Senior Opto-mechanical Engineer

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 a Senior Opto-mechanical Engineer

Commonwealth Fusion Systems is currently assembling the SPARC tokamak, which aims to be the first magnetic fusion device to produce more fusion power than it consumes (Q>1). Achieving this mission depends on the diagnostic systems that deliver the scientific and controls data needed for successful
operation and provide valuable learning for ARC design. The Photonics Engineering department is seeking a Senior Opto-mechanical Engineer who will be embedded with the Long Wavelength Diagnostics team, helping to deliver diagnostic capabilities such as Laser Interferometry, Thomson Scattering, UV/VIS/IR Imaging and Spectroscopy, Electron Cyclotron Emission Radiometry, and Edge Scanning Reflectometry.

As SPARC moves from design into assembly and commissioning, this engineer will work with a cross- disciplinary team of diagnosticians, scientists, engineers, CAD designers, and technicians to close out the remaining designs and bring these systems from the tokamak, through the Tokamak Hall, and into the Diagnostic Labs. They will work to package optical and waveguide assemblies and the design of active and passive alignment systems that keep long beam paths aligned through thermal cycles, machine motion, and harsh environments expected during the operation of SPARC (high magnetic fields, vacuum, and radiation). As a senior member of the team, they will lead opto-mechanical work on medium to long-term problems, mentor other engineers, and help build CFS’s core competency in opto-mechanics for future CFS project work.

What you'll do:

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Lead the opto-mechanical design and close-out of remaining SPARC long wavelength diagnostic sub- systems (Laser Interferometry, Thomson Scattering, UV/VIS/IR Imaging and Spectroscopy, ECE, and Edge Scanning Reflectometry), carrying designs through final design review, release, procurement, and build

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Design mounts, enclosures, and packaging for optical and waveguide assemblies (mirrors, lenses, windows, fiber bundles, metallic and corrugated waveguide, and quasi-optical components) along beamlines from the tokamak, through the Tokamak Hall, to the Diagnostic Labs

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Design and implement active and passive alignment systems (kinematic and flexure mounts, motorized stages, alignment references, and position or beam-pointing sensing) to establish and maintain alignment over long paths and through thermal and mechanical disturbances

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Develop tolerance and alignment error budgets, perform or direct structural, thermal, and vibration (FEA / STOP) analyses, feeding results back into the optical and microwave designs

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Work side-by-side with diagnosticians, scientists, and optical/microwave engineers to turn measurement requirements into detailed, cost-effective, manufacturable designs, and manage interfaces with the tokamak, building, and mechanical integration teams

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Work with CAD designers to produce models and drawings (GD&T), prepare specifications and design review packages; work with vendors and machine shops on build, inspection, and cost/lead-time tradeoffs

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Plan and provide hands-on support for assembly, installation, alignment, calibration, and commissioning in the Tokamak Hall and Diagnostic Labs; resolve technical issues found during manufacturing and installation

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Provide technical leadership and mentorship; review the work of other engineers, designers, and contractors, and contribute to Photonics Engineering opto-mechanical standards, workflows, and best practices

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Contribute to a strong safety culture, including laser, microwave, vacuum, and high magnetic field safety practices, while helping commission and operate SPARC diagnostics

What we’re looking for:

- At least a bachelor’s degree in mechanical engineering, optical engineering, engineering physics, or a related field

- 8+ years of experience in opto-mechanical or precision mechanical design (or 6+ years with an advanced degree)

- Led the opto-mechanical design of precision optical instruments or systems from concept through build, test, and deployment (e.g., scientific instrumentation, aerospace, defense, semiconductor, or laser systems)

- Designed optical mounts and packaging, including kinematic and semi-kinematic mounts, flexures, optic bonding, and athermal design

- Designed and implemented alignment mechanisms and alignment procedures for multi-element optical systems

- Performed tolerance analysis and error budgets, and used structural/thermal FEA to predict optical performance

- Proficiency with 3D CAD and producing drawings to GD&T (ASME Y14.5)

- Hands-on lab experience assembling and aligning optical systems

- Strong communication skills to gather inputs and share information across several partner teams.

- First-principles approach and the ability to understand tradeoffs that bridge engineering and physics

- Bias toward action, with the engineering judgement to produce robust, simple designs quickly

- Attention to detail with an ability to pivot between topics multiple times per day

Bonus points for:

- A master's degree or PhD in mechanical engineering, optical engineering, engineering physics, or a related field

- Familiarity with optical design and CAD software such as Zemax OpticStudio and Siemens NX (and Teamcenter) is a strong plus

- Packaging of microwave/millimeter-wave waveguide or quasi-optical assemblies (e.g., corrugated waveguide, miter bends, horn antennas, polarizers)

- Contributed to plasma diagnostics or large physics facilities (e.g., tokamaks, laser facilities, accelerators, telescopes)

- Design for harsh environments: ultra-high vacuum, high magnetic fields, radiation, cryogenic, or high vibration.

- Active alignment and beam stabilization (motorized mounts, PSDs/quad cells, camera- based feedback) and Python/MATLAB for analysis and automation

- Design of optically transparent vacuum boundaries (windows) and optics for harsh environments

- Beam delivery for high-power or pulsed lasers and familiarity with laser safety (ANSI Z136).

- Experience managing suppliers and external engineering resources

- An ability to clearly express and critique ideas, and to mentor others

- An emphasis on elegance and simplicity over complexity

Must-have Requirements:

- Ability to occasionally lift up to 50 lbs

- Perform activities such as stooping, climbing, typing, standing, or sitting for extended periods of time

- Dedication to safety to mitigate industrial hazards that may include heat, cold, noise, fumes, strong magnets, lead (Pb), high voltage, and cryogenics

- Willingness to occasionally travel or work required nights/weekends/on-call

#LI-Hybrid

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.