[logan-nc]

Release note

• Audience: users
• Numerical impact: every SLAYER layer quantity of a default run moves. On the DIII-D-like layer deck the minor radius rs moves by up to 46 %, the r-based shear by 57 %, the Lundquist number by 10 %, D_norm, tau_k, Q_e, Q_i and the Q roots by 17 to 84 %, the growth rate by up to 66 % and the real frequency by 0.05 %. Ideal DCON and perturbed-equilibrium quantities are untouched (harness @ 88a0f1e)
• Migration: callers of build_slayer_inputs, radial_label or resistive_layer_overlap that want the old outboard-midplane chord must now pass rs_method=:midplane explicitly. The TOML interface is unchanged because the label was never exposed there.

SLAYER's layer stack (minor radius, r-based shear, Lundquist number, resistive and diffusion times, Delta-prime reference length) is now expressed by default in the toroidal-flux radial label r = sqrt(2 psi_t / B0), the coordinate the Fitzpatrick layer formalism is derived in, instead of the outboard midplane chord.

Regression report

Run from the repo root on feynman, --cases diiid_slayer_n1,diiid_n1 --refs develop,refactor/slayer-flux-radial-label (4 threads). The SLAYER rows are expected to move; a clean report would have meant the flip did nothing.

Regression Report: diiid_slayer_n1
==================================================================================================================
Ref 1: develop  @ db90e824d (2026-10-26)
       env: julia 1.11.7, x86_64-linux-gnu, manifest cb9237e9 (pinned), 4 threads/4 BLAS, jit build
Ref 2: refactor/slayer-flux-radial-label  @ 88a0f1e31 (2026-10-26)
       env: julia 1.11.7, x86_64-linux-gnu, manifest cb9237e9 (pinned), 4 threads/4 BLAS, jit build
------------------------------------------------------------------------------------------------------------------
Quantity                            develop   refactor/slayer-flux-radial-label  Diff                Status       
------------------------------------------------------------------------------------------------------------------
SLAYER surface indices              [6 elem]  [6 elem]                           0.0e+00             OK           
SLAYER poloidal m                   [6 elem]  [6 elem]                           0.0e+00             OK           
SLAYER toroidal n                   [6 elem]  [6 elem]                           0.0e+00             OK           
SLAYER minor radius rs              [6 elem]  [6 elem]                           2.486e-01 (45.90%)  ** CHANGED **
SLAYER r-based shear                [6 elem]  [6 elem]                           5.347e+01 (57.27%)  ** CHANGED **
SLAYER Lundquist S                  [6 elem]  [6 elem]                           7.344e+06 (9.85%)   ** CHANGED **
SLAYER D_norm                       [6 elem]  [6 elem]                           3.499e-01 (16.76%)  ** CHANGED **
SLAYER P_perp                       [6 elem]  [6 elem]                           0.0e+00             OK           
SLAYER tauk                         [6 elem]  [6 elem]                           1.756e-05 (29.61%)  ** CHANGED **
SLAYER iota_e                       [6 elem]  [6 elem]                           1.1e-16             OK           
SLAYER Q_e                          [6 elem]  [6 elem]                           1.428e+00 (84.27%)  ** CHANGED **
SLAYER Q_i                          [6 elem]  [6 elem]                           1.009e+00 (84.27%)  ** CHANGED **
SLAYER Q_root [2/1,3/1,4/1]         [3 elem]  [3 elem]                           5.442e-01 (29.59%)  ** CHANGED **
SLAYER ω_Hz [2/1,3/1,4/1]           [3 elem]  [3 elem]                           1.703e+01 (0.05%)   ** CHANGED **
SLAYER γ_Hz [2/1,3/1,4/1]           [3 elem]  [3 elem]                           7.427e+02 (66.11%)  ** CHANGED **
SLAYER no_root flags [2/1,3/1,4/1]  [3 elem]  [3 elem]                           0.0e+00             OK           
SLAYER enabled flag                 1         1                                  0.0e+00             OK           
Runtime (s)                         313.7s    304.9s                                                 --           
==================================================================================================================
Summary: 10 changed, 7 unchanged
Regression Report: diiid_n1
===================================================================================================================
Ref 1: develop  @ db90e824d (2026-10-26)
       env: julia 1.11.7, x86_64-linux-gnu, manifest cb9237e9 (pinned), 4 threads/4 BLAS, jit build
Ref 2: refactor/slayer-flux-radial-label  @ 88a0f1e31 (2026-10-26)
       env: julia 1.11.7, x86_64-linux-gnu, manifest cb9237e9 (pinned), 4 threads/4 BLAS, jit build
-------------------------------------------------------------------------------------------------------------------
Quantity                                      develop          refactor/slayer-flux-radial-label  Diff       Status
-------------------------------------------------------------------------------------------------------------------
total energy Re(et[1])                        8.006121e-01     8.006121e-01                       0.0e+00    OK    
total energy Im(et[1])                        7.924895e-05     7.924895e-05                       0.0e+00    OK    
plasma energy Re(ep[1])                       -1.372262e+00    -1.372262e+00                      0.0e+00    OK    
vacuum energy Re(ev[1])                       2.172874e+00     2.172874e+00                       0.0e+00    OK    
vacuum matrix min eigenvalue                  1.873975e-01     1.873975e-01                       0.0e+00    OK    
plasma energy (all)                           [35 elem]        [35 elem]                          0.0e+00    OK    
vacuum energy (all)                           [35 elem]        [35 elem]                          0.0e+00    OK    
total energy (all)                            [35 elem]        [35 elem]                          0.0e+00    OK    
ODE steps (saved)                             786              786                                0.0e+00    OK    
ODE steps (total)                             781              781                                0.0e+00    OK    
q0                                            1.204212e+00     1.204212e+00                       0.0e+00    OK    
q95                                           4.781723e+00     4.781723e+00                       0.0e+00    OK    
beta_t                                        1.327024e-02     1.327024e-02                       0.0e+00    OK    
beta_n                                        1.372511e+00     1.372511e+00                       0.0e+00    OK    
internal inductance li1                       8.842269e-01     8.842269e-01                       0.0e+00    OK    
internal inductance li2                       7.080757e-01     7.080757e-01                       0.0e+00    OK    
internal inductance li3                       7.304340e-01     7.304340e-01                       0.0e+00    OK    
poloidal beta betap1                          6.680739e-01     6.680739e-01                       0.0e+00    OK    
poloidal beta betap2                          5.349836e-01     5.349836e-01                       0.0e+00    OK    
poloidal beta betap3                          5.518764e-01     5.518764e-01                       0.0e+00    OK    
# singular surfaces                           5                5                                  0.0e+00    OK    
singular psi locations                        [5 elem]         [5 elem]                           0.0e+00    OK    
singular q values                             [5 elem]         [5 elem]                           0.0e+00    OK    
current beta betaj                            4.236480e-01     4.236480e-01                       0.0e+00    OK    
plasma volume                                 1.829472e+01     1.829472e+01                       0.0e+00    OK    
plasma current                                1.152130e+00     1.152130e+00                       0.0e+00    OK    
mpert                                         35               35                                 0.0e+00    OK    
npert                                         1                1                                  0.0e+00    OK    
toroidal field bt0                            2.006573e+00     2.006573e+00                       0.0e+00    OK    
wall field bwall                              3.880145e-01     3.880145e-01                       0.0e+00    OK    
aspect ratio                                  2.845746e+00     2.845746e+00                       0.0e+00    OK    
elongation kappa                              1.708322e+00     1.708322e+00                       0.0e+00    OK    
q profile (checksum)                          b1111f97ec46...  b1111f97ec46...                    identical  OK    
pressure profile (checksum)                   b51fb6595b42...  b51fb6595b42...                    identical  OK    
Mercier D_I profile (checksum)                8b9e13cf4e89...  8b9e13cf4e89...                    identical  OK    
resistive interchange D_R profile (checksum)  46bc100c7b20...  46bc100c7b20...                    identical  OK    
ballooning Delta' profile (checksum)          21835494f41e...  21835494f41e...                    identical  OK    
island half-widths                            [5 elem]         [5 elem]                           0.0e+00    OK    
Chirikov parameter                            [5 elem]         [5 elem]                           0.0e+00    OK    
||resonant area-weighted field||              5.288517e-04     5.288517e-04                       0.0e+00    OK    
dominant-coupling singular values             [3 elem]         [3 elem]                           0.0e+00    OK    
|forcing overlap with dominant mode|          1.411539e-04     1.411539e-04                       0.0e+00    OK    
|delta_nominal| of coil set 1                 7.034579e-05     7.034579e-05                       0.0e+00    OK    
||ddelta/d(shift)|| over coil sets            1.245445e-04     1.245445e-04                       0.0e+00    OK    
||ddelta/d(tilt)|| over coil sets             4.177337e-07     4.177337e-07                       0.0e+00    OK    
PE plasma energy                              3.320466e+00     3.320466e+00                       0.0e+00    OK    
PE vacuum energy                              3.174319e+00     3.174319e+00                       0.0e+00    OK    
PE surface energy                             5.508586e+00     5.508586e+00                       0.0e+00    OK    
PE toroidal torque                            1.119360e-04     1.119360e-04                       0.0e+00    OK    
NTV torque FGAR [N·m]                         5.480623e-01     5.480623e-01                       0.0e+00    OK    
NTV kinetic energy dW FGAR [J]                8.163454e-02     8.163454e-02                       0.0e+00    OK    
Runtime (s)                                   306.9s           303.3s                                        --    
||forcing b~|| (root-area-weighted)           4.683171e-04     4.683171e-04                       0.0e+00    OK    
resonant area-weighted field b^r              [5 elem]         [5 elem]                           0.0e+00    OK    
===================================================================================================================
Summary: 53 unchanged

Notes for reviewers

Refs #417. This is the evidence PR the issue asked for: the three defaults flipped in one place, the harness magnitudes attached, and the decision left to the maintainers. It does not close the issue by itself.

• The change is exactly three rs_method defaults (radial_label, build_slayer_inputs, resistive_layer_overlap) plus their docstrings. No formula changed, so the label comparison testset in runtests_slayer_inputs.jl still covers every label.
• The layer-overlap driver already passed rs_method=:flux explicitly, so the overlap cut of a default run is unchanged. Only the direct SLAYER stage, which calls build_slayer_inputs with the default, moves.
• runtests_slayer_inputs.jl previously pinned the per-surface rs to the midplane helper. It now derives the expectation from radial_label(equil) so the test follows the default label instead of hard-coding one.
• Tests run on the branch: runtests_slayer_inputs.jl, runtests_layer_overlap_fitzpatrick.jl, runtests_innerlayer.jl, runtests_slayer_riccati.jl, all passing.
• No review package: a three-default change is below the threshold for one.

Suggested reviewer: @d-burg (Tearing and the layer-overlap evidence behind the issue). Opened as a draft so the maintainers can pick the reviewer and decide whether the flip ships for 2.0.

---

🤖 Generated with Claude Code

https://claude.ai/code/session_0186CLfjeJeSusNTva5RMfGU

[d-burg]

Thanks @logan-nc. The flip itself looks right to me: the flux label is the coordinate the Fitzpatrick layer formalism is written in, and the change is confined to the three defaults. A few claude things before it can land:

Checked on current develop. I merged develop 0b4b9fbfb into the branch locally (clean) and reran diiid_slayer_n1 on feynman. The shifts are essentially the ones in your report, so #501's P_perp_model=:D_perp default doesn't change the picture. The branch still needs the develop merge and a new stamp for CI.

theta_sample becomes a no-op. TearingProblem passes theta=control.theta_sample to build_slayer_inputs, and :flux ignores θ. Since rs_method isn't in the TOML, no deck can reach a θ-dependent label any more, but the [SLAYER] key is still accepted and its docstring (Tearing/Runner/Control.jl) still says it sets where the minor radius is sampled. So "the TOML interface is unchanged" isn't quite true: either warn when theta_sample is set, or document that it only affects rs_method=:midplane callers of the API.

Stale header. The file comment at the top of LayerInputs.jl still says the minor radius is taken at the outboard midplane from rzphi_rsquared((ψ, 0.0)).

Test. Deriving the expected rs from radial_label(equil) makes the test follow the default, which also means it can't catch the default changing again. Pinning rs_method=:flux explicitly would.

Interaction with #441 and #415. Neither conflicts textually with this branch.

• #441: its toroidal-D_geo wiring test in runtests_slayer_inputs.jl builds its reference k_ref from surface_minor_radius/surface_da_dpsi, so with this PR merged six assertions fail (dgeo_val, kpar_val, k_ref). The physics is fine: dgeo_val and k_ref move by the same factor (0.811), which is the expected scaling with K. It's a test that hard-codes the midplane label, and I'll make it label-agnostic on #441 so the merge order doesn't matter.
• #415: its tests pass on the combined tree, but its harness pins move: br_crit 5.8 %, Q_peak 40.8 %, Q0 29.6 % (through tauk). Whichever of the two merges second needs a new stamp.

Overall I'm in favor of shipping this in 2.0 for the improved inner layer model accuracy.