antimatter propulsion

INTRODUCTION

The history of antimatter begins with a young physicist named Paul A.M.Dirac (1902-1984) and the strange implications of a mathematical equation. This British physicist formulated a theory for the motion of the electrons in electric and magnetic fields. Such theories had been formulated before, but what was unique about Dirac’s was that his included the effects of Einstein’s Special Theory of Relativity. This theory was formulated by him in 1928.Mean while he wrote down an equation, which combined quantum theory and special relativity, to describe the behavior of the electron. Dirac’s equation won him a Nobel prize in I 933,but also posed another problem; just at the equation x2 = 4 can have two solutions (x 2, x = -2). So Dirac’s equation would have two solutions, one for an electron with positive energy, and one for an electron with negative energy. This led theory led to a surprising prediction that the electron must have an “antiparticle” having the same mass but a positive electric charge.

1n1932, Carl Anderson observed this new particle experimentally and it was named “positron”. This was the first known example of antimatter. In 1955, the anti proton was produced at the Berkeley Bevatron, and in 1995, scientists created the first anti hydrogen atom at the CERN research facility in Europe by combining the anti proton with a positron. Dirac’s equation predicted that all of the fundamental particles in nature must have a corresponding “Antiparticle”. In each case, the masses of the particle and anti particle are identical and other properties are nearly identical. But in all cases, the mathematical signs of some property are reversed. Anti protons, for example have the same mass as a proton, but the opposite electric charge.

Since Dirac’s time, scores of these particle-antiparticle pairings have been observed. Even particles that have no electrical charge such as the neutron have anti particle.

ANTIMATTER PRODUCTION

Anti protons do not exist in nature and currently are produced only by energetic particle collision conducted at large accelerator facilities (e.g. Fermi National Accelerator Laboratory, Fermi Lab, in US or CERN in Geneva, Switzerland). This process typically involves accelerating protons to relativistic velocities (very near to speed of light) and slamming them into a metal (e.g. Tungsten) target. The high-energy protons are slowed or stopped by collisions with nuclei of the target; the kinetic energy of the rapidly moving protons is converted into matter in the form of various subatomic particles, some of which are anti protons. Finally, the anti protons are electro magnetically separated from the other particles, then they are captured and cooled (slowed) by a Radio-Frequency Quadrapole (RFQ) linear accelerator (operated as a decelerator) and then stored in a storage cell called as a Penning Trap.

Note that anti protons annihilate spontaneously when brought into contact with normal matter, thus they must be stored and handled carefully. Currently the highest anti proton production level is in the order of nano-grams per year.

ANTI-MATTER PROPULSION

Matter Anti-matter propulsion offers the highest possible physical energy density of any known reaction substance. The ideal energy density (E = mc2) of 9 x 1016 J/Kg is order of magnitude greater than chemical (lx 107 J/Kg), fission (8 x 1013 J/Kg) or even fusion (3 x 1014 i/Kg) reactions. Additionally, the matter antimatter annihilation proceeds spontaneously, therefore not requiring massive or complicated reactor systems. These properties make antimatter very attractive for propulsive ambitious space missions. This section describes antimatter propulsion concepts in which matter antimatter annihilation provides all of the propulsive energy.

Once produced and stored, antimatter can annihilate with normal matter to produce energy for propulsion. The annihilation produces tremendous energy in the form of energetic, unstable, charged and neutral sub atomic particles (mostly pions,p). Note that for a propulsion application, proton antiproton annihilation is preferred over electron positron annihilation because the products of proton antiproton annihilation are charged particles that can be confined directed magnetically so as to transfer their energy to propulsive “working fluid” like normal H2. By contrast, electron-positron annihilation produces only high-energy gamma rays, which do not “couple” their energy efficiently to a working fluid. Thus, in the annihilation of proton (p+) and the antiproton (p-), the products include neutral and charged pions (p0, p+, p-). In this case, the charged ions can be trapped and directed by magnetic fields to produce thrust. However, pions do possess mass, so not all of the proton antiproton mass is converted into energy. This results in an energy density of the proton antiproton reaction of only 1.8 x l0^l6J/Kg.

To implement an antimatter rocket engine, the three main components required are antimatter storage system, feed system and thruster. In this fig. the antimatter is stored in the form of solid pellets of anti hydrogen. A high-density form of antimatter is required because storage as gaseous plasma in a Penning Trap is limited to about 1010 particles per cubic centimeter; the volume of 10mg of antimatter would be equivalent to 40 space shuttle cargo bays However storage as a solid requires low temperature to prevent sublimation of the pellets. Gaseous antihydrogen could not be contained; only the solid (or liquid) is diamagnetic and can be levitated by a magnetic field. Also, very high- quality vacuum in the storage chamber is required to prevent residual normal matter gas annihilating on the solid antihydrogen pellets. For eg. , in the image, both a vacuum pump and a series of air lock doors are required to prevent gas from the thruster entering the storage chamber. Finally normal hydrogen is used as the propellant working fluid; an excess of hydrogen is used such that the annihilation energy between a small amount of antihydrogen and normal hydrogen heats a large mass of normal hydrogen. This annihilation is accomplished inside the thruster.

ICAN PROPULSION VEHICLE ENGINE

The above picture shows the engine portion of the inertial confinement antiproton-catalyzed micro-fission/fusion nuclear (JCAN) propulsion concept vehicle, which employs the antiproton–catalyzed micro-fission/fusion concept under development at Pennsylvania State University.(This is the second and most recent configuration, thus it is called ICAN II).

The system has several similarities to inertial confinement fusion (ICF) propulsion concepts. For example, there is a particle beam (rather than laser- beam) driver” that compresses the micro-fission/fusion pellet prior to injection of antiprotons. After the micro-fission/fusion explosion which releases an energy equivalent to 20 tons of TNT, the expanding plasma ablates a layer of lead on the inside “cup of the thrust chamber. In fact, most of the total propellant mass is lead. Lead is used so as to efficiently capture the energy released the micro- fission/fusion explosion (which is in the form of-various, forms of high-energy photons and particles) and convert this energy into directed propulsive thrust.

Fig b.) antimatter production unit