Antimatter-catalyzed nuclear pulse propulsion | Wikipedia audio article

Antimatter catalyzed nuclear pulse propulsion
is a variation of nuclear pulse propulsion based upon the injection of antimatter into
a mass of nuclear fuel which normally would not be useful in propulsion. The anti-protons used to start the reaction
are consumed, so it is a misnomer to refer to them as a catalyst.==Description==
Traditional nuclear pulse propulsion has the downside that the minimum size of the engine
is defined by the minimum size of the nuclear bombs used to create thrust. A conventional nuclear H-bomb design consists
of two parts, the primary which is almost always based on plutonium, and a secondary
using fusion fuel, normally lithium-deuteride. There is a minimum size for the primary, about
25 kilograms, which produces a small nuclear explosion about 1/100 kiloton (10 tons, 42
GJ; W54). More powerful devices scale up in size primarily
through the addition of fusion fuel. Of the two, the fusion fuel is much less expensive
and gives off far fewer radioactive products, so from a cost and efficiency standpoint,
larger bombs are much more efficient. However, using such large bombs for spacecraft
propulsion demands much larger structures able to handle the stress. There is a tradeoff between the two demands. By injecting a small amount of antimatter
into a subcritical mass of fuel (typically plutonium or uranium) fission of the fuel
can be forced. An anti-proton has a negative electric charge
just like an electron, and can be captured in a similar way by a positively charged atomic
nucleus. The initial configuration, however, is not
stable and radiates energy as gamma rays. As a consequence, the anti-proton moves closer
and closer to the nucleus until they eventually touch, at which point the anti-proton and
a proton are both annihilated. This reaction releases a tremendous amount
of energy, of which, some is released as gamma rays and some is transferred as kinetic energy
to the nucleus, causing it to explode. The resulting shower of neutrons can cause
the surrounding fuel to undergo rapid fission or even nuclear fusion. The lower limit of the device size is determined
by anti-proton handling issues and fission reaction requirements; as such, unlike either
the Project Orion-type propulsion system, which requires large numbers of nuclear explosive
charges, or the various anti-matter drives, which require impossibly expensive amounts
of antimatter, antimatter catalyzed nuclear pulse propulsion has intrinsic advantages.A
conceptual design of an antimatter-catalyzed thermonuclear explosive physics package, is
one in which the primary mass of plutonium, usually necessary for the ignition in a conventional
Teller-Ulam thermonuclear explosion, is replaced by one microgram of antihydrogen. In this theoretical design, the antimatter
is helium-cooled and magnetically levitated in the center of the device, in the form of
a pellet a tenth of a mm in diameter, a position analogous to the primary fission core in the
layer cake/Sloika design). As the antimatter must remain away from ordinary
matter until the desired moment of the explosion, the central pellet must be isolated from the
surrounding hollow sphere of 100 grams of thermonuclear fuel. During and after the implosive compression
by the high explosive lenses, the fusion fuel comes into contact with the antihydrogen. Annihilation reactions, which would start
soon after the Penning trap is destroyed, is to provide the energy to begin the nuclear
fusion in the thermonuclear fuel. If the chosen degree of compression is high,
a device with increased explosive/propulsive effects is obtained, and if it is low, that
is, the fuel is not at high density, a considerable number of neutrons will escape the device,
and a neutron bomb forms. In both cases the electromagnetic pulse effect
and the radioactive fallout are substantially lower than that of a conventional fission
or Teller-Ulam device of the same yield, approximately 1 kt.==Amount needed for thermonuclear device
==The number of antiprotons required for triggering
one thermonuclear explosion were calculated in 2005 to be 10 18 {\displaystyle 10^{18}}
, which means microgram amounts of antihydrogen.Tuning of the performance of a space vehicle is also
possible. Rocket efficiency is strongly related to the
mass of the working mass used, which in this case is the nuclear fuel. The energy released by a given mass of fusion
fuel is several times larger than that released by the same mass of a fission fuel. For missions requiring short periods of high
thrust, such as manned interplanetary missions, pure microfission might be preferred because
it reduces the number of fuel elements needed. For missions with longer periods of higher
efficiency but with lower thrust, such as outer-planet probes, a combination of microfission
and fusion might be preferred because it would reduce the total fuel mass.==Research==
The concept was invented at Pennsylvania State University before 1992. Since then, several groups have studied antimatter-catalyzed
micro fission/fusion engines in the lab (sometimes antiproton as opposed to antimatter or antihydrogen).Work
has been performed at Lawrence Livermore National Laboratory on antiproton-initiated fusion
as early as 2004. In contrast to the large mass, complexity
and recirculating power of conventional drivers for inertial confinement fusion (ICF), antiproton
annihilation offers a specific energy of 90 MJ per 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. 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 programme for such applications. The current (2011) record for antimatter storage
is just over 1000 seconds performed in the CERN facility, a monumental leap from the
millisecond timescales that previously were achievable.==See also==
Antimatter rocket Antimatter weapon
Nuclear pulse propulsion

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