MADISON, Wis. – When the day comes that fusion produces enough energy to power a city, it will be thanks to nuclear physicists, computing experts and other scientists who combined to make a century-old theory come true.

Credit will also go to metal casting experts, machine shops, precision manufacturers and automation specialists whose skills will make the tools behind the theory.

A blend of Wisconsin’s expertise in the science behind fusion and the state’s hands-on manufacturing legacy will be the key to success. That was an underlying message with the recent announcement that Realta Fusion will stay in Wisconsin to pursue its goal of producing clean, virtually endless energy.

The company, a UW-Madison spinoff courted by several other states, will occupy part of the massive former Oscar Mayer plant on Madison’s northeast side – itself a symbol of the old and the emerging new. Private investors, the governor, state legislators, the state’s economic development arm, local officials, university leaders, utility experts and technology advocacy groups were all part of advancing the deal.

It is poised to pay dividends not only for Madison, but elsewhere in Wisconsin.

Nuclear fusion is the same atomic reaction that powers the sun. It’s an emissions-free form of energy generation that works by melding lightweight atoms (deuterium will be used in Realta’s case) to produce sub-atomic particle neutrons, helium and energy.

It is different than nuclear fission, which occurs when the nucleus of an atom splits into two or more smaller nuclei and other particles, producing energy through a controlled process.

With fusion, the fuel source is infinite, and the energy density is at least 10 million times that of fossil fuels. The neutrons produced by a fusion reaction are far more useful and valuable than the energy it takes to launch it. Plus, there are no carbon emissions or long-lived waste.

About 15% of what is now called “OM Station” will become home for “The Realta Forge,’’ a proving ground in the still-long road to producing fusion on a sustained scale. It aims to build on the company’s recent demonstration that plasma kinetic energy can be directly converted to electricity. Plasma in fusion is best described as a superheated, electrically charged “fourth state of matter.”

Realta broke through the direct energy conversion barrier this year by reviving a 1980s UW-Madison concept called the “magnetic mirror.” It is a machine that confines high-temperature plasma in a linear tube using strong magnetic fields at the ends (“mirrors”) to reflect charged particles back to the center.

Fusion energy production can wear out metals and alloys, however, as it bombards structural materials. That’s why people who know how to make the specialized parts inside that multi-million-dollar machine are vital.

“Fusion is not just a science problem,” said Sam Rikkers, deputy secretary of the Wisconsin Economic Development Corp. “It is also a manufacturing problem. It is a supply-chain problem. It is a workforce problem. It is a ‘can somebody actually make this part?’ problem.”

Realta co-founder and chief executive officer Kiernan Furlong reinforced that point when he said: “Across Wisconsin there are world-class capabilities in materials science, metallurgy, engineering and advanced manufacturing” that will foster a locally trained workforce.

That workforce is expected to grow from about 50 people today to 600. The company has already raised $50 million in venture capital, secured $10 million in venture debt and won $4 million in U.S. Department of Energy awards. It is one of just eight companies taking part in DOE’s Fusion Milestone program.

State and local incentives include sales and use tax exemptions on equipment purchases, $15 million in performance-driven enterprise zone tax credits in six intervals, and $2.8 million in local tax-increment financing. The latter hasn’t been done in Madison since the early days of Exact Sciences.

Much like Epic Systems and Exact Sciences have grown statewide supply chains over time, so will Realta Fusion. The company’s decision to stay in Madison is not just a victory for the city, but for a state that can help supply the hardware behind the innovation.

Still is past president of the Wisconsin Technology Council. He is an adviser to Competitive Wisconsin Inc., a non-profit public policy group.