A general critique of inertial-electrostatic confinement fusion systems

Abstract

The suitability of various implementations of inertial-electrostatic confinement (IEC) systems'for use as D-T, D-D, D-3 He, p-l 1 B, and p-6 Li reactors is examined; these IEC designs create a deep electrostatic potential well within the plasma in order to confine and accelerate ions, and they typically use magnetic fields or electrostatic grids to confine electrons. It is shown that while an IEC reactor would have the advantages of high power densities and relatively simple engineering design when compared with other fusion schemes, it suffers from several flaws. Foremost among these problems is that on the basis of velocity-space diffusion calculations, it does not appear to be possible for the dense central region of a reactor-grade device to maintain significantly non-Maxwellian ion distributions or to keep two different ion species at significantly different temperatures; this discovery contradicts earlier claims of the particular suitability of IEC systems for advanced fuels. Since the ions form a Maxwellian distribution with a mean energy not very much smaller than the electrostatic well depth, ions in the energetic tail of the distribution will likely be lost at rates greatly in excess of the fusion rate. Furthermore, even optimistic assumptions about the performance of the surrounding polyhedral cusp magnetic field lead to the conclusion that the electron losses from the machine will be intolerable for all fuels except DT. If electrostatic grids are used instead of magnetic cusps, the particle losses should be even worse. Finally, because the Maxwellian ion distributions are not fundamentally different than those in other fusion schemes, bremsstrahlung losses will be similar; in particular, the ratio of bremsstrahlung power to fusion power will at best be -1.7 for p-11 B and -5.4 for p-6 Li, demonstrating that IEC cannot utilize proton-based fuels in a practical manner. In order for IEC systems to be used as fusion reactors, it will be necessary to find methods to circumvent these problems.

The Periodically Oscillating Plasma Sphere

“…These collisions add angular momentum to the particles and cause the desired focus to expand. Consequently, either the energy cost of maintaining the beamlike ion distribution exceeds the fusion energy gain 9,10 or the fusion power density becomes too small as the ion focus spreads.…”

Convergence, electrostatic potential, and density measurements in a spherically convergent ion focus

“…Nevins 11 and Rider 12 predict that thermalization of ion flows through core collisions would lead to the collapse of the convergence in an idealized highly recycling central ion flow. Although the gridded experiments studied to date find a steady flow convergence, the particles are removed at a rate faster than the thermalization rate ͑i.e., via grid or charge-exchange collisions, see Sec.…”

“…10 While these gridless devices have more promise for higher reactivity, recent theoretical appraisals of such systems, which more extensively account for thermalizing collisional effects and the overall power balance, determine that a power production scheme is not possible based on these types of devices without circumventing these basic issues. 11,12 Despite the differences in the origin of the confining electrostatic fields, a common figure of merit for all proposed a͒ Electronic mail: thorson@uwmfe.neep.wisc.edu SCIF approaches is the attainable degree of focusing of the ion flow at the center. This is known as the flow convergence, and it is a critical parameter for all high-reactivity designs which rely on the counter-streaming ion flows providing the system reactivity.…”

Space charge neutralization in inertial electrostatic confinement plasmas

“…Theoretical studies using simple analytic models have indicated that such systems cannot scale to net energy producing devices. 11,12 However, these studies have several approximations, and a more complete study using a bounce averaged Fokker-Planck model indicated that if the ion distributions are close enough to thermal, net energy gains are possible, although the fusion power densities are small. 13 The underlying problem is that for nonthermal systems, the Coulomb scattering cross sections are larger than the fusion cross sections.…”