A Soft X-ray FEL (the SXL) using the existing 3 GeV linac at the MAX IV Laboratory is currently in the design phase. In this contribution, start-to-end simulations, including the photo-injector simulations using ASTRA, the linac simulations using ELEGANT and the FEL simulations using GENESIS, are presented for 100 pC and 10 pC operation modes. The features of the electron beam from the MAX IV linac and their impact on the FEL performance are discussed.

A Soft X-ray Laser project (the SXL) aiming to produce FEL radiation in the range of 1 to 5 nm is currently in a conceptual design phase and a report on the design is expected to be delivered by March 2021. The FEL will be driven by the existing 3 GeV linac at MAX IV laboratory, which also serves as injector for the two storage rings. The science case has been pushed by a large group of mainly Swedish users and consists of experiments ranging from AMO physics to condensed matter, chemistry and imaging in life science. In this contribution, we will present the current conceptual design of the accelerator and the FEL operation modes together with a general overview of the beamline and experimental station. In particular design options for the FEL will be discussed in conjunction with the features of the electron beam from the MAX IV linac and the connection with the proposed experiments. (Less)

The process of high-order harmonic generation requires laser intensities around 1014 W/cm2, most easily reached with laser pulses of high energy, thus implicitly limiting the repetition rate of attosecond sources. A route towards multi-MHz attosecond sources relies on HHG inside a passive enhancement cavity [1]. Although successfully demonstrated for attosecond pulse trains, the generation of single attosecond pulses (SAPs) inside a cavity remains an unsolved challenge, mainly limited by dispersion management and out-coupling problems. We recently proposed a new gating concept for SAP generation [2], noncollinear optical gating (NOG) which has the potential to facilitate SAP gating and efficient out-coupling at once. Similar to the recently introduced attosecond lighthouse [3] NOG employs attosecond angular streaking [4] and combines this concept with noncollinear HHG, proposed earlier [5] as out-coupling method for intra cavity HHG. (Less)

The FemtoMAX beamline facilitates studies of the structural dynamics of materials. Such studies are of fundamental importance for key scientific problems related to programming materials using light, enabling new storage media and new manufacturing techniques, obtaining sustainable energy by mimicking photosynthesis, and gleaning insights into chemical and biological functional dynamics. The FemtoMAX beamline utilizes the MAX IV linear accelerator as an electron source. The photon bursts have a pulse length of 100 fs, which is on the timescale of molecular vibrations, and have wavelengths matching interatomic distances (Å). The uniqueness of the beamline has called for special beamline components. This paper presents the beamline design including ultrasensitive X-ray beam-position monitors based on thin Ce:YAG screens, efficient harmonic separators and novel timing tools.

The MAX IV Laboratory is a synchrotron radiation user facility located just outside the city of Lund, Sweden. The facility is made up of two storage rings, at 3 GeV and 1.5 GeV, respectively, and a linear accelerator, serving as a full-energy injector for the rings as well as a driver for the Short-Pulse Facility (SPF) located downstream of the extraction point to the 3 GeV ring. Recently, as part of the Soft X-ray Laser (SXL) project, a design study towards using the linac as a soft X-ray free-electron laser (FEL) driver was started. Part of the study is the design and commissioning of a diagnostics beamline based on a Transverse Deflecting Structure (TDS). Moreover, the PlasMAX collaboration is working towards using the MAX IV linac also for beam-driven plasma-wakefield (PWFA) experiments. Therefore, the design of the diagnostics beamline is being done to also accommodate an interaction chamber and final focusing, located upstream of the TDS. This proceeding details the current status of the beamline design and shows some preliminary single- and double-bunch current measurements.

The design of the pre-injector, including the new gun, for the SXL project [1] is being finalised for the desired modes of operation, 100 pC and 10 pC with short bunches. The photocathode gun is currently being manufactured and experiments in the MAX IV guntest facility are under preparation to verify the design. In this paper we present the design of the gun and the pre-injector and show some results from simulations using MOGA indicating an emittance less than 0.3 mm mrad.

The ability to generate two-color free-electron laser (FEL) radiation enables a wider range of user experiments than just single-color FEL radiation. There are different schemes for generating the two colors, the original being to use a single bunch and two sets of undulators with different K-parameters. An alternative scheme was recently shown, where two separate bunches in the same RF bucket are used for lasing at different wavelengths in a single set of undulators. We here investigate the feasibility of accelerating and compressing a double-bunch time structure generated in the photocathode electron gun for subsequent use in a soft X-ray FEL at the MAX IV Laboratory.

The MAX IV linac is investigated as a FEL driver in the SXL project, but there is also an ongoing investigation in using the linac as a driver for beam driven plasma wakefield acceleration experiments. From both these applications, double pulses from the photoinjector within the same RF period is desired. In this paper we discuss the possibilities of using the current photoinjector at MAX IV as driver and show simulations results from the pre-injector, both for FEL applications and for PWFA applications.

Generation of few-cycle optical vortex pulses is challenging due to the large spectral bandwidths, as most vortex generation techniques are designed for monochromatic light. In this work, we use a spiral phase plate to generate few-cycle optical vortices from an ultrafast titanium:sapphire oscillator, and characterize them in the spatiotemporal domain using a recently introduced technique based on spatially resolved Fourier transform spectrometry. The performance of this simple approach to the generation of optical vortices is analyzed from a wavelength dependent perspective, as well as in the spatiotemporal domain, allowing us to completely characterize ultrashort vortex pulses in space, frequency, and time.

The MAX IV injector design predicts a beam with 100 pC of charge and an emittance lower than 1 mm mrad. The photocathode pre-injector is based on the now close to standard 1.6-cell gun adapted to 2.9985 GHz, in combination with a Ti:Sapphire laser system. This system reaches the requirements of the injector operation for the SPF, but can be tuned beyond specifications to open up new operation modes. During 2016 and 2017 several aspects where investigated to improve the emittance from the current gun, the goal was to meet the SPF specifications. In this paper we report on the progress, discuss the steps taken leading to a final emittance of ~ 1 mm mrad and beyond.

Beam-driven plasma-wakefield acceleration is an acceleration scheme promising accelerating fields of at least two to three orders of magnitude higher than in conventional radiofrequency accelerating structures. The scheme relies on using a charged particle bunch (driver) to drive a non-linear plasma wake, into which a second bunch (witness) can be injected at an appropriate distance behind the first, yielding a substantial energy gain of the witness bunch particles. This puts very special demands on the machine providing the particle beam. In this article, we use simulations to show that, if driver-witness-bunches can be generated in the photocathode electron gun, the MAX IV Linear Accelerator could be used for plasma-wakefield acceleration. (Less)

A Soft X-ray Laser (SXL) beamline utilising FEL technology is being designed for the Short Pulse Facility (SPF) at the MAX IV Laboratory. A conceptual design study has been started following on the scientific case already prepared in collaboration between several Swedish Universities and driven by a strong (Swedish) user demand. The baseline goal of the SXL beamline is to generate intense and short pulses in the range 1-5 nm (0.2-1 keV). The system is building on the MAX IV linac system, already today providing 100 fs 3 GeV and pulses compressed to 100 fs for other applications within the SPF. As a special feature we foresee a variety of pump-probe capabilities. INTRODUCTION The Short Pulse Facility (SPF) at the MAX IV laboratory is designed to utilize compressed electron pulses directly from the S-band linear accelerator at energies up to 3 GeV. In this facility (fig. 1) there is at the moment one beamline, FemtoMAX, but there are available “slots” for another 2-3 stations or experiments. Ideas for both a hard X-ray free electron laser extension and a station for plasma wake field acceleration [1] have been put forward. The most elaborated idea was put forward by a Swedish user consortium, detailed during a workshop in Stockholm in 2016 [2] gathering more than 100 participants. This is an advanced beamline in the soft X-ray range which will provide coherent pulses at high peak power in the range from 0.2-1 keV. To achieve the necessary requirements the accelerator will drive a free electron laser (FEL), the Soft X-ray Laser (SXL). The SXL will enable ground breaking scientific discoveries and understanding in many important fields such as atomic and molecular science, chemistry, condensed matter physics, and life science. These opportunities are created by the intense, ultrashort and coherent soft X-ray pulses generated by the SXL together with unique pumping options, detection schemes and imaging possibilities. A specific asset of the soft X-ray spectral region is that it provides access to many important absorption edges (e.g. C, N, O, and 3d transition metals) and thus permits the use of powerful spectroscopic and coherent techniques in a timeresolved manner. In combination with pump pulses covering the full spectral range from THz to soft X-rays, not accessible at any existing FEL, and with potential for attosecond temporal resolution, new exciting pump-probe studies can be performed which addresses several meaningful scientific questions. Scientifically and technically the SXL will complement the FemtoMAX beamline which can reach far higher photon energies in intense, short, partially coherent pulses. The SXL project is a collaboration among many research groups in Sweden with experience in both science at FELs and groups with experience of accelerators. Partners come from the MAX IV laboratory, the Stockholm-Uppsala FEL center, Uppsala University, Lund University, Stockholm University and the Royal Institure of Technology. The scientific interest of the SXL project though, spreads over all Swedish universities. Figure 1: The MAX IV linear accelerator. A Conceptual Design Study has been initiated and will mainly focus on the design of the FEL itself and the assurance of the performance of the MAX IV linear accelerator as FEL driver. In addition the beamlines and experimental stations will be defined, while the scientific case is basically in place [3]. The conceptual design should be ready after two years and provide the base for an application of funding of the full project. This is adjusted into the overall ___________________________________________ * Corresponding author: Sverker.werin@maxlab.lu.se WEPAB077 Proceedings of IPAC2017, Copenhagen, Denmark ISBN 978-3-95450-182-3 2760 Co py rig ht © 20 17 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs 02 Photon Sources and Electron Accelerators A06 Free Electron Lasers timeplan for expansion of experimental facilities at the MAX IV Laboratory. The strategy of the MAX IV Laboratory in an even longer perspective also includes an expansion with a hard X-ray FEL based on an extended energy of the linear accelerator. However the funding situation in a near perspective is not believed to be strong enough, and thus the SXL project will provide the first step from which competence and experience towards a full X-ray FEL can be realized beyond 5 years. THE FREE ELECTRON LASER The SXL beamline at MAX IV will provide high power pulses, with pulse lengths below 100 fs in the 0.25-1 keV photon energy range. This basic idea has been presented previously [4], but with input from the Swedish user community the focus of what has become the SXL project has been updated. The most important input on the SXL design is the discussion on seeding. Seeding can provide wavelength and power stability but is not fully available in the actual wavelength range today [5]. The available technology is selfseeding where a shorter FEL ends before saturation and the optical pulse is passed through a monochromator and reinjected onto the electron beam as a seed pulse. This method is still not easy to operate for users and thus the conclusion is to start in SASE mode and when seeding is developed further include this in a second phase. The scientific questions in the present wavelength range will benefit strongly from a two pulses and two colour scheme. This is regarded as fundamental, and should, if possible, be part of the first phase and fully implemented in a second phase. Short photon pulses are of interest, but initially most science will satisfy with pulses >10 fs. In a second phase the SXL should approach single fs pulses and possibly into the as-region. Schemes for generating few femtosecond pulses and shorter are currently being developed [6, 7, 8] and can be made available for the SXL. The SXL should be flexible enough that seeding schemes and ultrashort pulse operation modes can be implemented in a second phase. Special emphasis should be put on providing a set of multiple pump sources for which the integration and concepts should be developed. While visible and VUV lasers are already available in the FemtoMAX beamline, the implementation of soft X-ray and THz systems has to be addressed. In a first phase both a THz source and a UV-laser are required. Later this should be complemented with soft X-ray HHG lasers and possibly also a THz undulator or even a THz FEL. Pump-probe operation also sets the requirements for timing and synchronization which has to be integrated in the design. The undulator technology for the SXL is still an open question (see tab. 1). The user input is clear in that full polarization control is necessary. This probably removes the option of utilising only compact short period (below 20 mm) undulators, which would provide the most compact system. Compactness is otherwise a key feature as the SXL is to be fitted within the existing buildings or with a limited extension. As the linac at MAX IV also is used for top-up into the storage rings, it might turn out a feature if the energy could remain unchanged. Thus a rather long period (35-40 mm) undulator could be considered (compare SwissFEL [9]), which would cover the wavelength range in a limited energy span. It is also important to note that the undulators will be an (the) important cost driver. Table 1: Two Sets of Tentative Parameters for the SXL Based on Different Undulator Concepts (Values given by analytical approximation.) Undulator type Planar in-vacuum APPLE II/III Period (mm) 18 36 (mm mRad) 0.4 Wavelength (nm) 1 5 1 5 ̅̅ ̅̅ ̅̅ ̅(m) 10 Photon energy (keV) 1.24 0.25 1.24 0.25 ̂ (A) 1400 e-Energy (GeV) 3 1.35 3 2.6 Q (nC) 100 K 2.38 2.38 1.35 3.5 (fs) 30 L-saturation (m) 18 11 29 15 ∆ ⁄ 1e-4 Photon power (peak) some GW THE MAX IV LINEAR ACCELERATOR The MAX IV linear accelerator [10] is used for both fullenergy injection and top-up to two storage rings, and as a high brightness driver for a Short Pulse Facility (SPF) [11]. The linac was already in the initial plans around year 2000 drawn with the idea that it should be able to handle the high demands of a Free Electron Laser, such as short pulses, high peak current, low emittance and high beam stability (tab. 2). During spring and early fall of 2016 a pre-study concluded that the MAX IV linac design gives a performance that is within the assumed requirements for SXL. The initial measurements on the linac show no indications for the specifications not being possible to achieve. However, in order to reach the design goals, a couple of developments are foreseen and some upgrades and changes may be needed in areas like gun, diagnostics, laser, optics and bunch compressors. Many of these developments are already expected and prepared for, and none of them would be impossible to achieve within the current MAX IV linac design. Proceedings of IPAC2017, Copenhagen, Denmark WEPAB077 02 Photon Sources and Electron Accelerators A06 Free Electron Lasers ISBN 978-3-95450-182-3 2761 Co py rig ht © 20 17 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs Table 2: MAX IV Linac Parameters Energy 3 GeV Energy spread <0.05% + chirp RF Frequency 3 GHz Rep. rate 1-100 Hz Bunch length 10-500 fs Charge per bunch 20-200 pC Normalised emittance <1 μm INFRASTRUCTURE A compact solution may fit into the SPF building. There are two main alternatives for its placement. The FemtoMAX beamline already occupies the second branchline position and an easy solution is to place the SXL at the adjacent first branchline (fig. 2). This would require the smallest adaptions of the building but on the other hand it allows only for a short SXL system with a basic SASE FEL operation using planar undulators. A second option is to put the SXL in the tunnel called the “future klystron gallery”. This provides a longer available length for the undulators and more space for the experimental stations, and thus more flexibility. Even more flexible alternatives are created by extending the SPF

The MAXIV injector has two guns - a thermionic used for ring injections, and a photocathode used for short pulse facility operation. A commercial Ti:sapphire laser from KMLabs drives the copper based photocathode gun. It has been running without major issues for more than 3 years. The laser delivers up to §I{500}{\textmu J} on the cathode at the third harmonic, §I{263}{nm}, via a vacuum laser transport system. To achieve the desired pulse duration of 2–§I10{ps} the laser pulses, originally ~§I{100}{fs} long, are stretched with a prism pair and the resulting §I{1.5}{ps} pulses stacked by a series of birefringent \textalpha -BBO crystals. Diagnostics consist of photodiodes, spectrometers, and cameras. Longitudinal pulse characterization is done with a cross correlator and a UV FROG.

The gun test stand from MAX-Lab has been upgraded and moved to a new facility at the MAX IV Laboratory. The new test stand will reuse parts of the equipment from the old test stand but a number of improvements to the setup are be made. In this paper we report on the design of the new gun test stand, research plans in the near future as well as planned and possible future research topics.

The MAX IV Linac is now in routine operation for injection into two storage rings, and as a high-brightness driver for a Short Pulse Facility (SPF). In short-pulse mode the electron bunch is created in a photo cathode gun and compressed in two double achromat bunch compressors that also linearise longitudinal phase space with the second order transfer matrix element T566. T566 in the compressors canbe tweaked with weak sextupoles located at high dispersion. In this paper we present the current experience from operating the bunch compressors at MAX IV and results from initial measurements of longitudinal phase space using our version of the the zero-crossing method.

The MAX IV linac is used both for injection into a 3 GeVstorage ring, and as a high brightness driver for a Short PulseFacility (SPF). It has also been deigned to handle the highdemands of an FEL injector.The linac is now routinely injecting into the two storagerings,and commissioning work is focused towards deliveringhigh brightness pulses to the SPF. In this paper we presentresults from characterisation of the linac in ring injectionmode, as well as results from measurements of key parametersfor the SPF such as bunch length and emittance.

Electron dynamics induced by resonant absorption of light is of fundamental importance in nature and has been the subject of countless studies in many scientific areas. Above the ionization threshold of atomic or molecular systems, the presence of discrete states leads to autoionization, which is an interference between two quantum paths: direct ionization and excitation of the discrete state coupled to the continuum. Traditionally studied with synchrotron radiation, the probability for autoionization exhibits a universal Fano intensity profile as a function of excitation energy. However, without additional phase information, the full temporal dynamics cannot be recovered. Here we use tunable attosecond pulses combined with weak infrared radiation in an interferometric setup to measure not only the intensity but also the phase variation of the photoionization amplitude across an autoionization resonance in argon. The phase variation can be used as a fingerprint of the interactions between the discrete state and the ionization continua, indicating a new route towards monitoring electron correlations in time.

Photoionization with a single photon is one of the fundamental processes in nature, in which one electron is ripped away from its atom. Traditionally studied in the energy domain, this process was believed to be instantaneous, but recent advances in the production of attosecond pulses (1 as 10−18 s) in the eXtreme UltraViolet (XUV) have renewed interest in understanding the temporal aspects of electron emission in atoms, molecules and the solid state [1–8]. We present here our progress in understanding the influence of electronic correlations on the attosecond photoionization dynamics.