About Marathon Fusion

Marathon Fusion is building the technologies needed to make fusion practical. Our work spans high-flux fusion neutron sources for radioisotope production, fuel cycle technologies, and plant-level systems that will enable fusion power at climate-relevant scale.

We are developing compact, beam-driven fusion systems to produce radioisotopes for targeted cancer therapies and to test materials for future fusion power plants. Alongside this work, we develop stable isotope enrichment, tritium processing and recycling, and advanced blanket technologies to close the fusion fuel cycle and enable both energy generation and high-value co-products.

Founded in 2023, Marathon Fusion is advancing near-term applications of fusion in medicine and materials development while building the foundation for abundant, reliable energy in the 21st century.

Culture at Marathon Fusion

We are a startup environment characterized by a need for focus, adaptability and prioritization in a shifting landscape. Thriving in this environment requires excellent proactive communication across roles and backgrounds, the ability to build and maintain trust between team members, and the willingness to learn and develop new skills on the job. We place particularly high weight on each team member's ability to be self-directed.

Please review these points carefully before applying:

• This application is exclusively for the Mechanical Engineering Intern role.

• We provide both Internship and Co-op placements through this single posting.

• Application Deadline: December 2nd, 2026

Role Description:

You will join our R&D engineering team working on plasma centrifuge technology for isotope separation and the fusion fuel cycle. We are currently operating multiple working plasma centrifuge test stands spinning plasmas at 100s to 1,000s of m/s under various conditions, and have more in the detailed design stage.

Role Responsibilities:

• Building, modifying, leak-checking, and maintaining high-vacuum (< 10^-7 torr) and plasma systems

• Producing mechanical parts, assemblies, and drawings using 3D CAD software and communicating with vendors and machine shops to take your designs into the real world

• Conducting thermal, structural, and fluid flow analysis on on your designs

• Assisting scientist and engineers conducting experiments on isotope separation devices and testing sub-systems

• Building and modifying high-power electrical systems (wire harnesses, diagnostic systems, and controls hardware) as well as control system software

Minimum Requirements:

• Proficient with 3D CAD software (SolidWorks preferred)

• Have hands-on experience in areas such as fabrication, test engineering, or vacuum systems operation

• Studying mechanical or mechatronics engineering OR;

• Studying electrical engineering or engineering physics with substantial mechanical design/fabrication experience OR;

• Studying another engineering field or other technical field and have exceptional work ethic, eagerness to learn, and autonomy

Preferred Requirements:

• Experience with GD&T best practices

• Experience with high vacuum systems

• Experience working with compressed and flammable gases

• Experience with plasmas

• Small-scale experiment development

Soft Skills:

• Excellent written and oral communication

• Ability to think holistically about systems

• Capacity to learn new technical subjects quickly, collaborate cross-functionally, and consider problems from inter-disciplinary perspectives

• Organization and project management

• A high degree of conscientiousness and integrity

• Long-term vision while executing short-term goals

• Comfort with the inherent uncertainty of breakthrough technology

• Experimental mindset, ability to form and test hypotheses

Additional Desired Skills:

• Plasma physics

• Vacuum systems

• High-power battery systems

• High-voltage engineering

• Isotope separation systems

• Fabrication for scientific applications

• Python programming

• LabVIEW programming

Marathon Fusion considers all qualified applicants equally for employment. We do not discriminate on the basis 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, ordinance, or regulation.