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John F. Schmerge - One of the best experts on this subject based on the ideXlab platform.
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Quantum efficiency and thermal Emittance of metal photocathodes
Physical Review Special Topics - Accelerators and Beams, 2009Co-Authors: D.h. Dowell, John F. SchmergeAbstract:Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths with major advances occurring since the invention of the photocathode gun and the realization of Emittance compensation. These state-of-the-art electron beams are now becoming limited by the intrinsic thermal Emittance of the cathode. In both dc and rf photocathode guns details of the cathode emission physics strongly influence the quantum efficiency and the thermal Emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal Emittance. This paper investigates the relationship between the quantum efficiency and the thermal Emittance for metal cathodes using the Fermi-Dirac model for the electron distribution. We use a consistent theory to derive the quantum efficiency and thermal Emittance, and compare our results to those of others.
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Analysis of slice Emittance measurements for the SLAC Gun Test Facility
Proceedings of the 2003 Particle Accelerator Conference, 2003Co-Authors: D.h. Dowell, C. G. Limborg, J. E. Clendenin, S. M. Gierman, B.f. Murphy, P.r. Bolton, John F. SchmergeAbstract:The Linac Coherent Light Source (LCLS) at SLAC requires the rf photo-injector to produce a beam with a normalized, projected Emittance of 1 micron in a 10 ps long bunch with a charge of 1 nC. In addition, a small longitudinal Emittance is needed to attain the desired 3 kiloamperes peak current after compression in two chicane bunchers. To achieve this excellent beam quality, we are performing systematic studies of both the transverse and longitudinal beam properties from the rf photocathode gun at the SLAC Gun Test Facility (GTF). Time resolved Emittances (slice) are determined by using a bunch with a linear energy chirp which is dispersed by a magnetic spectrometer. By varying the strength of a quadrupole lens upstream of the spectrometer allows measurement of the individual slice Emittances. Spectrometer images at the various quadrupole settings are binned in small energy/time windows and analyzed for the slice parameters. Our measurements indicate a temporal resolution of approximately 100 femtoseconds. In addition, the longitudinal phase space distribution is determined by measuring the energy spectrum over a range of linac phases. The correlated and uncorrelated components of the phase space distribution are determined by fits to the energy spectra analogous to a quad scan in the transverse dimension. The combined analysis of the transverse and longitudinal data gives not only the slice and longitudinal Emittances, but also any correlations due to wakefields or other effects.
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Slice Emittance measurements at the SLAC gun test facility
Nuclear Instruments and Methods in Physics Research Section A: Accelerators Spectrometers Detectors and Associated Equipment, 2003Co-Authors: D.h. Dowell, C. G. Limborg, J. E. Clendenin, S. M. Gierman, Paul Emma, B.f. Murphy, W S Graves, P.r. Bolton, John F. SchmergeAbstract:A goal of the Gun Test Facility (GTF) at SLAC is to investigate the production of high-brightness electron beams for the Linac Coherent Light Source (LCLS) X-ray FEL. High brightness in the RF photocathode gun occurs when the time-sliced Emittance is nearly the same as the cathode thermal Emittance and when the slices are all lined up, i.e., their Twiss parameters are nearly identical. In collaboration with the BNL Source Development Lab (SDL), we have begun a systematic study of the slice Emittance at GTF. The technique involves giving the bunch a near linear energy chirp using the booster linac and dispersing it with a magnetic spectrometer. Combined with knowledge of the longitudinal phase space, this establishes the energy-time correlation on the spectrometer screen. The slice Emittances are determined by varying the strengths of the quadrupoles in front of the spectrometer. Spectrometer images for a range of quadrupole settings are then binned into small energy/time windows and analysed for the slice Emittance and Twiss parameters. Results for various gun parameters are presented. © 2003 Elsevier Science B.V. All rights reserved.
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Reduction of thermal Emittance of RF guns
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2000Co-Authors: J. E. Clendenin, T. Kotseroglou, G.a. Mulhollan, D.t. Palmer, John F. SchmergeAbstract:Abstract The transverse Emittance from optimized RF photoinjectors is limited by the thermal Emittance. The thermal Emittance can be lowered by a factor >2 by using a semiconductor photocathode.
D.h. Dowell - One of the best experts on this subject based on the ideXlab platform.
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the quantum efficiency and thermal Emittance of metal photocathodes
Physical Review Special Topics-accelerators and Beams, 2009Co-Authors: D.h. Dowell, J F SchmergeAbstract:Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths, with the principle improvements occurring since the invention of the photocathode gun. The state-of-the-art normalized Emittance electron beams are now becoming limited by the thermal Emittance of the cathode. In both DC and RF photocathode guns, details of the cathode emission physics strongly influence the quantum efficiency and the thermal Emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal Emittance. This paper investigates the relationship between the quantum efficiency and the thermal Emittance of metal cathodes using the Fermi-Dirac model for the electron distribution. We derive the thermal Emittance and its relationship to the quantum efficiency, and compare our results to those of others.
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Quantum efficiency and thermal Emittance of metal photocathodes
Physical Review Special Topics - Accelerators and Beams, 2009Co-Authors: D.h. Dowell, John F. SchmergeAbstract:Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths with major advances occurring since the invention of the photocathode gun and the realization of Emittance compensation. These state-of-the-art electron beams are now becoming limited by the intrinsic thermal Emittance of the cathode. In both dc and rf photocathode guns details of the cathode emission physics strongly influence the quantum efficiency and the thermal Emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal Emittance. This paper investigates the relationship between the quantum efficiency and the thermal Emittance for metal cathodes using the Fermi-Dirac model for the electron distribution. We use a consistent theory to derive the quantum efficiency and thermal Emittance, and compare our results to those of others.
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Analysis of slice Emittance measurements for the SLAC Gun Test Facility
Proceedings of the 2003 Particle Accelerator Conference, 2003Co-Authors: D.h. Dowell, C. G. Limborg, J. E. Clendenin, S. M. Gierman, B.f. Murphy, P.r. Bolton, John F. SchmergeAbstract:The Linac Coherent Light Source (LCLS) at SLAC requires the rf photo-injector to produce a beam with a normalized, projected Emittance of 1 micron in a 10 ps long bunch with a charge of 1 nC. In addition, a small longitudinal Emittance is needed to attain the desired 3 kiloamperes peak current after compression in two chicane bunchers. To achieve this excellent beam quality, we are performing systematic studies of both the transverse and longitudinal beam properties from the rf photocathode gun at the SLAC Gun Test Facility (GTF). Time resolved Emittances (slice) are determined by using a bunch with a linear energy chirp which is dispersed by a magnetic spectrometer. By varying the strength of a quadrupole lens upstream of the spectrometer allows measurement of the individual slice Emittances. Spectrometer images at the various quadrupole settings are binned in small energy/time windows and analyzed for the slice parameters. Our measurements indicate a temporal resolution of approximately 100 femtoseconds. In addition, the longitudinal phase space distribution is determined by measuring the energy spectrum over a range of linac phases. The correlated and uncorrelated components of the phase space distribution are determined by fits to the energy spectra analogous to a quad scan in the transverse dimension. The combined analysis of the transverse and longitudinal data gives not only the slice and longitudinal Emittances, but also any correlations due to wakefields or other effects.
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Slice Emittance measurements at the SLAC gun test facility
Nuclear Instruments and Methods in Physics Research Section A: Accelerators Spectrometers Detectors and Associated Equipment, 2003Co-Authors: D.h. Dowell, C. G. Limborg, J. E. Clendenin, S. M. Gierman, Paul Emma, B.f. Murphy, W S Graves, P.r. Bolton, John F. SchmergeAbstract:A goal of the Gun Test Facility (GTF) at SLAC is to investigate the production of high-brightness electron beams for the Linac Coherent Light Source (LCLS) X-ray FEL. High brightness in the RF photocathode gun occurs when the time-sliced Emittance is nearly the same as the cathode thermal Emittance and when the slices are all lined up, i.e., their Twiss parameters are nearly identical. In collaboration with the BNL Source Development Lab (SDL), we have begun a systematic study of the slice Emittance at GTF. The technique involves giving the bunch a near linear energy chirp using the booster linac and dispersing it with a magnetic spectrometer. Combined with knowledge of the longitudinal phase space, this establishes the energy-time correlation on the spectrometer screen. The slice Emittances are determined by varying the strengths of the quadrupoles in front of the spectrometer. Spectrometer images for a range of quadrupole settings are then binned into small energy/time windows and analysed for the slice Emittance and Twiss parameters. Results for various gun parameters are presented. © 2003 Elsevier Science B.V. All rights reserved.
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Compensation of bend-plane Emittance growth in a 180 degree bend
Proceedings of the 1997 Particle Accelerator Conference (Cat. No.97CH36167), 1997Co-Authors: D.h. DowellAbstract:Emittance preservation in beam bending systems is vitally important in the production of bright, high-current electron microbunches. Generally, the Emittance increase occurs in the bend plane and results from changes in the microbunch energy distribution as the beam transits the bend. This redistribution of electron energies increases the beam's divergence, and hence the Emittance, by spoiling the achromatic transport of the bending system. In this paper we investigate the correlated Emittance growth in a 180 degree isochronous bend due to coherent synchrotron radiation (CSR). Introducing sextupole fields in the high dispersion region of the bend partially cancels the CSR-induced correlation thereby reducing the bend plane Emittance growth. The generalization of this Emittance compensation scheme is discussed.
H Hayano - One of the best experts on this subject based on the ideXlab platform.
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achievement of ultralow Emittance beam in the accelerator test facility damping ring
Physical Review Letters, 2004Co-Authors: Yosuke Honda, K Kubo, Scott L Anderson, S Araki, K L F Bane, A Brachmann, J Frisch, Masafumi Fukuda, K Hasegawa, H HayanoAbstract:For high luminosity in electron-positron linear colliders, it is essential to generate low vertical Emittance beams. We report on the smallest vertical Emittance achieved in single-bunch-mode operation of the Accelerator Test Facility, which satisfies the requirement of the x-band linear collider. The Emittances were measured with a laser-wire beam-profile monitor installed in the damping ring. The bunch length and the momentum spread of the beam were also recorded under the same conditions. The smallest vertical rms Emittance measured at low intensity is 4 pm at a beam energy of 1.3 GeV, which corresponds to the normalized Emittance of 1.0x1.0(-8) m. It increases by a factor of 1.5 for a bunch intensity of 10(10) electrons. The measured data agreed to the calculation of intrabeam scattering within much better than a factor of 2.
Simon Leemann - One of the best experts on this subject based on the ideXlab platform.
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interplay of touschek scattering intrabeam scattering and rf cavities in ultralow Emittance storage rings
5th Int. Particle Accelerator Conf. (IPAC'14) Dresden Germany June 15-20 2014, 2014Co-Authors: Simon LeemannAbstract:When it goes into operation in 2016, the MAX IV 3 GeV storage ring will be the first ultralow-Emittance storage ring based on a multibend achromat lattice. Such ultralow-Emittance rings make use of a large number of weak bending magnets which leads to low radiation losses in the dipoles compared to power radiated from insertion devices. Therefore, the Emittance in such rings depends strongly on the insertion devices and gap settings. The large stored current along with the low transverse Emittance lead to strong intrabeam scattering which blows up the beam's 6D Emittance. The Touschek lifetime depends on the 6D Emittance: it grows with increasing longitudinal Emittance which makes bunch lengthening cavities attractive. On the other hand, in the ultralow-Emittance regime, reducing the transverse Emittance actually increases the Touschek lifetime. Damping wigglers and insertion devices reduce the transverse Emittance, but they can also increase the Touschek lifetime by reducing the available cavity overvoltage and thus increasing the bunch length. Using the MAX IV 3 GeV storage ring as an example, this paper demonstrates the intricate interplay between transverse Emittance (insertion devices, Emittance coupling), longitudinal Emittance (tuning of main cavities as well as harmonic cavities), and choice of stored current in an ultralow-Emittance ring as well as its implications for brightness optimization. (Less)
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interplay of touschek scattering intrabeam scattering and rf cavities in ultralow Emittance storage rings
Physical Review Special Topics-accelerators and Beams, 2014Co-Authors: Simon LeemannAbstract:The latest generation of storage ring-based light sources employs multibend achromat lattices to achieve ultralow Emittance. These lattices make use of a large number of weak bending magnets which considerably reduces the amount of power radiated in the dipoles in comparison to power radiated from insertion devices. Therefore, in such storage rings, parameters such as Emittance, energy spread, and radiated power are—unlike 3rd generation storage rings—no longer constant during a typical user shift. Instead, they depend on several varying parameters such as insertion device gap settings, bunch charge, bunch length, etc. Since the charge per bunch is usually high, intrabeam scattering in medium-energy storage rings with ultralow Emittance becomes very strong. This creates a dependence of Emittance on stored current. Furthermore, since the bunch length is adjusted with rf cavities but is also varied as insertion device gaps change, the Emittance blowup from intrabeam scattering is not constant either. Therefore, the Emittance, bunch length, and hence the resulting Touschek lifetime have to be calculated in a self-consistent fashion with 6D tracking taking into account not only the bare lattice and rf cavity settings, but also momentary bunch charge and gap settings. Using the MAX IV 3 GeV storage ring as an example, this paper demonstrates the intricate interplay between transverse Emittance (insertion devices, Emittance coupling), longitudinal Emittance (tuning of main cavities as well as harmonic cavities), and choice of stored current in an ultralow-Emittance storage ring as well as some implications for brightness optimization. (Less)
Akira Ohnishi - One of the best experts on this subject based on the ideXlab platform.
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a variable Emittance radiator based on a metal insulator transition of la sr mno3 thin films
Applied Physics Letters, 2002Co-Authors: Yuichi Shimakawa, Tsutomu Yoshitake, Yoshimi Kubo, T Machida, K Shinagawa, Akira Okamoto, Yasuyuki Nakamura, Atsushi Ochi, Sumitaka Tachikawa, Akira OhnishiAbstract:Variable-Emittance radiators based on the metal–insulator transition of (La,Sr)MnO3 thin films have been developed. The Emittance property of the films was evaluated from infrared reflectance spectra; that is, the (La,Sr)MnO3 thin films show low Emittance at low temperature but high Emittance at high temperature. Moreover, the Emittance property significantly changes at the metal–insulator transition temperature, where the material changes from a highly reflective (i.e., low emissive) metal to a less reflective (i.e., high emissive) insulator. The (La,Sr)MnO3 thin films fitted on a spacecraft surface can, therefore, be used to automatically control the emissive heat transfer from the spacecraft without the need for any electrical power. The developed radiators also greatly reduce the weight and production cost of the thermal control devices. The dependence of the Emittance property on film thickness reveals that 1500-nm-thick films can be used for variable-Emittance radiators.