Sven Sievers

INJECTOR UPGRADE FOR THE SUPERCONDUCTING ELECTRON ACCELERATOR S‐DALINAC

Since 1991 the superconducting Darmstadt linear accelerator S‐DALINAC provides an electron beam of up to 130 MeV for nuclear and astrophysical experiments. The accelerator consists of an injector and four main linac cryostats, where the superconducting cavities are operated in a liquid helium bath at 2 K. Currently, the injector delivers beams of up to 10 MeV with a current of up to 60 μA. The upgrade aims to increase both parameters, the energy to 14 MeV and the current to 150 μA. Due to an increase in the required RF power to 2 kW the old coaxial RF input couplers, being designed for a maximum power of 500 W, have to be replaced by new waveguide couplers. Consequently, modifications to the cryostat‐module had become necessary. We review the design principles, the necessary changes in RF components (i.e. couplers, transition line, stub tuner), the production of the SRF cavities and the new magnetic shielding. A report on the status will be given.

New injector cryostat module based on 3 GHz SRF cavities for the S-Dalinac

Each cryostat module of the superconducting Darmstadt electron linear accelerator S-DALINAC houses two 20 cell elliptical niobium cavities cooled by a helium bath at 2 K. They are operated at a frequency of 3 GHz and used to accelerate electron beams with gradients up to 5 MV/m. The accelerator itself consists of an injector and four main linac cryostats. A new cryostat module has been built to replace the actual injector module. It features a new waveguide transition line and will be operated with new cavities in order to increase the beam current and energy for nuclear physics experiments behind the injector section of the S-DALINAC. In addition, the frequency tuner for the cavities will be equipped with piezoelectric actuators, which will replace the current magnetostrictive fine tuner. We review the latest changes in the design of the module and its RF transition line and present some findings from the production of new cavities. The results of a measurement in liquid helium at 2 K with the piezoelect...

Upgrade of a UHV Furnace for 1700 C Heat Treatment and Processing of Niobium Samples

In 2005 a high temperature vacuum furnace was put into operation at the Institute for Nuclear Physics at the Technische Universität Darmstadt. It has been designed for firing pure Niobium at temperatures of up to 1870 °C. Until now several Nb cavities have been heat treated at 850 °C with a proven record of success [1]. The current focus of research in improving the superconductive characteristics of accelerator cavities is on new materials such as Nb3Sn or NbN or on the doping of Nb surfaces with nitrogen, so called N2-Doping [2]. The surface preparations generally take place at temperatures of not more than 1000 °C. To study phenomena that occur at higher temperatures, like the formation of δ-phase NbN at 1300 to 1700 °C, we refurbished the UHV furnace and equipped it with state-of-the-art infrastructure. The vacuum system was updated as well as a new power interlock was applied due to a failure of the previous system. We designed a new annealing pot and planned its construction; the dimensioning of an appropriate sample holder is