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.

Role Description

As a research scientist, you’ll work closely with plasma physicists, engineers, and technicians to design, deploy, and operate optical diagnostics that are central to advancing stable isotope production and fusion fuel cycle technologies.

This role requires deep hands-on experience with experimental plasma diagnostics, combined with systems-level thinking and the ability to lead diagnostics from concept through commissioning and operation. You will play a pivotal role in validating plasma performance and informing design decisions for a first-of-a-kind isotope separation system.

What You’ll Do:

• Lead the design, deployment, and iteration of optical plasma diagnostics and/or physical diagnostics for lithium plasmas and isotope separation experiments

• Develop and field diagnostics such as high-resolution spectroscopy, interferometry, or Langmuir probes, to measure plasma velocity, temperature, and density

• Design and execute experimental campaigns, including diagnostic calibration, validation, and uncertainty analysis

• Analyze and interpret experimental data, developing robust and well-documented data processing pipelines

• Work closely with plasma physicists, mechanical engineers, and controls engineers to integrate diagnostics with experimental systems

• Document experimental results and technical decisions to inform design iterations and program direction

• Mentor and support junior scientists and engineers on the diagnostics team, raising overall execution quality and scientific rigor

What You’ll Bring:

• M.S. or higher Plasma Physics, Applied Physics, or a closely related field

• 5+ years of hands-on experience developing and fielding experimental plasma diagnostics

• Demonstrated experience owning diagnostics from concept through commissioning and operation

• Strong background in optical diagnostics, such as spectroscopy, interferometry, or laser-based techniques

• Proven experimental skills including instrument calibration, signal processing, and data analysis

• Experience working in complex experimental environments such as high voltage, vacuum, strong magnetic fields

• Ability to collaborate effectively across disciplines and translate diagnostic data into actionable insights

• Comfort working in ambiguity, taking ownership of critical technical problems, and focusing effort on what moves the program forward

• Excellent written and oral communication skills

Preferred Experience, But Not Required

• PhD in Plasma Physics, Applied Physics, or a closely related field

• Prior experience mentoring or technically leading other scientists or engineers

• Experience in a startup or similarly fast-paced experimental R&D environment

Compensation and Benefits

Our compensation for this role is a wide range, determined by an evaluation of your experience and qualifications. All compensation packages for full-time employees include equity ownership in Marathon Fusion.

Annual Base Pay

$150,000 to $200,000

Benefits

We offer the following benefits, subject to applicable eligibility requirements:

• Medical, dental, and vision insurance

• Health FSA and Dependent Care FSA

• Generous paid time off and sick leave

• 401(k) plan, including 4% company contribution

• Commuter benefits

• Stocked office kitchen

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. If you need assistance or an accommodation during the interview process, please let us know.

Compensation Range: $150K - $200K