Asymmetric output profile of Xe Laser

A new set of asymmetric modes was recently revealed in a Xe slab laser with pronounced lens effects originating from gas heating in the discharge. The appearance of these modes is a threshold effect. Their domain of existence in the Xe laser is discussed. It is shown that mode competition can result in output radiation asymmetry. Theoretical results are compared with experimental data

The injector microtron for the TEUFEL infrared laser

Progress is reported on a 25 MeV injector racetrack microtron for a 10 ¿m radiation free electron laser (TEUFEL project). The accelerator exhibits transverse focusing in 180° inhomogeneous two-sector dipole magnets which are slightly rotated with respect to each other in the bending plane. This provides closed orbits, isochronism and a large transverse acceptance. Details on this unconventional microtron focusing system will be given. An analytical treatment, based on conformal mapping, of the field near pole boundaries and at the hill-valley boundaries in the microtron dipole is compared with Poisson calculated results and with field measurements. The design of a model accelerating cavity is presented together with field measurements based on the perturbation ball method

Zero slippage operation of TEUFEL

The Free Electron Laser in Twente TEUFEL is very suitable to operate near zero slippage conditions. The resonator is a waveguide structure with hole coupling for the electron beam to enter and exit and to out-couple the light. Due to the long wavelength, the diameter of the waveguide can have macroscopic dimensions to significantly affect the group velocity of the generated light via the dispersion relation. Whereas the longitudinal phase-velocity has to be equal to the longitudinal velocity of the electrons to be at resonance, the longitudinal group velocity has to be equal the longitudinal velocity of the electrons too, to operate in the zeroslippage regime. Both conditions can be fulfilled in a waveguide. Advantage of operation in the zero-slippage regime is to allow short pulse operation at high gain. The energy density of the light travels with the electron pulse. For our FEL we expect operation with the following parameters: Electron energy 4 MeV; diameter of circular waveguide 3.2 mm; generated wavelength 658 mm; pulse duration 25 ps. Due to the high quality beam, i.e. high current and low emittance we expect high gain

Het effect van transversale modi in een golfpijp-resonator op de resonantieconditie van een Compton Vrije-Elktronen-Laser

In een Vrije-Elektronen-Laser (FEL), waar de resonator de structuur heeft van een golfpijp, heeft de fasesnelheid van het licht een significante impact op de golflengte van het gegenereerde licht. Dit is een effect dat bekend is in Raman-FEL’s maar het is minder bekend dat het ook een belangrijke rol kan spelen in Compton FEL’s. Het effect is experimenteel geverifieerd in onze 6 MeV Compton FEL. De FEL heeft een golfpijp-resonator met vlakke eindspiegels waarin concentrisch een gat is gemaakt voor de inkoppeling van de elektronen en de uitkoppeling van het licht. Opeenvolgende transversale modes, die elk hun eigen fasesnelheid hebben, zijn duidelijk in het golflengte spectrum te onderscheiden. Gelijktijdige resonanties met een golflengte verschil van 5% zijn gemeten. In gangbare lasers is dit verschil doorgaans niet groter dan 0.1%

Tuning and characterisation of Twente Wiggler

For correcting field errors in the Twente wiggler small metal shims were placed on the pole faces. When applied to correct errors in the on-axis field a large increase in the errors in the off-axis field was found. When instead errors in the off-axis field are corrected, the errors in the on-axis field are reduced as well. Only small corrections were locally required to make the errors in the on-axis field acceptable. The focussing strength of the wiggler has been measured in both transverse planes and was found to lead to a slightly elliptical shape for a matched electron beam. Longitudinal phase errors have been measured for the Twente wiggler and are negligible

Never mind Brexit scaremongering – Turkey is a long way from joining the EU

An overview of the design of the undulator for the Twente free electron laser is presented. The undulator is of the planar hybrid type, i.e. alternating permanent magnetic material and poles. The overall design is based on the method of Halbach. The flux balance is set up for the three-dimensional fluxes which are derived from the two-dimensional calculations. The undulator, using magnetic materials Sm1Co5 and 2V-permendur, has a wavelength of 25 mm, K value of 1, and a betatron wavelength (at equal focusing) of 300 mm for an electron beam of 6 MeV. An optimization is performed on a circular shape of the pole faces. The entrance and exit are tapered to allow a straight passage of the electron beam through the undulator. The tapering is adjusted to the requirements of minimal steering and displacement of the electron beam