SEISM is a unique ECR ion source operating at a frequency of 60 GHz. The prototype is based on a simple magnetic geometry, the cusp, allowing the use of polyhelix coils (developed with LNCMI, Grenoble) to generate the closed ECR surface at 2.14 T. The plasma is sustained by a high intensity HF pulse (up to 300kW). Previous experiments at LNCMI have successfully demonstrated the establishment of the nominal magnetic field and the extraction of ion beams with a current density up to 1 A cm(-2). The presence of afterglow peaks was also observed, proving the existence of ion confinement in a CUSP ECR source. An experimental campaign is carried out in 2021 using a new transport line designed to improve the transmission of the beam to the new detectors. Short and long-term research plans are presented to transform this high current density into a high intensity ion beam that can be used for accelerators of the future.

Permanent magnet multipoles (PMMs) are widely used in accelerators to either focus particle beams or confine plasma in ion sources. The real magnetic field created by PMMs is calculated by magnetic field simulation software and then used in particle tracking codes by means of a three dimensional magnetic field map. A common alternative is to use the so-called "hard-edge" model, which gives an approximation of the magnetic field inside the PMM assuming a null fringe field. This work proposes an investigation of the PMM fringe field properties. An analytical model of the PMM magnetic field is developed using the Fourier multipole expansion. A general axial potential function with a unique parameter λ, able to reproduce the actual PMM magnetic field (including its two fringe fields) with an explicit dependence on the PMM length, is proposed. An analytical first order model including the axial fringe field is derived. This simple model complies with the Maxwell equations [curl(B) = 0 and div(B) = 0] and can replace advantageously the "hard-edge" model when fast analytical calculations are required. The higher order analytical multiple expansion model quality is assessed by means of χ2 estimators. The general dependence of the potential function parameter λ is given as a function of the PMM geometry for quadrupole, hexapole, and multipole, allowing one to use the developed model in simulation programs where the multipole geometry is an input parameter.

Spontaneous undulator radiation emission, after the COXINEL line using a Laser Plasma acceleration (LPA) source, has been observed. The line enables to manipulate the electron beam phase space such as emittance, dispersion and energy spread along a 10 m long transport. The large divergence is handled at a very early stage to mitigate the chromatic emittance, using high gradient permanent magnet based quadrupoles mounted on translation tables. The operating energy is between 161-180 MeV focused in a 2-m long cryo-ready undulator with a period of 18 mm emitting light in the Ultra-Violet range. The spectral flux is characterized using a spectrometer. The wavelength is tuned by either changing the electron beam energy or by adjusting the undulator gap. The radiation pattern signature is illustrated alongside its dependence on the energy spread that is modified by introducing a slit in a magnetic chicane where a small relative bandwidth of 5% has been achieved.

Laser-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.

The Free Electron Laser (FEL) application of Laser Plasma Acceleration (LPA) requires the handling of the energy spread and divergence. The COXINEL manipulation line, designed and built at SOLEIL for this purpose, consists of high gradient quadrupoles for divergence handling and a decompression chicane for energy sorting, enabling FEL amplification with baseline parameters. Installed at Laboratoire d’Optique Appliquee (LOA), it uses robust electrons generated and accelerated by ionization injection using a 30 TW laser. We report here on the work progress towards a FEL demonstration. The LPA measured electron beam characteristics deviates from the baseline reference case. After the installation of the equipment, the electron beam transport has first been optimized. The electron position and dispersion are independently adjusted. Then, undulator radiation has been measured. The spectral purity is controlled via the energy spread adjusted in the slit located in the chicane. FEL effect demonstration is within reach, with currently achieved performance on different LPA experiments.

Laser plasma acceleration (LPA) enables the generation of an up to several GeV electron beam with a short bunch length and high peak current within a centimeter scale. In view of undulator type light source applications, electron beam manipulation has to be applied. We report here on detailed electron beam transport for an LPA electron beam on the COXINEL test line, that consists of strong permanent quadrupoles to handle the electron beam divergence, a magnetic chicane to reduce the energy spread and a second set of quadrupoles for adjusting the focusing inside the undulator. After describing the measured LPA characteristics, we show that we can properly transport the electron beam along the line, thanks to several screens. We also illustrate the influence of the chromatic effects induced by the electron beam energy spread, both experimentally and numerically. We then study the sensitivity of the transport to the electron beam pointing and skewed quadrupolar components.

Since the laser invention [1, 2], the advent of Free Electron Lasers (FEL) [3, 4] in the X-ray domain half a century later, has opened new areas for matter investigation with higher temporal resolution. In parallel, the development of laser plasma acceleration (LPA) [5] that delivers today several GeV beam acceleration [6] in a short distance appears also very promising. The qualification of the LPA for FEL application can thus be viewed as an important challenge [7]. Nevertheless, present LPA electron beam parameters (e. g. energy spread and beam divergence) do not meet conventional accelerator state-of-the-art performance and FEL application requires a specific beam handling. In such a prospect, the COXINEL beam manipulation line [8, 9] using variable permanent magnet quadrupoles for emittance growth mitigation and de-mixing chicane for the energy spread handling developed at SOLEIL has been installed for using electrons produced with an intense laser of Laboratoire d'Optique Appliquee (LOA). Strategies for controlling electron beam position and dispersion have been elaborated and demonstrated [10]. Finally, undulator spontaneous emission has been measured at the end of the line.

The recent spectacular development of laser plasma ac- celerators that now can deliver GeV electron beams in an extremelyshortdistancemakesthemverypromising. Ap- plications for light sources based on undulator radiation and free electron laser appear as an intermediate step to move from an acceleration concept to an accelerator qual- ification. However, the presently achieved divergence and energy spread require some electron beam manipulations. The COXINEL test line was designed for enabling Free Elec- tron Laser operation with baseline reference parameters. It comprises variable permanent magnet quadrupoles for di- vergence handling, a magnetic chicane for electron energy sorting, a second set of quadrupole for chromatic focusing and an undulator for synchrotron radiation emission and/or free electron laser gain medium. The transport along the line is controlled [1]. The synchrotron radiation emitted by the undulator radiation is studied under different conditions of detection (CCD camera, spectrometer), electron beam manipulation and undulator parameters. These observations pave the way towards Laser Plasma Acceleration based Free Electron Laser.

Laser plasma acceleration (LPA) capable of providing femtosecond and GeV electron beams in cm scale distances brings a high interest for different applications, such as free electron laser and future colliders. Nevertheless, LPA high divergence and energy spread require an initial strong focus to mitigate the chromatic effects. The reliability, in particular with the pointing fluctuations, sets a real challenge for the control of the dispersion along the electron beam transport. We examine here how the magnetic defects of the first strong quadrupoles, in particular, the skew terms, can affect the brightness of the transported electron beam, in the case of the COXINEL transport line, designed for manipulating the electron beam properties for a free electron laser application. We also show that the higher the initial beam divergence, the larger the degradation. Experimentally, after having implemented a beam pointing alignment compensation method enabling us to adjust the position and dispersion independently, we demonstrate that the presence of non-negligible skew quadrupolar components induces a transversal spread and tilt of the beam, leading to an emittance growth and brightness reduction. We are able to reproduce the measurements with beam transport simulations using the measured electron beam parameters.

Undulator based synchrotron light sources and Free Electron Lasers (FELs) are valuable modern probes of matter with high temporal and spatial resolution. Laser Plasma Accelerators (LPAs), delivering GeV electron beams in few centimeters, are good candidates for future compact light sources. However the barriers set by the large energy spread, divergence and shot-to-shot fluctuations require a specific transport line, to shape the electron beam phase space for achieving ultrashort undulator synchrotron radiation suitable for users and even for achieving FEL amplification. Proof-of-principle LPA based undulator emission, with strong electron focusing or transport, does not yet exhibit the full specific radiation properties. We report on the generation of undulator radiation with an LPA beam based manipulation in a dedicated transport line with versatile properties. After evidencing the specific spatio-spectral signature, we tune the resonant wavelength within 200–300 nm by modification of the electron beam energy and the undulator field. We achieve a wavelength stability of 2.6%. We demonstrate that we can control the spatio-spectral purity and spectral brightness by reducing the energy range inside the chicane. We have also observed the second harmonic emission of the undulator.

It is now well established that laser plasma acceleration (LPA) is an innovative and good candidate in the beam acceleration field. Relativistic beams are indeed produced up to several GeV but their quality remains to be demonstrated in the highly demanding case of free-electron lasers (FELs). Several experiments have already shown the feasibility of synchrotron radiation delivery based on LPA but free-electron lasing has still to be achieved. Since the quality of the LPA beam inside the undulator is the critical issue, any LPA-based FEL experiment requires a refined characterization of the beam properties along the transport line and of the photon beam at the undulator exit. This characterization relies on diagnostics which must be adapted to the LPA specificities. Here, the electron and photon diagnostics already used on LPAs and required for LPA-based FELs are reviewed, and the critical points are illustrated using recent experiments performed around the world.

The COXINEL project aims at demonstrate the Free electrons laser amplification using Laser plasma accelerator. The control of electron beam properties of such accelerators, permit an observation of the spontaneous emission light from the udulator.

Cryogenic Permanent Magnet Undulator (CMPU) is capable of achieving high brightness radiation at short wavelengths, by taking advantage of the permanent magnet’s enhanced performance at low temperature. A CPMU of period 18 mm (U18) that has been built at Synchrotron SOLEIL is used for the COXINEL project to demonstrate Free Electron Laser (FEL) at 200 nm using a laser plasma acceleration source. Another undulator of period 15 mm (U15) is currently being built to replace U18 undulator for FEL demonstration at 40 nm. A new method is also introduced, using SRWE code, to compute the spectra of the large energy spread beam (few percent) taking into account the variation of the Twiss parameters for each energy slice. The construction of U18 undulator and the magnetic measurements needed for optimization, as well as the mechanical design of U15, are presented.

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 free-electron 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.

Laser Plasma Acceleration (LPA) is capable of producing a GeV beam within a cm accelerating distance, but with a rather high initial divergence and large energy spread. COXINEL aims to demonstrate a compact Free Electron Laser using such a source, where a specific transport line with adequate elements is used, such as tunable high gradient quadrupoles for handling the divergence. An innovative permanent magnet based quadrupole (QUAPEVA) made of two quadrupoles superimposed capable of generating a gradient of 200 T/m is presented. The first quadrupole consists of magnets shaped as a ring and attaining a constant gradient of 155 T/m, and the second one made of four cylindrical magnets surrounding the ring and capable of rotating around their axis to achieve a gradient tunability of ±46 T/m. Each tuning magnet is connected to a motor and controlled independently, enabling the gradient to be tuned with a rather good magnetic center stability (±10 μm) and without any field asymmetry. The measurements and field optimization of seven quadrupoles with different magnetic lengths are reported. A set of QUAPEVA triplet, installed at COXINEL, achieved good focusing and enabled beam based alignment.

Since the laser invention, the advent of X-ray Free Electron Lasers (FEL) half a century later, opens new areas for matter investigation. In parallel, the spectacular development of laser plasma acceleration (LPA) with several GeV beam acceleration in an extremely short distance appears very promising. As a first step, the qualification of the LPA with a FEL application sets a first challenge. Still, energy spread and beam divergence do not meet the state-of-the-art performance of the conventional accelerators and have to be manipulated to fulfill the FEL requirement. We report here on the undulator spontaneous emission measured after a transport manipulation electron beam line, using variable permanent magnet quadrupoles of variable strength for emittance handing and a demixing chicane equipped with a slit for the energy spread. Strategies of control electron beam position and dispersion have been elaborated. The measured undulator radiation provides an insight on the electron beam properties.

Laser Plasma Accelerators (LPA) can sustain GeV/m accelerating fields offering outstanding new possibilities for compact applications. Despite the impressive recent developments, the LPA beam quality is still significantly lower than in the conventional radio-frequency accelerators, which is an issue in the cases of demanding applications such as Free Electron Lasers (FELs). If the electron beam duration is below few tens of femtosecond keeping pC charges, the mrad level divergence and few percent energy spread are particularly limiting. Several concepts of transfer line were proposed to mitigate those intrinsic properties targetting undulator radiation applications. We study here the robustness of the chromatic matching strategy for FEL amplification at 200~nm in a dedicated transport line, and analyze its sensitivity to several parameters. We consider not only the possible LPA source jitters, but also various realistic defaults of the equipment such as magnetic elements misalignements or focussing strength errors, unperfect undulator fields, etc...

The ERC Advanced Grant COXINEL aims at demonstrating free electron laser amplification, at a resonant wavelength of 200 nm, based on a laser plasma acceleration source. To achieve the amplification, a 10 m long dedicated transport line was designed to manipulate the beam qualities. It starts with a triplet of permanent magnet with tunable gradient quadrupoles (QUAPEVA) that handles the highly divergent electron beam, a demixing chicane with a slit to reduce the energy spread per slice, and a set of electromagnetic quadrupoles to provide a chromatic focusing in a 2 m long cryogenic undulator. Electrons of energy 176 MeV were successfully transported throughout the line, where the beam positioning and dispersion were controlled efficiently thanks to a specific beam based alignment method, as well as the energy range by varying the slit width. Observations of undulator radiation for different undulator gaps are reported.

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.