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The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern free electron lasers. A continuous experimental optimization of the L-band photo injector for such FEL facilities like FLASH and the European XFEL has been performed for a wide range of electron bunch charges – from 20 pC to 2 nC – yielding very small emittance values for all charge levels. Experience and results of the experimental optimization will be presented in comparison with beam dynamics simulations. The influence of various parameters onto the photo injector performance will be discussed.

20 pp. (2007)., In some special parts of present projects, such as X-FEL and ILC, normal conducting cavities are applied, operating with high electric and magnetic fields. RF guncavities with an electric field up to 60 MV/m at the photo cathode are now under development. Capture cavities in the ILC positron source should operate with an accelerating gradient of up to 15 MV/m , practically the same value (14 MV/m ), as for the CDS booster cavity in the Photo Injector Test Facility at DESY in Zeuthen (PITZ). Such operating conditions, together with long (∼ 1ms) RF pulse, lead to the apparent cavity pulsed heating effect. In this report we describe the procedure and results of pulsed heating effect simulations in L-band cavities, operating with high pulsed RF loss density and long RF pulse.

The 7th European Particle Accelerator Conference EPAC 2000, EPAC 2000, Vienna, Austria, 26 Jun 2000 - 30 Jun 2000; Hamburg : DESY 2069-2071 (2000)., The basic elements of the TESLA linear collider with integrated X-ray FEL are superconducting accelerating cavities. The standard TESLA rf system is designed for a long (1300μs) rf pulse with a flat-top of 800μs and has several elements for the rf power distribution and protectionagainst reflected rf power. Together with the superconducting cavities, normal conducting (NC) cavities are used in TESLA for different purposes, for example as a rf gun. As a rule, one NC cavity uses the total rf power from one klystron (5MWor 10 MW). During the short transient period (the filling time for the L-band NC cavity is near 3μs) the reflected rf power and overvoltage in the waveguide (due to the interference of the forward and backward waves) exceeds the safety limit for the L-band waveguide operation (without SF6 filling). With a special shape of the start up of the rf pulse it is possible to reduce the reflected power several times and limit the overvoltage to a safe level. The increasing of the total pulse length is in the order of two filling times (6μs) and hence negligible in comparison with the total pulse length of 800μs. Different shapes of the beginning of the rf pulse are both considered to reduce the reflected power and to restrict the overvoltage. Results of experiments are presented., Published by DESY, Hamburg

The 7th European Particle Accelerator Conference EPAC 2000, EPAC 2000, Vienna, Austria, 26 Jun 2000 - 30 Jun 2000; Hamburg : DESY 462-464 (2000)., The TESLA linear collider with integrated X-ray FEL is based on superconducting accelerating cavities. Behind the positron production target normal conducting cavities have to be used in order to cope with high particle losses and with focusing solenoids surrounding the cavities. With the long rf pulse (800$\mu$s flat-top) the achievable gradients are limited by rf power and heat load restrictions. Beam dynamics calculations of a standing wave preaccelerator will be discussed. The proposed preaccelertor includes an electron-positron beam separator section and is followed by a long transfer line and a matching section into a superconducting booster linac in which the positrons are accelerated to the damping ring energy of 5 GeV. The overall layout of the injector linac and the optimization of relevant parameters, as well as beam dynamics calculations will be presented., Published by DESY, Hamburg

The 7th European Particle Accelerator Conference EPAC 2000, EPAC 2000, Vienna, Austria, 26 Jun 2000 - 30 Jun 2000; Hamburg : DESY 842-844 (2000)., The Positron Pre-Accelerator (PPA) for the TESLA linear collider should be a normal conducting linac and use the standard TESLA rf hardware. For L-band frequency range both Standing (SW) and TravellingWave (TW) operations are possible. For comparison, rf parameters for TW Disk LoadedWaveguide (DLW) as well as for SW Coupled Cells Structures (CCS) have been optimized at an operating frequency of 1300 MHz in a wide range of cells dimensions. General properties for the two operating modes have also been compared. Taking into account the beam dynamic particularities, a SW mode has been chosen. It provides a higher flexibility and allows one to combine the required beam performance with a cost saving problem solution. With an increased aperture diameter, the SW PPA has an enlarged acceptance, in comparison with the TW PPA, and a reduced power consumption., Published by DESY, Hamburg