Twin Orbit operation successfully tested at BESSY II

A synchrotron source point image of a bending magnet of the Twin Orbit modus. The second orbit closes after three revolution and is winding around the standard orbit at the center. Credit: HZB

The first “Twin Orbit User Test week” at BESSY II in February 2018 was a big success and can be considered as an important step towards real user operation. Physicists at Helmholtz-Zentrum Berlin have been able to store two separate electron beams in one storage ring. The twin orbit operation mode can serve users with different needs of the time structure of the photon pulses simultaneously and offers elegant options regarding the future project BESSY VSR.

The Twin Orbit operation mode makes use of non-linear beam dynamics and provides two stable well separated orbits for storing two electron beams in one storage ring. The bunch fill patterns of both orbits can be chosen, to some extent, independently, which allows for fulfilling normally incompatible user needs, simultaneously. For example, one orbit can be used to store a homogenous multi bunch fill to deliver high average brilliance for photon hungry experiments, whereas only one single bunch is stored on the other orbit for timing experiments, providing a much lower pulse repetition rate.

First experiments in 2015

It is a long process from an idea to a real operational week, especially at a running multi user facility. First studies of this mode started already 2015 at the smaller ring, the Metrology Light Source (MLS), resulting in a successful user experiment with the Physikalisch Technische Bundesanstalt (PTB) [1]. In parallel a group of HZB experts implemented and optimized this mode at BESSY II in single machine commissioning shifts. Important milestones have been the operation of a large number of insertion devices as well as the topping up injection scheme to keep the stored current constant. In 2017 a successful overnight run with topping up injection and some participating beamlines gave confidence for a first longer test week [2].

Excellent availabilty of synchrotron light

The days of this “Twin Orbit User Test week” have been used for common experiments of machine group and beamline scientists in order to characterize this operational mode and generate feedback for further optimization. During the nights and the complete weekend ‘normal’ user time was scheduled with two different fill patterns (multibunch and single bunch) on both orbits. The availability and stability of the synchrotron source were comparable to the current standard user mode and exceeds/reaches 99 per cent.

Elegant option for BESSY VSR

“There is still a lot of work to do, but nevertheless this proof-of-principle week showed that a development towards a realistic user mode should be possible. And even more, for the future BESSY VSR project, it could be a very elegant way to separate short and long bunches”, Prof. Andreas Jankowiak concludes.

[1] http://accelconf.web.cern.ch/AccelConf/IPAC2015/papers/mopwa021.pdf

[2] http://accelconf.web.cern.ch/AccelConf/ipac2017/papers/wepik057.pdf


Dr. Paul Goslawski