The Stanford Linear Accelerator Center

Based on a tour of parts of the Stanford Linear Accelerator Center (SLAC) in August of 2004, here are some photos and explanations. Tours and seminars at SLAC often are open to the public; they are announced at the SLAC web site.

The SLAC accelerator is housed in the second-longest building in the world, over 3 km long. One of the terminals in Beijing Airport is slightly longer.
Most of the facility is concentrated around the detectors which are used to identify and record the particles created at the interaction point, where the accelerated electrons and positrons collide.
Here is a view of the accelerator housing, which is in a ditch running under Interstate 280 (visible as an overpass) near Palo Alto, California.

Klystrons manufactured by Varian are used to accelerate the particles. Each klystron is capable of generating 65 megawatts of microwave power; 280 of them are arrayed at ground level in the building in the ditch shown above. Two klystrons are visible as red cylinders about the size of 55-gallon drums. They are water-cooled; two flow meters may be seen on the far left, where a copper waveguide (not shown) descends through the floor to the beam line several meters below. The beam line is buried for environmental stability and to shield personnel and equipment from the intense microwave flux during operation. These klystrons accelerate electrons to a maximum of about 50 giga-electron-volts (GeV) energy; the electrons are collided with positrons of comparable energy, for a maximum total of around 100 GeV.

The actual beam line, deep in the ground below the klystrons, was not shown during the tour. However, a visitor display illustrates what a segment of the beam line looks like. The horizontal copper cylinder near the top of the photo is the beam pipe itself, which would be evacuated to a high vacuum; it is water cooled, and some of the cooling pipes can be seen descending from above. To the far left (not shown) would be a copper waveguide descending from the klystron gallery above and supplying microwaves to accelerate the particles in the beam pipe.

The large, round aluminum pipe, about 70 cm in diameter, supports a finely-adjustable I-beam which provides structural support for the beam pipe. The aluminum pipe is air-filled and a laser may be aimed down its middle to align the particle beam.

The dark blue coils are those of a quadrupole magnet used to steer the particle beam; the particles, being electrically charged electrons or positrons, can be deflected by magnetic fields. The dipole shown just to the right of the quadrupole is one of hundreds used to shape and focus the accelerated particles in the beam line.

SLAC has maintained a prototype development facility for the Next Linear Collider (NLC), which is planned to be 30 km long.
The SLAC prototype, which operates near room temperature, uses higher microwave accelerating potentials than SLAC. The SLAC beam line runs on 2.5 GHz microwaves; the prototype uses a much shorter wavelength, making it possible for the microwave components to be smaller than those now at SLAC. The NLC is expected to accelerate particles to ten times the energy at SLAC, or more. The actual NLC will employ superconducting magnets operating at a very low temperature, so the SLAC prototype here only partially represents the currently planned NLC. The prototype at SLAC not only has been used for NLC planning but also for insight into improvements at SLAC itself.

The prototype beam pipe is shown here. The round, silvery beam pipe, about 2 cm in diameter, enters from the lower left and is joined to a copper accelerator segment in the middle of the photo. Microwaves are supplied from above by rectangular copper waveguides, somewhat silvery in the photo, one side of which each has a blue paper label pasted on it. The orange tubing is a plastic water cooling system. The prototype beam pipe is supported on a rectangular aluminum block and is only about 20 m long in its present form.

Two prototype quadrupole magnets are shown on the far left here, with some of the tour participants in the passageway next to the prototype. The beam pipe runs through the center of the magnets, the coils of which, on the far left, are painted dark blue. Other magnets, farther down the beam line, also are visible. Cooling water and electrical cables descend from the cable runs near the ceiling. The klystrons are close to the beam pipe and are not visible in this photo. The beam was turned off, of course, during the tour.

In May of 2008, SLAC contributed 38 special-purpose power supplies to a segment of the ILC development project at KEK, Japan. These power supplies will be used at the Advanced Accelerator Test Facility in an experiment intended to demonstrate focussing of an electron beam down to a spot no more than a few tens of nanometers in diameter. A small beam diameter concentrates colliding particles and increases the collision event rate.

SSRL

SLAC also maintains an electron storage ring separate from the linear collider. This facility supplies the Stanford synchrotron radiation laboratory (SSRL) which is used by biologists, chemists, solid-state physicists, and others from all over the world. Synchrotron radiation is a source of short-wavelength X-rays for crystallography and other probes of the atomic details of matter.

This photo shows a typical experimental setup at SSRL: A Seiko D-Tran robot arm loads a sample into a holder which may be seen at the tips of the lathe-like device at the lower right center of the photo. The robot speeds up repeated sampling because it is capable of accurate mechanical activity and does not require a human to enter the setup room during the experiment.

A flexible-neck lamp is shown pointing down at the sample location, which receives X-rays from the horizontal, brass-colored, round pipe entering the setup room by a clamp on the wall at the middle of the far left. The sample is kept cool by liquid nitrogen flowing in tubing shown wrapping around from the lower center of the photo. The sample mounting can be rotated around several axes during irradiation, so that a tomographic database can be built up from the CCD sensor array in the red-lined white box at far right.

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