Thermodynamic Analogy for Electrons Interacting with a Magnetic Nozzle

Kazunori Takahashi, Christine Charles, Rod W. Boswell, Akira Ando

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


The polytropic index of free electrons expanding in a magnetic nozzle of varying strength is experimentally investigated under a nearly zero electric field, allowing all the electrons to escape to the axial boundary and never return to the source. The measurements clearly demonstrate a continuous change in the polytropic index from adiabatic 5/3 for a strong magnetic field to isothermal unity for a weak magnetic field, showing that the polytropic index depends on the magnetic field strength. It is shown that the cross-field diffusion and the resultant plasma loss out of the magnetic nozzle effectively reduce the polytropic index. The azimuthal current induced in the plasma is diamagnetic, does work on the magnetic nozzle, and contributes to the reduction of the electron internal energy during the expansion.

Original languageEnglish
Article number165001
JournalPhysical review letters
Issue number16
Publication statusPublished - 2020 Oct

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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