Mechanical Engineer, RF Systems

Devens, MA
Engineering – Electrical Engineering /
Full-time /
On-site
About Commonwealth Fusion Systems:
Commonwealth Fusion Systems is on a mission to deliver the urgent transition to fusion energy.
Combining decades of research, top talent, and new technologies, we’re designing and building commercially viable fusion power plants. And we're working with policymakers, suppliers, and many others to build the energy industry of the future.
We’re in the best position to make it happen. Since 2018, we’ve raised $4 billion of capital, making us the largest and leading fusion company in the world.
Now we’re looking for more thinkers, doers, builders, and makers to join us. People who’ll bring new perspectives, solve tough problems, and thrive as part of a team.
If that’s you and this role fits, we want to hear from you.
Join the power movement as an Mechanical Engineer, RF Systems

SPARC sustains fusion reactions by feeding >25MW of 120MHz RF power into the tokamak to heat the plasma to 100 million Kelvin. We need a Mechanical Engineer to design the critical physical infrastructure that routes this massive power, from coax transmission lines that span the entire plant to the intricate cooling plates required for high-power electronics.

At this level, you will own the physical design and integration of robust mechanical systems, translating requirements into manufacturing-ready hardware. You will design everything from large-scale utility interfaces and custom bellows to sheet metal parts and custom heat sinks, taking designs from ideation and CAD modeling through fabrication and direct plant integration.

For more information on the SPARC RF plant, see the SPARC journal papers here:

What you'll do:

  • Design specialized RF Heating plant components working closely with RF Engineers. These include large-diameter coaxial transmission lines and devices such as stub tuners and RF testing loads
  • Decompose high-level system requirements into actionable mechanical specifications, owning the mechanical designs for the RF Heating system
  • Collaborate daily with a dedicated CAD drafting team, providing clear guidance to detail, rigorously reviews, and releases
  • Partner cross-functionally with RF engineers, electronics engineers, process engineers, and other disciplines
  • Architect thermal management solutions by integrating complex water and air cooling loops directly into high-power electronics enclosures and plant systems
  • Develop large sheet metal components, precise mounting hardware for custom printed circuit board assemblies, cold plates, and more
  • Perform structural loads analysis and thermal analyses to ensure design viability

What we’re looking for:

  • Bachelor’s degree in Mechanical Engineering, Physics, or a related field
  • 5+ years of hands-on mechanical design experience in industrial, heavy machinery, high-power electronics, electric vehicle, or aerospace environments
  • Demonstrated experience as the primary creator and owner of mechanical design architectures, operating as a core design engineer
  • Direct experience performing structural loads analysis and thermal analyses to validate mechanical designs
  • High proficiency in 3D CAD software and creating detailed manufacturing drawings utilizing GD&T standards
  • Possess a strong fundamental understanding of heat transfer, structural mechanics, and fluid dynamics

Bonus points for:

  • Experience using Siemens NX for 3D modeling and Teamcenter for product lifecycle management and drawing release workflows
  • Background decomposing complex system requirements into clear mechanical hardware specifications
  • Experience designing large-scale pipe routing, coaxial transmission lines, flanges, bellows, or active water and air cooling systems
  • Experience with complex electronics assemblies and the thermal management of such assemblies
  • Deep familiarity with sheet metal fabrication processes, machining capabilities, and communicating directly with contract manufacturers

Must-have Requirements:

  • Ability to lift up to 50lbs
  • Perform activities such as stooping, climbing, standing, typing or sitting for extended periods of time
  • Willingness to travel or work required nights/weekends/on-call occasionally
  • Work in a facility that contains industrial hazards including heat, cold, noise, fumes, strong magnets, lead (Pb), high voltage, high current, pressure systems, and cryogenics
$90,000 - $145,000 a year
Salary range for this full-time position + equity + benefits. The actual salary will depend on level, location, qualifications, and experience. The range displayed on each job posting reflects new hire salaries for the position across all US locations.
Benefits include:
• Competitive compensation with equity
• 13 Company-wide Holidays
• Flexible vacation days
• 10 sick days
• Generous parental leave policy
• Health, dental, and vision insurance
• 401(k) with employer matching
• Professional growth opportunities
• Team-building activities
At CFS, we excel in fast-paced environments, driven by our values of integrity, execution, impact, and self-critique. As we grow, we’re eager to bring on mission-driven folks who offer diverse perspectives and fresh ways to tackle challenges.
We value diversity deeply and are proud to be an equal opportunity employer by choice. We consider all qualified applicants equally, regardless of race, color, national origin, ancestry, citizenship status, protected veteran status, religion, physical or mental disability, marital status, sex, sexual orientation, gender identity or expression, age, or any other basis protected by law.
This role requires compliance with U.S. laws concerning the export of controlled or protected technologies or information (collectively, “Export Control Laws"). Any offer of employment will be contingent on the need for compliance with such Export Control Laws.