BESSY II is back in operation after maintenance shutdown
In the storage ring, three new 1.5 GHz active higher-harmonic cavities have been installed.
On 7 September 2026, BESSY II was set into operation after a four-week shutdown. BESSY II is scheduled to resume full user operation on 22 September.
Installation of three innovative cavities
In the storage ring, the vacuum system had to be opened to install, among other components, three new 1.5 GHz active higher-harmonic cavities (see picture). These cavities make it possible to vary the length of the stored electron bunches. The bunches can be shortened to generate photon pulses with an high time resolution of about 10 picoseconds, or lengthened to reduce the electron-bunch density and thereby increase the Touschek lifetime. The latter is the standard operating mode at BESSY II.
Following the successful commissioning of the new cavities, which will take several more months, as the necessary RF transmitters still need to be installed and commissioned, they will replace the existing 20 year old outworn passive higher-harmonic cavities during user operation. The development and testing of this kind of cavities was done together with our colleagues from ALBA, Spain and DESY, Hamburg.
New cavities pave the way for BESSY III
The purchase and installation is part of our BESSY II+ upgrade program. "This technology, coming soon into user operation at BESSY II, lays also the ground for the new RF systems of our future facility BESSY III. In that sense: BESSY III already starts to be alive", said Prof. Andreas Jankowiak, Technical Director of BESSY II.
From 22 September on, BESSY II will be back in user operation
The next two weeks will be dedicated to further improving the vacuum conditions to user mode values by “cleaning” the storage ring vacuum chamber with synchrotron radiation, as well as detailed commissioning of the storage ring and beamlines. BESSY II is scheduled to resume full user operation on 22 September.
Many thanks to all colleagues for the successful completion of the shutdown activities and for bringing BESSY II back online so quickly.
Note: Investments in BESSY are worthwhile for Berlin and Germany
An impact analysis by DIW Econ demonstrates the scientific and economic value of BESSY II. Every euro invested yields three euros for Germany and as much as ten euros for the State of Berlin. Furthermore, the study provides an economic forecast for the construction of BESSY III.
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