LIKE many tools of high-energy physics, linear induction accelerators have been improving in small steps over the past several decades. Now a breakthrough design for the accelerator power source has advanced their capabilities immensely. The new design, based for the first time on solid-state components, promises important progress for the Department of Energy's Stockpile Stewardship Program as well as imaginative new uses for accelerators, ranging from waste treatment to space exploration.|
The new accelerator power source, called the Advanced Radiographic Machine (ARM) modulator, is the product of a six-year development effort by a team of researchers from Lawrence Livermore and Bechtel Nevada Corporation. The technology enables linear induction accelerators, which typically generate thousand-ampere electron-beam currents at high energies, to fire at up to 2 megahertz (millions of times per second)-a rate some 400 times greater than that of current machines.
A prototype ARM modulator built at Livermore reliably delivers a burst of 45-kilovolt, 4.8-kiloampere pulses that can be varied in length from 200 nanoseconds (billionths of a second) to 2 microseconds (millionths of a second). Its solid-state components permit high recovery rates and are easy to cool, thereby ensuring enormous high-average-power levels.
In addition to performance increases, the solid-state technology provides an unprecedented degree of control over the voltage waveform at each stage of the accelerator, thereby permitting unparalleled flexibility in shaping pulses. The machine also generates pulses in a single-step operation, a feature that differs from conventional technology and contributes to substantial cost savings.
Technology Has a Kicker
Power Modulators at the Heart|
Six years ago, a Livermore-Bechtel Nevada team led by Livermore electrical engineer Hugh Kirbie took on the challenge of developing new technology to image imploding warheads over time and from multiple axes. The resulting design is based on power modulators that integrate energy storage, high-speed solid-state electronics, and a hybrid form of transformer, all into one compact package. The modulators can be stacked like flashlight batteries to achieve high voltage and power-to 50-megawatt pulses per modulator and higher.
Even though modern solid-state devices are unmatched in speed, precision, long life, reliability, and cost, their use in the ARM technology is the most radical aspect of its design. Traditionally, it has been difficult to use transistors for high-voltage, pulsed-power systems; they are susceptible to large voltage and current spikes. However, the team overcame those problems with a robust design based on newly available metal-oxide-semiconductor field-effect transistors (MOSFETs).
As testimony to the exhilarating pace of solid-state component development, the original MOSFETs already can be replaced by integrated gate bipolar transistors, which are presently used in bullet trains. The use of these new devices reduces the total parts count drastically and further lowers ARM's overall cost.
The ARM technology will be used to power the kicker system of the Dual-Axis Radiographic Hydrotest Facility (DARHT), now under construction at Los Alamos National Laboratory. The kicker system will create four approximately 50-nanosecond pulses from a 2-microsecond pulse to enable four stop-action radiographs from two axes for every experiment. Although not truly three dimensional, the images will be far more informative than any similar radiograph produced to date. For the first time, researchers will obtain time-resolved information, including shapes, densities, and chemical explosive material distribution within the detonating warhead.
Valuable and Varied Uses
Key Words: Advanced Radiographic Machine (ARM), Bechtel Nevada Corporation, integrated gate bipolar transistors, metal-oxide-semiconductor field-effect transistor (MOSFET), Next Linear Collider, Stanford Linear Accelerator Center.
For further information contact Hugh Kirbie (925) 423-8224 (firstname.lastname@example.org).