Cryogenic Systems Engineer
Fuse · San Leandro
About Fuse
We are building one of the most potentially consequential companies of the century. Our mission is to accelerate the world's transition to fusion energy while safeguarding humankind. This is not a normal company. This is not a normal job. We are committed for the long term to win.
About the Role
Fuse is constructing Z-Star, a next-generation pulsed-power facility. Z-Star requires two deeply integrated cryogenic systems: a high-vacuum cryopumping system and a 4 K target/liner cryogenic cooling system.
As the Cryogenic Systems Engineer, you'll design, commission, operate, and maintain both systems and serve as the facility's resident expert in cryogenic and vacuum science.
Core Responsibilities
Cryopump System Design & Operations
Design, procure, install, and commission the multi-stage vacuum system for the Z-Star chamber, including turbomolecular roughing pumps, cryopump arrays, and associated gate valves, interlocks, and controls.
Define cryopump sizing, placement, and regeneration schedules to meet target base pressure and shot-repetition-rate requirements.
Develop and maintain vacuum protocols including chamber venting, backfilling with inert gas, and controlled pump-down procedures compatible with shot operations.
Monitor and trend vacuum performance; diagnose and resolve outgassing sources, virtual leaks, and pump degradation.
4 K Target Cryogenic System
Design and commission the liquid helium cryostat and cryogenic delivery system for liner/target cooling, including vacuum-jacketed transfer lines, LHe reservoir management, and temperature-control instrumentation.
Develop procedures for target loading, cool-down, hold time at 4 K, and rapid warm-up following a shot.
Characterize and minimize cryogenic heat loads from radiation, conduction, and parasitic pathways to maintain stable 4 K conditions through the target preparation window.
Cryogenic Infrastructure Management
Manage liquid helium and liquid nitrogen supply, storage dewars, and transfer operations on-site, including logistics, safety, and vendor relationships.
Maintain all cryogenic hardware: cryopumps, compressors, cold heads (Gifford-McMahon or Pulse Tube), transfer lines, pressure-relief systems, and monitoring instrumentation.
Develop and implement a preventive-maintenance program for all cryogenic and vacuum equipment aligned with the facility shot schedule.
Train facility operations staff on cryogenic safety procedures and emergency response.
Diagnostics & Instrumentation
Specify, install, and maintain cryogenic instrumentation: Cernox or PT-100 temperature sensors at multiple stages, capacitance manometers, ionization gauges, residual gas analyzers (RGA), and pressure transducers.
Integrate cryogenic-system monitoring into the facility control and interlock system.
Safety & Compliance
Author and enforce cryogenic safety procedures, including ODH assessments, pressure-vessel requirements, LHe handling, and cold-burn precautions, in compliance with applicable U.S. codes.
Perform pressure-vessel and cryostat inspection and documentation per applicable ASME/CSA standards.
Minimum Qualifications
B.Sc. or M.Sc. in Physics, Mechanical Engineering, Engineering Physics, or Chemical Engineering with demonstrated cryogenics specialization.
2+ years of hands-on experience designing, operating, or maintaining cryogenic systems at liquid-helium temperatures (4 K) in a research or industrial facility.
Proficiency with cryopump systems including sizing, installation, and regeneration cycles.
Strong working knowledge of vacuum science and technology: pumping speed, conductance, outgassing, leak detection using He mass spectrometry, residual gas analysis, and pressure measurement.
Experience designing or operating liquid-helium dewars, cryostats, and VJ transfer lines.
Familiarity with cryogenic instrumentation including thermometry, pressure, flow, and liquid-level measurement from 4 K to 300 K.
Preferred Qualifications
Experience with fusion energy, pulsed power, or particle-accelerator cryogenic systems, particularly high-voltage-isolated cryogenic assemblies.
Familiarity with MagLIF-type target cryostats or ICF cryogenic target-preparation systems.
Experience with Gifford-McMahon (GM) or Pulse Tube (PT) cryocoolers for closed-cycle refrigeration.
Knowledge of cryogenic safety standards including ASME Section VIII, CGA G-5.4, ODH analysis procedures, and pressure-relief system design.
Experience with large vacuum-chamber systems (>10 m³) in a pulsed or repetitive-shot experimental facility.
Proficiency in thermal modeling and simulation using ANSYS, COMSOL, or equivalent tools.
What We Value
Give a shit. Build things you're proud of.
Take responsibility. If something is broken and you can fix it, fix it. See things through.
Move fast. Make decisions, learn quickly, and keep moving forward.
Think bigger. Simplify relentlessly. Don't default to the safe answer.
Disagree and commit. The best idea wins. Once a decision is made, we move.
Desire to win. This is hard. Expect intensity. We are here to win.
Plan B is to make Plan A work.
Benefits
Medical, dental, and vision coverage.
Relocation assistance for roles that require it.
Flexible time off. Take what you need, no accrual tracking.
2 weeks of paid time off built into the end of each year, subject to team and business needs.
Supportive leave of absence policies.
Paid leave for new parents.
ITAR Requirements
To conform to U.S. Government technology export regulations, including the International Traffic in Arms Regulations (ITAR), you must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State.
Equal Opportunity
Fuse is an Equal Opportunity Employer; employment with Fuse is governed on the basis of merit, competence, and qualifications and will not be influenced by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, ancestry, immigration status, sexual orientation, gender identity, marital status, mental or physical disability, or any other legally protected status.