MENLO PARK, California, April 29 -- The SLAC National Accelerator Laboratory issued the following news release: * * * Groundbreaking instrument back online, marking a key milestone in high-energy upgrade to SLAC's X-ray laser * By Erin Woodward Key takeaways:  * XPP, an instrument at SLAC's X-ray laser that has enabled groundbreaking science, is returning to normal operations this spring after a year-long rebuild. * The overhaul is a key milestone for the ongoing high-energy upgrade to t  more