Applications of Antimatter

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2.2 Applications of Antimatter

Antiprotons currently can only be produce at large facilities.  The creation of antiprotons is accomplished by sending protons, near the speed of light, into a metal, usually tungsten.  When the proton hits the target, it is slowed or stopped by collisions with nuclei of the target.   Then, the mass increase due to traveling near the speed of light is converted into matter in the form of various subatomic particles, some of which are antiprotons.  The antiprotons are then separated from the other subatomic particles electromagnetically.  The collection, storage, and handling of antimatter protons are very complicated because antiprotons annihilate when they come into contact with normal matter.  To prevent this, they must be contained within a vacuum by electromagnetic fields [6].

Antiprotons can be used in propulsion to produce direct thrust, energize a propellant, or heat a solid core.  There are many different concepts regarding antimatter propulsion.  The “simplest” concept uses antiprotons to heat a sold metal core, usually tungsten [7].  The tungsten absorbs the gamma rays and pions from the antimatter/matter annihilation and is heated.  Small holes are placed in the cylinder containing the core where hydrogen gas can enter.  As the hydrogen gas enters, the tungsten core is cooled while the hydrogen gas is heated.  The hydrogen propellant is then expanded through a nozzle to produce thrust [7].  The performance of an antiproton solid core generated thrust rocket is about equal to that of a nuclear rocket [7]. Another concept of propulsion is the use of a plasma core instead of a beam core.  In a plasma core, antiprotons are injected to annihilate and heat the plasma.  Heat is rapidly transferred to the propellant and released out of the vehicle at a very high velocity [7].  The beam core concept strays away from the concept of heating a secondary fluid.  In a beam core vessel, the charged particles of the antiproton annihilation are directly released out of the vehicle along an axial magnetic field at a very high velocity near the speed of light [Schmidt].  When the antiprotons and protons collide and annihilate, about 62% of the mass is converted into charge pions.  The pions are then deflected by the magnetic nozzle which causes a very high specific impulse [8].  The very high specific impulse allows a beam core system to travel near the speed of light.  Energy efficiency is very high in this system, but the thrust and flow rates remain very low [7].  Figure 1 shows a basic representation of a beam core propulsion system.  In this figure a ring shaped magnet is used to generate the magnetic field for the nozzle.  A radiation shield is placed between the magnetic nozzle and the engine to protect the engine from the gamma rays produced by the antiproton-proton annihilation and the decay of neutral pions.  A shadow shield is placed between the magnetic nozzle and the rest of the vehicle to protect the vehicle from exposure to radiation [8].


Figure 1.  Beam Core Propulsion System [8]


Presently, there exist a few problems with the beam core concept.  The amount of antimatter required for this type of system is far beyond what is capable of being produced today.  A magnetic nozzle that can handle high temperatures still needs to be developed as well as a cooling system in order to use the beam core concept in propulsion activities.  A beam core spacecraft would also have to be very long because the annihilating particles travel near the speed of light.  Figure 2 shows an artist representation of a beam core spacecraft.


Figure 2.  Artist representation of a beam core spacecraft [9].


There are many other systems that use antiprotons to initiate fission of fusion processes.  All of the energy in these systems used for propulsion comes from fusion reactions.  There are two concepts that use this type of energy, which are being researched and developed at Pennsylvania State University.  First, there is Antimatter-Catalyzed Micro-Fission/Fusion (ACMF).  In this application a pellet of Deuterium-Tritium (D-T) and Uranium-238 (U-238) is compressed with particle beams and irradiated with a low-intensity beam of antiprotons [7].  Antiprotons are absorbed by the U-238 and initiate a hyper-neutronic fission process that rapidly heats and ignites the D-T core, which then expands to produce a pulsed thrust.  Figure 3 is a design of a spacecraft using an ACMF engine.


Figure 3.  ICAN-II Spacecraft (ACMF System) [10].


The second concept is called Antimatter-Initiated Microfusion (AIM).  Electric and magnetic fields continuously compress antiproton plasma while droplets containing D-T are injected into the plasma.  The antiprotons annihilate with a fissile seed, which together heat the plasma.  The resulting product is expelled out a magnetic nozzle to produce thrust [7].  Figure 4 shows a profile model of an AIMStar spacecraft which uses the AIM system for propulsion.  In the AIMStar the engine, reaction traps, and antiproton storage are located behind the payload attached to a booster.  When the burnout occurs the booster separates and only the payload continues on the mission [7].  Figure 5 shows a 3-D model of the AIMStar spacecraft and displays its characteristics. 

Figure 4. AIMStar Spacecraft [11].

Figure 5.  AIMStar Spacecraft [11].

Antimatter requirements are minimized in ACMF and AIM systems for missions that require a smaller velocity (ΔV = 103 km/sec).  ACMF also shows the best performance for planetary and simple interplanetary missions.  ACMF systems were originally designed to accommodate a manned vehicle so ACMF vessels are restricted to missions requiring ΔV’s less than 100 km/sec.  The relationship between the amounts of mass required for a spacecraft of a given payload with respect to its ΔV is given in Figure 6 below


Figure 6.  Antimatter Requirements for Different Propulsion Concepts [7]


Portable antiproton traps are being developed to capture antiprotons and then transfer them to research facilities.  Penn State University developed a Mark I portable antiproton Penning Trap in 1999 that was designed to hold 1010 antiprotons as shown in figure 7.  NASA Marshall Spaceflight center is currently constructing an improved Mark II with a 100-fold greater capacity [6].  Figure 8 is a design of a portable Penning trap used to transfer antiprotons for propulsion activities.

Figure 7. Antiproton Penning Trap Developed by Penn State University [11].

Figure 8. Portable Penning Trap [10].




Physics of Antimatter | Applications of Antimatter | Comparisons to other Systems

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Last updated: 12/07/03.