Build a Nachamkin plasmoid on purpose
University. · 1 min de lecture
Ce qu'elle propose
There is a family of solutions to Maxwell's equations, in a partially ionised gas, that behaves like electromagnetic energy trapped in a ball and holding itself together — with a calculable critical frequency and calculable resonant sizes at which the object exchanges no energy at all with its surroundings. Nobody has built one to the specification and measured it. That is a strange omission for a result published by an Air Force laboratory thirty years ago.
À qui elle s'adressePlasma experimentalistsRadio-frequency engineersComputational electromagnetics engineers
Why the library suggests it
Jack Nachamkin, writing for the Air Force's Phillips Laboratory, works the spherically symmetric time-harmonic case and finds two things worth building against: a critical frequency below which the current can no longer be carried by the electrons and the object stays stable, and resonant sizes at which the plasmoid's boundary conditions are met by ordinary vacuum solutions, so no energy flows in or out. A stable vortical motion of the plasma exactly cancels the dominant electromechanical stress, and what is left falls away steeply as frequency rises (Force-Free Time-Harmonic Plasmoids, 1992). A separate line asks what holds many nanometre-scale plasmoid kernels together as one visible object, and finds a quantum exchange force between dipole-carrying ions that reaches a few per cent of the electromagnetic energy at liquid-water ion densities (Quantum exchange interaction of spherically symmetric plasmoids, 2012). The relaxation argument that says why any such object settles into one shape is Magnetic Helicity, Spheromaks, Solar Corona Loops, and Astrophysical Jets (2017).
The experiment or build
Build a radio-frequency discharge cell whose drive frequency and chamber dimensions are set from Nachamkin's own critical-frequency and resonant-size formulas, in a partially ionised gas at the pressure the analysis assumes. Sweep the frequency through the predicted critical value and sweep the cavity dimension through the predicted resonance. The settling measurement is plasmoid lifetime as a function of drive frequency and cavity size, with a peak appearing at the predicted resonant size and a stability threshold appearing at the predicted critical frequency. A lifetime peak that lands where a 1992 calculation said it would is a strong result; a lifetime peak that lands somewhere else is a better one, because it corrects the theory.
Où elle en est
Designed, not yet built — a peer-reviewed analysis with named parameters, published under Air Force sponsorship, and no experiment on record built to its specification.
Prenez cette fiche
- La mesure qui tranche
- The settling measurement is plasmoid lifetime as a function of drive frequency and cavity size, with a peak appearing at the predicted resonant size and a stability threshold appearing at the predicted critical frequency.
- Ce qu'il faut pour commencer
- University.
- L'ingénieur qu'elle forme
- This is the most neglected buildable proposal in the library.
Ce sur quoi elle repose
Sa place dans le programme
Plasmoïdes, amas de charge et les orbesMachines à fusion : pincements, appareils à focalisation et pilotes inertiels