(FORTUNE Magazine) – LAST MAY, IN A DARK townhouse basement in Cinnaminson, N.J., Dan McCauley, a 32-year-old radar engineer with Lockheed Martin, became Zeus.

With his hand on the dial of a Variac, a souped-up version of a power controller for toy trains, McCauley cranked up the juice feeding into what looks like a mushroom-shaped technoprop from Frankenstein's laboratory. An inch-high fountain of sparks spewed from a wire nub that McCauley had taped to the toroidal top of the device, known as a tesla coil. Another twist of the knob, and the sparks grew longer and fatter into little-tyke lightning bolts.

When he cranked the dial a bit more, all hell broke loose. Like an angry snake held by its tail, a continuously morphing spark lashed out, nipping the ceiling, a camera tripod, whatever it could reach. All the while, microthunder filled the basement. Any neighbor within earshot must have thought the condo complex was about to blow.

McCauley was buzzing. This successful test run meant he was likely to do well in August when he was slated to unveil his state-of-the-art tesla coil at an annual gathering of about 60 high-voltage enthusiasts. Like community-theater troupes and dog-show aficionados, HV hobbyists share a passion--only theirs mixes a NASCAR-like craving for powerful machinery with an MIT-style affection for geekery.

After a minute of playing Zeus, McCauley dialed the Variac down and flicked on the lights. There was a nose-wrinkling smell. "Ozone," McCauley said.

That is the smell of success for McCauley and his loose fraternity, for whom making big sparks simply is one of life's necessities. "Once you build a coil, you want to build a bigger one," he says. "It's a disease."

Hero to many coilers is Nikola Tesla, the Serbian-born turn-of-the-20th-century pioneer in alternating-current (AC) power transmission and a fearless experimenter with high voltage. The lightning-making coils that go by his name have been emulated in small and big ways for over a century.

In recent years the HV community has been diversifying. There are the coin shrinkers, who use high voltage to generate magnetic fields muscular enough to shrink quarters into sub-dime dimensions. There's the "fusor" crowd, which aims to achieve fusion power using tabletop high-voltage particle accelerators. And on the darker fringes are those who channel their mostly homespun know-how into building electromagnetic rail guns that propel metal slugs not even Keanu Reeves, invoking Matrix time, could dodge, or high-energy radio frequency (HERF) guns that are to electronics what a bull is to a china shop.

It's all about shock and awe. To cavort with high voltage is to handle snakes, walk on fire, chase tornadoes. It's the way some technophiles choose to honor the awesome power of nature.

"When I see a manifestation of electrical power, like a lightning strike, or if my rail gun fires, it's a thing of beauty," says Sam Barros, a 23-year-old electrical-engineering student at Michigan Technical University in Houghton, Mich. Barros's love affair with electricity began at the age of 7, when he bent a wire into a U and stuck the ends into an electric socket. The wire exploded and blackened the wall. His parents were appalled. "It was at that moment that I started really admiring electricity," Barros says.

Like most HV hobbyists, Barros has made tesla coils. At the heart of a typical coil are about a dozen thick windings surrounded by a secondary spool-like coil that can have thousands of windings. Atop the nested coils is a metal toroid, sometimes made on the cheap by wrapping a ring of corrugated vinyl drainage tubing with aluminum foil. When a voltage is applied to the primary windings, a much higher voltage is induced in the secondary coil, shunting charge to the toroid. When that charge builds up enough, it overcomes the air's insulating properties and strikes out with a spark. It's like filling a balloon with a charge instead of air. The little wire McCauley tapes to his toroids functions like a hole in a balloon, opening a pathway for electricity. McCauley says his solid-state coil probably ups the 110 volts from the wall to hundreds of thousands of volts.

Barros has been pushing the boundaries of the HV community by working on an electromagnetic rail gun. He used to do this work in his parents' basement. Now he's getting more official, having secured lab space at MTU, the backing of a research advisor, and a donation of capacitors from the company Cornell Dubilier.

Lining the two-foot-long rail is a gantlet of coils connected to the capacitors, each of which stores electrical energy like a battery but delivers the stored charge all at once. With the flick of a switch, Barros initiates what might be considered a supremely fast electromagnetic variant of peristalsis. The capacitor-coil combos generate a series of intense magnetic fields, which propel a projectile down and out of the rail with a blaze of white-hot sparks, a head-jerking bang, and the smell of ozone. On the receiving end are aluminum cans or sheets of plywood in front of a cinder-block laboratory wall. He can shoot finger-length metal slugs and, with some modification, even mostly nonmetal projectiles, including aluminum-backed Teflon slugs.

Cut from the same cloth as Barros is Rostislav Persion, a Ukrainian-born, twentysomething wunderkind halfway through an electrical-engineering program at the State University of New York at Stony Brook. As a kid, he built a toy electric chair. On the home page of his website, titled Voltage Labs, is a picture of a nuclear mushroom cloud and the motto "Applied Science for Military Applications." May Slava, as Persion likes to be called, never turn to the dark side.

In high school Slava's attention turned to HERF gizmos after he learned about EMPs, or electromagnetic pulses, which are generated by nuclear explosions. With no nuclear weapons readily available, Slava figured out how to use the magnetrons inside microwave ovens to build his own HERF weapons. The gadgets are essentially bright lamps, only they emit invisible microwaves from a cone-shaped antenna instead of visible light from a bulb. Since wires and chips can pick up microwaves, HERF guns can wreak electrical and electronic havoc. Plenty of classified R&D is devoted to developing offensive and defensive electromagnetic technologies like HERF guns.

When Slava flicked on his first homemade HERF gun, the computers in his house crashed and had to be rebooted. "All the speakers were buzzing, and the phones wouldn't work for 20 minutes," he adds. It was a moment of teenage triumph.

Last year Winn Schwartau, an organizer of information-warfare meetings, invited Slava to a conference in Washington, D.C. After warning those in the audience to leave their computers outside the room, Slava flicked on his HERF gun. A sacrificial computer across the room crashed instantly. "His demonstration blew people away," says Schwartau. Slava's goal now is to finish school and work as a military researcher.

McCauley already has a job. What drives him these days are gatherings called teslathons. One of the most prestigious, invitation-only teslathons takes place annually in late August near Rochester, N.Y. "I live for these," says McCauley, who was thrilled when he got his first invitation two years ago. Teslathon organizer Ed Wingate, a retired toolmaker for Kodak, describes the experience as "being in a building with a contained thunderstorm." For a special thrill, Wingate built a "cage of death," in which a person can stand and experience lightning up close (the cage shunts all the electricity into the ground).

On Aug. 20, at the latest Rochester tesla-thon, McCauley was able to show off his coil. In a shed, with heavy rain pelting the metal roof, McCauley cranked up his Variac. An angry spark lashed out, this time stretching beyond five feet. "Everyone was completely stoked," says McCauley. Bert Hickman, a coin shrinker from the Chicago area, concurs. "What we were seeing there was the state of the art."

It was a transient spark of glory, of course. For HV enthusiasts, no spark is big enough.

IVAN AMATO's latest book is Super Vision: A New View of Nature.