Abstract:High-bunch-charge photoemission electron-sources operating in a continuous wave (CW) mode are required for many advanced applications of particle accelerators, such as electron coolers for hadron beams, electronion colliders, and free-electron lasers (FELs). Superconducting RF (SRF) has several advantages over other electron-gun technologies in CW mode as it offers higher acceleration rate and potentially can generate higher bunch charges and average beam currents. A 112 MHz SRF electron photoinjector (gun) wa… Show more
“…The photocathode stalk insertion system and cathode related components were designed and fabricated by BNL and Department of Physics and Astronomy at Stony Brook University (SBU). Detailed description of the gun RF design and its performance can be found in reference 25 . Figure 1 SRF gun 3D model.…”
High brightness, high charge electron beams are critical for a number of advanced accelerator applications. The initial emittance of the electron beam, which is determined by the mean transverse energy (MTE) and laser spot size, is one of the most important parameters determining the beam quality. The bialkali photocathodes illuminated by a visible laser have the advantages of high quantum efficiency (QE) and low MTE. Furthermore, Superconducting Radio Frequency (SRF) guns can operate in the continuous wave (CW) mode at high accelerating gradients, e.g. with significant reduction of the laser spot size at the photocathode. Combining the bialkali photocathode with the SRF gun enables generation of high charge, high brightness, and possibly high average current electron beams. However, integrating the high QE semiconductor photocathode into the SRF guns has been challenging. In this article, we report on the development of bialkali photocathodes for successful operation in the SRF gun with months-long lifetime while delivering CW beams with nano-coulomb charge per bunch. This achievement opens a new era for high charge, high brightness CW electron beams.
“…The photocathode stalk insertion system and cathode related components were designed and fabricated by BNL and Department of Physics and Astronomy at Stony Brook University (SBU). Detailed description of the gun RF design and its performance can be found in reference 25 . Figure 1 SRF gun 3D model.…”
High brightness, high charge electron beams are critical for a number of advanced accelerator applications. The initial emittance of the electron beam, which is determined by the mean transverse energy (MTE) and laser spot size, is one of the most important parameters determining the beam quality. The bialkali photocathodes illuminated by a visible laser have the advantages of high quantum efficiency (QE) and low MTE. Furthermore, Superconducting Radio Frequency (SRF) guns can operate in the continuous wave (CW) mode at high accelerating gradients, e.g. with significant reduction of the laser spot size at the photocathode. Combining the bialkali photocathode with the SRF gun enables generation of high charge, high brightness, and possibly high average current electron beams. However, integrating the high QE semiconductor photocathode into the SRF guns has been challenging. In this article, we report on the development of bialkali photocathodes for successful operation in the SRF gun with months-long lifetime while delivering CW beams with nano-coulomb charge per bunch. This achievement opens a new era for high charge, high brightness CW electron beams.
“…BNL has two SRF guns with bialkali photocathodes. One is the 704 MHz SRF gun, used as the prototype for the Energy Recovery Linac (ERL) [6], and the other is the 112 MHz QWR SRF gun used for the proof-of-principle experiments for coherent electron cooling (CeC) [7].…”
High-average-current, high-brightness electron sources have important applications, such as in highrepetition-rate free-electron lasers, or in the electron cooling of hadrons. Bialkali photocathodes are promising high-quantum-efficiency (QE) cathode materials, while superconducting rf (SRF) electron guns offer continuous-mode operation at high acceleration, as is needed for high-brightness electron sources. Thus, we must have a comprehensive understanding of the performance of bialkali photocathode at cryogenic temperatures when they are to be used in SRF guns. To remove the heat produced by the radio-frequency field in these guns, the cathode should be cooled to cryogenic temperatures. We recorded an 80% reduction of the QE upon cooling the K 2 CsSb cathode from room temperature down to the temperature of liquid nitrogen in Brookhaven National Laboratory (BNL)'s 704 MHz SRF gun. We conducted several experiments to identify the underlying mechanism in this reduction. The change in the spectral response of the bialkali photocathode, when cooled from room temperature (300 K) to 166 K, suggests that a change in the ionization energy (defined as the energy gap from the top of the valence band to vacuum level) is the main reason for this reduction. We developed an analytical model of the process, based on Spicer's three-step model. The change in ionization energy, with falling temperature, gives a simplified description of the QE's temperature dependence. We also developed a 2D Monte Carlo code to simulate photoemission that accounts for the wavelength-dependent photon absorption in the first step, the scattering and diffusion in the second step, and the momentum conservation in the emission step. From this simulation, we established a correlation between ionization energy and reduction in the QE. The simulation yielded results comparable to those from the analytical model. The simulation offers us additional capabilities such as calculation of the intrinsic emittance, the temporal response, and the thickness dependence of the QE for the K 2 CsSb photocathode.
“…With this assumption and from Eqs. (4), (5), (7), and (9), the maximum response of the system at any harmonic excitation can be completely obtained.…”
Section: A One-dimensional Motionmentioning
confidence: 99%
“…The coaxial quarter wave resonator (QWR) is widely used in the low β section of heavy ion superconducting accelerators [1][2][3][4][5] and in addition has been developed in a deflecting mode geometry for high-luminosity colliders [6] and even as a superconducting rf gun [7]. Its operational rf mode resonated in a quarter wavelength brings compactness but also an up and down asymmetry, which poses issues of beam steering as addressed in Refs.…”
The mechanism of the damper parameters impacting on the maximum cavity detuning at a given excitation is investigated. An analytical model of the damper has been derived to predict the nonlinear response. Numerical results from simulations in ANSYS confirmed the model over a wide range of excitation. An experimental demonstration has been conducted successfully on a test bench. Online measurements taken on the ISAC-II superconducting linac at TRIUMF further verify the analytical model.
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