The systems described herein offer a means to approach useful specific powers. The reactor utilizes a reaction where neither the fuel nor the reaction products are radioactive. By operating a deuterium-lean fuel mixture, the side reactions are suppressed to the point that neutron output power is less than 1% of the total and the radioactive (tritium) inventory is ~0.5% [2], Moreover, such neutron output as occurs is concentrated in the low-energy (~4 MeV) end of the spectrum such that shielding can be minimized. In addition to minimizing shielding mass to the overall benefit of specific power, this also offers the possibility of hands-on maintenance. Unlike the deuterium-tritium reaction, Eq. 3, pursued as the mainline fusion effort, the deuterium-helium-3 reaction puts out most of its power in the form of kinetic energy of charged particles (as opposed to neutrons). This makes possible the contemplation of direct conversion of fusion to electrical power. As we shall see, the scaling relations governing direct converters are such that they are likely to be practical only for relatively low-power systems. This question needs to be pursued. We shall attempt to show that a space power system is possible where the limits and constraints on specific power are exclusive of the reactor, that is, they are a function of power conversion, power conditioning and radiator technology. The analysis is a qualitative one and does not aspire to high precision as regards state-of- the-art engineering. Error bars of a factor of 2-4 are readily admitted. Even so, the goal of a specific power of one megawatt per Mg appears as though it may be attainable by an approach such as the one described. 2. The Migma Concept In 1969, R. Macek and B. Maglich introduced the concept of‘self-colliding orbits' and presented the theory of a weak-focusing precession-based high-luminosity storage and collision device (‘precetron') for high energy uncollimated particles [3]. Their study was motivated by a desire to produce an observable number of 7t + 7t and muon-muon scattering events. This was the beginning of the ‘migma' (Greek for mixture') system of precessing intersecting ion orbits, all passing through the axis of an axisymmetric magnetic mirror field. Experiments with weak-focusing self-colliders demonstrated that a migma of MeV ions can be neutralized by oscillating electrons and thus the ion density in the intersecting region can exceed the space charge limit by a factor of at least 102. Since the system allowed storage and collision of MeV ions, it was clear that the principle was applicable to aneutronic fusion, which requires ion energies between one and two orders of magnitude higher than those for neutronic DT fusion (5 keV). We will define a reactor as aneutronic if the power carried by neutrons is equal to or less than 1% of the power released. Migma is thus far the only fusion system in which storage and collision of MeV ions has been experimentally demonstrated. Migma amounts to many superposed intersecting rings with no vacuum walls nearby. The orbits have zero or very small canonical angular momentum and a highly
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