Sun in a Bottle - Charles Seife [110]
Indeed, Utah’s history with tabletop fusion goes back decades before the Pons and Fleischmann fiasco. The first person to achieve fusion with a cheap device was Utah born, a young man who grew up on a farm. His name was Philo Farnsworth.
Farnsworth is best known for inventing electronic television. As a young boy, he was plowing a potato field—back and forth, back and forth—when he was inspired with an idea. He could use the same back-and-forth motion to “dissect” a photographic image with a stream of electrons. Though it took years for him to perfect the device itself, at age fourteen Philo Farnsworth had invented a rudimentary television camera.
Farnsworth’s device, known as the image dissector, first turned a picture into a set of electrons. Light causes a peculiar material—cesium oxide—to emit electrons, so an image shining on a plate of cesium oxide will change from a pattern of light and dark spots into a pattern of electrons streaming from the plate. Electrons, unlike photons, are strongly affected by electric and magnetic fields, and Farnsworth exploited this property by using electromagnetic fields to move the electron image back and forth, plowlike, over a detector. This allowed Farnsworth to convert an image into an electronic format that could then be transmitted over the airwaves. Though it was a relatively crude device, it worked. The age of electronic television had begun.81 Unfortunately, a nasty patent battle ensued. Farnsworth won, but he never got rich from his invention. (Just the opposite; it nearly drove him to madness. At one point, he committed himself to an insane asylum and received shock therapy.)
Farnsworth was a brilliant inventor, particularly when it came to manipulating charged particles—like electrons—with electric and magnetic fields. So when he first heard about attempts to create a fusion reactor in a magnetic bottle, he came up with the design for a device that he thought would do it. In the 1960s, he mortgaged his house and borrowed against his life insurance to make his dream a reality. The result was the Farnsworth fusor.
While Farnsworth’s television camera manipulated electrons, his fusor manipulated deuterium nuclei. Stripped of its electrons, a deuterium nucleus has a charge equal and opposite to the electron’s; though deuterium is much more massive than an electron, it, too, can be guided and accelerated by a powerful electric field.
Over the years, Farnsworth and his colleagues patented a number of slightly different designs for the fusor, but in principle they were all relatively simple. A fusor takes deuterium nuclei (or the nuclei of other elements) and injects them into a vacuum chamber that contains a pair of charged metal electrodes. The electrodes have to be shaped to allow the nuclei to pass through them; for example, they might be two concentric wire-mesh spheres, a big positively charged sphere surrounding a smaller negatively charged one. When a deuterium nucleus is squirted past the outer sphere, it is repelled by the positive charge and attracted to the negative charge of the inner sphere, so it zooms inward with ever increasing speed. If the spheres are kept at high voltages, the ions will be moving so fast that they will overshoot the inner sphere and plunge toward the center of the device, where they might strike other ions that have fallen inward from other directions. They might even fuse, releasing energy.
The fusor wasn’t tough to build. The inventors had to be able to create a decent vacuum inside their chamber, construct electrodes designed to handle a very high voltage, and of course, get themselves some deuterium to inject into the device. Other than that, building the fusor was really pretty easy, thus well within the reach of a dedicated amateur. A small one can fit on a tabletop. And it works, too. Farnsworth got neutrons right away. Soon he and his colleagues were producing so many neutrons they had to run the