Identifying the science involved in nuclear fusion Essay

Both windings of the transformer is what the current is induced from to heat up the plasma. Although this type of Ohmic heating technique can heat plasmas into temperatures of around 20-30 million Kelvin, it is not quite effective because the amount of heat generated depends on the resistance between the plasma and the current (the Joule Effect which states that the amount of electrical energy produced is dependent upon the resistance of the substance through which electricity is passing). The reason for the ineffectiveness of Ohmic heating from the Joule effect principle is because at temperatures of over 1 million degrees centigrade, the electrical conductivity of the plasma is very high which means that there is very low resistance. In needing higher temperatures for larger fusion reactions to occur, other methods of plasma heating are introduced to enhance the Ohmic heating technique (in order to reach higher temperatures for bigger scaled fusion reactions to occur). Neutral Beam Heating: This is an enhancing plasma heating technique of ohmic heating whereby accelerated neutral beams of deuterinium or tritium ions are injected into the already heated plasma. The beams of ions carry large kinetic energies and are neutralized in order for easier access through the magnetic fields confining the plasma. When these beams are injected into the plasma, electrons are lost and the nuclei become ionized due to high temperature particle collisions (making them positively charged ions). â€Å"In the series of subsequent ion-ion, ion-electron and electron-electron collisions, the group velocity of beam ions is transferred into an increased mean velocity of chaotic motion of all plasma particles†. This results in the neutral beam of ions heating up the pre heated plasma and increasing it’s temperature by a maximum of 21MW. http://www. jet. efda. org/pages/focus/006heating/index. html#ohmic Lower Hybrid Current Drive: This additional pre-heating technique is a process whereby micro electromagnetic waves of up to 10MW propel charged particles in a plasma at 3. 7GHz of cycles per second to produce currents of up to 3MA which increases plasma temperature. http://www. jet. efda. org/pages/focus/006heating/4c. jpg Radiofrequency Heating: This type of plasma heating technique is also known as Ion Cyclotron Resonant Heating (in a more scientifical understanding). It is a process whereby the antennae in the vacuum vessel of the tokamak â€Å"propagate waves in the frequency range of 25-55 MHz into the core of the plasma to increase the energy of the ions† thus increasing the temperature for more fusion reactions to occur. This heating method provides additional energy of up 20MW of power t http://www. jet. efda. org/pages/focus/006heating/index. html#ohmic Magnetic Confinement Of Plasma A magnetic field is defined as a force produced by moving electric charges or currents that exerts a power on other moving charges. Because the incredible temperature of plasma (which is over 100 million i C) inside the tokamak cannot be contained inside the inner vessel walls of the nuclear reactor alone, the use of magnetic fields gives an alternative technique in actually restraining the high temperature plasma particles from touching the walls of the reactor. This is called confinement. The reason why plasma is restrained from touching the walls of the reacting vessel is that it cools down very rapidly and terminates itself at once when contact is made. A plasma is made up of ionized particles. In the absence of magnetic fields, the ionized particles move in straight lines and in random directions. This eventually leads to contact with the inner chamber walls of the reacting vessel and results in the plasma quickly cooling down and terminating itself. But when a constant presence of a magnetic field is introduced, the ionized particles in the plasma flow through these fields in a spiral path on the magnetic lines. The movement of the particles across the magnetic field lines are restricted and this also prevents contact to the walls of the containment vessel. Below is a picture illustrating the movement of charged particles with and without the presence of magnetic fields: . http://www. plasma. inpe. br/LAP_Portal/LAP_Site/Text/Plasma_Confinement. htm On the torus, there two main components of magnetic fields used. The main type of magnetic field used in the plasma confining process is the toroidal field. This is a field whereby 32 large (D-shaped) coils surround the vacuum vessel of the nuclear reactor and when current flows around these coils, a toroidal magnetic field is generated which controls the position of the plasma inside the torus and also modifies the poloidal field (the second magnetic field). The other magnetic field (the poloidal field) is produced by current being flown through the plasma which is initially induced from transformers. The created poloidal field with the combination of the toroidal field confines the plasma well and stabilizes it which allows confinement times of plasma temperatures to be longer. . http://www. fys. uio. no/plasma/plasma/norsk/tokamak. gif Limitations Of The Jet Fusion Tokamak The foremost limitation on the Jet fusion tokamak is the small amount of time the plasma lasts for inside the reactor. This is because of the plasma being continuously cooled down by tiny impurities inside the chamber walls. Also, the efficiency of the fusion reaction inside the nuclear reactor is quite an important aspect of limitations that has a need to be solved. This is because large amounts energy are put in initially just to start the fusion reaction at a plasma state and only half the energy is acquired when fusion is completed. On a typical Jet experiment, 30MW of energy is the power input used and only 16MW of energy is successfully extracted out from the reactor as power output . From an efficiency equation (Pout / Pin), this gives an efficiency of 53. 3% . Another important limitation of fusion reactions inside the tokamak reactor is the instability of the plasma that has a need to be controlled. This is because of excited and charged particles inside the plasma wanting to escape as they are being compressed into higher temperatures. Although this is controlled by the use of magnetic fields, the slightest error in confining these charged particles could result in the plasma escaping and quickly cooling down and thus all the total energy put initially put into the reaction being wasted. Also if the plasma escapes, this results in it touching the inner walls of the tokamak and eroding or damaging the components surrounding the plasma and by therefore reducing the lifetime of these components. Although these problems or limitations cause less energy efficiencies inside the tokamak, modern day advances of computer aided technology is gradually providing remedies in sorting these limitations out. Future Developments. From my knowledge of future developments in nuclear reactors, experimental studies which is currently being carried on the JET experiment is believed to provide some detailed background information in acquiring similar basic properties in the building process of ITER.. Currently, The JET experiment holds the world record for released fusion power at 16 million Watts (16MW). This is â€Å"a value comparable to the power needed for heating one thousand households in a cold winter. † http://www. jet. efda.org/pages/focus/010jetanditer/index. html#overall In future developments, it is predicted that the ITER experiment which is estimated to finish construction at the end of year 2006 in France would release an amazing fusion power of 500 Million Watts. This, by my accurate calculations, is enough to power up to 31,250 homes on a cold winter night. The future properties of ITER when construction is finished is going to be entirely based around a hydrogen plasma torus which would operate at temperatures of above 200 Million i C and also by the use of super conducting coils to generate high temperature plasmas which would yield better energy efficiencies give more energy outputs. In the size of ITER’s components compared to the current JET nuclear reactor, ITER is estimated to be 10 times bigger than JET in size. Bibliography Books Name Of Book Authors Name ISBN Number Name Of Publisher’s Year Of Publishment Understanding Physics For Advanced Level (Second Edition) Jim Breithaupt 0-7487-0510-4 Stanley Thornes Publishers Ltd 1990 Salters Horners Advanced Physics Heinimann 0435 628909Heinimann Educational Publishers 2000. Internet 1) http://www. jet. efda. org/images/gallery/images/82-348cmed. jpg. 2) http://www. plasma. inpe. br/LAP_Portal/LAP_Site/Text/Plasma_Confinement. htm 3) http://www. sbf. admin. ch/htm/international/org/fusion-e. html 4) http://europa. eu. int/comm/research/energy/fu/fu_rt/fu_rt_mc/article_1227_en. htm 5) http://www-fusion-magnetique. cea. fr/gb/fusion/principes/principes01. htm 6) http://www. jet. efda. org/pages/focus/006heating/index. html#ohmic 7) http://www-fusion-magnetique. cea. fr/gb/fusion/principes/principes01. htm.