Tearing - Tell a limited plasma from a padded g-file before placing surfaces past the boundary

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Domain
backend

Research direction

Start with the g-file reader, which currently drops the limiter contour, and with the overlap scan that places surfaces past ψ_N = 1 when separatrix_q_law fires on a limited plasma. First keep the limiter contour when it is present, then have the scan check whether the boundary touches the limiter and skip any surface past ψ_N = 1 in that case, with a message saying so. Done when a limited EFIT-style test file with a nearby X-point produces no phantom surface and no overlap warning.

Written by the indexing model from the issue text.

Description

separatrix_q_law builds a law whenever a poloidal-field minimum on the outermost surface leads to a saddle and the law reproduces the traced shear. A limited plasma with an X-point nearby passes both: one EFIT reconstruction checked gives an X-point at ψ_N = 1.093 and a shear ratio of 0.86. The overlap scan then treats it like a padded diverted file. It places one rational past ψ_N = 1, where no closed surface exists, and warns that no overlap could be established.

Today the domain is unchanged, so this is only a spurious warning. But if the kinetic profiles extend past ψ_N = 1 (p-files often reach about 1.12), that phantom surface would be scored and could move the cut one rational inward.

The size of the gap cannot distinguish the two cases, since a plasma close to diverting can have an X-point just outside ψ_N = 1. The reliable discriminator is the g-file's limiter contour, which GPEC's reader does not keep: a boundary touching the limiter is limited, and no surface past it should be placed.

Done when:

  • The reader keeps the limiter contour, where present.
  • The scan places no surface past ψ_N = 1 when the boundary touches the limiter, and says so.
  • A test with a limited EFIT-style file that has an X-point nearby.

🤖 Generated with Claude Code

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