Historical research guide · 0987 · 2007
Space charge neutralization in inertial electrostatic confinement plasmas
E. G. Evstatiev · R. A. Nebel · L. Chacón · J. Park · G. Lapenta
In one minute
An inertial electrostatic confinement machine holds a fusion plasma with voltage instead of magnets: ions are pulled inwards towards a point, overshoot it, fall back through it, and keep doing that. One way to build the pull is to inject electrons and let their negative charge make the well. But a cloud of electrons pushes hard on itself, and that self-repulsion — its space charge — is what caps how dense the core can get. Evstatiev and colleagues at Los Alamos National Laboratory develop a new formalism for cancelling it, and their answer splits in two. If the plasma is made to oscillate, which is how compression is won, then holding the charge neutralised while also holding the background potential in the parabolic shape the scheme needs puts a firm ceiling on how far the core can be squeezed. If the plasma is run steady instead, no such ceiling appears, and neutralisation still holds even as the plasma goes quasineutral.
Connection
Chapter 12 needs a small source of very large energy, and the electrostatic machines are the least expensive route anyone has to one; this paper is the design rule that decides how such a machine should be run, because it says which operating mode pays for compression with a ceiling and which does not. Chapter 9 keeps the record of oscillating and self-organising plasma structures held in a laboratory, and the breathing plasma treated here is one of them.
From the source
Space charge neutralization is the major issue for inertial electrostatic confinement devices that make their confining potential well by injecting electrons — the injected electron cloud’s own repulsion is what limits the machine.Abstract, first sentence
The paper develops a new formalism that allows that neutralization to occur, and it covers both operating modes — plasmas that oscillate and plasmas held in steady state.Abstract, second sentence
For oscillating plasmas the results give limits on how much compression can be achieved while simultaneously maintaining space charge neutralization and the parabolic background potential the oscillating scheme depends on — compression and neutralization are in competition in that mode.Abstract, third sentence
For steady-state plasmas there are no such limits, and space charge neutralization can be achieved even when the plasma becomes quasineutral, that is even when the ion and electron densities have come into balance.Abstract, fourth sentence
The design question this poses for anyone building one of these machines is which mode to run: oscillation buys compression but caps it, steady state removes the cap, and the measurement that settles it is whether a steady-state electron-injected device holds its neutralization all the way into the quasineutral, high-density regime.Abstract, third and fourth sentences read together
The way in
https://doi.org/10.1063/1.2711173How to cite it
E. G. Evstatiev, R. A. Nebel, L. Chacón, J. Park, G. Lapenta (2007) Space charge neutralization in inertial electrostatic confinement plasmas doi:10.1063/1.2711173