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Powering the LCLS

When the Linac Coherent Light Source (LCLS) turns on in 2009, it will pack one trillion x-ray photons into a single pulse of the needle-thin beam. Shaping, focusing and directing the beam is a complex task requiring hundreds of magnets of various shapes and sizes. And each of those magnets must be powered and controlled with precision of within 0.001 percent. To accomplish this task, a team of SLAC engineers including Antonio de Lira, Briant Lam, Dave MacNair and Paul Bellomo have created a controller for the hundreds of power supplies required by the LCLS.

The controller is a newly designed upgrade of an older model. It uses Ethernet technology, which is both 250 times faster and cheaper than the Bitbus system it replaced, and offers more protection from magnet-destroying shorts and hot-spots. The SLAC-designed controller is the result of thousands of hard-worked hours.

"From concept to reality, building a controller like this takes a long time," said Dave MacNair, the engineer that led the controller's development. "I've been living with it for years."

The majority of magnets in the LCLS will have their own power source with its own controller. The power sources typically convert AC electricity—taken from the SLAC grid—to DC for magnets that range from tens of watts to megawatts, depending on the size of the magnet. Combined, the magnets will draw 560 kilowatts of power, roughly the amount used by 460 average American homes. The individual controllers are then linked to a larger system operated by Experimental Physics and Industrial Control Systems (EPICS) software, which is commonly used to monitor hardware.

According to MacNair, powering single magnets with single power sources has become a trend in accelerator design. This allows smaller power sources and more control over the beam's characteristics. There are a few strings of magnets connected to the same power sources in the LCLS, but are limited to eight. The PEP ring contains strings of 96.

The LCLS will use a linear accelerator needing fewer magnets and fewer power sources than the PEP ring, which requires more to guide the beam around the ring. However, larger projects with more power supplies and more complex controllers are quickly approaching.

"Scientists are predicting the International Linear Collider will require several thousand power sources," said MacNair. "That will be quite a project."

Ken Kingery, SLAC Today, September 21, 2007