Space Plasmas: What They Are and Where They Come From

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Space PlasmasWhat They Are and Where They Come
From
Joe Borovsky ISR-1, Los Alamos National Laboratory
The Plasmas Solar Wind Magnetosheath
Plasma Sheet Plasmasphere Radiation
Belts Ionosphere
For Each Plasma Location Properties
Space-Physics Issues Plasma-Physics Research



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Naturally Occurring Plasmas
1 eV 11,600 K



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Measuring Space Plasmas Scientific Spacecraft
Instruments plasma instrument
measures ion and electron distribution functions
one particle at a time magnetometer
measures DC magnetic field (boom)
energetic-particle detector measures
ions and electrons with energies gt 50 keV
waves instrument measures magnetic-
and/or electric-field fluctuations in the plasma
(antenna) electric fields
measures DC electric field (booms) Price Tag
(including launch) 100M (cheap) --- 2.4G
(Cassini at Saturn) Chief Sponsors NASA,
Air Force (USA) ESA (Europe) IKI
(Russia) ISAS (Japan)
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Advantages for Plasma Physics
Studying space plasmas provides unique
opportunities Micro diagnostics
spacecraft are smaller than the plasma
scalesizes Debye lengths
gyroradii unperturbing measurements
Slow evolution compared to measurement times
Collisionless plasmas Large scale
plasmas Unique phenomena



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1. The Solar Wind
Supersonic wind 300-600 km/sec 106
Tons/sec 100 hours old (at Earth)
1 AU 1.5?108 km



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The Solar Wind Is Highly Variable
The solar wind has variations that range from
seconds to the 11-year solar cycle

• n 2 - 30 cm-3
• Ti 2 - 20 eV
• Te 5 - 30 eV
• B 2 - 50 nT
• ? 0.1 - 2
• 96 H
• 4 He

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The Solar-Cycle Variation ofthe Solar Wind



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The Solar Wind Varies Systematically with Distance
owing to the 1/r2 expansion of the plasma as it
flows outward from the sun.



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Solar-Wind Research
Origin of the solar wind Cosmic-ray transport in
the solar wind Dynamics and evolution of solar
ejecta



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Plasma Physics in the Solar Wind MHD Turbulence



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2. The Magnetosheath
1 RE 6340 km
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The Magnetosheath Properties Change with Location
and with Time

• n 8 - 200 cm-3
• Ti 300 - 1100 eV
• Te (1/6) Ti
• B 8 - 250 nT
• ? 1 - 10
• 96 H
• 4 He

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Magnetosheath Research
Physics of the collisionless bow shock Nature
of magnetosheath fluctuations Solar-wind/magneto
sphere coupling Boundary layers and plasma
transport



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Plasma-Physics Research in the Magnetosheath
Kinetic Instabilities
The bow shock produces ring-ion
distributions ion temperature anisotropies
electron temperature anisotropies
The ions drive mirror mode waves
electromagnetic ion-cyclotron waves
The electrons drive electron mirror waves
whistlers



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3. The Plasma Sheet

• n 0.2 - 3 cm-3
• Ti 5 - 15 keV
• Te (1/6)Ti
• B 10 - 30 nT
• ? 1-10
• H
• He
• O

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Plasma-Sheet Research
Origin from the solar wind H He Origin from
the ionosphere O H Magnetosphere-ionosphere
coupling plasma generators plasma
circuits Alfven waves MHD
turbulence Magnetospheric substorms The aurora



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Plasma Physics in the Earth's Plasma Sheet
Reconnection
Plasma Physics in the Earth's Plasma Sheet
Reconnection
The reconnection of magnetic field lines enables
the global magnetosphere to move into a
lower-energy state.
The reconnection of magnetic fields enables the
global magnetsphere to move into a lower-energy
state.
Research focuses on the conditions that allow
reconnection to proceed in the absence of
resistivity.
Research focuses on the conditions that allow
reconnection to proceed in the absence of
collisional resistivity.



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4. The Plasmasphere
The plasmasphere is a cold dense plasma in the
dipolar regions near the Earth.

• n 10 - 2000 cm-3
• Ti 1 - 10 eV
• Te Ti
• B 100 - 2000 nT
• ? ltlt 1
• H
• He
• O

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The Plasmasphere in the Recurring-Storm Cycle
ExB-Drift Orbits
Space-Research Topics Dynamics of ExB flows
Density structures Plasma waves Effect on
the magnetosphere
draining 34 tons of protons 39 tons of He 77
tons of O



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Plasma Physics in the Plasmasphere Ambipolar
Diffusion
The plasmasphere comes from the (electrical)
evaporation of the ionosphere. Magnetic fields
guide the particles, electric fields control the
up/down motions. The charge density of five
particle populations must be accounted for
ionospheric ions, ionospheric electrons,
photoelectrons, plasmaspheric ions,
plasmaspheric electrons.
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5. The Radiation Belts
The radiation belts are populations of trapped
energetic ions and electrons in the dipolar
regions of the magnetosphere. Can be long lived
(decades). Origins Cosmic-ray-neutron
decay Inward diffusion of particles In
situ energization



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Plasma-Physics in the Radiation Belts
Wave-Particle Interactions
The radiation belts are co-located with the
dense plasmasphere and many types of plasma waves
live in the plasmasphere. Owing to the wave
fluctuations, radiation-belt particle orbits are
slowly perturbed and belt particles are lost into
the atmosphere.
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6. The Ionosphere
The ionosphere is the ionized upper
atmosphere. The ionization comes about from (1)
solar ultraviolet radiation and (2) the
precipitation of energetic magnetospheric
electrons and ions.



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Plasma Physics in the IonosphereElectromagnetic
Waves in Plasmas
HAARP ionospheric heater in Alaska
1. Powerful radio waves are broadcast upward. 2.
The plasma frequency increases with altitude. 3.
At the critical altitude the plasma frequency
equals the radar frequency strong
interaction (reflection, energy absorption,
plasma instabilities)
1. Powerful radio waves are broadcast upward. 2.
The plasma frequency increases with altitude. 3.
At the critical altitude the plasma frequency
equals the radar frequency ?strong
interaction (reflection, energy absorption,
plasma instabilities)