High Temperature Superconductivity Allen Moussa

single crystal x-ray diffraction Single crystal X-ray diffraction technique can be used to determine crystal structure, a collimator is used to narrow the X-ray beam as show in the image When X-rays reflect off layers in a crystal they produce patterns of destructive and constructive interference on photographic film (see image) X-rays have a small enough wavelength to allow the atomic spacing between planes in crystals to act as a diffraction grating X-rays produce an interference pattern after reflecting off several layers of atoms in a pure crystal. The superposition of many reflected waves results in a pattern of bright spots on the photographic film, this pattern is analyzed.

SEM - Scanning electron microscope High powered electron beams are fired at the surface of the sample in a raster like fashion providing a 3D image of the surface Electrons are reflected from the surface of the crystal when hit by the beam, this causes the emission of X-rays which are then detected The electron beam causes the sample to displace inner-shell electrons,a higher energy electron fills the shell and energy is released B14FDB14.gif

powder x-ray diffraction This technique requires the sample to be grounded into a finely powdered material and placed onto a diffractometer Involves diffraction of a monochromatic X-ray beam from a sample containing an enormous number of tiny crystals having random orientation A detector moves around the crystal to measure the intensity of X-rays at different angles, and plots a relative intensity pattern at these different positions

advances leading to HTS - ceramics Heike Onnes the ‘farther of superconductivity’ began experimentation with pure metals such as mercury Ceramic materials are normally insulators, although in 1986 a layered ceramic compound (Ba-La-Cu oxide) was created that superconducted at the highest temperature then known, 30 K The problem with ceramics is that they are hard and brittle making it a challenge to make long, flexible wires out of them Improvements in transmission electron microscopy have led to increased understanding of the crystalline structure of high temperature superconductors The Meissner effect can be used to identify properties of different types of HTS, by analyzing the HTS critical magnetic field strength perconductivity101/images/superconductivity-meissner.jpg

advances leading to HTS - BCS theory High temperature superconductors are made from ceramic materials largely containing copper oxide The discovery of HTS meant that liquid nitrogen could now be used as opposed to liquid helium which is expensive to produce BSC provided a firm understanding of the mechanism underlying low temperature superconductivity which eventually led to HTS At critical temperatures electrons attract the positive ions and create a region of excess positive charge, which than attracts another nearby electron, these two electrons are now cooper pairs

Superconductor applications - maglev train Maglev (magnetic levitation) trains use the Meissner effect, they use superconducting magnets in the train and levitation coils attached to the side track High temperature superconductors are now being used and this means that liquid nitrogen can be utilized, which lowers the operating cost significantly Since there is no friction with the track air resistance is the only force slowing the train, the front has a streamlined design to reduce drag In image 1 the levitation coils attached to the track have north and south polarities due to Lenz’s law that they must oppose the change in flux caused by the moving superconducting magnets In image 2 a substation constantly reverses the polarity of the levitation coils so that each superconducting magnet is either being repelled of pulled along the track Image 1Image 2

Superconductor applications - SQUID SQUID magnetometers are so sensitive that they can detect magnetic fields caused by electrical currents produced by the brain SQUIDs use a superconducting ring to resists changes in flux from the external environment and give recordings of magnetic field strength SQUIDs provide a safer method to analyze electrical currents in the brain, this has allowed researchers to further understand the brain differences between individuals with a disorders and those without

future applications - computers ComponentAdvantagesDisadvantages Society ★ Significantly smaller computers and increased speed of computer chips ★ The superconductive approach has advantages in power consumption ★ Faster calculations will help engineers to analyze problems faster and more accurately ★ Powerful computers can be used by the military or terrorist groups to develop weapons ★ Cyber criminals e.g. hackers will now be able to take advantage of faster computing Environment ★ Computers will have a low energy consumption ★ Increased mining for rare Earth elements ★ Many HTS are made of toxic metals and disposal of them can affect the environment

future applications - transmission of electricity ComponentAdvantagesDisadvantages Society ★ HTS wires can carry 150 times as much as a standard copper wire of the same dimensions ★ Transformers will no longer be required ★ Reduced electricity costs ★ The manufacturing cost will be 100 times that of todays conventional wires ★ Keeping the wires at the required critical temperature Environment ★ HTS wires conduct with 100% efficiency when cooled with environmentally friendly liquid nitrogen ★ Replacement of existing overhead transmission lines with underground cable ★ Increased mining for rare Earth elements

future applications - motors and generators ComponentAdvantagesDisadvantages Society ★ HTS generators and motors are substantially smaller and lighter than copper based machines ★ Heat is eliminated and life expectancy of motors and generators increases Environment ★ HTS generators reduced pollution per unit of energy produced ★ Reduction in fossil fuel usage since HTS generators are very efficient ★ Smaller size means that less materials is needed for construction

future applications - superconducting magnetic energy storage ComponentAdvantagesDisadvantages Society ★ SMES recharges within minutes and can be charged thousands of times without any degradation of the magnet. ★ Power is available almost instantaneously, no loss of power SMES requires a large space to provide useful storage of energy Possible adverse health effects Environment ★ Future power storage that would have no hydrocarbon emission ★ Large magnetic fields in SMES could possibly disrupt the Earth’s magnetic field

Bibliography Physics Contexts 2 - Textbook Mac os x dictionary application mentals/fundamentals.htm mentals/fundamentals.htm eports/m/ornlm3063r1/contents.html eports/m/ornlm3063r1/contents.html Get smart Physics - written by Winston Grossley Alasdair Hey - the physics guy