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In this issue:
New Life for Linac
Colloquium Monday: Seismic Tomography
Another LCLS Tunnel Breakthrough

SLAC Today

Monday - November 26, 2007

Crews working in the linac tunnel install two 4,000-pound magnets as part of the second bunch compressor for the LCLS.

New Life for Linac

After years of planning and hard work involving teams from every corner of the lab, SLAC's venerable linac has undergone the most radical set of alterations in its 40+ year career. Although a handful of minor tweaks remain, the effort to reconfigure the linac for the Linac Coherent Light Source (LCLS) is now just about complete.

"It's an exciting time and our first experiences have been very positive. We all look forward to the next level," said Paul Emma, head of the LCLS accelerator physics group. "The entire team is very happy with the results, but also glad for a break."

For decades, SLAC's two-mile long linac has enjoyed a resume of superlatives. Add to the list its new role as the injector and accelerator portion of the LCLS, the world's first hard-x-ray free electron laser. Commissioning of the injector portion began last April, and now, not only does the quality of the beam—emittance values, total charge, beam stability, etc.—meet or exceed design expectations, but the electron injector system is considered to be the brightest electron source in the world.  Read more...

Colloquium Monday

Seismic Tomography

In the last two decades, seismic tomography has generated spectacular images of 3D structure in the earth's interior, providing insights on mantle flow and the dynamic processes that drive plate tectonics.

In this afternoon's colloquium, Professor Barbara Romanowicz of U.C. Berkeley will discuss some key unresolved issues in global dynamics of the earth's interior and review the current status of global mantle tomography, contrasting images obtained using different datasets and inversion methodologies, and discussing their various strengths and limitations. She will also will point out how features associated with the downward convective flow appear better understood at the present time than those associated with upwellings. She will then describe how new waveform inversion approaches can lead to significant progress in seismic imaging of "hotter" regions, and discuss the much debated issue of "mantle plumes," and will discuss evidence which shows that heterogeneity in the deep mantle cannot be purely thermal, but must involve strong lateral variations in composition. Romanowicz will conclude by identifying promising new approaches, both in data gathering and theory, that aim at imaging the scattered wavefield and obtain higher resolution constraints on mantle heterogeneity.

The colloquium will take place at 4:15 p.m. today in Panofsky Auditorium. All are invited to attend.

Another LCLS Tunnel Breakthrough

(Photo - Tunnel)
Crews digging the X-ray Transport Hall broke through into the Near Experimental Hall last week.

Last week, tunneling crews mining the X-ray Transport Hall (XTH) broke through the final few inches of earth into the Near Experimental Hall (NEH), marking attainment of another milestone in the Linac Coherent Light Source (LCLS) construction project. Last June, SLAC celebrated a similar break-through event when the road header crew working in the Undulator Hall punched through into daylight. This time, however, the punch-through occurred in a far less visible corner of the NEH, which is still under construction.

The XTH will eventually connect the Far Experimental Hall (FEH) and the NEH. Last August, construction crews opened a third tunnel port, or adit, behind the Collider Hall to speed up tunneling progress. Originally, only two tunnel ports were planned—the Access Tunnel and the Research Yard side of the Undulator Hall—but the third port was added to save money and speed up excavation. Because the third port into the middle of the XTH, crews will now return to the intersection and focus their efforts on finishing the last 120 feet remaining in the other direction to connect to the FEH.

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