Experimental studies of dark current in a superconducting rf photoinjector

Xiang, Rong; Arnold, A.; Kamps, T.; Pan, Lü; Michel, P.; Murcek, Petr; Vennekate, Hannes; Staats, G.; Teichert, J.

doi:10.1103/physrevstab.17.043401

Cited by 21 publications

(14 citation statements)

References 18 publications

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“…The average dark current from a normal conducting rf gun at Los Alamos National Laboratory is 70 μA [22]. A superconducting rf photoinjector at Rossendorf shows nanoampere levels of dark current [23,24]. Although the dark current from the Advanced Photo-injector EXperiment (APEX) warm rf gun at the Lawrence Berkeley National Laboratory was measured to be greater than nanoampere level [25], a recent study showed the dark current was 0.1 nA at 750 keV [26].…”

Section: Dark Current Measurementmentioning

confidence: 99%

Operational experience of a 500 kV photoemission gun

Nishimori

Nagai

Hajima

et al. 2019

Phys. Rev. Accel. Beams

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Operational experience of a 500 kV photoemission gun at the compact energy recovery linac (cERL) of the High Energy Accelerator Research Organization is presented. The gun, developed at the Japan Atomic Energy Agency, was found to have failures in two out of the ten-segment ceramic insulator just after installation at cERL. The gun had been operated at 390 kV with eight segments until April 2015 and provided a 0.9 mA beam. An additional two-segment insulator was installed on the top of the existing insulators to recover the high-voltage performance. The gun was then conditioned up to 539 kV and has been operated stably at 500 kV. No discharge caused by the gun itself was observed at 500 kVonce the high threshold voltage for stable operation exceeded 500 kV. A dark current of a few picoamperes was generated at 500 kV from a photocathode puck with a semiconducting wafer, while no dark current was observed without a semiconducting wafer. Stable generation of a 500 keV beam with current greater than 0.8 mA was demonstrated for more than two hours.

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Section: Dark Current Measurementmentioning

confidence: 99%

Operational experience of a 500 kV photoemission gun

Nishimori

Nagai

Hajima

et al. 2019

Phys. Rev. Accel. Beams

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“…It should be emphasized that dark current suppression is a fundamental issue, entailing resolution of the nature of the field enhancement factor dating back to Fowler and Nordheim [116]. Another promising approach is to remove dark current after the gun using strip line kickers that may leave only a few nsec open to beam propagation [117]. This may be necessary, in particular for very low charge operation [36].…”

Section: Prospects For Higher Rf Frequency Higher Field Photoinjmentioning

confidence: 99%

Next generation high brightness electron beams from ultrahigh field cryogenic rf photocathode sources

Rosenzweig

Cahill

Dolgashev

et al. 2019

Phys. Rev. Accel. Beams

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Recent studies of the performance of radio-frequency (rf) copper cavities operated at cryogenic temperatures have shown a dramatic increase in the maximum achievable surface electric field. We propose to exploit this development to enable a new generation of photoinjectors operated at cryogenic temperatures that may attain, through enhancement of the launch field at the photocathode, a significant increase in fivedimensional electron beam brightness. We present detailed studies of the beam dynamics associated with such a system, by examining an S-band photoinjector operated at 250 MV=m peak electric field that reaches normalized emittances in the 40 nm-rad range at charges (100-200 pC) suitable for use in a hard x-ray free-electron laser (XFEL) scenario based on the LCLS. In this case, we show by start-to-end simulations that the properties of this source may give rise to high efficiency operation of an XFEL, and permit extension of the photon energy reach by an order of magnitude, to over 80 keV. The brightness needed for such XFELs is achieved through low source emittances in tandem with high current after compression. In the XFEL examples analyzed, the emittances during final compression are preserved using microbunching techniques. Extreme low emittance scenarios obtained at pC charge, appropriate for significantly extending temporal resolution limits of ultrafast electron diffraction and microscopy experiments, are also reviewed. While the increase in brightness in a cryogenic photoinjector is mainly due to the augmentation of the emission current density via field enhancement, further possible increases in performance arising from lowering the intrinsic cathode emittance in cryogenic operation are also analyzed. Issues in experimental implementation, including cavity optimization for lowering cryogenic thermal dissipation, external coupling, and cryocooler system, are discussed. We identify future directions in ultrahigh field cryogenic photoinjectors, including scaling to higher frequency, use of novel rf structures, and enabling of an extremely compact hard x-ray FEL.

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“…Two kinds of kickers have been evaluated, a low frequency resonant kicker and a stripline kicker [25][26][27]. The resonant kicker, shown in Fig.…”

Section: B Active Removalmentioning

confidence: 99%

Dark current studies on a normal-conducting high-brightness very-high-frequency electron gun operating in continuous wave mode

Huang

Filippetto

Papadopoulos

et al. 2015

Phys. Rev. ST Accel. Beams

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We report on measurements and analysis of a field-emitted electron current in the very-high-frequency (VHF) gun, a room temperature rf gun operating at high field and continuous wave (CW) mode at the Lawrence Berkeley National Laboratory (LBNL). The VHF gun is the core of the Advanced Photo-injector Experiment (APEX) at LBNL, geared toward the development of an injector for driving the next generation of high average power x-ray free electron lasers. High accelerating fields at the cathode are necessary for the high-brightness performance of an electron gun. When coupled with CW operation, such fields can generate a significant amount of field-emitted electrons that can be transported downstream the accelerator forming the so-called "dark current." Elevated levels of a dark current can cause radiation damage, increase the heat load in the downstream cryogenic systems, and ultimately limit the overall performance and reliability of the facility. We performed systematic measurements that allowed us to characterize the field emission from the VHF gun, determine the location of the main emitters, and define an effective strategy to reduce and control the level of dark current at APEX. Furthermore, the energy spectra of isolated sources have been measured. A simple model for energy data analysis was developed that allows one to extract information on the emitter from a single energy distribution measurement.

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Experimental studies of dark current in a superconducting rf photoinjector

Cited by 21 publications

References 18 publications

Operational experience of a 500 kV photoemission gun

Operational experience of a 500 kV photoemission gun

Next generation high brightness electron beams from ultrahigh field cryogenic rf photocathode sources

Dark current studies on a normal-conducting high-brightness very-high-frequency electron gun operating in continuous wave mode

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