DC High Voltage Conditioning of Photoemission Guns at Jefferson Lab FEL

Hernandez‐Garcia, C.; Benson, S.V.; Biallas, G.; Bullard, D.; Evtushenko, P.; Jordan, K.; Klopf, Michael; Sexton, Daniel; Tennant, Christopher; Walker, R.P.; Williams, Gwyn

doi:10.1063/1.3215595

Cited by 14 publications

(11 citation statements)

References 1 publication

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“…It is believed the krypton becomes ionized in the presence of field emission and then attracted to the field emitters, changing their geometrical shape from sharp to blunt via sputtering [29]. Helium inert gas processing is a common technique to eliminate field emission inside SRF cavities [30], but is not very effective at eliminating field emission inside DC high voltage photoguns [28]. It is believed the heavier krypton gas imparts more kinetic energy to the field emitter.…”

Section: Krypton Processingmentioning

confidence: 99%

“…When stubborn field emitters would not burn off via conventional high voltage processing, the cathode samples were subjected to krypton processing [28]. This technique involved introducing a small amount of krypton gas into the vacuum chamber while the cathode electrode was biased at high voltage using a gap/field strength that produced significant field emission ($ few As).…”

Section: Krypton Processingmentioning

confidence: 99%

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Evaluation of niobium as candidate electrode material for dc high voltage photoelectron guns

BastaniNejad

Mohamed

Elmustafa

et al. 2012

Phys. Rev. ST Accel. Beams

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The field emission characteristics of niobium electrodes were compared to those of stainless steel electrodes using a DC high voltage field emission test apparatus. A total of eight electrodes were evaluated: two 304 stainless steel electrodes polished to mirrorlike finish with diamond grit and six niobium electrodes (two single-crystal, two large-grain, and two fine-grain) that were chemically polished using a buffered-chemical acid solution. Upon the first application of high voltage, the best large-grain and single-crystal niobium electrodes performed better than the best stainless steel electrodes, exhibiting less field emission at comparable voltage and field strength. In all cases, field emission from electrodes (stainless steel and/or niobium) could be significantly reduced and sometimes completely eliminated, by introducing krypton gas into the vacuum chamber while the electrode was biased at high voltage. Of all the electrodes tested, a large-grain niobium electrode performed the best, exhibiting no measurable field emission (< 10 pA) at 225 kV with 20 mm cathode/anode gap, corresponding to a field strength of 18:7 MV=m.

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Section: Krypton Processingmentioning

confidence: 99%

Section: Krypton Processingmentioning

confidence: 99%

Evaluation of niobium as candidate electrode material for dc high voltage photoelectron guns

BastaniNejad

Mohamed

Elmustafa

et al. 2012

Phys. Rev. ST Accel. Beams

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“…The basis for these introductory comments stems from reports of accelerator operation at a handful of locations [4][5][6][7][8]. Notably, the Jefferson Lab (JLab) free electron laser (FEL) employs GaAs inside a dc high voltage photogun biased at 350 kV and routinely operates at 5 mA average current [8], although occasional high voltage discharges sometimes necessitate time consuming photocathode replacement.…”

Section: Introductionmentioning

confidence: 99%

“…Notably, the Jefferson Lab (JLab) free electron laser (FEL) employs GaAs inside a dc high voltage photogun biased at 350 kV and routinely operates at 5 mA average current [8], although occasional high voltage discharges sometimes necessitate time consuming photocathode replacement. The Boeing FEL used K 2 CsSb inside a normal conducting rf gun and produced a maximum average current of 32 mA [3].…”

Section: Introductionmentioning

confidence: 99%

Charge lifetime measurements at high average current using aK2CsSbphotocathode inside a dc high voltage photogun

Mammei

Suleiman

Feingold

et al. 2013

Phys. Rev. ST Accel. Beams

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Two K 2 CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure $10 À11 Torr. These photocathodes were evaluated using a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at wavelengths 440 or 532 nm, to generate dc electron beams at currents up to 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without measurable quantum efficiency decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. Under other conditions the charge lifetime was poor due to extensive ion bombardment under severely degraded vacuum conditions, and as a result of localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope to determine surface morphology.

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“…9 Such electron guns are under development for future ERLs in many laboratories. [10][11][12][13] The goals of these gun development programs are average current of 10-100 mA and normalized emittance of 0.1-1 mm mrad. To suppress emittance growth by space charge effect, the gun voltage must be 500 kV or higher.…”

Section: Introductionmentioning

confidence: 99%

High-voltage testing of a 500-kV dc photocathode electron gun

Nagai

Hajima

Nishimori

et al. 2010

Review of Scientific Instruments

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A high-voltage dc photocathode electron gun was successfully conditioned up to a voltage of 550 kV and a long-time holding test for 8 h was demonstrated at an acceleration voltage of 500 kV. The dc photocathode electron gun is designed for future light sources based on energy-recovery linac and consists of a Cockcroft-Walton generator, a segmented cylindrical ceramic insulator, guard-ring electrodes, a support-rod electrode, a vacuum chamber, and a pressurized insulating gas tank. The segmented cylindrical ceramic insulator and the guard-ring electrodes were utilized to prevent any damage to the insulator from electrons emitted by the support-rod electrode.

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DC High Voltage Conditioning of Photoemission Guns at Jefferson Lab FEL

Cited by 14 publications

References 1 publication

Evaluation of niobium as candidate electrode material for dc high voltage photoelectron guns

Evaluation of niobium as candidate electrode material for dc high voltage photoelectron guns

Charge lifetime measurements at high average current using aK2CsSbphotocathode inside a dc high voltage photogun

High-voltage testing of a 500-kV dc photocathode electron gun

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