High-brightness beam tests of the very high frequency gun at the Advanced Photo-injector EXperiment test facility at the Lawrence Berkeley National Laboratory

Sannibale, F.; Filippetto, D.; Qian, Houjun; Mitchell, Chad; Zhou, Feng; Vecchione, T.; Li, R. K.; Gierman, S.M.; Schmerge, John

doi:10.1063/1.5088521

Cited by 20 publications

(15 citation statements)

References 24 publications

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“…It is deployed to generate electron bunch with low emittance and high brightness. As the APEX-type electron gun cavity works at a relatively low frequency compared with the common rf-band gun, the beam dynamics properties evolution is intricate [31,32,33]. The relatively low energy of the beam at the exit of the gun cavity induces a strong and dominant space charge effect during the beam delivery, causing the nonlinear emittance growth that can not be compensated.…”

Section: Principle Of the Compensation Methodsmentioning

confidence: 99%

“…The two beam dynamics properties, transverse emittance and bunch length, are usually selected as the two objectives in the injector beam dynamics optimization strategy [30,31,32,33,34,35]. Normally, the tradeoff between the two parameters is obvious in particle accelerator beam dynamics design.…”

Section: Many-objective Photoinjector Beam Dynamics Optimization For ...mentioning

confidence: 99%

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Inhibition of Current-spike Formation Based on Longitudinal Phase Space Manipulation for High-Repetition-Rate X-ray FEL

Zhu,

Gu,

Yan

et al. 2021

Preprint

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The formation of a double-horn current profile is a challenging issue in the achievement of electron bunch with high peak current, especially for high-repetition-rate Xray free-electron lasers (XFELs) where more nonlinear and intricate beam dynamics propagation is involved. Here, we propose to correct the nonlinear beam longitudinal phase space distortion in the photoinjector section with a dual-mode buncher. In combination with the evolutionary many-objective beam dynamics optimization, this method is shown to be effective in manipulating the longitudinal phase space at the injector exit. Furthermore, the formation of the current spike is avoided after the multi-stage charge density modulation and electron bunch with a peak current of 1.6 kA is achieved for 100-pC bunch charge. Start-to-end simulations based on the Shanghai high-repetition-rate XFEL and extreme light facility demonstrate that the proposed scheme can increase the FEL pulse energy by more than 3 times in a cascading operation of echo-enabled harmonic generation and high-gain harmonic generation. Moreover, this method can also be used for longitudinal phase space shaping of electron beams operating at a high repetition rate to meet the specific demands of different researches.

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Section: Principle Of the Compensation Methodsmentioning

confidence: 99%

Section: Many-objective Photoinjector Beam Dynamics Optimization For ...mentioning

confidence: 99%

Inhibition of Current-spike Formation Based on Longitudinal Phase Space Manipulation for High-Repetition-Rate X-ray FEL

Zhu,

Gu,

Yan

et al. 2021

Preprint

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“…From all these electron guns, the VHF RF photo-gun is particularly advantageous for employment in user facilities due to its high performance and high reliability. In particular, the VHF RF photo-gun APEX developed at Lawrence Berkeley National Laboratory [17,18] is employed in the next generation FEL, LCLS-II [19].…”

Section: Introductionmentioning

confidence: 99%

Nanometre-scale emittance beams from a continuous-wave RF gun

Opanasenko,

Tibai,

Pepitone

et al. 2021

Preprint

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The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy gain of 0.4 MeV and a peak cathode field of 35 MV/m. Via massive numerical simulations, we exemplify three regimes of the gun operation: (i) 160 fC electron beams with a 5-nm-scale emittance for UEDs, (ii) 1.6 pC beams with a 20-nm-scale emittance for table-top FELs and dielectric-based accelerators, and (iii) 16 pC beams with a 50-nm-scale emittance for inverse Compton sources and other accelerator-based photon sources. We introduce a simple analytical model for the formation of the virtual cathode -the onset of the suppression of photoemission current due to space-charge forces. The model accounts for the laser pulse duration. Furthermore, our extensive numerical simulations indicate a well-pronounced maximum in the 5D beam brightness for the laser spot radius approximately 150% of that corresponding to the onset of the virtual cathode. The finding does not support the common approach in the literature that in the blowout regime the laser spot radius must be much larger than the critical radius corresponding to the virtual cathode onset.

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“…A dual-feed racetrack coupling scheme was analyzed in detail for the LLNL gun [15]. For the LCLS-II FEL [22], the APEX VHF-gun developed at LBNL [31][32][33] is adopted as the electron source. The power coupling is realized through two diametrically opposed, magnetic loop couplers on the cathode back wall of the cavity [34].…”

Section: Introductionmentioning

confidence: 99%

Frequency-detuning dependent transient coaxial rf coupler kick in an L -band long-pulse high-gradient rf photogun

Chen

Qian

Krasilnikov

et al. 2020

Phys. Rev. Accel. Beams

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A transverse kick resulting from the coaxial rf coupler in the L-band rf gun at the photoinjector test facility at DESY in Zeuthen (PITZ) has been systematically studied in simulations and further characterized in experiments. The used rf macro-pulse for the gun is typically 600 μs long and applied to produce a train of up to 2700 electron bunches. The kick is transient and found to be dependent on the detuning of the resonance frequency of the gun cavity. The frequency detuning within the rf pulse results in a variation in the kick strength along the pulse. This leads to a downstream orbit and size change of individual bunches within the train. Using 3D rf field distributions, calculated at resonant and detuned frequencies of the cavity, particle tracking simulations are performed to evaluate the integral kick location and strength, simulate its transient behaviors with respect to gun launch phase and detuned frequency of the gun cavity, and thereby emulate its impacts onto the electron bunch. In the experiments, the temperature of the cooling water for the gun is tuned, allowing detailed characterization of the frequency detuning within the rf pulse and thus measurements of the kick which are of practical interest for machine operation. The resulting orbit and size change along a 240 μs bunch train have been measured downstream at the injector exit for an rf gun peak power of about 5.7 MW. A measured focusing difference between head and tail of the bunch train is evaluated in terms of the gun solenoid current which provides more relevant information for overall tuning of the FELs. This is exemplarily given for both the under-and over-focusing case. The obtained results will be presented and discussed.

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High-brightness beam tests of the very high frequency gun at the Advanced Photo-injector EXperiment test facility at the Lawrence Berkeley National Laboratory

Cited by 20 publications

References 24 publications

Inhibition of Current-spike Formation Based on Longitudinal Phase Space Manipulation for High-Repetition-Rate X-ray FEL

Inhibition of Current-spike Formation Based on Longitudinal Phase Space Manipulation for High-Repetition-Rate X-ray FEL

Nanometre-scale emittance beams from a continuous-wave RF gun

Frequency-detuning dependent transient coaxial rf coupler kick in an L -band long-pulse high-gradient rf photogun

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