On the Utility of Antiprotons as Drivers for Inertial Confinement Fusion
By contrast to the large mass, complexity and recirculating power of conventional drivers for inertial confinement fusion (ICF), antiproton annihilation offers a specific energy of 90MJ/µg and thus a unique form of energy packaging and delivery. In principle, antiproton drivers could provide a profound reduction in system mass for advanced space propulsion by ICF. We examine the physics underlying the use of antiprotons ( p) to drive various classes of high-yield ICF targets by the methods of
... by the methods of volumetric ignition, hotspot ignition and fast ignition. The useable fraction of annihilation deposition energy is determined for both p-driven ablative compression and p-driven fast ignition, in association with 0-D and 1-D target burn models. Thereby, we deduce scaling laws for the number of injected antiprotons required per capsule, together with timing and focal spot requirements. The kinetic energy of the injected antiproton beam required to penetrate to the desired annihilation point is always small relative to the deposited annihilation energy. We show that heavy metal seeding of the fuel and/or ablator is required to optimize local deposition of annihilation energy and determine that a minimum of ~3x10 15 injected antiprotons will be required to achieve high yield (several hundred megajoules) in any target configuration. Target gains -i.e., fusion yields divided by the available p -p annihilation energy from the injected antiprotons (1.88GeV/ p) -range from ~3 for volumetric ignition targets to ~600 for fast ignition targets. Antiproton-driven ICF is a speculative concept, and the handling of antiprotons and their required injection precision -temporally and spatially -will present significant technical challenges. The storage and manipulation of low-energy antiprotons, particularly in the form of antihydrogen, is a science in its infancy and a large scale-up of antiproton production over present supply methods would be required to embark on a serious R&D program for this application. * NIF  offers a real example of a conventional ICF driver designed to deliver 1.8MJ of laser light to a DT capsule. The facility is the scale of a sports stadium with a total mass in excess of 100,000tonnes and total project cost of ~$2.3B. Note that in assessing total mass, NIF would also be implicitly burdened with the external electricity supply system required to charge the capacitor banks between every shot. In an ICF reactor with net energy gain, a portion of the output fusion energy would be recycled via the onsite/onboard electricity generating plant to resupply the driver but at the expense of extra plant mass and, in space, additional heat radiator mass. In the case of antiproton drive, nearly all this mass and complexity could be eliminated. * The proton is composed of two "up" quarks, each of charge +2/3, plus one "down" quark of charge -1/3. The neutron is composed of two down quarks plus one up quark, while the antiproton has two anti-up quarks (charge -2/3) plus one anti-down quark (charge +1/3). The mesons resulting from the annihilation reactions are composed of quark-antiquark pairs; e.g. the positive pion is composed of an up quark (charge +2/3) and an anti-down quark (charge +1/3).