Transcript Plasma - MIT Haystack Observatory

Plasma - What It Is, What It
isn’t
A Shocking Exposé with
Investigations by McGourty and
Rideout
4th State of Matter
• Superheated gas
• Has absorbed enough energy to allow electrons
to break free from atoms (free electrons)
• Made up of free electrons and positive ions
• Most abundant state of matter in the universe
• You can find out more by visiting this cool
website
4 States of Matter - This Shouldn’t
Even Phase You
Where Do We Find Plasma?
• The Sun
• Other Stars
• The
Ionosphere
• Lightning
• Neon Lights
Properties of Plasmas
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•
•
•
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Remain electrically charged
Carry electric currents
Produce both electric and magnetic fields
Produce electromagnetic radiation
Has a characteristic frequency called the
“plasma frequency”
Plasma Frequency
• Since plasma has both positive and negative charges,
they are constantly oscillating back and forth. This
results in a characteristic frequency called the Plasma
Frequency
• The plasma frequency is a resonant frequency of the
ionized gas - it depends on the square root of the
electron density
+
Plasma and the Ionosphere
• Radio waves can only penetrate the ionosphere
if the frequency of the wave is higher than the
plasma frequency; otherwise the signal is
reflected back
• We have to use high frequencies to
communicate with satellites.
• Frequencies lower than the plasma frequency
have to be used to communicate with a radio
station beyond the horizon so that the signal will
be reflected back to Earth
Why Do We Care About Plasma?
Faraday Rotation
• As a wave moves through a plasma, the
polarization plane can rotate because of
the influence of the magnetic field. This
effect is known as Faraday rotation
• Strength of magnetic fields can be
measured using knowledge of rotation and
electron density
• Pulsars, heliospheric information - look at
known source and changes in polarization
due to FR to create models
The solar wind
causes energy
changes in the
incoming
wavefront