Emittance growth and energy loss due to coherent synchrotron radiation in a bunch compressor

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In an experiment conducted on the Jefferson Laboratory IR free-electron laser driver, the effects of coherent synchrotron radiation (CSR) on beam quality were studied. The primary goal of this work was to explore CSR output and effect on the beam with variation of the bunch compression in the IR recirculator. Here we examine the impact of CSR on the average energy loss as a function of bunch compression as well as the impact of CSR on the energy spectrum of the bunch. Simulation of beam dynamics in the machine, including the one-dimensional CSR model, shows very good agreement with the measured effect of CSR on the average energy loss as a function of compression. Finally, a well-defined structure is observed in the energy spectrum with a feature in the spectrum that varies as a function of the compression. This effect is examined in simulations, as well, and a simple explanation for the variation is proposed.

Section: Energy Spectra Measurementsupporting

confidence: 60%

Measurement and simulation of the impact of coherent synchrotron radiation on the Jefferson Laboratory energy recovery linac electron beam

Hall

Biedron

Edelen

et al. 2015

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“…However, nonlinear terms in the chirp, caused by accelerator structure wakefields [3][4][5][6], typically result in a final bunch shape that is double horned-with one horn leading and the other trailing-rather than one that is uniform [7]. In the horn regions of the distribution the peak current can be greatly enhanced (compared to the current in the core), resulting in negative consequences such as: in the chicane, induced coherent synchrotron radiation (CSR) [8][9][10] leading to emittance growth [9,11], and a limit on the bunch compression that can be achieved; in the undulator, an increase in wake-induced energy variation and a nonuniformity in the lasing process [12]. Also, having a nonuniform beam distribution in the undulator makes it difficult to transversely match the beam.…”

Section: Introductionmentioning

confidence: 99%

Measurements and analysis of a high-brightness electron beam collimated in a magnetic bunch compressor

Zhou

Bane

Ding

et al. 2015

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A collimator located in a magnetic bunch compressor of a linear accelerator driven x-ray free electron laser has many potential applications, such as the removal of horns in the current distribution, the generation of ultrashort beams, and as a diagnostic of the beam slice emittance. Collective effects, however, are a major concern in applying the technique. Systematic measurements of emittance and analysis were performed using a collimator in the first bunch compressor of the Linac Coherent Light Source (LCLS). In the nominal, undercompressed configuration using the collimator we find that the y emittance (nonbending plane) is not increased, and the x emittance (in the bending plane) is increased by about 25%, in comparison to the injector emittance. From the analysis we conclude that the parasitic effects associated with this method are dominated by coherent synchrotron radiation (CSR), which causes a "systematic error" for measuring slice emittance at the bending plane using the collimation method. In general, we find good agreement between the measurements and simulations including CSR. However, for overcompressed beams at smaller collimator gaps, an extra emittance increase is found that does not agree with 1D simulations and is not understood.

“…Such perturbations can lead to instabilities that disrupt the beam under certain circumstances. For example, in electron machines, coherent synchrotron radiation can be generated from a density-modulated beam in a bend, causing the growth of energy spread and emittance [1][2][3], beam instability, and microbunching [4][5][6]. Hence, in order to preserve high beam quality, it is important to understand the longitudinal space-charge beam dynamics in the injector region.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of large-amplitude perturbations in space-charge dominated beams

Tian

Kishek

Haber

et al. 2010

Detailed experimental measurements are presented concerning the propagation of space-charge waves of varying amplitudes in an intense, charged-particle beam. A short perturbation to the density profile is applied at the electron gun, and both current and mean energy profiles are measured at two locations downstream. The measurements are compared to predictions of a linear 1D cold-fluid model, and selfconsistent particle-in-cell simulations. For sufficiently small perturbation amplitudes, the experiment, simulation, and 1D theory agree. For larger amplitudes, the simulation begins to diverge from theoretical predictions due to nonlinear effects. Experimental observations for large-amplitude perturbations differ markedly from either theory or simulation. With the aid of simulations with mismatched and misaligned beams, this departure of experiments from predictions is demonstrated to be caused by the loss of beam current due to scraping aided by the larger radius of the perturbation.