Positive-Ion Sources

Damage Characterisation of Tantalum Ion Source Electrodes and Reconditioning by Wire- and Powder-Based Laser Metal Deposition

“…This must have formed at the end of the deposition process, when the already solidified but still hot metal was exposed to environmental oxygen once the shielding gas flow was turned off. This oxide layer may have a beneficial effect by increasing the secondary emission coefficient of the material (i.e., the ratio of the emitted secondary electrons to the incident primary electrons), thus helping to sustain the glow discharge and produce the ion beam [3,40]. However, its actual effect on the electrode performance still needs to be evaluated by testing the restored cathodes under service conditions.…”

“…Due to its excellent high-temperature stability, corrosion resistance, and biocompatibility, tantalum is employed in specialised applications in the electronics, aerospace, nuclear, chemical, biomedical, and military fields [1,2]. Tantalum is also used to manufacture components for particle accelerators [3], such as the cathodes used in the Penning Ionisation Gauge (PIG) ion source of the compact superconducting cyclotron developed within the Advanced Molecular Image Technologies (AMIT) project [4,5] (Fig. 1a).…”

“…The ion source operates in a pure hydrogen atmosphere to generate high-energy H − ion beams for the production of 18 F and 11 C isotopes for positron emission tomography (PET) [4,6]. Tantalum is employed owing to its high melting point (3017 • C), low discharge voltage (1700 V), low work function (4.25 eV), and low sputtering coefficient in H 2 (16 mg/Ah) [3,7,8].…”