A "Rooftop" testbed ground facility provides the backbone of the SATCOM research. The testbed is equipped with an array of SATCOM systems, including the Milstar ARC-208 Airborne Command Post (ABCP) satellite terminals, various UHF/SHF/EHF subsystems and a multiple element antenna farm.
Electrons are injected into the booster synchrotron, a racetrack-shaped ring of electromagnets, and accelerated from 450 MeV to 7 billion electron volts (7 GeV) in one-half second. (By comparison, the electron beam that lights a TV screen is only 25,000 electron volts.) The electrons are now traveling at >99.999999% of the speed of light. The accelerating force is supplied by electrical fields in four radio frequency (rf) cavities. In order to maintain the orbital path of the electrons, bending and focusing magnets increase the electron field strength in synchronization with the rf field.
Producing brilliant x-ray beams at the APS begins with electrons emitted from a cathode heated to ~1100° C. The electrons are accelerated by high-voltage alternating electric fields in a linear accelerator (linac; photo below). Selective phasing of the electric field accelerates the electrons to 450 million volts (MeV). At 450 MeV, the electrons are relativistic: they are traveling at >99.999% of the speed of light, which is 299,792,458 meters/ second (186,000 miles/second).
The 7-GeV electrons are injected into the 1104-m-circumference storage ring, a circle of more than 1,000 electromagnets and associated equipment, located in a radiation-proof concrete enclosure inside the experiment hall, which is large enough to encircle Chicago's U.S. Cellular Field. A powerful electromagnetic field focuses the electrons into a narrow beam that is bent on a circular path as it orbits within aluminum-alloy vacuum chambers running through the centers of the electromagnets.
Synchrotron storage rings optimized for insertion devices (photo below) are called "third-generation" light sources. Some, like the Advanced Light Source in California and the SuperACO in France, provide radiation in the ultraviolet/soft x-ray part of the spectrum. The 7-GeV APS and its sister facilities, the 6-GeV European Synchrotron Radiation Facility in France, and the Super Photon Ring 8-GeV (SPring-8) in Japan, can produce a range of x-rays up to those of the hard (highly penetrating) variety because of higher machine energies.
The ratchet-shaped radiation-shielding wall between the APS storage ring and the experiment hall serves as a line of demarcation. Thirty-five "sectors" are marked on the experiment hall floor. Each of these sectors comprises at least two x-ray beamlines, one originating at a bending magnet in the storage ring lattice, the other at an insertion device. With all APS sectors equipped and operating, the APS, in effect, has 35 discrete laboratories under one roof. More information about APS beamlines, including maps and specifications, are available at Find a Beamline.
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