Sandia circuit passes muster

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An electrical circuit that should carry enough power to produce controlled high-yield nuclear fusion every 10 seconds has undergone tests at Sandia National Laboratories’ Z machine facility.

Z, when it fires, is already the largest producer of X-rays on Earth and has been used to produce fusion neutrons. But rapid bursts are necessary for future generating plants to produce electrical power from seawater. This had not been thought achievable until now.

For the Z machine’s inertial confinement method of producing energy, the circuit must deliver enough energy to fuse pellets of hydrogen every 10 seconds and keep that pace up for millions of shots. The circuit is easily able to fire every 10.2 seconds in brief, powerful bursts.

The new system, called a linear transformer driver (LTD), was created by researchers at the Institute of High Current Electronics in Tomsk, Russia, in collaboration with colleagues at Sandia.

The circuit, consisting of a switch tightly coupled to two capacitors, is about the size of a shoebox and is termed a ‘brick.’ When bricks are tightly packed in groups of 20 and electrically connected in parallel in a ring-shaped container, the aggregate, or ‘cavity’ can transmit a current of 0.5 megamperes at 100 kilovolts.

A test cavity in Sandia’s Technical Area 4 has fired without flaw more than 11,000 times.

Because the cavities are modular, they can be stacked on a metal prong called a stalk. Arranged in a suitable configuration, they could generate 60 megamperes and six megavolts of electrical power, enough, theoretically, to generate high-yield nuclear fusion within the parameters necessary to run an electrical power plant.

The next-generation cavity model, now being tested in Tomsk, transmits 1.0 megamperes at the same voltage and with the same rapidity. Five such units have been built; four have been purchased by Sandia, and one by the University of Michigan.

The new switch eliminates the need for the hundreds of thousands of litres of insulating water and oil carried by the present Z structure. The linear transformer driver produces its 100-nanosecond pulse from start up. It works so well because its design lowers inductances that ordinarily slow electrical transmission.

The technology is 50 per cent more efficient than current Z machine firings, in terms of the ratio of useful energy out to energy in. Z is currently 15 per cent efficient to its load, already a very high efficiency among possible fusion machines.