Comment on Nuclear Fusion 66, 016012 (2026) and arXiv:2508.03561 by Richard Fitzpatrick, A Simple Model of Current Ramp-Up and Ramp-Down in Tokamaks

Allen H Boozer

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arXiv · 2601.05977

Comment on Nuclear Fusion 66, 016012 (2026) and arXiv:2508.03561 by Richard Fitzpatrick, A Simple Model of Current Ramp-Up and Ramp-Down in Tokamaks

Allen H Boozer

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Abstract

The paper Nuclear Fusion \textbf{66}, 016012 (2026) by Richard Fitzpatrick is based on fundamental errors in the physics of the evolution of the poloidal magnetic flux in tokamaks. With the certainty of Faraday's Law, the slippage of the poloidal relative to the toroidal flux is given by the loop voltage. Some of the errors may be endemic to the tokamak community, such as the focusing on a quantity $\psi$ that has a subtle relation to the poloidal flux while essentially ignoring the toroidal flux. Other errors are due to an entanglement of in principle separable concepts and unjustified assumptions. Although Nuclear Fusion allowed the use ``private communication" as a reference to bolster misquotes, the response must be in arXiv because Nuclear Fusion will not allow any mention of ``private communication" in a response. This comment also derives a new and simple expression for the loop voltage, which has the validity of the parallel component of Ohm's law.

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Allen H Boozer. 2026-01-09. Comment on Nuclear Fusion 66, 016012 (2026) and arXiv:2508.03561 by Richard Fitzpatrick, A Simple Model of Current Ramp-Up and Ramp-Down in Tokamaks. https://arxiv.org/abs/2601.05977

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