Abstract
The possibility of utilizing plasma undulators and plasma accelerators to produce compact ultraviolet and X-ray sources, has attracted considerable interest for a few decades. This interest has been driven by the great potential to decrease the threshold for accessing such sources, which are mainly provided by a few dedicated large-scale synchrotron or free-electron laser (FEL) facilities. However, the broad radiation bandwidth of such plasma devices limits the source brightness and makes it difficult for the FEL instability to develop. Here, using multi-dimensional particle-in-cell (PIC) simulations, we demonstrate that a plasma undulator generated by the beating of a mixture of high-order laser modes propagating inside a plasma channel, leads to a few percent radiation bandwidth. The strength of the undulator can reach unity, the period can be less than a millimeter, and the number of undulator periods can be significantly increased by a phase locking technique based on the longitudinal tapering. Polarization control of such an undulator can be achieved by appropriately choosing the phase of the modes. According to our results, in the fully beam loaded regime, the electron current in the plasma undulator can reach 0.3 kA level, making such an undulator a potential candidate towards a table-top FEL.
Highlights
The possibility of utilizing plasma undulators and plasma accelerators to produce compact ultraviolet and X-ray sources, has attracted considerable interest for a few decades
Plasma undulators can be realized by ultra-intense laser plasma interactions in the bubble regime[8,9,10], a laser pulse propagating in plasma perpendicularly to the electron beam propagation direction[20], a laser pulse interaction with a nanowire array[21], or using laser pulse offset injection in a matched plasma channel[22,23,24]
We show for the first time that a solution exists for a plasma undulator that meets the stringent conditions required for the free-electron laser (FEL) lasing
Summary
The possibility of utilizing plasma undulators and plasma accelerators to produce compact ultraviolet and X-ray sources, has attracted considerable interest for a few decades. In the case of plasma undulators one of the major challenges is the large radiation spread caused by varying values of undulator strength K throughout the beam or by strong focusing and large electron beam divergence inside the wakefield, while for the FEL process to develop a very narrow bandwidth is required[8,15] Another challenge is that the phase slippage between the electrons and the wakefield limits the length of a plasma undulator. The beam loading limit indicates that the current of the beam can reach approximately 0.3 kilo-Ampere for typical laser-plasma parameters These properties imply that such a plasma undulator is a miniaturised electron device naturally matching the extremely compact scale of a plasma accelerator, similar in significance to the recent breakthrough development of plasma lenses[25,26,27], and plasma accelerator staging[28,29], and may have great potential in incoherent XUV and X-ray sources or future compact FELs
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