Kanazawa Short Stay Program Lecture Essay Report Plasma Lecture by Prof. Kamata Oswin Bustari Priambodo Department of Physics, Faculty of Mathematics and Natural Science, Bandung Institute of Technology Email:
[email protected]
Plasma is one of the four fundamental states of matter, and the other being gas, liquid and solid. Plasma itself can be created by heating a gas or exposing it to a strong electromagnetic field with a laser or microwave generator, this process decreases or increases the number of electrons, creating charged particles, either positive or negative called ions, an if present accompanied by the dissociation of molecular bonds. The presence of a non-negligible number of charge carriers makes plasma highly electrically conductive because of this properties plasma responds strongly to electromagnetic fields. Plasma does not have a definite shape or volume, unless enclosed in a container, and under the influence of electromagnetic field, it may form structures such as filaments, beams and double layers Plasma itself is the most abundant form of ordinary matter in the universe, most of which is in the rarefied intergalactic regions, particularly the intracluster medium and in stars, the most common form of plasma in our daily life is seen in neon lights. Plasma is loosely described as an electrically neutral medium of unbound positive and negative particles, even though the particle is unbound, this particle is not free in the sense of not experiencing force, because when the charges move they generate electrical currents with magnetic fields, and because of this they are affected by each other’s fields, this effect governs the collective behavior of the particle itself with many degrees of freedom, the definition of plasma itself can be split into three criteria: 1. The plasma approximation: Charged particles must be closed enough together that each particle influences many nearby charged particles Charged particles must be close enough together that each particle influences many nearby charged particles, rather than just interacting with the closest particle (these collective effects are a distinguishing feature of a plasma). The plasma approximation is valid when the number of charge carriers within the sphere of influence (called the Debye sphere whose radius is the Debye screening length) of a particular particle is higher than unity to provide collective behavior of the charged particles. The average number of particles in the Debye sphere is given by the plasma parameter 2. Bulk interactions: The Debye screening length (defined above) is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place. When this criterion is satisfied, the plasma is quasineutral.
3. Plasma frequency: The electron plasma frequency (measuring plasma oscillations of the electrons) is large compared to the electron-neutral collision frequency (measuring frequency of collisions between electrons and neutral particles). When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics. Plasma parameters can take on values varying by many orders of magnitude, but the properties of plasmas with apparently disparate parameters may be very similar (see plasma scaling). The following chart considers only conventional atomic plasmas and not exotic phenomena like quark gluon plasmas: Typical ranges of plasma parameters: orders of magnitude (OOM) Characteristic Terrestrial plasmas Cosmic plasmas Size
10−6 m (lab plasmas) to
10−6 m (spacecraft sheath) to
in meters
102 m (lightning) (~8 OOM)
1025 m (intergalactic nebula) (~31 OOM)
Lifetime
10−12 s (laser-produced plasma) to
101 s (solar flares) to
in seconds
107 s (fluorescent lights) (~19 OOM)
1017 s (intergalactic plasma) (~16 OOM)
Density
107 m−3 to
1 m−3 (intergalactic medium) to
in particles per
1032 m−3 (inertial confinement plasma)
1030 m−3 (stellar core)
cubic meter Temperature
~0 K (crystalline non-neutral plasma[11]) to
102 K (aurora) to
108 K (magnetic fusion plasma)
107 K (solar core)
10−4 T (lab plasma) to
10−12 T (intergalactic medium) to
103 T (pulsed-power plasma)
1011 T (near neutron stars)
in Kelvin Magnetic fields in teslas
In order for plasma to exist, ionization is needed, and the degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, and is controlled mostly by the temperature, even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma from the response to magnetic fields and high electrical conductivity. Plasma is often called the fourth state of matter after solid, liquids and gases. It is distinct from these and other lower-energy states of matter. Although it is closely related to the gas phase in that it also has no definite form or volume, it differs in a number of ways, including the following: Property
Electrical conductivity
Gas Very low: Air is an excellent insulator until it breaks down into plasma at electric field strengths above 30 kilovolts per centimeter.[17]
Plasma
Usually very high: For many purposes, the conductivity of a plasma may be treated as infinite.
Two or three: Electrons, ions, protons and neutrons One: All gas particles behave in can be distinguished by the sign and value of their Independently a similar way, influenced by charge so that they behave independently in many acting species gravity and by collisions with circumstances, with different bulk velocities and temperatures, allowing phenomena such as new one another. types of waves and instabilities.
Velocity distribution
Maxwellian: Collisions usually lead to a Maxwellian velocity distribution of all gas particles, with very few relatively fast particles.
Interactions
Binary: Two-particle collisions Collective: Waves, or organized motion of plasma, are are the rule, three-body very important because the particles can interact at collisions extremely rare. long ranges through the electric and magnetic forces.
Often non-Maxwellian: Collisional interactions are often weak in hot plasmas and external forcing can drive the plasma far from local equilibrium and lead to a significant population of unusually fast particles.
Plasmas are by far the most common phase of ordinary matter in the universe, both by mass and by volume. One of the most famous and most common plasma in our daily life is actually the sun. The Sun is the star at the center of the Solar System. It is by far the most important source of energy for life on Earth. The Sun is a nearly perfect spherical ball of hot plasma with internal convective motion that generates a magnetic field via a dynamo process. The diameter of the Sun is about 109 times that of Earth, and it has a mass about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System, Chemically, about three quarters of the Sun's mass consists of hydrogen, whereas the rest is mostly helium, and much smaller quantities of heavier elements, including oxygen, carbon, neon and iron. The core is the source of all the Sun's energy. Fortunately for life on earth, the Sun's energy output is just about constant so we do not see much change in its brightness or the heat it gives off. The Sun's core has a very high temperature, more than 15 million degrees Kelvin, and the material in the core is very tightly packed or dense. It is a combination of these two properties that creates an environment just right for nuclear reactions to occur. In the core of a star the intense heat destroys the internal structure of an atom and consequently all atoms are broken down into their constituent parts. An atom is constructed of protons, electrons and neutrons. Neutrons have no electric charge and therefore do not interact much with the surrounding medium. As a result neutrons leave the core fairly quickly. The protons, which have positive electric charge, and the electrons, which have negative electric charge, remain in the core and drive the reactions which fuel the Sun. The charge neutral material of protons and electrons that makes up the core is called plasma. The high temperature provides the protons and electrons with a large amount of thermal energy and as a result they move around quite quickly. This motion, combined with the high density of the plasma, causes the particles to continuously slam into one another creating nuclear reactions. It is the fusion, or slamming together, of particular combinations of particles that provides the energy source of the Sun.
Another common source of plasma that we may or may not realized, is the fluorescent lamp, A fluorescent lamp converts electrical energy into useful light , the fundamental means for conversion of electrical energy into radiant energy in a fluorescent lamp relies on inelastic scattering of electrons when an incident electron collides with an atom in the gas. If the (incident) free electron has enough kinetic energy, it transfers energy to the atom's outer electron, causing that electron to temporarily jump up to a higher energy level. The collision is 'inelastic' because a loss of kinetic energy occurs. This higher energy state is unstable, and the atom will emit an ultraviolet photon as the atom's electron reverts to a lower, more stable, energy level. Most of the photons that are released from the mercury atoms have wavelengths in the ultraviolet (UV) region of the spectrum, predominantly at wavelengths of 253.7 and 185 nanometers (nm). These are not visible to the human eye, so they must be converted into visible light. This is done by making use of fluorescence. Ultraviolet photons are absorbed by electrons in the atoms of the lamp's interior fluorescent coating, causing a similar energy jump, then drop, with emission of a further photon. The photon that is emitted from this second interaction has a lower energy than the one that caused it. The chemicals that make up the phosphor are chosen so that these emitted photons are at wavelengths visible to the human eye. The difference in energy between the absorbed ultra-violet photon and the emitted visible light photon goes toward heating up the phosphor coating. When the light is turned on, the electric power heats up the cathode enough for it to emit electrons (thermionic emission). These electrons collide with and ionize noble gas atoms inside the bulb surrounding the filament to form a plasma by the process of impact ionization. As a result of avalanche ionization, the conductivity of the ionized gas rapidly rises, allowing higher currents to flow through the lamp. The fill gas helps determine the operating electrical characteristics of the lamp, but does not give off light itself. The fill gas effectively increases the distance that electrons travel through the tube, which allows an electron a greater chance of interacting with a mercury atom. Argon atoms, excited to a metastable state by impact of an electron, can impart this energy to a neutral mercury atom and ionize it, described as the Penning effect. This has the benefit of lowering the breakdown and operating voltage of the lamp, compared to other possible fill gases such as krypton A fluorescent lamp tube is filled with a gas containing low pressure mercury vapor and argon, xenon, neon, or krypton. The pressure inside the lamp is around 0.3% of atmospheric pressure. The inner surface of the lamp is coated with a fluorescent (and often slightly phosphorescent) coating made of varying blends of metallic and rare-earth phosphor salts. The lamp's electrodes are typically made of coiled tungsten and usually referred to as cathodes because of their prime function of emitting electrons. For this, they are coated with a mixture of barium, strontium and calcium oxides chosen to have a low thermionic emission temperature, because of the gas for the filling is mainly hazardous, a special kind of coating need to be applied in order for minimize the risk of shattering and become hazardous to the user.
For the coating, usually light-emitting phosphors are applied to the inside of the tube. The organic solvents are allowed to evaporate, then the tube is heated to nearly the melting point of glass to drive off remaining organic compounds and fuse the coating to the lamp tube. Careful control of the grain size of the suspended phosphors is necessary; large grains, 35 micrometers or larger, lead to weak grainy coatings, whereas too many small particles 1 or 2 micrometers or smaller leads to poor light maintenance and efficiency. Most phosphors perform best with a particle size around 10 micrometers. The coating must be thick enough to capture all the ultraviolet light produced by the mercury arc, but not so thick that the phosphor coating absorbs too much visible light. Because of this coating, even though the reaction inside the fluorescent tube exceeds the melting point of the glass, the glass didn’t break or shattered. Inside the earth itself there is a kind of plasma, this plasma inside earth is the result of nuclear radioactivity, this radioactivity is the result of a great deal of pressure resulted from earth’s gravity trying to compress matter, and because of this the middle part, which is the core get the most pressure, as the earth itself contain many radioactive elements like uranium-238, uranium-235 and thorium-232, this radioactive elements is the source of the plasma and because of this elements, the earth’s core become very hot, and the heat produced is trying to come out from the core, but was resisted by the earth’s crust, and If there are a high enough concentration of radioactive elements, it will cause a metamorphism of the earth’s crust and thus creating magma. There is another way of how magma can be formed, that is by convection. Convection itself is a form of heat transfer where the heat moves with the material. Plate tectonics appears to be driven by convection in some form, because if there is a convection current, hotter material at depth will rise, carrying its heat with it, as it rises to lower pressure it will cool, but the temperature is still higher than the surroundings, and because of the decompression the local geothermal gradient is rising, and if this temperature continue rising to the point that it is greater than the peridotile solidus, partial melting and magma can occur, and this mechanism is called decompression melting. This two method is the 2 way that magma can occurred. In the class we were given a demonstration about plasma by using the means of plasma ball, what is exactly is a plasma ball? A plasma globe or plasma lamp (also called plasma ball, dome, sphere, tube or orb, depending on shape) is generally a clear glass sphere filled with a mixture of various noble gases with a high-voltage electrode in the center of the sphere. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light (see corona discharge and electric glow discharge). The most amusing thing to do when you have a plasma ball is to put your finger in the glass, and the suddenly the plasma flow right into your finger, how is this happening? Why? Placing a fingertip on the glass creates an attractive spot for the energy to flow, because the conductive human body (having non-ohmic resistance of about 1000 ohms at room temperature) is more easily polarized than the dielectric material around the electrode (i.e. the gas within the globe) providing an alternative discharge path having less resistance. Therefore, the capacity of the large conducting body to accept radio frequency energy is greater than that of the surrounding air. The energy available to the filaments of plasma within the globe will preferentially flow toward the better acceptor. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner. The filament is brighter because there is more current flowing through it and into the 150 pF capacity, or capacitance, presented by an object, a conducting body, the size of a human.
