Preventing SwissFEL electrons from going astray
Cost-effective and with a minimal error rate – PSI-engineers from the power electronics section have set ambitious goals for the SwissFEL magnet power supplies. Beginning 2016, the PSI’s new large-scale research facility SwissFEL will generate extremely bright x-ray light. For that purpose, electrons have to be accelerated to close to the speed of light. Magnets placed along the accelerator will keep the electrons exactly on track for several hundred metres – approximately 650 magnet power supplies will be providethese magnets with electricity. Digital controllers will measure the electric current in the magnets up to 600,000 times a second with an accuracy of 0.0001 per cent and will continually adjust it to a reference value.
You can’t buy devices like thatunless you have them developed,
explains section head René Künzi with regard to the challenges. So why not just do it yourself? For SwissFEL, the engineers are building on experience gathered during the development and operation of units for the Swiss Light Source (SLS). The controller they developed back then has been a true success story, and it is now used in labs under a PSI licence all over the world. The PSI engineers have refined the system for SwissFEL. The delicate SwissFEL beam generally requires weaker magnets for its regulation and thus low-current supplies – but it requires more of them. A massive cost reduction was vital,given the quantity needed,
stresses Künzi. The engineers could only achieve this by optimizing the electronic configuration. In the case of SwissFEL, three power supplies are operated via one controller. Moreover, the controls are constructed based on a modular concept. This allows expensive precision components to only be used where they are actually needed,
says Künzi.
Production costs halved
As a result, the engineers have almost managed to halve the production costs. However, their creativity was still not exhausted. After all, it is not only production that costs money, but also the susceptibility to error during operations. For instance, certain power modules in the SLS supplies tended to break down as the years went by. Every supply had its own power module. In the case of SwissFEL, however, as many as twenty-one supplies are to be housed in a common cabinet and fed by a single power module, and a second unit ensures operation in the event of a breakdown.
Cooling proved to be another Achilles heel. Künzi: After about five years, we noticed an increase in breakdowns in the fans used to cool the units.
The lower-power supplies at SwissFEL can make do without fans. For the electronics, attention is being paid to energy efficiency, and thus the amount of waste heat was reduced. Moreover, the cabinet is fitted with cooling baffles, which are constructed in such a way that a draught develops in the cabinet by itself and transports the waste heat away.
The power supplies, including the cabinet, have been developed and are currently under serial production. The engineers are still working on special high-performance magnet power supplies that are also needed for SwissFEL. These will require forced cooling. However, it should be achieved in such a way that a single broken fan does not trigger a power supply breakdown. That would also reduce the failure rate for these units,
Künzi is convinced.
Text: Paul Scherrer Institute/Martina Gröschl
