Then the Intel International Science and Engineering Fair kicked him out for a rules violation. He was devastated, and his story grew larger.
Almost 74,000 page views. Another story in The Huffington Post and on Fox News. The Colbert Report even called Farnsworth to talk about a possible appearance.
Reflecting on the past year from outside his lab at South Dakota School of Mines, Farnsworth said the fame was unexpected and the outcome exactly what was meant to be.
About one year ago, Farnsworth hoped to go to Massachusetts Institute of Technology and achieve honors at the international science fair with his reactor.
He didn't make it into MIT, and on May 14, one day into the Intel science fair in Arizona, he was disqualified. He had participated in too many science fairs in the wrong order.
Students are only allowed to go to one qualifying regional fair and then one qualifying state fair. The rule keeps students from jumping from one fair to another until he or she qualifies. Newcastle competitors went to the Wyoming State Science Fair in Laramie, then went to South Dakota's regional science fair, since it was less than 100 miles away. Conrad qualified in South Dakota but not in Laramie.
His teachers said they didn't know about the rule.
Since May, the International Science Fair has not changed its stance on order or number of fairs, said Michele Glidden, director of science and education programs for the Society for Science and the Public, the organization that runs the Intel International Science and Engineering Fair.
But it gave the Wyoming State Science Fair more spots for students to use to qualify for the international fair.
"We granted those extra spots so they can better represent the students from Wyoming," Glidden said.
Any change is too late for Farnsworth's science fair future. He graduated from high school shortly after the disqualification. It was his last fair competition.
He's not bitter or disappointed anymore.
"I've been thinking on it a lot and praying on it, and the more I do the more I realize this is where I was supposed to be," he said. "I've come to terms and the main theme I've taken away is let it be."
His passion for science hasn't changed. His fusion reactor, the one he built in his dad's shed on a hill outside of Newcastle, is now resting in a formal lab at the School of Mines.
He has his permits from health and safety, but still needs a radiation permit from the university before he can start working on it again.
And when he's done, Farnsworth has dozens of other projects waiting.