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Bates development could boost radar performance

Recent upgrades of the high-power microwave transmitters which drive the linear electron accelerator at the Bates Laboratory have found applications missile tracking at Kwajalein Atoll in the Pacific, the site of last weekend's missile-defense test launch.

At Bates, 12 modulators provide pulsed power to 12 tubes called klystrons and produce the microwaves that accelerate the electron beam. These pulses of up to 120,000 volts and 100 amperes (equivalent to a maximum power of 12 megawatts) need to be switched on and off in less than one-millionth of a second.

Over the past five years, a group at Bates led by Abbi Zolfaghari in collaboration with Diversified Technologies Inc. of Bedford, Mass., has designed and built a new switching circuit by combining traditional switch tubes with state-of-the-art solid-state switches recently developed by the company.

The new circuit is intended to improve reliability, efficiency and ease of accelerator operation at Bates. This is essential for delivering electron beams at maximum energy and at high pulse repetition frequency. "We expect to increase transmitter and accelerator availability by 5 to 10 percent, equivalent to providing a substantial amount of increased beam time each year," said Bates Associate Director Chris Tschalaer.

Based on the successful developments at Bates, Diversified Technologies has pursued the new high-voltage solid-state switching technology in a number of applications. One such application is to replace vacuum tube modulators in the transmitters for two important U.S. Navy shipboard radar systems. In addition, missile-range instrumentation radar systems have transmitter pulse modulators which are candidates for solid-state upgrades.

Chip Wolcott, a member of the Bates team that developed the new systems, is a senior engineeer with Raytheon Corp., and is based at Kwajalein Atoll, where he is studying the applicability of the Bates technology to radar systems there. "I believe this new technology represents the next step forward in modern high-power radar design. The Bates Laboratory should be proud of its contribution to modulator engineering," he said.

"We're very pleased with the application of the technology developed at Bates. It shows the value of investment in basic research to the security of the United States," Zolfaghari said.

The Bates development was made possible by $1.6 million in funding under a program for Accelerator Improvement Projects by the nuclear physics division in the Office of Science of the U.S. Department of Energy.

A version of this article appeared in MIT Tech Talk on July 18, 2001.

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