TL;DR: We achieve Q>1 by combining a high-field superconducting magnet with a compact spherical tokamak, dramatically improving plasma confinement efficiency. Our stepwise engineering approach—validated on legacy devices—reduces physics risk, making net energy gain a practical certainty rather than a gamble.
Step 1: Understand Why Q>1 Is a Systems Problem, Not Just a Plasma Problem
Before touching hardware, internalize that Q (fusion power out ÷ heating power in) depends on three coupled variables: plasma density, temperature, and confinement time. The triple product (n·T·τ) must exceed ~3×10²¹ keV·s/m³. Do not chase heroic single-parameter records—optimize the *product* by using a high-field magnet to shrink the device while raising density limits. This is the core of CFS’s “net energy” philosophy.
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Step 2: Adopt a High-Temperature Superconductor (HTS) Magnet as Your Enabling Technology
Design your toroidal field coils using REBCO (rare-earth barium copper oxide) tape. Unlike conventional copper or low-temp superconductors, REBCO operates at 20 K with a magnetic field >20 T at the coil. This allows a plasma major radius of ~1.8 m instead of 6 m. Tip: test your HTS magnet assembly in a dedicated test facility (like CFS’s TFMC) at full current and field *before* integrating into the tokamak—this de-risks the single most expensive component.
Step 3: Use a Spherical Tokamak to Maximize Confinement Efficiency
Choose a low-aspect-ratio (A ≈ 1.6) spherical tokamak. This shape increases the “bootstrap current” fraction (self-driven plasma current), reducing external power needed for sustainment. Your instruction: maintain a strong vertical elongation (κ ≈ 2.0) and triangularity to stabilize plasma at high β (pressure/magnetic pressure). Tip: Run a dedicated “H-mode” campaign early to confirm edge transport barriers persist at your high field—this directly boosts τ.
Step 4: Engineer for a “Testing-First” Timeline
Build a prototype (like SPARC) that is *not* a commercial plant but a testbed. Set a hard milestone: achieve Q>1 in a 10-second pulse, then scale to longer pulses. Use existing data from MIT’s Alcator C-Mod and JET to calibrate your transport models. Do not extrapolate more than 2× in any single parameter—if your model predicts Q>1 only with three simultaneous record-breaking leaps, redesign.
Step 5: Manage the “Ignition Gap” with Auxiliary Heating
Plan for Q between 1 and 10 using ion cyclotron and lower hybrid heating—not just neutral beams. These are mature and efficient. Tip: Over-specify the auxiliary power by 30% in early runs; you can always dial down, but you cannot add power mid-pulse. Also, install real-time disruption mitigation (shattered pellet injection) to protect the HTS magnets—a single quench can cost months.
Step 6: Validate with a “Q>1” Acceptance Test Protocol
Define Q>1 as: total fusion neutron power (measured by calibrated fission chambers) ÷ total external heating power injected into the plasma. Use a 5-second steady-state window with <±10% variation. Cross-check with two independent diagnostics (e.g., neutron array + magnetic equilibrium reconstruction). If your measured Q ≥ 1.1, you’ve proven net energy gain. Tip: Publish the raw shot data—transparency builds investor and regulatory confidence.
FAQ
Q: How do you handle the risk of HTS magnet failures under neutron bombardment?
A: We place a 0.5 m thick water-cooled neutron shield (borated steel) between the plasma and the coils, reducing fast neutron flux by 1000