---
title: TGLF datasets for MAST-U and ITER, version 1
date: '2026-10-02'
categories:
- built
entry: 17
milestone: M2
---

::: {.entry-meta}
[new component]{.chip .built} Entry 17 · milestone M2
:::

The surrogates of M3 learn TGLF's fluxes from examples ([entry 16](16-tglf-build-and-cost.qmd)).
The owner set one dataset per machine, MAST-U and ITER, so that either can be used alone or
both pooled. Each dataset is a set of TGLF input points and the fluxes TGLF returns for them.

## How the points were chosen

Each TGLF input is a local description of the plasma at one radius. We split the inputs into
two groups. The **geometry** inputs (major radius, elongation, triangularity and their radial
derivatives, q, magnetic shear) were measured, not guessed: we computed them the way TORAX
computes them, on the flux surfaces of real equilibria, and took each range from the 1st to
99th percentile. For MAST-U the equilibria are 42 FreeGSNKE free-boundary solutions on the
MAST-U machine description. For ITER they are TORAX's ITER hybrid equilibrium plus the q
profiles of TORAX's current ramp-up example. The **kinetic** inputs (temperature and density
gradients, temperature ratio, beta, collisionality, effective charge, flow shear) were
proposed by the agent and approved by the owner per machine ([OQ-16](/Blog/tokamak-toolkit/decisions.qmd#oq-16)). The generator refuses to
write a dataset for a region until its kinetic inputs are marked approved.

The inputs are drawn by Latin hypercube sampling. Drawn independently, high beta and steep
gradients combine into pressure gradients far beyond ballooning stability, where TGLF returned
fluxes of 10^4^ to 10^5^ gyro-Bohm units in the timing run. Points are therefore rejected above
a fixed normalised pressure gradient α~MHD~, set per machine for version 1; a cap that depends
on the magnetic shear is to follow ([OQ-16](/Blog/tokamak-toolkit/decisions.qmd#oq-16)). The cap keeps about half the draws and shifts the
kept set towards low q and low beta.

## What was produced and checked

Two cluster jobs, one per machine, each of 10^5^ cases. Each dataset is written once, made
read-only, and stored with a provenance record that binds the file's hash, the sampling space
and the measured geometry. Both are also stored on the run tracker (Simvue) with their
provenance, and the uploaded files match the local hashes.

| quantity | MAST-U and ITER |
|---|---|
| cases completed, fluxes finite | [100000 of 100000 cases completed, all six fluxes finite]{.claim}[C-071](/Blog/tokamak-toolkit/claims.qmd#c-071){.cid .st-measured}; [100000 of 100000 cases completed, all six fluxes finite]{.claim}[C-072](/Blog/tokamak-toolkit/claims.qmd#c-072){.cid .st-measured} |
| draws kept under the cap | [MAST-U 0.490 kept (220936 drawn), ITER 0.425 (258597 drawn); kept mean beta_e 23-25% below the box mean on both; kept median q 1.90 (MAST-U) and 1.73 (ITER, sampled log-uniform over 1.02-11.1)]{.claim}[C-073](/Blog/tokamak-toolkit/claims.qmd#c-073){.cid .st-measured} |
| cost | [91.6 core-h (MAST-U) and 92.4 core-h (ITER); 3.3 s per case mean; 35 min wall per job]{.claim}[C-074](/Blog/tokamak-toolkit/claims.qmd#c-074){.cid .st-measured} |
| cases with Q~e~ + Q~i~ above 10^4^ gyro-Bohm units | [MAST-U 0.283 above 10^4 and 0.122 above 10^5; ITER 0.097 above 10^4 and 0.0065 above 10^5]{.claim}[C-075](/Blog/tokamak-toolkit/claims.qmd#c-075){.cid .st-preliminary} |

The brief's acceptance test for M2 includes plotting the sampled domain against the intended
operating space. The plot is in the technical section. It shows that the geometry inputs, drawn
independently, cover combinations that no measured equilibrium has, for example high q at low
shear on MAST-U ([MAST-U 0.72 (triangularity) to 0.94 (q); ITER 0.63 (q) to 0.94 (triangularity shear)]{.claim}[C-076](/Blog/tokamak-toolkit/claims.qmd#c-076){.cid .st-measured}; ceiling [K-018](/Blog/tokamak-toolkit/ceilings.qmd#k-018)).

The last row is not explained yet. Even under the cap, a large fraction of cases have heat
fluxes several orders of magnitude above typical values, mostly at steep electron temperature
gradients. We have not established whether these are physical, for example electromagnetic
modes at high beta, or come from how the inputs are constructed. The cases are kept as computed,
and the question is recorded as ceiling [K-019](/Blog/tokamak-toolkit/ceilings.qmd#k-019), to be resolved before training at M3.

## Where this stands

M2: datasets exist, load and validate. Open before M3: [K-016](/Blog/tokamak-toolkit/ceilings.qmd#k-016) (ITER v1 has one plasma shape),
[K-017](/Blog/tokamak-toolkit/ceilings.qmd#k-017) (fixed cap), [K-018](/Blog/tokamak-toolkit/ceilings.qmd#k-018) (independent geometry sampling), [K-019](/Blog/tokamak-toolkit/ceilings.qmd#k-019) (high-flux cases).

Technical details → [Datasets](../technical/datasets.qmd#sampling-space).
Decisions → [OQ-15](../decisions.qmd#oq-15), [OQ-16](../decisions.qmd#oq-16).

::: {.entry-links}
**Technical details →** [Datasets › sampling space](/Blog/tokamak-toolkit/technical/datasets.qmd#sampling-space) · [Datasets › datasets v1](/Blog/tokamak-toolkit/technical/datasets.qmd#datasets-v1)  
**Decisions →** [OQ-15](/Blog/tokamak-toolkit/decisions.qmd#oq-15) · [OQ-16](/Blog/tokamak-toolkit/decisions.qmd#oq-16)
:::