• F. Klarner, O. Boldt, W. Hillert, N. Hofmann, D. Krönung
  ELSA, Bonn
• S. Aderhold
  DESY, Hamburg

In order to enhance the operating capabilities of the Bonn University Accelerator Facility ELSA, a new injector is currently under commissioning. Its purpose is to allow a single pulse mode as well as to increase the current of the unpolarized beam provided to the external hadron physics experiments. The injector will produce an up to 2 μs long pulse of 500 mA beam current or a single electron bunch with 2 A pulse current. Design and optimization of the injector were performed with Egun, PARMELA and numerical simulations based on the paraxial equation. A 1.5 ns long pulse is produced by a thermionic electron gun with 90 kV anode-cathode voltage, then compressed and pre-accelerated by a 500 MHz RF cavity and a four-cell travelling wave buncher. After acceleration of the electrons up to 25 MeV in the main linac the natural broadening of the energy distribution in the particle ensemble due to the acceleration process will be reduced by an energy compression system. Studies have been conducted concerning the adaptation of the optical elements in the transfer beamline to the booster synchrotron with respect to the new requirements of the injection into the synchrotron and its acceptance.

• F. Schlander, S. Aderhold, E. Elsen, D. Reschke
  DESY, Hamburg

Superconducting cavities have long been used in particle accelerators. The 1.3 GHz cavities developed in the TESLA collaboration will be the basis of the European XFEL and are the cavity of choice for the International Linear Collider (ILC). The fabrication of the cavities has been optimised over the past 20 years and will now be applied in industrial production of the 800 cavities foreseen for the XFEL. The DESY ILC group is developing tools to monitor those aspects of the production that affect the gradient of these cavities. The main obstacle in achieving a high gradient >30 MV/m is the quench induced in surface structures in the niobium. Such features are explored in an optical inspection of the 9-cell cavity structures and supplemented by measurements of the second sound that originates from the phase transition of the liquid helium at the position of the quench. Oscillating Superleak Transducers (OST) are used to record the signal of the second sound. The second sound measurements are thought to replace the time consuming direct temperature measurements on the outer cavity surface with a resistor system. The status of the various tools will be described.