| Paper | Title | Page |
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| TUPWA059 | Modeling of Photoemission and Electron Spin Polarization from NEA GaAs Photocathodes | 1556 |
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Funding: Work supported by The George Washington University and Thomas Jefferson National Accelerator Facility. Many nuclear-physics and particle-physics scientific laboratories, including Thomas Jefferson National Accelerator Facility, Newport News, VA 23606 (Jefferson Lab) which studies parity violation and nucleon spin structure, require polarized electron sources. At present, photoemission from strained GaAs activated to negative electron affinity (NEA) is a main source of polarized electrons. Future experiments at advanced electron colliders will require highly efficient polarized electron beams, which sets new requirements for photocathodes in terms of high quantum efficiency (QE) (>>1%) and spin polarization (~85%). Development of such materials includes modeling and design of photocathodes, material growth, fabrication of photocathodes, and photocathode testing. The purpose of the present work is to develop a semi-phenomenological model, which could predict photoemission and electron spin polarization from NEA GaAs photocathodes. Detailed Monte Carlo simulation and modeling of physical processes in photocathodes is important for optimization of their design in order to achieve high QE and reduce depolarization mechanisms. Electron-phonon interactions near the surface and influence of the presence of quantum heterostructures on the diffusion length are studied in depth. Simulation results will be compared to the experimental results obtained at Jefferson Lab and can be used to optimize the photocathode design and material growth, and thus develop high-polarization high-brightness electron source. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA059 | |
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| TUPHA013 | Skew-Quad Parametric-Resonance Ionization Cooling: Theory and Modeling | 1993 |
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Funding: This work was supported in part by U.S. DOE STTR Grants DE-SC0005589 and DE-SC0007634. Muon beam ionization cooling is a key component for the next generation of high-luminosity muon colliders. To reach adequately high luminosity without excessively large muon intensities, it was proposed previously to combine ionization cooling with techniques using a parametric resonance (PIC). Practical implementation of PIC proposal is a subject of this report. We show that an addition of skew quadrupoles to a planar PIC channel gives enough flexibility in the design to avoid unwanted resonances, while meeting the requirements of radially-periodic beam focusing at ionization-cooling plates, large dynamic aperture and an oscillating dispersion needed for aberration corrections. Theoretical arguments are corroborated with models and a detailed numerical analysis, providing step-by-step guidance for the design of Skew-quad PIC (SPIC) beamline. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPHA013 | |
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| WEPJE002 | Photoinjector Improvement and Control by Surface Acoustic Waves | 2678 |
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| A new technique is being developed to enhance the efficiency of photocathodes used for electron sources to improve emission capabilities of electron sources, such as bunch charge and average current. The proposed technique is based on the use of surface acoustical waves (SAW) generated on the piezoelectric surface of a GaAs photocathode. The generation of SAW on piezoelectric substrates is known to produce strong piezoelectric fields that propagate on the surface of the material. These fields can significantly suppress recombination effects and result in enhanced quantum efficiency of photoemission. Experimental measurements of photoemission quantum efficiency will be done on semiconductors used as photocathode materials (e.g., GaAs) in presence of SAW with varied parameters. The experimental results will be used as input for physics modeling that will provide a basis for design of operational SAW-enhanced photocathodes. While the improved quantum efficiency and parameter control expected from the use of SAW will be useful for many research devices and accelerators, the commercialization of such a widespread field as electron microscopy is compelling. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPJE002 | |
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| WEPJE015 | Muon Tracking Studies in a Skew Parametric Resonance Ionization Cooling Channel | 2705 |
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Funding: This work was supported in part by U.S. DOE STTR Grant DE-SC0005589. This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Skew Parametric-resonance Ionization Cooling (SPIC) is an extension of the Parametric-resonance Ionization Cooling (PIC) framework that has previously been explored as the final 6D cooling stage of a high-luminosity muon collider. The addition of skew quadrupoles to the PIC magnetic focusing channel induces coupled dynamic behavior of the beam that is radially periodic. The periodicity of the radial motion allows for the avoidance of unwanted resonances in the horizontal and vertical transverse planes, while still providing periodic locations at which ionization cooling components can be implemented. A first practical implementation of the magnetic field components required in the SPIC channel is modeled in MADX. Dynamic features of the coupled correlated optics with and without induced parametric resonance are presented and discussed. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPJE015 | |
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