plasma

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Plasma : 

Plasma A Basic Introduction & Some Cool Stuff Matthew WanPHYS 420

What Is It? : 

What Is It? A hot ionized gas The ‘fourth state of matter’ Unlike gases, solids, or liquids, plasma does not contain molecules Instead, it is a gas that is composed of ions Composes more than 99% of the known visible universe

So What’s In It? : 

So What’s In It? Some, or all, of the electrons in the outer orbitals have been stripped away The result is a collection of ions and electrons, which are no longer bound together

What Did That Mean? : 

What Did That Mean? Because the particles are not neutral: Plasma behaves differently then regular gases For instance, in the presence of electromagnetic fields

Who Found It? : 

Who Found It? First discovered by Sir William Crookes, in 1879 But it wasn’t called ‘plasma’ until 1928, when Irving Langmuir coined the term

Characteristics: Temperature : 

Characteristics: Temperature Defines two kinds of plasma: Cold and Hot Refers to the electron temperature Ion temperature may be very different (lower)

Cold Plasma : 

Cold Plasma Isn’t really cold Typical electron temperatures for cold plasmas are in the thousands of degrees Only a small fraction of the gas molecules are ionized (degree of ionization) Usually on the order of 1% Often created using strong electric fields

CoolWhere Can I Find Cold Plasma? : 

CoolWhere Can I Find Cold Plasma? Fluorescent Lights Strobe Lights Experimental Fusion Research Devices

Hot Plasma : 

Hot Plasma Really hot Like the Sun (15,000,000° C at the core) The molecules are nearly if not fully ionized Created by heating the molecules to extremely high temperatures

ScorchingWhere Can I Find Hot Plasma? : 

ScorchingWhere Can I Find Hot Plasma? In Nature, actually The Sun and other stars Lightning The Aurora Borealis

Characteristics: Density : 

Characteristics: Density Plasma (electron) density The number of free electrons per unit volume Ion density Related to above by the average charge state:

Density : 

Density Neutral Density In hot plasmas, this quantity is very small, but may still determine important physics The degree of ionization is given by:

Characteristics: Potentials : 

Characteristics: Potentials Plasmas are excellent conductors Simple view: Due to the above, the electric fields in plasmas tend to be very small Quasineutrality: On the one hand, we can assume that densities of positive and negative charges are equal However, we can assume that electric fields exist as needed for the physics at hand

An Application:Let’s Get Hands On (sort of) : 

An Application:Let’s Get Hands On (sort of) Plasma Globes An electrode sitting inside a vessel containing some kind of inert gas The electrode is energized by a high-voltage, high-frequency power supply This globe uses voltages around 10 000 volts, and frequencies ranging from a few kilohertz to a few 10’s of kilohertz

The Power Supply: : 

The Power Supply:

How It Works : 

How It Works The IC sends out pulses which trigger a transistor This causes a pulse of voltage to pass through the coil This induces a large burst of voltage on the secondary of the coil

Which Does? : 

Which Does? The large voltage produced by the coil can be harnessed to produce a cold plasma The light bulb contains an inert gas that is relatively easy to ionize With any gas, a small fraction of the particles are always ionized

Cosmic : 

Cosmic Cosmic rays that are constantly bombarding the Earth ionize some of the particles The voltage and current from the power supply accelerate these particles As they move around the vessel, they ionize other particles

Exciting : 

Exciting The other particles are excited into a higher energy state As they come back down to their ground state, they release the extra energy: Light, in the form of photons Because particles have unique wavelengths, the colour of the plasma depends on the gas inside the vessel

Pressure : 

Pressure The gas vessel is at a reduced pressure As a result, the particles are spaced out This gives them time to accelerate If the particles were tightly packed, they would not build up enough energy to initiate a cascade effect

BE CAREFUL : 

BE CAREFUL The currents and voltages in this project are extremely dangerous Touching the wrong part could seriously harm you I’ve already zapped myself. It hurt.