A critique of recent semi-classical spin-half quantum plasma theories

TL;DR

This paper critically examines recent semi-classical spin-half quantum plasma theories, highlighting their internal inconsistencies and demonstrating that spin effects are negligible compared to classical effects in typical plasmas.

Contribution

It provides a detailed critique showing that these theories are inconsistent and that spin effects are much smaller than classical effects, questioning their relevance to real plasmas.

Findings

Spin effects are negligible compared to classical effects in plasmas.

Semi-classical theories contain internal inconsistencies and contradict established quantum principles.

Claims of dominant spin effects in plasma dynamics are invalid.

Abstract

Certain recent semi-classical theories of spin-half quantum plasmas are examined with regard to their internal consistency, physical applicability and relevance to fusion, astrophysical and condensed matter plasmas. It is shown that the derivations and some of the results obtained in these theories are internally inconsistent and contradict well-established principles of quantum and statistical mechanics, especially in their treatment of fermions and spin. Claims of large semi-classical effects of spin magnetic moments that could dominate the plasma dynamics are found to be invalid both for single-particles and collectively. Larmor moments dominate at high temperature while spin moments cancel due to Pauli blocking at low temperatures. Explicit numerical estimates from a variety of plasmas are provided to demonstrate that spin effects are indeed much smaller than many neglected classical effects. The analysis presented suggests that the aforementioned `Spin Quantum Hydrodynamic' theories are not relevant to conventional laboratory or astrophysical plasmas.