Thursday - December 4, 2008
SLAC Today is
available online at:
http://today.slac.stanford.edu
In this issue:
Symmetry Explains it in 60 Seconds: Magnet Quench
Science Today: Free Electron Laser Basics—An LCLS Primer
Colloquium Monday: The Global Climate and Energy Project
Reminder: LCLS Tour Today
New Uniform Fittings Required
Financial Counseling and Classes Offered on Campus
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Thursday - December 4, 2008 |
Symmetry Explains it in 60 Seconds: Magnet Quench A magnet quench is a dramatic yet fairly routine event within a particle accelerator. It occurs when one of the superconducting magnets that steer and focus the particle beams warms above a critical temperature, bringing operations to an abrupt halt. A quench often starts when stray particles from the beam enter a magnet’s coils, producing an initial burst of heat. Within a fraction of a second, parts of the superconducting wire in the magnet lose their ability to conduct electricity without resistance, generating more heat that quickly spreads throughout the entire magnet. The coolant surrounding the magnet begins to boil. In the case of a large superconducting magnet, which can be several meters long and carry currents of 10,000 amps or more, the quench creates a loud roar as the coolant—liquid helium with a temperature close to absolute zero—turns into gas and vents through pressure relief valves, like steam escaping a tea kettle. Such a quench generates as much force as an exploding stick of dynamite. A magnet usually withstands this force and is operational again in a few hours after cooling back down. If repair is required, it takes valuable time to warm up, fix, and then cool down the magnet—days or weeks in which no particle beams can be circulated, and no science can be done. |
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Free Electron Laser Basics: An LCLS Primer
In a few short months, the Linac Coherent Light Source will start operation as the world's first hard X-ray free electron laser, pushing SLAC National Accelerator Laboratory to the frontier of photon science. Using SLAC's linac to drive a free electron laser, or FEL, the LCLS will generate X-rays an eye-popping 10 billion times brighter than the current cutting-edge technology, while simultaneously providing pulses lasting less than one millionth of one billionth of a second. How does an FEL accomplish these feats of X-ray wizardry? Although it reaches nearly two kilometers end-to-end, the LCLS contains the same basic components as a pocket laser pointer: an energy source, a light source, a monochromater to select a single wavelength and an amplifier. The energy source provides the power, which the light source uses to generate X-rays. The monochromater and amplifier give the X-rays the ultra-bright, coherent properties of a laser. The LCLS pulls its energy from electrons accelerated in the final kilometer of the SLAC linac. The 14 GeV electron beam is so powerful that the LCLS requires less than 0.1% of the linac's energy to create 10 billion watts in X-rays. Read more... Colloquium MondayNext Monday, Stanford Professor Sally Benson will present "The Global Climate and Energy Project" at 4:15 p.m. in Panofsky Auditorium. All are welcome. |
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