Using the longitudinal space charge instability for generation of VUV and X-ray radiation

TL;DR

This paper proposes using the longitudinal space charge instability as a novel method to generate VUV and X-ray radiation, offering a broadband, cost-effective alternative to traditional FELs with potential for attosecond pulse production.

Contribution

It introduces a new application of the longitudinal space charge instability as a broadband radiation source for VUV and X-ray regimes, enhancing existing FEL technology.

Findings

LSCA can generate broadband VUV and X-ray radiation from shot noise.

The scheme allows for wavelength compression without high stability requirements.

Potential to produce attosecond pulses and a second color for pump-probe experiments.

Abstract

Longitudinal space charge (LSC) driven microbunching instability in electron beam formation systems of X-ray FELs is a recently discovered effect hampering beam instrumentation and FEL operation. The instability was observed in different facilities in infrared and visible wavelength ranges. In this paper we propose to use such an instability for generation of VUV and X-ray radiation. A typical longitudinal space charge amplifier (LSCA) consists of few amplification cascades (drift space plus chicane) with a short undulator behind the last cascade. If the amplifier starts up from the shot noise, the amplified density modulation has a wide band, on the order of unity. The bandwidth of the radiation within the central cone is given by inverse number of undulator periods. A wavelength compression could be an attractive option for LSCA since the process is broadband, and a high compression stability is not required. LSCA can be used as a cheap addition to the existing or planned short-wavelength FELs. In particular, it can produce the second color for a pump-probe experiment. It is also possible to generate attosecond pulses in the VUV and X-ray regimes. Some user experiments can profit from a relatively large bandwidth of the radiation, and this is easy to obtain in LSCA scheme. Finally, since the amplification mechanism is broadband and robust, LSCA can be an interesting alternative to self-amplified spontaneous emission free electron laser (SASE FEL) in the case of using laser-plasma accelerators as drivers of light sources.