ABSTRACT

Plasma the fourth state of matter is naturally produced in the sun’s core throughout the D-T fusion reaction of hydrogen, then the plasma will be transmitted out through the sun’s layers to reach the atmosphere and then into space by the solar wind consisting of charged particles which stimulates the creation of aurora by colliding with earth's atmosphere atoms that generates displays in various colors and shapes depending on the gas type as it goes excitation or ionization. The two main generators for aurora are oxygen and nitrogen.

Aurora helps in discovering life on other planets as it indicates the presence of atmosphere.

ACKNOWLEDGEMENTS

I would like to thank every single person who has worked hard in this university facilitating our road of success especially our chemist doctors who has encouraged and helped us through the years and all the appreciation to Dr. Sami Tlais for his patience, motivation, and immense knowledge guiding me to write this project.

Secondly I would like to thank my husband, parents and friends who helped me a lot through this journey.

CHAPTER Ⅰ: Plasma

Ⅰ.1 - Introduction to Plasma

Plasma the fourth state of matter is an electrically neutral medium consisting of an equal number of positive and negative charged particles that responds to electric and magnetic field which gives plasma a uniqueness property differentiating it from the other states of matter [1]^,[2].

The plasma is constituted in more than 99% of the visible matters in the universe, in the other hand it can’t be found naturally on the earth’s surface but it can be formed artificially 1^,[3]. Plasma is formed artificially by ionizing gas atoms such possessing low ionization energies as potassium, sodium, and cesium 1. There are two ways of transforming gas to reach plasma state either by applying a massive charge variation or by displaying an intense powerful temperature. Artificial plasma is utilized mostly in micro and nano technologies as 50% of appliances include plasma reactors also in neon, xenon headlamps of vehicles, sodium vapor lamps , laser, surface treatment (figure 1), biomedical applications (figure 2), display technology (figures 3 & 4), welding arcs (FIGURE 5), fusion devices
and power production which will be the most important future application of plasma 1^,2^,[4],[5].

Figure 1: Plasma surface treatment [6].

Figure 2: Plasma biomedical application for drug delivery [7].

Figure 3: Cross section of TV high plasma display [8].

Figure 4: Ionized gases plasma cells. Upon charging the gas emits UV light leading to the color emissions from phosphors [9].

Figure 5: Plasma arc welding for coating functionalized materials [10].

Plasma can be found naturally in the sun, stars, interplanetary space (space between planets), interstellar space (space between stars), disks surrounding black holes, solar wind, ionosphere, lightning and aurora 4^,5. Photo-ionization is the major process of plasma formation in space causing the emission of electron from an excited gas upon absorbing photons from sunlight or starlight where plasma might be ionized partially or fully 1.

The basic plasma is the completely ionized hydrogen plasma 1. It is known as nuclear fusion reaction produced from the sun where the nuclei of deuterium and tritium merge to form helium-4 and an excess of energy is released.

Reaction 1: Fusion reaction: ³₁H + ²₁H à¹₀n + ⁴₂He + 17.6 MeV [11].

One of the key properties of plasma that allows its different applications in many sectors is that it can exist in various scales of temperature and density. That’s why the particle density (number/cm³) and temperature (K) are the two main important plasma parameters (table 1) 3.

	Plasma	plasma densities	Temperatures	plasma frequencies
Artificial plasmas	Fusion reactor	10¹⁵	10⁴	3×10¹¹
	Laser	10²⁰	10²	9×10¹³
	Glow discharge	10⁸	2	9×10⁷
	Arc discharge	10¹⁴	1	9×10¹⁰
Earth plasmas	ionosphere	10⁶	0.1	9×10⁶
Earth plasmas	magnetosphere	10	10⁶	8×10³
Natural plasmas	thermonuclear reaction	10²⁵	10⁵
	Solar corona	10⁶	10²	9×10⁶
	Solar atmosphere	10¹⁴	1	9×10¹⁰
	solar wind	3-20	50-100	2×10¹⁵
	Interstellar medium	1	1	9×10³

Table 1: Typical values of plasma densities (no in cm^-3), the temperature (eV) and plasma frequencies in (s^-1) of different plasma types 1^,2.

Ⅰ.2 - Plasma wave

Plasma behaves as a wave and since the plasma-oscillation frequency is greater particle-particle collision rate plasma responds to electromagnetic forces more than simple collisions. Ion acoustic wave is a plasma wave aligned with magnetic field and formed by the electric field to attach electrons and ions due to their mass difference 1.

Ⅰ.2.1 - Low-frequency waves

The sun emits large-amplitude of transverse Alfvén waves which plays an important role in heating corona to 1,000,000 K. its velocity of propagation depends on the particles density and strength of the magnetic field which is essential for its existence. Almost all natural and laboratory plasma waves are linked by a magnetic field 1.

Solar wind propagates through Alfvén waves that are responsible for its variations and influences the development of magnetic storms and auroras 1.

Electromagnetic waves are of moderate frequencies, caused by interruptions in the magnetic field creating an electric field 1.

Ⅰ.2.2 - Higher frequency waves

Plasma acts as a whole with a velocity independent of frequency. Alfvén wave are divided into electron cyclotron and ion cyclotron waves generating their resonance frequencies where particles in these waves are accelerated and move in a circular path along the magnetic field. Transverse waves can’t propagate below these resonances, in order to propagate they have to reach or exceed the plasma frequency 1.

CHAPTER Ⅱ: Natural plasma's

Hydrogen plasma which is produced from the nuclear reaction in the sun is the basic for all natural phenomenons 1^,11.

Ⅱ.1 - Regions of the sun

The sun is divided into two parts; the interior and the solar atmosphere. The suns interior is made up of three parts: core, radiative zone, and the convective zone. The central and the hottest part is the core where a nuclear fusion reaction takes place [12]. This part includes intense temperature (10⁵ eV) and density (10²⁵/cm^-3) which approaches the nuclei in order to merge and prevent their repulsion 11. Then energy is transported through photons as thermal radiation into the radiative zone. After that the energy circulates up like a bubbling movement in the convection zone to reach the photo-sphere which is the first part of the sun^’s solar atmosphere 12.

Ⅱ.1.1 - Sunspots

The photo-sphere is the observable face of the sun 12. It includes the sunspots that are the main factor of solar storms and aurora^’s [13]. Sunspots show dark areas at the sun’s surface, they appear dark since the plasma in it is cooler (4,000 K) than its neighborhood (5,800 k) 13 due to the sun’s magnetic field disturbances where they interrupt and spread out into sun’s atmosphere Sunspots survive for weeks [14], days or months 13.

Ⅱ.1.1.1 - 11 year cycle

The standard number of visual sunspots varies and differs between years. Historical data show a mean interval around 11 years. The sunspots sum is not accurate due to sunspots size difference where some are huge others are small, also the might be combined with their boundaries or arise as groups. 11-year sunspot cycle is accurately half the 22-year cycle of solar activity where the magnetic fields in the north and south switch their polarities 13.

Ⅱ.1.1.2 - Solar max & solar min

Solar maximum indicates the high energetic sun’s activity is related to highest sunspots sum [15] where they appear near the sun’s poles and the negligible ones are solar minimum where sunspots appear near the sun’s equator (table 2) 13.

year

1986

1989

1996

Number of sunspots

157

Solar max

> 9

Solar minimum

Table 2: The sunspots cycle through years 13.

The sunspots are signs for strong magnetic field areas surrounding it called active regions 13.

Ⅱ.1.2 - Active Regions

Active regions are seen bright in X-ray and ultraviolet images of the Sun. They produce solar storms in the form of solar flares and coronal mass ejections (CME) and blow up high energy in the form of X-ray and UV photons. Active regions magnetic fields are 1000 times powerful than the sun’s normal magnetic field. Solar prominence's and coronal loops often develop throughout active regions 15 and grow up along chromosphere to reach corona [16].

Ⅱ.1.2.1 - Solar Prominence's

Huge bright loop shaped tied up to the sun’s surface, they can expand thousands of kilometers, formed by sun’s magnetic field and consists of cool and dense plasma. They can remain for weeks or months. Their explosion snaps them to produce coronal mass ejections (CME) [17].

Ⅱ.1.2.2 - Coronal mass ejections (CME)

Are eruptions of plasma solar wind which transfers billion tons of matter mainly protons, electrons and strong magnetic field in hundreds of kilometers per second outside sun’s atmosphere, some approach earth colliding with its magnetosphere transferring radiation into its superior atmosphere as it hits gas molecules it makes them shine generating the aurora. CMEs highly occur in solar maximum rich with sunspots and magnetic field disturbances [18].

Ⅱ.1.2.3 - Coronal loops

Originating and arcing between sunspots partner with opposite polarities where hot plasma circulates along strong its magnetic arc lines allowing them to glow [19] as the charged electron and proton particles are accelerated [20]Coronal loops exist in different sizes and might reach thousands of kilometers which can be detected through extreme ultraviolet and X-ray spectrum's. They are predictable in solar maximum where frequent number of sunspots and disturbance of magnetic field are reached 19.

Ⅱ.1.2.4 - Solar flares

When high magnetic field twists too long it remains few minutes before blowing up in the form of solar flare and releases excess energy such as electromagnetic radiation, including X-rays, ultraviolet radiation, visible light, and radio waves. In X-ray and ultraviolet images solar flares appears extreme bright white light [21].

Next comes the chromosphere, the first solar atmosphere zone with low plasma density making it non visual only through solar eclipse as a red ring. Temperature ranges between 4,000° - 6,000°C depending on the height above the photo-sphere and due to the emitted propagating waves from the sun it jumps rapidly into hundreds, thousands or millions as it reaches the corona and plasma density decreases relatively [22]^,[23].

The uppermost atmosphere is the corona elongating thousands of kilometers above photo-sphere the sun’s surface where it’s reshaped into the solar wind streaming into the solar system. In the sunspots max the corona stretches with an intense solar wind and disturbance of the magnetic field forming coronal holes 23.

Ⅱ.1.2.5 - Coronal holes

Are shown as dark regions where plasma is cooler and denser than in other parts of the corona moving across magnetic field lines which are describes as "open field lines" as they are not looped shaped increasing the release of plasma raising the solar wind speed into 800 k/s. In the solar minimum they appear near the poles or they might disappear due to the stability of the magnetic field [24].

Ⅱ.1.2.6 - Solar wind

Flow of light conducting plasma that consists charged energetic particles mainly electrons and protons traveling from the sun into the interstellar space passing through planets to reach earth with 300-800 Km/s leading to a bow shock in its magnetic field ranging about 12– 18 RE [25], this high pressure presses magnetic field lines in the day side about 10 Earth radii and extends them in the nightside around 1,000 Earth radii forming the magnetosphere tail which prevent the solar wind from approaching earth surface directly 1^,2 Some of the solar wind escapes from magnetosphere interacting with earth’s atmosphere through Alfvén waves circulating along the magnetic field lines 1 during magnetosphere disturbances 25.

CHAPTER Ⅲ: Regions of Earth

As the solar wind transfers plasma into the earth’s magnetosphere and ionosphere it will be observed through aurora, lightning phenomenons 2^,4.

Ⅲ.1 – Magnetosphere

The magnetosphere is splited into two regions at around 1.5 and 3.5 Earth radii known as the Van Allen radiation 1 which adapts energetic particles below 5MeV and traps in a mirror system and deflect others to protect earth’s atmosphere from damaging [26] which is a common characteristic for all planets in the solar system 2.

The outer belt is wider than the inner belt since it includes more trapped energetic particles mainly electrons and O⁺ oxygen ions, ions in the form of protons, this size increase as it traps more particles during solar storm 26.

The inner belt basically composed of energetic protons that are powered by wave-particle interactions and spiraling across magnetic field lines which become weaker and denser at the poles, the particles velocity is reversed and decreased causing most particles to circulate between the poles where ions shift westward direction while electrons eastward 26 The ones that flows parallel to the field line penetrate into earth’s atmosphere causing the aurora which is affected by solar activity 1^,2^,[27].

Variations of the solar activity have many effects on the magnetosphere by changes its shape, size, ions and exciting electrons and protons25.

The cavity between the two belts is called safe zone caused by the Very Low Frequency waves, solar storms can push particles to the gap26.

Plasma in the magnetosphere is hot which accelerates electrons 1 into high energetic particles at the tail of the magnetosphere 27.

Around 4 Earth radii the precipitated plasma cools and becomes denser in the ionosphere where it rotates with the atmosphere around the earth generating an electric field that guides the inner magnetosphere to rotate around earth’s axis 1.

From long time into another magnetic field low down reversing the north and south poles. At this time cosmic rays penetrate easy which increase the rate of genetic mutations 1.

Ⅲ.2 – Ionosphere

All solar system planets have ionosphere but they differ in their atmosphere composition 2. Ionosphere lies between 50-1000 km2 consisting of plasma where ionization is done through energetic photons emitted from the sun 1.

Ionosphere composition (figure 6) depends on the intensity of the sun’s emission of UV-rays and x-rays that are able to heat up gases and ionize earth’s atmosphere atoms 1 generating good amount of electrically charged ions and free electrons in day time where some bind again to go back to its normal neutral state at night 27.

Figure 6: Ionosphere composition 2.

CHAPTER Ⅳ: Aurora Borealis

Ⅳ.1 - Introduction

Aurora is a night sky show light occurring only at the poles in the thermosphere region between 100 km and 300 km above the Earth’s surface. At the north they are called aurora borealis and at the south by aurora australis 27 Aurora reveals the electric relationship between earth and sun as the trapped charged particles in the magnetic field mainly oxygen and nitrogen are excited by sun’s energy releasing light [28]^,[29] with different moving shapes and several colors such as green, red, blue, violet, pink, and white 27.

The atmosphere consists of 78.08% nitrogen molecules (N₂) and about 20.95% oxygen molecules (O₂) which are destroyed by intensive ultraviolet and X-ray photons from the Sun in the thermosphere making atomic oxygen (O), atomic nitrogen (N), and helium (He) as its basic constituents 27.

Ⅳ.2 - Importance of Aurora

As they are detected on Jupiter, Saturn, and Uranus they become a sign of the existence of atmosphere and especially the magnetosphere which in sense serves in discovering life in other planets solar system 27.

Ⅳ.3 - Process

The sun supplies flow of charged protons and electrons as a main through the solar wind into space in all directions, while travelling these particles loses its energy and as the solar wind reaches earth’s magnetic field the bow shock they gain back energy [30].

The bow shock occurs around15.0 RE where the solar wind magnetic field lines and the earth’s magnetic field lines unite at the night side then they flip back over the earth into the night side forming the magnetosphere tail by the time the magnetic field lines becomes denser leading to a sub-storm development called the magneto-pause around10 RE which collects and discontinues the tails of the magnetic field lines together directing them toward the earth’s poles 27^,30.

The directed magnetic field lines are filled with solar wind that is resisted by the earth’s magnetic field 29.

Few amount of the solar wind penetrate into the magnetosphere where energy is transformed into electromagnetic energy and stored mainly in the magnetosphere tail, as the number of stored energy extremely high the magnetosphere becomes unstable liberating extra energy of fast moving electrons 30 of 3-6 KV 1 which accelerate trapped particles by transmitting their high energy into oxygen and nitrogen mainly and as they become excited they pass though many collisions (figure 7) before producing photons in the shape of aurora going back to stability 27 and electrons deflect after collision 30.

Figure 7: A single electron undergoes several collisions on its travel toward Earth. Each collision can potentially change the electron’s energy and position 30.

The photon wavelength depends on the transmitted energy, the type of atom and its excited state and the height of interaction 27.

As an example, an electron with 10 keV (60000km/s) can collide 300 times before being resting at an altitude of about 100 km above the ground [31].

Protons transmit their energy with atomic oxygen easily and turn into hydrogen. This hydrogen does not rotate along the magnetic field, instead of that it precipitate into the atmosphere passing through many collisions until it loses its electrons 27.

Ionization also produce electrons with hundreds of eV involved in producing aurora27.

The deflected electrons spiraling downward with a velocity vector Ʋ^à are separated by an angle called the pitch angle α from the magnetic field vector B^à. At the lower aurora existence the height reaches 100 km a loss cone of lower pitches angles degrees is designated by α_D (around 2-3° )( graphs 1 & 2) 30.

Electrons with α < α_Dpenetrate into the atmosphere through the loss cone 30.

Aurora is a good conductor with a powerful electric current stream around 1,000,000 amperes 1.

Ⅳ.4 - Shapes of Aurora

Aurora appears in various shapes with different intensities, it might pass through different shapes in a night 28 depending on electrons energy, density and earth’s magnetic field fluctuations caused by magnetic substorms motivating auroras motion which can increase during powerful substorms in sunspots peak. Aurora shapes appear in motion and classified into two types: diffuse and discrete 30.

The diffuse type shines with no specific shape design in the form of smooth flat curtains, rays or arcs. This type is due to the acceleration of electrons into the atmosphere parallel to the earth's magnetic field lines 30.

Curtains are formed by a flow of precipitating falling electrons as sheets with thickness ranging between 1- 10 km. Where rays extends to 1 km to many hundreds of kilometers while arcs stretch over 1000 km with thickness ranging between 100 m – 10 km with height around 20-30 m and 10-100 km gap between arcs 30.

The diffuse can change into discrete which designate specific shapes events such as bands, spirals and rarely corona by folding, swirling or ruffling28.

The spirals are large curved arcs ≈ 50 km apart. Curls and folds are of rotational curves, where curls present small curved arcs ≈ 2-10 km apart that arise only for 0:25- 0:75s while folds are of medium curved arcs ≈ 20 km apart which lives for second or few minutes as a max 30.

The corona is the most amazing auroral rayed structure; it looks like a center point projecting rays all around 28.

Ⅳ.5 - Aurora’s Colors

Aurora exists in many colors such as red, pink, orange, green, and white 29 based on the type of the excited gas; oxygen and nitrogen (figure 3), speed of electrons and their energy during collision 28 with various intensities according to the amount of precipitating electrons stored energy, on the observer’s direction where naked eye can observe about 1 kilo Rayleigh (1 R = 10⁶ photon/cm²/s) and on the wavelength of the emitted light (figure 8) 30.

Figure 8: Colors of aurora depending on type of the excited gas and the emitted light wavelength [32].

Depending on the quantity of the absorbed energy 29 , about 100 km oxygen remains up to 0:7s in the transition state then emits green light at 557:7 nm 30 with high energy electrons and red light with low energy electrons 28 at 630 nm after remaining for 110s in the transition state 30.

Red emissions occur at high altitude is weaker than the green occurring at low altitude since at low heights the atmosphere density rise which increase the opportunity of collision losing magnitude for light emission as it stands longer in the excited state 30.

Nitrogen emits blue at 427:8nm 30 upon gaining electron after ionization, remaining for less than 0:001s in its transition state and red if it loses energy 29.

Figure 9: Ionization colors emission [33].

Purples, pinks, and whites are the results of the colors when they merge28.Aurora looks brighter because the peak of light sensitivity in human eye is around 555 nm 30.

Ⅳ.6 - Sounds of Aurora

Aurora’s viewers heard crackling, swishing, and hissing sounds 28. Lightning’s produce plasma waves called whistle waves at frequencies between the ion and electron frequencies. The sounds originate from the lightning electrical signals moving through earth’s magnetic field from one pole into another 1.

Ⅳ.7 - When can you see Aurora?

Light aurora occurs daily at the northern and southern poles and because they are pale they might not always appear. The perfect time to view is at midnight and especially in winter as the nights time extends longer 28.

In solar maximum that arises every 11 year, aurora occurs numerously and powerfully 28^,29 since the tail of the magnetosphere will contains huge amounts of electromagnetic energy at the night side producing powerful attractive auroras 27.

Ⅳ.8 - Where can you see aurora?

Auroral ring shaped oval can reach ~150 km in the southern magnetic pole and ~740 km in the northern magnetic pole varying proportionally with the disturbance intensity of the geomagnetic field 29.

Aurora can reach Alaska, Canada, Greenland, Siberia and northern regions of the United states, Europe, Scandinavia and Russia in the northern hemisphere. In the southern hemisphere it reaches Antarctica and the southern boundaries of Australia and New Zealand28^,29.

During high sunspot cycles, Texas or Florida might observe the aurora once or twice in the year and one of the rarest observations was recorded in 1909 near the equator in Singapore which is related to the highest geomagnetic storm 28.

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