Design, construction and status of all niobium superconducting photoinjector at BNL

Abstract

We present here the design and construction of an all niobium superconducting RF injector to generate high average current, high brightness electron beam. A ?4 cell superconducting cavity has been designed, built, and tested. A cryostat has been built to cool the cavity to-2 K. The RF system can deliver up to 500 W at 1.3 GHz to the cavity. A mode-locked NdYV04 laser, operating at 266 nm with 0.15 W average power, phase locked to the RF, will irradiate a laser cleaned Nb surface at the back wall of the cavity. Description of critical components and their status are presented in the paper. Based on DC measurements, QE of up to lo4 can be expected from such cavity

Schemes and challenges for electron injectors operating in high repetition rate X-ray FELs

“…Nevertheless, in superconducting RF guns that operate in the low charge per bunch regime ($10 pC and less), cathodes made of superconducting metals such as niobium (QE $10 À5 at 250 nm) or lead (QE $10 À4 at 250 nm), still present an interesting option [56,57]. Indeed, these types of cathodes are able to operate at the cryogenic temperatures of the electron gun, significantly simplifying the mechanical and RF design of the cathode area and eliminating the issue of contamination of the cryogenic environment.…”

Nb-Pb Superconducting RF Gun

“…The design presented here follows the all niobium RFgun at BNL [4]. It preserves the simplicity of the BNL gun which utilizes cavity niobium back wall as the photoemitter to avoid all complications associated with inserted cathodes.…”

Optimization and beam dynamics of a superconducting radio-frequency gun

“…A simple and attractive approach to cavity/cathode design has been proposed at BNL [10]. The basic idea is to illuminate the back wall of the superconducting Nb cavity with UV laser, obtaining photoemission and the electromagnetic cavity from a single integral structure.…”

“…Some experimental efforts have been made recently to investigate the feasibility of an SRF photocathode gun [8,9]. Various proposals have been made to address the photocathode issue, including the direct use of the superconducting Nb material [10], the deposition of a thin layer of higher quantum efficiency material on the Nb substrate [11], and the introduction of a non-superconducting cathode that is thermally isolated from the rest of the SRF cavity [12]. It is crucial that a relatively high quantum efficiency (Z) be obtained from the photocathode, in order to lower the needed drive laser flux impinging on the cavity.…”