STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
USTRAT/SUPA, Glasgow
Cockcroft Institute, Warrington, Cheshire
Start-to-end modelling of a SASE mode-locked FEL amplifier scheme [1] is presented using a superconducting re-circulating linac design[2]. Locking of the modes is achieved by modulating the electron beam energy at the mode frequency spacing. Previous studies [3] have shown that in a High Harmonic Generation (HHG) seeded mode-coupled FEL amplifier scheme (no electron beam energy modulation), although the attosecond pulse train structure of the seed is amplified through to saturation, temporal broadening of the individual pulses occurs. An HHG seeded mode-locked FEL amplifier scheme is modelled and it is seen that the temporal spikes of the HHG seed must be correctly phase-matched with the electron beam energy modulation for successful operation. By using a filtered HHG seed, which removes the seed’s attosecond pulse train structure, no such phase matching is required. Despite the absence of an initial attosecond pulse structure, a modal structure develops and is subsequently amplified to generate an attosecond pulse train with the good temporal coherence properties of the seed, significantly shorter individual pulse widths and higher peak powers than may be achieved in the other schemes.
[1] N.R. Thompson, B.W.J. McNeil, Phys. Rev. Lett. 100, 203901 (2008)
[2] P.H. Williams et al, WE5RF, 23rd PAC, Vancouver (2009)
[3] B.W.J. McNeil et al, MOCAU04, 30th Int. FEL Conf., Gyeongju (2008)
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
KEK, Ibaraki
The University of Liverpool, Liverpool
STFC/DL/SRD, Daresbury, Warrington, Cheshire
ALICE (Accelerators and Lasers In Combined Experiments), a 35 MeV energy recovery linac based light source, is being commissioned and developed as an experimental R&D facility for a wide range of projects that could employ synchronized ultra-short (<1ps) electron bunches and light pulses. A suit of light sources includes an IR FEL, Compton backscattering (CBS) X-ray source, high power THz source and a multi-TW femtosecond laser. The full energy recovery and coherently enhanced, due to shortness of the electron bunches, THz radiation have been already demonstrated on ALICE. Completion of the first phase of the CBS x-ray source experiment and first lasing of the IR FEL by the end of 2009. Status of ALICE experimental facility and latest results on FEL, THz, and CBS development are reported in this paper.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
STFC/DL, Daresbury, Warrington, Cheshire
The ALICE (Accelerators and Lasers in Combined Experiments) facility (formerly known as ERLP) is currently being commissioned at Daresbury Laboratory. It serves as a test facility for novel accelerator and photon science applications. As part of this facility, an oscillator-type FEL will be commissioned later in 2009. The FEL will be used to test energy recovery with a disrupted beam and to provide output for a select experimental programme. The FEL output will be measured and used to determine the accuracy of FEL modelling techniques. The facility could also potentially be used as a testbed for novel FEL concepts. In this paper, an overview of the FEL design is presented, together with an update of the status of commissioning preparations, including time-dependent modelling using the expected electron beam parameters.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
JAI, Oxford
USTRAT/SUPA, Glasgow
The New Light Source (NLS) project was launched in April 2008 by the UK Science and Technology Facilities Council (STFC) to consider the scientific case and develop a conceptual design for a possible next generation light source based on a combination of synchronised conventional laser and free-electron laser sources. The requirement identified for the FELs was continuous coverage of the photon energy range 50-1000eV with variable polarisation, 20fs pulse widths and good temporal coherence to as high a photon energy as possible. This paper presents a design study of three separate FELs which in combination satisfy these requirements. It is proposed to use an HHG seed source tunable from 50-100eV giving direct seeding at the fundamental FEL wavelength up to 100eV, then one or two stages of harmonic upconversion within the FEL to reach the higher photon energies. FEL simulations using realistic electron beam distributions tracked from the gun to the FEL will be presented, illustrating the predicted coherence properties of the FEL output at different photon energies.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
STFC/DL, Daresbury, Warrington, Cheshire
The choice of undulator design and minimum magnet gap is crucial in the definition of every short wavelength FEL and is ultimately a cost driver for that project. The magnet gap selection is a compromise between wanting to minimise harmful wakefield effects whilst at the same time generating high magnetic fields with short periods. The NLS project has tried to take a holistic approach in the definition of the undulators. This has been carried out by first assessing the impact of resistive wall wakefields in general on the FEL performance and then selecting the maximum level of wakefield which has a just tolerable impact on the FEL. This wakefield is then translated into equivalent circular and elliptical vessel geometries. Suitable vessel thickness and mechanical tolerances are then added to define the undulator magnet gap for the case of a circular vessel (Delta undulator) and an elliptical vessel (APPLE-2 undulator). Finally, the two types of undulator have been modelled, their parameters compared, and a selection made. This paper summarises this global self-consistent approach to undulator definition and reports on the result for the NLS.