Reversed-field pinch
A relaxed, current-dominated torus: the plasma current generates most of the confining field, and the edge toroidal field is reversed relative to the axis. SCPN-RFP-CORE owns the device truth of the reversed_field_pinch configuration.
What the configuration is
The reversed-field pinch is a torus like the tokamak, but its safety factor is below unity everywhere and its toroidal field is mostly made by the plasma itself. Driven hard enough, the plasma relaxes toward Taylor's minimum-energy state, in which the toroidal field reverses sign near the edge — the feature that names the device. The relaxation is sustained by a dynamo of tearing and relaxation fluctuations in the 1–500 kHz range; whether the plasma sits in a multiple-helicity or quasi-single-helicity regime is a configuration facet the diagnostics are declared to identify.
What the core owns
- the analytic device physics models: closed-form and 0-D models from the reversed-field-pinch literature evaluated on the validated configuration; the Bessel kernels they use are the shared kernel library's, pinned here, not owned here;
- the device boundary: plant and experiment truth, pulse lifecycle and configuration policy for toroidal devices confined by a relaxed, current-dominated state;
- the declared configuration: major and minor radius; reversal parameter, pinch parameter and average toroidal field as the field programme; plasma current and flat-top duration as operational limits;
- diagnostic semantics (magnetics-heavy mode analysis, regime identification), reference frames and clock identity declarations; actuator-response model boundaries, the safety envelope and the CONTROL adapter specification; the registry binding (version 1.0.0) and the domain manifest.
What it explicitly excludes
- Axisymmetric tokamaks (safety factor above unity, externally dominated toroidal field): SCPN-TOKAMAK-CORE; stellarators: SCPN-STELLARATOR-CORE; spheromak (simply connected, no toroidal-field circuit): SCPN-SPHEROMAK-CORE; self-magnetic pinches (linear Z-pinch class): SCPN-Z-PINCH-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
The Bessel-function model of the Taylor state, \(B_\phi = B_0 J_0(\mu r)\), \(B_\theta = B_0 J_1(\mu r)\), taken from Paccagnella 2015 (eqs. 4–5) in its single-region limit, with \(\mu = 2\Theta/a\), \(B_0 = \langle B_\phi\rangle\Theta/J_1(2\Theta)\), \(F_{\mathrm{bfm}} = \Theta J_0(2\Theta)/J_1(2\Theta)\), the reversal radius \(j_{0,1}/\mu\) and the cylinder's safety factor profile; the Bessel functions and their zeros through the pinned shared kernel library (NIST DLMF 10.2.2, 10.21; OEIS A115368, A115369), each wrapper proven to return the library value bit for bit, with a Rust crate mirroring every kernel in identical operation order and float64 bit patterns compared over a 112-point grid.
Anchored on identities of the model and the printed zeros, not on a machine: the reversal threshold \(\Theta_{\mathrm{rev}} = j_{0,1}/2 = 1.2024\ldots\) is the model's own identity and the configuration's advisory 1.2 is proven to be its rounding; \(F_{\mathrm{bfm}}(\Theta_{\mathrm{rev}}) = 0\) exactly in double arithmetic; \(F_{\mathrm{bfm}} \to 1\) as \(\Theta \to 0\) with a deviation bounded by \(\Theta^2\) over four decades; the product identity \(B_0 J_1(2\Theta) = \langle B_\phi\rangle\Theta\) holds to \(10^{-15}\) relative; the model refuses \(\Theta \le 0\) and \(\Theta \ge j_{1,1}/2\) with the stated reason. A benchmark measures per-point evaluation cost of the two implementations, not physics.
Move the pinch parameter across the reversal in the explorer →
Non-claims
- Every number is a closed-form evaluation of the cylindrical Bessel-function relaxed state on a synthetic configuration; no equilibrium, transport, dynamo or stability equation is solved, and no eigenvalue problem exists here.
- The Bessel-function model is the fully relaxed single-region state; the source records that real reversed-field pinches depart from it, so the model's reversal parameter is reported against the declared one as an advisory, never as a prediction.
- The anchors are identities of the model and the printed zeros of the Bessel functions; they are not correlations with experimental data.
- No confinement, fusion power, gain or breakeven statement is made; no value describes, approximates or validates any real machine.
Capabilities and evidence
Evidence maturity computational_prototype, three implemented capabilities, each with its evidence record in VALIDATION.md: the device configuration model, the diagnostic and clock semantics model (with an advisory band for tearing and relaxation fluctuations at 1–500 kHz after Ortolani & Schnack 1993, reported and never clamped) and level-0 device physics (the relaxed state on this page, with native parity and a benchmark). No parameter set or channel describes any real machine or diagnostic; the claim inventory is empty and verified by the domain validator.