Operation of the cryogenic and RF infrastructure of the 3rd generation light source BESSY II

Activities of the Institute for SRF Science and Technology in the POF III Programme From Matter to Materials and Life (MML)

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

The Institute for SRF Science and Technology (G-ISRF) contributes to the topic Research on Matter with Brilliant Light Sources within the subtopic BESSY II.  The focus here is three-fold:

  • Operate the cryogenic and RF infrastructure of the 3rd generation light source BESSY II.
  • Modernize BESSY II to improve the performance and reliability of the facility. 
  • Upgrade BESSY II to provide completely new (short-pulse) operating modes previously not possible with storage rings (BESSY-VSR).

Modernization of BESSY II

BESSY II has been in user operation since 1999 as Europe’s brightest VUV/soft-x-ray light-source facility.  It remains a leading facility due to a continuous modernization program, including the recent implementation of top-up operation and fast-orbit feedback. 

New RF-Cavity System

The BESSY-II RF-cavity system will undergo a major upgrade.  The existing DORIS cavities are about 40 years old and are at the end of their life span.  G-ISRF is replacing these by new EU-Cavities previously developed by a HZB-led European collaboration.  These cavities are expected to operate more reliably and their impedance (interaction with the beam) is lower, thereby benefiting the stability of BESSY II and the future upgrade to BESSY-VSR.

The first two of four EU-Cavities to be installed in BESSY II, replacing the old DORIS accelerating system.


New RF transmitter System

The BESSY-II accelerating cavities are powered by 80-kW RF transmitters (40 kW in the booster) that employ klystron tubes.  Nearly all of HZB’s tubes have accumulated over 100,000 hours of operating time, exceeding their life expectancy, so that their modernization is essential.  The development of solid-state amplifiers has made huge advances in the last decade, and G-ISRF will replace the RF system by such systems.  These are more reliable than klystron-based systems and offer the option of “hot-swapping” defective units in a very short time, thus improving the overall up-time of BESSY II.

Upgrade of superconducting wavelength shifters

Several superconducting wigglers are installed in BESSY II to extend the photon spectrum into the x-ray range.  These units are being upgraded to permit their operation independent of the BESSY II cryogenic plant – step necessary to provide uninterrupted top-up operation of the BESSY II. 


A multipole superconducting wiggler that recently received an improved cryostat.


Upgrade of BESSY II to BESSY-VSR: Enabling the study of the dynamics of matter

Modern user experiments not only demand a high beam brilliance and stability for static materials studies but also short pulses to analyze dynamic processes.  To maintain BESSY II’s world-leading position, a major upgrade to BESSY-VSR is planned.  It will provide a high average flux of short and long photon pulses simultaneously so that the maximum number of users can benefit.  This unique mode is realized by implementing a completely new superconducting RF system operating at two harmonics of the 500-MHz EU-cavities.  

The BESSY-VSR concept and prototype cavity units are being developed by G-IA and G-ISRF within the Topic Accelerator Research and Development (ARD) of the Program Matter and Technology.  Later, the implementation of the system in BESSY II and its operation will take place within the MML (LK-II) program.

Next Generation Multi-User Synchrotron Radiation Source

Synchrotron light sources such as BESSY II require extensive investments and have long life times.   Eventually, though, the facility will no longer be able to deliver the beam properties required for the most modern, cutting-edge user experiments that will be devised in the coming years.  New accelerator concepts are therefore being studied to address the future needs. These include (but are not limited to) ERL-based light sources, free-electron lasers and so-called ultimate storage rings.  Given the long development times for such facilities, HZB is already starting the process of evaluating potential successors for BESSY-VSR.  This includes the development of new technologies (within the ARD topic of MaT).  HZB is making the first step in this process by building the ERL demonstration facility bERLinPro.  In future HZB will analyze additional schemes for a next-generation light source in order to make a well-founded decision as to what facility will be proposed.