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Linear Connected Array of Non-Adiabatic Traps

Author: Hiromu Momota
Requested Type: Consider for Invited
Submitted: 2006-12-19 14:23:56

Co-authors: George H. Miley, Osamu Motojima

Contact Info:
Fusion Studies Laboratory, University of Illinois
214 Nuclear Engineering Labora
Urbana, Illinois   61801

Abstract Text:
A simple fusion system with linearly connected units of non-adiabatic trap is proposed. A cylindrical unit has a pair of inner coils anti-parallel to a simple magnetic mirror. Positions and currents on respective coils are adjusted to achieve zero magnetic fields at the center of the coil system. A large major radius and a high current density on the pair coils is required to isolate the accessible domain of charged particles from the coil structure as well as the vacuum chamber. A charged particle is initially trapped within the magnetic mirror. Because of the zero-magnetic field near the center, however, it suffers a random change in its magnetic moment or pitch-angle at every passage of the central region and eventually falls into the loss-cone of the magnetic mirror without any inter-particle collisions. A Monte Carlo code verifies non-adiabatic trapping of charged particles and shows a spherically distributed plasma. Low-energy charged particles stay within a unit for longer time while high-energy fusion products escape the unit rapidly. The magnetic configuration is “minimum B” and magnetic curvatures are good for plasma stability. On the bases of the simulations, the confinement is analyzed self-consistently to obtain a scaling. The estimated confinement, however, is far behind the requirement for a commercial fusion power reactor, because of poor confinement capability of a single non-adiabatic trap.
However, once non-adiabatic traps are linearly connected, a charged particle escaping a trap will be re-trapped at the next trap. Because the particle changes its pitch angle randomly, particle escape becomes disturbed among traps even if the length of a trap is as short as several meters. Consequently, a connection of non-adiabatic trap improves plasma confinement. The non-adiabatic re-trapping is verified with Monte Carlo codes, i.e., re-trapping appears a stochastic transition of a particle from a unit to next units. Further improvement of plasma the confinement can be achieved by attaching a pair of connected arrays of units to both ends of a fusion array as plasma leakage suppresser. Resultant improvement of plasma confinement is appreciable. Layout of the unit is versatile and has to be determined so as to meet engineering requirements.
A series of units each of which has a pair coils of 2m in major radius and traps 30m3 of 10keV -DT plasma gives, for example, a plasma energy confinement time of ~ 5mSec. A small coil that provides magnetic field as strong as 35T is used to connect each unit. A system of 30 non-adiabatic units (a series of 8 fusion core units and arrays of 11 units at both end) improves the energy confinement time more than 1.14Sec, which is enough to ignite DT fuel fusion. D-3He fuel fusion with this concept requires a large output more suitable for a future nuclear power manufacturing complex than present power networks.

Characterization: D


University of Maryland

Innovative Confinement Concepts Workshop
February 12-14, 2007
College Park, Maryland

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