Record high-average current from a high-brightness photoinjector

Dunham, Bruce; Barley, J.; Bartnik, Adam; Bazarov, Ivan; Cultrera, L.; Dobbins, John; Hoffstaetter, Georg; Johnson, Brent A.; Kaplan, R.; Karkare, Siddharth; Kostroun, V. O.; Li, Yulin; Liepe, Matthias; Liu, Xianghong; Loehl, F.; Maxson, Jared; Quigley, Peter; Reilly, J.; Rice, D.; Sabol, Daniel; Smith, Eric N.; Smolenski, K.; Tigner, M.; Vesherevich, V.; Widger, D.; Zhao, Zhi

doi:10.1063/1.4789395

Cited by 139 publications

(98 citation statements)

References 14 publications

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“…[1][2][3][4] Recently they have been investigated for use as high-current, low emittance electron sources for next generation accelerator applications such as Linac Coherent Light Source II (LCLS-II). 5 These applications require high quantum efficiency (QE) and long operational lifetime, just as photodetectors do, but also require good correlation of the emitted electrons (e.g., low beam emittance). Unfortunately, while traditional growth methods produce cathodes with a peak quantum efficiency in excess of 30%, these films are very rough and this roughness impacts the beam emittance.…”

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Synthesis and x-ray characterization of sputtered bi-alkali antimonide photocathodes

et al. 2017

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Synthesis and x-ray characterization of sputtered bi-alkali antimonide photocathodes

et al. 2017

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“…With this property in mind, we turn to the main purpose of this work: demonstrating that the Cornell ERL injector, a 5-15 MeV machine featuring a DC gun followed by a short SRF linac, can produce beams with a high degree of emittance preservation in the beam dynamics regime set by next generation light sources. Originally designed to create low emittance, moderate bunch charge (≤77 pC) beams at high (1.3 GHz) repetition rate for a full hard x-ray ERL, the Cornell injector currently holds the world record for high average current from a photoinjector with cathode lifetimes suitable for an operating user facility [18], as well as the record for lowest demonstrated emittance from a DC gun-based photoinjector at bunch charges of 19 and 77 pC [17]. As of this work, the Cornell injector remains largely the same as described in [17], with the most notable difference being the current operation of the DC gun at 395 kV.…”

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Demonstration of cathode emittance dominated high bunch charge beams in a DC gun-based photoinjector

Gulliford

Bartnik

Bazarov

et al. 2015

Applied Physics Letters

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We present the results of transverse emittance and longitudinal current profile measurements of high bunch charge (≥100 pC) beams produced in the DC gun-based Cornell Energy Recovery Linac Photoinjector. In particular, we show that the cathode thermal and core beam emittances dominate the final 95% and core emittance measured at 9-9.5 MeV. Additionally, we demonstrate excellent agreement between optimized 3D space charge simulations and measurement, and show that the quality of the transverse laser distribution limits the optimal simulated and measured emittances. These results, previously thought achievable only with RF guns, demonstrate that DC gun based photoinjectors are capable of delivering beams with sufficient single bunch charge and beam quality suitable for many current and next generation accelerator projects such as Energy Recovery Linacs (ERLs) and Free Electron Lasers (FELs).Linear electron accelerators boast a wide range of current and planned applications in the physical sciences. Examples include: x-ray sources [1-3], electron-ion coolers [4], Ultra-fast Electron Diffraction (UED) experiments [5][6][7][8], and fixed-target nuclear physics experiments [9]. A key feature of many of these applications is the potential to produce beams where the initial beam quality, set by the source, dominates the final beam quality at the usage point. This has lead to the design of a next generation of machines, such as high energy Energy Recovery Linacs (ERLs) [2], and Free Electron Lasers (FELs) [3] which could provide diffraction limited hard x-rays with orders of magnitude brighter beams than modern storage rings. The successful design and implementation of such machines has the potential to impact an impressively broad range of research in physics, chemistry, biology, and engineering.For next generation high energy x-ray sources like the proposed Linac Coherent Light Source-II (LCLS-II) [10], the creation (at MHz repetition rates) and effective transport of multi-MeV beams with high bunch charges (≥100 pC), picosecond bunch lengths, and sub-micron normalized transverse emittances represents a beam dynamics regime previously thought attainable only with RF gun based photoinjectors [11]. In this letter, we challenge this assumption, and show that the DC gun-based Cornell ERL injector can produce cathode emittance dominated beams which meet the bunch charge, emittance, and peak current specifications of a next generation light source. In doing so, we also demonstrate excellent agreement between measurement and simulation of the injector, and show that ultimate optimization of the emittance in high-brightness photoinjectors may require advanced transverse laser shaping along with the use of low intrinsic emittance photocathodes.Before discussing our experimental results, we review the definitions of the key figures of merit for beam quality in high-brightness accelerators relevant for this work: emittance and brightness. For the beam densities encountered in this work (10 17 -10 18 e/m 3 ), classical relativisti...

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“…That is not to say that these thermal limitations cannot be overcome: indeed the DC photoemissive gun recently developed at Cornell [29] has impressive specifications and is the only photocathode gun we are aware of with similar repetition rates (1.3 GHz), bunch charge (77 pC), and average current (65 mA). However the complexity and cost of such a system make it impractical for the niche for which we propose the thermionic gun is better suited: cavity enhanced inverse Compton x-ray and gamma ray systems.…”

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confidence: 99%

Back-bombardment compensation in microwave thermionic electron guns

Kowalczyk

Madey

2014

Phys. Rev. ST Accel. Beams

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The development of capable, reliable, and cost-effective compact electron beam sources remains a long-standing objective of the efforts to develop the accelerator systems needed for on-site research and industrial applications ranging from electron beam welding to high performance x-ray and gamma ray light sources for element-resolved microanalysis and national security. The need in these applications for simplicity, reliability, and low cost has emphasized solutions compatible with the use of the long established and commercially available pulsed microwave rf sources and L-, S-or X-band linear accelerators. Thermionic microwave electron guns have proven to be one successful approach to the development of the electron sources for these systems providing high macropulse average current beams with picosecond pulse lengths and good emittance out to macropulse lengths of 4-5 microseconds. But longer macropulse lengths are now needed for use in inverse-Compton x-ray sources and other emerging applications. We describe in this paper our approach to extending the usable macropulse current and pulse length of these guns through the use of thermal diffusion to compensate for the increase in cathode surface temperature due to back-bombardment.

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Record high-average current from a high-brightness photoinjector

Cited by 139 publications

References 14 publications

Synthesis and x-ray characterization of sputtered bi-alkali antimonide photocathodes

Synthesis and x-ray characterization of sputtered bi-alkali antimonide photocathodes

Demonstration of cathode emittance dominated high bunch charge beams in a DC gun-based photoinjector

Back-bombardment compensation in microwave thermionic electron guns

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