Design, conditioning, and performance of a high voltage, high brightness dc photoelectron gun with variable gap

Maxson, Jared; Bazarov, Ivan; Dunham, Bruce; Dobbins, John; Liu, Xianghong; Smolenski, K.

doi:10.1063/1.4895641

Cited by 30 publications

(20 citation statements)

References 17 publications

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“…Currently, polarized electron beams are mainly produced in storage rings via radiative polarization due to the Sokolov-Ternov effect [8] or by extracting polarized electrons [9] directly from polarized atoms and polarized photocathodes [10]. However, the maximal electric current of polarized electron beams both from storage rings [11,12] and from photocathodes [13][14][15] is limited to less than 10 −1 ampere due to their operational voltages. Other methods based on spin filters [16], Stern-Gerlach-like beam splitters [17], and radiative polarization [18] also yield relatively low currents.…”

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confidence: 99%

Polarized Laser-WakeField-Accelerated Kiloampere Electron Beams

2019

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High-flux polarized particle beams are of critical importance for the investigation of spin-dependent processes, such as in searches of physics beyond the Standard Model, as well as for scrutinizing the structure of solids and surfaces in material science. Here we demonstrate that kiloampere polarized electron beams can be produced via laser-wakefield acceleration from a gas target. A simple theoretical model for determining the electron beam polarization is presented and supported with self-consistent three-dimensional particle-in-cell simulations that incorporate the spin dynamics. By appropriately choosing the laser and gas parameters, we show that the depolarization of electrons induced by the laser-wakefield-acceleration process can be as low as 10%. Compared to currently available sources of polarized electron beams, the flux is increased by four orders of magnitude.

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confidence: 99%

Polarized Laser-WakeField-Accelerated Kiloampere Electron Beams

2019

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“…1 shows the Cornell injector, merger section, diagnostic beamline, and main linac. For these measurements, the segmented Cornell DC gun was high voltage processed up to roughly 350 kV using the same techniques described in [20]. However, given the limited number of photocathodes currently available for the CBETA project, the gun voltage was set to 300 Screen MS1CRV02 MS1DIP03 MS1QUA03 MS1QUA04 MS1DIP04 MS1DIP05 MS1QUA05 MS1QUA06 MS1DIP06 MS1CRV03 MS1QUA07 MS1DIP07 MS1CRV04 MS1QUA08 MS1DPB08 IFASCR0A IFABPM01 IFASCR01 IFABPM02 IFABPM03 IFASCR02 IFABPM04 IFASCR0B IS1SCR02 IS1BPM05 IS1SCR01 IS1BPM06 IS1BPM04 IS1BPM03 IS1BPM02 IS1BPM01 H Dipole V Dipole Quad FAT Splitter (S1) and 1st Arc Girder (FA) Layout kV in order to eliminate any risk of degradation from possible vacuum activity at higher voltages.…”

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confidence: 99%

Beam Commissioning Results from the CBETA Fractional Arc Test (CBETA Note 030)

Gulliford

Peggs

Banerjee

et al. 2019

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This work describes first commissioning results from the Cornell Brookhaven ERL Test Accelerator fractional arc test. These include the recommissioning of the Cornell photoinjector, the first full energy operation of the main linac with beam, as well as commissioning of the lowest energy matching beamline (splitter) and a partial section of the Fixed Field Alternating gradient (FFA) return loop featuring first production Halbach style permanent magnets. Achieving these tasks required characterization of the injection beam, calibration and phasing of the main linac cavities, demonstration of the required 36 MeV energy gain, and measurement of the splitter line horizontal dispersion and R56 at the nominal 42 MeV. In addition, a procedure for determining the BPM offsets, as well as the tune per cell in the FFA section via scanning the linac energy and inducing betatron oscillations around the periodic orbit in the fractional arc was developed and tested. A detailed comparison of these measurements to simulation is discussed.

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“…Once fabricated at the machine shop, the relatively rough surface of the electrode must be mechanically polished by hand using silicon carbide paper and diamond grit, to obtain a smooth surface free of protrusions [28]. This is a time- electropolishing as a means to speed electrode preparation [31,102]; however, our recent tests indicate electropolished electrodes do not respond to gas conditioning as favorably as mechanically polished electrodes [103,104]. Niobium electrodes perform well at a high voltage when surfaces are etched with a mixture of strong acids-a technique known as buffered chemical polishing (BCP) [92].…”

Section: Introductionmentioning

confidence: 99%

Thin film studies toward improving the performance of accelerator electron sources

Mamun

2016

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Future electron accelerators require DC high voltage photoguns to operate beyond the present state of the art to conduct new experiments that require ultra-bright electron beams with high average current and higher bunch charge. To meet these demands, the accelerators must demonstrate improvements in a number of photogun areas including vacuum, field emission elimination in high voltage electrodes, and photocathodes. This dissertation illustrates how these improvements can be achieved by the application of suitable thin-films to the photogun structure for producing ultra-bright electron beams.This work is composed of three complementary studies. First, the outgassing rates of three nominally identical 304L stainless steel vacuum chambers were studied to determine the effects of chamber coatings (silicon and titanium nitride) and heat treatments. For an uncoated stainless steel chamber, the diffusion limited outgassing was taken over by the recombination limited process as soon as a low outgassing rate of ~1.79(0.05)  10 -13 Torr L s -1 cm -2 was achieved. An amorphous silicon coating on the stainless steel chambers exhibited recombination limited behavior and any heat treatment became ineffective in reducing the outgassing rate. A TiN coated chamber yielded the smallest apparent outgassing rate of all the chambers: 6.44(0.05)  10 -13 Torr L s -1 cm -2 following an initial 90 °C bake and 2(20)  10 -16 Torr L s -1 cm -2 following the final bake in the series. This perceived low outgassing rate was attributed to the small pumping nature of TiN coating itself.Second, the high voltage performance of three TiN-coated aluminum electrodes, before and after gas conditioning with helium, were compared to that of bare aluminum electrodes and electrodes manufactured from titanium alloy (Ti-6Al-4V). This study suggests that aluminum electrodes, coated with TiN, could simplify the task of implementing photocathode cooling, which is required for future high current electron beam applications. The best performing TiNcoated aluminum electrode demonstrated less than 15 pA of field emission current at -175 kV for a 10 mm cathode/anode gap, which corresponds to a field strength of 22.5 MV/m. Third, the effect of antimony thickness on the performance of bialkali-antimonide photocathodes was studied. The high-capacity effusion source enabled us to successfully manufacture photocathodes having a maximum QE around 10% and extended low voltage 1/e lifetime (> 90 days) at 532 nm via the co-deposition method, with relatively thick layers of antimony (≥ 300 nm). We speculate that alkali co-deposition provides optimized stoichiometry for photocathodes manufactured using thick Sb layers, which could serve as a reservoir for the alkali.In summary, this research examined the effectiveness of thin films applied on photogun chamber components to achieve an extremely high vacuum, to eliminate high voltage induced field emission from electrodes, and to generate photocurrent with high quantum yield with an extended operational lifetime. Simult...

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Design, conditioning, and performance of a high voltage, high brightness dc photoelectron gun with variable gap

Cited by 30 publications

References 17 publications

Polarized Laser-WakeField-Accelerated Kiloampere Electron Beams

Polarized Laser-WakeField-Accelerated Kiloampere Electron Beams

Beam Commissioning Results from the CBETA Fractional Arc Test (CBETA Note 030)

Thin film studies toward improving the performance of accelerator electron sources

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