Modeling two-stage bunch compression with wakefields: Macroscopic properties and microbunching instability

Bosch, Robert; Kleman, K.J.; Wu, Juhao

doi:10.1103/physrevstab.11.090702

Cited by 19 publications

(21 citation statements)

References 25 publications

(50 reference statements)

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“…LSC-EEHG simulations were produced with three different particle tracking codes, starting with a quick 1D code, based on [23] with the LSC impedance given by [24],…”

Section: Methodsmentioning

confidence: 99%

longitudinal space charge assisted echo seeding of a free electron laser

Hacker

2015

SPIE Proceedings

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Seed lasers are employed to improve the temporal coherence of free-electron laser light. However, when seed pulses are short relative to the particle bunch, the noisy, temporally incoherent radiation from the un-seeded electrons can overwhelm the coherent, seeded radiation. In this paper a new seeding mechanism to improve the contrast between coherent and incoherent free electron laser radiation is employed together with a novel, simplified echo-seeding method. The concept relies on a combination of longitudinal space charge wakes and an echo-seeding technique to make a short, coherent pulse of FEL light together with noise background suppression. Several different simulation codes are used to illustrate the concept with conditions at the soft x-ray Free-electron LASer in Hamburg, FLASH. The impacts of coherent synchrotron radiation, intra beam scattering, and high peak current operation are investigated.

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“…LSC-EEHG simulations were produced with three different particle tracking codes, starting with a quick 1D code, based on [23] with the LSC impedance given by [24],…”

Section: Methodsmentioning

confidence: 99%

longitudinal space charge assisted echo seeding of a free electron laser

Hacker

2015

SPIE Proceedings

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show abstract

“…This requires more peak power for the shorter wavelength seed compared to a modulator that is not tuned to a subharmonic; however, for short, intense seed pulses, this is technically feasible. These simulations were produced with three different particle tracking codes, starting with a quick 1D code, based on [22], with the LSC impedance given by [23] Z LSC ðkÞ ¼ iZ 0 πkr…”

Section: Kirsten Hackermentioning

confidence: 99%

Longitudinal space charge assisted echo seeding of a free-electron laser with laser-spoiler noise suppression

Hacker

2014

Phys. Rev. ST Accel. Beams

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Seed lasers are employed to improve the temporal coherence of free-electron laser (FEL) light. However, when these seed pulses are short relative to the particle bunch, the noisy, temporally incoherent radiation from the unseeded electrons can overwhelm the coherent, seeded radiation. In this paper, a technique to seed a particle bunch with an external laser is presented in which a new mechanism to improve the contrast between coherent and incoherent free electron laser radiation is employed together with a novel, simplified echo-seeding method. The concept relies on a combination of longitudinal space charge wakes and an echo-seeding technique to make a short, coherent pulse of FEL light together with noise background suppression. Several different simulation codes are used to illustrate the concept with conditions at the soft x-ray free-electron laser in Hamburg, FLASH. Short-wavelength, high-brightness light sources, like free-electron lasers (FELs) driven by particle accelerators, are in demand for experiments studying ultrafast processes in matter. The FEL community has pursued methods to improve the temporal coherence properties of the light [1][2][3][4][5][6][7] and to generate shorter, tunable FEL pulses [5][6][7][8][9][10][11][12]. When the temporal coherence of FEL light is determined by the shot noise of an electron beam, as in self-amplified spontaneous emission (SASE), it is poor [13][14][15], but if it is determined by an external seed laser, the FEL light takes on the excellent temporal coherence properties of the external laser in the region that has been seeded. However, if the seed pulse is short while the electron bunch is long, the noisy SASE background signal can overwhelm the seeded radiation, wiping out the benefits of the seed.To reduce this noisy background, the FEL radiator is typically made short enough that the unseeded portion of the bunch does not reach saturation while the seeded portion does, but this can be limited in the case of short seeds with low seed power [1,[5][6][7]. Alternatively, the electron bunch could be made short relative to the seed, but this puts challenging constraints on the synchronization between the femtosecond-scale seed and the electron bunch. Ideally, the electron bunch would be much longer than the femtosecond duration seed, so that with the best observed 25 fs (rms) synchronization between electron beam and external laser in an FEL facility [16], the seed laser would hit the electron bunch on every shot, but then a method is needed to suppress the SASE background in conjunction with the seeding of the short pulses.As a relativistic seeded and bunched beam propagates along a drift, the microbunches experience a longitudinal space charge (LSC) impedance that modulates the energy of the beam in proportion to the peak current of the microbunches according towhere Z 0 ¼ 377 Ω is the impedance of free-space, I A ¼ 17 kA is the Alfen current, ρ k is a small current perturbation at some wave number k, and γ is the Lorentz factor. Depending on the strength of th...

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“…2 Such an effect of energy modulation microbunching due to longitudinal space charge (LSC) and consequent growth of current microbunching in dispersive sections was analyzed in the limit of small collective interactions (linear current-voltage response) in terms of an LSC impedance model. 3,4 Unexpected optical frequency phase correlation effects in electron beams have been observed by means of optical transition radiation (OTR) diagnostics. 5,6 In particular, an effect of coherent optical transition radiation (COTR) referred to as "unexplained physics" was observed in the injector of SLAC's LCLS x-ray FEL accelerator.…”

Section: Introductionmentioning

confidence: 99%

Collective microdynamics and noise suppression in dispersive electron beam transport

et al. 2011

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A general formulation is presented for deep collective interaction micro-dynamics in dispersive e-beam transport. In the regime of transversely coherent interaction, the formulation is applicable to both coherent and random temporal modulation of the electron beam. We demonstrate its use for determining the conditions for suppressing beam current noise below the classical shot-noise level by means of transport through a dispersive section with a small momentum compaction parameter.

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Modeling two-stage bunch compression with wakefields: Macroscopic properties and microbunching instability

Cited by 19 publications

References 25 publications

longitudinal space charge assisted echo seeding of a free electron laser

longitudinal space charge assisted echo seeding of a free electron laser

Longitudinal space charge assisted echo seeding of a free-electron laser with laser-spoiler noise suppression

Collective microdynamics and noise suppression in dispersive electron beam transport

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