With gigaelectron-volts per centimetre energy gains and femtosecond electron beams, laser wakefield acceleration (LWFA) is a promising candidate for applications, such as ultrafast electron diffraction, multistaged colliders and radiation sources (betatron, compton, undulator, free electron laser). However, for some of these applications, the beam performance, for example, energy spread, divergence and shot-to-shot fluctuations, need a drastic improvement. Here, we show that, using a dedicated transport line, we can mitigate these initial weaknesses. We demonstrate that we can manipulate the beam longitudinal and transverse phase-space of the presently available LWFA beams. Indeed, we separately correct orbit mis-steerings and minimise dispersion thanks to specially designed variable strength quadrupoles, and select the useful energy range passing through a slit in a magnetic chicane. Therefore, this matched electron beam leads to the successful observation of undulator synchrotron radiation after an 8 m transport path. These results pave the way to applications demanding in terms of beam quality.
High gradient quadrupoles are necessary for different applications such as
laser plasma acceleration, colliders, and diffraction limited light sources.
Permanent magnet quadrupoles provide a higher field strength and compactness
than conventional electro-magnets. An original design of permanent magnet based
quadrupole (so-called "QUAPEVA"), composed of a Halbach ring placed in the
center with a bore radius of 6 mm and surrounded by four permanent magnet
cylinders capable of providing a gradient of 210 T/m, is presented. The design
of the QUAPEVAs, including magnetic simulation modeling, and mechanical issues
are reported. Magnetic measurements of seven systems of different lengths are
presented and confirmed the theoretical expectations. The variation of the
magnetic center while changing the gradient strength is +/- 10 micrometer. A
triplet of three QUAPEVA magnets are used to focus a beam with large energy
spread and high divergence that is generated by Laser Plasma Acceleration
source for a free electron laser demonstration.Comment: 4 pages, 9 figure
This paper presents an innovative compact permanent magnet quadrupole with a strong gradient for potential use in future light source lattices. Its magnetic structure includes simple mechanical parts, rectangular permanent magnet blocks and soft iron poles. It has a wide aperture in the horizontal plane to accommodate an x-ray beam port, a common constraint in storage ring-based light sources. This specificity introduces field quality deterioration because of the resulting truncation of the poles; a suitable field quality can be restored with an optimized pole shape. A 82 T=m prototype with a bore radius of 12 mm and a 10 mm vertical gap between poles has been constructed and magnetically characterized. Gradient inhomogeneities better than 10 −3 in the good field region were obtained after the installation of special shims.
The original version of this Article contained an error in the last sentence of the first paragraph of the Introduction and incorrectly read 'A proper electron beam control is one of the main challenges towards the Graal of developing a compact alternative of X-ray freeelectron lasers by coupling LWFA gigaelectron-volts per centimetre acceleration gradient with undulators in the amplification regime in equation 11, nx(n-β) x β: n the two times and beta the two times should be bold since they are vectorsin Eq. 12, β should be bold as well.' The correct version is 'A proper electron beam control is one of the main challenges towards the Graal of developing a compact alternative of X-ray free-electron lasers by coupling LWFA gigaelectron-volts per centimetre acceleration gradient with undulators in the amplification regime.' This has been corrected in both the PDF and HTML versions of the Article.
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