About Marathon Fusion

Marathon Fusion is building the engineering technologies needed to scale fusion from breakeven experiments into real power plants. While much of the industry is focused on proving new fusion devices, our focus is on the practical systems that will make fusion deployable at climate-relevant scale.

We develop core fuel cycle and plant-level technologies for stable isotope production, fuel cycle closure, and advanced blanket systems that enable both energy generation and high-value co-products.

Founded in 2023, Marathon Fusion is building the components and systems that will help fusion become a practical, abundant, and reliable energy source for 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.

About the Role

As a Senior Mechanical Engineer on the Lithium Team, you’ll work closely with electrical and mechanical engineers, physicists, and scientists to prototype, test, and deploy solutions in the pursuit of advancing the development of the fusion fuel cycle. With your hands-on experience designing and testing electromechanical systems, you’ll play a pivotal role in the development and iteration of a first of kind isotope separation device.

What You’ll Do

• Lead the iterative design and improvement of an isotope separation system, driving toward robust, scalable deployment.

• Prototype, test, and troubleshoot components and integrated systems in close collaboration with other engineers, physicists, and technicians.

• Develop first-principles understanding of key physical processes and guide improvements based on experimental data and literature.

• Document experimental results and decisions clearly to inform design iterations and process development.

• Mentor and support junior engineers, fostering technical growth and strong engineering judgment on the team.

What You Bring

• B.S. or higher in Mechanical or Aerospace Engineering or related field.

• 5+ years of experience in designing, prototyping, and testing of electromechanical systems.

• Demonstrated experience with high vacuum, high temperature, and/or with reactive material systems (e.g lithium, liquid metals, or molten salts).

• Strong experimental skills and ability to draw insights from physical systems. Bonus if you’ve led large scale or complex designs and experiments.

• Proficiency in mechanical design, including CAD, GD&T, and DFM best practices.

Preferred Experience, But Not Required

• Experience in electric propulsion systems (Hall thrusters) and developing in an experimental R&D setting.

• Experience with handling, containment, or processing of reactive materials.

• Success in mentoring interns and new grads.

• Experience in a start up or a similarly fast paced environment.

Compensation and Benefits

Our compensation for this role is purposefully wide to encompass a variety of levels we're willing to hire. Your final compensation package will be determined by an evaluation of your experience and qualifications. All full-time employees receive equity as part of their compensation.

We're proud to offer the following benefits:

• Medical, dental, and vision insurance

• Generous paid time off and sick leave

• 401(k) plan with 4% employer match

• Commuter benefits

• Fully stocked kitchen

This role is open to applicants who require relocation to the Bay Area and is supported with a $5,000 relocation reimbursement.

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.