Undulator design for Laser Plasma Based Free electron laser

The fourth generation of synchrotron radiation sources, commonly referred to as the Free Electron Laser (FEL), provides an intense source of brilliant X-ray beams enabling the investigation of matter at the atomic scale with unprecedented time resolution. These sources require the use of conventional linear accelerators providing high electron beam performance. The achievement of chirped pulse amplification allowing lasers to be operated at the Terawatt range, opened the way for the Laser Plasma Acceleration (LPA) technique where high energy electron bunches with high current can be produced within a very short centimeter-scale distance. Such an advanced acceleration concept is of great interest to be qualified by an FEL application for compact X-ray light sources. We explore in this paper what the LPA specificities imply on the design of the undulator, part of the gain medium. First, the LPA concept and state-of-art are presented showing the different operation regimes and what electron beam parameters are likely to be achieved. The LPA scaling laws are discussed afterwards to better understand what laser or plasma parameters have to be adjusted in order to improve electron beam quality. The FEL is secondly discussed starting with the spontaneous emission, followed by the different FEL configurations, the electron beam transport to the undulator and finally the scaling laws and correction terms in the high gain case. Then, the different types of compact undulators that can be implemented for an LPA based FEL application are analyzed. Finally, examples of relevant experiments are reported by describing the transport beamline, presenting the spontaneous emission characteristics achieved so far and the future prospects

Erratum to: EuPRAXIA Conceptual Design Report – Eur. Phys. J. Special Topics 229, 3675-4284 (2020), https://doi.org/10.1140/epjst/e2020-000127-8

International audienceThe online version of the original article can be found at http://https://doi.org/10.1140/epjst/e2020-000127-8</A

Undulator design for a laser-plasma-based free-electron-laser

International audienceThe fourth generation of synchrotron radiation sources, commonly referred to as the Free Electron Laser (FEL), provides an intense source of brilliant X-ray beams enabling the investigation of matter at the atomic scale with unprecedented time resolution. These sources require the use of conventional linear accelerators providing high electron beam performance. The achievement of chirped pulse amplification allowing lasers to be operated at the Terawatt range, opened the way for the Laser Plasma Acceleration (LPA) technique where high energy electron bunches with high current can be produced within a very short centimeter-scale distance. Such an advanced acceleration concept is of great interest to be qualified by an FEL application for compact X-ray light sources. We explore in this paper what the LPA specificities imply on the design of the undulator, part of the gain medium. First, the LPA concept and state-of-art are presented showing the different operation regimes and what electron beam parameters are likely to be achieved. The LPA scaling laws are discussed afterwards to better understand what laser or plasma parameters have to be adjusted in order to improve electron beam quality. The FEL is secondly discussed starting with the spontaneous emission, followed by the different FEL configurations, the electron beam transport to the undulator and finally the scaling laws and correction terms in the high gain case. Then, the different types of compact undulators that can be implemented for an LPA based FEL application are analyzed. Finally, examples of relevant experiments are reported by describing the transport beamline, presenting the spontaneous emission characteristics achieved so far and the future prospects

QUAPEVA: Variable High Gradient Permanent Magnet Quadrupole

International audienceWe present the magnetic and the mechanical design of tunable high gradient permanent magnet (PM) quadrupoles. The tunable gradient of the so-called QUAPEVAS extends from 100T/m up to 200T/m. Seven of them with various lengths, ranging from 26mm up to 100mm, for different integrated quadrupole strengths were manufactured. The measured magnetic performance of these devices is also reported. These devices were successfully developed to transport laser plasma accelerated electron beam. Such applications have however less stringent multipole harmonic content constraints than diffraction limited Light sources. Trails for lowering the multipole harmonics will be discussed

Development and operation of a Pr_{2}Fe_{14}B based cryogenic permanent magnet undulator for a high spatial resolution x-ray beam line

Short period, high field undulators are used to produce hard x-rays on synchrotron radiation based storage ring facilities of intermediate energy and enable short wavelength free electron laser. Cryogenic permanent magnet undulators take benefit from improved magnetic properties of RE_{2}Fe_{14}B (Rare Earth based magnets) at low temperatures for achieving short period, high magnetic field and high coercivity. Using Pr_{2}Fe_{14}B instead of Nd_{2}Fe_{14}B, which is generally employed for undulators, avoids the limitation caused by the spin reorientation transition phenomenon, and simplifies the cooling system by allowing the working temperature of the undulator to be directly at the liquid nitrogen one (77 K). We describe here the development of a full scale (2 m), 18 mm period Pr_{2}Fe_{14}B cryogenic permanent magnet undulator (U18). The design, construction and optimization, as well as magnetic measurements and shimming at low temperature are presented. The commissioning and operation of the undulator with the electron beam and spectrum measurement using the Nanoscopmium beamline at SOLEIL are also reported

Energy spread tuning of a laser-plasma accelerated electron beam in a magnetic chicane

International audienceLaser-plasma accelerators (LPA) deliver relativistic electron beams with high peak current and low emittance, with energies up to the GeV-level in only few centimetres. However, the divergence and the energy spread of these beams remain too large for potential light source applications. A magnetic transfer line can be used to manipulate the electron beam phase-space and select the transmitted energies with a slit located at its center. We will show that with a proper focusing optics along the line, one can tune the energy spread of the beam at a given energy without loss and produce undulator radiation with controlled bandwidth. We present analytic studies, numerical simulations and experimental results on the controled electron beam transport and application to undulator radiation with a control of the bandwidth

Energy spread tuning of a laser-plasma accelerated electron beam in a magnetic chicane

International audienceLaser-plasma accelerators (LPA) deliver relativistic electron beams with high peak current and low emittance, with energies up to the GeV-level in only few centimetres. However, the divergence and the energy spread of these beams remain too large for potential light source applications. A magnetic transfer line can be used to manipulate the electron beam phase-space and select the transmitted energies with a slit located at its center. We will show that with a proper focusing optics along the line, one can tune the energy spread of the beam at a given energy without loss and produce undulator radiation with controlled bandwidth. We present analytic studies, numerical simulations and experimental results on the controled electron beam transport and application to undulator radiation with a control of the bandwidth

Variable high gradient permanent magnet quadrupole (QUAPEVA)

International audienceDifferent applications such as laser plasma acceleration, colliders, and diffraction limited light sources require high gradient quadrupoles, with strength that can reach up to 200 T/m for a typical 10 mm bore diameter. We present here a permanent magnet based quadrupole (so-called QUAPEVA) composed of a Halbach ring and surrounded by four permanent magnet cylinders. Its design including magnetic simulation modeling enabling us to reach 201 T/m with a gradient variability of 45% 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 μm. A triplet of QUAPEVA magnets is used to efficiently focus a beam with large energy spread and high divergence that is generated by a Laser Plasma Acceleration source for a free electron laser demonstration and has enabled us to perform beam based alignment and control the dispersion of the beam