emittance growth.

Emittance growth impacts radiographic resolution.

Particle-in-cell simulations help identify causes.

Abstract

The Dual-Axis Radiographic Hydrotest (DARHT) facility uses bremsstrahlung radiation source spots produced by the focused electron beams from two linear induction accelerators (LIAs) to radiograph large hydrodynamic experiments driven by high explosives. Radiographic resolution is determined by the size of the source spot, and beam emittance is the ultimate limitation to spot size. Some of the possible causes for the emittance growth in the DARHT LIA have been investigated using particle-in-cell (PIC) codes, and are discussed in this article. The results suggest that the most likely source of emittance growth is a mismatch of the beam to the magnetic transport, which can cause beam halo.