US embarks on quest for high-energy defensive weapon
Test Site 300, near Tracy, Calif.
Scientists working in a new, $55 million facility hidden in the dry, brown hills between Livermore and Tracy hope to advance development of a defensive weapon any future adversary of the United States will respect - a particle beam device that could destroy incoming nuclear warheads.Skip to next paragraph
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The possibility of developing charged-particle beam (CPB) weapons has long been discussed, and research has been going on for some 25 years in the Soviet Union and the US. But when President Reagan, in a speech early this year, speculated on the use of such devices as defensive weapons, his remarks created quite a stir.
Development of this ''ray gun,'' to use comic-book terminology, is by no means a certainty. Among scientists who have expressed serious doubts about its feasibility are John Parmentola and Kosta Tsipis, physicists at the Massachusetts Institute of Technology (MIT). They and other critics have cited problems of accuracy, cost, and the ability of an adversary to devise countermeasures.
Recently, a group of reporters and photographers was admitted to Site 300 - a tightly guarded and usually off-limits test facility of the Lawrence Livermore National Laboratory - for a guided tour of the new Advanced Test Accelerator (ATA).
Scientists who conducted the tour clearly hope the ATA will enable them to take a concept that first appeared decades ago in science fiction closer to scientific fact.
Later this summer, the ATA team headed by Richard J. Briggs will begin ''beam physics experiments'' at the new facility. Basically, that means generating and controlling electronic pulses that eventually will be directed at a target at the end of a 540-foot-long, three-section tunnel.
In the words of the scientists themselves: ''The ATA is designed to produce short pulses of electrons, each about 21 meters long, in several modes. Typical modes are 1 pulse per second, 5 pulses per second, and a burst of 10 pulses separated by one-thousandth of a second, repeated every two seconds.
''The current of the electron beam rises from zero to 10,000 amps in about 20 billionths of a second, and is maintained at that level for at least 50 billionths of a second before decreasing to zero in another 20 billionths of a second.''
To generate this powerful beam, ATA takes 18,000 volts of electricity from a Pacific Gas and Electric Company substation, uses transformers to boost it to 250,000 volts, then stores it in a series of 235 capacitors called Blumlein sections. These sections store the electricity for 20 millionths of a second and release it in 70 billionths of a second. When this pulsed voltage is applied to a cold cathode ''disc,'' a plasma of electrons is created. These particles are injected into a strong magnetic field, which accelerates them to an energy level of 2.5 million electron volts (MeV).
When the electrons come out of the 64-foot-long injector chamber, their velocity is 0.985 times the speed of light. That increases to 0.999 times the speed of light by the time the pulse leaves the 256-foot accelerator chamber - and the electron beam's energy increases, at the same time, from 2.5 MeV to 50 MeV.
Next the electrons are magnetically guided through a 140-foot-long transport section, which separates the accelerator section from the experimental section. It also provides a chamber for evaluating the beam's characteristics before beginning the actual experiment. A nearly complete vacuum is maintained in the accelerator, but the experimental tank is at atmospheric pressure.