Retrofitting with superbend magnets allows the ALS to produce hard x-rays as well as ultraviolet and soft x-ray radiation.

This retrofit, the first ever to take place in an operating synchrotron radiation source, elevated the ALS up from being the nation's premier source of low-energy or "soft" x-rays to being an important source of high-energy or "hard" x-rays as well. Future plans call for even more upgrading and the addition of new light-source companions.

The recently released U.S. Department of Energy 20-year facilities plan lists 28 science priorities and included the ALS as one of eight far-term projects. Ideally, an ALS upgrade would include the implementation of full-energy injection and higher radio-frequency current to increase beam brightness, plus the replacement of aging insertion devices with the latest in insertion device technology, and replacing multipurpose beamlines with an array of application-specific beamlines.

Says ALS director Daniel Chemla, "In the coming year, I intend to engage our advisory committees, in particular the Users' Executive Committee and Scientific Advisory Committee, to flesh out the details and present me with a vision of what the ideal suite of insertion devices and beamlines should look like ten years from now."

In a best-case scenario, two additional facilities would be added as complementary companions to the upgraded ALS. The first, called CIRCE, for Coherent InfraRed CEnter, would be a small new synchrotron ring built atop the ALS booster ring, dedicated to generating beams of far-infrared (terahertz frequency, trillion-cycles-per-second) radiation. These "T-rays" would be thousands of times more powerful than those obtained from tabletop and even free-electron lasers, making them ideal for a variety of purposes including the nondestructive imaging of biological and other materials, the manipulation of electronic properties of semiconductors, medical imaging, and security inspections.

The second proposed facility, which could be adjacent to the ALS, is called LUX, for Linac-based Ultrafast X-ray source. Optimized to produce substantial fluxes of tunable x-rays at pulse lengths ranging from 50 to 200 femtoseconds, LUX could also be capable of generating bursts of x-rays at attosecond pulse lengths. An attosecond is one thousandth of a femtosecond, the timescale of electronic motion—it takes an electron about 24 attoseconds to orbit a hydrogen nucleus. With attosecond x-ray spectroscopy capabilities, it is possible that scientists could steer the motion of electrons and control not only chemical reactions but even the emission of light.

"In our long-range vision," says Chemla, "the ALS, CIRCE and LUX would become parts of a light-source cluster sharing a common infrastructure."

Additional information

• More about retrofitting the ALS with superbends
• More about CIRCE
• More about LUX

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