• C. Koschitzki, A. Hoehl, R. Klein, R. Thornagel
  PTB, Berlin
• J. Feikes, M.V. Hartrott, G. Wüstefeld
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin

For the operation of the Metrology Light Source (MLS)*, the electron storage ring of the Physikalisch-Technische Bundesanstalt (PTB), as a primary radiation source standard all storage ring parameters have to be known absolutely. For the measurement of the electron beam size and the monitoring of the stability of the orbit location a new imaging system has been set up, that operates at very different intensity levels covering more than 11 decades, given by the variation of the electron beam current. The system uses a commercial zoom lens for the achromatic optical imaging of the electron beam source point onto two different camera systems. One camera system is for life-imaging of the electron beam at electron beam currents from 200 mA down to some μA. The second system is a cooled CCD-camera that allows imaging of the electron beam size and location at very low currents, down to only one stored electron.

* R. Klein et al., Phys. Rev. ST-AB 11, 110701 (2008).

• O. Dressler, M.V. Hartrott
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
• N. Hauge
  Danfysik A/S, Jyllinge

The pre-accelerator microtron supplies an electron beam at 10⁵ MeV for the Metrology Light Source (MLS) of the Physikalisch-Technische Bundesanstalt (PTB) in Berlin. The beam is delivered via the transfer line to the injection septum and then into the storage ring. This septum magnet has its stainless steel vacuum beam pipe placed inside a laminated silicon iron magnet core. Hence, the pulsed magnetic field (half sine) used for the beam deflection must propagate through the thin metallic beam pipe. During the commissioning of the injection process, it became apparent that the calculated nominal pulse current for this energy and geometry had to be increased by 30 % to achieve proper beam transfer and accumulation. Two problems were apparent. Firstly, the injected beam trajectory had to be set at an angle away from the main beam axis. Secondly, the beam transfer from the septum entrance to exit was disturbed. As a first measure, the septum current pulse length was extended from 35 to 10⁷ μs. Further on, the septum magnet was insulated from the transfer line beam pipe by a ceramic brake. This paper reports on measurements of pulsed magnetic fields inside the septum magnet.

* Commissioning and Operation of the Metrology Light Source, J. Feikes et al., BESSY, Berlin, Germany; R. Klein, G. Ulm, Physikalisch-Technische Bundesanstalt, Berlin, Germany; EPAC08, Genoa, Italy.

• G. Wüstefeld, J. Feikes, M.V. Hartrott, M. Ries
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
• A. Hoehl, R. Klein, R. Müller, A. Serdyukov, G. Ulm
  PTB, Berlin

The Metrology Light Source* is the first storage ring optimized for THz generation**. It applies a bunch shortening mode, based on a flexible momentum compaction factor 'alpha'. The emitted THz radiation is very sensitive to the machine tuning, its power could vary by many orders of magnitude. We report on coherent THz signal intensities as a function of different machine parameters, such as beam energy, beam current, rf voltage and alpha tuning.

* R. Klein et al., Phys. Rev. ST. Accel. Beams vol. 11, 110701 (2008). ** J. Feikes et al., The Metrology Light Source: The First Electron Storage Ring Optimized for Generating Coherent THz Radiation, submitted to Phys. Rev. ST. Accel. Beams (2009).