The people building fusion :

First-hand perspectives from the young engineers at FUSE

02

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10

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2026

John Deneen

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MECHANICAL ENGINEER

John Deneen

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MECHANICAL ENGINEER

I found Fuse after a long, discouraging recruiting cycle in aerospace. After enough rejections, I started cold emailing headhunters and venture studios, which eventually led me to FUSE who was interested in my background and experience.

Up to that point, nearly everything I had done revolved around aerospace. I studied Mechanical Engineering and Computer Science at Harvard, served as Chief Engineer of the Harvard Rocket Propulsion Group, worked at an aerospace startup and at Northrop Grumman, and wrote my thesis on an airship drone sponsored by JPL.

Fusion was not aerospace, but it had always fascinated me. What drew me to FUSE was the combination of ambition and practicality. FUSE is pursuing fusion through real, dual use systems tied to national security and delivered as working hardware. It felt serious and worth committing to.

My first conversation with the founder, JC did not feel like a typical interview. He asked about motivation and purpose, not just experience. That conversation clarified something important for me. I want to use my education on problems that actually matter.

When I joined FUSE, I was immediately out of my depth. A design review on my second day made that clear. Concepts flew by that I did not fully understand, and that feeling has not entirely gone away. There is always more to learn. I learned quickly to read, ask questions, and keep working.

A few weeks in, I took ownership of a high voltage spark gap switch. Legacy systems were unreliable and expensive, so I spent months reverse engineering and iterating on the design, slowly building intuition around something that had felt opaque at first.

One moment that captured FUSE for me came just before a live demo of Pico, our ultra low jitter pulsed power system. Days before the demo, it failed. We disassembled and rebuilt the system the day before the visit and got it running in time. The demo succeeded. It was stressful, but it showed how the team operates.

As a Responsible Engineer, I own projects end-to-end. This includes design, procurement, assembly, testing, and presenting our work. I have helped build a one terawatt pulsed power generator twenty feet tall and designed components that fit in a five inch cube. We work at scales that still feel unreal.

What makes this possible is the culture. FUSE is a low ego place where responsibility is given early and trust is real. When something breaks, I fix it. That accountability has pushed me to grow faster than I ever expected.

FUSE is exactly the experience I hoped for in my first role out of college. It is challenging work with real responsibility, alongside people I am proud to build with.

Interested in learning more about Fuse?
Visit our Careers page.
PULSED POWER PUSION