SUPER CONDUCTIVITY.pptx PHYSICS PROJECT SEM

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1. SUPER CONDUCTIVITY P.SELVADHARSHINI XII-A 510

2. Definition Superconductivity is a remarkable physical phenomenon observed in certain materials when they are cooled below a critical temperature. In this state, these materials lose all electrical resistance, allowing for the free flow of electric current without any loss of energy due to resistance. Additionally, superconductors have the ability to expel magnetic fields from their interior, a behavior known as the Meissner effect. This combination of zero resistance and perfect diamagnetism makes superconductivity a fascinating area of study with profound implications for technology and fundamental physics. 2

3. History Superconductivity was discovered in 1911 by HEIKE KAMERLINGH-ONNES . For this discovery, the liquefaction of helium, and other achievements, he won the 1913 Nobel Prize in Physics. Five Nobel Prizes in Physics have been awarded for research in superconductivity (1913, 1972, 1973, 1987, and 2003). Approximately half of the elements in the periodic table display low temperature superconductivity, but applications of superconductivity often employ easier to use or less expensive alloys. For example, MRI machines use an alloy of niobium and titanium. HEIKE KAMERLINGH ONNES

4. Introduction At what most people think of as “normal” temperatures, all materials have some amount of electrical resistance. This means they resist the flow of electricity in the same way a narrow pipe resists the flow of water. Because of resistance, some energy is lost as heat when electrons move through the electronics in our devices, like computers or cell phones. For most materials, this resistance remains even if the material is cooled to very low temperatures. The exceptions are superconducting materials. Superconductivity is the property of certain materials to conduct direct current (DC) electricity without energy loss when they are cooled below a critical temperature (referred to as Tc). These materials also expel magnetic fields as they transition to the superconducting state.

5. Microscopic Mechanism In 1957, three physicists at the University of Illinois used quantum mechanics to explain the microscopic mechanism of superconductivity. They proposed a radically new theory of how negatively charged electrons, which normally repel each other, form into pairs below Tc. These paired electrons are held together by atomic-level vibrations known as phonons, and collectively the pairs can move through the material without resistance. For their discovery, these scientists received the Nobel Prize in Physics in 1972. Following the discovery of superconductivity in mercury, the phenomenon was also observed in other materials at very low temperatures. The materials included several metals and an alloy of niobium and titanium that could easily be made into wire. Wires led to a new challenge for superconductor research. The lack of electrical resistance in superconducting wires means that they can support very high electrical currents, but above a “critical current” the electron pairs break up and superconductivity is destroyed. Technologically, wires opened whole new uses for superconductors, including wound coils to create powerful magnets. In the 1970s, scientists used superconducting magnets to generate the high magnetic fields needed for the development of magnetic resonance imaging (MRI) machines. More recently, scientists introduced superconducting magnets to guide electron beams in synchrotrons and accelerators at scientific user facilities.

6. Meissner Effect When a material makes the transition from the normal to superconducting state, it actively excludes magnetic fields from its interior; this is called the Meissner effect. Meissner and Ochsenfeld in 1933 observed- When a superconducting material at temp. T> Tc, is placed in ext. magnetic field, lines of magnetic induction pass through its body, but when it is cooled below the critical temp. i.e., T< Tc, these lines of induction are pushed out of the superconducting body. So, inside the SC body B = 0 , This is known as Meissner Effect , which is the characteristic property of a superconductor

7. Application of Meissner Effect This effect of superconductivity, is used in magnetic levitation which is the base of modern high-speed bullet trains. In superconducting state (phase), due to expulsion of external magnetic field, the sample of superconducting material levitates above magnet or vise-versa. Modern high-speed bullet trains use the phenomenon of magnetic levitation. Standard test Proof for a superconductor. A separation technique, based on the Meissner effect, to purify and classify superconducting powders was developed.

8. Critical Magnetic Field (Hc) A superconductor when placed in ext. magnetic field, at a particular value looses its superconducting property. The magnetic field responsible for the destruction of superconducting property is called critical magnetic field (Hc). It is a function of temp. at T, He is zero, i.e., Hc(Tc)=0. SC state is stable for definite ranges of magnetic field and temp. Normal conducting state is more stable at high temp. and high magnetic field.

9. Types of Superconductors Type 1 Superconductors Superconductors that exhibit complete Meissner effect[complete expulsion of all magnetic field] are type 1 superconductors. They have low Hc [critical magnetic field] values. Due to their tendency to allow field penetration even for lower applied field they are also called "soft superconductors“ E.g. pure elements like Al, Lead, Hg, MAGNETIZATION CURVE FOR TYPE 1 SUPERCONDUCTORS As seen from magnetization curve, transition at He is reversible i.e. if field is again lowered below H then material again becomes superconductor.

10. Type 2 Superconductors Superconductors that exhibit partial Meissner effect are type 2 superconductors. They have Hc1 [lower magnetic field] & Hc2 [upper magnetic field]. In region between them it is in vortex/mixed state. Since they need large magnetic field to bring them back to superconducting state they are also called "hard superconductors“. As Hc2, Tc are high for type 2 superconductors they are widely used in engineering applications. E.g. YBCO, Nb3Sn, Nb3Ge, ... MAGNETIZATION CURVE FOR TYPE 2 SUPERCONDUCTORS As seen from magnetization curve, transition at He is not reversible.

11. Applications of Superconductors in Transportation (Maglev Train) Introduction to Maglev Train: MAGLEV (MAGNETIC LEVITATION) trains use superconducting magnets to achieve levitation and propulsion, enabling high-speed and frictionless transportation. The working principle of Maglev (Magnetic Levitation) trains relies on the interaction between superconducting magnets and guideways to achieve levitation and propulsion. Here's a breakdown of the working principle: Superconducting Magnets: Maglev trains utilize superconducting magnets, which are cooled to cryogenic temperatures using liquid nitrogen or helium. At these low temperatures, the superconducting magnets exhibit zero electrical resistance, allowing them to generate strong magnetic fields without energy loss.

12. Levitation: The superconducting magnets mounted on the underside of the train generate a magnetic field that interacts with the guideway, which typically contains a series of coils or permanent magnets. According to the principles of magnetic repulsion and attraction, the magnetic fields of the superconducting magnets and the guideway create a repulsive force, lifting the train off the track. This levitation effect enables the train to float above the guideway, eliminating friction between the wheels and the track. Propulsion: In addition to levitation, the interaction between the superconducting magnets and the guideway also provides propulsion for the train. By adjusting the magnetic fields, the superconducting magnets can create a forward or backward force, propelling the train along the guideway. The absence of friction allows Maglev trains to achieve high speeds with minimal energy consumption. Stability and Control: To ensure stability and control, Maglev systems incorporate sensors and control systems to monitor and adjust the magnetic fields. These systems continuously optimize the levitation and propulsion forces to maintain the desired speed and stability of the train.

13. The Advantages of Maglev trains utilizing superconducting magnets include: High speeds Smooth ride Energy efficiency Safety Reduced maintenance Environmental benefits Reduced travel time

14. Application of Superconductivity The applications of superconductivity includes: Magnetic Resonance Imaging (MRI) Power generation and transmission Magnetic Levitation (Maglev) Transportation Particle accelerators Quantum computing Superconducting electronics Magnetic resonance spectroscopy Magnetic levitation bearings

15. Disadvantages of Superconductivity The disadvantages of superconductivity includes: High cost of production. Energy-intensive cryogenic cooling requirements. Material brittleness and sensitivity. Bulky and heavy devices. Complexity in maintenance and operation. Potential magnetic interference. Limited operating conditions. Environmental and health concerns with certain materials.

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