Benchmarking of 3D space charge codes using direct phase space measurements from photoemission high voltage DC gun

In situ Observation of Dark Current Emission in a High Gradient RF Photocathode Gun

Undesirable electron field emission (a.k.a. dark current) in high gradient RF photocathode guns deteriorates the quality of photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 um) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Dark current from the cathode has been observed to be dominated by several separated strong emitters. The field enhancement factor, beta, of selected regions on the cathode has been measured. The post scanning…

Single shot cathode transverse momentum imaging in high brightness photoinjectors

In state of the art photoinjector electron sources, thermal emittance from photoemission dominates the final injector emittance. Therefore, low thermal emittance cathode developments and diagnostics are very important. Conventional thermal emittance measurements for the high gradient gun are time-consuming and thus thermal emittance is not measured as frequently as quantum efficiency during the lifetime of photocathodes, although both are important properties for the photoinjector optimizations. In this paper, a single shot measurement of photoemission transverse momentum, i.e., thermal emitta…

Sources of Emittance in RF Photocathode Injectors: Intrinsic emittance, space charge forces due to non-uniformities, RF and solenoid effects

Advances in electron beam technology have been central to creating the current generation of x-ray free electron lasers and ultra-fast electron microscopes. These once exotic devices have become essential tools for basic research and applied science. One important beam technology for both is the electron source which, for many of these instruments, is the photocathode gun. The invention of the photocathode gun and the concepts of emittance compensation and beam matching in the presence of space charge and RF forces have made these high-quality beams possible. Achieving even brighter beams requ…

Thermal emittance measurements of a cesium potassium antimonide photocathode

Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56+/-0.03 mm-mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.

Nanometre-scale emittance beams from a continuous-wave RF gun

The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy…

碱金属锑化物光电阴极的高场亮度极限

High-Field Brightness Limits of Alkali-Antimonide Photocathodes

本研究在超过100 MV/m的射频枪中验证了碱金属锑化物光电阴极的稳健光发射，首次系统测量其高场亮度极限，发现近阈值发射可降低固有发射度并提升亮度。

Photoemission characterization of N-polar III-Nitride photocathodes as bright electron beam source for accelerator applications

We report on the growth and characterization of a new class of photocathode structures for application as electron sources to produce high brightness electron beams for accelerator applications. The sources are realized using III-Nitride materials and are designed to leverage the strong polarization field characteristic of this class material while grown in their wurtzite crystal structure to produce a negative electron affinity condition without the use of Cs, possibly allowing these materials to be operated in RF gun. A Quantum Efficiency (QE) of about 1x10$^{-3}$ and a Mean Transverse Energ…

Systematic benchmarking of planar nitrogen-incorporated ultrananocrystalline diamond field emission electron source: rf conditioning and beam spatio-temporal characteristics

Planar nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, has emerged as a unique field emission source attractive for accelerator applications because of its capability to generate high charge beam and handle moderate vacuum conditions. Most importantly, (N)UNCD sources are simple to produce: conventional high aspect ratio isolated emitters are not required to be formed on the surface, and the actual emitter surface roughness is on the order of only 100~nm. Careful reliability assessment of (N)UNCD is required before it may find routine application in accelerator systems. In the pre…