Paper | Title | Page |
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TUPSO21 | SwissFEL Cathode Load-lock System | 259 |
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The SwissFEL electron source is an RF photo-injector in which the photo-cathode plug can be exchanged. Without load-lock, the cathode exchange takes about one week and cathode surface gets contaminated in the atmosphere during installation, leading to unpredictable quantum efficiency (QE) fluctuations. This motivated the construction of a load lock system to prepare and insert cathodes in the photo-injector. This load lock system consists of three parts: the preparation chamber, the transportable vacuum suitcase and the gun load lock chamber. This three parts system gives the possibility to prepare the cathode surface with methods like vacuum firing and plasma cleaning. The QE can be checked and the plug can be inserted in the gun without breaking vacuum. This will allow establishing an optimized a reproducible cathode preparation procedure. Since several cathodes can be loaded in advance, the exchange procedure reduces the machine shutdown to a few hours (shorter RF conditioning). The system is described and first experience with its use is reported. | ||
TUPSO86 | Photocathode Laser Wavelength-tuning for Thermal Emittance and Quantum Efficiency Studies | 434 |
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SwissFEL compact design is based on extremely low emittance electron beam from an RF photoinjector. Proper temporal and spatial shaping of the photocathode drive laser is employed to reduce the space charge emittance contribution. However, the ultimate limit for the beam emittance is the thermal emittance, which depends on the excess energy of the emitted photoelectrons. By varying the photocathode laser wavelength it is possible to reduce the thermal emittance. For this purpose, we developed a tunable Ti:sapphire laser and an optical parametric amplifier which allow to scan the wavelength between 250 and 305 nm. The system permits to study the thermal emittance and the quantum efficiency evolution as function of the laser wavelength for the copper photocathode in the RF gun of the SwissFEL injector test facility. The results are presented and discussed. | ||
TUPSO88 | New Concept for the SwissFEL Gun Laser | 442 |
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The operation of Swiss FEL put very stringent constrains on the gun laser system. First the parameters, such as energy stability, timing jitter, double pulse operation, temporal and spatial pulse shape of the ultra-violet laser pulses used to generate the photo-electrons are challenging even for the state of the art laser technologies. Second, the laser system must be extremely stable, reliable and its maintenance cost as low as possible. In this perspective, we prospected for alternative technologies to the well known, commonly used but costly Ti:sapphire laser systems. We show that a hybrid Yb fiber and solid state Yb:CaF2 amplifier system can be a very interesting approach. This gain medium allows the production of sub-500 fs, high fidelity, high stability, high energy pulses in the ultra-violet with low timing jitter. The system profits of the mature, stable direct diode pumping technology and optimized design. It delivers the two high-energy, shaped UV pulses separated by 28 ns to produce the photo-electrons, a short IR probe (<100 fs FWHM) to temporally characterize those pulses and the two stretched IR pulses ( 50 ps FWHM) necessary for the laser heater. | ||
WEPSO70 | Fully Phase Matched High Harmonics Generation in a Hollow Waveguide for Free Electron Laser Seeding | 693 |
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Funding: LASERLAB-EUROPE, grant n◦ 228334 PARIS ERC project (Contract No. 226424) Swiss National Science Foundation under grant PP00P2_128493 A bright high harmonic source is presented delivering up to 1011 photons per second around a central photon energy of 120 eV. Fully phase matched harmonics are generated in an elongated capillary reaching a cut-off energy of 160 eV. The high HHG fluence opens new perspectives towards seeding FELs at shorter wavelengths than the state of the art. Characterization of the phase matching conditions in the capillary is presented. |
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