Comment on "ENN's roadmap for proton-boron fusion based on spherical torus" [Phys. Plasmas 31, 062507 (2024)]

TL;DR

This paper critically evaluates the feasibility of achieving hot ion mode with a temperature ratio of 4 for proton-boron fusion, questioning the practicality and economic viability of such conditions in fusion research.

Contribution

It provides a detailed analysis showing that the hot ion mode ratio of 4 is unlikely under optimal fusion heating conditions and discusses the impracticality of achieving it through ideal external heating methods.

Findings

Hot ion mode ratio of 4 is not accessible under optimal fusion heating.

Achieving the ratio by external heating would require nearly 20 times the fusion power.

Such high ratio conditions are economically questionable.

Abstract

This comment discusses the feasibility of hot ion mode ${{T}_{i}}/{{T}_{e}}=4$ for proton-boron fusion which is critical for the roadmap proposed in Liu, M et al [Phys. Plasmas 31, 062507 (2024)]. The hot ion mode ${{T}_{i}}/{{T}_{e}}=4$ has been calculated to be far from accessible (${{T}_{i}}/{{T}_{e}}<1.5$ for ${{T}_{i}}=150\text{keV}$) under the most optimal conditions if fusion provides the heating (Xie, H [Introduction to Fusion Ignition Principles: Zeroth Order Factors of Fusion Energy Research (in Chinese), USTC Press, Hefei, 2023]), i.e., that all fusion power serves to heat the ions and that electrons acquire energy only through interactions with ions. We also discuss if hot ion mode of ${{T}_{i}}/{{T}_{e}}=4$ could be achieved by an ideal heating method which is much more efficient than fusion itself (near 20 times fusion power for ${{T}_{i}}=150\text{keV}$) and only heats the ions, whether it makes sense economically.