Translating Physics Limits to Millimetres

Simon McIntosh

Yuri Gribov

Simon Pinches

Richard Pitts

Alberto Loarte

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ITER Organization

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Thursday 14^th September 2023

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Simons Hour Talk

Hidden Symmetries and Fusion Energy

This presentation focuses on the development of ITER’s assembly strategy to ensure compliance with key physics limits.

Physics limits

Monte-Carlo trials

Gaussian Process alignment

The alignment of ITER’s 17 meter high, 360 tonne D-shaped Toroidal Field magnets is a feat of precision engineering.

Exceptionally low tolerances that are repeatable and stable over time.

Field line deviations with resect to the first wall generate high start-up heat loads.

Field lines and first wall should be approximately concentric and circular with a long wave peak-peak misalignment H < 6mm .

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

Error fields slow plasma rotation and increase disruptivity.

Overlap error field limits are defined via a semi-empirical scaling for n=1 & n=2 modes (GPEC) .

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

Component alignment is governed by targets and tolerances.

Subsector assembly tool

In-pit sector alignment

Torus closure & coil energization

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

The machine is assembled in a warm discharged state but is operated in a cold active state with currents flowing in the coils.

A single high-fidelity analysis pipeline takes ~4 weeks.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

Coil energization aligns the toroidal field coil vault.

magnification x50

High-field and low-field sides of the TF coils are structurally decoupled.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

Structural and electromagnetic models map warm coil assemblies to field line displacements.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

A transfer to the spectral domain permits the separation of excitation and response waveforms for structural and EM analysis.

signal

FFT

Filter

inverse FFT

response

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

High-fidelity ANSYS simulations validate the structural proxy.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

High-fidelity ANSYS simulations validate the structural proxy.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

High-fidelity EM simulations validate the electromagnetic proxy.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

Spectral filters accelerate single point solution time from 4 weeks to 50 micro seconds with an RMS error <5%.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

A computational graph visualizes the mapping from mm to first wall heat flux limit.

Estimates are presented as 99% prediction intervals

Two models (green) implementing 8 filters

One output PDF P(H)

Large impulse response dataset provides overlap error field filter.

Impulses have a very board frequency response (that is, uniform for all frequency components).

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

A computational graph visualizes the mapping from mm to overlap error field limit.

Three output PDFs P(B)

One model with 27 filters

Large scale Monte-Carlo simulations highlight critical links between TF coil assembly tolerances and First Wall customization capacity.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

Fiducial targets are used to track the location of the coil’s effective current centerline from manufacture to machine assembly.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

The closure of TF coil case welds generates large deformations.

Maximum deformation of ~3mm compared to a tolerance of ±1.5mm (shown magnified by 500x).

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

A periodic Gaussian Process Regressor filters measurement noise.

A periodic kernel is applied to deformations in each coordinate direction.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

Successful demonstration of in-pit sector alignment.

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023

In summary we have shown how ITER’s assembly targets and tolerances are defined to comply with key operational physics limits.

Multi-objective optimization = design

In-pit sector alignment

Spectral filters & Monte Carlo trials

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Translating Physics Limits to Millimetres

Simon McIntosh 14/09/2023