Cryogenic Engineer

ABOUT SUBCRITICAL SYSTEMS

Subcritical Systems, Inc. is a venture-backed startup in Austin, Texas building accelerator driven systems and the only US commercial manufacturer of accelerator cavities. What SpaceX did for rockets, we plan to do for accelerator cavities and commercialize across applications of power production, medical isotopes, semiconductors and waste transmutation.

We are in the process of building the Energy Amplifier, a novel nuclear fission system in which a particle accelerator drives a subcritical core, making meltdown physically impossible for clean power production. Due to its inherent safety, our system has a more streamlined licensing process. Our founding team includes successful entrepreneurs with a track record of building several multibillion dollar companies in deep-tech, and scientists who were leading U.S. national labs with deep experience in accelerator \& nuclear technologies.

We are actively hiring to expand our team as we work toward licensing, regulatory submissions, and construction of our first energy amplifier. More information is available at subcritical.com.

ROLE SUMMARY

We are seeking an experienced Cryogenic Engineer to lead the design, procurement, installation, and commissioning of the cryogenic refrigeration plant and helium distribution system that will cool the superconducting RF (SRF) linac and superconducting solenoid magnets at the heart of SSI's Energy Amplifier. Reporting to the SVP for Accelerator, the selected candidate will be a core member of the accelerator systems team, working closely with SRF cavity, magnet, RF, and cryomodule engineers to deliver a reliable 2 K / 4\.5 K cryogenic architecture that meets availability targets for first power in 2028\. The ideal candidate brings hands-on experience with large-scale helium refrigeration plants in accelerator, fusion, or industrial cryogenic environments and thrives in a fast-paced, build-first deep-tech setting.

KEY RESPONSIBILITIES

Cryogenic Plant Design \& Procurement

• Own the end-to-end design of the helium refrigeration plant, including 4\.5 K cold boxes, 2 K sub-atmospheric cooling, compressors, oil removal, gas management, and warm/cold piping distribution.
• Develop heat load budgets (static and dynamic) across the SRF linac, solenoid magnets, cryomodules, and distribution system, with appropriate contingency for operational modes and off-normal conditions.
• Lead RFQ/RFP development, vendor qualification, and technical negotiation with cryogenic plant suppliers (e.g., Linde, Air Liquide, ULVAC, or equivalent); own vendor delivery to spec, cost, and schedule.
• Specify and procure ancillary systems: transfer lines, valve boxes, sub-atmospheric cold compressors, helium inventory and recovery systems, and instrumentation.

Integration with SRF \& Magnet Systems

• Interface directly with SRF cavity and cryomodule designers to define thermal interfaces, cooldown/warmup procedures, and operational envelopes.
• Collaborate with the superconducting solenoid magnet team to specify cryogenic supply conditions, quench recovery, and protection interlocks.
• Coordinate with RF, vacuum, and controls teams on integrated commissioning sequences.

Installation, Commissioning \& Operations

• Develop installation plans, P\&IDs, and commissioning procedures in partnership with the facility team and general contractors.
• Lead pre-operational testing, cold commissioning, and acceptance of the plant and distribution system.
• Define operational procedures, alarm and interlock logic, and maintenance plans; train operators ahead of first beam and first power.

Safety, Codes \& Regulatory

• Ensure designs comply with ASME B31\.3, ASME BPVC Section VIII, CGA, and relevant cryogenic safety standards (ODH analysis, pressure relief sizing, helium inventory management).
• Prepare supporting documentation for NRC Part 70/Part 30 licensing interactions and internal safety reviews.
• Own cryogenic hazard analyses and contribute to the integrated safety case.

Program Delivery

• Track technical milestones against the Master Program Schedule and Accelerator LOE WBS; flag critical-path risks early.
• Document work in design reports, technical specifications, vendor packages, and regulatory submissions.

QUALIFICATIONS

Required

• 7\+ years of professional experience in cryogenic engineering, with hands-on delivery of helium refrigeration plants or large cryogenic distribution systems.
• Deep technical knowledge of 4\.5 K and 2 K helium cycles, cold compressors, Joule-Thomson expansion, turboexpanders, and sub-atmospheric pumping.
• Demonstrated experience specifying, procuring, and commissioning cryogenic plants in accelerator, fusion, detector, or industrial settings.
• Fluency in cryogenic process simulation and heat load modeling (e.g., Aspen HYSYS, EcosimPro/PROOSIS, or equivalent).
• Strong working knowledge of ASME pressure vessel and piping codes, ODH analysis, and cryogenic safety practice.
• Ownership mindset: comfortable moving fast, making decisions with incomplete information, and owning outcomes from spec through cold commissioning.
• B.S. or M.S. in Mechanical Engineering, Cryogenic Engineering, Chemical Engineering, or a related field. Ph.D. welcome but not required.

Preferred

• Direct experience with SRF cryomodule cryogenics (ILC / LCLS-II / XFEL / FRIB / ESS heritage or similar).
• Experience with helium inventory management and large-scale helium recovery.
• Familiarity with NRC licensing environments or DOE nuclear/accelerator safety frameworks.
• Experience leading vendor negotiations and technical delivery with Tier-1 cryogenic plant suppliers.
• Prior startup or skunk works experience delivering first-of-a-kind hardware on aggressive timelines.

BENEFITS

We offer health, dental, and vision insurance.

LOCATION \& WORK POLICY

This role is fully in person in Austin, Texas. Our facility is located next to Austin Airport.

HOW TO APPLY

Apply on LinkedIn or submit your resume and a brief cover letter to [email protected] with the subject line "[Job Title] - Application". Applications are reviewed on a rolling basis.