FEL2015 - Table of Session: TUC (Electron Beam Dynamics)

Paper

Title

Page

The Microbunching Instability and LCLS-II Lattice Design

308

M. Venturini
LBNL, Berkeley, California, USA

The microbunching instability is a pervasive occurrence when high brightness electron beams are accelerated and transported through dispersive sections like bunch-compression chicanes or distributions beamlines. If uncontrolled the instability can severely compromise the performance of x-ray FELs, where beam high brightness is crucial. In this talk we discuss how consideration of the microbunching instability is informing the LCLS-II design and determining the specifications for the laser heater and transport lines. We also review some of the expected and not so-expected phenomena that we have encountered while carrying out high-resolution macroparticle simulations of the instability and the analytical models we have developed to interpret the numerical results.

Slides TUC01 [4.206 MB]

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TUC02

Ultra-Low Charge, Ultra-High Brightness Frontiers of Photoinjectors: Challenges and Perspectives

R.K. Li
SLAC, Menlo Park, California, USA

Photoinjectors deliver high brightness electron beams that are essential to the success of FELs. Higher beam brightness can boost the performances of existing facilities and enable new capabilities of future ones. Ultralow charge (a few pC and lower) is the choice to reach higher brightness thanks to the favorable scaling, as well as longitudinally coherent, single-spike FELs. This parameter space is particularly relevant for future high rep-rate machines. Despite the ultralow total charge, the charge density is still high and collective effects need to be studied in-depth. The extreme emittance, bunch length, spot size, and charge also pose challenges on the diagnosis of these beams. In this talk, we will discuss recent progress on the generation, manipulation, and diagnosis of ultralow charge beams, including e.g. shaping the space charge dominated beams to maximize the phase space density, new techniques to characterize the nm-rad-level emittance, and new advances in photocathode physics and rf structures. Many of the above progress are motivated by the recent development of ultrafast electron diffraction and microscopy using photoinjectors. Understanding and controlling the high brightness beams in accelerators with the high stability and precision typical in the electron microscopy community, constitutes an R&D frontier on electron beams and sources for the coming decades.

Slides TUC02 [2.858 MB]

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TUC03

Low Slice Emittance Preservation in Bunch Compressors

S. Bettoni, M. Aiba, M. Pedrozzi, E. Prat, S. Reiche, T. Schietinger
PSI, Villigen PSI, Switzerland
B. Beutner
DESY, Hamburg, Germany

Minimize the dilution of the beam emittance is crucial for accelerators, and in particular for Free Electron Lasers, where the length of the machine and the finally the efficiency of the lasing process depend on it. At the SwissFEL Injector Test Facility we measured unexpected slice emittance increase after compressing the bunch also for moderate compression factors. We experimentally characterized the dependency of this phenomenon on the beam and machine parameters relevant for the compression. In order to qualitatively reproduce all the measurements outcomes it was necessary to use a 3D beam dynamic model along the bunch compressor including coherent synchrotron radiation. After excluding space charge forces, spurious dispersion and microbunching instability as possible sources for the observed emittance dilution, we identified the coherent synchrotron radiation and its interaction with the electron beam as the main responsible of the phenomenon. We also studied both experimentally and with simulations the contribution of the mismatch along the bunch to the longitudinal variations of the slice emittance. These experimental and theoretical investigations allowed a re-optimization of the injector. Typically with 150 A peak current, 200 pC charge it was possible to reach less than 200 nm.rad for the central slice with a moderate increase up to less than 300 nm.rad on the tails.

Slides TUC03 [1.395 MB]

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TUC04

Image Charge Effect on Emittance Reduction Phenomenon in Electron Gun

T. Nogi
Kyoto Univeristy, Kyoto, Japan
T. Katsurayama, T. Kii, K. Masuda, K. Morita, T. Murata, K. Nagasaki, H. Ohgaki, S. Suphakul, K. Torgasin, H. Yamashita, H. Zen
Kyoto University, Kyoto, Japan

Development of next generation light sources requires reduction of beam emittance. The emittance can be influenced in the vicinity of a cathode, where electron energy is low and the beam dynamics is dominated by space charge and image charge effect. Recently it was discovered that for ideal DC acceleration emittance rises near cathode and subsequently decreases due to self-linearization force caused by space charge effect [*]. This phenomenon occurs for accelerating field, which is lower than usually applied at conventional electron guns. It is an issue that this concept is feasible for electron gun configuration of real injectors. In this research we numerically investigate the transverse emittance and its dependence on parameters such as current density, accelerating field and the distance from the cathode. As a result, the position of minimal emittance was found to be correlated to perveance. This position can be varied by proper settings of parameters. In this conference, we will present these phenomena seen numerically in the SCSS thermionic gun geometry.
* A. Mizuno, et al., Nucl. Instr. Meth. Phys. Res. A 774 (2015) 51-59.

Slides TUC04 [1.604 MB]

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Paper	Title	Page
TUC01	The Microbunching Instability and LCLS-II Lattice Design	308
	M. Venturini LBNL, Berkeley, California, USA
	The microbunching instability is a pervasive occurrence when high brightness electron beams are accelerated and transported through dispersive sections like bunch-compression chicanes or distributions beamlines. If uncontrolled the instability can severely compromise the performance of x-ray FELs, where beam high brightness is crucial. In this talk we discuss how consideration of the microbunching instability is informing the LCLS-II design and determining the specifications for the laser heater and transport lines. We also review some of the expected and not so-expected phenomena that we have encountered while carrying out high-resolution macroparticle simulations of the instability and the analytical models we have developed to interpret the numerical results.
	Slides TUC01 [4.206 MB]
Export •	reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)

TUC02	Ultra-Low Charge, Ultra-High Brightness Frontiers of Photoinjectors: Challenges and Perspectives
	R.K. Li SLAC, Menlo Park, California, USA
	Photoinjectors deliver high brightness electron beams that are essential to the success of FELs. Higher beam brightness can boost the performances of existing facilities and enable new capabilities of future ones. Ultralow charge (a few pC and lower) is the choice to reach higher brightness thanks to the favorable scaling, as well as longitudinally coherent, single-spike FELs. This parameter space is particularly relevant for future high rep-rate machines. Despite the ultralow total charge, the charge density is still high and collective effects need to be studied in-depth. The extreme emittance, bunch length, spot size, and charge also pose challenges on the diagnosis of these beams. In this talk, we will discuss recent progress on the generation, manipulation, and diagnosis of ultralow charge beams, including e.g. shaping the space charge dominated beams to maximize the phase space density, new techniques to characterize the nm-rad-level emittance, and new advances in photocathode physics and rf structures. Many of the above progress are motivated by the recent development of ultrafast electron diffraction and microscopy using photoinjectors. Understanding and controlling the high brightness beams in accelerators with the high stability and precision typical in the electron microscopy community, constitutes an R&D frontier on electron beams and sources for the coming decades.
	Slides TUC02 [2.858 MB]
Export •	reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)

TUC03	Low Slice Emittance Preservation in Bunch Compressors
	S. Bettoni, M. Aiba, M. Pedrozzi, E. Prat, S. Reiche, T. Schietinger PSI, Villigen PSI, Switzerland B. Beutner DESY, Hamburg, Germany
	Minimize the dilution of the beam emittance is crucial for accelerators, and in particular for Free Electron Lasers, where the length of the machine and the finally the efficiency of the lasing process depend on it. At the SwissFEL Injector Test Facility we measured unexpected slice emittance increase after compressing the bunch also for moderate compression factors. We experimentally characterized the dependency of this phenomenon on the beam and machine parameters relevant for the compression. In order to qualitatively reproduce all the measurements outcomes it was necessary to use a 3D beam dynamic model along the bunch compressor including coherent synchrotron radiation. After excluding space charge forces, spurious dispersion and microbunching instability as possible sources for the observed emittance dilution, we identified the coherent synchrotron radiation and its interaction with the electron beam as the main responsible of the phenomenon. We also studied both experimentally and with simulations the contribution of the mismatch along the bunch to the longitudinal variations of the slice emittance. These experimental and theoretical investigations allowed a re-optimization of the injector. Typically with 150 A peak current, 200 pC charge it was possible to reach less than 200 nm.rad for the central slice with a moderate increase up to less than 300 nm.rad on the tails.
	Slides TUC03 [1.395 MB]
Export •	reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)

TUC04	Image Charge Effect on Emittance Reduction Phenomenon in Electron Gun
	T. Nogi Kyoto Univeristy, Kyoto, Japan T. Katsurayama, T. Kii, K. Masuda, K. Morita, T. Murata, K. Nagasaki, H. Ohgaki, S. Suphakul, K. Torgasin, H. Yamashita, H. Zen Kyoto University, Kyoto, Japan
	Development of next generation light sources requires reduction of beam emittance. The emittance can be influenced in the vicinity of a cathode, where electron energy is low and the beam dynamics is dominated by space charge and image charge effect. Recently it was discovered that for ideal DC acceleration emittance rises near cathode and subsequently decreases due to self-linearization force caused by space charge effect []. This phenomenon occurs for accelerating field, which is lower than usually applied at conventional electron guns. It is an issue that this concept is feasible for electron gun configuration of real injectors. In this research we numerically investigate the transverse emittance and its dependence on parameters such as current density, accelerating field and the distance from the cathode. As a result, the position of minimal emittance was found to be correlated to perveance. This position can be varied by proper settings of parameters. In this conference, we will present these phenomena seen numerically in the SCSS thermionic gun geometry. A. Mizuno, et al., Nucl. Instr. Meth. Phys. Res. A 774 (2015) 51-59.
	Slides TUC04 [1.604 MB]
Export •	reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)