Tokamak — conventional and spherical
An axisymmetric torus whose strong external toroidal field is combined with the poloidal field of a large driven plasma current; the spherical tokamak does the same at low aspect ratio. SCPN-TOKAMAK-CORE owns the device truth of the conventional_tokamak and spherical_tokamak configurations.
What the configuration is
The tokamak is the most developed closed-field device: toroidal field coils make a strong field along the torus, a central solenoid drives a toroidal plasma current whose own poloidal field twists the field lines into nested flux surfaces, and poloidal field coils shape and position the plasma. The safety factor \(q\) — how many toroidal turns a field line makes per poloidal turn — stays above unity in the tokamak, which is what separates it from the reversed-field pinch. At aspect ratios below about two the same device becomes the spherical tokamak, with the higher natural elongation and the higher normalised current the family's filed source pairs with that regime.
What the core owns
- the device boundary: plant and experiment truth, shot lifecycle and configuration policy for conventional and spherical tokamaks;
- the declared configuration: major and minor radius, elongation and triangularity; toroidal-field, poloidal-field coil counts and the presence of a central solenoid; toroidal field, flat-top plasma current, safety-factor floor, Greenwald fraction and flat-top duration as operational limits;
- diagnostic semantics, reference frames and clock identity declarations; actuator-response model boundaries and the declared safety envelope; the device-owned CONTROL adapter specification with explicit no-direct-actuation semantics;
- the binding to the SCPN Phase Orchestrator reactor registry (version 1.0.0) and the machine-readable domain manifest.
What it explicitly excludes
- Stellarator, heliotron and torsatron systems: SCPN-STELLARATOR-CORE; reversed-field pinch: SCPN-RFP-CORE; spheromak: SCPN-SPHEROMAK-CORE; field-reversed configuration: SCPN-FRC-CORE.
- Solver mathematics and validation evidence: SCPN-Fusion-Core, the canonical owner of shared solver surfaces, until an exact surface passes the reactor family migration gate; no solver code exists in, or was copied into, the device core.
- Typed signal semantics and comparability: SCPN-Phase-Orchestrator (review-only output, never actuation).
- Control admission and action formation: SCPN-Control is the sole software authority that forms an admitted control action.
- Machine protection: independent systems retain the final veto. Portfolio presentation, identity, entitlement and execution gating: SCPN-Studio.
Level-0 physics and its anchor
Three closed forms nothing in the repository owned before: the plasma volume \(2\pi^2 R_0 a^2 \kappa\) by Pappus's theorem, exact for the elliptic cross-section; the vacuum toroidal field \(B_0 R_0/R\) at the inboard and outboard edges and their ratio, with the ordering inboard > axis > outboard asserted; and the normalised current \(I_p/(aB_t)\). The Greenwald limit and the cylindrical safety factor stay on the operational limits and are composed, not restated: a test asserts the record's values are exactly what those methods return, so there is one source of truth per number.
Anchored on a pair of regimes rather than a machine. Greenwald 2002 verifies the relation already implemented: its equation 1.3 prints \(n_G = I_p/(\pi a^2)\) in units of \(10^{20}\,\mathrm{m^{-3}}\), the form and units of the core's limit. Peng & Strickler 1985 print regime pairings, and the two fixtures sit at them: the spherical one at an aspect ratio of exactly 1.5 (radii 1.5 and 1.0, chosen because 1.2/0.8 is not exactly 1.5 in binary) with the elongation 2 the source pairs with it; the conventional one above 2.5 with an elongation below the 1.4 the source calls natural there. Both stay under the printed normalised-current ceiling of about 7 MA/(m T). Declared, and said to be declared: every absolute dimension, field and current — neither source prints a machine.
Load both fixtures in the explorer →
Non-claims
- No equilibrium, stability, transport or current-drive equation is solved.
- The toroidal field is the vacuum field; the plasma's own paramagnetism and the discreteness of the coils are not modelled.
- The density limit and the cylindrical safety factor are empirical consistency instruments with documented applicability, not predictions of disruption or stability; the safety-factor floor is reported, never enforced.
- The volume is exact for the elliptic cross-section only; the triangularity does not enter it, and a test asserts that limitation.
- No yield, gain, confinement or breakeven statement is made, and no value describes or validates a real machine. Fuel-cycle choices are configuration facets, not separate claims.
Capabilities and evidence
Evidence maturity computational_prototype, five implemented capabilities, each with its evidence record in VALIDATION.md: the device configuration model (validated parameter objects with documented consistency estimates, canonical serialisation, a data-only SPO registry pin); the diagnostic and clock semantics model (synthetic channel and clock declarations aligned fail-closed with the pinned SPO observability catalogue, typed frames, clock topology, signal inventories); level-0 device physics (the closed forms on this page); the device 3D model and the device CAD model (tessellated on the shared kernel library and built again as exact solids). No parameter set or channel describes any real machine or diagnostic; the claim inventory is empty and verified by the domain validator.