Review and demonstration of ultra-low-emittance photocathode measurements

In this paper we report on the generation of cold electron beams using a Cs 3 Sb photocathode grown by codeposition of Sb and Cs. By cooling the photocathode to 90 K we demonstrate a significant reduction in the mean transverse energy validating the long-standing speculation that the lattice temperature contributes to limiting the mean transverse energy or intrinsic emittance near the photoemission threshold, opening new frontiers in generating ultrabright beams. At 90 K, we achieve a record low intrinsic emittance of 0.2 μm (rms) per mm of laser spot diameter from an ultrafast (subpicosecond) photocathode with quantum efficiency greater than 7 × 10 −5 using a visible laser wavelength of 690 nm.

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“…1) [17]. We'll refer to this electron gun setup with the name of transverse energy meter (TEmeter) from now on.…”

Section: Resultsmentioning

confidence: 99%

Cold electron beams from cryocooled, alkali antimonide photocathodes

Cultrera

Karkare

Lee

et al. 2015

Phys. Rev. ST Accel. Beams

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“…The bialkali antimonide photocathodes, which have 10% electron yield at green light, can produce electron beams with smaller emittance than other semiconductor photocathodes (such as Cs 2 Te) and metal photocathodes driven by UV lasers. The MTE can be estimated by the following equation 17 where is the work function, is the reduction in the work function due to Schottky effect in the presence of the applied field gradient E , and is the photon energy. For the same accelerating gradient, at typical photon energies used with semiconductor cathodes as electron sources, bialkali antimonide photocathode shows smaller thermal emittance than Cs 2 Te photocathode 14 , 18 .…”

Section: Introductionmentioning

confidence: 99%

Long lifetime of bialkali photocathodes operating in high gradient superconducting radio frequency gun

Wang

Litvinenko

Pinayev

et al. 2021

Sci Rep

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High brightness, high charge electron beams are critical for a number of advanced accelerator applications. The initial emittance of the electron beam, which is determined by the mean transverse energy (MTE) and laser spot size, is one of the most important parameters determining the beam quality. The bialkali photocathodes illuminated by a visible laser have the advantages of high quantum efficiency (QE) and low MTE. Furthermore, Superconducting Radio Frequency (SRF) guns can operate in the continuous wave (CW) mode at high accelerating gradients, e.g. with significant reduction of the laser spot size at the photocathode. Combining the bialkali photocathode with the SRF gun enables generation of high charge, high brightness, and possibly high average current electron beams. However, integrating the high QE semiconductor photocathode into the SRF guns has been challenging. In this article, we report on the development of bialkali photocathodes for successful operation in the SRF gun with months-long lifetime while delivering CW beams with nano-coulomb charge per bunch. This achievement opens a new era for high charge, high brightness CW electron beams.

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“…The MTEs of photoelectrons were measured using the Transverse Energy meter (the TEmeter a low energy photoelectron gun) installed at the photocathode lab of Cornell University using the method of the voltage scan with electron beam energies in the range of 4 to 10 keV [21]. Due to the low average electron beam current achievable using an LED light source and the relative low QE of the sample at these wavelengths, the MTE measurements for sample A were only possible at the wavelengths of 265 and 300 nm.…”

Section: Photoemission Characterizationmentioning

confidence: 99%

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

Cultrera,

Rocco,

Shahedipour-Sandvik

et al. 2021

Preprint

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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 Energy (MTE) of electron of about 100 meV are measured at the operating wavelength of 265 nm. In a vacuum level of 3x10 −10 Torr the QE does not decrease after more than 24 hours of continuous operation. The lowest MTE, about 50 meV, is measured at 300 nm where the measured QE is 1.5x10 −5 . Surface characterizations reveal possible contribution to the MTE due to the surface morphology calling for more detailed studies.

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Review and demonstration of ultra-low-emittance photocathode measurements

Cited by 26 publications

References 32 publications

Cold electron beams from cryocooled, alkali antimonide photocathodes

Cold electron beams from cryocooled, alkali antimonide photocathodes

Long lifetime of bialkali photocathodes operating in high gradient superconducting radio frequency gun

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

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