# Presentation: 498336

## Lecture: The Plasma Universe

**Lecturer: Dr. Steven A. Curtis**
**Program: International Space University**

## The Plasma Universe: Course Outline

- An overview of the nature and rationale for studying plasmas
- Key concept 1: Plasma component characteristics
- Key concept 2: Plasma distribution and structure
- Key concept 3: The enormous range of plasma properties
- Key concept 4: The influence of magnetic fields
- Key concept 5: Measuring and simulating plasma behavior
- Ongoing and future unveiling of the plasma universe

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**Where are plasmas found naturally around the Earth?**
- Although a relatively uncommon form of matter on the Earth’s surface, plasmas are found in lightening as well as in auroras.

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## Can plasmas be induced on the Earth?

**Can plasmas be induced on the Earth?**
- Plasmas are induced in flames and fluorescent bulbs.  High energy plasmas produced in laboratory simulations of, for example, nuclear fusion, must be contained.

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- Beyond the atmosphere of the Earth, the planets, and other cool, dense objects, plasmas comprise a large portion of non-dark matter in the universe.  *In fact, 99.99% of the universe is in the plasma state!*

- Slide wallpaper is TRACE image of EUV emissions from highly ionized iron atoms in a coronal loop of the solar corona showing  reconnection, a universal process which converts magnetic into kinetic particle energy.

- Solar Hot Spots

- Comet Hyakutake

- Tarantula Nebula

- SuperNova

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## Plasma: A distinct state of Matter

- Plasmas are a state of matter, like solids, liquids, and gases, with properties quite distinct from gases.
- The fluid states of gas and liquid are treated with the Navier-Stokes equation whereas plasmas are treated with the Maxwell, Boltzmann, and Vlasov equations.
- The environments where plasmas are found are so severe that  ‘neutral’ components (atoms, molecules) found in gases are partially or fully ionized. The resulting ions and electrons exhibits collective effects due to interactions with electric and magnetic fields.

## Why study plasmas?

- These goals can be achieved both through performing laboratory experiments and designing and flying space instruments and missions to obtain in situ measurements to determine the nature and evolution of plasma structures.

- Plasma structures induced by currents simulated in the laboratory.

**Why study plasmas?**

## Plasma Universe Key Concept 1: Plasma Component Characteristics

**Plasma Universe Key Concept 1: Plasma Component Characteristics**

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- Many of plasma's unique properties derive from the behavior of electrons. Electrons have so little mass that they are far more responsive to acceleration by electric fields. They travel much faster and even bunch together in interacting with the heavier, slower protons and other atomic nuclei that may be present in plasma. Electrons accelerated to high speeds yield the abundant radiation characteristic of plasmas in the laboratory and space. Electrons form the aurora shown in the picture.

**How are Plasmas Generated?**

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## What keeps the charged components of a plasma from recombining?

- Increasing **Temperature (T)** increases speed and decreases the likelihood of electron capture.

- Decreasing **Density (D)** decreases separation and the likelihood of interaction between components.

- For given Density, there is a minimum Temperature  required for ionization and a higher minimum Temperature  above which components are completely ionized.  Partial ionization occurs between these two temperatures.

**What keeps the charged components of a plasma from recombining?**

## The Nature of Plasma: The Debye Length

- The charge interaction, or Coulomb force, will obviously be greater between near neighbors. Every plasma particle has a characteristic ‘sphere of influence’ with a radius defined by the Debye Length, a typical distance over which the impact of a charged particle's bare electric field is substantial. In terms of the density and temperature of the plasma components the Debye length can be defined by
- where n, q, and T are, respectively, the density, charge and temperature of the particle species α, and k is Boltzmann's constant. For distances exceeding the Debye length, the electric field of an individual charged particle is effectively shielded out by the surrounding plasma. Not surprisingly, the density of plasma particles within the Debye length greatly influences the collisional properties of the plasma and determines the significance of discrete particle effects. In plasma physics the so-called *plasma parameter* is related to this number.

## The Nature of Plasma: The Plasma Parameter

- The plasma parameter, *g,* depends on the particle density as defined by
- The greater the plasma density in a Debye sphere, the smaller the plasma parameter. If g is sufficiently small, as a result of n being relatively large, the average kinetic energy of a plasma particle, kT, exceeds the average inter-particle potential energy, and the collision frequency increases. The plasma behaves, statistically, much like an *ideal gas* (an ideal gas has zero potential energy and essentially no interaction between the particles).
- As the density decreases, the average kinetic energy and the collision frequency decrease, and g increases.

## Plasma in Motion:  Frequencies

- Plasma particles, behaving collectively, can support a wide variety of motions and oscillations.
- A basic oscillation arises if a group of electrons is slightly displaced from their equilibrium positions. Displaced electrons experience an electrostatic force seeking to return them to their equilibrium positions but upon arrival there they now have a kinetic energy equal to the potential energy of their initial displacement. The electrons overshoot, reconvert their kinetic energy to potential energy and a simple oscillation is set up.
- The frequency of this fundamental oscillation is known as the *plasma frequency* where *n* is the mean plasma density and m is the electron mass.

**Plasma in Motion:  Frequencies**

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- If the wave is electromagnetic in nature, the magnetic field obeys a similar relation. The (angular) frequency and the wave vector are functionally related to one another, in linear theories of plasma waves, by a dispersion relationship. A knowledge of the dispersion characteristics of the propagating waves is necessary for an understanding of the plasma state.
- A plasma, however, is a nonlinear medium and unless the waves are truly of small amplitude, nonlinear effects must be taken into account. Such nonlinear effects produce non-linear wavelike disturbances including the solitons (solitary waves) and double layers frequently observed in space plasmas. More generally, the presence of nonlinear effects leads to plasma turbulence.

**Plasmas in motion: Waves**

- plasma waves detected at Ganymede

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## Plasmas in motion: To Collide or not to Collide

- Collisionless transport of electron visualized as skier.

- Turbulent or collisional transport with particle performing random walk.

**Plasmas in motion: To Collide or not to Collide**

## Collisional versus Collisionless Plasmas

- The Earth’s ionosphere is partially ionized collisional plasma with a density of 1,000,000 per cubic centimeter and a temperature of 1,000 K.
- The Earth’s outer magnetosphere is a fully ionized collisionless plasma with a density of 1 per cubic centimeter and a temperature of 1,000,000 K.
- The Solar Core is a fully ionized collisional plasma.

**Collisional versus Collisionless Plasmas**

## The Plasma Universe Key Concept 2: Plasma Structure and Distribution

- As a result, plasmas display a complexity in structure that far exceeds that found in matter in other states. In addition to the cellular structure, most visible on the Sun, plasmas display a filamentary structure.
- Plasma’s free electrons are better conductors of electricity than metals. The gas in a fluorescent bulb, though weakly ionized,  would completely short circuit the electrical main supply without the resistor in the ballast. When charged particles flow in a neutralizing medium, such as free electrons in a background of ions, the charged particle flow or current produces a ring of magnetic field around the current, pinching the plasma into multi-filamentary strands of conduction currents.
- Energetic plasmas in space are prodigious producers of electromagnetic radiation. In the diagram are examples of phenomena that are controlled (left to right) by gravity, combined forces, and EM forces.

**The Plasma Universe Key Concept 2: Plasma Structure and Distribution**

## Plasmas in space and time: Distribution and Dynamics

- Plasma behavior can be described quantitatively by Maxwell’s Equations along with Boltzmann and Vlasov Equations in Maxwellian form.

**Plasmas in space and time: Distribution and Dynamics**

## Maxwell’s Equations

**Maxwell’s Equations**

## Slide 20

## Slide 21

## Slide 22

## Particle Distribution Equations

- Collisional Systems (Boltzmann Equation):
- Collisionless Systems (Vlasov Equation) in two forms:

**Particle Distribution Equations**

## Plasma Dimensionality

- 3 dimensions for instantaneous location in space:
- (X, Y, Z)
- Plus 3 dimensions (vectors) to indicate change in position with time (velocity):
- (Vx, Vy, Vx)

**Plasma Dimensionality**

## Distribution of Collisional Plasmas

**Distribution of Collisional Plasmas**

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**Examples of Maxwellian Distributions in Nature**

- Saturn’s Ring Particles

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## Distribution of Collisionless Plasmas

**Distribution of Collisionless Plasmas**

## Kinetic Instabilities in Collisionless Plasmas

- were found to be emanating from the region of the Io plasma torus, providing evidence for instabilities induced by a magnetic dipole field and magnetosphere interactions as illustrated below.

**Kinetic Instabilities in Collisionless Plasmas**

## Plasma Universe Key concept 3: Plasma’s enormous range

**Plasma Universe Key concept 3: Plasma’s enormous range**

## Range of Plasma Parameters in accessible regimes

-  from less than 1 to greater than 1016 particles per cubic centimeter
- Temperature ranges over several orders of magnitude:
- from 10,000K (1 electron volt) to 10,000 electron volts
- Magnetic field intensity varies by greater than 12 orders of magnitude: from 10-6 to 106 gauss

**Range of Plasma Parameters in accessible regimes**

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**Inducing greater range of plasma parameters**

- Tokomak Simulation

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## Plasma Universe Key Concept 4: Great influence of magnetic fields

**Plasma Universe Key Concept 4: Great influence of magnetic fields**

## Planetary Magnetic Fields

| Magnetic Property | Mercury | Earth | Jupiter | Saturn | Uranus | Neptune |
| --- | --- | --- | --- | --- | --- | --- |
| Magnetic Moment/MEarth | 
1/2700 | 
1 | 
20,000 | 
600 | 
50 | 
25 |
| Surface FieldBO (Gauss):Max/Min: | 
0.003? | 
0.312.8 | 
4.284.5 | 
0.224.6 | 
0.2312 | 
0.14
9 |
| Magnetosphere SizePredicted:Observed: | 
1.2 RM1.4-1.6 RM | 
8 RE6-12 RE | 
34 RJ50-100 RJ | 
16 RS16-22 RS | 
20 RU18-19 RU | 
20 RN23-26 RN |

**Planetary Magnetic Fields**

## Planetary Magnetospheres

- The size of the magnetosphere varies greatly depending on the strength of its magnetic field and  the pressure from the solar wind in which all planets are embedded.
- Magnetospheres range in size from that of Mercury, which is on slightly larger than the planet, to that of Jupiter that is more than a 100 times larger than the planet. In fact, if the Jupiter magnetosphere could be made visible in the sky, it would appear larger than any other object, including the Earth’s Moon. Magnetospheres of Saturn (left) and Mercury (right) are shown below.

**Planetary Magnetospheres**

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## Magnetosphere Structures and Boundaries

**Magnetosphere Structures and Boundaries**

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**Reconnection of Plasma in the Magnetosphere**

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## Reconnection of Plasma on a larger scale

- Understanding the underlying physics of collisionless reconnection is one of the greatest scientific challenges of the present time.  What kind of in situ mission strategy would lead to a breakthrough in understanding reconnection using relatively accessible structure: the Earth’s magnetosphere?

**Reconnection of Plasma on a larger scale**

## Reconnection: Present ‘In Situ’ Model

**Reconnection: Present ‘In Situ’ Model**

- Reconnection Diagram from STDT MMS Report with Insert from Ma and Bhattacharjee, 1996

- Relevant Scales
- Electron Inertial Length
- Ion Inertial Length
- Temporal Scales

## Reconnection: Present ‘Global’ Model

- From Birn et al, 2003
- http://www-solar.mcs.st-andrews.ac.uk/~mhd03/TALKS/JBirn.pdf

**Reconnection: Present ‘Global’ Model**

## Plasma Universe Key Concept 5: Measuring/Simulating Plasma Behavior

| Remote Measurements of Emissions
Plasma Emissions 
Aurora 
Energetic Neutrals | In Situ Measurements of Particles
Particles-F(v) 
B,E Fields 
Waves |
| --- | --- |
| Characterization of Large-scale Structures | Details of Particle-level Interactions |

**Plasma Universe Key Concept 5: Measuring/Simulating Plasma Behavior**

- Measurements of plasmas in space are either done remotely or in situ (at the position of the instrument) but only in situ measurements allow a quantitative comparison between theoretical prediction and experimental observation.

## Earliest work in Plasma Physics

- Langmuir worked for General Electric, studying electronic devices based on ionized gases in the laboratory. The way the electrified fluid carried high velocity electrons, ions and impurities reminded him of the way blood plasma carried red and white corpuscles and microorganisms.
- As a result of those studies, carried out on relatively cool and dense plasmas, scientists now talk of "Langmuir waves" and fly "Langmuir probes" aboard satellites. Gradually plasma research spread in other directions.

**Earliest work in Plasma Physics**

## Developments in Plasma Physics

**Developments in Plasma Physics**

## Advanced Computing: Breakthrough in Plasma Physics

**Advanced Computing: Breakthrough in Plasma Physics**

## Spatial and Temporal Processes in Plasmas: Multi-platform Formations

- To compare theory (computer modeling), experiments (laboratory simulations), and observations (mission measurements) quantitatively, we need to have a complete set of measurements of fields and particles at definite locations. This can only be done in situ and requires at least four spacecraft flying in a tetrahedral formation.
- Why a tetrahedron? A tetrahedron is the simplest  figure to uniquely separate space and time. Are the observed variations in given measurements the result of variations which are spatial (varying from location to location but not varying at a given location) or temporal (varying at a given location but not varying from location to location) or both? One way to look at this is that relative to any given spacecraft, two others constrain the spatial variation (X, Y, Z) by defining a plane, while the fourth provides the temporal variation relative to this plane (dX, dY, dZ).

## Plasma Study via Tetrahedral Formation: Magnetospheric Multi-Scale (MMS) Mission Concept

- The MMS mission consists of four spacecraft flying with identical instrument suites flying in tetrahedral formation. These instrument suites will provide the first measurements of  the 3D structure and dynamics of the magnetosphere across the range of spatial and temporal scales.
- These observations will be crucial in understanding how plasma particles interact in space in time, a process called reconnection, as well as in characterizing the magnetosphere’s principle interfaces with external plasma: the subsolar magnetopause and magnetotail.

## MMS Mission Design

- 4 Identical Spacecraft in tetrahedral formation
- Robust particle and fields payload including
- Multiple plasma heads and 3D electric fields
- Onboard ranging capability (≤10 KM to  ≤1000 KM)
- Onboard Delta-V ≈ 1 KM/Second
- Distinct orbital phases

## Present understanding of Reconnection from Combined Observations

**Present understanding of Reconnection from Combined Observations**

- Combined mission observations from August 27, 2001 showing a global magnetic storm suggesting reconnection in the midtail region, as modeled on the right.
- From top to bottom, on the left, for ACE VBz, Auroral electrojet indices, GOES8 Magnetometer, LANL 50-500 keV energetic electron data, POLAR TIMAS H+ data and POLAR HIST electron flux, CLUSTER Spacecraft 1 H+ and O+ data.
- On the right is a model for reconnection derived by Baker et al, 2001.

## MMS Raises the bar on Plasma Investigations

- Simultaneous or sequential magnetospheric measurements from several spacecraft have been combined already, most recently as part of a multi-platform mission called Cluster. How will the tetrahedral spacecraft formation of MMS will study plasma in the magnetosphere in a way that hasn’t been possible before?
- Spacecraft locations are known to far greater accuracy in real time allowing much greater accuracy in space and time.
- Spacecraft are in much closer formation, allowing exploration of much smaller spatial and temporal scales of variation.
- Instrument suites are designed to be identical allowing exact measurement comparisons and minimizing instrumental errorbars.

**Spatial Scales**	 Range  ≤10 KM to  ≤1000 KM
- 		 ≥ Electron Inertial length  ≈ 10 KM
**Temporal Scales **≥ 10’s msec

## The future of plasma study: Unveiling the Plasma Universe

- Recent discoveries about the Sun and its plasma environment combined with rapid advancement in our knowledge of the interstellar medium make it likely that plasmas will be the focus of 21st century astronomy in a way that gravity was the focus of the 20th century.
- Advances in instrumentation have allowed more extensive measurement in space and testing in the laboratory of plasma behaviors found in space.
- Clear evidence of inter- and intra-galactic magnetic fields have been found. Current filaments have been detected in the interstellar medium.
- Supercomputer capabilities have ushered in a new era of advanced modeling of plasmas and cosmological phenomena.

## Unveiling: Studying the Large-Scale Structure of Plasmas

- electrical current induced structures in lab, solar prominence, and milky way.

- Alfvén thought that currents generated within plasmas should give the universe a cellular and filamentary structure. The plasma universe consists of swirling streams of electrons and ions flowing in filaments. Where pairs of these structures interact, the particles gain kinetic energy and at narrow 'pinch' regions produce the entire range of galaxy types as well as the full spectrum of cosmic electromagnetic radiation. Thus galaxies must lie 'like pearl beads on a necklace' along filaments, much as they are observed to do on a large scale. The bulk of the filaments are invisible from a distance, much like the currents that circle the Earth but are invisible from its surface. At the time of this suggestion, supporting evidence in the form of huge filaments, sheets, and walls of galaxies were unknown.  Now, there is a growing body of observational evidence.

**Unveiling: Studying the Large-Scale Structure of Plasmas**

## Unveiling: Doubleness in Large-Scale Structure Development

- This doubleness phenomena is observed in the laboratory when very high currents are passed through parallel arrays of wires, that explode into plasma currents called "pinches". The pinches often interact in pairs.

**Unveiling: Doubleness in Large-Scale Structure Development**

## Unveiling: ‘Pinching’ Plasmas in Cosmic Evolution

- Pinching leads to the generation of synchrotron radiation so ubiquitous in radio galaxies and quasars. The macroscopic picture is of a charged particle beam confined in a self-consistent magnetic field or compressed against expansion due to thermal pressure. On the microscopic scale, relativistic electrons in the magnetized beam are prodigious producers of synchrotron radiation. An enhancement of the synchrotron power is achieved when the sum of the radial forces seen by the relativistic electrons is increased, as is the case when the azimuthal magnetic fields of neighboring pinches are present. A burst of synchrotron radiation is observed.

**Unveiling: ‘Pinching’ Plasmas in Cosmic Evolution**

## Unveiling: Theoretical Simulation of Large-Scale Structure of Plasmas

- Evolution of a galaxy at 20 megayears (radio galaxy), 100 megayears (quasar), 120 megayears (Peculiar or Seyfert Galaxy) and 500 megayears (early spiral) according to recent theoretical modeling.
- Note that while the energy to produce a galaxy is delivered via a current-conducting plasma filament that may stretch for hundreds or thousands of gigaparsecs, the initial plasma ‘pinch regions’ forming the galaxy are disks 35 kiloparsecs in diameter, 10 kiloparsecs thick, spaced 80 kiloparsecs apart.

**Unveiling: Theoretical Simulation of Large-Scale Structure of Plasmas**

- Radio  Galaxy
- Quasar
- Seyfert Galaxy
- Spiral Galaxy

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- Galaxy-Scale Phenomena: Black Hole Eating Gas

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##  Drivers for The Plasma Universe

- Inevitably, an increasing number of researchers have extended their plasma interests beyond Earth, into such realms as interplanetary "space weather" and plasma laboratory astrophysics. Their fundamental view on cosmology is that electromagnetic forces sculpt the broad outlines of the universe; gravitational forces shape the details only after electromagnetic forces have first drawn the diffuse matter close enough together for gravity to become significant.

** ****Drivers for The Plasma Universe**

## The Plasma Universe: A New Cosmology?

- At the same time, mainstream cosmology is not about to welcome the plasma model. Cosmology of the twentieth century remains dominated by gravitation modeling, based especially on Albert Einstein's general relativity theory. Although cosmologists tried at the beginning of the century to include electromagnetic forces in their calculations, the equations proved too complicated to handle, and, in any case, the gravity dominated models became extremely popular to the lay-person. Thus today in cosmology, gravity rules, and its progeny, the big bang model, is widely accepted as providing the "true" explanation of the nature of the universe.

**The Plasma Universe: A New Cosmology?**

**From the ‘Big Bang’ to the ‘Big Pinch’?**

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