Anomalous Beam Transport through Gabor (Plasma) Lens Prototype

Toby Nonnenmacher,Hin-Tung Lau,Robert Bingham,Colin Whyte,Ken Long,Jürgen Pozimski,Titus-Stefan Dascalu,Chung Lim Cheung

doi:10.3390/app11104357

Toby Nonnenmacher, Hin-Tung Lau + Show 6 more

Open Access

https://doi.org/10.3390/app11104357

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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.

Highlights

One of the principal challenges that must be addressed to deliver high-flux pulsed proton or positive-ion beams for many applications is the efficient capture of the ions ejected from the source
An attractive approach to providing the strong-focusing element required to capture the low-energy (∼15 MeV) ion flux produced in the laser-target interaction is to exploit the strong focusing forces that can be provided by a cloud of electrons trapped within a cylindrical volume by crossed electric and magnetic fields. Such an electron-plasma lens was initially proposed by Gabor in 1947 [27]
Discharge-capillary active plasma lenses were investigated as compact devices for focusing 100 MeV-level electron beams produced by a gas-jet-based laser-plasma accelerator

Summary

Introduction

One of the principal challenges that must be addressed to deliver high-flux pulsed proton or positive-ion beams for many applications is the efficient capture of the ions ejected from the source. An attractive approach to providing the strong-focusing element required to capture the low-energy (∼15 MeV) ion flux produced in the laser-target interaction is to exploit the strong focusing forces that can be provided by a cloud of electrons trapped within a cylindrical volume by crossed electric and magnetic fields Such an electron-plasma lens was initially proposed by Gabor in 1947 [27]. Discharge-capillary active plasma lenses were investigated as compact devices for focusing 100 MeV-level electron beams produced by a gas-jet-based laser-plasma accelerator Both weak and strong chromatic effects [48] were observed with the potential to cause emittance degradation [49]. Simulation of the plasma discharge within the lens indicated that a high electron density, ∼5 × 10−7 cm−3, was produced

Plasma Characterisation

Findings

Conclusions