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

TL;DR

The Comment critiques Fitzpatrick:2026 for fundamental errors in poloidal flux physics, arguing that neglecting the external flux and the central solenoid flux yields incorrect disruption-avoidance criteria. It presents a rigorous decomposition of poloidal flux components and derives the correct time evolution $\frac{\partial \psi_p(\psi_t,t)}{\partial t}=V_\ell(\psi_t,t)$, highlighting how Fitzpatrick’s approach omits essential flux contributions. The analysis shows that disruption avoidance cannot be established from a single diffusivity profile and requires staying within the Cheng-Furth-Boozer stability region, with complete removal of poloidal flux during shutdown and a steady-state current profile across magnetic surfaces. It also documents misrepresentations by Fitzpatrick, including how private communications were used, and argues for urgent public discussion given the practical implications for tokamak power plants and funding.

Abstract

The article Nuclear Fusion \textbf{66}, 016012 (2026) by Richard Fitzpatrick is based on fundamental errors in the physics of the poloidal magnetic flux in tokamaks. His paper was inspired by an article that I posted on arXiv in various versions [arXiv:2507.05456]. The September 9, 2025 version was submitted to the Physics of Plasmas, which flatly rejected the article. Before I can resubmit, the Physics of Plasmas stated that the issues with the Fitzpatrick article must be explained. Not only did Fitzpatrick make numerous fundamental errors in science, he totally misrepresented my views as clearly stated in my article and even more explicitly in email exchanges, called ``private communication" in his paper. Enquiries were made to the journal Nuclear Fusion staring on November 24, 2025 of the consistency of Fitzpatrick's article with the scientific and ethical standards of the journal. On January 5, 2026, Nuclear Fusion said they had "no evidence of intentional misrepresentation," but others may disagree after reading the emails. Both grants and the publication of an important paper make the public availability of this Comment urgent.

Figures (1)

• Figure 1: The lines of the poloidal magnetic field produced by the toroidal plasma current are shown together with the magnetic field produced by the central solenoid of a tokamak.