Initial beam dynamics simulations of a high-average-current field-emission electron source in a superconducting radiofrequency gun

In electron beams where space charge plays an important role in the beam transport, the beams’ transverse and longitudinal properties will become coupled. One example of this is the transverse–longitudinal correlation produced in a current-modulated beam generated in a DC electron gun, formed through the competition between the time-dependent radial space charge force and the time-independent radial focusing force. This correlation will cause both the slice radius and divergence of the beam extracted from the gun to depend on the slice current. Here we consider the transport of such a beam in a linearly tapered solenoid focusing channel. Transport performance was generally improved with longer taper lengths, minimal initial correlation between slice divergence and slice current, and moderate degrees of initial correlation between initial slice radius and slice current. Performance was also generally improved with lower slice emittances, although surprisingly transport was improved by slightly increasing the assumed slice emittance in certain limited circumstances.

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Supression of shielding effect of large area field emitter cathode in radio frequency gun environment

Sathya,

Sarkar,

Bakhtsingh

et al. 2024

Phys. Scr.

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Using large area field emitters (LAFE) as cathodes for RF gun injectors offers significant potential for creating compact, high-power, and high-brightness electron beams, crucial for advanced accelerator technologies. However, when subjected to DC electric fields, LAFEs face significant challenges due to the shielding effect, which limits emission from central emitters and decreases overall current density. Overcoming the shielding effect in an RF gun environment is essential to meet the required beam quality in accelerators. The current distribution of LAFE under DC conditions is influenced by several geometric parameters, such as emitter height, inter-emitter distance, aspect ratio, and the number of emitters. Moreover, in an RF gun setup, LAFEs experience varying macroscopic electric fields at different emitter positions, altering the current distribution compared to DC fields. In this study, we have systematically examined the impact of various LAFE parameters on their field emission performance in an RF gun environment. We have adopted a semi-analytical approach to estimate the current distribution of LAFE, combining analytically calculated field enhancement factors (γ) with numerically calculated applied RF field values. After validating the method with COMSOL simulations, we have applied it to estimate the current distribution of an LAFE cathode integrated into a ½ cell S-band (2856 MHz) gun. The simulation results indicate that, under favorable conditions, a Gaussian spatial beam distribution can be achieved with LAFE, thus mitigating the shielding effect typical in DC fields. By optimizing various LAFE parameters, the desired current and beam distribution patterns can be attained. This study highlights a promising approach for designing LAFE cathodes for RF guns, which could advance accelerator-related technologies.

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Initial beam dynamics simulations of a high-average-current field-emission electron source in a superconducting radiofrequency gun

Cited by 4 publications

References 10 publications

Design of a compact integrated high-average power superconducting radio-frequency (SRF) electron beam source

Design of a compact integrated high-average power superconducting radio-frequency (SRF) electron beam source

Transport of intense beams with current-dependent initial conditions in linearly tapered solenoid channels

Supression of shielding effect of large area field emitter cathode in radio frequency gun environment

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