Emittance measurements and minimization at the SwissFEL Injector Test Facility

Abstract

The emittance of the electron beam is crucial for Free-Electron Laser facilities: it has a strong influence on the lasing performance and on the total length of the accelerator. We present our procedure to measure and minimize the projected and slice emittance at the SwissFEL Injector Test Facility. The normalized slice emittance resolution achieved is about 3 nm and the longitudinal resolution is about 13 fs, with measurement errors estimated to be below 5%. After performing a full optimization we have obtained, for uncompressed beams, a slice emittance of about 200 nm for a beam charge of 200 pC, and a slice emittance of about 100 nm for 10 pC. These values are consistent with our simulations and are well below the requirements of the SwissFEL under construction at the Paul Scherrer Institute. At these bunch charges our measured slice emittances are, to our knowledge, the lowest reported so far for an electron linear accelerator.

Simple Method to Generate Terawatt-Attosecond X-Ray Free-Electron-Laser Pulses

“…longitudinal profile with a peak current of 6 kA and a total charge of 200 pC, an energy of 5.8 GeV, an energy spread of 350 keV, a normalized slice emittance of 300 nm, and an average β function along the undulator of 10 m. The assumed emittance value is consistent with our measurements at the SwissFEL Injector Test Facility [31,32]. Each undulator module is 4 m long and has a period length of 15 mm and a variable gap with a nominal undulator-parameter value of 1.2.…”

Performance of a second generation X -band rf photoinjector

“…rf guns offer low emittance beams that can be accelerated to the necessary operating energy to lower the geometric emittance, and temporally compressed to the required peak current for free-electron laser (FEL) operation [3][4][5]. X-band rf technology is capable of up to 200 MV=m accelerating gradients, making novel compact accelerator systems possible.…”

Generation of ultra-large-bandwidth X-ray free-electron-laser pulses with a transverse-gradient undulator

“…the part whose betatron oscillations are small enough to allow a good transverse overlap between the electron and photon beams. This concept has been proposed to reduce the XFEL pulse duration and to generate high-power and short XFEL pulses (Prat et al, 2015). In our case, however, all the electrons need to produce XFEL radiation and the transverse positions of the electrons must be as constant as possible in order for a longitudinal slice to radiate at the same frequency.…”

“…The transverse tilt of the beam can be generated with different methods, all relying on standard components of XFEL facilities: applying a transverse deflecting RF structure to streak the beam (Loew & Altenmueller, 1965), introducing dispersion to an energy chirped beam (Prat & Aiba, 2014), or using the transverse wakefields (Zotter & Kheifets, 1998) of the accelerating or any other structures of the beamline. The beam tilt can be easily tuned if it is generated with a transverse deflector by simply varying the deflector voltage.…”