Negative-Triangularity Shape Scans

Wide equilibrium and stability campaigns mapping the breeder's delta -0.30 ELM-free shape and its operating margins.

Why scan the shape

The breeder's edge shape is a deliberate design choice: negative triangularity, delta -0.30, chosen to access an ELM-free edge that avoids the pulsed heat loads of edge-localized modes. To trust that choice, L0 scans the shape space around delta -0.30, computing equilibria and their stability so the design point is understood as a region, not a single fragile setting.

What the scan varies

Each point in the scan is a full equilibrium solve, followed by stability and edge-transport evaluation. The campaign varies triangularity, elongation, and edge gradients around the target, holding the design anchors, R0 1.2 m, aspect ratio 2.5, plasma current 9.66 MA, near their design values, to map how edge behavior changes with shape.

• Triangularity around delta -0.30
• Elongation and squareness of the boundary
• Edge pressure gradient and current
• Proximity to stability and operational limits

An independent-solve campaign

Because each shape is an independent equilibrium plus stability solve, the scan parallelizes cleanly across the solver farm. It behaves like the neutronics TBR sweep: a wide, embarrassingly parallel exploration that produces a response surface, here mapping shape to edge stability and confinement rather than blanket design to breeding.

The scan quantifies margin. It shows how far the design can drift from delta -0.30 before the ELM-free benefit is lost or a stability limit is approached, which tells the control system how tightly it must hold the shape. That margin becomes a requirement on the twin's equilibrium tracking and the MPC agents that maintain the boundary.

Selected points are re-run on the reproducible core and become training data for the twin's shape-control surrogate. In this way a broad offline exploration of negative triangularity turns into a specific, fast, validated capability to hold the delta -0.30 shape in real time once the breeder operates.