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The DCU laser ion source

Yeates, Patrick and Costello, John T. and Kennedy, Eugene T. (2010) The DCU laser ion source. Review of Scientific Instruments, 81 (4). 043305-1. ISSN 0034-6748

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Abstract

Laser ion sources are used to generate and deliver highly charged ions of various masses and energies. We present details on the design and basic parameters of the DCU laser ion source (LIS). The theoretical aspects of a high voltage (HV) linear LIS are presented and the main issues surrounding laser-plasma formation, ion extraction and modeling of beam transport in relation to the operation of a LIS are detailed. A range of laser power densities (I ∼ 108–1011 W cm−2) and fluences (F = 0.1–3.9 kJ cm−2) from a Q-switched ruby laser (full-width half-maximum pulse duration ∼ 35 ns, λ = 694 nm) were used to generate a copper plasma. In “basic operating mode,” laser generated plasma ions are electrostatically accelerated using a dc HV bias (5–18 kV). A traditional einzel electrostatic lens system is utilized to transport and collimate the extracted ion beam for detection via a Faraday cup. Peak currents of up to I ∼ 600 μA for Cu+ to Cu3+ ions were recorded. The maximum collected charge reached 94 pC (Cu2+). Hydrodynamic simulations and ion probe diagnostics were used to study the plasma plume within the extraction gap. The system measured performance and electrodynamic simulations indicated that the use of a short field-free (L = 48 mm) region results in rapid expansion of the injected ion beam in the drift tube. This severely limits the efficiency of the electrostatic lens system and consequently the sources performance. Simulations of ion beam dynamics in a “continuous einzel array” were performed and experimentally verified to counter the strong space-charge force present in the ion beam which results from plasma extraction close to the target surface. Ion beam acceleration and injection thus occur at “high pressure.” In “enhanced operating mode,” peak currents of 3.26 mA (Cu2+) were recorded. The collected currents of more highly charged ions (Cu4+–Cu6+) increased considerably in this mode of operation.

Item Type:Article (Published)
Refereed:Yes
Subjects:Physical Sciences > Physics
DCU Faculties and Centres:Research Initiatives and Centres > National Centre for Plasma Science and Technology (NCPST)
DCU Faculties and Schools > Faculty of Science and Health > School of Physical Sciences
Publisher:American Institute of Physics
Official URL:http://dx.doi.org/10.1063/1.3374123
Copyright Information:Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments and may be found at http://dx.doi.org/10.1063/1.3374123 .
Funders:Enterprise Ireland
ID Code:15629
Deposited On:06 Aug 2010 11:11 by DORAS Administrator. Last Modified 06 Aug 2010 11:14

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