Abstract
In order to find electron sources of low emittance and high quantum efficiency, single tip cathodes with a microstructured surface are investigated. Emission currents up to 310 A were obtained, by combining a 2 ns, 50 kV accelerating voltage pulse with a 266 nm wavelength, picosecond (sigma(t) = 6.2 ps) laser delivering a few mu J pulse energy. The multifilamentary cylindric Nb3Sn tip with a typical diameter of 0.8 mm provides quantum efficiencies up to 0.5%. The microstructured needle has also been tested in a combined diode-rf electron gun with 500 kV, 250 ns pulsed bias voltage as a first step towards reducing emittance-spoiling space-charge forces.
Highlights
In order to find better metallic cathode materials, capable of producing high-charge beams with low emittance, we have recently investigated [1] metallic composite multifilamentary wires of the type used in the superconducting magnet technology (LHC, ITER) and known in the literature as low-temperature, technological superconductors
Gated field emitter arrays (FEA) could in principle deliver the required low emittance but the technology suffers from very low charge extraction, cumbersome preparation, and inhomogeneous electron beam profiles
The surface roughness with a moderate geometrical field enhancement of the same order as that observed in the low-charge regime ( $ 2000 mÀ1), together with a surface plasmon effect, can enhance the charge emission at the filament level or even at a smaller length scale, resulting in the large fictitious values of the field-enhancement factor from the three-step fit with the Schottky effect included
Summary
In order to find better metallic cathode materials, capable of producing high-charge beams with low emittance, we have recently investigated [1] metallic composite multifilamentary wires of the type used in the superconducting magnet technology (LHC, ITER) and known in the literature as low-temperature, technological superconductors. Gated FEAs could in principle deliver the required low emittance but the technology suffers from very low charge extraction, cumbersome preparation, and inhomogeneous electron beam profiles. This makes them still inappropriate as reliable electron sources for large scale facilities [2,6,9,10,11,12,13]. The multifilamentary Nb3Sn wire is an excellent candidate for a high brightness electron source For these metal wires we have estimated a low emittance in spite of the large beam charge. IV where the results of the multifilamentary-wire cathode in a 500 kV combined diode-rf electron gun [15] are discussed
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