Anomalous beam transport through Gabor (plasma) lens prototype

TL;DR

This paper reports on the development and testing of a Gabor plasma lens prototype capable of focusing low-energy proton beams, revealing complex beam shaping effects linked to plasma instabilities.

Contribution

The study introduces a Gabor plasma lens prototype and analyzes its stable operation and beam focusing performance during a proton beam test.

Findings

The lens successfully focused 1.4 MeV protons into rings on a scintillator screen.

The plasma exhibited an off-axis rotation similar to diocotron instability.

Simulations suggest the instability influences the beam ring formation.

Abstract

An electron plasma lens is a cost-effective, compact, strong-focusing element that can ensure efficient capture of low-energy proton and ion beams from laser-driven sources. A Gabor lens prototype was built for high electron density operation at Imperial College London. The parameters of the stable operation regime of the lens and its performance during a beam test with 1.4 MeV protons are reported here. Narrow pencil beams were imaged on a scintillator screen 67 cm downstream of the lens. The lens converted the pencil beams into rings that show position-dependent shape and intensity modulation that are dependent on the settings of the lens. Characterisation of the focusing effect suggests that the plasma column exhibited an off-axis rotation similar to the $m=1$ diocotron instability. The association of the instability with the cause of the rings was investigated using particle tracking simulations.