Antimmatter Essay, Research Paper

Really long Physics paper

We stand at the base of a new age. We are just now beginning to learn the intricate details of life, both macroscopic and microscopic. Ultimately these discoveries will benefit all of mankind. Never before have we enjoyed such a golden age for science and discovery. The scientific horizon looks fruitful. One such fruit is the discovery and application of a thing called antimatter. During the next few decades our ability to produce, accumulate, and contain large quantities of antimatter should become feasible, leaving us just to research possible uses for this promising, radically new, form of energy.

Antimatter is exactly what the name suggests. It is the opposite of matter in which the charges associated with electrons and protons are switched. This means a proton and antiproton are attracted to each other. When they collide pane energy is produced in the form of three pions and four gamma rays.

Since their discovery in 1955, antiproton production rates have increased by approximately an order of magnitude (which is one exponential increase) every 2.5 years as seen in fig. 1. It is predicted that a milligram to a gram of antimatter could be produced annually within the next decade. At present the main hinderence to antimatter production is the ability to accumulate, cool, and decelerate the antiprotons.

Antimatter production is a relatively easy concept, but the details are mind bogeling. In 1932, Carl Anderson, was examining tracks produced by cosmic rays in a cloud chamber. One particle made a track like an electron, but carvature of its path in the magnetic field was one consistent with a possitive charged particle. He named this new particle a positron. Later, in the 1950?s, physicists at the Lawrence Radiation Lab used the Beratron accelerator to produce the anti-proton. Upon examination of this particle they found that it had the same mass and spin as a proton, but with negative charge and opposite magnetic moment. The process they used to create this particle with first to accelerate a proton to a very high speed, and then smash it into a target. This collision produces an antiproton and three protons, or in other words a proton antiproton pair and the two original protons. This seems to suggest that for each antiproton produced, there is one proton. This would sugget whole other worlds made of antimatter. However, this is a whole other debate.

Now, the main problem with this process is accumulation, cooling, and deceleration, as already mentioned. Once the collision has taken place the products are moving at high speeds with large amount of kinetic energy. It requires large amounts of energy to accelerate the proton, and even more to decelerate and cool the products. Accumulation brings up another problem, which is storage.

Antimatter is more reactive then any other substance ever created because it will react with any form of matter. So, storage must keep it from colliding with other particles. Currently, storage is limited to electromagnectic confinement using large magnetic rings to accelerate the protons at low speeds in a vaccumn. This type of storage is costly and cannot hold large amounts of antiprotons or positrons. Due to this impediment, antimatter is only stored for short amount of time (hours) before it is used in experiments. However, there are two new ideas for forms of storage. The first is for bulk storage. This process implies storage at extreme low temperatures in a vacuum. The second way is called dispersed storage, where antimatter is stored in a uniform mix with normal matter. In both cases the antimatter can be stored in the form of a single charged particle (antiproton) or as a antihydrogen neutral molecule.

Another simple, and obvious, way to prevent antiprotons from reacting with the walls of a storage vessel is to electrically charge such walls to repel the particles. Intense studies on storage devices such as these are underway using normal matter ions. This type of storage device is known as an ion trap. This is a good intermediate holding device for antimatter because it allows time for the particles to be cooled and decelerated. The Japanese have created traps that can hold 10 to 1016 antiprotons. However, these traps would be so large, that they would require huge amounts of energy. Although, the future is looking promising. The combination of these methods and new technology may allow for high density storage. This combined with the production notes expected in the next decade open the possibility of using antiprotons in applications other than basic research.

Anti Protons have the highest energy density (9×1016 J./kg.) of any other material known to man. The annihilation of an antiproton with a proton produces 1000 times the energy per unit mass of reactants thatn the fission of Uranium. Extrapolation of current technological growth reveals a future potential for low mass antiproton storage, transfer, and conversion to energy. However, the energy, and therefore financial investment is large. Consequently, antiproton energy sources would only be useful in areas where a low mass/high energy yield is important. Two such fields are biomedical and deep space propulsion application. The difficulty in these concepts is the conversion of the form of energy yielded by annilation (4 gamma rays and 3 pions), to the desired form of energy. The average kinetic energy?s produced from a single annialation are 243 MeV and 196 MeV for pions and gamma rays, respectively.

The biomedical need for antiproton seem to be the most promising and near term use for the particles. The particular use for antimatter ifs in the area of biomedical radioisotope generation. These isotopes are currently used in established procedures such as Positron Emission Tomography (PET), which detects many forms of cancer, maps activity in the brain, and helps to understand pathological afflictions such as Alzheimer?s disease. The availability of the isotopes is currently limited to expensive production facilities and to the range that can be covered within the half life of the isotope. Only 40 cyclotrons for PET isotope production exist nationwide whereas 1700 hospitals possess the imaging capabilities. A portable source of antiprotons would due away with the expensive cyclotron machines. The isotopes could be created by bombarding larger atoms with antiprotons to annialate protons and thus form the necessary isotopes. This process would increase the availability of PET machines 100 fold.

Another use would be for advanced propulsion systems. The problem we now face in space exploration is we are limited in efficiency with current technology. Spoken plainly, bigger is no longer better. To get to some of our closest astrological destinations (Kulper Belt, the heliopause, or even our closest star, Alpha Centari) will require more then just a big ass rocket. Instead reaching such destinations will require revolutionary advances in propulsion to achieve their goals within reasonable time frames.

As mentioned before antimatter has the highest specific energy of any source known to man. It would be of great use as part of a propulsion system. The problem with such an idea is the form of energy. The way a conventional rocket works is a fuel is burned and the volume of the products is greater then the fuel. Therefore it shoots out the bottom of the rocket. The more mass you can shoot out of a given space (in a given time) determines the thrust force the rocket can deliver. In the case of antimatter there is no mass to be shot out of the bottom. The pre dominate plan for bridging this gap is using a solid core engine.

Solid core engines are not new concepts. They were developed and tested in the 1960?s under the NERVA program. They were originally developed using a nuclear fission reaction as the source of energy. The basic engine design revolves around the use of a solid, honeycomb tungsten core. This design, and other components, had been thoroughly tested in the NERVA program so the design seems reasonable. The way the engine would work (in basic terms) is antimatter would be annialated and core would be heated up by the reaction. This energy would then be used to heat a propellant. The likely repellant would be liquid hydrogen (LH2). This would involve liquid hydrogen turbo pumps which have already been tested. Also, the heating of liquid hydrogen would present a large volume expansion (from liquid to gas phase) and therefore propel large quantities of mass out of the engine.

The core is the problem in such an engine. Tungsten has a high melting point, but it is the limiting factor because of the high heat associated with this reaction. A more advanced engine concept composed of concentric rings of tungsten to enhance the heat transfer characteristics has also been looked into. This is the type of engine that NASA officials are considering for the manned missions to Mars. The mission would require about 400 metric tons of material which is 4.5 times less material then that which would be required for a conventional, chemically propelled system.

Another engine plan would utilized a reaction chamber filled with high pressure gas into which the antiprotons are deposited. The changed annihilation products are trapped by the intense magnetic field, are slowed down, and heat the gas for expulsion. The advantage to this engine is the ability to adjust the ratio of antimatter to matter. This allows the thrust to be adjusted according to conditions.

Another even more possible use for antimatter propulsion combines fission. The main problem with antimatter engines such as the one previously describes is both size and feasibility. Several tons of antimatter would be required to complete such a job on antimatter alone. To add to that you need even more regular matter. Also, current production of antimatter is around micrograms, which puts the previous designs far into the future. However, do not rules antimatter out. Enter physicist Gerald Smith from Penn state. He has formulated an idea of combining antimatter with current technology. ?We?ll never have even a ton of antimatter, in my view,? he says. ?We think we can ignite with a microgram of antimatter, which we can foresee doing with the current technology.? His proposition is to use antimatter to begin, and aid, a fusion reaction.

His first objective was the problem of containment. After several successful attempts they doveloped a shoebox-size antimatter trap that could, in theory, hold up to 100 million antiprotons. Currently, researchers at the Marshall Space Flight Center in Huntsville, Alabama are building and even larger trap in hopes of such containment. This trap could possibly hold up to 10,000 times as many particles as the small trap. Tests have been planned combining this trap with a antimatter plasma gun which will be used to ignite the fusion reaction.

Nuclear Fusion is very complicated, and would probably require a whole other paper. It is present in nature and is the basis for most of the energy around us. Fusion requires large amounts of pressure and high temperatures. It is at the heart of the energy radiated by our stars. To give an idea of the temperature required for such a process; ?low? temperature fusion starts at 1.5 million degrees Celsius. This is where the antimatter fits in. The antimatter plasma gun is intended to create the high temperatures required for fusion. Fusion attempts so far, on earth, have been short lived. Fusion reactions have only been able to be sustained for a few seconds (without using antimatter). However, Gerald Smith (from Penn state) has been working on developing a engine that creates a self-sustaining fusion reaction triggered by both an antimatter annihilation and a fission reaction. It starts with a small amount of antimatter, which is used to induce a fission reaction in lead or uranium. The energy released, in the form of heat and pressure, by this reaction is to help drive the fusion reaction using deuterium, or ?heavy? hydrogen, and a form of helium. This creates a plasma of negative electrons and positive nuclei of atoms. These particles shoot out of the magnetic nozzle, and are sent in the correct direction for efficient propulsion. The problem with this concept is the tremendous energy generated by the reactions. The nozzle would have to withstand huge forces of both heat and pressure. This problem has yet to be solved. Another problem is the size and weight of this device. One idea for reducing the weight is dumping most of the hydrogen and instead building a huge collection scoop. This scoop would be the size of one third the distance to the moon, and magnetized so that it would separate hydrogen form the space dust. It would then condense it and use it as fuel. This scoop however would have to be far bigger then anything ever created on earth, and incredibly strong.

All three of these methods are glimses into the future. They are, however, possibilities. The third system will probably be the one realized in my lifetime. In general, the antiproton powered engine may allow low mass-ration ships and fast transit-time missions to become possible. These two characteristics may not be simply enhancing but actually enabling to certain space missions such as interplanetary, and intergalaxy exploration.

The human imagination, however, cannot be forgotten. The purpose in such exploration may not be apparent now, but someday it will. Even if there is no purpose, let our reasons be for our own amusment, or to answer our many questions. Lately, funding of such projects has come at higher costs. It seems that people no longer have the sense of adventure that they once had. Two of the big missions planned for the next decade or two are, a manned mission to Mars and a mission to break out of our system?s heliosphere (That is the point where the stream of charged particles from our sun, called solar winds, are overwhelmed by interstellar space.). Both of these missions offer the ability to do ground breaking research, but more then that they offer a boost for the imagination. However, both of these missions require new technology, especially in the form of propulsion. It is these types of systems that will allow us to reach for the stars.

Antimatter looks to be very promising. There are dozens of uses for it, they only need to be discovered. Just with the two uses I have mentioned there exist a potential to revolutionize old concepts, and it is through this revolution the we can learn new things, and make new discoveries that will allow us to fill in the blanks in the macro/micro-scopic world around us.