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In this issue:
From the Director of PPA: Following the Science and Expanding the Toolkit
SLAC Retiree Takes "Closest to the Pin" at Annual DOE Golf Challenge
Word of the Week: Hohlraum

SLAC Today

Friday - September 25, 2009

From the Director of PPA: Following the Science and Expanding the Toolkit

(Photo - David MacFarlane)
 (Photo by Brad Plummer.)

Last Thursday's annual meeting of the SLAC Users Organization was another reminder of both the fundamental nature of the questions confronting particle physics, particle astrophysics and cosmology today and the breadth of the toolkit being arrayed to address these questions. It was also a reminder of the importance of maintaining the partnership between Particle Physics and Astrophysics at SLAC and the university community, as together we expand physics horizons and the experimental toolkit.

At the meeting we were treated to spectacular science from the Fermi Gamma-Ray Space Telescope, just past the first anniversary of its launch into high Earth orbit last June. In the first year of operation some 50 gamma-ray pulsars, a number of remarkably energetic emissions from gamma-ray bursts, a very high statistics measurement of the cosmic electron/positron flux and an array of searches for dark matter signatures are just a sampling from this unique observatory. Fermi is also a pioneering marriage of particle physics and astrophysics, as well as university and laboratory capabilities, that points the way to our future.

That future, now in the planning stages, focuses on the nature of dark energy using a variety of precision measurements to map out the history of the expansion rate of the Universe. The Large Synoptic Survey Telescope on a Chilean mountaintop and the Joint Dark Energy Mission in space will provide definitive next-generation measurements addressing perhaps the greatest mystery emerging from cosmology. Clearly these projects expand the toolkit well beyond accelerator-based experiments, but they nevertheless are also powerful examples of the blend of astrophysics and particle physics techniques driven by a common fundamental science question.  Read more...

SLAC Retiree Takes "Closest to the Pin" at Annual DOE Golf Challenge

(Photo - the SLAC team, 2009 DOE Golf Challenge)
The 2009 SLAC team (left to right): Les Cottrell, Phil Cutino, Ben Smith, Don Arnet, Mike Hogaboom, Mike McDaniel, Brian Sherin, Mike Racine, Tanya Boysen and Scot Wenholz. Not pictured: Bill Olson and guest player Amy Davis. (Photo courtesy Les Cottrell.)

The 22nd Annual DOE Golf Challenge Tournament, hosted this year by National Security Technology, was held last week at Mare Island Golf Club. Turnout was down from previous years, but those who played had a great time.

SLAC retiree Ben Smith was the only member of the SLAC team to win a prize. Ben won "closest to the pin" on one of the par three holes. The course was challenging and scores were higher than years past. Lawrence Livermore National Lab won the team competition, so they will hold the perpetual trophy until next year.

(Image - hohlraum)
(Image: National Ignition Facility, Lawrence Livermore National Laboratory.)

Word of the Week: Hohlraum

German for a small hollow area, the word hohlraum in physics refers to a gold-lined, pencil-eraser-sized chamber to contain nuclear energy experiments called inertial confinement fusion reactions. In ICF experiments, lasers heat a pellet containing deuterium and tritium to 100 to 300 million kelvin, causing the outer layer of the pellet to explode. Following Newton's third law, this explosion triggers an equal and opposite implosion of the interior fuel. With temperatures and pressures as high as in the center of stars, atoms within the pellet fuse and release an enormous amount of energy, causing the remaining fuel to burn.

Originally, ICF reactions were created by targeting the pellet with a laser from one side, but the pellet often shifted in space or exploded asymmetrically, allowing the interior fuel to escape. By placing the pellet in a hohlraum and aiming multiple lasers at the gold-lined walls, physicists can create a symmetric explosion. The hohlraum walls heat and emit X-rays, bombarding the pellet from all sides. This keeps fuel from escaping and drives the reaction to completion.

The National Ignition Facility at Lawrence Livermore National Laboratory will direct 192 ultraviolet laser beams at a hohlraum to bombard a fuel pellet with two million joules of energy—sixty times more energy than any existing system. Research from this facility seeks practical fusion energy as well as advancements in security.


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