The Wabe → The Roadtrip → The Roadtrip Reports → Year 4 → Roadtrip Report: 20 February 1999
On a whim, Rob decides to extend his educational horizons by visiting the linear accelerator run by Stanford University and drags a yawning Richard Chio along for the ride.
The tour of SLAC started in the visitor's center, which has a lot of interesting exhibits. Here's a cutaway view of the accelerator itself. The tubes on the outside are for the coolant; this thing gets hot. Note that the accelerator tube isn't hollow, but rather a series of chambers surrounding a conduit. It's a common belief that accelerators used external electric fields to speed up the electrons; but that's wrong. Each of those chambers acts as a tiny electromagnetic resonant cavity, which allows precise control over the magnitude, direction, and oscillation of the electric field vector. Section 38-5 of Haliday/Resnick (3rd ed.) gives the details.
This is one of the monster focusing magnets that keeps the pulses coherent. It's known as a quadrupole.
The shadow in front of the screen is our tour guide. He was interesting, to say the least. He seemed to be on a one-man crusade against Star Trek, saying that it was impossible for one person to have all that technical knowledge, that the science was always the extreme theories about cosmology, and so on, and so on. My personal theory about his extreme aversion to Star Trek is that he got into physics after watching too many episodes, then found out that: a) physicists do not save the universe every week, and b) they never have sex.
Star Trek wasn't his only windmill: he also took a few shots at James Joyce. ("Stream-of-consciousness writing does not impress me.") Richard unkindly pointed out that in a few years Rob may find himself in a similar position, preaching to the uninterested masses from his bully pulpit.
A screw-up left us standing in the rain, as our guide hopped into his green Camry and chased our tour bus all over the campus. Not exactly the most organized tour...
The building above the accelerator is two miles long (the accelerator tube itself is underground for shielding purposes). It's one of the longest buildings in the world, and houses the klystrons that power the accelerator. It's easy to see this building being used in a movie, with the hero having to race from one end to the other, except by the time he reached the end he'd collapse from exhaustion.
All of SLAC is built upon a monolithic plate, meaning it's safe from the shearing forces of earthquakes. It took only two weeks for SLAC to come back online after the 1989 Loma Prieta earthquake.
Fun Fact: The next-generation linear accelerator (NLC) will be ten times as long.
This is one of over 250 monster klystron tubes that are used to pump microwaves into the accelerator. The microwaves enter the resonator cavities and set up oscillating electric fields, which motivate the electrons and positrons down the tube.
This is a segment of the accelerator that was removed because of damage. The ridged copper pipe is the accelerator itself-- the metal girder underneath provides structural support, and the large pipe on the bottom is used to verify the entire setup is indeed linear (a laser is fired down the length, and special lenses amplify any distortions to the accelerator). The "U"-shaped projection is one of the microwave wave guides from the klystrons.
The microwaves are channeled via a waveguide from the klystron above, split, and injected into the accelerator. The copper tubes are for the cooling water.
This is the detector, which sits at the end of the accelerator and analyzes the results of the electron-positron collisions. It is four stories high.
This model gives a better feel of the size of the detector. Note the staircases on the side; it really is that large. Each of these layers-- white, blue, maroon, red-- detects a different property of the particles. Some detect charge, others mass, angle, and velocity.
Last Modified: 2003/12/08 07:58:40 GMT
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