Further improvement of the 3rd generation synchrotron radiation light source BESSY II

Collaborative Activities of the Institute "Accelerator Physics" and the User Platform "Operation Accelerator BESSY II" in the POF III Programme

Topic 2: Research on Matter with Brilliant Light Sources [Photons (LK II)]

The institute of Accelerator Physics, G-IA, and the user platform 'Operation Accelerator BESSY II', NP-ABS, participate in the Helmholtz Research Program 'From Matter to Materials and Life' on the topic 'Research on Matter with Brilliant Light Sources'  within the subtopic 'BESSY II'. The focus is put on the continuous improvement of the 3rd generation synchrotron radiation light source BESSY II and the upgrade into a variable pulse length storage ring BESSY VSR.

Courtesy A. Schälicke (HZB)

Sustaining BESSY II

Since starting user-operation in 1999 the radiation source BESSY II has been given scientists the opportunity to experiment in various fields of fundamental and applied research. Through complete understanding of the accelerator complex and the continuous implementation of state-of-the-art technologies for over more than a decade BESSY II is one of the top-level synchrotron radiation facilities. The institute presently looks for major advancements in two particular areas:


  • Top-Up Project Phase II: Operation with Transparent Injection
  • Fast Orbit Feedback Project Phase II

The already well established Top-Up user-operation and the fast orbit feedback system improved the beam stability by a factor of ten. On completion of 'Phase I' a subsequent 'Phase II' is planned. It covers a advanced injection system which based on a new non-linear kicker, does not disturb the stored electron beam and makes the injection process transparent to the user's experiments. In addition new BPMs and a new corrector setpoint distribution of the fast orbit feedback system are foreseen. This will improve the beam stability by damping higher frequencies (well above girder resonances) and extend the versatility and the user performance.


  • Insertion Device Tailored Magnet Optics
  • Pseudo-Single Bunch / Pulse-Picking @ 1.25 MHz
  • Single Bunch Injection

By splitting the different quadrupoles and sextupoles circuits into separate-powered magnets, the Magnet Optics can be tailored locally for each insertion device or installation inside the storage ring. This will result in smaller beta functions for example. Just like the already modified sections such as the injection area, the planned sections, like the two ID's of EMIL, the performance levels of BESSY II will continue to improve. Furthermore, the Pulse-Picking mode (single bunch excitation) is going to be enhanced and a Pseudo-Single Bunch mode (orbit distortion) at 1.25 MHz will be investigated. Both methods allow experiments with single bunch and multi bunch patterns in parallel and increase the availability of user stations.

Innovation in Synchrotron Radiation Research

HZB and BESSY pursue a continuous upgrading strategy of the storage ring as well as its instrumentation. In order to maintain its position and to be competitive with other radiation sources worldwide in the future, major upgrades on a timescale of 10 years and finally a successor of BESSY II have to be thought of, evaluated and designed.

Upgrade: BESSY VSR

The variable pulse length storage ring BESSY VSR is a novel concept that will create long and short electron bunches in the existing BESSY II storage ring simultaneously. Working at high gradients and different frequencies, a pair of superconducting cavity systems provide such photon pulses at every beamline. This idea was developed by members of the G-IA. The beam dynamics is and will be under investigation in detail contributing to the technical design report.

Next Generation Multi-User Synchrotron Radiation Source

Large facilities are projects with extensive volume of investment and lifetime. Therefor future technologies are evaluated for a successor of BESSY VSR beyond the year 2020. Schemes like Diffraction Limited Storage Rings, cw Free-Electron Lasers or Energy Recovery Linacs are possible candidates. The feasibility of goal parameters (high current, short pulses, etc.) is partially addressed in the planned ERL teststand bERLinPro.